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SR785 User`s Manual - Stanford Research Systems

1. U Trace to Arb C Return C SR785 Dynamic Signal Analyzer 4 80 Arbitrary Source Menu Arb Source Start Select the Arbitrary Source Start position within the selected source buffer either Arbitrary Waveform memory or Capture buffer The start position is specified as a bin number or individual point position During Arbitrary playback the points are separated by a time equal to 1 Play Rate The corresponding start time relative to the start of source buffer is displayed as well Command ASTR 7 1 Arb Source Length Select the Arbitrary Source Length in 2 kPoint 2048 points increments The Arbitrary Source Length in points plus the Arbitrary Source Start cannot exceed the length of the Arbitrary source buffer either the Arbitrary waveform memory or the Capture Length The corresponding source time length is displayed as well Command ALEN 1 Set Left Edge The Arbitrary Source playback must be from a Capture Buffer and the Measurement of the active display must be the Capture Buffer for this key to be active Choose the correct Capture Buffer as the Measurement and use Zoom and Pan to show the region of interest Press lt Set Left Edge gt to set the Arbitrary Source Start to the marker position The Arbitrary Source Length is not changed If the requested Source Start plus the Source Length in points exceeds the Capture Length of the buffer the Source Length is reduced Set Right Edge
2. Rep indicates that the new term replaces the highlighted one Use lt Insert Replace gt to toggle between insert and replace Insert the Group Delay operator in front of the transfer function Closing parentheses are not required if they are at the very end of the string Enter the equation Select the Display Setup menu Change the measurement of the active display DisplayA Choose FFT User Function 2 Change the view Group delay is the derivative of the phase with respect to and is a real time Choose Real Part The units automatically switch to linear units User Functions are dimensionless quantities You can choose dB logarithmic or units linear Scale the display The group delay is the delay time caused by the filter at different frequencies The data values are seconds of delay Most points are in the neighborhood of 10 to 600 us At the 1 kHz notch the group delay has a singularity Remember the notch filter has a phase discontinuity at the notch frequency 8 Press Display Options Press lt d dx Window gt Press 1 Enter Press 2 Enter User Math Functions 1 55 Select the Display Options menu The group delay is the derivative of the phase The derivative operation requires an aperture or window Set the window to 0 1 of the display length This increases the resolution makes things narrower of the graph while decreasing the smoothing of noisy data
3. Command LDLT d 1 Shift All Shift all of the Limit Segments up or down together Enter a value or use the knob to shift by 1 10 s of a division Command LSFT d x SR785 Dynamic Signal Analyzer 4 156 Marker Statistics Menu Marker Statistics Menu The Marker Statistics menu displays various statistics about the marker Y values Marker Stats 6 0179 Min 6 0189 _ Mean 6 0185 Std Dev 0 00029156 Max Display B 6 0154 Min 6 0164 Mean 6 0158 Std Dev 0 00029351 Marker Stats Reset Turn the accumulation of marker statistics On or Off When Marker Statistics are On the various statistical quantities are updated whenever new data is available on the display The accumulation of the statistical quantities continues even when this menu is not displayed Return to this menu to see the latest statistical values When Marker Statistics are Off the various quantities are frozen New data is not included in the statistics Command MSAO d 1 Reset and start the accumulation of marker statistics The various quantities are reset to zero and the accumulation of marker statistics begins Use this key whenever the marker position is changed to avoid mixing data from different marker positions Command MSRS SR785 Dynamic Signal Analyzer Marker Statistics Menu 4 157 Max Display A This menu box displays the maximum value of the marker Y value for display A sinc
4. Expand indicator SR785 Dynamic Signal Analyzer Marker Screen Display 3 15 Marker located at Max Marker Region nc Po defined by Le ce solid vertical lines TERNE ey i Kai i i Figure Chapter 3 7 Marker Region The Marker Region is the graph region between the two solid vertical marker lines The Marker Region Width may be set to 1 division Wide 1 2 division Normal or a single vertical line Spot The Marker Region is associated with the display and does not change with graph scaling The Marker is the small square within the Marker Region The Marker finds the Minimum Maximum or Mean of the data in the Marker Region When seeking Min or Max the Marker is located at the position of the minimum or maximum This allows peaks and valleys in the data to be found easily When seeking the Mean the X position of the Marker is at the center of the Marker Region and the Y position is the mean of the data within the region When a Spot Marker Region is used the Marker is confined to a single X location Use the Marker menu to configure the Marker for each display The Marker position is shown in the Marker Position Bar above the graph Use the knob to move the marker in the active display The knob always moves the marker unless a menu softkey has been pressed and an entry field is displayed at the top of the screen To move the marker to the next peak in the display press Enter and move the knob T
5. Input Noise Noise measurements in FFT analyzers are usually made using Power Spectral Density PSD units PSD units simply normalize the amplitude of each frequency bin by the square root of the linewidth A window correction factor is also included to compensate for the bandwidth of the different windows PSD units have the form Vrms VHz or dB Vrms VHz SR785 Dynamic Signal Analyzer 2 66 Signal Inputs Most noise sources including the amplifier input noise are Gaussian in nature The amount of noise is proportional to the square root of the bandwidth in which the noise is measured A noise measurement made using normal units would yield different amplitudes depending upon the linewidth of the FFT span By using PSD units the measured noise is independent of linewidth and span The input noise of the SR785 inputs is about 10 nVrms VHz The input noise of the analog to digital A D converter is about 300 nVrms VHz referenced to a full scale of 1 Vpk What does this mean in terms of the FFT noise floor For input ranges below 30 dBV input gain greater than 30 dB the measured noise floor is determined by the signal inputs This is because the signal gain gt 30 times the input noise 10 nVrms VHz exceeds the input noise of the A D converter For input ranges above 30 dBV input gain less than 30 dB the measured noise floor is determined by the A D converter There is not enough gain to amplify the input noise to a level great
6. Phase suppress sets the phase of small data values to zero This avoids the messy phase display associated with the noise floor Remember even a small signal has phase Set the phase suppress threshold in the Display Options menu Nyquist Plot The Nyquist plot graphs complex measurement data as imaginary part along the Y axis versus real part along the X axis The graph is scaled linearly Adjacent frequency points are connected by a line This view is generally meaningful only for measurements which have data at every frequency point such as chirp source or swept sine The marker readout shows the real and imaginary parts of each point as well as its frequency The marker moves sequentially through the frequency points and can be linked to the frequency of the other display Real measurement data such as baseband time record have zero imaginary part This view is entirely along the X axis Nichols Plot The Nichols plot graphs complex measurement data as log magnitude along the Y axis versus unwrapped phase along the X axis The Y axis is logarithmic and the X axis is linear Adjacent frequency points are connected by a line This view is generally meaningful only for measurements which have data at every frequency point such as chirp source or swept sine The marker readout shows the log magnitude and phase of each point as well as its frequency The marker moves sequentially through the frequency points and can be lin
7. The target trace must already store data of the type and length to be loaded from disk The file only contains data points no measurement information is recalled The recalled data simply takes the place of the stored trace data and assumes the trace s measurement parameters Measurement Averaging Window Frequency span and length The binary file contains N complex points Each complex data point is two floating point numbers representing the real and imaginary parts Thus the file contains 2N floating point numbers The values are linearly scaled usually with units of Vpk The first value in the file is N 4 byte long integer followed by the real part of the first point 4 byte IEEE float then the imaginary part of the first point 4 byte IEEE float etc There are no delimiters in a binary file The data is packed Traces which are entirely real should store the value 0 0 as the imaginary part of every point The binary file has the following form where represents a single byte N Isb N N N msb X0 Isb XO XO XO msb YO Isb YO YO YO msb X1 Isb X1 X1 X1 msb Y1 Isb YCN 1 msb where XO YO is the first complex data point and XN 1 YN 1 is the Nth data point Each value is 4 byte IEEE float The value of N depends upon the type and length of the target trace N should be picked at least as large as the number of points displayed in the trace If N is specified too small the trace wi
8. When the integration is complete the source moves to the next frequency in the sweep A Settle Time is allowed to pass before any measurement is made at the inputs This allows the device under test to respond to the frequency change This can be especially important if the device under test has a high Q The Settle Time is also specified in both time and cycles of the source Times are converted to cycles and the larger of the two specified cycles is used The Integration and Settle Times are set within the Average menu Sweep Frequency and Auto Resolution The span of a swept sine sweep is determined by the Start and Stop frequencies The entire 102 4 kHz frequency range of the SR785 is available for swept sine measurements Note that starting a sweep at DC is not possible In fact beware of starting at any frequency much less than Hz since the Settle and Integration times are always a minimum of cycle If the start frequency is very low the first point can take longer to measure than the entire remainder of the sweep The Sweep Number Of Points or resolution can be set from 10 to 2047 The points can be in a linear or a logarithmic progression In many cases it is desirable to sweep over a wide frequency range while still detecting narrow features in the response function An example might be a filter with many zeroes or a narrow notch In order to resolve the narrow features a large number of points must be used in the sweep to impr
9. X 1 X x jy l x jy SR785 Dynamic Signal Analyzer 4 128 User Math Menu where r V x y and 0 tan y x Sqrt computes all angles positive from 0 The X 1 X operator is generally used on real arguments only The jOmega operator is simply j and zeroes the real part and fills the imaginary part with the value of 27 frequency at each point in the array The frequency is determined by the span of the operand A measurement operand FFT 1 or Time 1 uses the current frequency span A Trace operand uses the span of the measurement which is stored in the Trace FFT is the windowed FFT operator These operations switch the X axis type The current window chosen in the Window menu is used on the operand before the FFT FFTu is the un windowed FFT operator The uniform window is always used The FFT and FFTu operators do not calibrate their results since their operands are not necessarily input time records To use a calibrated FFT use the measurement operand FFT 1 or FFT 2 IFFT is the inverse complex FFT operation This operation switches the X axis type d dx is the derivative operator The derivative is performed with respect to the X axis bin number not the x axis values For example to convert d dx to d df for a linear frequency display divide by the frequency spacing of the bins In the case where the X axis is logarithmic the function needs to correct for dlogx dx Th
10. Each band represents a full octave with very poor frequency resolution Change the number of bands per octave again Use the knob to select Twelfth and press Enter 7 Press lt Octave Resolution gt Use the knob to select Third and press Enter Press lt Highest Band gt Use the knob to select 20 kHz and press Enter Press lt Octave Channels gt Use the knob to select 1 Channel and press Enter Press lt Highest Band gt Use the knob to select 40 kHz and press Enter 8 Press Display Setup Octave Analysis 1 25 Choose 1 12 octave bands Each band represents 1 12 of an octave with very good frequency resolution Note that the measurement requires a long settling time Narrow bands increases the settling time 1 bandwidth Choosing narrow bands also increases the number of calculations required and decreases the maximum frequency which can be measured Change the number of bands per octave again Let s return to 1 3 octaves Change the highest measured band Remember changing the octave resolution has lowered the highest band in the measurement Set the highest band to 20 kHz This is the highest allowed band for 2 channel 1 3 octave analysis We can change the number of channels which are being measured Choose single channel octave analysis This limits the insturment to analyzing only one input but increases the measurement bandwidth Change the highest measured ban
11. Modes Internal External External TTL Post Trigger Pre Trigger Tachometer Input Modes External Time Capture Mode Maximum Rate 2 50 dBV 3 16 mVpk to 34 dBV 50 Vpk in 2 dB steps 57 Vpk Single ended A or True Differential A B 1 MQ 50 pF Floating Mode 1 MQ 0 01 uF Grounded Mode 50 Q Shields are always grounded in differential input A B 4 Vpk 3 dB rolloff at 0 16 Hz 90 dB at 1 kHz Input Range lt 0 dBV 80 dB at 1 kHz Input Range lt 10 dBV 50 dB at 1 kHz Input Range 10 dBV Current Source 4 8 mA Open Circuit Voltage 26 V ANSI Standard S1 4 1983 10 Hz to 25 6 kHz Type 0 Tolerance lt 145 dB below signal Input to Input and Source to Inputs 50 Q receiving input source impedance lt 10 nVrms VHz lt 160 dBVrms VHz above 200 Hz Continuous Internal External or External TTL Level adjustable to 100 of input scale Positive or Negative slope Minimum Trigger Amplitude 5 of input range Level adjustable to 5V in 40 mV steps Positive or Negative slope Input Impedance 1 MQ Max Input 5V Minimum Trigger Amplitude 100 mV Requires TTL level to trigger low lt 0 7V high gt 3 0V Measurement record 1s delayed up to 100 000 samples after the trigger Measurement record starts up to 8000 samples prior to the trigger External or External TTL Level adjustable to 5V in 4 mV steps or 25V in 20 mV steps Positive or Negative slope
12. SR785 Dynamic Signal Analyzer User Math Functions 2 61 User Math Functions What is a User Function User Functions are used to define measurements which are not already available in each Measurement Group A User Function is an equation defined by the user in the User Math menu User Functions use Operands such as FFT 1 FFT 2 Traces or Constants and Operators such as x as well as FFT IFFT Avg Mag Phase etc To make a measurement of a defined User Function select the User Function as the Measurement for the active display User Functions behave exactly the same as the predefined measurements in general The display will show the measurement results using real time input data if the function requires input data Frequency Averaging and Displays operate normally for most User Functions Triggering operates normally within each Measurement Group a function using an FFT time record is triggered normally User Functions are saved and recalled to disk with the instrument Settings Measurement Groups and Traces Each Measurement Group contains 5 User Functions in addition to its predefined measurements User Functions can only be measured displayed within their own Measurement Group Each Measurement Group allows different Operands FFT 1 Oct 1 or Swept Sine Spec 1 as well as different Operators User Functions can also use the 5 stored Traces as operands In this case in order to display this Use
13. Setup to analyze the source output The default source is a 10 24 kHz sine Turn the source on Scale the display to show all of the data Select the Analysis menu Choose Limit Test Show the Edit Limits menu We can t turn on any testing until limits are defined Press lt New Segment gt Press lt XQ gt Press 8 0 0 0 Enter Press lt Y0 gt Press 1 0 Enter Press lt X1 gt Press 1 2 0 0 0 Enter Press lt Y 1 gt Press 1 0 Enter Press lt Return gt Press lt Limit Testing gt Use the knob to select On and press Enter Press lt Edit Limits gt Limit Testing 1 57 This function adds a new segment The new segment has a default position and length The segment is defined by its endpoints XO YO and X1 Y1 These values are specified for the current view and units in this case Hz for the x values and dBVpk for the y values The segments are drawn in half intensity The arrow markers at the end points point down for upper limits and point up for lower limits The current segment whose endpoints are shown and edited in the menu has two additional arrows at the endpoints Select XO first Enter a value of 8000 Hz Select YO Enter a value of 10 dBVpk Select X1 Enter a value of 12000 Hz Select Y1 Enter a value of 10 dBVpk The segment should intersect the signal peak at 10 24 kHz Return to the Limit Test menu Select Limit Testing Turn
14. Trace operands are simply the data stored in the Traces For example Traces can hold reference data used for normalization or calibration There are 5 Traces which can be stored These Traces are shared by all 3 Measurement Groups Constants are complex constants which are the same for every array point Constants such as pi are commonly used in equations There are 5 user defined constants which are shared by all 3 Measurement Groups Operands have an X axis type frequency or time as well as an X axis array length The X axis type of the User Function determines the X axis labeling of its display In general the length of a User Function is determined by the length of the longest operand array Operations between operand arrays are performed on a point by point basis starting at the beginning of each array Operands of different lengths 400 point FFT 1 and 800 point FFT1 stored in a Trace can be combined in an User Function The math is performed over the longest operand with the shorter operand array being used in a circular fashion This usually leads to meaningless results Measurement operands FFT 1 Time 1 etc and Traces have an X axis type either frequency or time domain Arrays of frequency data start at the lowest frequency Arrays of time data start at time 0 A frequency domain operand FFT 1 can be added to a time domain operand Time 1 point by point even though the result is meaningless The X axis type of a User
15. i The MKMX command performs Marker to Max on display d Same as Marker Max key This command is not valid if the Marker of display d is Off The MKMN command performs Marker to Min on display d Same as Marker Min key This command is not valid if the Marker of display d is Off The MKCN command performs Marker to Center on display d Same as Marker Center key The center frequency of the FFT span is set to the marker frequency on display d The span is decreased if necessary This command is only valid when the Measurement Group is FFT and display d is Live This command is not valid if the Marker of display d is Off The DREF command sets and clears the Display Reference for display d If i is 0 the Display Reference is turned Off If i is 1 the current data becomes the Display Reference and the Display Reference is turned On DREF d 1 only sets the Display Reference 1f the Display Reference is currently off This is similar to the Display Ref key The SNAP command rescales the Reference Display of display d to the current display scale Same as Snap Ref key This command has no effect if there is no Reference Display in display d The SBRI command sets queries the Screen Brightness The parameter 1 is a brightness level from 150 dimmest to 255 brightest The SCON command sets queries the Screen Contrast The parameter i is a contrast level from O no contrast to 90 most contrast SR785 Dyna
16. paper Command PGRF 1 Plot Color Selections Many plotters have a multipen carousel In this case different items on the graph may be plotted using different color pens When using a single pen plotter all items are plotted using the one pen regardless of the pen definitions Only the graph display areas are plotted Plotter Text Pen Assign a plotter pen number to the text labels on the graphs 1 to 8 Command PLTX 1 Plotter Grid Pen Assign a plotter pen number to the graph grid 1 to 8 Command PLGD 1 Plotter Trace Pen Assign a plotter pen number to the graph data trace 1 to 8 Command PLTR 1 Plotter Marker Pen Assign a plotter pen number to the graph marker 1 to 8 Turn the marker off to avoid plotting it Command PLMK 1 SR785 Dynamic Signal Analyzer System Menu 4 191 System Menu The System menu configures the interfaces clock calendar and system preferences and edits recorded macros The Diagnostics menu accesses various hardware tests System Preset Remote Mil Preferences Date Time i Diagnostics li Macro a Macro 0 0 EditMacro Macro l Show Version ii Show Settings EA Preset Reset the instrument to the default settings Only the remote interface settings are not changed All stored data are lost This function requires pressing the Enter key to confirm To completely reset the instrument including rem
17. 19 selects a rate equal to the maximum rate divided by 2 to the ith power Thus i 0 selects the maximum rate and 1 1 selects half the maximum rate This command is valid only when the Source Type is Arbitrary The ASRC command sets queries the Arbitrary Source Buffer The parameter 1 selects Arbitrary Waveform memory 0 Chl Capture 1 or Ch2 Capture 2 The selected buffer must contain data otherwise an error occurs This command is valid only when the Source Type is Arbitrary The ASTR command sets queries the Arbitrary Source Start point The parameter 1 is a point in the Arbitrary Waveform either in Arbitrary memory or a Capture buffer This command is valid only when the Source Type is Arbitrary The ALEN command sets queries the Arbitrary Source Length The parameter 1 is the length in kPts in the Arbitrary Waveform either in Arbitrary memory or a Capture buffer i must be an even number from 2 to the length of the waveform This command is valid only when the Source Type is Arbitrary The TARB command copies Trace i to the Arbitrary Waveform buffer The Arbitrary Length is changed to 2 kPoints and the Arbitrary Source is change to Arb Buffer Trace 1 must contain FFT measurement data usually a time record This command is valid only when the Source Type is Arbitrary SR785 Dynamic Signal Analyzer 5 58 Source Commands Swept Sine Source Commands SSAL 7 i The SSAL command sets queries the Auto
18. In the case of triggered measurements skip 1 times the trigger period This allows the time between stored records to be determined exactly In Octave group the Storage Interval is set as a time In this case a snapshot is stored to memory every Storage Interval amount of time 4 ms minimum with 4 ms resolution The Skip Storage Interval has a slightly different effect if the measurement is linear averaged In this case the result of every Nth complete linear average is stored in the waterfall buffer and the average is reset and started over again Change the Number of Averages FFT et al or Integration Time Octave to change the storage rate Depending upon the storage rate the waterfall display may not scroll fast enough to show every record being saved In this case the displays are redrawn with all visible records shown when the measurement is paused Command WESK d 1 or WOSK D d x Set the Waterfall View Count for the active display 2 2048 The View Count is the number of records shown within the display This number is independent of the Total Count number of records stored The View Count is the Z axis scaling of the waterfall display and should be less than the Total Count in order to use the display area effectively Setting the View Count to a large number gt 40 or so will cause the display to skip some records In this case every nth record is drawn in order to show the desired View Count range of
19. Pressing Enter terminates the entry and removes the Alt Save the measurement data in DisplayA to disk using the specified file name The extension 78D is appended automatically Save the measurement again Notice that the lt File Name gt ahs been changed to DATA2 The SR785 will try to autoincrement any filename containing a number Make DisplayB bottom the active display To recall a file first specify the file name You can either enter the name or select from the file catalog Turn the knob to display the file catalog Use the knob to select one of the disk files and press Enter Press lt Disk to Display gt Press Display Options Press lt Display gt Use the knob to select Live and press Enter Saving and Recalling 1 51 Turning the knob while lt File Name gt is highlighted displays the file catalog of the current directory The knob selects a file and scrolls the display Only the files with the appropriate extension 78D are shown To show all files press Exp Recall the data in the file to the active display DisplayB Once again DisplayB is Off Line indicating that it is showing static data Select the Display Options menu Make DisplayB live again Choose Live to return the live measurement to DisplayB This concludes this example Remember Off Line displays are showing stored data not live measurement results Many measurement parameters can
20. Return Turn the Data Table display for the active display On or Off The Data Table is shown in the inactive display s location If the Display Format is Single the Format is first changed to Dual Turning off the Data Table does not change the Display Format back Command DTBL D d 1 Insert a new line in the Data Table for the active display This key has no effect unless the Data Table is turned On Move the marker to the desired frequency or time and press this key to insert a new line in the Data Table The new line will be inserted after the highlighted entry To select an entry in the table use the backspace key lt or press Alt and turn the knob Press Alt again to return the keypad to normal mode Command DINS d 1 x Modify the x value for an existing line in the Data Table for the active display This key has no effect unless the Data Table is turned On Move the marker to the desired frequency or time and press this key to change the x value for the selected line in the Data Table To select an entry in the table use the backspace key lt or press Alt and turn the knob Press Alt again to return the keypad to normal mode Command DMOD d 1 x SR785 Dynamic Signal Analyzer Data Table Analysis Menu 4 151 Delete Line Delete the highlighted line in the Data Table display for the active display This key has no effect unless the Data Table is turned On To select an entry in the table us
21. The TAPR command sets queries the number of tach pulses per revolution The parameter x is the number of pulses per revolution The TARG command sets queries the Tachometer Trigger Range The parameter 1 selects 5V 0 25V 1 or TTL 2 The TALV command sets queries the Tachometer Trigger Level The parameter x is the tach trigger level in volts The TARG command sets queries the Tachometer Trigger Slope The parameter 1 selects Rising 0 or Falling 1 The TAHO command sets queries the Tachometer Holdoff Enable The parameter 1 selects Off O or On 1 The TAHD command sets queries the Tachometer Holdoff Time The parameter x is the holdoff time in seconds The TASH command sets queries the Show Tach status The parameter 1 selects Off 0 or On 1 SR785 Dynamic Signal Analyzer Input Commands 5 65 Input Playback Commands ISTR 2 i ILEN 2 i IMOD 7 i ISPD 2 i The ISTR command sets queries the Capture Playback Start point The parameter 1 is a point in the Capture buffer This command is valid only when the Input Source is Playback The ILEN command sets queries the Capture Playback Length The parameter 1 is the length in kPts in the Capture buffer 1 must be an even number from 2 to the length of the waveform This command is valid only when the Input Source is Playback The IMOD command sets queries the Capture Playback Mode The parameter 1 selects 1 Shot 0 or Circu
22. Trace Delete Item Deletes the highlighted item in the curve table This option is only available when the highlighted item is a pole zero residue or polynomial coefficient Table Format Changes the representation of the curve in the curve fit table polynomial pole zero or pole residue SR785 Dynamic Signal Analyzer 4 166 Edit Table Menu In the polynomial format the curve is described as the ratio of polynomials in s multiplied by an overall gain factor bs b 8s b Freq Resp s Goins PSS PaaS Fst aS Fa as tata In the pole zero fomat the numerator and denominator polynomials are factored so that the frequency response curve is described by the ratio of the products of the poles and zeros To ensure a real impulse repsonse all complex poles and zeros only occur in complex conjugate pairs S28 a Je Sy Freq Re sp s Gain S Py XS Pmi CS Po In the pole residue format a partial fraction expansion of the pole zero form is performed to yield the frequency response as a sum of single pole terms weighted by residues R R R Freq Re sp s Gain a l 4 4 a S Pm S Pm s Po Command EITM 1 J Copy Other Table Copies the curve from the other curve fit table into the table currently being edite d Since this option will erase the curve currently being edited the analyzer will prompt for a confirmation before copying the table data Clear Table Clears all dat
23. d f SSFR SSKP d i SSLL x SSLO d x SSRF x SSTM d x SSTP d f SSTR d f SSTY 2 d i SSUL x STMD i STRT STYP i SVNI i SVRF d i SVTR d i TARB i TARM TASC 2 i n TASC i n TAVM 2 i TDIC 2 d i TD2C 2 d i TDLA x TDLB 7 x TGET i TGET i TIAS 2 x TIME i j k TLOD i n TLOD i n TLVL x TMAN TMOD i 5 73 5 73 5 59 5 104 5 33 5 54 5 59 5 50 5 58 5 95 5 53 5 58 5 32 5 58 5 58 5 95 5 73 5 50 5 32 5 33 5 59 5 33 5 58 5 73 5 32 5 32 5 32 5 58 5 66 5 102 5 53 5 118 5 103 5 102 5 57 5 66 5 109 5 109 5 69 5 62 5 63 5 66 5 66 5 111 5 111 5 67 5 100 5 109 5 109 5 66 5 66 5 66 SR785 Dynamic Signal Analyzer Swept Sine Int Cycles Swept Sine Int Time Swept Sine Max Level Snap Reference Swept Sine Number of Points Sine Offset Swept Sine Offset Query the Sideband Power Swept Sine Ramp Rate Recall Settings Source On Off Swept Sine Source Ramping Off On Swept Sine Repeat Mode Swept Sine Auto Level Swept Sine Amplitude Settings to Disk Swept Sine Settle Cycles Sideband Separation Swept Sine Progress Swept Sine Max Step Size Swept Sine Lower Limit Swept Sine Slower Threshold Swept Sine Ideal Reference Swept Sine Settle Time Swept Sine Stop Frequency Swept Sine Start Frequency Swept Sine Sweep Type Swept Sine Upper Limit Trigger
24. i I2MD 2 i I2GD i l2CP 7 i Input Commands 5 61 The I1AW command sets queries the Chl A Weighting Filter Off On The parameter 1 selects Off O or On 1 The I2MD command sets queries the Ch2 Input Mode The parameter 1 selects A single ended 0 or A B differential 1 The I2GD command sets queries the Ch2 Input Grounding The parameter 1 selects Float 0 or Ground 1 The I2CP command sets queries the Ch2 Input Coupling The parameter 1 selects DC 0 AC 1 or ICP 2 I2RG x lt dBVpk dBVpp dBVrms Vpk Vpp Vrms dBEUpk dBEUpp dBEUrms EUpk EUpp EUrms gt I2AR i A2RG i I2AF 7 i I2AW i IAOM i The I2RG command sets queries the Ch2 Input Range The parameter x is the full scale input range in the specified untis If the exact input range specfied is not available the closest available input range will be used The query command returns a value of the form x j where x is the value and j is the index into the list of units If Ch2 AutoRange is On the I2RG i command will turn Ch2 AutoRange Off and the set the Ch2 Range to f The I2AR command sets queries the Ch2 AutoRange Mode The parameter 1 selects Normal 0 or Tracking 1 The A2RG command sets queries the Ch2 AutoRanging Off On The parameter 1 selects Off Manual 0 or On AutoRanging 1 If i 1 and Ch2 AutoRange is already On a new AutoRange is performed Th
25. 1 The following Views are available Log Magnitude Log magnitude view graphs the log of the magnitude of the measurement data The magnitude is simply V x y where x is the real part and y is the imaginary part The Y axis of the display is logarithmic If lt dB Units gt in the lt Units gt submenu are Off the Y axis will display a logarithmic grid If lt db Units gt are On the Y axis will have a grid which is linear in decibels The shape of the graph is the same in the two cases Linear Magnitude Linear magnitude view graphs the magnitude of the measurement data The magnitude is simply V x y where x is the real part and y is the imaginary part The Y axis of the display is linear in scaling Magnitude Magnitude view graphs the magnitude squared of the measurement data The magnitude squared is simply x y where x is the real part and y is the imaginary part The Y axis of the display is linear in scaling Real Part Real Part view graphs the real part of the measurement data The Y axis of the display is linear in scaling Imaginary Part Imag Part view graphs the imaginary part of the measurement data The Y axis of the display is linear in scaling Real measurement data such as baseband time record have zero imaginary part This view is zero for all points SR785 Dynamic Signal Analyzer Display Setup Menu 4 39 Imaginary data arises from the multiplication of the time data by sine and cosi
26. 2 i ILAW 2 i ICP 2 i LGD 2 i IMD i IIRG x 5 92 5 68 5 68 5 68 5 68 5 28 5 28 5 109 5 28 5 94 5 29 5 100 5 28 5 94 5 95 5 68 5 95 5 94 5 69 5 95 5 94 5 28 5 28 5 28 5 78 5 78 5 79 5 94 5 43 5 43 5 43 5 36 5 50 5 36 5 49 5 50 5 49 5 36 5 49 5 60 5 60 5 61 5 60 5 60 5 60 5 60 SR785 Dynamic Signal Analyzer Zeros Average On Display Average Average Number Average Type Base Frequency FFT Base Frequency Read Display d Bin Number FFT Center Frequency Save Recall Directory FFT End Frequency Frequency Format FFT Resolution Save Recall File Name Read Disk Catalog FFT Time Record Increment Disk to Display Disk Free Space FFT Overload Reject Reset Disk Catalog Display to Disk FFT Frequency Span Sampling Time FFT Start Frequency Force Length Window Expo TC File Exist Number of Grid Divisions Nyquist Grid Type Grid On Off Histogram Bins Harmonic Sideband Display Histogram Length Query the Harmonic Power Harmonic Sideband Readout Number of Harmonics Histogram Repeat Query the Total Harmonic Distortion Chl Anti Alias Filter Chl AutoRange Mode Chi A Weight Filter Ch1 Input Coupling Ch1 Input Grounding Ch1 Input Mode Ch1 Input Range I2AF i I2AR i I2AW 2 i I2CP 2 i I2GD 2 i I2MD i I2RG x IAOM i ILEN 2 i IMOD i INPC i INPC i INPE i j INPS i INSE
27. 5 60 5 60 5 60 5 60 5 60 5 60 5 60 5 60 5 60 5 61 5 61 5 61 5 61 5 61 5 61 5 61 5 61 5 61 5 61 5 122 5 62 5 62 5 62 5 62 5 62 Swept Sine Auto Level Swept Sine Amplitude Swept Sine Ideal Reference Swept Sine Source Ramping Off On Swept Sine Ramp Rate Swept Sine Upper Limit Swept Sine Lower Limit Swept Sine Max Level Swept Sine Offset Input Source Analyzer Configuration Ch1 Input Mode Ch1 Input Grounding Ch1 Input Coupling Ch1 Input Range Chl AutoRange Off On Chl AutoRange Mode Chl Anti Alias Filter Chl A Weight Filter Ch2 Input Mode Ch2 Input Grounding Ch2 Input Coupling Ch2 Input Range Ch2 AutoRange Off On Ch2 AutoRange Mode Ch2 Anti Alias Filter Ch2 A Weight Filter Auto Offset Input Ovld Read Chl Engineering Units Off On Chl EU Label Chl EU Volt Ch1 User Label Chl Transducer Convert SR785 Dynamic Signal Analyzer 5 6 Index of Commands EU2M i 5 62 Ch2 Engineering Units Off On EU2L i 5 63 Ch2 EU Label EU2V x 5 63 Ch2 EU Volt EU2U s 5 63 Ch2 User Label TD2C d 1 5 63 Ch2 Transducer Convert Input Playback ISTR i 5 65 Capture Playback Start ILEN 1 5 65 Capture Playback Length IMOD i 5 65 Capture Playback Mode ISPD 1 5 65 Capture Playback Speed Trigger TMOD 1 5 66 Trigger Arming Mode TSRC i 5 66 Trigger Source TLVL x 5 66 Trigger Level TSLP i 5 66 Trigger Slope TDLA x 5 66 Trigger
28. AOVL i SAVR i SDLY i FFMT 7 i The OUTX command sets queries the Output Interface The parameter 1 selects GPIB 0 or RS232 1 The OUTX 1 command should always be sent at the start of any program to direct query responses to the correct interface The OVRM command sets queries the GPIB Overide Remote mode The parameter 1 selects No 0 or Yes 1 When Overide Remote is set to Yes the front panel is not locked out when the unit is in the REMOTE state The KCLK command sets queries the Key Click Off On The parameter 1 selects Off 0 or On 1 The ALRM command sets queries the Alarms Off On The parameter 1 selects Off 0 or On 1 The ALRT command sets queries the Alarms Volume The parameter 1 selects Quiet 0 or Noisy 1 The ADON command sets queries the Done Volume The parameter 1 selects Quiet 0 or Noisy 1 The AOVL command sets queries the Audible Overload The parameter 1 selects Off 0 or On 1 The SAVR command sets queries the Screen Saver Off On The parameter 1 selects Off 0 or On 1 The SDLY command sets queries the Screen Saver Delay The parameter 1 is a delay in minutes from 1 to 59 The FFMT command sets queries the Frequency Format The parameter 1 selects Exact Bin 0 or Rounded 1 TIME 7 i j k The TIME command sets queries the System Time SR785 Dynamic Signal Analyzer System Commands 5 101 The TIME command qu
29. All complete averages are stored to a waterfall to examine the sound level decay Both displays always have the same Linear Average Trigger Command OLAT d 1 SR785 Dynamic Signal Analyzer Swept Sine Average Menu 4 119 Swept Sine Average Menu Settle Time When the Measurement Group is Swept Sine this menu sets the settle and integration times These parameters govern the measurement of both channels See Swept Sine in Chapter 2 for a discussion about swept sine measurement fundamentals Settle Cycles Integration Cycles 10 Set the Settle Time in increments of 3 906 ms 7 8125 ms 1 ks At each frequency point a settling time is allowed to pass before any measurement is made This allows the device under test to respond to the frequency change The Settle Time is rounded up to the next multiple of 3 906 ms The actual settling time is the larger of the Settle Time and the Settle Cycles rounded to the next multiple of 3 906 ms The settling time is always a minimum of 1 cycle or 7 8125 ms Changes made to the Settle Time during a sweep take effect immediately The estimated sweep time is displayed in the Horizontal Scale Bar This time is simply the sum of the Settle and Integrate times for all points in the sweep Auto functions Source Auto Level Auto Range Auto Resolution will change the actual sweep time Command SSTM d x Settle Cycles Set the number of Settle Cycles 1 32767
30. Continuous 1 or One Shot 2 The set command requires d 2 both displays This command is not valid when the Measurement Group is Swept Sine WESB 7 d i The WFSB command sets queries the Waterfall Save Option for display d The parameter 1 selects Save All Measurements 0 or Save Active Measurement Only 1 This command is not valid when the Measurement Group is Swept Sine WTOT d i The WTOT command sets queries the Waterfall Total Count for display d The parameter 1 is a number of records If the allocated memory is too small for the requested number of records an error occurs This command is not valid when the Measurement Group is Swept Sine WAVA d The WAVA command queries the number of records available in the waterfall buffer for display d Records are not stored in the buffer unless Waterfall Storage is on Continuous or One Shot This command is not valid when the Measurement Group is Swept Sine WFSK d i The WFSK command sets queries the Waterfall Skip count for FFT measurements for display d The parameter 1 is a number of records This command is valid only when the Measurement Group is FFT Correlation Order or Time Histogram WOSK d x lt ks S ms gt The WOSK command sets queries the Waterfall Skip count for Octave measurements for display d The parameter x is a time from 008 to 1000 s SR785 Dynamic Signal Analyzer Waterfall Commands 5 81 This
31. Control Keys Start Reset If the unit is already making measurements Start Reset resets any averages and starts the measurement over If the measurement is paused Start Reset starts the measurement over again The Run Pause indicator shows Run when measurements are in progress Start Reset also puts into effect any measurement related changes which may have been made since the last measurement was completed For instance if a set of averages is completed and the frequency span is changed the new span does not take effect until the next time Start Reset is pressed If the measurement is triggered Start Reset does not supply a trigger If the trigger is manual armed Start Reset does not arm the trigger If the displays don t update see the Operating Hints in Chapter 2 for help A TTL rising edge at the rear panel Start input is equivalent to pressing the Start Reset key Command STRT Pause Cont If the unit is already making measurements Pause Cont halts data acquisition The measurement is paused where it is and the displays are not updated The Run Pause indicator shows Pause when measurements are paused If the measurement is paused Pause Cont resumes the measurement where it was left off To start over press Start Reset The Run Pause indicator shows Run when measurements are in progress For Exponential averaging Pause Cont simply resumes data acquisition without resetting
32. DELF Del Cur Dir Delete the Current Directory from disk Make sure that the directory is correct before pressing this key The directory must be empty before it can be deleted Command DELD Format Floppy Format the disk The disk capacity is 720k for DS DD disks and 1 44M for DS HD disks A disk must be formatted before files can be stored on it Formatting a disk involves erasing all information from the disk and rewriting the directory Formatting a disk destroys all data presently on disk SR785 Dynamic Signal Analyzer 4 184 Output Menu Output Menu The Output menu prints or plots the screen display Printer and plotter configurations are set in this menu Hardcopy Output Hard Copy Button Bitmap Print Bitmap Printer i PC X 8 bit Bitmap area Vector Plotter PostScript Destination Disk File Edit A Note C File Start Number 0 Colors Hard Copy Button Assign either Bitmap Print Vector Plotter ASCII Dump to the Print Screen hardkey The Print Screen hardkey allows you to print plot or dump the screen from any menu Command POUT Bitmap Print Prints the screen using the selected Bitmap Printer and Bitmap Area to the selected Destination Interface or Disk Other front panel operations are disabled until printing is completed Pressing backspace will abort the operation Command PRNT Vector Plot Plot the screen using the selected Vector Plotter to the selected Destina
33. Delete the highlighted term in a User Function equation To move the cursor in a User Function equation use lt Func String gt and the knob Clear Eq Clear the entire equation definition If a cleared User Function 1s entered it will be undefined and unavailable for display If a display is currently measuring this function then it may not be cleared In this case change the measurement and then clear the equation Cancel Discard any changes made in this menu and exit this menu Enter Eq Enter the displayed equation as the new User Function and exit this menu The new User Function definition is used immediately if it is being displayed If the new function uses an incompatible or empty Trace it may not be displayed as a measurement If a display is already measuring this function then it may not be entered In this case change the measurement and then change the equation Edit Constant Display the Edit Constant menu Press lt Return gt or User Math for the main User Math menu Constants may be used as operands in a User Function There are 5 constants which may be defined and are shared by all Measurement Groups Command USRC i x y SR785 Dynamic Signal Analyzer 4 130 User Math Menu Imag Part 0 Mag 1 Phase deg Marker gt Ma C Return Constant Use the knob to pick one of the five Constants to edit and press Enter Real Part Enter a new value for the real part of the sel
34. Enter the playback configuration submenu It is generally a good idea to playback an exact number of time records This way the last record doesn t wrap around and use points from the start of the buffer At this span with no overlap each time record is 62 5 ms long The capture sampling rate was 131 1 kHz so 2 kPoints of capture represents 15 625 ms of data Thus each time record is 8 kPoints of capture long We want the Playback Length to be an integer multiple of 8 kPoints 112 time records uses 896 kPoints and is close to the full capture length Change the Playback Length to an exact number of time records Start the playback again Capture 1 33 This concludes this example Capture and Playback is a way to record a signal and re analyze it over and over SR785 Dynamic Signal Analyzer 1 34 Waterfall Display Waterfall Display This example demonstrates the use of waterfall displays Waterfalls are available for FFT and Octave measurements for analog inputs as well as capture playback In this example we will simulate a reverberation measurement measuring the SR785 source To perform a real measurement you would use the source to drive a power amplifier and a microphone to receive the signal 1 Press System Press lt Preset gt Press Enter to confirm Preset 2 Connect the Source Output to the Channel 1 A Input 3 Press Display Setup Press lt Measure Group gt Select Octave with the knob a
35. If no menu box is highlighted pressing a numeric entry key automatically selects the most recently modified parameter within the menu and begins numeric entry This is convenient when a measurement requires a single parameter within a menu or menus to be modified repeatedly Numeric Values Parameters with numeric values display their current value in their menu box Examples of numeric parameters are lt Span gt lt Avgs gt and lt Ch1 Input Range gt Some numeric values are continuous such as lt Avgs gt while others can only have discrete values such as lt Span gt To enter a new value press the softkey to highlight its menu box The parameter value is displayed in the entry field at the top of the screen For example to change the Span press Freq for the menu and then lt Span gt 1st softkey The lt Span gt menu box will be highlighted and the current Span value will be shown at the top of the screen The numeric entry keys are used to enter values directly For example to set the Span to 12 8 kHz press 1 2 8 As soon as the 1 is pressed the entry field shows the new value as it is entered The list of appropriate units is displayed as well The entry field displays the characters as the keys are pressed The _ is the entry point If an error is made the backspace lt key will erase the last character Pressing the same softkey again or another softkey to modify another parameter will abor
36. Level is not really required but illustrates its use Change the active display to DisplayB which is still measuring the spectrum of Ch2 SR785 Dynamic Signal Analyzer 1 46 Swept Sine Measurement Press Auto Scale B 12 Press Active Display SR785 Dynamic Signal Analyzer Scale the display On both sides of the notch you can see Auto Level keeping the Ch2 signal level at 10 mV 40 dBV The reference tolerance is 3 dB and is set by the Ref Limits As the sweep moves into the notch the source level reaches the Max Source level of 1 V and the Ch2 signal drops to 60 dBV The spectrum of Chl measures the actual source level at each point and the Frequency Response is still calculated correctly Switch back to DisplayA Frequency Response This concludes this measurement example You should have a basic understanding of Swept Sine measurements The Input Range Resolution and Source Level optimizations greatly extend the dynamic range of the measurement while minimizing the measurement times Saving and Recalling Saving and Recalling 1 47 This example illustrates saving and recalling displays to reference displays traces and disk files 1 Press System Press lt Preset gt Press Enter to confirm Preset 2 Connect the Source Output to the Channel 1 A Input Press Source lt On gt Press Span Down twice to change the span to 25 6 kHz Press Auto Scale A 3 Press Display Ref Press Input
37. Marker to Mag Window Menu Window Channel 1 Window Channel 2 Window Force Length Expo TC Trace to Window Window to Trace Window Form Waterfall Menu Display Storage Save Option Total Count Skip Storage Interval View Count Angle Marker to Z Allocate Memory More Trace Height Fast Angles Threshold Hidden Lines Paused Drawing Record to Trace Slice to Trace Capture Menu Capture Channels Capture Mode Capture Length Sampling Rate Allocate Memory SR785 Dynamic Signal Analyzer 4 120 4 120 4 122 4 122 4 122 4 123 4 126 4 128 4 128 4 129 4 129 4 129 4 129 4 129 4 130 4 130 4 130 4 130 4 130 4 130 4 131 4 131 4 133 4 133 4 133 4 133 4 134 4 134 4 134 4 135 4 135 4 136 4 136 4 137 4 137 4 138 4 138 4 139 4 139 4 140 4 140 4 141 4 141 4 141 4 141 4 142 4 142 4 143 4 143 4 143 4 144 4 144 4 145 Total Available Capture Memory Waterfall Memory Arb Memory Confirm Allocation Clear Allocation View Header Auto Pan Analysis Menu Data Table Limit Test Marker Stats Exceedance Stats Curve Fit Data Table Analysis Menu Data Table Insert Line Modify Line Delete Line Clear Table Limit Testing Analysis Menu Limit Segments Limit Testing Limit Beep Clear Limits Edit Limits New Segment Limit Type Segment XO YO X1 Y1 Delete Segment Shift All Marker Statistics Menu Marker Stats Reset Max Display A Min Display A Mean Display A
38. Press Input Press lt Input Source gt SR785 Dynamic Signal Analyzer Reconnect the analog signal to both Chl and Ch2 inputs Select the Input menu Change the Input Source Choose Analog input again The Capture parameters can not be modified while the measurement input is Playback Select the Display Setup menu Change the Measurement for DisplayB Measure the Ch2 input also Select the Capture menu Change which channels are captured Choose both channels The Capture Length is automatically halved to accommodate both channels in the allocated memory We can increase the capture time by decreasing the Sampling Rate This decreases the bandwidth of the stored signal Choose 131 1 kHz as the Sampling Rate The capture bandwidth is now 51 2 kHz reduced from 102 4 kHz During playback from this buffer the measurement bandwidth will not be allowed to exceed 51 2 kHz Capture both inputs for 7 03 seconds Watch for the Capture Progress indicator to reach 100 The signal should disappear from the spectrum in both displays Select the Input menu Change the Input Source Use the knob to select Playback and press Enter Press Auto Scale A and Auto Scale B Press Start Reset Press lt Playback Config gt Press lt Playback Speed gt Use the knob to select Every Time Rec and press Enter Press Start Reset Press Trigger Press lt Trigger Source gt Capture 1 31 Choose
39. SDBN 2 d i SDLY i SFST d x 5 97 5 103 5 97 5 97 5 97 5 40 5 103 5 103 5 107 5 118 5 118 5 118 5 43 5 118 5 119 5 119 5 54 5 54 5 54 5 54 5 32 5 100 5 100 5 104 5 50 5 100 5 33 Index of Commands 5 17 Pause Accept Preview Average Preview Reject Preview Preview Time Print Black Print Bright GPIB Control Print Dim Print Plot Destination File Start Number Print Graph Phase Suppress Threshold Play Tune Plotter Grid Pen Plotter Marker Pen Plot Screen Plot Screen Plotter GPIB Address Vector Plotter Type Plotter Trace Pen Plotter Text Pen Print Screen hardkey Print Screen Print Screen Bitmap Printer Type Bitmap Area PSD Units On Off Trace to Reference Trace i to Display d Read Ref Display d bin j Reference Node Direction Reference Node Name Reference Node Number RPM Frequency Response Node Direction Response Node Name Response Node Number Sine Amplitude 1 Sine Frequency 1 Sine Amplitude 2 Sine Frequency 2 Swept Sine Auto Resolution Screen Saver On Screen Brightness Screen Contrast Number of Sidebands Screen Saver Delay Swept Sine Faster Threshold SR785 Dynamic Signal Analyzer 5 18 Index of Commands SICY d i SITM d x SMAX x SNAP d SNPS d i SOFF x SOFF x SPWR d i SRAT x SRCL i SRCO i SRMP i SRPT d i SSAL i SSAM x SSAV SSCY 2 d i SSEP
40. SR785 Dynamic Signal Analyzer 2 56 Order Analysis The combination of Maximum Order and Delta Order also determine the length and resolution of the Order time records The resolution of the time record in revolutions 1s given by Resolution 1 5 12 Effective Max Order where Effective Max Order is equal to Delta Order 400 if Max Order Delta Order gt 200 Delta Order 200 if 100 lt Max Order Delta Order lt 200 Delta Order 100 if 50 lt Max Order Delta Order lt 100 or Delta Order 100 Uf MaxOrder Delta Order lt 50 The length of the time record in revolutions is 1 Delta Order The combination of these parameters also determines the Capture Sampling Rate While in other measurement groups the Capture Sampling Rate is determined explicitly by the user with the sampling rate softkey In the order measurement group the sampling rate is given by Sampling Rate 5 12 Effective Max Order where the sampling rate is then rounded up to the nearest integer submultiple of 256 kHz Order Measurements Linear Spectrum The Linear Spectrum in the order measurement group 1s similar to the FFT measurment in the FFT measurement group except that the x axis is calibrated in orders instead of absolute frequency The Linear Spectrum includes both magnitude and phase information Phase in the Linear Spectrum is measured relative to the tachometer pulse unless an external trigger is used in which case the phase is measure
41. SR785 Dynamic Signal Analyzer Output Remote Interface Overide Remote Key Click Alarms On Alarms Volume Done Volume Audible Overload Screen Saver On Screen Saver Delay Frequency Format Time Date Active Display Start Reset Pause Continue Unsettle Measurement Capture Start Capture Stop Display d to Trace 1 Trace i to Display d Reference to Trace Trace to Reference Dump Display Data Print Screen Plot Screen AutoScale Chl AutoRange Off On Ch2 AutoRange Off On Set Marker to Ref Move the Marker to the Maximum Move the Marker to the Minimum Center of FFT Span to Marker Display Ref Snap Reference Screen Brightness Screen Contrast Key Press Knob Tone Play Tune Display d to Trace 1 Trace i to Display d Trace 1 to Disk Disk to Trace 1 Download Trace 1 Binary Download Trace i Ascii Upload Trace i Buffer Download Trace i Buffer Data Transfer DSPN d DSPY d j REFY d j DSPB d j DBIN d j FBIN d x TLOD 1 n TASC 1 n ALOD n TGET 1 TPUT 1 AGET 1 APUT 1i CGET i j CPUT i j WGET WPUT Interface RST IDN LOCL i OVRM i Status CLS PSC 2 i SRE i 5 STB i ESE i J ESR i ERRE i J ERRS i INSE i 93 INST i DSPE i J DSPS i INPE i 93 INPS i INPC 1 Nodal Degree of Freedom Information SVNI i RFNA s RFNU i RFEDR
42. SRCL 1 Macros Include stored macros in the recall Command SRCL 1 Recall from Disk Recall the selected instrument settings from the Current File in the Current Directory The recalled settings become effective immediately Command SRCL 1 SR785 Dynamic Signal Analyzer Disk Buffers Menu 4 177 Disk Buffers Menu File Name Buffers File Name MYFILE Current Directory Ld Tre Data Ascii C Ld Tre Data Bin C Buffer Ch 1 Captur peery wehe PFP Disk to Buffer C Enter the save and recall Current File Name Turn the knob to bring up the file catalog display listing all files in the Current Directory with the extension 78 SR785 files Press Exp to display all files in the directory Choose a file name with the knob and press Enter to make it the Current File Name This file name is used for saving and recalling displays traces and settings Remember saving to this file will write over the existing file New file names are entered using the Alt key and the letters associated with each key Press Alt again to return to normal keypad operation DOS file name conventions must be followed File names are 8 characters or less with an extension ext of up to 3 characters Default extensions are automatically supplied if no extension is specified The default extensions should be used since the directory display assumes an extension appropriate for the current menu
43. The Reference Upper and Lower Limits are the allowable tolerances for the Reference Channel The source level is changed only if the reference channel measures an input which exceeds the Ideal Reference by more than the Upper Limit or which is less than the Ideal Reference by more than the Lower Limit If a source amplitude greater than the Maximum Source Level is required then the Reference Channel signal may fall below the Reference Lower Limit The Reference Lower Limit may be changed during a sweep Command SSLL x Maximum Source Level Set the Maximum Source Level 0 mV 5000 mV This parameter is adjustable only if Auto Level Reference is set to Channel 1 or Channel 2 SR785 Dynamic Signal Analyzer 4 86 Swept Sine Source Menu The Maximum Source Level is the largest allowed source amplitude This is limited by the SR785 source output or the device under test input range If the Reference Lower Limit requires a source amplitude greater than the Maximum Source Level then the source amplitude is set to the Maximum Source Level In this case the Reference Channel may fall below the Reference Lower Limit The Maximum Source Level may be changed at any time during a sweep Command SMAX x Offset Set the DC Offset of the Swept Sine Source 5V 5V The offset resolution is 0 1 mV Note that the sum of the offset and Amplitude if Auto Level Reference is off or Maximum Source if Auto Level Reference is on cannot
44. The Start frequency is usually less than the Stop frequency If the Start frequency is greater than the Stop frequency then the sweep proceeds downward from the Start frequency If the Start frequency is changed during a sweep the sweep will be reset Command SSTR d f Set the Stop frequency 1 mHz 102 4 kHz Note that measurements at frequencies less than Hz take a significant amount of time The Stop frequency is usually greater than the Start frequency If the Stop frequency is less than the Start frequency then the sweep is downward from the Start frequency If the Stop frequency is changed during a sweep the sweep will be reset Command SSTP d f SR785 Dynamic Signal Analyzer 4 16 Swept Sine Frequency Menu Repeat Type Select the Sweep Repeat Mode Single Shot Continuous In Single Shot mode the measurement is paused at the completion of the sweep and the source ramps off In Continuous mode the measurement is repeated at the completion of each sweep The source moves immediately to the Start frequency and begins the sweep again Data from the previous sweep is preserved on the display and can be examined with the cursor Command SRPT d 1 Select the Sweep Type Linear Log Linear sweep computes the measurement points in a linear progression from the start to the stop frequency Choosing linear sweep also sets the X axis to linear Log sweep uses a logarithmic progression
45. UNIT d The UNIT query command queries the Units of display d The unit string depends on the measurement the view and the settings of dB Units pkUnits PSD Units and Phase Units UNDB 7 d i The UNDB command sets queries the dBUnits setting for display d The parameter 1 sets dBUnits to Off 0 On 1 dBm 2 and dBspl 3 UNPK d i The UNPK command sets queries the pk units setting for display d The parameter 1 sets pkUnits to Off 0 pk 1 rms 2 and pp 3 PSDU 7 d i The UNPK command sets queries psd units setting for display d The parameter 1 sets psd Units to Off 0 or On 1 UNPH d i The UNPH command sets queries phase units setting for display d The parameter 1 sets phase Units to Degrees 0 or Radians 1 DBMR 7 x The DBMR command sets queries the dBm Reference Impedance for BOTH displays The parameter x is a real value of Ohms This affects the calculation of dBm units in both displays YMAX d x The YMAX command sets queries the Y Maximum top reference of display d The parameter x is a real number in the display units This command is not valid when the View is Nichols or Nyquist YMID d x The YMID command sets queries the Y Midpoint center reference of display d The parameter x is a real number in the display units This command is not valid when the View is Nichols or Nyquist SR785 Dynamic Signal Analyzer Display Setup Comm
46. Zoomed time records are complex they have both a real and an imaginary part You can display the magnitude and phase as well as the real or imaginary part The sampling rate is always half of the equivalent baseband span Why Use The Time Record The time record display can be useful in determining whether the time record is triggered properly If the analyzer is triggered and the signal has a large component synchronous with the trigger then the signal should appear stationary in the time record If the signal triggers randomly then the time display will jitter back and forth Remember the time record has a resolution of 1 sample rate A triggered time record will always jitter by 1 sample This jitter is removed in the computation of the phase of the spectrum relative to the trigger Watch Out For Windowing The SR785 can display both the time record and the windowed time record Most window functions taper off to zero at the start and end of the time record If a transient signal occurs at the start of the time record the corresponding windowed time record and FFT may not show anything because the window function reduces the transient to zero SR785 Dynamic Signal Analyzer 2 12 FFT Windowing FFT Windowing A signal which is not exactly periodic within the time record does not fall on an exact frequency bin of the FFT spectrum integer multiple of the FFT frequency resolution Its energy is split across multiple adjacent frequency
47. and Auto Scale B Press Average Press lt Integration Time gt Press 1 select s with the knob and press Enter Press Freq Press lt Octave Resolution gt Use the knob to select Full and press Enter Press lt Octave Resolution gt SR785 Dynamic Signal Analyzer Select the Source menu Choose Noise as the source type Octave measurements are generally used to measure noise Change the type of noise Choose Pink noise Pink noise rolls off at 3dB per octave This maintains equal power per octave band and yields a flat octave spectrum Adjust the input ranges to remove overloads Notice that the measurement needs to settle after the input range is changed This is because the measurement is invalid until the input change has propagated through all of the octave band filters This settling time is related to 1 bandwidth of each filter Bands which are un settled are graphed in half intensity Settle is displayed until all bands in the display are settled DisplayA Ch1 shows the flat source spectrum and DisplayB Ch2 shows the notch filter output Select the Average menu Note that this menu is changed in Octave group The Integration Time is the averaging time constant All Octave measurements are rms averaged Increase the Integration Time to smooth the fluctuations in the spectrum Select the Frequency menu Change the number of bands per octave Choose Full octave bands
48. averaged for 8 ms and each starting when the previous average is complete Linear Avg Mode Continuous 9 Press Waterfall Press lt Display gt Use the knob to select Waterfall and press Enter Press lt Storage gt Press Save Options and press ENTER Use the knob to select Active Meas Only and press ENTER Use the knob to select One Shot and press Enter Press lt Total Count gt Press 5 0 Enter 10 Press Trigger Press Start Reset Waterfall Display 1 37 Select the Waterfall menu Change the Display Choose Waterfall display This shows measurements scrolling down Without waterfall storage this is purely graphical no data can be read from measurements other than the most recent Select waterfall Storage Choose One Shot to fill the waterfall buffer once and stop Change the number of measurements to store in the waterfall buffer The Total Count is linked to both displays by default Entering 50 changes the total count for both displays to 50 Select the Trigger menu again Start Reset starts the measurement Since the measurement is triggered not Free Run nothing happens until the first trigger is received SR785 Dynamic Signal Analyzer 1 38 Waterfall Display Press lt Manual Trigger gt 11 Press Alt and turn the knob clockwise Continue until the display does not scroll any further Press Alt Turn the knob clockwise to move the marker alo
49. band with solid vertical markers The pairs of vertical markers are connected by shaded bands at the bottom of the graph These shaded bands define the bins within the Upper and Lower bands Use lt Modify Band gt to modify either the Upper or Lower band Use the knob to move selected band Use Alt knob to re size the selected band The two Band Powers are calculated within the Marker menu in Vrms Only those frequencies within the two band limits contribute to the Band Powers Band Exclude can be used to remove a small band from a larger band For example exclude 2from1 excludes those bins in the Upper band from the Lower band The Lower Band Power only includes those bins in the Lower band which are not also in the Upper band The Band Ratio is the ratio of the Upper Band Power to either the Lower Band Power or the sum of the two band powers The ratio is displayed in and dB Band Ratio can be used to measurement THD N In this case use the Lower 1 band to define a small region around the fundamental and the Upper 2 band to define the total bandwidth of interest Exclude Ifrom2 so the Upper 2 band does not measure the fundamental Choose the 2 1 2 ratio mode to measure THD N power with fundamental notched out total power including fundamental Band Marker is only available for frequency domain FFT Order and Octave measurements Band Marker is not available for the Swept Sine Correlation or Time Histogr
50. binary transfer is in progress the analyzer will not respond to any other queries and the displays will not update If the host program does not start reading the points within second or pauses for 1 second while reading the binary transfer will be aborted To read the data in a Trace recall the Trace to a display and then read the display The DBIN command queries the frequency or time of bin j in display d The parameter d selects Display A 0 or Display B 1 The parameter j is bin from 0 to length 1 SR785 Dynamic Signal Analyzer FBIN d x TLOD i n TASC i n Data Transfer Commands 5 109 The returned value is either a frequency spectra a time time record or correlation or a band center frequency octave The FBIN command queries the bin number of x frequency or time in display d The parameter d selects Display A 0 or Display B 1 The parameter x is a floating point value of Hz or seconds The returned value is an integer bin number The TLOD command loads binary data into Trace 1 The parameter 1 selects Trace 1 through 5 This command is valid only via the GPIB interface The target Trace 1 must already store data of the measurement type and length to be loaded from the interface The loaded data simply takes the place of the stored trace data and assumes the measurement parameters Measurement Averaging Window Frequency span etc and length of Trace 1 TLOD loads the actual complex da
51. dBVpk dBVpp dBVrms gt The S2AM command sets queries the Amplitude of Sine Tone 2 The parameter x is the amplitude in the specified units The query returns two numbers of the form y 1 where y is a real number and 1 is an index indicating the units This command is valid only when the Source Type is Sine SR785 Dynamic Signal Analyzer Source Commands 5 55 Chirp Source Commands CAMP x lt mV V dBVpk gt CBUR 7 x CSRC i The CAMP command sets queries the Chirp Amplitude The parameter x is the amplitude in the specified units The query returns two numbers of the form y 1 where y is a real number and 1 is an index indicating the units This command is valid only when the Source Type is Chirp The CBUR command sets queries the Chirp Burst Percentage The parameter x is a percentage from 1 to 100 This command is valid only when the Source Type is Chirp and the Measurement Group is FFT or Correlation The CSRC command sets queries the Source Display The parameter 1 selects DisplayA 0 or DisplayB 1 This command is valid only when the Source Type is Chirp or Noise and the Measurement Group is FFT or Correlation SR785 Dynamic Signal Analyzer 5 56 Source Commands Noise Source Commands NAMP x lt mV V dBVpk gt NTYP 7 i NBUR 7 x The NAMP command sets queries the Noise Amplitude The parameter x is the amplitude in the specified units The query returns t
52. defined within the Octave Analysis Measurement Group may include octave measurement results Use the User Math menu to define a math function A User Function may not be selected as the measurement if it uses a Trace which is empty or which contains data taken in a different Measurement Group The number of Octave Channels limits the measurement choices of both displays If 1 Octave Channel is selected then only one input may be analyzed If both displays are making an octave measurement they must both use the same input Changing the input of the active display will change the measurement or input of the other display if necessary User Functions which use both inputs may not be measured Choosing 1 Octave Channel may change the current measurements so that both displays use the same input See User Math later in this section for more Octave Averaging All octave measurements are averaged There are four types of averaging Linear Time Exponential Time Equal Confidence and Peak Hold Linear Time The band filter outputs are equally weighted and averaged for an Integration Time While Linear averaging is in progress the integration time completed is shown in the Horizontal Scale Bar below the graph When the Integration Time has been completed the measurement stops and Done is displayed below the graph If Waterfall Storage is On the waterfall buffer only stores the completed linear averages not each individual measur
53. larger indexes are older The total number of records currently stored and available in the waterfall buffer is displayed in the Vertical Scale Bar The Start Index should not exceed the total number of records in the buffer Both displays use the same Start Index Command ESTR 1 Set the stop record in the waterfall buffer for the calculation of L exceedance centile The analysis starts at the start index and includes all records through the stop index Index 0 is the most recent record larger indexes are older The total number of records currently stored and available in the waterfall buffer is displayed in the Vertical Scale Bar The Stop Index should not exceed the total number of records in the buffer Both displays use the same Stop Index Command ESTP 7 1 SR785 Dynamic Signal Analyzer 4 160 Exceedance Statistics Menu Exceedance Pct Set the Exceedance Centile L L is the amplitude at each bin which is exceeded by n of the records in the waterfall L is a large amplitude exceeded only 1 of the time Log is a small amplitude exceeded by 99 of the measurements The range of records within the waterfall buffer which are analyzed is specified by the Start and Stop index Both displays use the same Exceedance Centile Command EPCT 1 Calculate Excd Start the exceedance centile calculation for the active display Choose a Trace to store the result and press Enter to proceed The
54. local remote states In the LOCAL state both command execution and keyboard input are allowed In the REMOTE state command execution is allowed but the keyboard and knob are locked out except for the Help Local key which returns the SR785 to the LOCAL state In the LOCAL LOCKOUT state all front panel operation is locked out including the Help Local key The OVRM command sets queries the GPIB Overide Remote mode The parameter 1 selects No 0 or Yes 1 When Overide Remote is set to Yes the front panel is not locked out when the unit is in the REMOTE state SR785 Dynamic Signal Analyzer 5 118 Nodal DOF Commands Nodal Degree of Freedom Commands SVNI i The SVNI command determines queries whether nodal degree of freedom information will be stored with SR785 data 78D files If this softkey is set to on nodal DOF information will be saved with the files and will be available for use by external programs which convert SR785 files into formats used by modal analysis programs If set to off no nodal DOF information will be saved and the external programs must obtain this information from the user RFDR 7 i The RFDR command sets queries the reference node direction The parameter 1 specifies the direction according to the following table i Node Direction 0 0 Z 1 0 Y 2 0 X 3 Z 4 Y 5 X 6 Scalar no direction l X 8 Y 9 Z 10 0 X 11 0 Y 12 0 Z RFNA s The RFNA command sets queries the name of
55. lt Memory Allocation gt menu to allocate memory between the capture buffer waterfall and order track storage and the arbitrary source waveform Capture memory must be allocated before the capture buffer may be used To playback from the capture buffer change the Input Source to Playback Command CSTR Stop Capture Stop Capture stops storing data in the capture buffer If the Capture Mode is 1 Shot capture stops when the buffer is full Press Stop Capture to halt capture before the buffer is full If the Capture Mode is Continuous once capture is started it continues indefinitely and fills the capture buffer in a circular fashion In this case press Stop Capture to halt capture with the most recently acquired data stored in the buffer Turn off Auto Offset during capture to avoid interrupting the input signal To playback from the capture buffer change the Input Source to Playback Command CSTP Active Display Pressing Active Display toggles the active display In single and overlay display format the display switches between Display A and Display B The display label A or B is at the upper left of each display In dual display format Active Display switches which display is active as indicated by the highlighted Marker Position bar above the graph The active display determines which display s parameters are displayed in the menus For example activating Display A and pressing Display Setup allows you to sel
56. of the time Log is a small amplitude exceeded by 99 of the measurements The range of records within the waterfall buffer which are analyzed is specified by the Start and Stop index The Exceedance Pct sets the centile 1 99 Press lt Calculate Excd gt to start the calculation The result is stored in a data trace and has the same measurement type as the waterfall measurements To view the result recall the trace to a display or reference graph Display the Curve Fit Synthesis menu SR785 Dynamic Signal Analyzer Analysis Menu 4 149 Curve fitting is used to identify a mathematical model with closely approximates a measured frequency response Curve synthesis generates a SR785 frequency response from a mathematical model that can be compared with actual data The SR785 does curve fitting and synthesis in two curve tables Each table contains a model of frequency response function containing up to 20 poles and zeros The model can be expressed in pole zero format pole residue format or polynomial format Either table can be synthesized into a trace When fitting the best fit model is calculated and placed in curve table 1 SR785 Dynamic Signal Analyzer 4 150 Data Table Analysis Menu Data Table Analysis Menu Data Table Insert Line Modify Line The Data Table menu is used to edit and display the data table for the active display Data Table Data Table Insert Line Modify Line Delete Line Clear Table
57. so the Upper 2 band does not measure the fundamental Choose the 2 1 2 ratio mode to measure THD N power with fundamental notched out total power including fundamental Command BEXC d 1 Band Ratio Mode Band Power Band Ratio Select the Band Ratio Mode for the Band Marker in the active display 2 1 2 1 2 The calculated ratio is displayed in the lt Band Ratio gt menu box 2 1 specifies that the Band Ratio is computed from the ratio of the Upper 2 band power to the Lower 1 band power 2 1 2 specifies that the Band Ratio is computed from the ratio of the Upper 2 band power to the sum of the Lower 1 and Upper 2 band powers For example to measure THD N use the Lower 1 band to define a small region around the fundamental and the Upper 2 band to define the total bandwidth of interest Exclude lfrom2 so the Upper 2 band does not measure the fundamental Choose the 2 1 2 ratio mode to measure THD N power with fundamental notched out total power including fundamental Command BRAM d 1 This menu box displays the Upper top and Lower bottom Band Powers of the active display The Band Power is the sum of the squared magnitudes of all bins within each Band Marker The result is shown in Vrms or dB Vrms depending on the setting of dB Units To convert a value in Vrms to power square the result Command BPWR d 1 This menu box displays the band ratio either 2 1 or 2 1 2 as
58. the frequency components in the source add up and the peak source amplitude within the time record generally exceeds the amplitude of each frequency component by about 30 dB Since the input range must be set to accommodate the amplitude peak each component is measured at 30 dB relative to full scale This effectively reduces the dynamic range of the measurement by about 30 dB If the frequency response has a variation from 0 to 100 dB within the measurement span then each bin of the FFT must measure signals from 30 dBfs to 130 dBfs Even with a large number of vector averages this proves difficult especially with large measurement spans Swept sine measurements on the other hand can optimize the measurement at each frequency point Since the source is a sine wave all of the source energy is concentrated at a single frequency eliminating the 30 dB chirp dynamic range penalty In addition if the transfer response drops to 100 dBV the input range of Channel 2 can auto range to 50 dBV and maintain almost 100 dB of signal to noise In fact simply optimizing the input range at each frequency can extend the dynamic range of the measurement to beyond 140 dB For frequency responses with both gain and attenuation the source amplitude can be optimized at each frequency Reducing the source level at frequencies where there is gain prevents overloads and increasing the amplitude where there is attenuation preserves signal to noise To optimize
59. until the RPM passes the threshold If Start RPM is Off the threshold setting is ignored If Start RPM is On the RPM threshold must be met for both the RPM arming and Time Arming trigger modes Command TRSM 1 Delta RPM Set the RPM increments for which the trigger will be armed Once the Start RPM condition if any has been met The trigger will arm each time the rpm changes by the specified amount SR785 Dynamic Signal Analyzer Trigger Menu 4 105 If Delta RPM Sense is set to Incr RPM the trigger will arm only on an increasing RPM change If it is set to Decr RPM the trigger will arm only on a decreasing RPM change If set to Abs Change the trigger will arm on any change by this amount Command TRDR f Delta RPM Sense Sets the sign of the rpm change which arms the trigger in the RPM Arming trigger mode The trigger can be set to arm on positive negative or any change in RPM of an amount set by the Delta RPM softkey Command TRDM 7 1 Time Arm Step Sets the time interval for the Time Arming trigger mode Once the Start RPM condition if any has been met the trigger will arm repetitively with this time interval Command TIAS f Manual Arm Manually arm the trigger This function only applies if the Trigger Mode is Manual Arm Manual Arm enables triggering after Start Reset only after the trigger is armed using lt Manual Arm gt or from an interface command Once the trigger is
60. where is 27 times the noise frequency V noise is the noise amplitude and Cstray is the stray capacitance For example if the noise source is a power circuit then f 60 Hz and V noise 120 V Cstray can be estimated using a parallel plate equivalent capacitor If the capacitance is roughly an area of 1 cm separated by 10 cm then Cstray 18 0 009 pF The resulting noise current will be 400 pA at 60 Hz This small noise current can be larger than the signal SR785 Dynamic Signal Analyzer 2 72 External Noise Sources current If the noise source is at a higher frequency the coupled noise will be even greater If the noise source is at the signal frequency then the problem is much worse Vector averaging rejects noise at other frequencies but pick up at the signal frequency appears as signal Cures for capacitive noise coupling include 1 Removing or turning off the noise source 2 Keeping the noise source far from the signal source reducing Cty Do not bring the signal cables close to the noise source 3 Designing the experiment to measure voltages with low impedance noise current generates very little voltage 4 Installing capacitive shielding by placing the signal source in a metal box Inductive Coupling An AC current in a nearby piece of apparatus can couple to the signal path via a magnetic field A changing current in a nearby circuit gives rise to a changing magnetic field which induces an emf d dt in the
61. window functions have a great deal of impact on the resulting FFT spectrum A poorly designed window can result in significant measurement errors SR785 Dynamic Signal Analyzer 2 16 FFT Measurements FFT Measurements Definitions In the measurement definitions which follow the following conventions are used Angle brackets lt gt imply that the real and imaginary parts of the quantity within the brackets are averaged with either linear or exponential weighting over some number of time records MAX implies that the complex quantity inside the parentheses is replaced by the maximum magnitude which that complex value takes over some number of time records The asterisk is used to denote the conjugate of a complex quantity FFT Spectrum The FFT spectrum is the basic measurement of an FFT analyzer It is simply the FFT of a time record The FFT spectrum is a complex quantity it contains phase as well as amplitude information This is sometimes referred to as the linear spectrum The phase of the spectrum is meaningful only if the time record is triggered with a fixed relationship to the input signal If the signal 1s repetitive as well the signal and trigger repeat then vector averaging can be used to reduce the noise level of the spectrum The vector averaged spectrum is still a complex quantity The precise definition of the FFT1 measurement for all averaging modes is as follows No Average FFT 1 FFT1 Vector Average FFT
62. 1 Right Bin j Band Exclude Band Ratio Mode Band Power Band Ratio Frequency Damping Results Source On Off Source Type Sine Frequency 1 Sine Amplitude 1 Sine Frequency 2 Sine Amplitude 2 Sine Offset Chirp Amplitude Chirp Burst Percentage Source Display Noise Amplitude Noise Type NBUR x NPER x CSRC 1 Arbitrary Source AAMP D i ARAT 2 i ASRC i ASTR i ALEN D i TARB 1 ALOD n AGET 1 APUT 1 5 56 5 56 5 56 5 57 5 57 5 57 5 57 5 57 5 57 5 110 5 112 5 113 Index of Commands 5 5 Noise Burst Percentage Noise Source Period Source Display Arbitrary Source Amplitude Arbitrary Source Rate Arbitrary Source Buffer Arbitrary Source Start Arbitrary Source Length Trace to Arb Download Arbitrary Binary Upload Arbitrary Buffer Download Arbitrary Buffer Swept Sine Source Swept Sine Measurement Group SSAL i SSAM x SSRF x SRMP i SRAT 2 x SSUL x SSLL x SMAX 2 x SOFF x Inputs ISRC i LINK i I1IMD i I1GD i I1CP i IIRG x AIRG i ILAR i I1AF i I1AW i I2MD i I2GD i I2CP i I2RG x A2RG i I2AR i I2AF i I2AW i IAOM i INPC 1 Transducer Parameters EUIM d 1 EUIL d 1 EUIV d x EUIU d s TDIC d 1 5 58 5 58 5 58 5 58 5 58 5 58 5 59 5 59 5 59
63. 2 i j INST i ISPD i ISRC 2 i ISTR 2 i K KCLK i KEYP i KNOB i L LALM d i LCLR d LDLT d i LFAL d LINK i LMAX d 1 LOCL 1 LSEG d i J xO yO x1 yl LSFT d x LSON d 1 LTST d i M MALC i j k MBIN d i MDIR s MEAS d i MGRP 2 d i MKCN d MKCN d MKMD J d i MKMN d MMCA d MMEM MREL 2 d i MRKB d MRKR d i MRKX d 5 61 5 61 5 61 5 61 5 61 5 61 5 61 5 61 5 65 5 65 5 122 5 122 5 122 5 122 5 121 5 122 5 65 5 60 5 65 5 100 5 104 5 106 5 87 5 87 5 88 5 87 5 60 5 87 5 117 5 87 5 88 5 87 5 87 5 84 5 45 5 94 5 37 5 37 5 104 5 46 5 45 5 104 5 52 5 84 5 47 5 45 5 45 5 45 Index of Commands 5 15 Ch2 Anti Alias Filter Ch2 AutoRange Mode Ch2 A Weight Filter Ch2 Input Coupling Ch2 Input Grounding Ch2 Input Mode Ch2 Input Range Auto Offset Capture Playback Length Capture Playback Mode Input Ovld Read Input Ovld Read Input Status Enable Input Status Read Instrument Status Enable Instrument Status Read Capture Playback Speed Input Source Capture Playback Start Key Click Key Press Knob Limit Beep Clear Limits Delete Limit Segment Limit Test Fail Analyzer Configuration Last Limit Segment Local Remote Set Limit Segment 1 Shift Limit Segments Show Limit Segments Limit Testing On Allocate Memory Marker Move to bin i Make Dir
64. 6 4 SDF Files 6 4 Matlab MAT Files 6 4 Universal File Format 6 4 SR780 78D Files 6 4 Using the File Conversion Utility 6 5 Using SRTRANS 6 5 Converting Files to ASCII 6 5 Converting Files to SDF 6 7 Converting Files to 78D Format 6 8 Converting Files to MATLAB Format 6 8 Converting Files to Universal File Format 6 9 Converting Files to Capture File Format 78C 6 10 Converting Files to Arbitrary Waveform Format 78C 6 10 6 1 SR785 Dynamic Signal Analyzer 6 2 Why File Conversion Why File Conversion Data from the SR785 will often need to be exported to external programs such as spreadsheets plotting programs or modal analysis programs In addition it is often convenient to be able to import data prepared by external programs into the SR785 for display and comparison In order to meet both these needs the SR785 is shipped with a file conversion program designed to import and export data as flexibly as possible Stanford Research Systems is committed to supporting as many file formats as possible as a result we are constantly adding new formats Contact Stanford Research Systems to obtain a list of supported programs and file formats and to obtain a free upgrade to the latest file conversion utilities SR785 Dynamic Signal Analyzer SR785 File Types 6 3 SR785 File Types Three distinct native SR785 file types are supported by the SR785 file conversion utility 8D Files 78D files or display files are gen
65. 80 5 81 5 81 Index of Commands 5 19 Tone Download Trace 1 Buffer Download Trace 1 Buffer Disk to Trace 1 Disk to Trace 1 Delta RPM Mode Delta RPM Start RPM Mode Starting RPM Trace ito User Window Trace 1 to Disk Trigger Slope Trigger Source dB Units Display Units Phase Units Peak Units Unsettle Measurement User Constant 1 FFT User Function 1 Time Histogram User Function 1 Octave User Function 1 Correlation User Function 1 Swept Sine User Function 1 Order User Function 1 Display View Waterfall Angle Waterfall Records Stored Waterfall Display Waterfall Save Option Waterfall FFT Skip Waterfall Fast Angles Upload Waterfall Buffer Upload Waterfall Buffer Waterfall Hidden Lines Waterfall Trace Height Window to Trace 1 Waterfall Octave Skip Download Waterfall Buffer Download Waterfall Buffer Waterfall Paused Drawing Waterfall Slice to Trace Waterfall Storage Window Form Waterfall Threshold Waterfall Total Count Waterfall Record to Trace Waterfall View Count SR785 Dynamic Signal Analyzer 5 20 Index of Commands X XAXS d i XCEN d x XDIV d x XPAN d i XZOM d i Y Y2DV d x YCEN d x YDIV d x YMAX d x YMDX d x y YMID d x YMIN d x 5 43 5 4 5 4 5 4 5 42 5 4 5 4 5 4 5 40 5 4 5 40 5 4 SR785 Dynamic Signal Analyzer X Axis Scale Type X Center Polar X Division Polar X Pan
66. 95 4 95 4 95 Menus Tach Slope Hold Off Enable Tach Hold Off Show Tach Playback Submenu Playback Start Playback Length Set Left Edge Set Right Edge Playback Mode Playback Speed Trigger Menu Trigger Mode Trigger Source Trigger Level Trigger Slope Delay 1 Delay B Trigd Source Mode RPM Time Arm Setup Start RPM Start RPM On Off Delta RPM Delta RPM Sense Time Arm Step Manual Arm Manual Trigger Average Menus FFT Correlation Order Average Menu Compute Averages Averaging Type Number of Averages Display Average Time Record Increment More Overload Reject Trigger Average Mode Average Preview Preview Time Accept Reject Octave Average Menu Averaging Type Integration Time Confidence Power Bin Linear Average Trigger Swept Sine Average Menu Settle Time Settle Cycles 4 3 4 96 4 96 4 96 4 96 4 97 4 97 4 97 4 97 4 98 4 98 4 98 4 100 4 100 4 101 4 102 4 102 4 102 4 102 4 103 4 104 4 104 4 104 4 104 4 105 4 105 4 105 4 105 4 107 4 107 4 107 4 108 4 109 4 109 4 111 4 112 4 112 4 113 4 113 4 114 4 114 4 114 4 115 4 115 4 116 4 117 4 117 4 117 4 119 4 119 4 119 SR785 Dynamic Signal Analyzer 4 4 Menus Integration Time Integration Cycles User Math Menu Function Edit Function Operands Operations Function String Insert Replace Delete Clear Eq Cancel Enter Eq Edit Constant Constant Real Part Imaginary Part Mag Phase deg
67. A If the Arbitrary source is selected the triggered FFT measurement phase is stable only if the input signals are derived from the triggered source output Turn the source off or set it to Sine when making triggered measurements of external signals not the source Command STYP 1 SR785 Dynamic Signal Analyzer Sine Source Menu 4 71 Sine Source Menu Frequency 1 Amplitude 1 The Sine Source menu is used to set the frequency offset and amplitude of the sine source SOUPCE nn Off oe Sine Chirp Noise Arb I Frequency 1 ____ 10 24 kA 24 kHz men 1 200 0 mV 0 mv Offset T 0 0 mV Tone 2 ee Set the Frequency of Tone 1 The sine output is the sum of two tones sine waves When the knob is used to adjust the frequency the resolution is equal to the Linewidth of the active display FFT Span The knob always sets the frequency to an exact multiple of the Linewidth For octave analysis the Linewidth of the most recent FFT Spans are used with an FFT Base of 100 0 kHz The keypad allows arbitrary frequencies to be entered Remember the output is periodic over the FFT time record only if the frequency is an exact multiple of the Linewidth Source Trigger will not result in a stable phase for non periodic frequencies The sine source is not triggered The output is always continuous Command S1FR f Set the peak Amplitude of Tone 1 0 5V The amplitude resolution is 0 1 mV The sine output is the sum
68. After the time record is accepted or rejected the display reverts back the measurement display until the next time record is available usually triggered When Average Preview is Timed the input time record is automatically accepted after the Preview Time unless rejected first The preview time records are displayed in place of the actual measurements For single channel measurements the appropriate channel input time record is shown in each display For 2 channel measurements the DisplayA shows Ch1 time record and DisplayB shows Ch2 time record In this case use the dual display format to view both time records While the preview time records are displayed the displays are labeled Preview instead of Live in the Vertical Scale Bar While previewing the time record the measurement SR785 Dynamic Signal Analyzer 4 114 Average Menus can be changed so as to preview any other measurement in the current measurement group Subsequent time records will return to the newly selected measurement rather than the time record for preview Command PAVO 7 d 1 Preview Time Select the Preview Time for both displays 0 5 s 1 ks When Average Preview is Timed the input time record is automatically accepted after the Preview Time unless rejected first Command PAVT d x Accept Accept the displayed preview time record and add the measurement to the average Average Preview allows each individual measureme
69. Analyzer Waterfall Menu 4 141 Fast Angles Select the Waterfall Fast Angles for the active display On Off The View Count and the Trace Height determine the available scroll Angles When Fast Angles is On the available Scroll Angles are limited to those which update faster due to the graphics architecture Each display has its own Fast Angles mode This entry field can be linked to both displays by using the Link key Command WEST d 1 Threshold Set the Waterfall Threshold for the active display 0 99 The Threshold is specified as a percentage of the Y axis Trace Height Only those portions of each record which exceed the Threshold are displayed This removes baseline noise from the waterfall display Note that the marker still moves along the actual data in each record even if it is below the threshold In this case the marker will be located where there is no displayed data The Marker Position Bar displays the actual data value in all cases Each display has its own Waterfall Threshold This entry field can be linked to both displays by using the Link key Command WTHR d 1 Hidden Lines Set the Waterfall Hidden Line Mode for the active display Invisible Visible In a waterfall display as the older records scroll downward they are considered to move towards the front of the display New records which appear at the top are behind the older records Invisible Hidden Lines will
70. Base Frequency set to 102 4 kHz Data digitized at 256 kHz can be played back in both Octave and FFT Group as long as the FFT Base Frequency set to 100 0 kHz Data that is to be played back in the Order group must be captured in Order group This is because the order group capture must also capture the tachometer data as well as the signal input Choose Playback as the Input Source in any Measurement Group except Swept Sine Set the Playback Start point within the capture buffer and the Playback Length When playing back in FFT Group it is best to set the Playback Length to a multiple of the FFT time record Acquisition Time The Capture Progress indicator shows the playback progress through the buffer relative to Playback Length The capture buffer itself can be displayed as a measurement Use Zoom and Pan to inspect a portion of the buffer During playback the capture buffer display can automatically pan as the playback progresses through the buffer During playback a marker at the bottom of the graph indicates the current time record position within the buffer The capture data represents a frequency span from 0 Hz to the sampling rate 2 56 The playback measurement cannot exceed this measurement bandwidth In the Frequency menu this places a limitation on the maximum FFT span and stop frequency or highest Octave band during playback The Average Window and Waterfall menus all operate normally during playback The Playback Mode can
71. Ch1 is selected items on the menu will display and change parameters for the Chl input When Ch2 is selected items on the menu will display and change parameters for the Ch2 input When Both is selected the menu will display parameters for the Chl input but any changes made will affect both inputs Select the Input Mode for the selected input A single ended A B differential The Input indicator shows the current mode at the top of the screen In general when looking at very small signals connect A to the signal source and B to the signal ground and use A B In this case make sure that the two input cables do not encompass any loop area twist them together or run them side by side Command IIMD 1 Command I2MD 1 Select the Input Grounding for the selected input shields Float Ground The shields of A and B are connected Float connects the shields to chassis ground through 1 MQ 0 01 uF This allows the shield of a single ended input to float SR785 Dynamic Signal Anaylzer 4 90 Input Configuration Menu Coupling Input Range AA Filter Ground connects the shields to chassis ground with 50 Q In this mode do not exceed 3 V on the shields The impedance between signal input and chassis ground is always 1 MQ Command I1GD 7 1 Command I2GD 1 Select the Input Coupling for the selected input DC AC ICP The Input indicator shows the current coupling at the top of the screen
72. Command FNAM s Command FREE Command FXST s Command FRST Command FNXT Current Directory Enter the Current Disk Directory SR785 Dynamic Signal Analyzer 4 178 Disk Buffers Menu Turning the knob will bring up the directory tree display which lists all of the sub directories on the disk Choose a directory with the knob and press Enter to make it the Current Directory A directory may be entered using the Alt key and the letters associated with each key Press Alt again to return to normal keypad operation An error results 1f the entered directory does not exist New directories are created with lt Make Directory gt Command FDIR s Load Trace Data ASCII Load ASCII data from the Current File in the Current Directory into an existing Trace This is a way to import calibration data from a file into a trace The trace can then be used in a user function to calibrate live measurements The target trace must already store data of the type and length to be loaded from disk The file only contains data points no measurement information is recalled The recalled data simply takes the place of the stored trace data and assumes the trace s measurement parameters Measurement Averaging Window Frequency span and length The ASCII file consists of N pairs of ASCII floating point values Each pair of values represents the real and imaginary parts of a single complex data point Thus the file contai
73. Correlation User Function 1 USRO 1 j k 1 5 74 Octave User Function 1 USRS 1 Jj k 1 5 74 Swept Sine User Function 1 USRT 1 j k 1 5 74 Order User Function 1 USRH 1 j k 1 5 74 Time Histogram User Function 1 USRC 1 x y 5 77 User Constant 1 Window FWIN d i 5 78 Window FWFL d 1 5 78 Force Length FWTC d 1 5 79 Expo TC TRWI i 5 79 Trace i to User Window WITR d i 5 79 Window to Trace i WSYM d 1 5 79 Window Form Waterfall WDSP d 1 5 80 Waterfall Display WSTO d 1 5 80 Waterfall Storage WESB 7 d 1 5 80 Waterfall Save Option WAVA d 5 80 Waterfall Records Stored WTOT d 1 5 80 Waterfall Total Count WESK d 1 5 80 Waterfall FFT Skip WOSK d x 5 80 Waterfall Octave Skip WVCT D d 1 5 81 Waterfall View Count WHIT d 1 5 81 Waterfall Trace Height WANG d 1 5 81 Waterfall Angle WEST 7 d 1 5 81 Waterfall Fast Angles WTHR d 1 5 81 Waterfall Threshold WHID d 1 5 81 Waterfall Hidden Lines WREV d 1 5 81 Waterfall Paused Drawing WTRC d 1 j 5 81 Waterfall Record to Trace WSLC d 1 j 5 82 Waterfall Slice to Trace WGET 5 114 Upload Waterfall Buffer WPUT 5 115 Download Waterfall Buffer Capture CCHN 7 1 5 83 Capture Channels CMOD 1 5 83 Capture Mode SR785 Dynamic Signal Analyzer 5 8 Index of Commands CLEN i CRAT i CPAN i CSTR CST
74. Delay A TDLB x 5 66 Trigger Delay B TARM 5 66 Manual Trigger Arm STMD i 5 66 Triggered Source Mode TMAN 5 66 Manual Trigger TRSR x 5 67 Starting RPM TRSM 1 5 67 Start RPM Mode TRDR x 5 67 Delta RPM TRDM 7 1 5 67 Delta RPM Mode TIAS x 5 67 Time Arm Increment Average FFT Correlation and Order FAVG d 1 5 68 Average On FAVM d 1 5 68 Display Average FAVT d 1 5 68 Average Type FAVN d 1i 5 68 Average Number NAVG d 5 68 Averages Completed FOVL d x 5 68 FFT Time Record Increment FREJ d 1 5 69 FFT Overload Reject TAVM 1 5 69 Trigger Average Mode PAVO d 1 5 69 Average Preview PAVT d x 5 69 Preview Time PAVA 5 69 Accept Preview PAVR 5 69 Reject Preview SR785 Dynamic Signal Analyzer Index of Commands 5 7 Average Octave Measurement Group OTYP d 1 5 71 Octave Average Type OTIM d x 5 71 Octave Average Time NAVG d 5 71 Octave Averages Completed OCNF d 1 5 71 Octave Confidence Level OIMP Dd 1 5 71 Octave Power Bin OLAT d 1 5 72 Octave Linear Average Mode Average Swept Sine Measurement Group SSTM d x 5 73 Swept Sine Settle Time SSCY d 1 5 73 Swept Sine Settle Cycles SITM d x 5 73 Swept Sine Int Time SICY d 1 5 73 Swept Sine Int Cycles User Math Functions USRE 1 Jj k 1 5 74 FFT User Function 1 USRR 1 j k 1 5 74
75. Disk Catalog Display to Disk Disk to Display Settings to Disk Recall Settings Trace 1 to Disk Disk to Trace 1 Upkeep File Name Delete File Delete Directory Print Screen hardkey Print Plot Destination File Start Number Dump Display Data Print Screen Bitmap Printer Type Bitmap Area Print Bright Print Dim Print Black Print Graph Plot Screen Vector Plotter Type Plotter GPIB Address GPIB Control Plotter Text Pen Plotter Grid Pen Plotter Trace Pen Plotter Marker Pen Display Note 5 9 SR785 Dynamic Signal Analyzer 5 10 Index of Commands System OUTX i OVRM 7 i KCLK i ALRM 7 i ALRT i ADON i AOVL i SAVR 2 i SDLY 2 i FEMT 7 i TIME i j k DATE i j k Front Panel ACTD i STRT PAUS CONT UNST d CSTR CSTP SVTR d i RCTR d i SVRF d i RCRF d i DUMP PRNT PLOT ASCL d AIRG i A2RG i MRON d MKMX d MKMN d MKCN d DREF d i SNAP d SBRI 2 i SCON i KEYP i KNOB i TONE i j PLAY i Traces SVTR d i RCTR d i TSAV i TRCL i TLOD i n TASC i n TGET 1 TPUT 1 5 100 5 100 5 100 5 100 5 100 5 100 5 100 5 100 5 100 5 100 5 100 5 101 5 102 5 102 5 102 5 102 5 102 5 83 5 83 5 102 5 103 5 103 5 103 5 103 5 103 5 103 5 103 5 103 5 103 5 103 5 104 5 104 5 104 5 104 5 104 5 100 5 104 5 104 5 106 5 106 5 106 5 102 5 103 5 96 5 96 5 109 5 109 5 111 5 112
76. DisplayB to show the time history of Leq The points in a slice are numbered and displayed from O oldest to 49 newest Note that this differs from the waterfall display in which the newest record is numbered 0 This is because the slice is a time record with time advancing to the right and it is more natural to number it this way Note that the first 12 records 96 ms show a large value for Leq during the noise burst If this was a real reverberation measurement the signal would not decay in a single 8 ms measurement but would last for a reverberation time Make the top display active DisplayA Select the Waterfall menu Change the View Count This is the number of records which are displayed Enter 50 to show the entire waterfall buffer Move the marker to a specific record number SR785 Dynamic Signal Analyzer 1 40 Waterfall Display Press 0 Enter Press lt Angle gt Use the knob to select 45 and press Enter Press lt More gt Press lt Paused Drawing gt Use the knob to select Oldest at Top and press Enter SR785 Dynamic Signal Analyzer Enter record O most recent at the back Change the skew angle of the display Choose 45 to skew the opposite way Show More of the Waterfall menu Change the waterfall direction While the measurement is running the newest records are added at the top of the waterfall display When the measurement is done or paused the waterfall may be drawn wit
77. ESB can only be generated after clearing the INST DISP INPT IERR or ESB bits in the Serial Poll status word The controller should respond to the SRQ by performing a serial poll to read the Serial Poll status word to determine the requesting status bit Bit 6 SRQ will be reset by the serial poll For example to generate a service request when a TRIGGER occurs bit 0 in the Instrument Status enable register needs to be set INSE 1 command and bit 0 in the Serial Poll enable register must be set SRE 1 command When a trigger occurs bit 0 in the Instrument status word is set Since bit O in the Instrument status word AND enable register are set this ALSO sets bit 0 INST in the Serial Poll status word Since bit 0 in the Serial Poll status word AND enable register are set an SRQ is generated Bit 6 SRQ in the Serial Poll status word is set Further triggering will not generate another SRQ until the TRIGGER status bit is cleared The TRIGGER status bit is cleared by reading the Instrument status word with INST or clearing bit 0 in the Instrument status enable register with INSE Presumably the controller is alerted to the trigger via the SRQ performs a serial poll to clear the SRQ does something in response to the trigger read data for example and then clears the TRIGGER status bit by reading the Instrument status register A subsequent trigger will then generate another SRQ SR785 Dynamic Signal Analyzer 5 126 Status Word
78. FFT Base Frequency is 102 4 kHz and 256 kHz when the FFT Base Frequency is 100 0 kHz OR the Measurement Group is Octave When capturing data in the FFT Measurement Group it is important to choose the 100 0 kHz Base Frequency if the captured data will be played back in the Octave Group Only data captured in the Order Measurement Group can be played back in the Order Measurement group because the capture buffer contains special tachometer data in that group that is not present in the other measurement groups After the inputs are digitized they may be filtered and downsampled before being stored in the capture buffer This allows longer capture times at lower sampling rates The capture data represents a frequency span from 0 Hz to the sampling rate 2 56 All captured data is baseband Capturing at less than the maximum sampling rate restricts the playback measurement span to sampling rate 2 56 In the order measurement group the sampling rate is determined by the user selected maximum order and maximum rpm The Capture Length is selected in 2 kPoint 2048 increments limited by the user memory allocation A single input or both inputs may be captured The maximum capture length for a single input is twice the length for both inputs at a given memory allocation Capture Fill To start capture press the Start Capture key If the Trigger Mode is Auto Arm and the Trigger Souce is Continuous capture starts immediately Otherwise the selected Tri
79. Fitting and Synthesis If the order of the numerator in the polynomial representation 1s equal to or greater than the order of the denominator polynomial the Pole Residue representation will contain an additional polynomial whose order is the difference between the numerator order and denominator order This polynomial is added to the equation shown above The coefficients of this extra polynomial cannot be adjusted by the user use one of the other representations if this is necessary The SR785 will convert curve parameters between any of these three formats Results of curve fits are always initially presented in pole zero format although they can always be subsequently converted to any format Frequency Scale Often a theoretical model frequency response function will be specified with respect to a nominal frequency such as Hz The curve table contains a frequency scale parameter to allow such a nominal transfer function to be synthesized to any actual frequency In terms of the pole zero representation the poles and zeros are all multiplied by the scaling factor before synthesizing the curve When fitting after the poles and zeros corresponding to the measured frequency response function are determined the values are all divided by the Frequency Scale factor For example if the curve table contains a pole s 1 and the frequency scale is 1000 this will create a pole at 1 kHz when synthesizing the table Delay The three formats for
80. Fityoe lanear PZSR 799 PAVN 2 250 aumber 250 TxSR785 FAVG 2 1 J fag On TROR TOS C SRCO 1 3 turn on the source ff ESSERE Query Chose parancters tor Disp layA 74 eee GetSR785 FAVM 0 mode atoi recv GetSR785 FAVT O type atoi recv GetSR785 FAVN 0 number atoi recv printf Disp Avg d type d number d n n mode type number DeLne Ae Stare aa S WaitAvg start a linear average and wait until done primer lt done n yy TXSR785 ASCL 0 ASCE 1 autoscale the displays KKKKKKKKKKKKKKKKKKKKKKKK KKK KKKKKEKKKKKKKKKEKKKKKKKKKKKK KKKKKK read data points KKKKKK dispAVal GetData 0 40 read DisplayA bin 40 peak dispBVal GetData 1 40 read DisplayB bin 40 printf DisplayA 1f dBVpk n dispAVal printf DisplayB 2 6 dBVek n dispBVal KKKKKKKKKKKKKKKKKKKKKKKRKKKKKKKKKEKKKKKKKKKEKKKKKKKKKKKK REARS Binary kranser all of Display spectrum 4 A We need to send the DSPB 0 command WITHOUT waiting for f LEC in Seriad DOLL status sa1nce IFC will not be sec Until AFTER the transfer is complete This section needs to be modified for your GPIB interface printf nReading entire Displaya J gt TZGpPIO SRS DSPBe 0 Ty3 use TxGpib don t wait for IFC transmit MLA TALK 10 amp status make the PC listen SR785 talk rarray rxBuff 1604 amp length amp status binary read 1604 bytes 401
81. Frequency Menu 4 17 Measurements which differ by more than the Faster Threshold on EITHER channel but less than the Slower Threshold on BOTH channels maintain the present sweep speed The number of points skipped remains the same in this case If the marker position is displayed with a the point has not actually been measured but is interpolated from actual measured points The measurement of these points was skipped due to sweep Auto Resolution Command SARS d 1 Number of Points Set the Number Of Points 10 2048 The points are in a Linear or a Logarithmic progression as set by the Sweep Type If the Number Of Points is changed during a sweep the sweep will be reset A sweep with a large number of points can detect narrow features A sweep with a small number of points will take less time In order to save time while maintaining a high resolution use Auto Resolution Command SNPS d 1 Maximum Step Size Set the Maximum Step Size for Auto Resolution frequency sweeps 2 256 When Auto Resolution is On each successive time the Faster Threshold condition 1s met on BOTH channels the frequency step size is increased until the Maximum Step Size is reached This sets the maximum speed at which the sweep will continue until the Slower Threshold is exceeded Generally this number should not exceed 5 of the Number Of Points in the sweep Command SSKP 7 d 1 Faster Threshold Set the Faster
82. Function is determined by examining its equation from left to right SR785 Dynamic Signal Analyzer User Math Functions 2 63 and keeping track of domain switching IFFT and FFT operations Operand terms with an incompatible X axis type have no effect on the function s X axis type though the entire equation is still evaluated Constants are simply constant for each point They also have no effect on the function s X axis type If a User Function is defined simply in terms of constants no other operands then the X axis type defaults to frequency If a User Function s X axis type or length is determined by a Trace then changing the data in the Trace may change the function s X axis type or length as well Operations Operands are combined with Operations to define a function Arithmetic operations x combine operand terms on a point by point basis It is the user s responsibility to ensure that the operand terms have the correct X axis type and lengths in order to produce meaningful results View operations Mag Mag Phase Real Imag simply convert the complex operand array into the desired form Mag and Mag compute the magnitude V x y or magnitude squared x y with a real result Phase computes the phase tan y x unwrapped with a real result Real simply zeroes the imaginary part Imag zeroes the real part Conj Ln Exp and Sqrt are defined as
83. Hence the time data amplitudes are not calibrated Windowed Time Record The FFT operates on windowed time records The window function is applied to the time record immediately before the FFT Most window functions taper off to zero at the start and end of the time record If a transient signal occurs at the start of the time record the corresponding windowed time record and FFT may not show anything because the window function reduces the transient to zero SR785 Dynamic Signal Analyzer 4 28 Display Setup Menu Orbit The Orbit measurement is a two channel measurement whose real part is the real part of Time Record Ch1 and whose imaginary part is the real part of Time Record Ch2 Orbit is normally displayed with the Nyquist View Time2 vertical vs Time horizontal For baseband spans the time records are entirely real and the Nyquist view of the Orbit measurement is a Lissajous figure Cross Spectrum The cross spectrum sometimes called cross power spectrum is a two channel measurement defined as No Average Cross Spectrum FFT1 e FFT2 Vector Average Cross Spectrum lt FFT1 gt lt FFT2 gt RMS Average Cross Spectrum lt FFT1 FFT2 gt Peak Hold Average Cross Spectrum MAX FFT2 y lt FFT1 FFT1 gt The cross spectrum contains both magnitude and phase information The phase is the relative phase at each frequency between the two channels Vector averaging can be used to eliminate signals which do n
84. Horizontal Scale Bar 3 14 ea shane i Marker 3 15 op cep uire a Marker Position Bar 3 15 anve Display sigan Link 3 30 Active Display 3 16 Print Screen 3 31 Reference Graphs 3 16 Menu Display 3 16 HE p oral T Alt Control Key 3 31 Status Indicators 3 18 Play Macro Alt Start Reset 3 31 Input Ranges 3 18 Macro Rec Alt Pause Cont 3 31 Overloads 3 18 End Rec Alt Stop Capture 3 32 Input Configurations 3 18 Snap Ref Alt Start Capture 3 32 SR785 Dynamic Signal Analyzer 3 2 Operation Ref to Trace Alt Active Display 3 32 Trace to Ref Alt Link 3 32 Display to Trace Alt Print Screen 3 32 Trace to Display AIt Help Local 3 33 Function Keys 3 34 Auto Scale A 3 34 Auto Scale B 3 34 Auto Range Ch1 3 34 Auto Range Ch2 3 35 Span Up 3 35 Span Down 3 35 Marker Ref 3 36 Display Ref 3 36 Marker Center 3 37 Marker Max 3 37 Marker Min 3 37 Show Setup 3 37 Macros 3 38 Keypad Macros 3 38 Choosing From Lists 3 38 Menus 3 38 SR785 Dynamic Signal Analyzer Overview 3 3 Overview ENTRY es ef SS 5 AR DE EEE EE 100 00 trig aT EES 7 R ttih r F SRS 2 4 NTRO L View Log Mag Start Start Active Print 1 2 3 aeneeeaanmmnmmmmmnana Reset Capture Display Screen Units Aa eoeeoeoeee PLAYMACRO SNAPREF REFACE DISP TRACE pepeni j Pause Sto Link Help io CD ETE 100 m MACRO REC END REC TRACE gt REF TRAC E gt DISP
85. Input Range moves up for overloads and down when the signal falls below half scale In Swept Sine group Auto Range is always tracking The Ch1 Input Range indicator at the top of the screen will be shown in inverse if Chl is Auto Ranging Auto Range responds to all frequencies present at the input except those attenuated by AC coupling not just those within the measurement span Link Auto Range Ch1 toggles the Input Ranging of both channels Command AIRG 1 SR785 Dynamic Signal Analyzer Status Indicators 3 35 Auto Range Ch2 Auto Range Ch2 toggles Channel 2 Input Ranging between Manual and Auto In Manual Ranging the Input Range is set within the Input lt Input Config gt submenu In Auto Ranging the Input Range is adjusted automatically according to the Ch2 AutoRange Mode also in the Input menu In Up Only Auto Range only overloads cause the range to change In Tracking Auto Range the Input Range moves up for overloads and down when the signal falls below half scale In Swept Sine group Auto Range is always tracking The Ch2 Input Range indicator at the top of the screen will be shown in inverse if Ch2 is Auto Ranging Auto Range responds to all frequencies present at the input except those attenuated by AC coupling not just those within the measurement span Link Auto Range Ch2 toggles the Input Ranging of both channels Command A2RG 1 Span Up In FFT group Span Up increases t
86. Limit Testing on The limit test result is displayed to the left of the graph In this case Fail should be shown The limit that we drew is an upper limit Since the data peak exceed this limit the test fails Go back to the Edit Limits menu 1 58 Limit Testing Press lt Shift All gt Press 7 Enter Press lt New Segment gt Press lt XQ gt Press 2 0 0 0 0 Enter Press lt Y0 gt Press 8 0 Enter Press lt X1 gt Press 9 0 0 0 0 Enter Press lt Y 1 gt Press 8 0 Enter Press lt Segment gt Press 0 Enter Press lt Limit Type gt Use the knob to select Lower and press Enter Select Shift All limit segments This moves all of the segments together In this case there is only one segment Enter 7 to move the segment up by 7 dBVpk The new segment is above the signal peak and the limit test passes Add another segment Select XO first Enter a value of 20000 Hz Select YO Enter a value of 80 dBVpk Select X1 Enter a value of 90000 Hz Select Y1 Enter a value of 80 dBVpk The segment should be above the noise floor The limit test should still pass Change the segment which we are editing The current segment is identified in the order in which they are created Select segment O the first one Before editing a segment make sure that you have chosen the correct one The current segment is identified in the display by
87. Live indicates that the display is Showing live measurement results from either the inputs or from capture Done indicates that the display is showing a completed measurement An Off Line display is showing a frozen measurement A display is Off Line whenever data is recalled to the display from a Trace or from disk Preview only occurs when Average Preview is On and indicates that the display is showing a preview time record and is waiting for accept or reject The Y Max and Y Min reference values are shown along the right edge Y Max 1s the top reference and Y Min is the bottom The vertical scale per division is shown between Y Max and Y Min The units and scale division are selected in the Display Setup menu The No Anti Aliasing Filter warning is shown if any measurement input has its anti aliasing filter off Measurements made without the anti aliasing filter may contain alias signals with frequencies above 102 4 kHz The Limit Test Result either Pass or Fail is displayed if limit testing is on for this display The Waterfall Storage Count shows how many measurement records are currently stored in the waterfall buffer This count is not displayed when Waterfall Storage is Off SR785 Dynamic Signal Analyzer 3 14 Screen Display Horizontal Scale Bar X Axi X Axis Right Ed e E xis Center xis Rig ge Fa FFT ch2Log Measurement View Average Type Graph and FFT Window Average Figure Chapt
88. Move the Marker to the notch minimum Read the notch depth and frequency in the marker Position display Select the Average menu Change the Integration Time Enter 40 ms The Integration Time is set in increments of 3 9 ms so the entry is rounded to 39 ms The new estimated sweep time is displayed below the graph At each frequency point the inputs measure the amount of signal at the source frequency This is done by multiplying the input data by the source sine and cosine and averaging the results over an integration time The actual integration time 1s always rounded up to an exact number of cycles of the source frequency This rejects signals which are at different frequencies such as noise and harmonics Long integration times improve signal to noise while increasing the measurement time The greater of the Integration Cycles and Integration Time rounded to the next complete cycle is used at each frequency The sweep is at 1 kHz so each cycle is 1 ms Setting the Integration Time to 40 ms increases the integration time So far the Input Ranges Source Level and Sweep Resolution have been constant over the sweep Let s change these to optimize both the measurement and the measurement time Change both inputs to Auto Range the Input Range indicators at the top of the screen are highlighted SR785 Dynamic Signal Analyzer 1 44 Swept Sine Measurement Press Input lt Input Conifg gt Press lt Channel gt se
89. Overview 3 5 Knob The knob normally moves the markers within the displays If a parameter has been highlighted by its softkey the knob adjusts the parameter Parameters which have a list of choices are most easily modified with the knob Numeric entry fields may also be adjusted with the knob Disk Drive The 3 5 disk drive is used to store data and instrument settings Double sided high density disks DS HD have a capacity of 1 44M bytes and double sided double density disks DS DD have a capacity of 720k bytes The disk format is DOS compatible Use the Disk menu to format a disk or access disk files SR785 Dynamic Signal Analyzer 3 6 Front Panel Connectors Front Panel Connectors Ch1 Signal Inputs The Channel A and B inputs are voltage inputs with 1 MQ 50 pF input impedance The Input Coupling is either DC or AC The Input Mode may be single ended A or differential A B The A and B connector shields are common and grounded to the chassis by 1 MQ 0 01 uF Float or 50 Q Ground The shields should never exceed 4V Do not apply more than 50 V to either input If the input exceeds 57 V the input range will be set to 34 dBV to protect the input from damage and the HighV overload status is set The input range can not be changed while HighV is detected For two channel measurements such as Frequency Response Channel 1 is the reference input to the device under test Ch2 Signal Inputs The Channel 2 A and B inpu
90. Parameter Submenu Engineering Display the Transducer Parameters menu Press lt Return gt or Input for the main Input menu Transducers such as accelerometers or microphones convert a physical quantity such as acceleration or pressure into a voltage at the analyzer s input By assigning Transducer Units to an input measurements based upon the transducer signal may be displayed in units of the actual physical quantity being measured such as m s or Pascals Transducer Units require a transducer which 1s linear over the frequency range of interest Measurements of inputs which are assigned units of acceleration velocity or displacement may be displayed with any of these three units using Transducer Convert in the Input lt Transducer Parameter gt submenu Transducer Units Channel Chi Ch1 Eng Units Ch1 EU Label m s Ch1 EU Volt 1 EUN kei Eda gi Werer l Ch1 User Label Trnsducer Convert mis Return C Units Select Engineering Units for the selected input On Off Measurements which require input data from an input which has Engineering Units On will be displayed with units of EU Labels instead of Volts The two inputs may have different Engineering Units For instance if Ch2 has engineering units On and EU Label set to Pascals and Ch1 has engineering units off then the units of the frequency response measurement will be Pascals Volt Note that this softkey applies to an inpu
91. Real Part Unwrapped Phase Single Waterfall with Skew Linear Magnitude Imaginary Part Nichols Plot Dual Upper Lower Zoom and Pan 100 200 400 or 800 FFT lines Hanning Kaiser User defined T 2 T 2 RMS Linear or Exponential Harmonic Peak Finding Data Table Waterfall Slice Se eae i Real Imaginary jo Group Delay Blackman Harris Uniform T 4 T 4 Vector Preview Time Records Sideband THD THD N Exceedance Ly Curve Fitting Conjugate Sqrt Log Exp A B C Wt Windowed Time Power Spectrum Orbit Time Record User Math Functions User Math Functions Cross Spectrum Cumulative Density Time Capture Magnitude Squared Phase Nyquist Plot Front Back Flattop Force Exponential 0 T 2 Peak Hold Equal Confidence Band Limit Testing Statistics Curve Synthesis Magnitude Phase FFT Inverse FFT d dx SR785 Dynamic Signal Analyzer X Features Source Outputs Trigger Arming Trigger Sources Time Capture Storage Hard Copy File Translation Interfaces Help Sine Two Tone Swept Sine Offset White Pink Noise Burst Noise Chirp Burst Chirp Arbitrary Auto Arm Manual Arm RPM Arm Time Arm Continuous Internal External External TTL Source Manual Capture time data for later analysis FFT or Octave Up to 2 Msamples of data can be saved with standard memory 8 Msamples with optional memory 3 5 1 44 Mbytes DOS formatted disk Save data setups and
92. Reporting Commands 5 120 Status Word Definitions 5 124 Example Program 5 129 Chapter 6 File Conversion Why File Conversion 6 2 SR785 File Types 6 3 Supported External File Types 6 4 Using the File Conversion Utility 6 5 vii Table of Figures Figure 2 1 Waterfall Display 2 30 Figure 2 2 Transfer Functions 2 48 Figure 2 3 Capacitive Coupling 2 71 Figure 2 4 Inductive Coupling 2 72 Figure 2 5 Resistive Coupling 2 73 Figure 3 1 Front Panel 3 3 Figure 3 2 Rear Panel 3 8 Figure 3 3 Dual Display Screen 3 11 Figure 3 4 Overlay Display Screen 3 12 Figure 3 5 Vertical Scale Bar 3 13 Figure 3 6 Horizontal Scale Bar 3 14 Figure 3 7 Marker Region 3 15 Figure 3 8 Marker Position Bar 3 15 Figure 3 9 Status Indicator Panel 3 18 Figure 3 10 Front Panel Keypad 3 23 SR785 Dynamic Signal Analyzer vill Features Measurements Views Displays FFT Resolution FFT Windows Correlation Windows Averaging Analysis User Math FFT Group FFT Linear Spectrum Time Record Time Capture Cross Spectrum User Math Functions Correlation Group Cross Correlation Windowed Time Frequency Response Coherence Autocorrelation Time Capture Octave Analysis Group 1 1 1 3 1 12 Octave Leo Swept Sine Group Spectrum Normalized Variance Time Capture Impulse Transfer Function User Math Functions Time Histogram Group Histogram Probability Density Unfiltered Time Record User Math Functions Log Magnitude
93. SELECTOR set for the wrong AC line voltage or if the wrong fuse is installed Hardware Reset Turn the power on while holding down the backspace lt key and continue to hold backspace for at least 3 seconds to reset the unit The unit will perform power on tests and assume the default settings including the default remote interface settings SR785 Dynamic Signal Analyzer 3 4 Overview Software Reset lt Preset gt in the System menu resets the instrument to the default settings Only the remote interface settings are not changed All stored data are lost This function requires pressing the Enter key to confirm Video Display The monochrome video display is the user interface for data display and front panel programming operations The resolution of the display is 800H by 600V The brightness is adjusted using the Brighter and Dimmer buttons below the softkeys The contrast is adjusted using Alt Brighter and Alt Dimmer As with most video displays do not set the brightness higher than necessary To extend the life of the display use the Screen Saver in the System lt Preferences gt menu A complete description of the screen display follows later in this chapter Keypad The keypad consists of four groups of hardkeys keys with printed labels Hardkeys are referenced in braces like Active Display or Input The ENTRY keys are used to enter numeric parameters which have been highlighted by a soft key
94. SENDES EERS BEREE 1 pVpk 12 5 Hz a 10 kHz y Y mid q Oct ch1 Log Mag LinAvg 4s 316 228 CD M MENU a FUNCTION N 1 3747 u Vpk sa 10 ff am gy Y min D M Displ Displ Mark Aut AUS Mark meee SOENE EEE z E F decades aA N A B 2 2 3 1 eeeeee Levoete tend heimi E emt nt eet i Auto i J K L M N anc EES eee Guu h i pretest cotati PENS l Source Window ter Capture pee paner Marker nVpk 125Hz 10kHz T Gap p ax nter Mag 9 eee o P Q R s T U Ge Oct ch2Log Analysis Disk Output System Marker Show Min Setup V Ww X Y zZ i Space i 0 STANFORD RESEARCH SYSTEMS MODEL SR785 2 CHANNEL DYNAMIC SIGNALANALYZER SOURCE OUT TRIGGER IN A CHANNEL ONE CHANNEL TWO s POWER KEYBOARD IMQ 1 MQ 50PF 1 MQ 50PF Figure Chapter 3 1 Front Panel Power Switch The power switch is located on the rear panel The SR785 is turned on by depressing the upper half of the power switch The green power LED on the front panel indicates that the unit is powered The video display may take a few seconds to warm up and become visible The brightness is adjusted using the Brighter and Dimmer buttons below the softkeys The firmware revision serial number memory size and calibration dates of the unit are displayed when the power is turned on This power on screen may be displayed at any time using System lt Show Version gt Caution This instrument may be damaged if operated with the LINE VOLTAGE
95. Set the window to 2 This decreases the resolution makes thing wider while increasing the smoothing of noisy data This concludes this example User Functions allow you to define your own measurements starting with the basic SR785 measurements User Functions can also use stored trace data for calibrations and normalizations and user constants SR785 Dynamic Signal Analyzer 1 56 Limit Testing Limit Testing This example is intended to familiarize the user with limit testing Limit Testing tests the measurement data against a set of defined Limit Segments When measurement data exceeds a Limit Segment at any point the test fails Each display has its own set of Limit Segments A Limit Segment is defined as the line between the pair of points X0 YQ and X1 Y1 The segment values between the endpoints are calculated for the displayed span A segment may be defined as either an Upper or Lower limit Measurement data which is greater than an Upper limit or less than a Lower limit cause the test to fail 1 Press System Press lt Preset gt Press Enter to confirm Preset 2 Connect the Source Output to the Channel 1 A Input Press Source lt On gt Press Auto Scale A 3 Press Analysis Press lt Limit Test gt Press lt Edit Limits gt Display the System menu Preset returns the unit to its default settings Preset requires confirmation to prevent accidental reset Wait until the self tests are completed
96. Snail Human Baby Adult Lunatic Turning the knob will move the marker around the circle verifying knob action and direction Press lt Return gt for the lt Diagnostics gt menu RS232 Printer Test Display the RS232 Printer Test screen SR785 Dynamic Signal Analyzer System Diagnostics Menu 4 201 A loop back adapter is required to complete the RS232 test This adapter is simply a mating connector with pins 2 and 3 connected so characters transmitted by the interface will be received as well Press lt Begin gt to start the test Press lt Return gt for the lt Diagnostics gt menu String to RS232 Send an ASCII test string to a serial printer connected to the RS232 port String to Printer Send an ASCII test string to a parallel printer connected to the Printer port Memory Test Disk Test Display the lt Memory Test gt menu Select a test and press lt Begin gt System RAM Display the System RAM Test screen Press lt Begin gt to test the main CPU program RAM Press lt Return gt for the lt Memory Test gt menu System ROM Display the System ROM Test screen Press lt Begin gt to test the main CPU program ROM Press lt Return gt for the lt Memory Test gt menu Video RAM Display the Video Ram Test screen Press lt Begin gt to test the video display memory Press lt Return gt for the lt Memory Test gt menu Help ROM Display the Help ROM Test screen Press lt Begin gt to test the help syste
97. Std Dev Display A Max Display B Min Display B Mean Display B Std Dev Display B Exceedance Statistics Menu Start Index Stop Index Exceedance Pct Calculate Excd 4 145 4 145 4 145 4 145 4 146 4 146 4 146 4 146 4 147 4 147 4 147 4 148 4 148 4 148 4 150 4 150 4 150 4 150 4 15 4 151 4 152 4 152 4 152 4 152 4 153 4 153 4 153 4 153 4 154 4 154 4 154 4 154 4 154 4 155 4 155 4 156 4 156 4 156 4 157 4 157 4 157 4 157 4 157 4 158 4 158 4 158 4 159 4 159 4 159 4 160 4 160 Curve Fit Menu Start Fit Synthesize Table 1 and 2 Table Fit Setup Submenu Number Poles Number Zeros Weighting Weighting Trace Set Fit Region Edit Table Submenu Edit Item Delete Item Table Format Copy Other Table Clear Table Enter j Disk Menu File Name Current Directory Display to Disk Disk to Display Settings to Disk Recall Settings Trace to Disk Disk to Trace Buffers Disk Upkeep Nodal Degree of Freedom Menu Reference Name Reference Number Reference Direction Response Name Response Number Response Direction Abort Save Continue Save Recall Settings Menu File Name Current Directory Measurements Sources Analysis Inputs Triggers DRAM settings General System Macros Recall from Disk Disk Buffers Menu File Name Current Directory 4 161 4 161 4 161 4 162 4 163 4 163 4 163 4 163 4 164 4 164 4 165 4 165 4 165 4 165 4 166 4 166 4 166 4 1
98. Storage Interval This allows the waterfall memory to hold a longer time history as well as setting a variable storage rate In FFT Order and Time Histogram group for every record added to memory a skip number of measurements are not stored For example a skip of O stores every measurement in memory A skip of 10 stores every 11th measurement in memory store 1 skip 10 The skipped measurements are still computed and affect exponential averaging they are simply not stored The elapsed time between stored records 1 storage rate is simply skip 1 times the FFT acquisition time times the time record increment In the case of triggered measurements skip 1 times the trigger period This allows the time between stored records to be determined exactly In Octave group the Storage Interval is set as a time In this case a snapshot is stored to memory every Storage Interval amount of time Waterfall Display To view a waterfall display set Waterfall lt Display gt to Waterfall The View Count sets the number of records displayed and the Trace Height sets the percentage of the display height for the Y axis Scroll Angle and Fast Angles set the angle at which successive records are scrolled in the display Scrolling at an angle allows changes at a constant frequency to be viewed more easily but takes longer to update the display Fast Angles limits the choice of Angles to those which scroll faster The Threshold sets the baseline suppress thr
99. Swept Sine or Time Histogram The set command requires display d to be Live FAVM d i The FAVM command sets queries the type of averaging shown on display d The parameter 1 selects None 0 Vector 1 RMS 2 or Peak Hold 3 This command is valid only when the Measurement Group is FFT Correlation or Order The set command requires display d to be Live FAVT d i The FAVT command sets queries the FFT Averaging Type for display d The parameter 1 selects Linear Fixed Length 0 or Exponential Continuous 1 This command is valid only when the Measurement Group is FFT Correlation or Order The set command requires display d to be Live FAVN 7 d i The FAVN command sets queries the Number of Averages for display d The parameter 1 is a number of averages from 2 to 32767 This command is valid only when the Measurement Group is FFT Correlation or Order The set command requires display d to be Live NAVG d The NAVG command queries the Number of Averages completed for display d For linear averaging the returned value is less than or equal to the FFT Number of Averages For exponential averaging the returned value is the actual number of averages completed and eventually exceeds the FFT Number of Averages This command is valid in the FFT Correlation Order and Octave Measurement Groups FOVL 7 d x The FOVL command sets queries the FFT Time Record Increment for display d The p
100. Table Insert bin j at line 1 Display Update Mode Data Table Length Upkeep File Name Display Ref Read Display d Binary Display Status Enable Display d Length Display Status Read Read Display d bin j ASCII Data Table On Data Table Query Dump Display Data Dump Display Data Table Delay Start Fit Table Frequency Scale Table Gain Table Item Query Number Poles Number Zeros Exceed Centile Polynomials Poles Residues Fit Range Error Status Enable Error Status Read Exceed Stop Index Exceed Start Index Synthesis Table Trace Ch1 EU Label Ch1 Engineering Units Off On Ch1 User Label Chl EU Volt Ch2 EU Label Ch2 Engineering Units Off On Ch2 User Label Ch2 EU Volt Weighting Trace Weighting Calculate Exceedance SR785 Dynamic Signal Analyzer 5 14 Index of Commands EZER i j x y F FAVG d i FAVM d 1 FAVN d i FAVT d 1 FBAS d i FBAS d i FBIN d x FCTR d f FDIR s FEND d f FFMT i FLIN d i FNAM 7 s FNXT FOVL d x FRCL d FREE FREJ d 1 FRST FSAV d FSPN d f FSPN d 1 FSTR d f FWFL d i FWIN d i FWTC d 1 FXST s G GDIV d i GPOL d i GRID X d i H HBIN d i HDSP d i HLEN d f HPWR d HRDO d i HRMN d i HRPT 2 d i HTHD d i l I1AF i IAR
101. The 3 dB bandwidth of the AC coupling is 0 16 Hz ICP coupling connects a5 mA current source 26 VDC open circuit to the center conductor of the A input connector This supply powers ICP accelerometers The signal is AC coupled from the center conductor Set the Input Mode to A not A B Command I1CP 1 Command I2CP 1 Select the Input Range for the selected input 50 dBV 34 dBV The Input Range is the full scale signal input just before overload The actual underlying Input Range of the SR785 varies by 2 dB steps from 50 dBVpk to 34 dBVpk The input range can be set in units of dB Vpk dB Vrms dBVpp Vpk Vrms dBEUpk dBEUrms dBEUpp EUpk EUrms or EUpp If a value is entered in one of these units the closest actual hardware input range is selected The Input Range indicator shows the current range at the top of the screen Pressing this softkey turns off Auto Range for the selected input channels If the input signal exceeds 35 dBV the input range is automatically set to 34 dBV The range may not be changed while this HighV condition exists Command I1RG 1 Command I2RG 1 Select the Anti Aliasing Filter for selected input Off On The anti aliasing filter should generally be left On Frequency domain measurements may have spurious alias signals if the filter is Off SR785 Dynamic Signal Anaylzer A Wt Filter Autoranging Input Configuration Menu 4 91 For time domain measurements i
102. The Arbitrary Source playback must be from a Capture Buffer and the Measurement of the active display must be the Capture Buffer for this key to be active Choose the correct Capture Buffer as the Measurement and use Zoom and Pan to show the region of interest Press lt Set Right Edge gt to set the Arbitrary Source Length to the marker position minus the Source Start The Source Start is not changed The Source Length is always set to a 2 kPoint 2048 points increment If the marker position is to the left of the Source Start then the Source Length is set to the minimum 2 kPts SR785 Dynamic Signal Analyzer Arbitrary Source Menu 4 81 Allocate Memory Display the Memory Allocation menu Total Available Displays the total memory available for storage either 980 2004 or 4052 blocks depending upon the amount of installed memory Each block is 2 kPoints 2048 points The total of the Capture Waterfall and Arbitrary memory allocations cannot exceed the Total Available memory It may be necessary to decrease one allocation in order to increase another Command MMEM Capture Memory Allocates memory blocks for the capture buffer The allocated Capture Memory sets the limit for the Capture Length Capture memory must be allocated before the capture buffer may be used Waterfall Memory Allocates memory blocks for waterfall storage Waterfall memory must be allocated before waterfall displays may be used Arb Memory Allo
103. The Y axis of the display is linear in scaling Real measurement data such as baseband time record have zero imaginary part This view is zero for all points Imaginary data arises from the multiplication of the input time data by sine and cosine heterodyne Signals in phase with cosine result in real data signals in phase with sine result in imaginary data The real and imaginary parts represent data 90 degrees out of phase Phase Phase view graphs the phase of the measurement data The phase is a four quadrant quantity defined as 9 arctan y x where y is the imaginary part and x is the real part and y is positive If y is negative the phase is negated Phase is graphed linearly from 180 7 to 180 m degrees radians To show unwrapped phase choose the Unwrapped Phase view Real measurement data such as baseband time record have zero imaginary part The phase is zero for all points SR785 Dynamic Signal Analyzer 2 22 Views Single channel phase is relative to the center of the time record for Uniform BMH Hanning Flattop and Kaiser windows For Force and Exponential windows phase 1s relative to the start of the time record For User windows the Window Form is user specified In general single channel phase is useful only when the time record is triggered in phase with the signal For two channel measurements the phase is relative between channel 2 and channel 1 Triggering is not always required for meaningful t
104. The capture buffer display can automatically pan with the capture fill or playback progress through the buffer During capture fill if the capture accumulates points faster than they can be displayed some points are not shown This speeds up the display update so that it keeps up with the real time capture but allows visual aliasing to occur Once capture is complete the display is redrawn showing the envelope of all points eliminating any visual aliasing effects To measure from a region of the buffer set the Playback Start and Stop in the Input menu The capture data is filtered and down sampled according to the capture sample rate Only baseband data data bandwidth starts at DC are captured The capture buffer resembles a digital oscilloscope display Signals at frequencies above the sample rate 2 56 have been filtered out The capture buffer is not a continuous representation of the input signal The data is sampled and has a time resolution of I sample rate High frequency signals will appear SR785 Dynamic Signal Analyzer Octave Measurements 2 43 distorted in the time record However ALL of the spectral information is preserved by the Nyquist sampling theorem as long as the value of each sample is accurate Amplitude calibration is performed in the frequency domain Hence the captured time data amplitudes are not calibrated User Function User Function displays the results of a user defined math function User Functions
105. The phase is the relative phase at each frequency between the two channels SR785 Dynamic Signal Analyzer Display Setup Menu 4 35 Frequency Response measures the response of a network or device under test The reference channel 1 measures the signal at the input to the device and the response channel 2 measures the device output The result is the complex Frequency Response of the device User Functions A User Function displays the results of a user defined math function User Functions defined within the Swept Sine Measurement Group may include swept sine measurement results Use the User Math menu to define a function A User Function may not be selected as the measurement if it uses a Trace which is empty or which contains data taken in a different Measurement Group See User Math Functions in Chapter 2 for more Measurement Order Linear Spectrum The Order Linear Spectrum displays the complex spectrum of the input signal as a function of order e g multiples of the rotation frequency This complex measurement contains both magnitude and phase information The phase of the order linear spectrum is relative to the point on the machine shaft corresponding to the tachometer pulse In the case of several tach pulses per revolution the choice of which tach pulse is arbitrary but is consistent from record to record Power Spectrum The Order Power Spectrum displays the power in the input signal as a function of ord
106. X Zoom Y Division Polar Y Center Polar Y Division Y Maximum Ymax Y Division Y Midpoint Y Minimum Remote Programming 5 21 Introduction The SR785 Dynamic Signal Analyzer may be remotely programmed via either the RS232 or GPIB IEEE 488 interfaces Any computer supporting one of these interfaces may be used to program the SR785 Both interfaces are receiving at all times however the SR785 will send responses only to the Output Interface specified in the System lt Remote gt menu Use the OUTX command at the beginning of every program to direct the SR785 responses to the correct interface Communicating With GPIB The SR785 supports the IEEE 488 1 1978 interface standard It also supports the required common commands of the IEEE 488 2 1987 standard Before attempting to communicate with the SR785 over the GPIB interface the SR785 s Device Address must be set in the System lt Remote gt menu Communicating With RS232 The SR785 is configured as a DCE transmit on pin 3 receive on pin 2 device and supports CTS DTR hardware handshaking The CTS signal pin 5 is an output indicating that the SR785 is ready while the DTR signal pin 20 is an input that is used to control the SR785 s data transmission If desired the handshake pins may be ignored and a simple 3 wire interface pins 2 3 and 7 may be used The RS232 interface Baud Rate Word Length and Parity must be set in the System lt Remote gt menu Sc
107. a terminator If the DSPY d command is used with the RS232 interface the host computer interface must be fast enough to keep up with the data stream The DSPY command returns data from the last available display update To keep the data static pause the measurement or take the display Off Line The returned data depends upon the display View and Units The data values are the same as if they were read with the marker In the case of a 2 D view Nyquist or Nichols two values per bin are returned separated by a comma The values are in the same order as shown in the Marker Position Bar In this case there are twice as many points returned To read the data in a Trace recall the Trace to a display and then read the display When the display d is a waterfall display this command queries the value for the trace corresponding to the waterfall marker The REFY command queries the data in Reference Graph of display d The parameter d selects Display A 0 or Display B 1 An error occurs if the display has no Reference Graph SR785 Dynamic Signal Analyzer 5 108 Data Transfer Commands DSPB d j DBIN d j The REFY d j command queries the Reference Graph data value of bin j only The bins are numbered from 0 to length 1 The value is returned as an ASCII real number The returned data depends upon the display View and Units The data values are the same as if they were read with a marker The DSPB d command r
108. a macro To play a recorded macro press Play Macro AIt Start Reset and choose the desired macro with the knob Snap Ref Alt Start Capture Snap Ref scales the Reference Display within the active display to the current display scale Changing the display scale does NOT rescale the Reference Display This allows the live measurement display to be offset from the Reference Display by changing either Ymax Ymid or Ymin in the Display Setup menu Press Display Ref to copy the display data into the Reference Display The Reference Display is graphed in the background Command SNAP d Ref to Trace Alt Active Display Ref to Trace saves the active display s Reference Display if it is on to a Trace buffer Select a Trace 1 5 with the knob and press Enter to save the Reference Display to the Trace A stored trace can be recalled to a Display or Reference Display used in a User Math Function saved to disk or copied to the Arbitrary Waveform buffer Command SVRF d 1 Trace to Ref Alt Link Trace to Ref copies Trace data into the active display s Reference Display Select a Trace 1 5 with the knob and press Enter to copy the Trace to the Reference Display Only those Traces which currently have data can be selected In addition the Trace data must be compatible with active display measurement For example if the Trace is a time record it cannot be copied into the Reference Display
109. a stable phase for non periodic frequencies The sine source is not triggered The output is always continuous Command S2FR f Set the Amplitude of Tone 2 0 5V The amplitude resolution is 0 1 mV The sine output is the sum of two tones sine waves and the DC offset constant To generate a single tone set the amplitude of one of the tones to zero Note that the sum of the amplitudes of Tone 1 Tone 2 and the absolute value of the offset cannot exceed 5 V Command S2AM x SR785 Dynamic Signal Analyzer Chirp Source Menu 4 73 Chirp Source Menu Amplitude Burst The Chirp Source menu is used to configure the chirp source Off On Chirp Noise Arb pooope 1000 0 mV 100 Source lt gt Display Display A Set the peak Amplitude of the chirp The peak output level is approximate due to the ripple in the source output reconstruction filter Changing the FFT Resolution changes the amplitudes of the individual frequency components relative to the peak If the FFT Resolution is 400 lines the amplitude of each frequency component is about 30 dB relative to the peak amplitude If the individual frequency components were perfectly random each component would be 1 V400 26 dB relative to the peak However the chirp waveform is identical from time record to time record and each component has a fixed phase relative to all the other components This worsens the crest factor by a few dB and reduces
110. active display B SR785 Dynamic Signal Analyzer 1 20 Triggering and the Time Record Select Time1 with the knob and press Enter 5 Press Trigger Press lt Trigger Source gt Select Ch 1 with the knob and press Enter Press lt Trigger Level gt Press 3 0 select with the knob and Enter Press Auto Scale B Press Window Press lt Window gt Select Uniform with the knob and press Enter Press Auto Scale A Press lt Window gt Select Hanning with the knob and press Enter Press Display Setup SR785 Dynamic Signal Analyzer Choose Time Record of Ch1 for the measurement in DisplayB bottom You should see the pulse on the bottom display Select the Trigger menu Change the Trigger Source Select internal triggering from the Ch 1 input Adjust the trigger level Set the trigger level as a percentage of full scale Adjust the level for a stable time record in DisplayB DisplayB bottom should display the pulse waveform at the left edge In this case the display shows the signal pulse as a digital oscilloscope would Select the Window menu Because the pulse is much shorter than the time record we need to use the Uniform or Force window The other window functions taper to zero at the start and end of the time record Always be aware of the effect windowing has on the time record and the FFT Select a new window type for both displays window type is
111. active display The frequency Span ranges from the FFT Base Frequency 102 4 kHz or 100 0 kHz to 2 times the Base Frequency 195 3 mHz or 191 mHz in factors of 2 A numerically entered value is rounded to the nearest allowable Span If the new frequency Span would extend below 0 Hz or above the Base Frequency then the Start and End frequencies will be adjusted Changing the Span will change the Linewidth Span FFT Resolution and Acquisition Time FFT Resolution Span The Linewidth and Acquisition time are other ways to change the Span The two displays can have different FFT Spans if the Analyzer Configuration is set to Independent Channels In this configuration no two channel measurements are allowed frequency response cross spectrum etc but the entry field can be linked to both displays using the Link key If Analyzer Configuration is set to Dual Channel the field is automatically linked to both displays SR785 Dynamic Signal Analyzer 4 8 FFT Frequency Menu Linewidth Command FSPN d f Select the Linewidth of the active display The Linewidth is defined as the Span divided by the FFT Resolution 100 200 400 or 800 lines A numerically entered value is rounded to the nearest allowable Linewidth Changing the Linewidth will change the Span Linewidth x FFT Resolution and Acquisition Time 1 Linewidth The Linewidth and Acquisition Time are other ways to change the Span If the new frequency Span would exten
112. be either 1 Shot once through the buffer or Circular repeat over and over In 1 Shot playback the buffer is played a single time The playback halts when the end of the buffer is reached In Circular playback the playback starts over when the end of the buffer 1s reached There is often a discontinuity in the playback measurement when the playback jumps from the end to the start of the buffer In either mode press Start Reset to restart playback at the start again SR785 Dynamic Signal Analyzer Capture Buffer 2 35 Normal Playback Speed plays back the capture buffer in real time i e 1 second of capture takes 1 second to play back Normal Playback Speed looks like the live real time measurement When the playback is in Octave Group playback is always Normal Speed When playback is in FFT or Time Histogram Group the Playback Speed can be either Normal or Every Time Record Normal Playback Speed plays back the capture buffer in real time i e 1 second of capture takes 1 second to playback Normal Speed playback looks like the live real time measurement Normal playback is limited to the real time limitations of the equivalent real time analog input measurement Not all time records are displayed during Normal playback though all time records contribute to averaged measurements For example 1 second of capture contains 256 full span FFT time records Normal Speed playback at full span takes 1 second and updates the displ
113. bins This is true but it s actually worse than that An FFT spectrum models the time domain as if a time record repeated itself forever This means the end of the time record is followed by the start of the time record in a circular fashion If the data is not continuous across the stop to start boundary the FFT will actually compute the spectrum of the discontinuity and leak energy into all frequencies in the spectrum Windows are functions defined over a time record which are periodic in a circular time record They generally start and end smoothly at zero and are smooth functions in between When the time record is windowed its data samples are multiplied by the window function time point by time point and the resulting windowed time record is definitely periodic in the circular sense Windowing eliminates the leakage in the spectrum from signals not exactly periodic with the time record In The Frequency Domain In the frequency domain a window acts like a filter The amplitude of each frequency bin is determined by centering this filter on each bin and measuring how much of the signal falls within the filter If the filter is narrow then only frequencies near the exact bin frequency will contribute to the bin A narrow filter is called a selective window it selects a small range of frequencies around each bin However since the filter 1s narrow frequencies slightly off bin are attenuated and phase shifted Selective windows are u
114. bit signals that the SR785 is requesting service The SRQ bit will be set 1 the first time the SR785 is polled SR785 Dynamic Signal Analyzer Status Word Definitions 5 125 following a service request The serial poll automatically clears the service request Subsequent serial polls will return SRQ cleared O until another service request occurs Polling the status word and reading it with STB can return different values for SRQ When serial polled SRQ indicates a service request has occurred When read with STB SRQ indicates that an enabled status bit 1s set Service Requests SRQ A GPIB service request SRQ will be generated whenever a bit in both the Serial Poll status word AND Serial Poll enable register is set Use SRE to set bits in the Serial Poll enable register A service request is only generated when an enabled Serial Poll status bit becomes set changes from 0 to 1 An enabled status bit which becomes set and remains set will generate a single SRQ If another service request from the same status bit is desired the requesting status bit must first be cleared In the case of the INST DISP INPT IERR and ESB bits this means clearing the enabled bits in the Instrument Display Input Error or Standard Event status words by reading them or clearing the appropriate bits in the corresponding enable registers Multiple enabled bits in these status words will generate a single SRQ Another SRQ from INST DISP INPT JERR or
115. called shot noise This can appear as voltage noise when current is passed through a resistor The shot noise or current noise is given by Troise rms 2qIAf me where q is the electron charge 1 6x10 Coulomb I is the RMS AC current or DC current depending upon the circuit and Af is the bandwidth usually the FFT linewidth 1 f Noise Every 10 Q resistor no matter what it is made of has the same Johnson noise However there is excess noise in addition to Johnson noise which arises from fluctuations in resistance due to the current flowing through the resistor For carbon composition resistors this is typically 0 1 to 3 uV of rms noise per Volt applied across the resistor Metal film and wire wound resistors have about 10 times less noise This noise has a 1 f spectrum and makes measurements at low frequencies more difficult Other sources of 1 f noise include noise found in vacuum tubes and semiconductors Total Noise All of these noise sources are incoherent The total random noise is the square root of the sum of the squares of all the incoherent noise sources Thus the largest noise source easily dominates all others in determining the noise floor of the measurement SR785 Dynamic Signal Analyzer External Noise Sources 2 71 External Noise Sources In addition to the intrinsic noise sources discussed previously there are a variety of external noise sources within the laboratory Most of these noise sources are asyn
116. d x YCEN d x Y2DV d x XPAN d i XZOM d i Display Options DISP d i DEMT i ACTD i XAXS d i RPMF i GRID d i GDIV d i GPOL 2 d i PHSL d x DDXW d x Marker MRKR d i MKMD d i MBIN d i MWEL d i MRKX d MRKB d MRKY d MRKZ d MKMX d MKMN d MKCN d 5 36 5 36 5 28 5 36 5 37 5 37 5 39 5 40 5 40 5 40 5 40 5 40 5 40 5 40 5 40 5 4 5 4 5 4 5 4 5 4 5 4 5 4 5 4 5 42 5 43 5 43 5 43 5 43 5 43 5 43 5 43 5 43 5 44 5 44 Index of Commands 5 3 Histogram Length Histogram Bins Base Frequency Histogram Repeat Measurement Group Display Measurement Display View Display Units dB Units Peak Units PSD Units On Off Phase Units dBm Reference Impedance Y Maximum Y Midpoint Y Minimum Y Division Ymax Y Division X Center Polar X Division Polar Y Center Polar Y Division Polar X Pan X Zoom Display Update Mode Display Format Active Display X Axis Scale Type RPM Frequency Grid On Off Number of Grid Divisions Nyquist Grid Type Phase Suppress Threshold d dx Window Marker Tracking Marker Mode Marker Move to bin 1 Marker Move Waterfall to record 1 Query the Marker X Position Query the Marker Bin Query the Marker Y Position Marker Z Read Move the Marker to the Maximum Move the Marker to the Minimum Center of FFT Span to Marker SR7
117. disk file or from a stored trace The Capture buffer is filled with input samples The Arbitrary source can play a portion of memory starting at a specified point The output sampling rate can also be specified The full scale amplitude of the source is set as a percentage of 1 Vpk Windowing The Sine Two Tone and Chirp sources can be used with or without a window function The Sine and Two Tone frequencies can be set at exact bin frequencies of the spectrum hence they can be exactly periodic in the time record As long as the signal to noise at the input is high windowing is not required The Chirp waveform consists of many sine waves each one perfectly periodic in the time record The Chirp waveform REQUIRES a Uniform window to result in a flat spectrum This is because the individual frequency components do not have a constant amplitude over the time record Windowing will attenuate certain portions of the spectrum Windowing is required when using the Noise source Source Trigger The Sine Two Tone Chirp and Arbitrary sources can trigger the FFT time record to measure phase response and or vector average Select Source as the Trigger Source in the Trigger menu For Sine and Two Tone the source frequencies must be set to a multiple of the linewidth in order for stable time records to be acquired Random frequencies are not exactly periodic over a time record and do not result in a stable phase even with triggering For Bur
118. done n n TRORTOS RUSVIR Oy 5 gt save DisplayA to Trace5 TOR Go CURIE dg a 3 recall Trace5 to DisplayB GetSR785 DSPN 1 nlen atoi recv query the length of DisplayB printf DisplayB Length sdn nen KKKKKKKKKKKKKKKKKKKKKKKEKKKKKKKKKEKKKKKKKKKEKKKKKKKKKKKK 5 EERE DOWN Load An Otave trace eee re AJ Make Trace5 a constant 27 dBVpk for all bins jy Convert A27 GBVek t Volts 410 27720 0 04467 Trace5 is already defined as an Octave measurement so the downloaded points are assumed to be Volts squared SR785 Dynamic Signal Analyzer Example Program 5 133 octreal 0 04467 0 04467 44 67 mV 2 real part octimag 0 0 no imaginary part This section needs to be modified for your GPIB interface printi Loading Trace Oses TODI SR79395 TASC D 34m3 use TxGpib no wait for IFC RDY TASC downloads ASCII data use TLOD to download binary data transmit mla talk 10 amp status make SR785 a talker pc a listener rarray amp ack 4 amp length amp status binary read 4 bytes long int return value should be 1 pranttl sd bytes recvd val sld 2 length ack TASC TLOD replaces the data in an existing Trace 5 The Trace measurement and length are not changed Download 34 bins of data real imaginary with commas to separate and EOI at the end First 33 bins are the spectrum last bin is the Total Power bin AALL po
119. each centered on a frequency bin The signal within each filter shows up as the amplitude of each bin If a signal s frequency is between bins the filters cause phase errors Because these filters are very steep and selective they introduce very large phase shifts for signals not exactly on a frequency bin Use the SR785 source to generate exact bin frequencies whenever possible Unwrapped Phase Unwrapped Phase view graphs the phase of the measurement data as a continuous function without wrapping around at 180 degrees This view is generally meaningful only for measurements which have data at every frequency point such as chirp source or swept sine The phase 8 is calculated for each point as in the wrapped Phase view The value of O n x 360 deg which is closest to the phase of the previous point is assigned to each point n is an integer The wrapping starts at the left edge of the display Single channel phase is relative to the center of the time record for Uniform BMH Hanning Flattop and Kaiser windows For Force and Exponential windows phase is relative to the start of the time record In general single channel phase is useful only when the time record is triggered in phase with the signal SR785 Dynamic Signal Analyzer 4 40 Display Setup Menu Units For two channel measurements the phase is channel 2 relative to channel 1 Triggering is not generally required for meaningful two channel phase measurements
120. exceed 5 V Also using large offsets with small tone amplitudes will degrade the distortion performance of the sine source Command SOFF x SR785 Dynamic Signal Analyzer Input Menu 4 87 Input Menu The Input menu configures the analog signal inputs the tachometer input and sets the parameters for capture playback aput a Analog Analyzer Config Input Source eT Dual Chan eee Trnsder Params Tach Input Auto Offset Input Source Select the measurement Input Source Analog Playback Analog uses the Chl and Ch2 front panel inputs as the source for all measurements This menu adjusts the input configurations for both inputs Playback uses the data stored in the capture buffer as the input for all measurements This selection is not valid until capture data has been acquired This menu sets the playback parameters Capture is not available for swept sine measurements Both displays use the same Input Source for their measurements The Analog Playback indicator shows the input source at the top of the screen Command ISRC 1 Analyzer Configuration Select the analyzer configuration Independent Channels Dual Channel Independent Channels allows the two displays to have different frequency parameters For instance Display A could be set to full span while Display B showed a zoomed high resolution display of a single spectral feature In Independent Channels mode only single channel measurement
121. follows Conj x jy X jy Conj x jy xX Jy Ln x jy In r 38 Exp x Jy exp x cos y jsin y Sqrt x jy y re cos 0 2 jsin 2 X 1 X x jy x jy where r V x y and tan y x Sqrt computes all angles positive from 0 The X 1 X operator is generally used on real arguments only The jOmega operator is simply jo and zeroes the real part and fills the imaginary part with the value of 27 frequency at each point in the array The frequency is determined by the span of the operand A measurement operand FFT 1 or Time 1 uses the current frequency span A Trace operand uses the span of the measurement which is stored in the Trace In the Order Analysis measurement group the current RPM is used to generate the frequency axis FFT is the windowed FFT operator These operations switch the X axis type The current window chosen in the Window menu is used on the operand before the FFT FFTu is the un windowed FFT operator The uniform window is always used The FFT and FFTu operators do not calibrate their results since their operands are not necessarily input time records To use a calibrated FFT use the measurement operand FFT 1 or FFT 2 SR785 Dynamic Signal Analyzer 2 64 User Math Functions IFFT is the inverse complex FFT operation This operation switches the X axis type d dx is the derivative operator The derivative is perfor
122. for your GPIB card kkxkxkxk xkxkxkxk xkxkxkxk xkxkxkxk xk xkxkxk xk xkxkxk xk xkxkxk xkxkxkxkxk xkxk xkxkxkxkxkx xkxkxkxkxkxkxkxkxkxxk kxxkxxk Connect the Source output to the Chl A and Ch2 A inputs kkxkxkxk xkxkxkxk xkxkxkxk xkxkxkxkxkxkxkxkxkxkxk xk xkxkxkxk xkxkxkxkxkxkxk xkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxxk kxxkxx k Finclu ude lt stdio h gt include lt stdlib h gt tinc lude lt string gt include lt conio h gt include lt math h gt include lt ieee c h gt This is the CEC header file fUse the ah file for your interface card send enter transmit rarray tarray are CEC routines defined in ieee c h char recv 80 global GPIB receive string Char cma teo global GPIB command string float rxBuff 401 array of IEEE floats to receive binary data float txBuff 2048 array of IEEE floats to send binary data int status length CEC interface routines use these variables define SR785 10 default GPIB address for SR785 F Subroutines at the end of this Listing Zr you May need to modify these for your interface card vorid TRG hie Char 4 void GetGpib int void TxSR785 char void GetSR785 char void WaitAvg void double GetData int int void WaitIFC void void GetSpace void void main void KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKEKKKKKKKKKEKKKKKKKKKKKK void main void KKKKKKKKKKKKKKKKKKKKKEKKKKKKKKKEKKKKKKKKKKKKKKKKK
123. greater than the number of records stored in the waterfall buffer minus one This command is not valid when the measurement group is swept sine The EPCT command sets queries the Exceedance Centile for both displays The parameter 1 is a centile from 1 to 99 This command is not valid when the measurement group is swept sine The EXCE command starts the exceedance centile calculation for display d The parameter 1 selects a Trace 1 5 to store the result Display d must be paused or done with waterfall storage on and records stored in the waterfall buffer using the active measurement only save option Waterfall display is not required to be on The result is stored in a data trace and has the same measurement type as the waterfall measurements This command is not valid when the measurement group is swept sine SR785 Dynamic Signal Analyzer Curve Fit Commands 5 91 Curve Fit Commands EFIT d ESYN i d ENPL j ENZE j EWTU 7 j EWTT j The EFIT command starts the curve fit calculation for display d The fit parameters will be stored in curve table 1 Display d must be a non waterfall FFT or Swept Sine measurement with a frequency x axis The ESYN command synthesizes the parameters in one of the two curve tables and displays the result The parameter 1 specifies curve table 1 0 or curve table 2 1 The parameter d specifies the display on which the result will appear Display A 0 or D
124. hardcopy Print to dot matrix or LaserJet InkJet printers Plot to HPGL or Postscript plotters Print Plot on line serial parallel or IEEE 488 or to disk file GIF EPS and PCX graphic formats available for disk output Native SR785 binary files can be converted to ASCH MATLAB MAT Files Universal File Format and HP SDF v3 Files SDF and SR780 files can be converted to native SR785 binary format RS232 serial Centronics parallel and IEEE 488 On screen help system provides Operating Manual and Programming Reference on line Specifications Frequency Range FFT Spans FFT Resolution Real Time Bandwidth Accuracy FFT Dynamic Range Dynamic Range Harmonic Distortion Intermodulation Distortion Spurious Alias Responses Full Span FFT Noise Floor Residual DC Response Amplitude Accuracy Single Channel Cross Channel Phase Accuracy Single Channel Cross Channel XI Specifications apply after 30 minutes of warm up and within 2 hours of last auto offset All specifications are with 400 line FFT resolution and anti alias filters enabled unless stated otherwise 102 4 kHz or 100 kHz both displays have the same range 195 3 mHz to 102 4 kHz or 191 mHz to 100 kHz The 2 displays can have different spans and start frequencies 100 200 400 or 800 lines 102 4 kHz highest FFT span with continuous data acquisition and averaging on both inputs 25 ppm from 20 to 40 C 90 dBfs typical 80 dBfs guaran
125. i TMAN The TDLB command sets queries the Trigger Delay 2 The parameter x is the delay in the specified units This command is valid only when the Measurement Group is FFT or Correlation The TARM command Manually Arms the trigger This command may not be queried The STMD command sets queries the Triggered Source Mode The parameter 1 selects 1 Shot 0 or Continuous 1 The TMAN command Manually Triggers if armed This command may not be queried SR785 Dynamic Signal Analyzer Input Commands 5 67 TRSR x The TRSR command sets queries the RPM Arming Start RPM The parameter x is the start RPM TRSM 7 i The TRSM command sets queries the RPM Arming Start RPM mode The parameter 1 selects Start RPM Off 0 or On 1 TRDR 7 x The TRDR command sets queries the RPM Arming Delta RPM The parameter x is delta rpm TRDM i The TRDM command sets queries the RPM Arming Delta RPM sense The parameter 1 selects Absolute Change 0 Increasing RPM 1 or Decreasing RPM 2 TIAS 7 x The TIAS command sets queries the Time Arming Step The parameter x is the time increment in seconds SR785 Dynamic Signal Analyzer 5 68 Average Commands Average Commands FFT Correlation and Order FAVG d i The FAVG command sets queries the Compute Average Off On for display d The parameter 1 selects Off 0 or On 1 This command not valid only when the Measurement Group is Octave
126. i RSNA s RSNU i RSDR i 5 107 5 107 5 107 5 107 5 108 5 109 5 109 5 109 5 110 5 111 5 112 5 112 5 113 5 113 5 32 5 114 5 115 5 117 5 117 5 117 5 117 5 120 5 120 5 120 5 120 5 120 5 121 5 121 5 121 5 121 5 122 5 122 5 122 5 122 5 122 5 122 5 118 5 118 5 118 5 118 5 119 5 119 5 118 Index of Commands 5 11 Display d Length Read Display d bin j ASCII Read Ref Display d bin j Read Display d Binary Read Display d Bin Freq or Time Read Display d Bin Number Download Trace 1 Binary Download Trace i Ascii Download Arbitrary Binary Upload Trace i Buffer Download Trace i Buffer Upload Arbitrary Buffer Download Arbitrary Buffer Upload Capture Buffer Download Capture Buffer Upload Waterfall Buffer Download Waterfall Buffer Reset Device Identification Local Remote Overide Remote Clear All Status Registers Power On Status Clear Serial Poll Status Enable Serial Poll Status Read Standard Event Status Enable Standard Event Status Read Error Status Enable Error Status Read Instrument Status Enable Instrument Status Read Display Status Enable Display Status Read Input Status Enable Input Status Read Input Ovld Read Save Nodal Information Reference Node Name Reference Node Number Reference Node Direction Response Node Name Response Node Number Response Node Direction SR785 Dynamic Signal Analyzer 5 12 Index of Commands Alphabetical List of Commands x CL
127. interface Example Program An example program is included at the end of this chapter This program is a good reference for writing your own programs to control the SR785 SR785 Dynamic Signal Analyzer Remote Programming 5 25 Command Syntax The four letter mnemonic shown in CAPS in each command sequence specifies the command The rest of the sequence consists of parameters Parameters shown in are not always required Generally parameters in are required to set a value in the SR785 Multiple parameters are separated by commas Multiple commands may be sent on one command line by separating them with semicolons The present value of a parameter may be determined by sending a query command Commands that may be queried have a question mark in parentheses after the mnemonic Commands that may ONLY be queried have a after the mnemonic Commands that MAY NOT be queried have no A query is formed by including the question mark after the command mnemonic and omitting the queried parameter from the command The query parameters shown in are NOT sent with a query The query returns the value of these parameters Values are returned as a string of ASCII characters unless otherwise noted Do NOT send or as part of the command For example the command sequence FSTR d f is used as follows FSTR 0 1 024E3 Set the Start Frequency of DispA to 1024 Hz FSTR 0 Query the Start Frequency of DispA Var
128. is displayed on a spectrum analyzer the harmonic frequencies and amplitudes are displayed with amazing clarity Another example is noise analysis Looking at an amplifier s output noise on an oscilloscope basically measures just the total noise amplitude On a spectrum analyzer the noise as a function of frequency is displayed It may be that the amplifier has a problem only over certain frequency ranges In the time domain it would be very hard to tell Many of these types of measurements can be done using analog spectrum analyzers In simple terms an analog filter is used to isolate frequencies of interest The filtered signal power is measured to determine the signal strength in certain frequency bands By tuning the filters and repeating the measurements a reasonable spectrum can be obtained The FFT Analyzer An FFT spectrum analyzer works in an entirely different way The input signal is digitized at a high sampling rate Nyquist s theorem says that as long as the sampling rate is greater than twice the highest frequency component of the signal then the sampled data will accurately represent the input signal in the frequency domain In the SR785 sampling occurs at 262 kHz To make sure that Nyquist s theorem is satisfied the input signal passes through an analog anti aliasing filter that removes all frequency components above 102 4 kHz The resulting digital time record is then mathematically transformed into a frequency spectrum using a
129. is not allowed if the Averaging Type is not Peak Hold Peak power is automatically selected if the Averaging Type is Peak Hold Use the OTYP command to set Peak Hold averaging SR785 Dynamic Signal Analyzer 5 72 Average Commands For 1 Channel octave analysis the set command requires d 2 This command is valid only when the Measurement Group is Octave The set command requires display d to be Live OLAT d i The OLAT command sets queries the Octave Linear Average Mode for display d The parameter 1 selects Triggered 0 or Continuous 1 The set command requires d 2 both displays have the same mode This command is valid only when the Measurement Group is Octave The set command requires a display to be Live SR785 Dynamic Signal Analyzer Average Commands 5 73 Average Commands Swept Sine SSTM d x lt ks s ms gt The SSTM command sets queries the Swept Sine Settle Time for display d The parameter x is a settle time from 0 008 to 1000 seconds The set command requires d 2 both displays This command is valid only when the Measurement Group is Swept Sine The set command requires a display to be Live SSCY d i The SSCY command sets queries the Swept Sine Settle Cycles for display d The parameter 1 is a number of cycles from 1 to 32767 seconds The set command requires d 2 both displays This command is valid only when the Measurement Group is Swept Sine The set command req
130. keeps up with the real time capture but allows visual aliasing to occur Once capture is complete the display is redrawn showing the envelope of all points eliminating any visual aliasing effects To measure from a region of the buffer set the Playback Start and Stop in the Input menu The capture buffer is not a continuous representation of the input signal The data is sampled and has a time resolution of 1 sample rate High frequency signals will appear distorted in the time record However ALL of the spectral information is preserved by the Nyquist sampling theorem as long as the value of each sample is accurate User Function User Function displays the results of a user defined math function User Functions defined within the Time Histogram Measurement Group may include time histogram measurement results Use the User Math menu to define a math function SR785 Dynamic Signal Analyzer 2 60 Trace Storage Trace Storage Measurement data may be stored in one of 5 Trace buffers Trace buffers are simply temporary storage for complex measurement results and are shared by all Measurement Groups Trace data is not retained when the power is turned off Display or Reference Display data may be saved to a Trace Waterfall records or slices may also be saved to a Trace Trace data is associated with the Measurement Group in which the data was originally taken A Trace into which an FFT measurement has been saved is associated with t
131. keypad or knob input is allowed To return to front panel operation press the Help Local key Alt Control Key Pressing Alt and a Control Key performs the function written below each key These functions are described below Play Macro Alt Start Reset Play Macro plays a recorded keypad macro Use the knob to select a defined macro and press Enter The Macro indicator at the top of the screen reads Play while the macro is playing Macro Rec Alt Pause Cont Macro Rec starts recording a macro Use the knob to select which macro 0 9 will be recorded and press Enter The Macro indicator at the top of the screen reads Record Press the desired sequence of keys The instrument responds to these keys while the macro is being recorded Press End Rec Alt Stop Capture to stop recording the macro Use the numeric keys to choose a parameter from a list instead of the knob while recording a macro The list choices are numbered 0 through 9 Use Alt and the numeric keys to choose the units of a numeric parameter while recording a macro The units choices are numbered starting with 0 as the first leftmost units To play a recorded macro press Play Macro Alt Start Reset and choose the desired macro with the knob SR785 Dynamic Signal Analyzer 3 32 Status Indicators To edit a recorded macro use System lt Edit Macro gt End Rec Alt Stop Capture End Rec stops recording
132. least one display to be Live HRPT 7 d i The HRPT command sets queries the histogram repeat mode for display d The parameter 1 sets the repeat mode to Off 0 or On 1 This command is valid only when the Measurement Group is Time Histogram The set command requires the display d 2 both displays SR785 Dynamic Signal Analyzer Display Setup Commands 5 37 Display Setup Commands MGRP 7 d i The MGRP command sets queries the Measurement Group of display d The parameter 1 selects FFT 0 Correlation 1 Octave 2 Swept Sine 3 Order 4 ord Time Histogram 5 Changing the Measurement Group changes the Frequency Display Setup and Average menus In addition the Source and Capture menus may also change The Measurement Group specific settings in these menus change to those last used with the new group Parameters within these menus may only be changed with commands which are valid within the new group The set command requires d 2 both displays MEAS 7 d i The MEAS command sets queries the Measurement of display d The parameter 1 selects the measurement from the list below Only those measurements available in the current Measurement Group are allowed Each measurement has an associated view Changing the Measurement changes the View to the view last used with the new Measurement The set command requires display d to be Live FFT Group Measurement FFT 1 FFT 2 Power Spectrum 1 P
133. linked by default Notice how the spectrum in DisplayA is changed by the Uniform window The spectrum in DisplayA is the sinx x envelope of a rectangular pulse The zeroes in the spectrum occur at the harmonics of 1 pulse width 1 100us or 10 kHz Choose a non optimum window Choose the Hanning window Notice how the spectrum in DisplayA goes away Select the Display Setup menu Press lt Measurement gt Select WinTimel with the knob and press Enter Press Trigger Press lt Delay1 gt Press 2 select ms with the knob and Enter Press Auto Scale B Triggering and the Time Record 1 21 Change the Measurement of DisplayB to show the effect of the Hanning window on the time record The Hanning window is zero at the beginning of the time record and large in the center This effectively zeroes the signal pulse at the start of the time record leaving nothing in the windowed time record The FFT operates on this windowed time record and thus the spectrum shows no evidence of the signal pulse Select the Trigger menu again Change the Trigger Delay for the signal on Ch 1 We can get the spectrum back by delaying the time record relative to the trigger so that the pulse is positioned in the center of the time record A negative delay means that the time record starts before the trigger event In this case the time record is about 4 ms long so a delay of 2ms will put the signal pulse in the
134. loop connecting the signal source to the analyzer This is like a transformer with the analyzer source loop as the secondary winding Source Source Figure Chapter 2 4 Inductive Coupling Cures for inductively coupled noise include 1 Removing or turning off the interfering noise source 2 Reduce the area of the pick up loop by using twisted pairs or coaxial cables or even twisting the 2 coaxial cables used in differential connections 3 Using magnetic shielding to prevent the magnetic field from crossing the area of the signal path 4 Measuring currents not voltages from high impedance sources SR785 Dynamic Signal Analyzer External Noise Sources 2 73 Resistive Coupling Ground Loops Currents flowing through the ground connections can give rise to noise voltages This is especially a problem with signal frequency ground currents Noise Source Figure Chapter 2 5 Resistive Coupling In this illustration the analyzer is measuring the signal relative to a ground far from the signal source The analyzer senses the signal plus the voltage due to the noise source s ground return current passing through the finite resistance of the ground between the analyzer and the source The analyzer and the source are grounded at different places which in this case are at different potentials Cures for ground loop problems include 1 Grounding everything to the same physical point 2 Using a heavy ground bus to reduce the re
135. lt Input Conifg gt Press lt Ch1 Input Range gt Press 3 0 select dbVpk with the knob and Enter Display the System menu Preset returns the unit to its default settings Preset requires confirmation to prevent accidental reset Wait until the self tests are completed Setup to analyze the source output The default source is a 10 24 kHz sine Turn the source on Narrow the span to display the signal better Scale the display to show the entire measurement range Copy the current measurement data into the reference graph for the active display A The reference graph is stored data which is associated with each display The reference graph is Shown in half intensity We need to change the measurement data in order to see the reference graph since it is underneath the current data Select the Input Configuration submenu Change the input range to raise the noise floor Select 30 dBV for the Ch1 Input Range Now you can see the reference graph below the current measurement s noise floor The reference graph allows visual comparison of live data with stored data The marker can also be set to read the current data relative to the reference graph The reference graph can be loaded by copying the current live data or by copying a stored trace SR785 Dynamic Signal Analyzer 1 48 Saving and Recalling 4 Press Display Setup Press lt Ymid gt Press 4 0 and Enter Press Alt Star
136. maximum Capture Length of 500 kPoints for two inputs The Capture Length can be less than the allocated memory Command CLEN 1 Sampling Rate Select the capture Sampling Rate The Sampling Rate can be 1 1 2 1 4 1 8 times the maximum sampling rate The inputs are always digitized at the maximum sampling rate The maximum sampling rate is 262 1 kHz when the FFT Base Frequency is 102 4 kHz and 256 kHz when the FFT Base Frequency is 100 0 kHz OR the Measurement Group is Octave If the selected capture Sampling Rate is the maximum rate then the digitized input data is stored in the capture buffer If the Sampling Rate is less than the maximum rate the input data is filtered and downsampled to the desired rate and then stored in the capture buffer This allows the capture buffer to hold a longer time period of data at a lower bandwidth The captured data represents a frequency span from 0 Hz to 1 2 56 times the Sampling Rate Capturing at less than the maximum sampling rate restricts the playback measurement span to 1 2 56 times the sampling rate In the order measurement group the sampling rate cannot be directly set by the user Instead the analyzer calculates the sampling rate based on the Max Order and Delta Order Based on the computed sample rate and the capture length the analyzer will display the length of the capture buffer in seconds Command CRAT 1 SR785 Dynamic Signal Analyzer Capture Menu 4 145 Allo
137. menu We ll use manual trigger to show how you can step through each time record in the capture buffer SR785 Dynamic Signal Analyzer 1 32 Capture Use the knob to select Manual and press Enter Press lt Manual Trigger gt several times Press lt Trigger Source gt select Cont with the knob and press Enter 11 Press Freq Press lt Span gt Use the knob to select 6 4 kHz and press Enter Press Start Reset 12 Press Input Press lt Playback Config gt Press lt Playback Length gt Press 8 9 6 and Enter Press Start Reset SR785 Dynamic Signal Analyzer Each manual Trigger will step one time record into the capture buffer Each time record is 1k points long or represents 11 of the 900k capture buffer Note that the playback indicator increments by 11 each time lt Manual Trigger gt is pressed Return to continuous playback Select the Frequency menu Change the measurement span The span can not be increased above 51 2 kHz since the captured data is bandwidth limited to 51 2 kHz because of our capture sampling rate Change the span to 6 4 kHz Capture playback allows the same captured data to be measured at different spans windows averaging etc This is useful if the signal is hard to reproduce or occurs infrequently At this span the capture buffer only holds 112 48 time records and takes only 14 seconds to playback every time record Select the Input menu
138. more convenient while the differential connection eliminates spurious pick up more effectively Single Ended Connection A In the first method the analyzer uses the A input in a single ended mode The analyzer detects the signal as the voltage between the center and outer conductors of the A input only The analyzer does not force the shield of the A cable to ground rather it is internally connected to the analyzer s ground via a resistor The value of this resistor is selected by the user Float uses 1 MQ and Ground uses 50 Q This avoids ground loop problems between the signal source and the analyzer due to differing ground potentials The analyzer lets the shield quasi float in order to sense the source ground In general if the source is floating use a Grounded input If the source is grounded use a Floating input Do not use a Floating input with a floating source since the shield is simply a noise antenna in this case Noise pickup on the shield alone will appear as noise to the analyzer Common mode noise which appears on both the center and shield is reyected by the common mode rejection CMR of the analyzer input but noise on the shield only is not rejected at all Differential Connection A B The second method of connection is the differential mode The analyzer measures the voltage difference between the center conductors of the A and B inputs Both of the signal connections are shielded from spurious pick up Noise pickup o
139. needs to be modified for your GPIB interface DElDTe beading Arb burrer s TxGpib SR78937 ALOR 204s 3 use TxGpib so we don t wait for IFC SR785 will return a binary 1 to acknowledge transmit mla talk 10 amp status make SR785 a talker pc a listener rarray amp ack 4 amp length amp status binary read 4 bytes long int rceturn value should be 1 princi sd bytes recvd val old length ack transmit mta listen 10 amp status make SR785 a listener pe a talker tarray txBuff 8192 1 amp status binary transfer of 8192 bytes to SR785 2048 points x 4 bytes point set EOI with last byte WaitIiFe f3 serial poll until IFC set ok to continue printi dene ny TSR 1059 QOTTI P oes change source type to Arb TXRSRI85 LIRG 47 T2RG 4 3 increase the input ranges TASR TOS ESPN 2 poss T gt narrow the span to display the spectrum GetSpace pause to look KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKEKKKKKKKKKEKKKKKKKKKKKK FR BeFLES Swe EO Octave Ana lysis 2 seas A EXSR LOS 0 STYE 2 ye switch to Noise source TXSRIS5 NIYR 2 3 choose Pink noise TSR ISS C MERP 27203 switch to Octave measurement group Print Ee WV Wait FOr OGrave cert lei caT GEESR SS DSPS clear any sticky bits in the Display status word and then wait until the settle bits become set do GetSR785 DSPS while atoi recv amp 0x0404 0x0404 prints
140. number of cycles The actual number of integration cycles is the larger of the Integration Time in cycles and the Integration Cycles The integration time is always a minimum of 1 cycle or 15 625 ms To measure each point for a time inversely proportional to the frequency set the Integration Time to 15 625 ms minimum and the Integration Cycles to the desired SR785 Dynamic Signal Analyzer Swept Sine Average Menu 4 121 number Remember the detection bandwidth increases with frequency in this case the cycles get shorter which may result in increased detected noise at higher frequencies Changes made to the number of Integration Cycles during a sweep take effect immediately The estimated sweep time is displayed in the Horizontal Scale Bar This time is simply the sum of the Settle and Integrate times for all points in the sweep Auto functions Source Auto Level Auto Range Auto Resolution will change the actual sweep time Command SSCY 7 d 1 SR785 Dynamic Signal Analyzer 4 122 User Math Menu User Math Menu Function The User Math menu sets up user defined measurements and math calculations Use a User Function to define measurements which are not already available in each Measurement Group To make a measurement of a defined User Function select the User Function as the Measurement for the active display See User Math Functions in Chapter 2 for more Enan OctUsrFnt To edit a User Functio
141. octave analysis the set command requires d 2 This command is valid only when the Measurement Group is Octave The set command requires display d to be Live OTIM d x lt ks S ms gt NAVG d OCNF 7 d i OIMP d i The OTIM command sets queries the Octave Averaging Time for display d The parameter x is the averaging time from 0 004 to 1000 seconds For 1 Channel octave analysis the set command requires d 2 This command is valid only when the Measurement Group is Octave The set command requires display d to be Live The NAVG command queries the amount of averaging completed for display d The returned value is the amount of averaging completed in 4 ms increments For example a completed linear average of 1 second returns 250 For exponential averaging the returned value is the actual averaging completed and eventually exceeds the Octave Average Time This command is valid in FFT and Octave Measurement Group The OCNF command sets queries the Octave Averaging Confidence Level for display d The parameter 1 selects 0 125 dB 0 0 25 dB 1 0 5 dB 2 1 0 dB 3 or 2 0 dB 4 For 1 Channel octave analysis the set command requires d 2 This command is valid only when the Measurement Group is Octave The set command requires display d to be Live The OIMP command sets queries the Octave Power Bin for display d The parameter 1 selects Total 0 Impulse 1 L 2 or Peak 3 Peak power
142. octave spectrum Change the Burst percentage Using a percentage less than 100 makes the noise source a triggered source 100 burst outputs noise continuously with 100 duty cycle Bursts less than 100 will output noise with less than 100 duty cycle and may be triggered In this case the noise will be output for 96 of the source period 100 ms default or 96 ms If the measurement is continuously or source triggered then the output is noise for 96 ms out of every 100 ms If the measurement is externally or manually triggered the output is 96 ms every trigger with the minimum trigger period equal to 100 ms the source period Select the Average menu Note that this menu is changed in Octave group Change the Averaging Type Use Linear Time for best time resolution Exponential Time averaging takes about 5 integration times to fully respond to a transient Linear Time averaging responds in a single integration time Change the Integration Time Choose the minimum time for the best resolution Change the Linear Average Trig This determines how measurements behave when triggering 1s enabled not Free Run SR785 Dynamic Signal Analyzer 1 36 Waterfall Display Use the knob to select Start and press Enter Press lt Power Bin gt Use the knob to select L and press Enter Press Trigger Press lt Trigger Source gt Use the knob to select Manual and press Enter Press lt Trigd Source Mo
143. of course the answers will be returned individually each with a terminator Examples of Commands TSLP 0 lt lf gt Set the Trigger Slope to Positive FCTR 1 10E3 lt lf gt Set the Center Frequency of DisplayB to 10000 Hz 10 kHz FCTR 1 Query the Center Frequency of DisplayB IDN lt lf gt Query the Device Identification String STRT lt lf gt Start the measurement same as Start Reset key Command Synchronization IFC Interface Ready bit 7 in the Serial Poll status signals that the SR785 is ready to receive and execute a command When a command is received this bit is cleared indicating that command execution is in progress No other commands will be processed until this command is completed Commands received during this time are stored in the buffer to be processed later Only GPIB serial polling will generate a response while a command is in progress When all pending commands have executed the IFC bit is set again By checking IFC with serial polls a host computer can ensure that all previously sent commands have finished before sending a new command SR785 Dynamic Signal Analyzer Remote Programming 5 23 Since most commands execute very quickly the host computer does not need to continually check the IFC bit Commands may be sent one after another and they will be processed immediately However some commands such as file and print plot commands and data transfer Operations may require a long time to execute I
144. of points from the start to the stop frequency Choosing log sweep also sets the X axis to logarithmic Command SSTY d 1 Auto Resolution Select Auto Resolution Off On If Auto Resolution is Off all points in the sweep are measured Auto Resolution On allows the sweep to skip points if sequential points do not vary by more than a specified amount Auto Resolution is specified by three parameters the Faster Threshold the Slower Threshold and the Maximum Step Size These parameters can only be adjusted when Auto Resolution is On Auto Resolution examines the results of successive measurements If the newest measurement is within the Faster Threshold of the previous measurement for BOTH channels then the sweep will take larger steps skipping frequency points Each successive time this threshold is met the step size is increased until the Maximum Step Size is reached This speeds up the sweep in regions where the response is flat varies less than the Faster Threshold If a measurement differs from the previous measurement by more than the Slower Threshold for EITHER channel then the sweep returns to the previously measured point and moves to the very next frequency point in the sweep with no skipping The sweep continues from this point speeding up if allowed and slowing down when required This fills in skips in the sweep which vary by more than the Slower Threshold SR785 Dynamic Signal Analyzer Swept Sine
145. of two tones sine waves and the offset constant To generate a single tone set the amplitude of one of the tones to zero Note that the sum of the amplitudes of Tone 1 Tone 2 and the absolute value of the offset cannot exceed 5 V Command SIAM x SR785 Dynamic Signal Analyzer 4 72 Chirp Source Menu Offset Tone 2 Frequency 2 Amplitude 2 Set the DC Offset of the Sine Source 5V 5V The offset resolution is 0 1 mV The sine output is the sum of two tones sine waves and the offset constant Note that the sum of the amplitudes of Tone 1 Tone 2 and the absolute value of the offset cannot exceed 5 V Using large offsets with small tone amplitudes will degrade the distortion performance of the sine source Command SOFF x Display the Tone 2 Settings menu Press lt Return gt for the main Source menu Frequency 2 51 2 kHz Set the Frequency of Tone 2 The sine output is the sum of two tones sine waves When the knob is used to adjust the frequency the resolution is equal to the Linewidth of the active display FFT Span The knob always sets the frequency to an exact multiple of the Linewidth For octave analysis the Linewidth of the most recent FFT Spans are used with an FFT Base of 100 0 kHz The keypad allows arbitrary frequencies to be entered Remember the output is periodic over the FFT time record only if the frequency is an exact multiple of the Linewidth Source Trigger will not result in
146. or minimum of the graph The Marker Position display above the graph shows the X position frequency or time and the Y value amplitude of the Marker The knob moves the Marker Region of the active display whenever there is no pending entry When the display is a Waterfall use Alt knob to move the marker from record to record along the Z axis and scroll the display through the waterfall memory Use the knob without Alt to move the marker along the X axis within a record Harmonic The Harmonic Marker Mode defines a Fundamental Marker with a solid vertical line In addition to the Fundamental Marker a number of harmonics are identified by small triangular Harmonic Markers The Marker Position Display can show the position of the Fundamental or of a single Harmonic The Total Harmonic Distortion THD is calculated within the Marker menu in dB and percent Only those harmonics within the measurement span which are identified by Harmonic Markers contribute to the THD The Harmonic Power in Vrms is also shown To measure THD N use Band Marker Harmonic Marker is only available for FFT and Order measurements in the frequency domain The knob moves the Fundamental Marker of the active display whenever there is no pending entry Use Marker Max to move the Fundamental Marker to the peak of the graph The harmonic identification works best if the fundamental frequency is a bin frequency If the fundamental is off bin then it is
147. pressing Alt and turning the knob When the fit parameters are calculated the fit curve will be synthesized only inside the fit region Outside of the fit region the data in the fit trace will be zero Command ERNG d i j SR785 Dynamic Signal Analyzer Edit Table Menu 4 165 Edit Table Submenu Edit Table Edit Item Clear Table Enter j Return C c Edit Item Edits the highlighted item in the curve table When a curve table is displayed turning the knob moves the highlighted item Items available for editing include the curve parameters poles zeros residues and polynomial coefficients the frequency scale delay gain or trace number Curve parameters may be edited or added using the Edit Item softkey To edit the item use the knob to move the higlighted region to the parameter to be edited Pressing Edit Item brings up the edit window and allows the value to be changed To add a new curve paramater use the knob to move the highlighted region to the blank field at the bottom of the appropriate column in the table Pressing Edit Items allows entry of a new curve parameter in that field Command EPOL 7 d 1 f g Poles Command EZER d 1 f g Zeros Command ERES d 1 f g Residues Command EPLY 7 d 1 j f Polynomial Coefficient Command EGAN d f Gain Command EFSC d f Frequency Scale Command EDLY d f Delay Command ETRC d 1
148. selected by the Band Ratio Mode for the active display The result is shown in and dB Command BRAT d 1 SR785 Dynamic Signal Analyzer 4 66 Frequency Damping Marker Menu Frequency Damping Marker Menu Calculate Frequency This menu is displayed when the active display Marker Mode is Frequency Damping Marker Setup Marker On Mode Freq Damping Calculate E Frequency 10 2 kHz Damping 3 50766 004 Calculate the resonant frequency and damping parameters for the data in the cursor region This calculation will only yield meaningful results for frequency response data Command MMCA d Displays the resonant frequency of the data in the cursor area The resonant frequency 1s calculated by fitting a single pole frequency response function to the data The resonant frequency is the imaginary part of this pole Command MMCA d Damping Ratio Displays the damping ratio of the data in the cursor area The damping ratio frequency is calculated by fitting a single pole frequency response function to the data The damping ratio is negative the ratio of the real part of the pole to the magnitude of the pole Command MMCA d SR785 Dynamic Signal Analyzer Source Menu 4 67 Source Menu A Source Off Source On Sine The Source menu selects and configures the source waveform The Measurement Group determines the available source types Choosing a source type selects the source wav
149. single channel over a sweep The spectrum is complex it contains phase and amplitude information The phase is relative to the source and is stable but arbitrary Single channel phase is not generally meaningful The spectrum measures the actual signal level at the inputs If source auto level is On then the spectrum will tend to be constant Use Frequency Response to remove the effects of a changing source level Normalized Variance Normalized variance is a measure of the signal to noise ratio of a swept sine measurement after the signal has been integrated for a specified time or a specified number of cycles Variance values near indicate that the final signal to noise ratio 1s high while values near zero indicate that the final signal to noise ratio is poor Cross Spectrum The swept sine cross spectrum is a two channel measurement defined as Cross Spectrum conj Specl Spec2 The cross spectrum contains both magnitude and phase information The phase is the relative phase at each frequency between the two channels The magnitude is simply the product of the magnitudes of each spectrum Frequencies where signal is present in both spectra will have large components in the cross spectrum Frequency Response The swept sine Frequency Response sometimes called frequency response is a two channel measurement defined as Frequency Response Spec2 Specl The Frequency Response contains both magnitude and phase information
150. tachometer input to synchronize the SR785 to a rotating machine for order tracking measurements or to trigger a measurment using RPM arming Parameters relating to the tachometer input are set in the Input lt Tach Input gt Submenu Start Input This TTL input provides a means of remotely starting a measurement A TTL rising edge at this input is equivalent to pressing the Start Reset SR785 Dynamic Signal Analyzer Screen Display 3 11 Screen Display Soft keys highlight an entry field or Marker Position Bar select an option When highlighted Status indicator indicates Active Display panel Menu q 51 2 kHz RmsAvg 10 Figure Chapter 3 3 Dual Display Screen Horizontal Scale Displays There are two displays labeled Display A and Display B Each display consists of a data graph vertical scale bar horizontal scale bar and marker position bar Each display has an associated measurement The displays may have different measurements such as spectrum and time record different views such as magnitude and phase and so on Many instrument parameters are set independently for each display The display format is selected in the Display Options menu The display shown above is the Dual display format The Active Display key toggles between the two displays Display A is always on top SR785 Dynamic Signal Analyzer 3 12 Screen Display i 3 Linear Lease wos A R RRETA 3 L
151. the L or LA bin is treated the same as the other octave bins with the exception of the A B and C weighting operators These operators do not change the L or LA bin Impulse Broadband Impulse sound level I is computed according to IEC 651 1979 Type O It is computed from real time low pass filtered input data not from the octave band outputs The Impulse bandwidth is DC 100kHz for 1 octave channel and DC 50kHz for 2 channels SR785 Dynamic Signal Analyzer Octave Measurements 2 45 To measure I set the Averaging Type to Exponential Linear or Equal Confidence and the Power Bin to Impulse The time constants for the Impulse measurement are defined by the IEC standard The Integration Time and Confidence Level are ignored by the Impulse calculation Impulse power is always an exponential average The last bin in the measurement displays the Impulse sound level The last bin is labeled T In a User Math function the I bin is treated the same as the other octave bins with the exception of the A B and C weighting operators These operators do not change the I bin Peak Broadband Peak sound level P is computed according to IEC 651 1979 Type 0 It is computed from real time low pass filtered input data not from the octave band outputs The Peak bandwidth is DC 100kHz for 1 octave channel and DC 50kHz for 2 channels To measure P set the Averaging Type Peak Hold In this case the Power Bin must be set to Peak The time con
152. the average For Linear averaging Pause Cont will complete the current average If the linear average was already complete Pause Cont will start a new measurement For Swept Sine measurements Pause Cont simply resumes the sweep where it was paused If measurement related parameters are changed while the unit is paused the measurement cannot be resumed The SR785 will display the message Can t continue Measurement has Changed In this case it is necessary to press Start Reset to restart the measurement Command PAUS and CONT Start Capture Start Capture starts storing data in the capture buffer SR785 Dynamic Signal Analyzer Status Indicators 3 29 If the Trigger Arming Mode is Auto Arm and the Trigger Source is Continuous capture starts immediately Otherwise the selected Trigger Arming Mode and Source will be in effect and the next trigger event will start capture While capture is in progress the displays do not update The Capture Progress indicator shows how much of the desired capture length has been completed If the Capture Mode is 1 Shot capture stops when the buffer is full Press Stop Capture to halt capture before the buffer is full If the Capture Mode is Continuous once capture is started it continues indefinitely and fills the capture buffer in a circular fashion In this case press Stop Capture to halt capture with the most recently acquired data stored in the buffer Use the Capture
153. the measurement time of sweeps covering orders of magnitude in frequency the detection bandwidth can be set as a function of frequency More time can be spent at lower frequencies and less time at higher frequencies In addition frequency points can be skipped in regions where the response does not change significantly from point to point This speeds measurements of narrow response functions The figure below illustrates the difference between FFT and swept sine when measuring the frequency response of an elliptic low pass filter This filter has a stop band of 80 dB and a zero of about 100 dB The 400 point FFT measurement was made with 2500 vector averages taking about 10 seconds to complete The swept sine also took 400 points Each point was averaged for 16 ms or 10 cycles whichever was longer The entire sweep also takes about 12 seconds SR785 Dynamic Signal Analyzer 2 48 Swept Sine Measurements 38 4 kHz OHZ 51 2 kHz KHz 39 07143 kHz 102 122 dB 10 3 Hz FFT Measurement Swept Sine Measurement Figure Chapter 2 2 Frequency responses The range of the FFT measurement is limited to about 80 dB This is because the response signal to Channel 2 contains frequency components within the filter pass band These components add to create amplitude peaks near 0 dBV for a 1V chirp amplitude This requires the input range of Channel 2 to be set near 0 dBV even though each pass band component is only at 30 dBV The n
154. time record starts 1 4 of a time record advanced from the start of the previous time record This is referred to as 75 overlap since the two time records share 75 of a record The overlap is simply 100 minus the Time Record Increment When the Time Record Increment is less than or equal to 100 the measurement is real time All time points contribute to one or more measurements If the increment 1s 200 the start of the next time record is advanced from the start of the previous time record by 2 time records leaving a gap of 1 record This means that the data between the two time records is not measured When the Time Record Increment is greater than 100 then the measurement is not real time and some time points do not contribute to a measurement The actual time record increment for the measurements in progress is displayed in the Real Time indicator in the status area below the Input Ranges If the indicator shows a value greater than the requested Time Record Increment it means that the measurement cannot be made with the requested increment but is running with the smallest increment possible Factors which affect the processor s ability to run real time include the measurement type averaging and source type Settling When the frequency span or input signal path gain filtering etc 1s changed a settling time is required before the FFT measurement is considered settled or valid The measurement is not settled until the disc
155. to 11 octaves Decreasing the Lowest Band will also decrease the Highest Band if necessary to keep the measurement span at 11 octaves The two displays can have different Lowest Bands if the Analyzer Configuration is set to Independent Channels If Analyzer Configuration is set to Dual Channel they field is automatically linked to both displays Command OLOB 7 d f Octave Resolution Select the Octave Resolution number of bands per octave for the active display Full Third Twelfth Full octave band centers are calculated by multiplying or dividing 1000 Hz by 2 Third octave band centers are calculated by multiplying or dividing 1000 Hz by 2 or 1 2599 Twelfth octave band centers are calculated by multiplying or dividing 1000 Hz by 2 or 1 0595 The exact band center frequencies are calculated according to the ANSI standard The displayed frequencies are sometimes rounded to even values for a simpler display The filter shapes are third order Butterworth with full 1 3 or 1 12 octave bandwidth Changing the Octave Resolution will change the Lowest Band and Highest Band to allowed bands of the new resolution The two displays can have different Octave Resolution if the Analyzer Configuration is set to Independent Channels If Analyzer Configuration is set to Dual Channel they field is automatically linked to both displays Command ORES d 1 SR785 Dynamic Signal Analyzer 4 14 Octave Frequency Menu Oct
156. to the Arbitrary Waveform buffer When the measurement is paused use Alt knob to move the marker from record to record in the Z axis and scroll the display through the waterfall memory Use the knob without Alt to move the marker along the X axis within a record Command WTRC d i j Slice to Trace Save a time slice from the waterfall to a Trace A slice is the history of a single X position data at the marker X position from all stored records Choose a Trace with the knob and press Enter to complete the operation The stored slice contains as many points as were stored in the Waterfall buffer up to Total Count The points in a slice trace are numbered and displayed from O data from oldest record to n data from newest record Note that this differs from the waterfall display in which the newest record is numbered 0 A recalled slice resemble a time record X axis is time advancing left to right with the X axis labeled as waterfall record number instead of time A stored slice trace can be recalled to a Display or Reference Display used in a User Math Function or saved to disk A slice can not be copied to the Arbitrary Waveform buffer Command WSLC d i j SR785 Dynamic Signal Analyzer Capture Menu 4 143 Capture Menu The Capture menu configures the Capture Buffer See Capture Buffer in Chapter 2 for more information Capture Capture Channels Chi Ch2 Capture Mode 1 Shot Captu
157. trigger the burst Chirp Noise and arbitrary source waveforms Source triggers synchronously with the source waveform The source runs continuously and Source Trigger synchronizes the time record with the source waveform Source Trigger is not valid for swept sine measurements For FFT measurements the phase of signals which are synchronous with the trigger is stable Vector averaging preserves these signals while attenuating random signals thus increasing the dynamic range of the measurement For Order measurements the phase is measured relative to the trigger rather than the tachometer pulse if a non continuous trigger source is used The Trigger Source applies to both displays Command TSRC 1 SR785 Dynamic Signal Analyzer 4 102 Trigger Menu Trigger Level Set the Trigger Level 100 99 The Trigger Level applies to Chl Ch2 and External Trigger Sources The Trigger Level is specified as a percentage of the Input Range for Chl or Ch2 and as a percentage of 5 V for External trigger The trigger detector requires a minimum signal amplitude of 4 of the Input Range 200 mV for External For Chl or Ch2 internal trigger the signal must exceed 28 dBfs in order to trigger Internal trigger is detected after the anti aliasing filter Gf On Command TLVL 1 Trigger Slope Delay 1 Delay B Select the Trigger Slope Rising Falling The Trigger Slope applies to Chl Ch2 External and Ext TTL Trigger Sou
158. two additional arrows at the endpoints and its endpoint coordinates are displayed in the menu Select the Limit Type for segment 0 Change the limit to a lower limit The limit test now fails since data falls below the segment Press lt Return gt Press lt Limit Beep gt Use the knob to select On and press Enter Press Display Setup Press lt Measurement gt Use the knob to select Time1 and press Enter Press lt Measurement gt Use the knob to select FFT ch1 and press Enter Press Analysis Press lt Limit Test gt Press lt Limit Segments gt Use the knob to select Show and press Enter Limit Testing 1 59 Return to the Limit Testing menu Select Limit Beep On enables the audible alarm This alarm alerts you to limit test failures Select the Display Setup menu Change the Measurement The limit segments are defined for the current measurement view and units Changing any of these parameters turns limit testing off The Limit Testing and Beep are turned off since the limit segments we defined have no meaning for this measurement Change the Measurement to Time Record Chl If we went back to the Limit Testing menu and tried to edit limits now the previous limit segments would be lost Each display only has a single set of limits and they are defined for a specific measurement view and units Change the Measurement back Select FFT ch1 again Select the Analysi
159. type averaging and source type Be sure to set the Time Record Increment to 100 when vector averaged measurements are being used The Time Record Increment is ignored whenever the measurement is triggered In this case the time records start with the trigger Settling When the frequency span or input signal path gain filtering etc is changed a settling time is required before the FFT measurement is considered settled or valid The SR785 Dynamic Signal Analyzer 4 112 Average Menus measurement is not settled until the discontinuity in the input data has propagated through the digital filters and a complete new time record has been acquired If the time record increment is 100 unsettled measurements are not displayed After a change is made which unsettles the measurement new data is not displayed until the filters are settled and a complete time record has been acquired If the measurement is running with a time record increment less than 100 and the measurement is unsettled unsettled measurements may be displayed New data is displayed after the filters are settled and a portion of the new time record has been acquired For example if the time record increment is 25 3 measurements are made before a complete new time record has been acquired These first 3 measurements have time records which contain data from before AND after the measurement was unsettled These unsettled measurements are displayed in half intensity indi
160. until a trigger is received Command NPER x SR785 Dynamic Signal Analyzer 4 78 Arbitrary Source Menu Arbitrary Source Menu Amplitude The Arbitrary Source menu is used to configure the arbitrary source Off Chirp Noise Arb pede HBAS Saeed 50 00 Source Play Rate 262 1 kHz Source Arb Buffer Set the Amplitude of the arbitrary source relative to 1V 0 500 The maximum output is 5V If the Arbitrary Waveform has been copied from a Trace the data is normalized so that the point with the largest absolute value is output at 1V when the Amplitude is 100 When the Arbitrary Waveform is loaded from the computer interface the data ranges from 1 0 to 1 0 A value of 1 0 is output at 1V when the Amplitude is 100 When playback is from a Capture buffer the input range corresponds to full scale For example if a 0 1 Vpk 20 dBV signal is captured on an Input Range of 20 dBV full scale at the input it will play back at 1V when the Amplitude is 100 To duplicate the actual signal amplitude set the Amplitude to 10 Command AAMP 1 Source Play Rate Select the Arbitrary Source Play Rate The Play Rate can be 1 1 2 1 4 1 8 times the maximum sampling rate The maximum sampling rate is 262 1 kHz when the FFT Base Frequency is 102 4 kHz and 256 kHz when the FFT Base Frequency is 100 0 kHz OR the Measurement Group is Octave SR785 Dynamic Signal Analyzer Source
161. up with the real time capture but allows visual aliasing to occur Once capture is complete the display is redrawn showing the envelope of all points eliminating any visual aliasing effects SR785 Dynamic Signal Analyzer 2 20 FFT Measurements To measure from a region of the buffer set the Playback Start and Length in the Input menu During playback a marker at the bottom of the graph indicates the current time record position within the buffer The capture data is filtered and down sampled according to the capture Sample Rate Only baseband data bandwidth starts at DC are captured The capture buffer resembles a digital oscilloscope display Signals at frequencies above the sample rate 2 56 have been filtered out The capture buffer is not a continuous representation of the input signal The data is sampled and has a time resolution of I sample rate High frequency signals will appear distorted in the time record However ALL of the spectral information up to the sampling rate 2 56 is preserved by the Nyquist theorem as long as the value of each sample is accurate Amplitude calibration is performed in the frequency domain Hence the captured time data amplitudes are not calibrated User Function User Function displays the results of a user defined math function User Functions defined within the FFT Measurement Group may include FFT measurements Use the User Math menu to define a math function A User Function may not
162. usually the device under test output Channel 2 In some cases where the device under test is not driven directly from the source output the device input Channel 1 may be the reference Command SSAL 1 Set the sine Amplitude 0 mV 5000 mV This parameter is adjustable only if Auto Level Reference is Off The swept sine source turns off whenever there are no measurements being made This is before the sweep is started at the end of a single sweep or while a sweep is paused If SR785 Dynamic Signal Analyzer 4 84 Swept Sine Source Menu Source Ramping is Off the source shuts off instantly in these situations If Source Ramping is On the source will ramp off When the sweep is started or re started the source will ramp on for the first measurement The amplitude may be changed at any time during a sweep Command SSAM x Ideal Reference Set the Ideal Reference 0 mV 5000 mV This parameter is adjustable only if Auto Level Reference is set to Channel 1 or Channel 2 The Ideal Reference is the signal level that the source maintains at the Reference Channel to within the Reference Limits This is determined by the limitations of the device under test or may simply be the desired signal level for the test If the Ideal Reference requires a source amplitude greater than the Maximum Source Level then the Reference Channel signal will fall below the Ideal Reference In cases where the required source amplitude is v
163. want a resolution better than 256 Hz We need to increase the duration of the time record There are two ways to do this take more points in each time record or lower the sampling rate Taking more points is difficult since both the memory and processing requirements increase with the number of points The longest time record the SR785 can process is 2048 points 800 point FFT Instead we take the approach of lowering the sample rate and making the same number of samples cover a longer time If we halve the sample rate this doubles the time record duration and gives us better resolution However the sample rate also determines the frequency span By halving the sample rate we also halve the frequency span At a constant number of points in the FFT we must tradeoff better resolution with narrower frequency spans Changing the sample rate of the A D converter is not practical since that requires changing the analog anti aliasing filter cutoff frequency Instead the incoming data samples at 262 kHz are digitally filtered and down sampled The advantage is that the digital filter s cutoff frequency can be easily changed For example to decrease the sampling rate from 262 kHz to 131 kHz the incoming data is low pass filtered to remove any signals above 51 2 kHz This filter rolls off steeply from 51 2 kHz to 65 6 kHz Since output of this filter only contains frequencies up to 65 6 kHz Nyquist only requires a sample rate of 131 kHz and only eve
164. wave are arranged so that they do not add in phase resulting in a low crest factor ratio of peak to rms This source is useful for measuring frequency responses quickly without having to make many discrete measurements using a single sine wave The Burst Chirp is a sweep over the FFT frequency span in a time less than the time record Burst Chirp is only available for FFT measurements Broadband noise is useful for characterizing circuits mechanical systems or even the audio response of an entire room White noise provides equal amplitude per root Hz from 0 to 102 kHz regardless of the measurement span White noise is useful in electronic applications Pink noise rolls off at 3 dB oct providing equal amplitude per octave Pink noise is preferred in audio applications White Noise can be bandlimited to the frequency span of the measurement Since the signal is noisy and random FFT windows are always required when using the Noise source Burst Noise is noise output for a fraction of the time record FFT or Source Period Octave Arbitrary The Arbitrary source plays a waveform stored in memory The waveform can be either Capture buffer or the Arbitrary Waveform memory Use the lt Memory Allocation gt menu to allocate memory between the capture buffer waterfall storage and the arbitrary source waveform SR785 Dynamic Signal Analyzer The Source 2 37 The Arbitrary waveform memory can be loaded via the computer interfaces from a
165. way to adjust the scales of both graphs is using the Auto Scale keys Pressing Link Auto Scale A first auto scales DisplayA and then changes the scale of DisplayB to match This is convenient when you are comparing the two displays The Link key temporarily links the two display Markers together Pressing any key removes the link between the Markers To permanently link the markers go to the Marker menu and change lt Marker gt to Link Marker Min moves the Marker in the active display B to the graph minimum Pressing Link first moves both Markers to their graph minimums at the same time Link preceding a function key generally performs the function on both displays at once Link Auto Scale matches the active display Span Up and Span Down are always linked This concludes this measurement example You should have a feeling for linking and unlinking and the flexibility of unlinked measurements Triggering and the Time Record 1 19 Triggering and the Time Record This example investigates the trigger and time record You will need a function generator capable of providing a 100 us wide pulse at 256 Hz with an amplitude of 1V The output should have a DC level of OV Make sure you have read The FFT Time Record in Chapter 2 before trying this exercise 1 Press System Press lt Preset gt Press Enter to confirm Preset 2 Turn on the generator and choose a pulsed output waveform Se
166. when 0 NEWA New data is available for DisplayA 1 AVGA DisplayA linear average has completed 2 STLA New settled data is available for DisplayA 3 LIMA DisplayA has failed a limit test 4 SSA Swept Sine sweep has finished 5 WFA Display A 1 shot Waterfall has finished 6 WFD Display A Waterfall has finished drawing 7 unused 8 NEWB New data is available for DisplayB 9 AVGB DisplayB linear average has completed 10 STLB New settled data is available for DisplayB 11 LIMB DisplayB has failed a limit test 12 SSB Swept Sine sweep has finished 13 WFB Display B 1 shot Waterfall has finished 14 WFB Display B Waterfall has finished drawing 15 unused The Display status bits stay set until read by DSPS They are also cleared by the CLS command Use DSPE to set bits in the Display status enable register The AVG STL LIM and SS bits are only updated when new data is available for the display no faster than 8 Hz Always test for NEWA or NEWB in the status word along with AVG STL LIM or SS The status updates for the two displays may not be exactly synchronous Always test the DisplayA status bits separately from the DisplayB status bits For example to wait for both displays to finish averaging do NOT test the Display status word for both AVGA and AVGB simultaneously The AVGA and AVGB bits may not be set at the same time Test for AVGA and AVGB separately and wait until both have occurred SR785 Dynamic Signal Analyzer 5 128 Status Word Defin
167. which are measurement results which are not enclosed in angle brackets such as FFT 1 or Timel represent unaveraged instantaneous versions of the measurement Operands which contain an explicit averaging type such as Vec lt F1 gt or PeakHold lt F2 always are averaged according to their indicated type regardless of the setting of the lt Display Average gt softkey Octave and Swept Sine measurements are always averaged measurements Use the Average menu to set the averaging parameters FFT 1 and FFT 2 are the FFT of the Chl and Ch2 inputs These operands use the window chosen in the Window menu for the display which is measuring the function FFTu 1 and FFTu 2 are un windowed FFT s of the Chl and Ch2 inputs Correlation operands such as RMS lt Ful F1 gt are used to compte the RMS and Vector averaged auto and cross correlation measurements See chapter 2 for a description of how to compute all the averaged versions of all the predefined measurments Trace operands are simply the data stored in the Traces For example Traces can hold reference data used for normalization or calibration There are 5 Traces which can be stored These Traces are shared by all 3 Measurement Groups SR785 Dynamic Signal Analyzer 4 126 User Math Menu Constants are complex constants which are the same for every array point Constants such as pi are commonly used in equations There are 5 user defined constants which are shared by all 3 Measurem
168. which ratios the spectrum of Ch 2 to the spectrum of Ch 1 Frequency response measures the response of a network or device under test The reference channel 1 measures the signal at the input to the device and the response channel 2 measures the device output The result is the complex frequency response of the device A broadband source such as chirp or noise should be used to measure frequency response The definition of frequency response depends on the type of averaging which is displayed No Average Freq Response FFT2 FFT 1 SR785 Dynamic Signal Analyzer FFT Measurements 2 19 Vector Average Freq Response lt FFT2 gt lt FFT1 gt RMS Average Freq Response RMSAvs cross spectrum power spectrum 1 Freq Response lt FFT1 e FFT2 gt lt FFT1 e FFTI gt Peak Hold Average Freq Response MAX FFT2 V lt FFT1 FFT1 gt Both the RMS averaged and Vector averaged frequency response contain both magnitude and phase information The phase is the relative phase at each frequency between the two channels The RMS averaged frequency response is computed by taking the ration of the cross spectrum to the input power spectrum a technique called the tri spectral average Coherence The coherence function is a two channel measurement defined as Coherence Mag RMSAvg CrossSpec Pwrl Pwr2 Averaging 1s always On and the Averaging Modes are defined by the measurement above The Type and Number Of Av
169. which repeat from time record to time record and are preserved Vector averaging can substantially improve the dynamic range of a measurement as long as the signals of interest have stable phases For single channel measurements vector averaging requires a trigger The signal of interest MUST be phase synchronous with the trigger to have a stable phase For a two channel measurement the phase is relative between Channel 2 and Channel 1 As long as the signals of interest have stable relative phases triggering is not required for vector averaging Triggering is still required to isolate time records which contain the signals of interest The Time Record Increment should be set to 100 when vector averaged measurements are being used SR785 Dynamic Signal Analyzer Average Menus 4 111 Peak Hold Averaging Peak hold averaging is similar to RMS averaging in that the RMS measurement quantities are calculated However instead of averaging the RMS measurements together in peak hold averaging the new data is compared to the old data and the maximum value is kept In Continuous Peak Hold Averaging the new data is continually compared with the current maximum In Fixed Length PeakHold Averaging a fixed number of records 1s examined for the maximum Time Record Increment Set the Time Record Increment for the active display 0 300 The Time Record Increment is how far the start of each time record is advanced between measurements a
170. window to use for accurate amplitude measurements The Flattop window function is w 1 0 1 93 cos 27 Bs 1 29 cos 4n 0 388 cos 6 0 028 cos 8x a N N N N for 1 0 N 1 and N number of time record points The BMH window combines good selectivity and reasonable accuracy about 0 8 dB for signals between exact frequency bins The BMH window has much lower side lobes than the Hanning window and very little broadening of non bin frequencies The BMH window is a good window to use for measurements requiring a large dynamic range The BMH window function is SR785 Dynamic Signal Analyzer 2 14 FFT Windowing Kaiser w 1 0 136109 cos 27 J 0 39381 cos 47 0 032557 cos 67 a N N N for 1 0 N 1 and N number of time record points The Kaiser window combines excellent selectivity and reasonable accuracy about 0 8 dB for signals between exact frequency bins The Kaiser window has the lowest side lobes and least broadening for non bin frequencies This makes this window the best for selectivity The Kaiser window is the best window to use for measurements requiring a large dynamic range w for1 0 N 1 and N number of time record points Io T a a 0 1R r R 120 0 and IO is the modified Bessel function of the first kind Force Exponential Many impact measurements require a Force window for excitation channel and an Exponential window for the response channel With the SR785 this is accompl
171. zero and pole residue Once parameters have been entered into the curve tables the corresponding frequency response function can be synthesized into a trace for comparison with measured data Polynomial In this format the curve table represents a frequency response function as the ratio of two polynomials in the complex frequency variable s b s b s b Freq Re sp s Gain 2 ___ _____ a S 4 8 a The curve tables allow entry of both the numerator and denominator coefficients as well as the order of the numerator and denominator polynomials The curve table also contains a constant gain factor which multiplies the polynomials Pole Zero In the pole zero format the numerator and denominator polynomials are factored so that the frequency response curve is described by the ratio of the products of the poles and zeros To ensure a real impulse response all complex poles and zeros only occur in complex conjugate pairs S Z 5 2 a iO 25 Freq Re sp s Gain S Py S gt Pmi CS Po Pole Residue In the pole residue format a partial fraction expansion of the pole zero form is performed to yield the frequency response as a sum of single pole terms weighted by residues R R R Freq Re sp s Gain 2 l 4 4 n S Pm S Pma s Po Once again the residues corresponding to complex conjugate pole pairs are complex conjugates themselves SR785 Dynamic Signal Analyzer 2 76 Curve
172. zeroes the second half of the time record and the T 4 T 4 window zeroes the first and last SR785 Dynamic Signal Analyzer Correlation 2 39 quarter of the time record The T 2 T 2 1s a uniform window which should only be used on data which is self windowing lasts less than half of the time record Cross Correlation Cross correlation is a two channel measurement In the time domain it is a comparison of a signal x t with a time shifted version of another signal y t t displayed as a function of t This is useful for detecting signals common to both channels but shifted in time The definition of Cross Correlation depends upon the displayed average selected in the Average menu No Averaging Cross Correlation invFFT FFTu2 FFT1 Peak Hold or RMS Averaging On Cross Correlation invFFT lt FFTu2 FFT1 gt Vector Averaging On Cross Correlation invFFT lt FFTu2 gt lt FFT1 gt where FFT 1 is the windowed FFT of Channel 1 FFTu2 is the un windowed FFT uniform window of Channel 2 and invFFT is an inverse FFT Correlation is a real function and requires a baseband span real time record Non baseband time records do not preserve the original signal frequencies and thus do not yield the correct correlation A correlation window is applied to the time record of Ch1 in the computation This is because the FFT models the time domain as a single time record repeating itself over and over Computing the
173. 0 to 65535 The INPS 1 command queries the value 0 or 1 of bit 1 0 15 INPS clears the entire word while INPS 1 clears just bit 1 The INPC command queries the current overload condition of input 1 The parameter 1 selects Ch1 0 or Ch2 1 INPC returns a value from 0 to 3 SR785 Dynamic Signal Analyzer Status Reporting Commands 5 123 return meaning 0 input is under half scale 1 input is over half scale 2 input is overloaded 3 input is HighV INPC always returns the current condition If an overload occurs and goes away INPC will not detect it Use the status words to detect momentary changes in the overload state SR785 Dynamic Signal Analyzer 5 124 Status Word Definitions Status Word Definitions The SR785 reports on its status by means of six status words the Serial Poll Standard Event Instrument Display Input and Error status words Upon power on the SR785 may either clear all of its status enable registers or maintain them in the state they were in on power down The PSC command determines which action will be taken The status bits are set to 1 when the event or state described in the tables below has occurred or is present Serial Poll Status Word Bit Name Set when 0 INST An enabled bit in the Instrument status word is set 1 DISP An enabled bit in the Display status word is set 2 INPT An enabled bit in the Input status word is set 3 IERR An enabled bit in the Error status word is se
174. 1 lt FFT1 gt RMS Average FFT 1 V lt FFT1 FFT1 gt Peak Hold Average FFT 1 V MAX FFT1 FFT1 Power Spectrum The Power Spectrum is derived from the FFT spectrum by multiplying the spectrum by its complex conjugate The averaged power spectrum is a good approximation to the rms signal and noise amplitudes The power spectrum is a real quantity and contains no phase information The precise definition of the Power Spectrum measurement for all averaging modes is as follows No Average Power Spectrum FFT 1 e FFT 1 Vector Average Power Spectrum lt FFT1 gt lt FFT1 gt SR785 Dynamic Signal Analyzer FFT Measurements 2 17 RMS Average Power Spectrum lt FFT1 FFT I gt Peak Hold Average Power Spectrum MAX FFT1 e MAX FFT1 Time Record A time record is simply a sequence of data samples The duration of the time record is equal to 1 FFT resolution For baseband spans spans which start at DC the time record resembles a digital oscilloscope display Signals at frequencies above the span have been filtered out Baseband time records are entirely real they have no imaginary part For zoomed spans spans which start above DC the time record display does NOT resemble the original data The data has been frequency shifted Signals at the center of the span appear at DC while frequencies at both edges of the span appear as high frequencies Zoomed time records are complex they have both a real and an imagina
175. 1 or Overlay 2 Use the ACTD command to select the active display in the Single format In the Single format the inactive display is still accessible via commands The ACTD command sets the Active Display to display 1 The parameter 1 selects DisplayA 0 or DisplayB 1 The XAXS command sets queries the X Axis Scale Type of display d The parameter 1 selects Linear 0 or Logarithmic 1 This command is valid only when display d is an FFT measurement with frequency as the X axis FFT measurements with a time X axis Time WinTime Capture or User Time Function always have a linear scale The RPMF command sets queries the RPM frequency scaling for both displays The parameter 1 selects Hz 0 or RPM 1 as the units for frequency The GRID command sets queries the Grid On Off Mode of display d The parameter 1 selects Off 0 or On 1 The GDIV command sets queries the number of Grid Divisions of display d The parameter 1 selects 8 0 10 1 12 2 or 15 3 Changing the Grid Divisions changes the vertical scaling Y div and horizontal scaling X div Nyquist and Nichols views The GPOL command sets queries the Nyquist Grid type for display d The parameter 1 selects Rectangular Grid O or Polar Grid 1 SR785 Dynamic Signal Analyzer 5 44 Display Options Commands PHSL d x The PHSL command sets queries the Phase Suppress Threshold of display d The parameter x is a real magnitude squared val
176. 2 11 duration is twice the full span time record The sample rate is 1 4 of the full span baseband sample rate In comparison the baseband O0 51 2 kHz span has a sample rate 1 2 of the full span baseband sample rate This is because the baseband time record is all real and the zoomed time record is complex Further filtering and down sampling reduces the span even further At each span the zoomed time record is complex and has half as many points half the sample rate as the corresponding real baseband time record The Time Record Display The baseband time record display resembles a digital oscilloscope display Signals at frequencies above the span have been filtered out The anti aliasing filters both analog and digital have a steep but finite roll off at their cutoff frequencies Signals which are just above the cutoff frequency are outside of the FFT span not in the displayed spectrum but appear attenuated in the time record Baseband time records are entirely real they have no imaginary part The zoomed time record display does not resemble the original data The data has been frequency shifted Signals at the center of the span appear at DC while frequencies at both edges of the span appear as high frequencies The anti aliasing filters have a steep but finite roll off at their cutoff frequencies Signals which are just outside of the span are not displayed in the FFT but appear frequency shifted and attenuated in the time record
177. 2 56 times the sample rate have been filtered out The capture buffer is not a continuous representation of the input signal The data is sampled and has a time resolution of I sample rate High frequency signals will appear distorted in the time record However ALL of the spectral information up to 1 2 56 times the Sample Rate is preserved by the Nyquist theorem as long as the value of each sample is accurate Amplitude calibration is performed in the frequency domain Hence the captured time data amplitudes are not calibrated User Functions A User Function displays the results of a user defined math function User Functions defined within the Octave Analysis Measurement Group may include octave measurement results Use the User Math menu to define a function A User Function may not be selected as the measurement if it uses a Trace which is empty or which contains data taken in a different Measurement Group SR785 Dynamic Signal Analyzer 4 34 Display Setup Menu See User Math Functions in Chapter 2 for more Measurement Swept Sine Select the Measurement of the active display when the Measurement Group is Swept Sine Each Measurement has an associated View Changing the Measurement changes the View to the View last used with the new Measurement Command MEAS d 1 The following Measurements are available in the Swept Sine Measurement Group Spectrum The swept sine spectrum is simply the measurement of a
178. 4000 blocks are available To increase Capture memory you must first decrease the other allocations so that the sum never exceeds the total available memory SR785 Dynamic Signal Analyzer 1 28 Capture Press 0 and Enter Press lt Capture Memory gt Press 9 0 0 and Enter Press lt Confirm Allocation gt and lt Return gt Press lt Capture Channels gt Use the knob to select Ch1 and press Enter Press lt Capture Length gt Press 1 8 0 0 and Enter Press Start Capture Press Active Display Press Display Setup Press lt Measurement gt Use the knob to select Capture1 and press Enter SR785 Dynamic Signal Analyzer Decrease the Waterfall allocation to the minimum allowed Note that the analyzer displays an allocation of 4 blocks The analyzer always maintains a minimum allocation for each function that uses memory Select the Capture allocation Increase it to 900 blocks 1 843 200 points You must confirm the new allocation Changing the memory allocation destroys previously stored data in the memory Select which inputs to capture Choose Ch1 only In this case the entire capture buffer is available for Chl When both channels are captured half of the buffer is available for each channel Increase the capture length All of the capture allocation 900 blocks is available Each block stores 2 kPoints for a total of 1800 kPoints Start the captur
179. 47 E 1 4 71 RPM Frequency 4 47 PA i Amplitude 1 4 71 Grid 4 47 ORENT Offset 4 72 Grid Div 4 48 Tone 2 4 72 Nyquist Grid 4 48 Frequency 2 4 72 Phase Suppress 4 48 penne as 4 72 d dx Window 4 49 eo Marker Menu 4 50 Chirp Source Menu 4 73 Amplitude 4 73 Marker 4 50 Burst 4 73 Mode 4 50 Source Display 4 74 SR785 Dynamic Signal Analyzer Noise Source Menu Amplitude Type Burst Source Display Source Period Arbitrary Source Menu Amplitude Source Play Rate Source More Arb Source Start Arb Source Length Set Left Edge Set Right Edge Allocate Memory Trace to Arb Swept Sine Source Menu Auto Level Reference Amplitude Ideal Reference Source Ramping Source Ramp Rate Reference Upper Limit Reference Lower Limit Maximum Source Level Offset Input Menu Input Source Analyzer Configuration Auto Offset Input Configuration Submenu Channel Input Mode Grounding Coupling Input Range AA Filter A Wt Filter Autoranging Transducer Parameter Submenu Engineering Units EU Label EU Volt EUs at Marker User Label Transducer Convert Tachometer Input Submenu Pulses per Rev Tach Trigger Range Tach Level 4 75 4 75 4 75 4 76 4 76 4 77 4 78 4 78 4 78 4 79 4 79 4 80 4 80 4 80 4 80 4 81 4 81 4 83 4 83 4 83 4 84 4 84 4 84 4 85 4 85 4 85 4 86 4 87 4 87 4 87 4 88 4 89 4 89 4 89 4 89 4 90 4 90 4 90 4 91 4 91 4 92 4 92 4 93 4 93 4 93 4 94 4 94 4 95 4
180. 65 66 67 68 69 70 71 1 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Display Setup Commands 5 39 Time 2 Windowed Time 1 Windowed Time 2 RPM Profile Orbit Track 1 Track 2 Capture Buffer 1 Capture Buffer 2 Order User Function 1 Order User Function 2 Order User Function 3 Order User Function 4 Order User Function 5 Time Histogram Group Measurement Histogram 1 Histogram 2 PDF 1 PDF 2 CDF 1 CDF 2 Time 1 Time 2 Capture Buffer 1 Capture Buffer 2 Histogram User Function 1 Histogram User Function 2 Histogram User Function 3 Histogram User Function 4 Histogram User Function 5 A measurement should be setup by first choosing the Measurement Group then the Measurement then the View then the Units Finally the display scale and references should be set VIEW d i The VIEW command sets queries the View of display d The parameter 1 selects the view from the list below Each view has associated units Changing the View changes the units parameters to the values last used with the new view SR785 Dynamic Signal Analyzer 5 40 Display Setup Commands View Log Magnitude Linear Magnitude Magnitude Squared Real Part Imaginary Part Phase Unwrapped Phase Nyquist Nichols CONAN BWNRK OK A measurement should be setup by first choosing the Measurement Group then the Measurement then the View then the Units Finally the display scale and references should be set
181. 67 4 167 4 168 4 168 4 168 4 169 4 169 4 169 4 169 4 170 4 170 4 171 4 171 4 171 4 172 4 172 4 172 4 172 4 173 4 173 4 174 4 174 4 174 4 175 4 175 4 175 4 175 4 175 4 176 4 176 4 176 4 177 4 177 4 177 Menus Load Trace Data ASCII Load Trace Data binary Buffer Interval Disk to Buffer Buffer to Disk Disk Upkeep Menu File Name Current Directory Make Directory Del File Del Cur Dir Format Floppy Output Menu Hard Copy Button Bitmap Printer Bitmap Area Vector Plotter Destination GPIB Control GPIB Address Edit A Note Text X Position Text Y Position Display Visible Text String File Start Number Colors Print Bright Print Dim Print Black Print Graph Plotter Text Pen Plotter Grid Pen Plotter Trace Pen Plotter Marker Pen System Menu Preset Remote Preferences Date Time Diagnostics Macro Edit Macro Show Settings Show Version System Remote Menu Output To GPIB Address Overide REM Baud Rate Word Length 4 5 4 178 4 179 4 179 4 180 4 180 4 181 4 182 4 182 4 182 4 183 4 183 4 183 4 183 4 184 4 184 4 185 4 185 4 185 4 186 4 186 4 187 4 187 4 187 4 187 4 188 4 188 4 188 4 188 4 189 4 189 4 189 4 189 4 190 4 190 4 190 4 190 4 190 4 191 4 191 4 191 4 191 4 192 4 192 4 192 4 192 4 193 4 193 4 194 4 194 4 194 4 194 4 194 4 195 SR785 Dynamic Signal Analyzer 4 6 Menus Parity View Queues System Prefe
182. 785 Dynamic Signal Analyzer Enter 1 1 kHz The 900 1100 Hz sweep covers the filter region of interest Adjust the Number Of Points in the sweep Enter 1024 points Reset and start the sweep The source is a sine wave whose frequency sweeps from 900 Hz to 1 1 kHz stopping at 1024 discrete frequencies At each frequency point the inputs are measured and displayed The small triangular marker moving across the bottom of the graphs indicates the position of the sweep in progress Scale the two displays The top display is the filter input source output and should be fairly flat The bottom display is the filter output and show the filter notch at 1 kHz Select the Display Setup menu Change the Measurement of DisplayA active display Choose Frequency Response filter output divided by filter input Select the Display Options menu Change the Display Format Choose a Single Display with DisplayA Frequency Resonse Function active Scale the display to show the Frequency Response Select the Marker menu Change the Marker Region width Choose Normal Width 1 2 division Change the Marker Seeks function Select Min with the knob and press Enter Press Marker Min Press Average Press lt Integration Time gt Press 4 0 select ms with the knob and press Enter Press Auto Range Ch1 and Auto Range Ch2 Swept Sine Measurement 1 43 Seek the Minimum data within the Marker Region
183. 85 Dynamic Signal Analyzer 5 4 Index of Commands Normal Marker MSEK d i MWID d 1 MREL d i MROX d x MROY d x MXRL d i MRON d Harmonic Marker HRMN d i HDSP d i HRDO d i HTHD d 1 HPWR d Sideband Marker SSEP d f SDBN d i HDSP d i HRDO d i SPWR d 1 Band Marker BMKL d i j BMKR d i j BEXC d i BRAM d i BPWR d 1 BRAT d i Frequency Damping Marker MMCA d Source SRCO i STYP i Sine Source S1FR f S1AM x S2FR f S2AM x SOFF 7 x Chirp Source CAMP x CBUR x CSRC i Noise Source NAMP x NTYP i 5 47 5 47 5 47 5 47 5 47 5 47 5 47 5 49 5 49 5 49 5 49 5 49 5 50 5 50 5 50 5 50 5 50 5 51 5 51 5 51 5 51 5 51 5 51 5 52 5 53 5 53 5 54 5 54 5 54 5 54 5 54 5 55 5 55 5 55 5 56 5 56 SR785 Dynamic Signal Analyzer Normal Marker Seeks Mode Normal Marker Width Normal Marker Relative Mode Normal Marker X Offset Normal Marker Y Offset Normal Marker X Rel Mode Set Marker to Ref Number of Harmonics Harmonic Sideband Display Harmonic Sideband Readout Query the Total Harmonic Distortion Query the Harmonic Power Sideband Separation Number of Sidebands Harmonic Sideband Display Harmonic Sideband Readout Query the Sideband Power Band i Left Bin j Band
184. A MA O a l ee ee l a ee ee ee ee a Ce Analyzing a Sine Wave Measuring a Frequency Response Function Linking Advanced Operation Triggering and the Time Record Octave Analysis Capture Waterfall Display Swept Sine Measurement Saving and Recalling User Math Functions Limit Testing Exceedance Statistics 1 7 1 11 1 15 1 19 1 23 1 27 1 34 1 41 1 47 1 52 1 56 1 60 SR785 Dynamic Signal Analyzer 1 2 Getting Started General Installation Caution This instrument may be damaged if operated with the LINE VOLTAGE SELECTOR set for the wrong AC line voltage or if the wrong fuse is installed Line Voltage Selection The SR785 operates from a 100V 120V 220V or 240V nominal AC power source having a line frequency of 50 or 60 Hz Before connecting the power cord to a power source verify that the LINE VOLTAGE SELECTOR card located in the rear panel fuse holder is set so that the correct AC input voltage value is visible Conversion to other AC input voltages requires a change in the fuse holder voltage card position and fuse value Disconnect the power cord open the fuse holder cover door and rotate the fuse pull lever to remove the fuse Remove the small printed circuit board and select the operating voltage by orienting the printed circuit board so that the desired voltage is visible when pushed firmly into its slot Rotate the fuse pull lever back into its normal position and insert the correct fuse into the fu
185. At each frequency point a settling time is allowed to pass before any measurement is made This allows the device under test to respond to the frequency change The actual settling time is the larger of the Settle Time and the Settle Cycles rounded to the next multiple of 3 906 ms The settling time is always a minimum of 1 cycle or 7 8125 ms Changes made to the number of Settle Cycles during a sweep take effect immediately The estimated sweep time is displayed in the Horizontal Scale Bar This time is simply the sum of the Settle and Integrate times for all points in the sweep Auto functions Source Auto Level Auto Range Auto Resolution will change the actual sweep time SR785 Dynamic Signal Analyzer 4 120 Swept Sine Average Menu Command SSCY 7 d 1 Integration Time Set the Integration Time in increments of 3 906 ms 15 625 ms 1 ks At each frequency point the inputs measure the signal at the source frequency This is done by multiplying the input data by the source sine and cosine wave and averaging the results over an integration time The actual integration time is always an exact number of cycles at the source frequency This rejects signals which are at a different frequency such as noise and harmonics A long integration time results in a narrow detection bandwidth at the source frequency This improves signal to noise at the cost of longer measurement times The Integration Time is converted to next largest
186. Auto Ranging always tracks the input signals during a swept sine measurement The signal connections are the same as for an FFT frequency response The SR785 measures Channel 2 response divided by Channel 1 as the frequency response The input to the device under test is measured by Channel 1 typically this is the source output and the device output is measured by Channel 2 Swept sine displays differ from FFT displays The sweep span is not limited to factors of two and the start and stop frequencies are not related to an FFT span Also the number of points can range from 10 to 2047 Y axis scaling and X axis zooming are the same as with FFT displays Each data point is graphed at its correct frequency and amplitude and connected to adjacent points with a line The marker only moves to the actual sweep points and the Marker Position Bar shows the actual frequency of each point If the marker position is displayed with a the point is interpolated from nearby measured points The actual measurement of these points was skipped due to sweep Auto Resolution While a sweep is in progress a small triangular marker moves across the bottom of the display to show the current sweep point The current frequency is displayed at the top of the screen Swept Sine Measurements Only Spectrum Cross Spectrum Normalized Variance Frequency response and User Function measurements are available Time record capture and waterfall are not available in t
187. Continuous real time data recording to memory 262 144 samples sec for both inputs Lower rates may be used for longer capture Maximum Capture Length Octave Analysis Standards Frequency Range Accuracy Dynamic Range Sound Level Source Output Amplitude Range Amplitude Resolution DC Offset Output Impedance Sine Amplitude Accuracy Offset Harmonics Sub Harmonics and Spurious Signals Two Tone Amplitude Accuracy Offset Harmonics Sub Harmonics and Spurious Signals White Noise Time Record Bandwidth Flatness Specifications xiii 2M samples standard 8M samples optional Conforms to ANSI S1 11 1986 Order 3 Type 1 D Band centers Single Channel 1 1 Octave 0 125 Hz 32 kHz 1 3 Octaves 0 100 Hz 40 kHz 1 12 Octaves 0 091 Hz 12 34 kHz Two Channels 1 1 Octave 0 125 Hz 16 kHz 1 3 Octaves 0 100 Hz 20 kHz 1 12 Octaves 0 091 Hz 6 17 kHz lt 0 2 dB 1 second stable average single tone at band center 80 dB 1 3 Octave 2 second stable average per ANSI S1 11 1986 Exponential time averaged broadband power L per ANSI S1 4 1983 Type 0 Broadband Impulse and Peak power per IEC 651 1979 Type 0 Sum of octave bands total power 0 1 mVpk to 5 Vpk 0 1 mVpk lt 10 0 mV typical lt 5 Q 100 mA peak output current 1 of setting 0 Hz to 102 4 kHz 0 1 Vpk to 5 0 Vpk high impedance load 0 V to 5 V max output 5 V ac dc 0 1 Vpk to 5 Vpk O V offset lt 80 dBc fundam
188. Definitions Standard Event Status Word ee ene ee p 0 e es nn Name unused unused QRY DDE EXE CME URQ PON unused Set when Too many responses are pending Too many commands received at once Command cannot execute successfully Command syntax error A key is pressed or the knob rotated Power is turned on reserved by IEEE standard The Standard Event status word is defined by IEEE 488 2 1987 and is used primarily to report errors in commands received over the interface These status bits remain set until read using ESR They are also cleared by the CLS command Use ESE to set bits in the Standard Event enable register Instrument Status Word Bit 0 OMAN NABWN 15 Name TRIG DISK OUTP TACH CAPT PAUS STRT PLBK PREV unused Set when A measurement has been triggered A disk operation has been completed A hardcopy output operation has completed A tach pulse has been received The capture buffer has filled Measurement has been paused Measurement has been started Single Shot Capture Playback has finished Measurement stopped to wait for average preview The Instrument status word reports on the overall measurement status of the instrument These status bits remain set until read by INST They are also cleared by the CLS command Use INSE to set bits in the Instrument status enable register SR785 Dynamic Signal Analyzer Status Word Definitions 5 127 Display Status Word Bit Name Set
189. Delete Segment gt to remove this segment The numbering of the remaining segments may change as a result Use the Current Segment markers to identify the correct segment before editing XO Enter or adjust the X coordinate for the Current Segment Start point The X coordinates are assumed to be in the display units usually Hz Use Zoom and Pan to expand the display when drawing small segments Command LSEG d 1 J xO yO x1 y1 YO Enter or adjust the Y coordinate for the Current Segment Start point The Y coordinates are assumed to be in the display units Use Zoom and Pan to expand the display when drawing small segments Command LSEG d 1 J xO yO x1 y1 X1 Enter or adjust the X coordinate for the Current Segment End point The X coordinates are assumed to be in the display units usually Hz Use Zoom and Pan to expand the display when drawing small segments Command LSEG d 1 J xO yO x1 yl Y1 Enter or adjust the Y coordinate for the Current Segment End point The Y coordinates are assumed to be in the display units Use Zoom and Pan to expand the display when drawing small segments Command LSEG d 1 J xO yO x1 yl SR785 Dynamic Signal Analyzer Limit Testing Analysis Menu 4 155 Delete Segment Delete the Current Segment The numbering of the remaining segments may change as a result Use the Current Segment markers to identify the correct segment before editing
190. E commands need to be separated by a pause which is at least as long as the preceding tone PLAY i The PLAY command plays one of the SR785 s pre programmed sounds The parameter 1 selects a sound from 0 to 6 most recent TONE For example PLAY 2 sounds an alert SR785 Dynamic Signal Analyzer Data Transfer Commands 5 107 Data Transfer Commands DSPN d DSPY d j REFY d j The DSPN command queries the length of display d The parameter d selects Display A 0 or Display B 1 The returned value is the length number of points or bins of display d The points are numbered from 0 to length 1 Always use the DSPN command to determine the display length before reading all of the data from a display The DSPY command queries the data in display d The parameter d selects Display A 0 or Display B 1 The DSPY d j command queries the data value of bin j only The bins are numbered from 0 to length 1 The value is returned as an ASCII real number The DSPY d command queries all of the data in display d Do not serial poll for IFC bit 7 in the Serial Poll status after this command is sent IFC will NOT be set until the transfer is complete Send the command and then make the host computer a listener and the SR785 a talker Data is returned continuously starting with bin O and ending with bin length 1 The data points are ASCII real numbers separated by commas and the last data point is followed by
191. Harmonic and Sideband Marker Readout for display d The parameter 1 selects Absolute 0 or Relative to Fundamental 1 This command is only valid if the Marker Mode for display d is Harmonic or Sideband HTHD d i The HTHD command queries the Total Harmonic Distortion for display d The parameter 1 selects percent 0 or dB Relative to Fundamental 1 and is required This command is only valid if the Marker Mode for display d is Harmonic HPWR d The HPWR command queries the Harmonic Power for display d The returned value is areal value of Vrms or dBVrms depending on the setting of dB Units gt This command is only valid if the Marker Mode for display d is Harmonic SR785 Dynamic Signal Analyzer 5 50 Marker Commands Marker Commands Sideband SSEP d f lt kHz Hz mHz wHz gt The SSEP command sets queries the Sideband Separation for display d The parameter f is the sideband separation in Hz This command is only valid if the Marker Mode for display d is Sideband SDBN d i The SDBN command sets queries the Number of Sidebands for display d The parameter 1 is a number of sidebands from 1 to 50 This command is only valid if the Marker Mode for display d is Sideband HDSP 7 d i The HDSP command sets queries the Harmonic and Sideband Marker Display for display d For Sideband Marker i 0 selects the Fundamental i 1 selects the first lower sideband i 1 selects the first upper s
192. Interface RS232 GPIB All interface query responses are directed to the selected Output Interface regardless of which interface received the query Use the OUTX command to select the correct interface at the beginning of every program Command OUTX 1 GPIB Address Enter or adjust the instrument GPIB Address 0 30 Overide REM Baud Rate Select the Overide Remote mode Yes No In general every GPIB interface command will put the unit into the REMOTE state with the front panel locked out To defeat this feature set this entry to Yes In this mode the front panel is not locked out when the unit is in the REMOTE state To return from REMOTE to LOCAL front panel enabled press Help Local Command OVRM 1 Select the RS232 Serial interface Baud Rate 300 1200 2400 4800 9600 19 2k Most PC s use 9600 as a default SR785 Dynamic Signal Analyzer System Remote Menu 4 195 Word Length Select the RS232 Serial interface Word Length 7 bits 8 bits 8 bits 1s standard Parity Select the RS232 Serial interface Parity None Even Odd None is standard View Queues Display the Remote Interface Queue The SR785 buffers the characters which are received or transmitted over the interface The Queue display shows the interface history The Queue display may slow down communications and should be displayed only when testing or debugging a host program The upper half of the screen is the Receive Que
193. KKK void TxGpib int address char command routine to transmit command to a GPIB address f f modity this routine for your GPIB intesrface send address command amp status send is the CEC routine to send a string to an address Jf SACS Status O to indicate result Ok if status 0 handle transmit errors here printf nCommand s n command printf Error at device sd status d n address status GetSpace SR785 Dynamic Signal Analyzer 5 134 Example Program KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK void GetGpib int address routine to get an answer from a GPIB address i MOdLry this routine for yotur GPIB Interface char temp 80 enter temp 80 amp length address amp status enter is the CEC routine to enter a string from an address Sets status 0 to indicate result OK 80 is maxlen actual received length is stored in amp length if status 0 handle receive errors here printf nError at device 5d status d n address status GetSpace strepy recy tempo set global r cy string KKKKKKKKKKKKKKKKKKKKKK KK KKK KKKKKKKKKKKKK KKK KKKKKKKKKKKKKKKKKKKKKKKKKK void TxSR 85 char command Send command to the SR785 and wait until IFC bit7 is set an the Serial Poll status indicating that the command is finished TxGpib SR785 command send
194. KKKKK You can see the commands received and responses generated by the SR785 by using System lt Remote gt lt View Qs gt to display the interface buffers on the screen kxkxkxk xk x xk xk xk xx xx x xx x x x x x xx x xx x xx x xx x x x x x x xx x xx x xx x xx x x xx xx xx xx xx xx xx xx xx int 1 mode type number nlen long ack double dispAVal dispBVal octreal octimag Prince nSRT eS Example Program in wi kkk Initialize your GPIB card here initialize 2100 controller settimeout 7500 GPIB timeout to 7 5 seconds ff FARAR E SA Lhe SRO OULpUbL aAnkeriace Tto GPIBII FATAR TXSR795 CLS gt 7 elear all status words TXSR785 OUTXO gt darect SR 7S5 responses to GPIB interface SR785 Dynamic Signal Analyzer Example Program 5 131 fo RREX Set the Standard Event enable reqister to catch EXE and CME Command errors will set the ESB bit in the Serial Poll status word TXSR 65 ESE 46 Set bits 4 sand 5 if Skaar EA Check Comunication iby iGuery ing SR 35 IDN String GetSR785 IDN printf GPIB IDN s n n recv PELINE Reset ORs 99w CK TXSR789950 Cle RST reset the SR785 to a default state printf done n n KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKEKKKKKKKKKEKKKKKKKKKKKK E REESE Sel UPL FEET averaging for Dorth displays 242 4 S7 TSR TSS RAVI 2r LEE display avg rms TX9R785 FAVT 270
195. L If TTL is selected the tachometer will trigger on a TTL rising edge If 5V is selected the tachometer trigger level can be set from 5V to 5V with 40 mV resolution If 25V is selected the threshold resolution is 200 mV TTL Trigger range will yield the best phase accuracy Command TARG 1 Sets the tachometer trigger level when the trigger range is set to 5V or 25V The resolution of the trigger level is 40 mV at the 5V range and 200 mV on the 25V range The tachometer will trigger when the input passes through the specified level in the direction specified by the tach slope softkey If the tachometer signal is noisy near the specified tach trigger level use the hold off to increase the noise immunity of the tach input SR785 Dynamic Signal Anaylzer 4 96 Tachometer Input Menu Tach Slope Command TALV f Sets the slope with which the tachometer signal must pass through the tachometer level to trigger the tachometer Rising Falling Command TASL 1 Hold Off Enable Enables or disables tachometer holdoff When tachometer holdoff 1s enabled the tachometer is prevented from triggering after a tach pulse has been received for a time specified by the Tach Hold Off If the tachometer signal is not noisy in the region near the tachometer trigger threshold it should not be necessary to use the holdoff If the signal is noisy 1 e passes through the threshold several times for a given tachometer pulse set the h
196. Level Reference The parameter 1 selects Off 0 Channel 1 1 or Channel 2 2 This command is valid only when the Measurement Group is Swept Sine SSAM x lt mV V dBVpk gt The SSAM command sets queries the Swept Sine Amplitude The parameter x is the amplitude in the specified units The query returns two numbers of the form y i where y is a real number and 1 is an index indicating the units This command is valid only when the Measurement Group is Swept Sine and Auto Level Reference is Off SSRF x lt mV V dBVpk gt The SSRF command sets queries the Swept Sine Ideal Reference The parameter x is the ideal reference in the specified units The query returns two numbers of the form y 1 where y is a real number and 1 is an index indicating the units This command is valid only when the Measurement Group is Swept Sine and Auto Level Reference is Ch1 or Ch2 SRMP 7 i The SRMP command sets queries the Swept Sine Source Ramping The parameter 1 selects Off O or On 1 This command is valid only when the Measurement Group is Swept Sine SRAT x The SRAT command sets queries the Swept Sine Source Ramp Rate The parameter x is the ramp rate in V s This command is valid only when the Measurement Group is Swept Sine SSUL 7 x The SSUL command sets queries the Swept Sine Reference Upper Limit The parameter x is a ratio in dB from 0 1 to 30 0 dB This command is valid only when the Measu
197. More Arbitrary Source Menu 4 79 When the Arbitrary source is a Capture buffer the Play Rate defaults to the capture Sampling Rate The Play Rate should be equal to the capture Sampling Rate to preserve the frequency content of the buffer When the Arbitrary source is the Arbitrary waveform memory the Play Rate should be set according to the rate used to calculate the waveform samples When the Arbitrary source is copied from a time record trace the Play Rate should be set to the sampling rate at which the time record was acquired Caution In both cases if the Play Rate is LESS than the maximum sampling rate the output will contain alias frequency components above 1 2 the sampling rate In general the frequency span of any measurement using this source should not exceed 1 2 times the Play Rate to avoid measuring these alias frequencies Command ARAT 1 Select Arbitrary waveform playback from the Arbitrary Waveform memory or from a Capture buffer Use the lt Memory Allocation gt menu to allocate memory between the capture buffer waterfall storage and the arbitrary source waveform The Arbitrary waveform memory can be loaded from a stored trace via the computer interfaces or from a disk file The Capture buffer is filled by capturing an input signal Command ASRC 1 Display the Arbitrary Source Settings menu Press lt Return gt for the main Source menu Arb Src Start A Arb Src Length Allocate Mem
198. Nichols or Nyquist Y2DV d x The Y2DV command sets queries the polar Y Division scale of display d The parameter x is a real number in the display units This command is only valid when the View is Nichols or Nyquist Changing the scale of a display may change the Y Center value Always use the YCEN command after the Y2DV command XPAN 7 d i The XPAN command sets queries the Pan translation of display d The parameter 1 is the left most displayed bin This command is only valid when the display is Zoomed expanded SR785 Dynamic Signal Analyzer 5 42 Display Setup Commands XZOM d i The XZOM command sets queries the Zoom factor X axis expand of display d The parameter 1 is the zoom factor 1 5 This command is not valid when the X axis is logarithmic or when the View is Nyquist or Nichols SR785 Dynamic Signal Analyzer Display Options Commands 5 43 Display Options Commands DISP d i DFMT 7 i ACTD i XAXS d i RPMF 7 i GRID d i GDIV d i GPOL d i The DISP command sets queries the Display Update Mode of display d The parameter 1 selects Off Line 0 or Live 1 Many parameters Frequency Measurement etc are not adjustable for an Off Line display Commands which set these parameters for an Off Line display are not valid The DFMT command sets queries the Display Format The parameter 1 selects Single 0 Dual
199. OCA 3 AERE 3 ARTA EARR ARA 3 R E 3 DENTET a an aA RP M frequency Me I E a EAEE E A EEE NTE E ESA ATA On Grid Div dBidiv i j Konan ayia hooker aaa MRK I te bal ik Car ied oog A prng cen fe arrg gorg pee p 3 j mee ee TE Ehe feat fe p he a i n w l aaa Phase Suppress Bist oe gua Ren ern ener ne eee PA PEM 0 0000e 000 didx window 0 5 ay LANA Pe AF x we SST ARASA R G at a oa Pe Be Be Y rah I RII NAPA FOR RAAT NET Sy rin A 160 3 dBVpk OHz 51 2 kHz _ FFT 1 Log Mag BMH RmsAvg 10 Figure Chapter 3 4 Overlay Display Screen The Overlay display format is shown above The measurement of the inactive display is shown in half intensity The Single display format is similar but the inactive display is not shown at all Data Graph Data is normally graphed with signal amplitude on the Y axis and frequency or time on the X axis The physical size of the graph remains constant while the vertical and horizontal scales may be changed The graph area has a dotted grid for reference There are 10 horizontal divisions and either 8 10 12 or 15 vertical divisions The horizontal span is determined by the measurement span or time The display normally shows the entire measurement span The X axis may be expanded Zoom and translated Pan to display less than the full measurement span This expansion does not change the measurement span or time it merely changes the display of the da
200. Operating Manual and Programming Reference Model SR785 Dynamic Signal Analyzer S RS Stanford Research Systems 1290 D Reamwood Avenue Sunnyvale CA 94089 U S A Phone 408 744 9040 Fax 408 744 9049 Email info thinkSRS com www thinkSRS com Copyright 1995 1996 1998 Stanford Research Systems Inc All Rights Reserved Revision 1 4 December 2006 Certification Stanford Research Systems certifies that this product met its published specifications at the time of shipment Stanford Research Systems further certifies that its calibration measurements are traceable to the United States National Institute of Standards and Technology NIST Warranty This Stanford Research Systems product is warranted against defects in materials and workmanship for a period of one 1 year from the date of shipment Service For warranty service or repair this product must be returned to a Stanford Research Systems authorized service facility Contact Stanford Research Systems or an authorized representative before returning this product for repair Information in this document is subject to change without notice Copyright Stanford Research Systems Inc 1995 1996 1998 All rights reserved Stanford Research Systems Inc 1290 D Reamwood Avenue Sunnyvale California 94089 Printed in U S A Safety and Preparation For Use WARNING Caution A Dangerous voltages capable of causing injury or death are pres
201. P CGET i j CPUT i j Memory MMEM MALC i j k Data Table DTBL D d i DMAX d i DINS d i j DDLT d i DCLR d DTRD d i Limit Testing LSON d 1 LTST d i LALM d i LFAL d LCLR d LMAX d 1 LSEG d i J xO yO x1 yl LDLT d i LSFT d x Marker Statistics MSAO d 1 MSRS MSAA MSIA MSEA MSSA MSAB MSIB MSEB MSSB Exceedance Statistics ESTR 2 i ESTP 2 i EPCT 2 i EXCE d 1 Curve Fit EFIT d ESYN i d ENPL i ENZE 7 i 5 83 5 83 5 83 5 83 5 83 5 113 5 32 5 84 5 84 5 85 5 85 5 85 5 85 5 86 5 86 5 87 5 87 5 87 5 87 5 87 5 87 5 87 5 88 5 88 5 89 5 89 5 89 5 89 5 89 5 89 5 89 5 89 5 89 5 89 5 90 5 90 5 90 5 90 5 91 5 91 5 91 5 91 SR785 Dynamic Signal Analyzer Capture Length Capture Rate Capture Auto Pan Capture Start Capture Stop Upload Capture Buffer Download Capture Buffer Total Memory Available Allocate Memory Data Table On Data Table Length Data Table Insert bin j at line 1 Data Table Delete Data Table Clear Data Table Query Show Limit Segments Limit Testing On Limit Beep Limit Test Fail Clear Limits Last Limit Segment Set Limit Segment 1 Delete Limit Segment Shift Limit Segments Marker Statistics On Reset Marker Statistics Marker Max A Read Marker Min A Read Marker Mean A Read Marker Std Dev A Read Marke
202. Playback from Capture Since there is captured data for both inputs both displays start measuring from the capture Scale the displays to show the measurements Start playback from the beginning of the buffer Since the default Playback Speed is Normal the entire playback takes as long as the equivalent real time measurement In this case the capture represents 7 73 seconds of data so the playback takes 7 73 seconds as well At the current span 51 2 kHz there are almost 1000 time records of captured data Not all time records are displayed during Normal playback though all time records contribute to averaged measurements The display is updated 8 times a second for 7 73 seconds for a total of 62 updates during this playback Normal playback is limited to the real time limitations of the equivalent real time analog input measurement Enter the Playback Configuration submenu Change the Playback Speed Choose Every Time Record Since the data is stored in memory we can choose to display every stored time record Start the playback at the beginning of the buffer In this case all 1000 time records are measured AND displayed The display still updates at 8 Hz so playback takes about 125 seconds to complete If the time records are overlapped there may be more than 1000 measurements to display and playback will take even longer Every Time Record playback is not limited by real time considerations Select the trigger
203. PostScript 1 PLTA i The PLTA command sets queries the Plotter GPIB Address The parameter 1 ranges from 0 to 30 and should agree with the address of the plotter in use PCIC i The PCIC command sets queries the GPIB Control mode The parameter 1 selects Host 0 or SR785 1 PLTX i The PLTX command sets queries the Plotter Text Pen Number The parameter 1 is a pen number from to 8 PLGD i The PLGD command sets queries the Plotter Grid Pen Number The parameter 1 is a pen number from to 8 PLTR 7 i The PLTR command sets queries the Plotter Trace Pen Number The parameter 11S a pen number from to 8 PLMK i The PLMK command sets queries the Plotter Marker Pen Number The parameter 1 is a pen number from to 8 SR785 Dynamic Signal Analyzer Output Commands 5 99 NOTE i j k m The NOTE command defines a Display Note The parameter 1 selects a Note from 0 to 9 The parameter j makes the note Not Visible 0 or Visible 1 To turn a Note On and Off use the NOTE 1 j command The parameter k puts the note in Display A 0 or Display B 1 The parameters l and m are the Text X and Text Y position from 0 to 100 The string s is the note text The parameters k 1 m and s must always be sent together SR785 Dynamic Signal Analyzer 5 100 System Commands System Commands OUTX i OVRM 7 i KCLK i ALRM 7 i ALRT 7 i ADON i
204. Preset requires confirmation to prevent accidental reset Wait until the self tests are completed In this instrument transfer function is defined as Ch2 response over Ch1 reference Thus Ch1 monitors the filter input source output and Ch2 measures the response of the device under test Select the Input Configuration submenu Adjust the Ch1 input range Set the range to 2 dBV Select the Display Setup menu There are six Measurement Groups FFT Correlation Octave Order Analysis Swept Sine and Time Histogram The Measurement Group determines which Measurements are available to the displays Choose the Swept Sine group The menus now configure swept sine measurements only Select the Frequency menu Adjust the sweep Start Frequency Enter 900 Hz Adjust the sweep Stop Frequency SR785 Dynamic Signal Analyzer 1 42 Swept Sine Measurement Press 1 1 select kHz with the knob and press Enter Press lt of Points gt Press 1 0 2 4 Enter 5 Press Start Reset Wait for the sweep to complete at least once Press Auto Scale A and Auto Scale B 6 Press Display Setup Press lt Measurement gt Select Freq Resp with the knob and press Enter Press Display Options Press lt Format gt Select Single with the knob and press Enter Press Auto Scale A 7 Press Marker Press lt Width gt Select Normal with the knob and press Enter Press lt Seeks gt SR
205. Press lt Return gt or Output for the main Output menu Hardcopy Colors Print Bright i 12 Print Dim White Print Black H Black Print Graph Black on VVhite Plotter Text Pen Plotter Grid Pen i 1 Plotter Trace Pen 1 Plotter Marker Pen Print Color Selections Printing is a bit mapped operation Different areas of the screen can be printed with different print densities giving a range of gray between black and white white paper These colors only affect Epson FX and 24 pin and HP Laser and Laser small printer types Print Bright Select the print density of highlighted areas e g active display marker display White none on white paper 6 12 25 50 100 Black Command PBRI 1 Print Dim Select the print density of the normal background e g X and Y axis graph labels White none on white paper 6 12 25 50 100 Black Command PDIM 1 Print Black Select the print density for black text Black White none on white paper Use White only if the Print Bright and Print Dim are both black or gray Command PBLK 1 SR785 Dynamic Signal Analyzer 4 190 Output Menu Print Graph Select the graph print mode Black on White White on Black The graph is normally printed as Black data and grid on White background This uses the least printer ink Choosing White data and grid on Black background prints a large black area on the
206. Reset key to start the measurements Make sure the Run Pause indicator at the top of the screen displays RUN instead of PAUSE Note that in many cases when settings are changed using the menus the new settings will not take effect until Start Reset is pressed Live Display If the displays are showing recalled trace data they are Off Line and do not display the live measurement data Set the Display to Live instead of Off Line in the Display Options menu Narrow Span If the FFT span is very narrow the time record is very long up to 1000 s of seconds Completely new data is available only every time record Change the Time Record Increment in the Average menu to display overlapped data more often Low Detection Frequency Swept Sine measurements at very low frequencies lt lt Hz take a very long time at least 2 cycles and maybe longer Do not set the sweep Start to a very low frequency to measure the DC response Octave measurements with a very low starting band take a long time to settle before the first measurement is valid The settling time is related to the bandwidth of the lowest octave band If the Lowest Band is less than 1 Hz the settling time can be very long Averaging Very long averaging times for any measurement may give the appearance that the display does not update Check the FFT Number Of Averages the Octave Integration Time or the Swept Sine Integration Time When Linear averaging
207. Resolution OCHN d 1 5 30 Octave Channels UNST d 5 30 Unsettle Measurement Frequency Swept Sine Measurement Group SSTR d f 5 32 Swept Sine Start Frequency SSTP d f 5 32 Swept Sine Stop Frequency SSFR 5 32 Swept Sine Progress SRPT d 1 5 32 Swept Sine Repeat Mode SSTY d 1i 5 32 Swept Sine Sweep Type SARS d 1 5 32 Swept Sine Auto Resolution SNPS d 1 5 33 Swept Sine Number of Points SSKP d 1 5 33 Swept Sine Max Step Size SFST d x 5 33 Swept Sine Faster Threshold SSLO d x 5 33 Swept Sine Slower Threshold Frequency Order Measurement Group ORMX d f 5 34 Max RPM ORMN d f 5 34 Min RPM OMAX d f 5 34 Max Order ODLT d f 5 34 Delta Order OTRK d 1 5 34 Order Tracking ONPT d 1 5 34 Track Points OSTO 7 d 1 5 35 Track Storage Mode O1TK d f 5 35 Track 1 Order OIBN d 1 5 35 Track 1 BNC O2TK d f 5 35 Track 2 Order O2BN d 1 5 35 Track 2 BNC Frequency Time Histogram Measurement Group FSPN d 1 5 28 Sampling Time SR785 Dynamic Signal Analyzer HLEN d f HBIN d i FBAS 2 d i HRPT d i Display Setup MGRP d i MEAS d i VIEW d i UNIT d UNDB d 1 UNPK d 1 PSDU d i UNPH d 1 DBMR x YMAX d x YMID d x YMIN d x YDIV d x YMDX d x y XCEN d x XDIV
208. S ESE i j ESR i IDN PSC 2 i RST SRE i 5 STB i A AIRG i A2RG i AAMP i ACTD i ADON i AGET i ALEN i ALOD n ALRM i ALRT i AOVL 9 i APUT i ARAT 2 i ASCL d ASRC i ASTR i B BEXC d i BMKL d i j BMKR 2 d i j BPWR d i BRAM d i BRAT d i C CAMP x CBUR x CCHN i CGET i j CLEN i CMOD i CONT CPAN 2 i CPUT i j CRAT 2 i CSRC 2 i CSTP CSTR 5 120 5 120 5 121 5 117 5 120 5 117 5 120 5 120 5 60 5 61 5 57 5 102 5 100 5 112 5 57 5 110 5 100 5 100 5 100 5 113 5 57 5 103 5 57 5 57 5 51 5 51 5 51 5 51 5 51 5 51 5 55 5 55 5 83 5 113 5 83 5 83 5 102 5 83 5 32 5 83 5 55 5 83 5 83 SR785 Dynamic Signal Analyzer Clear All Status Registers Standard Event Status Enable Standard Event Status Read Device Identification Power On Status Clear Reset Serial Poll Status Enable Serial Poll Status Read Chl AutoRange Off On Ch2 AutoRange Off On Arbitrary Source Amplitude Active Display Done Volume Upload Arbitrary Buffer Arbitrary Source Length Download Arbitrary Binary Alarms On Alarms Volume Audible Overload Download Arbitrary Buffer Arbitrary Source Rate AutoScale Arbitrary Source Buffer Arbitrary Source Start Band Exclude Band 1 Left Bin j Band 1 Right Bin j Band Power Band Ratio Mod
209. SP board use lt Serial Number gt to enter the unit serial number shown on the rear panel and use lt Program S N gt to store the serial number permanently Press lt Return gt for the lt Diagnostics gt menu Kill AutoOff Clear the internal input offset calibrations and disable Auto Offset Do not use this function unless you are making input offset or CMR adjustments to an analog input board See the Service Manual for more information The unit must be turned off and back on after using this function to restore the input calibrations SR785 Dynamic Signal Analyzer Edit Macro Menu 4 203 Edit Macro Menu Edit Macro _EditMacro Special Keys A mosini String ee i naia Dec Tans Barak ere i leak Macon mag meer He Knob Bann fo Enter Macro C Special Keys Use the knob to pick a lt Softkey gt or other special key from the display and press Enter to place it in the macro string at the cursor location To place Enter into the macro string use lt Special Keys gt Pressing the Enter key while the cursor is in the macro string display enters the macro and exits this menu To place lt backspace into the macro string use lt Special Keys gt The lt key deletes the term before the cursor Macro String Move the cursor to the macro string window at the top of the screen Use the knob to move the highlighted cursor within the string lt Delete gt will delete the hig
210. SR785 Dynamic Signal Analyzer SR785 keypad Softkeys Menu Keys Function Keys Control Keys Number Keys Knob slow Knob fast Alt Enter Front Panel Connectors 3 7 PC Keyboard equivalent F1 F10 Letter shown below the Menu key e g A to show the Frequency Menu Letter shown below the Function key e g E for AutoScale A Alt 1 through Alt 4 top row Alt 5 through Alt 8 bottom row 0 through 9 Left and Right arrow Up and Down arrow Escape Enter or Return The keyboard should only be connected when the power 1s off SR785 Dynamic Signal Analyzer 3 8 Rear Panel Connectors Rear Panel Connectors 000000000080 v 000000000000 wg XRAYS 000000000080 wer 000000000000 000000000 1 X rays generated in this instrument are 000000000080 0000000000 sufficiently screened A A Ag AAS Ay D P an E DIE IN DIESEM GER T ENTSTEHENDE eaa aae 00000000000 RONTGENSTRAHLUNG ISTAUSREICHEND 0000060 Sreeeeeeeee AB E ENRME 00000000000 000000000000 0000000000080 ACCEL VOLTAGE BESCHL SPB lt 15 KV 00000000000 KEE OAA 000000000000 00000000000 00000000000 000 0000 00 0 00 0000000000080 a 00000000000 0000000000680 f 00000000000 0000000000680 L L 00000000000 0000000000080 50 Vpk Max 000000000 CHASSIS PREAMP GROUND rN agja Verify that the LINE VOLTAGE SELECTOR WEANING card is set so the correct NO USER SERVICEABLE PARTS INSIDE AC input voltage value REFER TO USER MANUAL FOR SAFETY NOTICE vi
211. SR785 can usually compute the measurements in both displays in less than a time record for all spans This includes the real time digital filtering and heterodyning the FFT processing and averaging calculations The real time bandwidth in this case is 102 4 kHz Every input sample contributes to a time record and a measurement Averaging Speed Real time bandwidth has a direct affect on measurement times when Averaging is On Consider the averaging of full span 102 4 kHz 400 line FFT s If the real time bandwidth is only 10 kHz as in many analyzers it takes 40 ms to compute the measurement for a 4 ms time record This means 9 out of every 10 time records are ignored and only 25 full span measurements can be computed in a second When averaging is on this usually drops to 10 measurements per second At this rate it s going to take a couple of minutes to do 500 averages The SR785 on the other hand can make real time measurements at full span 102 4 kHz This results in 256 measurements per second on each display In fact this 1s so fast that the display can not be updated for each new measurement The display only updates about 8 times a second However when Averaging is On all of the measurements contribute to the average The time to complete 500 averages is only a few seconds Instead of a few minutes Overlap Processing What about narrow spans where the time record is long compared to the processing time The analyzer compute
212. Setup menu The capture buffer display will automatically pan as the capture fill and playback progress through the buffer During capture fill if the capture buffer contains more points than can be displayed points are skipped This speeds up the display update so that it keeps up with the real time capture but allows visual aliasing to occur Once capture is complete the display is redrawn showing the envelope of all points eliminating any visual aliasing effects User Functions A User Function displays the results of a user defined math function User Functions defined within the Histogram Measurement Group may include histogram measurement results Use the User Math menu to define a function SR785 Dynamic Signal Analyzer 4 38 Display Setup Menu View A User Function may not be selected as the measurement if it uses a Trace which is empty or which contains data taken in a different Measurement Group See User Math Functions in Chapter 2 for more Select the View of the active display Measurement A View is a way of looking at complex measurement data Each display has its own Measurement and each Measurement has an associated View Changing Measurements changes the View to the View associated with the new Measurement The two displays generally have different Measurements each with their own associated Views This entry field can be linked to the Measurement on both displays using the Link key Command VIEW d
213. Spectrum MAX FFT1 e MAX FFT1 Time Record A time record is simply a sequence of data samples The length of the time record 1s the FFT resolution span For baseband spans spans which start at DC the time record resembles a digital oscilloscope display Signals at frequencies above the span have been filtered out Baseband time records are entirely real they have no imaginary part For zoomed spans spans which start above DC the time record does NOT resemble the original data The data has been frequency shifted Signals at the center of the span appear at DC while frequencies at both edges of the span appear as high frequencies Zoomed time records are complex they have both a real and an imaginary part The sampling rate is always half of the equivalent baseband span Remember the time record is not a continuous representation of the input signal The data is sampled and has a time resolution of 1 sample rate High frequency signals will appear distorted in the time record However ALL of the spectral information is preserved by the Nyquist sampling theorem as long as the value of each sample is accurate A triggered time record will always jitter by 1 sample This jitter is removed in the computation of the phase of the spectrum relative to the trigger Averaging does not affect the time record Averaging is performed on the FFT spectrum and not on the time data Amplitude calibration is also performed in the frequency domain
214. Start then the Playback Length is set to the minimum 2 kPts Playback Mode Select the Capture Playback Mode 1 Shot Circular In 1 Shot playback the buffer is played a single time The playback halts when the end of the buffer is reached In Circular playback the playback starts over when the end of the buffer is reached There is often a discontinuity in the playback measurement when the playback jumps from the end to the start of the buffer In either mode press Start Reset to restart playback at the start again The Capture Progress indicator at the top of the screen shows the playback progress through the buffer Both channels playback with the same Playback Mode Command IMOD 1 Playback Speed Select the Capture Playback Speed Normal Every Time Record Normal Playback Speed plays back the capture buffer in real time i e 1 second of capture takes second to playback Normal Speed playback looks like the live real time measurement Normal playback is limited to the real time limitations of the equivalent real time analog input measurement Not all time records are displayed during Normal playback though all time records contribute to averaged measurements For example 1 second of capture contains 256 full SR785 Dynamic Signal Anaylzer Playback Input Menu 4 99 span FFT time records Normal Speed playback at full span takes 1 second and updates the display only about 8 times during playback E
215. Tee to connect the Source Output to the filter input and the Chl A Input Connect the filter output to the Ch2 A Input 3 Press Display Setup Press lt Measure Group gt Select Octave with the knob and press Enter Press Source lt On gt Press Link Auto Scale A Display the System menu Preset returns the unit to its default settings Preset requires confirmation to prevent accidental reset Wait until the self tests are completed Ch1 measures the source filter input and Ch2 measures the filter output Select the Display Setup menu Change the Measurement Group Choose the Octave group Both displays are now making Octave Analysis measurements Turn the source on Auto Scale DisplayA and change the scale of DisplayB to match DisplayA The Octave measurement displays the output of logarithmically spaced bandpass filters This is not an FFT based measurement The last bin at the right is a Sound Level measurement and may be calculated independently from the octave bands Note that even though the source is a single frequency sine wave the octave display shows a very broad peak This is because the individual bandpass filters are very broad 1 3 of an octave in this case SR785 Dynamic Signal Analyzer 1 24 Octave Analysis 4 Press Source Press lt Noise gt Press lt Type gt Use the knob to select Pink and press Enter Press Auto Range Ch1 and Auto Range Ch2 Press Auto Scale A
216. The MENU keys select a menu of soft keys Pressing a menu key will change the menu boxes which are displayed next to the soft keys Each menu presents a group of similar or related parameters and functions The CONTROL keys start and stop data acquisition toggle the active display and link parameters and functions These keys are not in a menu since they are used frequently and within any menu The FUNCTION keys perform common functions such as Auto Scale and Auto Range These keys can be accessed at any time A complete description of the keys follows Softkeys The SR785 has a menu driven user interface The MENU keys each display a menu of softkeys The softkeys are at the right of the video display and have different functions depending upon the displayed menu Softkeys are referenced in brackets like lt Span gt or lt Units gt There are three types of softkeys buttons lists and numeric values A button performs a function such as lt Full Span gt A list presents a list of choices or options in the entry field at the top of the screen Use the knob to make a selection and press Enter lt Measurement gt is an example of a list A numeric value presents the current value in the entry field and awaits numeric entry Enter a new value with the ENTRY keys and press Enter lt Start Freq gt is an example of a numeric value A complete description of the menu softkeys follows in the next chapter SR785 Dynamic Signal Analyzer
217. The marker is constrained to the most recent record at the back of the waterfall Older records are only shown graphically their data has not been saved and may not be accessed in any way In this case the display updates and scrolls as quickly as possible Waterfall display WITH storage shows only those records which are stored in waterfall memory While the measurement is running the display scrolls down and the newest record is added to the top back While running the display may not update fast enough to show every stored record in real time Pause the measurement to redraw the display with either the newest record at the top normal or the oldest record at the top reversed When paused the display shows every stored record which is visible The number of records stored in waterfall memory is displayed in the Vertical Scale Bar when storage is on A waterfall display may not be taken Off Line Moving the Marker The marker may be moved to a record other than 0 only if storage is on SR785 Dynamic Signal Analyzer 4 136 Waterfall Menu Storage Save Option Use Alt knob to move the marker from record to record along the Z axis and scroll the display through the waterfall buffer Use lt Cursor Z to gt to move to a specified record The marker position along the Z axis is displayed in the Marker Position Bar next to the marker frequency or time The Z axis position is the record number starting from 0 most recently store
218. The probability density function or PDF is similar to the histogram except it is normalized so that the integral of the PDF between any two points is equal to the probability that the amplitude of the input signal is between those two points Since the integral of the PDF over voltage is a probability i e unitless the units of the PDF must be inverse volts SR785 Dynamic Signal Analyzer Time Histogram 2 59 Cumulative Density Function CDF The cumulative density function or CDF is an integrated version of the PDF The value of the CDF at a voltage V is the integral of the PDF from the smallest amplitude up to V Thus the value of the CDF at V is the probability that the input signal has an amplitude smaller than V Capture The capture buffer stores sequential time domain data in memory See Capture Buffer for more details The Capture measurement displays the contents of the capture buffer Time Histogram measurements can use this stored data as input data by choosing Playback as the Input Source in the Input menu The capture buffer is often very long To graphically expand a region of the display use the Pan and Zoom functions in the Display Setup menu The capture buffer display can automatically pan with the capture fill or playback progress through the buffer During capture fill if the capture accumulates points faster than they can be displayed some points are not shown This speeds up the display update so that it
219. This indicator is on whenever a GPIB Service Request is generated by the SR785 SRQ stays on until a serial poll 1s completed SR785 Dynamic Signal Analyzer 3 22 Status Indicators Local Remote LOCK macro local indicates that the unit is under local control front panel enabled REM indicates that the unit is under remote interface control The front panel may be locked out by a computer interface To return the unit to local control press the Help Local key lt Overide Remote gt in the System lt Remote gt menu allows front panel control even in the REMOTE state LOCK indicates that the front panel is locked out and no front panel keypress will return the unit to the local state No front panel adjustments may be made An interface command LOCL is required to exit the LOCK state Record indicates that a keypad macro is being recorded Use Macro Rec to start recording Play indicates that a macro is being played Use Play Macro to playback a stored macro See Macros later in this chapter for more SR785 Dynamic Signal Analyzer Status Indicators 3 23 Keypad m AJ lt Q SO NINOIE i Start Capture e Active Display Start Reset Link Help Local Pause Stop ont Capture JUUUU JUUUU JUUUU 3 5 gt gt S MENU FUNCTION Auto Auto Marker Scale A Range Ref ch 1 EJ F lel Average Auto Au
220. Threshold 0 01 3 dB Auto Resolution examines the results of successive measurements If the newest measurement is within the Faster Threshold of the previous measurement for BOTH channels then the sweep will take larger steps skipping frequency points Each successive time this threshold is met the step size is increased until the Maximum Step Size is reached This speeds up the sweep in regions where the response is flat varies less than the Faster Threshold Measurements which differ by more than the Faster Threshold on EITHER channel but less than the Slower Threshold on BOTH channels maintain the present sweep speed SR785 Dynamic Signal Analyzer 4 18 Swept Sine Frequency Menu Generally the Faster Threshold should be set to the desired amplitude resolution In order for skipping to occur this should be something greater than the variations in the flattest regions of the measurement Command SFST d 1 Slower Threshold Set the Slower Threshold 0 05 6 dB If Auto Resolution is skipping points and a measurement differs from the previous measurement by more than the Slower Threshold for EITHER channel then the sweep returns to the previously measured point and moves to the very next frequency point in the sweep with no skipping The sweep continues from this point speeding up if allowed and slowing down when required This fills in skips in the sweep which vary by more than the Slower Threshold Measure
221. Threshold on BOTH channels maintain the present sweep speed The number of points skipped remains the same in this case In order to adjust these parameters appropriately some knowledge of the frequency response is required In order to save time the Faster Threshold must be set to allow some speeding up Set the Faster Threshold to the desired amplitude resolution remembering that some sacrifice is required to save time In order to avoid missing the major features in the response set the Slower Threshold to less than half of the feature size If the feature is narrow set the Maximum Step Size to less than half of the feature width in sweep points It is good practice to start by taking a sweep with Auto Resolution Off This ensures that the span and resolution of the sweep are correct as well as the averaging times Once these have been established turn Auto Resolution On to save time on successive measurements Start by setting the Faster Threshold to something greater than the variations of the flat regions of little interest Set the Slower Threshold to twice the Faster Threshold and the Maximum Step Size to no more than 5 of the Sweep Number Of Points Adjust the parameters as necessary to optimize the sweeps where needed A well specified Auto Resolution sweep can take 80 off of the sweep time while preserving the essential features of the frequency response This is very useful in repetitive measurements Input Auto Ranging Inpu
222. Total Count since more buffer memory is required to hold measurements with higher resolution The Total Count is limited to 2048 records per display regardless of the amount of installed memory The rate at which measurement records are added to waterfall memory is set by the Waterfall Skip This allows the waterfall memory to hold a longer time history as well as setting a variable storage rate Command WTOT d 1 Skip Storage Interval Set the Waterfall Skip Storage Interval for the active display The rate at which measurement records are added to waterfall memory is set by the Skip Storage Interval This allows the waterfall memory to hold a longer time history as well as setting a variable storage rate The interval has no effect if Storage is Off The Waterfall Display updates at the normal rate for the display measurement and span In the FFT Correlation Order and Time Histogram groups for every measurement added to memory a skip number of measurements are not stored For example a skip of 0 stores every measurement in memory A skip of 10 stores every 11th measurement in memory store 1 skip 10 The skipped measurements are still computed and affect exponential averaging they are simply not stored The elapsed time between stored records 1 storage rate is simply skip 1 times the FFT acquisition time times the time SR785 Dynamic Signal Analyzer 4 138 Waterfall Menu View Count Angle record increment
223. a frequency response function discussed above cannot model a pure delay term of the form exp sT where T is the delay time Because of this and because measured frequency response data often includes delay a delay parameter is included in the curve table On synthesis the analyzer multiplies the Frequency Response function by the delay factor exp sT When fitting the input data is divided by exp sT before the curve parameters are calculated Note that the curve fitter will not fit an appropriate value of the delay this value must be supplied by the user Trace The curve table also contains a field which determines which trace will be written to when the curve is synthesized Curve Fitting Before fitting a measured frequency response function several setup parameters must be specified The fit region determines the region of the active display that will be fit The number of poles and zeros determine the order of the frequency response function which will be fit to the measured data The active display must be in the FFT or Swept Sine measurement group to be fit When the user presses Start Fit the analyzer computes in a single pass the best fit parameters for the active display using the Delay and Frequency Scale parameters for Curve Table 1 These parameters are then placed in curve table in the pole zero representation Finally Curve Table 1 is synthesized and the synthesized trace is placed in the non active display so it can be com
224. a from the curve table currently being edited Since this option will erase the curve currently being edited the analyzer will prompt for a confirmation before clearing the table data Command ECLR 1 Enter j Allows the entry of complex poles zeros and residues into the curve tables To enter a complex value enter the real part then press the lt Enter J gt Softkey A will appear in the edit window Now enter the imaginary part Complex poles zeros or residues only occur as part of complex conjugate pairs Thus if the string 3 j 7 is entered for a pole for instance it corresponds to the term s 34 7 s 3 j7 in the frequency response SR785 Dynamic Signal Analyzer Disk Menu 4 167 Disk Menu The Disk menu saves and recalls data and settings to and from disk Utility functions are provided to manage directories erase files and format disks Files are saved as DOS files on either 720k or 1 4M 3 5 inch disks Storage File Name MYFILE Current Directory Display to Disk i Disk to Display Settings to Disk i Recall Settings Trace to Disk i Disk to Trace More il Disk Upkeep l File Name Enter the save and recall Current File Name Turn the knob to bring up the file catalog display listing all files in the Current Directory with the extension 78 SR785 files Press Exp to display all files in the directory Choose a file name with the k
225. able in certain groups The Window Capture and Waterfall parameters do not apply to all groups Each group has its own set of available measurements Only the FFT and Order group have time and frequency domain measurements The Time Histogram and Correlation groups have only time domain measurements while the Octave and Swept Sine groups have only frequency domain measurements To select a measurement choose the Measurement Group then the Measurement View and Units Analyzer Configuration Some measurements made by the SR785 are intrinsically two channel measurements for instance frequency response or cross correlation Other measurements such as Autocorrelation or FFT1 only involve a single input channel The SR785 has a uniquely flexible architecture with regard to processing single and dual channel measurements which is set by the Input lt Analyzer Contig gt softkey If two channel measurements are required this softkey should be set to the default Dual Channel setting This is the traditional mode in which 2 channel analyzers are operated All measurements including two channel measurements are allowed however many insturement parameters such as frequency span and number of FFT lines must be the same for both channels Obviously it wouldn t make much sense to take a frequency response measurement where the input and output had different frequency spans SR785 Dynamic Signal Analyzer Measurement Groups 2 5 If two ch
226. according to ANSI S1 4 1983 Type 0 Broadband Impulse and Peak measurements are made according to IEC 651 1979 Type 0 Band Center Frequencies Choose the number of bands per octave and the start and stop bands for the measurement within the Frequency menu The exact band center frequencies are calculated according to the ANSI standard The displayed frequencies are sometimes rounded to even values for a simpler display The filter shapes are third order Butterworth with full 1 3 or 1 12 octave bandwidth Full Octave Bands Full octave bands are defined ranging from 125 mHz to 32 kHz Up to 11 full octaves may be measured at one time The exact centers are given by Center Frequency 1000 x 2 forn 13 5 1 3 Octave Bands 1 3 octave bands are defined ranging from 100 mHz to 40 kHz Up to 11 octaves 33 bands may be measured at one time The exact centers are given by Center Frequency 1000 x 2 for n 10 46 1 12 Octave Bands 1 12 octave bands are defined ranging from 100 mHz to 12 34 kHz Up to 11 octaves 132 bands may be measured at one time The exact centers are given by SR785 Dynamic Signal Analyzer 2 42 Octave Analysis l n Center Frequency 1000 x la x glia for n 160 43 Octave Measurements Octave Analysis is a Measurement Group Choose the Measurement Group within the Display Setup menu The available measurements are rms averaged Octave spectrum power spectrum Capture Buffer and User F
227. age to power conversion is done by assuming that power volts volts impedance where impedance is the setting of the lt dBm Ref Imped gt softkey dBspl will convert measurement results to sound pressure level units dBspl measures sound pressure in decibels relative to a sound pressure of 20 WPascals dBspl is only allowed if the Engineering Units for the corresponding input are set to Pascals Command UNDB d 1 Determines whether the active display units will be peak peak to peak or rms This softkey is inactive if the underlying measurement and view is unitless e g frequency response Command UNPK d 1 SR785 Dynamic Signal Analyzer 4 42 Display Setup Menu PSD Units Phase Units Power Spectral Density PSD is the energy in each frequency bin normalized to the noise bandwidth of the bin The noise bandwidth is calculated from the FFT Linewidth and the Window function This allows comparison of results taken at different spans and ye ee Windows If lt PSD Units gt are on the units of the display will be V VHz or V Hz Command PSDU d 1 Selects radians or degrees as units for the phase and unwrapped phase views Command UNPH 7 d 1 dBm Reference Impedance Y Max Y Mid Set the dBm Reference Impedance for both displays The dBm Reference Impedance is used to calculate dBm units dBm is simply 10 log power 1mW where power Vrms Reference Impedance Command DBMR
228. am measurement groups SR785 Dynamic Signal Analyzer Marker Menu 4 53 Frequency Damping The Frequency Damping cursor fits the resonant frequency and damping ratio for a single degree of freedom in a frequency response curve The fit area is moved using the knob Use Alt knob to re size the fit region The Frequency Damping cursor should only be used with frequency response data The Frequency Damping Cursor is only available in the FFT and Swept Sine measurement groups SR785 Dynamic Signal Analyzer 4 54 Normal Marker Menu Normal Marker Menu Seeks Width This menu is displayed when the active display Marker Mode is Normal Marker Setup l Marker On Mode Normal Seeks Max Width Spot Rel off X Rel Y Rel 0 X Rel Off Marker X to c Target 0 Select the Normal Marker Seeks mode of the active display Max Min Mean The Marker searches the data points within the Marker Region for the Maximum or Minimum data value or calculates the Mean of the region The results are shown in the Marker Position display above the graph When Seeking Max or Min the Marker is located at the max or min data point When the Seeking the Mean the X position is the center of the Marker Region and the Y position is the Mean of the data within the region Each display has its own Marker Seeks Mode This entry field can be linked to both displays using the Link key Command MSEK d 1 Select the Normal Mar
229. ample when linear averaging is complete an alarm is sounded Command ADON 7 1 SR785 Dynamic Signal Analyzer System Preferences Menu 4 197 Audible Overload If Audible Overload is set to On an audible alarm is sounded whenever an input is overloaded Command AOVL 1 Screen Saver Turns the Screen Saver On or Off Using the Screen Saver extends the life of the video display and prevents screen burn When the Screen Saver is On and the Screen Saver Delay passes without a key press knob turn or interface command the screen will be blanked and random patterns are displayed Press any key to return the screen to normal Command SAVR 1 Screen Saver Delay Set the Screen Saver Delay in minutes 1 59 When the Screen Saver is on and the Screen Saver Delay passes without a key press knob turn or interface command the screen will be blanked and random patterns displayed Press any key to return the screen to normal Command SDLY 1 Frequency Format Select the Frequency Format Exact Bin Rounded Exact Bin displays frequencies exactly This can make the frequency display have many more digits than required to distinguish adjacent frequency bins However this format is useful when determining the exact frequency of a bin Rounded shortens the frequency displays to show only those digits which are required to distinguish adjacent frequency bins This simplifies and shortens the frequency
230. an be linked to both displays by using the Link key Command WANG d 1 Marker to Z Move the marker to a specified record within the waterfall buffer in the active display Storage must be on to move to records other than the most recent record 0 Enter a record number starting from 0 as the most recent and press Enter The waterfall display will re draw to include the specified record number Alt knob also moves the marker from record to record along the Z axis and scrolls the display through the waterfall buffer lt Marker to Z gt is a faster way to move to an arbitrary record The marker position along the Z axis is displayed in the Marker Position Bar next to the marker frequency or time The Z axis position is the record number starting from 0 most recently stored at the back of the waterfall lt Record to Trace gt saves the record selected by the marker to a Trace Command MWEL d 1 Allocate Memory Display the Memory Allocation menu Total Available Displays the total memory available for storage either 980 2004 or 4022 blocks depending upon the amount of installed memory Each block is 2 kPoints 2048 points The total of the Capture Waterfall and Arbitrary memory allocations cannot exceed the Total Available memory It may be necessary to decrease one allocation in order to increase another Command MMEM Capture Memory Allocates memory blocks for the capture buffer The allocated Captur
231. an have different scales This entry field can be linked to both displays using the Link key Command XDIV d x Y Center Polar Set the Y Center of the active display when the View is Nyquist or Nichols plot The Y Center is the Y axis value at the center of the graph The Y Center has the same units as the display The two displays can have different Y Center values This entry field can be linked to both displays using the Link key Command YCEN d x Y Div Polar Pan Set the Y Division scale of the active display when the view is Nyquist or Nichols plot This value is the vertical scale of the graph The knob adjusts the scale in a 1 2 5 10 sequence Changing the scale does not change the Y Center location If the Y axis is scaled linearly the vertical scale is expressed in the display units If the Y axis is logarithmic the vertical scale is always dB division The two displays can have different scales This entry field can be linked to both displays using the Link key Command Y2DV d x Set the Pan translation of the active display This value is the left most displayed bin when the X axis is Zoomed expanded The two displays can have different translations when expanded This entry field can be linked to both displays using the Link key Command XPAN 7 d 1 SR785 Dynamic Signal Analyzer Display Setup Menu 4 45 Zoom Select the Zoom factor X axis expand of th
232. ancel Discard any changes made in this menu and exit this menu Enter Macro Enter the displayed string as the new macro and exit this menu Use Play Macro to playback the macro string SR785 Dynamic Signal Analyzer Chapter 5 Remote Programming In This Chapter 5 1 Arbitrary Source Commands 5 57 meer Or GOmmMmandS oe Swept Sine Source Commands 5 58 Alphabetical List of Commands 5 12 Input Commands 5 60 Transducer Parameter Commands 5 62 Introduction 5 21 SIES Tachometer Input Commands 5 64 Communicating With GPIB 5 21 ee Input Playback Commands 5 65 Communicating With RS232 5 21 Trigger Commands 5 66 Screen Indicators And Queues 5 21 Average Commands FFT Correlation Command Format 5 22 at ae and Order 5 68 Command Synchronization 5 22 aegis Average Commands Octave 5 71 Data Synchronization 5 23 Average Commands Swept Sine 5 73 Command Context Errors 5 24 E le P 5 24 User Math Commands 5 74 a nt Window Commands 5 78 Command Syntax 5 25 Waterfall Commands 5 80 Commands and Units 5 25 Capture Commands 5 83 Help 5 26 Memory Allocation Commands 5 84 Things to Remember 5 27 Data Table Commands 5 85 Output Interface RS232 or GPIB 5 27 Limit Test Commands 5 87 Active Display and Linking 5 27 Marker Statistics Commands 5 89 Analyzer Configuration and Linking 5 27 Exceedance Statistics Commands 5 90 Command Context Errors 5 27 Curve Fit Commands 5 91 Frequency Commands FFT and Disk Commands 5 94 Correlatio
233. and in the Octave display 4 ms Integration Time is only available if the Lowest Band is 100 Hz or greater Decreasing the Lowest Band below 100 Hz increases the minimum value of the Integration Time The Start Reset key resets the current averages and starts the measurement over The Pause Cont key pauses the measurement Pressing Pause Cont again resets the averages and starts the measurement over SR785 Dynamic Signal Analyzer Confidence Power Bin Octave Average Menu 4 117 Each display has its own Integration Time This entry field can be linked to both displays by using the Link key Command OTIM d x Set the Confidence Level for the active display 0 125 dB 2 dB The Confidence Level only affects Equal Confidence averaging The Start Reset key resets the current averages and starts the measurement over The Pause Cont key pauses the measurement Pressing Pause Cont again resets the averages and starts the measurement over Each display has its own Confidence Level This entry field can be linked to both displays by using the Link key Command OCNF d 1 Choose the type of broadband power measurement for the active display Total Impulse L Peak If the Averaging Type is Peak Hold only Peak power may be selected If the Averaging Type is not Peak Hold Total Impulse and L may be selected In addition to the octave bands a broadband sound level is measured and displayed as the la
234. ands 5 41 YMIN d x The YMIN command sets queries the Y Minimum bottom reference of display d The parameter x is a real number in the display units This command is not valid when the View is Nichols or Nyquist YDIV d x The YDIV command sets queries the Y Division scale of display d The parameter x is a real number in the display units This command is valid for all Views Changing the scale of a display may change the Y Max and Y Mid values Always use a YMAX YMID or YMIN command after the YDIV command YMDX d x y The YMDX command sets the YMax value and Y Div value simultaneously The parameter x is the value of Ymax The parameter y is the value of Y div This command is not valid when the View is Nichols or Nyquist XCEN 7 d x The XCEN command sets queries the X Center of display d The parameter x is a real number in the display units This command is only valid when the View is Nichols or Nyquist XDIV d x The XDIV command sets queries the polar X Division scale of display d The parameter x is a real number in the display units This command is only valid when the View is Nichols or Nyquist Changing the scale of a display may change the X Center value Always use the XCEN command after the XDIV command YCEN d x The YCEN command sets queries the Y Center of display d The parameter x is a real number in the display units This command is only valid when the View is
235. annel measurements aren t required however the SR785 allows selection of the Independent Channel configuration In this mode each display of the SR785 functions as a completely separate single channel analyzer with an independent set of operating parameters For instance in the Independent Channel mode display A could be configured to show a broadband measurement of channel 1 with linear averaging while display B could show a narrowband detail of the same input with exponential averaging The restriction of course is that in Independent Channel mode no two channel measurments can be computed SR785 Dynamic Signal Analyzer 2 6 Analyzer Basics What is an FFT An FFT analyzer takes a time varying input signal as you would see on an oscilloscope trace and computes its frequency spectrum Fourier s basic theorem states that any waveform in the time domain can be represented by the weighted sum of pure sine waves of all frequencies If the signal in the time domain is periodic then its spectrum is probably dominated by a single frequency component The spectrum analyzer represents the time domain signal by its component frequencies Why Look At A Signal s Spectrum For one thing some measurements that are very hard in the time domain are very easy in the frequency domain Take harmonic distortion It is hard to quantify the distortion by looking at a good sine wave output from a function generator on an oscilloscope When the same signal
236. apture Length The parameter 1 is a length in kPts per channel i must be an even number from 2 to the maximum allocated memory This command is invalid it the source is arbitrary playback from the capture buffer or if the measurement group is Swept Sine The CRAT command sets queries the Capture Rate The parameter 1 0 19 selects a rate equal to the maximum rate divided by 2 to the ith power Thus i 0 selects the maximum rate and 1 1 selects half the maximum rate This command is invalid it the source is arbitrary playback from the capture buffer or if the measurement group is Swept Sine or Order The CPAN command sets queries the Capture Auto Pan The parameter 1 selects Off 0 or On 1 Same as Start Capture key Capture memory must already be allocated The Input Source cannot be Playback and the Source cannot be Arbitrary playback from Capture Same as Stop Capture key This command has no effect if Capture is not in progress SR785 Dynamic Signal Analyzer 5 84 Memory Allocation Commands Memory Allocation Commands MMEM The MMEM command queries the Total Available Memory for Capture Waterfall Order Track and Arbitrary Waveform MMEM returns the total number of memory blocks 2 kPts block in the instrument MALLC i j k The MALC command sets the Memory Allocation to i blocks for Capture J blocks for Waterfall Order Track and k blocks for Arbitrary Waveform The sum of i j k cannot exceed the Total A
237. arameter x is a percentage up to 300 This command is valid only when the Measurement Group is FFT The set command requires display d to be Live SR785 Dynamic Signal Analyzer FREJ d i TAVM i PAVO d i Average Commands 5 69 The FREJ command sets queries the Overload Reject The parameter 1 selects Off 0 or On 1 The set command requires d 2 both displays This command is valid only when the Measurement Group is FFT or Correlation The set command requires a display to be Live The TAVM command sets queries the Trigger Average Mode The parameter 1 selects Time Records 0 or Averages 1 This command is valid only when the Measurement Group is FFT Time Histogram or Correlation The set command requires a d 2 both displays The PAVO command sets queries the Average Preview The parameter 1 selects Off 0 Manual 1 or Timed 2 The set command requires d 2 both displays This command is valid only when the Measurement Group is FFT The set command requires a display to be Live PAVT d x PAVA PAVR The PAVT command sets queries the Preview Time The parameter x is a real number of seconds The set command requires d 2 both displays This command is valid only when the Measurement Group is FFT The set command requires a display to be Live The PAVA command accepts the previewed time record The averages of both displays is updated to include the previewed tim
238. arker Press lt Width gt Select Normal with the knob and press Enter Press lt Seeks gt Select Min with the knob and press Enter Move the Marker Region with the knob to find Set the Span to display the filter notch at 1 kHz The top display A is measuring the filter input and should show a fairly flat spectrum The bottom display B is measuring the filter output and should show a deep notch Both displays are measuring absolute signal levels Select the Display Setup menu Adjust the Measurement of the active display A Choose Frequency Response for the Measurement in DisplayA top Frequency Response is the ratio of the response Ch2 to the input Ch1 and is a unitless quantity Adjust the scale and reference for DisplayA to show the entire range of the data Select the Marker menu Adjust the Marker Width for DisplayA Change to Normal Width 1 2 division Adjust what the Marker Seeks within the Marker Region Seek the Minimum of the data within the Marker Region The Marker Region makes it easy to find narrow the notch frequency and depth Or press Marker peaks and valleys in the graph The notch should be Min 8 Press Display Options Press lt X Axis gt Press lt Link gt SR785 Dynamic Signal Analyzer around kHz and about 60 dB deep Select the Display Options menu The graph might look better on a log x axis The lt Link gt key lets you make a choice for both d
239. armed the next trigger event will trigger the measurement For FFT correlation and Time Histogram measurements each time record requires the trigger to be re armed For octave and swept sine measurements the first trigger after arming starts the measurement and subsequent triggers are ignored Command TARM Manual Trigger Trigger the measurements and burst Chirp amp Noise sources regardless of Trigger Source Manual Trigger Source requires lt Manual Trigger gt or an interface command to trigger Use Auto Arm Trigger Mode with Manual Trigger Source since unwanted triggers are not a problem SR785 Dynamic Signal Analyzer 4 106 Trigger Menu For FFT correlation and Time Histogram measurements each time record requires the trigger to be re armed For octave and swept sine measurements the first trigger after arming starts the measurement and subsequent triggers are ignored Command TMAN SR785 Dynamic Signal Analyzer Average Menus 4 107 Average Menus The Measurement Group determines which Average menu is displayed This menu sets the averaging parameters for the measurement A set of parameters is stored for each group No averaging parameters are available in the Time Histogram measurement group FFT Correlation Order Average Menu When the Measurement Group is FFT Correlation or Order this menu sets the averaging parameters for the active display If the Analyzer Configuration is Dual Channel the avera
240. as follows Host Send WGET Do NOT wait for IFC to be set in the Serial Poll status SR785 Returns n 4 byte binary long int which is the number of bytes needed to transfer the Waterfall buffer Host On receipt of n 4 byte binary long int executes a binary read from the SR785 of n bytes Expect EOI with the final byte of the transfer Serial Poll until IFC bit 7 is set in the Serial Poll status before sending another command The WPUT command downloads Waterfall buffer data to the SR785 This command is valid only via the GPIB interface The download data must be data which was originally uploaded by WGET in its entirety The WGET and WPUT commands allow a host computer to save and reload the Waterfall buffer without using disks The download sequence is as follows Host Send WPUT Do NOT wait for IFC to be set in the Serial Poll status SR785 Returns 1 4 byte binary long int when OK to begin binary transfer to the SR785 A return of 0 indicates that there is no Waterfall memory allocated Host On receipt of 1 4 byte binary long int executes a binary transfer to the SR785 of n bytes as uploaded using WGET Asserts EOI with the final byte of the transfer SR785 Receives n bytes and the EOL If an error is detected during transfer the Waterfall buffer reverts to the empty state and a command execution error occurs This may occur if there is insufficient Waterfall memory allocated Serial Poll until IFC
241. asurement for display d The parameter x is the order a real number The set command requires d 2 both displays This command is valid only when the Measurement Group is Order The set command requires a display to be Live O1BN d i The OIBN command sets queries the input channel associated with the track 1 measurement for display d The parameter 1 sets the input channel to Channel One 0 or Channel 2 1 The set command requires d 2 both displays This command is valid only when the Measurement Group is Order The set command requires a display to be Live O2TK d x The O2TK command sets queries the order associated with the track 2 measurement for display d The parameter x is the order a real number The set command requires d 2 both displays This command is valid only when the Measurement Group is Order The set command requires a display to be Live O2BN d i The O2BN command sets queries the input channel associated with the track 2 measurement for display d The parameter 1 sets the input channel to Channel One 0 or Channel 2 1 The set command requires d 2 both displays This command is valid only when the Measurement Group is Order The set command requires a display to be Live SR785 Dynamic Signal Analyzer 5 36 Frequency Commands Frequency Commands Time Histogram FSPN d f lt kHz Hz mHz wHz gt The FSPN command sets queries the sampling time for display
242. asurements channel measures an input which exceeds the Ideal Reference by more than the Upper Limit or which is less than the Ideal Reference by more than the Lower Limit In cases where the reference channel input must be limited the Ideal Reference plus the Upper Limit must be less than or equal to this limit Whenever Auto Level is used the measurement MUST be frequency response The signal connections must be made for a frequency response measurement This is because source level changes are not normalized in the individual measurements Only the ratio of Channel 2 to Channel 1 is source level independent The Source Ramp Rate is the rate at which the source level changes If Source Ramping is Off source level changes are made instantly If Source Ramping is On the source level changes are made at the ramp rate The Settle Time starts after the source reaches the new level This prevents fast level changes from disturbing the device under test Of course this adds to the sweep time The source ramps off whenever there are no measurements being made This occurs before the start of a sweep at the end of a single sweep or while a sweep is paused by the user If Ramping is Off the source shuts off instantly in these situations SR785 Dynamic Signal Analyzer Order Analysis 2 55 Order Analysis What is Order Analysis In vibration analysis or preventive maintenance of rotating machines it is often useful to identify spectral com
243. ate time records which contain the signals of interest Peak Hold Averaging Peak Hold averaging is similar to rms averaging in that the rms values of quantities are calculated but instead of combinging the rms values rather the magnitude of the new data is compared to the magnitude of the averaged data and if the new magnitude is larger then the new data becomes the averaged data This is done on a frequency bin by bin basis The result is averaged data with the largest magnitudes which occurred over a number of measurements Peak Hold can compare a fixed number of measurements or run continuously Linear Weighting Linear weighting combines N Number Of Averages measurements with equal weighting in either RMS or Vector averaging While Linear averaging is in progress the number of averages completed is shown in the Horizontal Scale Bar below the graph When the Number Of Averages has been completed the measurement stops and Done is displayed to the left of the graph Waterfall Storage If Waterfall Storage is on the waterfall buffer only stores the completed linear averages not each individual measurement Each time the linear average is done the result is stored in the waterfall buffer and the average is reset and started over instead of stopping Each completed average counts as a single waterfall record Exponential Weighting Exponential weighting weights new data more than old data For RMS and Vector averaging weightin
244. ation Analysis Correlation Measurements Capture User Function Octave Analysis What is Octave Analysis Band Center Frequencies Full Octave Bands 1 3 Octave Bands 1 12 Octave Bands Octave Measurements Octave Capture User Function Octave Averaging Linear Time Exponential Time Equal Confidence Peak Hold Sound Level Measurement Leq Impulse Peak Total Power Settling Time Swept Sine Measurements Why Use Swept Sine Swept Sine Measurement Setup Swept Sine Measurements Spectrum Cross Spectrum Frequency response Normalized Variance User Function Averaging Settling and Integration Sweep Frequency and Auto Resolution Input Auto Ranging Source Auto Level and Ramping Order Analysis What is Order Analysis Order Spectra and Order Tracking Order Measurement Setup Order Measurements Linear Spectrum Power Spectrum SR785 Dynamic Signal Analyzer 2 36 2 36 2 36 2 36 2 37 2 37 2 37 2 38 2 38 2 38 2 40 2 40 2 41 2 41 2 41 2 41 2 41 2 41 2 42 2 42 2 42 2 43 2 43 2 43 2 43 2 44 2 44 2 44 2 44 2 44 2 45 2 45 2 46 2 47 2 47 2 49 2 49 2 49 2 50 2 50 2 50 2 50 2 50 2 51 2 52 2 53 2 55 2 55 2 55 2 55 2 56 2 56 2 56 Time Record Windowed Time Record RPM Profile Orbit Track Capture User Function Time Histogram Measurements Time and Histogram Measurements Measurements in the Time Histogram Group Histogram Time Record Probability Density Function PDF Cumulative De
245. ave Channels Select the number of input channels for the octave measurement The number of Octave Channels affects the Measurements of both displays If 2 Octave Channels are selected then both inputs may be analyzed The Measurements of both displays are independent The Highest Band for all Octave Resolutions is decreased by 2 in this case If 1 Octave Channel is selected then only one input may be analyzed If both displays are making an octave measurement they must both use the same input Changing the input of the active display will change the Measurement or input of the other display if necessary User Functions which use both inputs may not be measured Choosing 1 Octave Channel may change the current Measurements so that both displays use the same input Command OCHN d 1 SR785 Dynamic Signal Analyzer Swept Sine Frequency Menu 4 15 Swept Sine Frequency Menu Start Stop When the Measurement Group is Swept Sine this menu sets the frequency sweep parameters These parameters govern the measurements on both displays See Swept Sine in Chapter 2 for a discussion about swept sine measurement fundamentals Frequency Frequency Start E ok kHz Signa T 20 kHz kHz Roar Continuous Tes Linear Auto Resolution Faster Threshold lt 0 1 dB SiW Threshold EE Set the Start frequency 1 mHz 102 4 kHz Note that measurements at frequencies less than Hz take a significant amount of time
246. axis data value at the marker position The returned value is always the absolute position of the marker even when the on screen marker is relative MRKY queries the position along the vertical axis and MRKX queries the time or frequency If the display is a waterfall MRKZ queries the Z axis record number of the marker Lower record numbers are more recent This command is not valid if the Marker of display d is Off The MKMX command performs Marker to Max on display d Same as Marker Max key The marker of each display must be moved separately d 2 is not allowed This command is not valid if the Marker of display d is Off The MKMN command performs Marker to Min on display d Same as Marker Min key The marker of each display must be moved separately d 2 is not allowed This command is not valid if the Marker of display d is Off The MKCN command performs Marker to Center on display d Same as Marker Center key The center frequency of the FFT span is set to the marker frequency on display d The span is decreased if necessary The center of each display must be moved separately d 2 is not allowed This command is only valid when the Measurement Group is FFT and display d is Live This command is not valid if the Marker of display d is Off SR785 Dynamic Signal Analyzer Marker Commands 5 47 Marker Commands Normal MSEK d i The MSEK command sets queries the Normal Marker Seeks Mode of display
247. ay only about 8 times during playback Every Time Record playback displays the measurement result for every captured time record Since the data is stored in memory Every Time Record playback is not limited by real time considerations For example second of capture can contain 256 full span FFT time records In this case all 256 time records are measured AND displayed The display still updates at 8 Hz so playback takes about 32 seconds to complete If the time records are overlapped there may be more than 256 measurements to display and playback will take even longer When the measurement time records are very long narrow spans the time to process and display each measurement is much less than the real time record length Since the data is already available in the capture buffer Normal Speed playback means waiting unnecessarily for a real time record to elapse between updates In this case Every Time Record playback displays the measurements of all captured time records much faster than Normal Speed real time playback When the playback is in Octave Group playback is always Normal Speed Capture as the Arbitrary Source The contents of the capture buffer can be used as the arbitrary source This allows a captured waveform to be output as the source The output sample rate should be the same as the capture sample rate to maintain the correct signal frequencies If the output sample rate is less than the maximum sampling rate 262 or 256
248. be selected as the measurement if it uses a Trace which is empty or which contains data taken in a different Measurement Group See User Math later in this section for more SR785 Dynamic Signal Analyzer Views 2 21 Views Each measurement has an associated view A view is a way of looking at the complex measurement data Log Magnitude Log magnitude view graphs the log of the magnitude of the measurement data The magnitude is V x y where x is the real part and y is the imaginary part The appearance of a display showing the Log Magnitude view depends on the setting of the lt dB Units gt softkey If lt dB Units gt are on the graph is shown plotted with a Y axis scaled linearly in dBs If lt dB Units gt are off the Y axis is shown scaled logarithmically in the units of the measurement Linear Magnitude Linear magnitude view graphs the magnitude of the measurement data The magnitude is V x y where x is the real part and y is the imaginary part The Y axis of the display is linear in scaling Magnitude Magnitude view graphs the magnitude squared of the measurement data The magnitude squared is x y where x is the real part and y is the imaginary part The Y axis of the display is linear in scaling Real Part Real Part view graphs the real part of the measurement data The Y axis of the display is linear in scaling Imaginary Part Imag Part view graphs the imaginary part of the measurement data
249. best to use the Flattop window to broaden all of the peaks Harmonic Marker is not available for Correlation Octave Swept Sine or Time Histogram measurement groups Sideband The Sideband Marker Mode defines a Fundamental carrier Marker with a solid vertical line In addition to the Fundamental Marker a number of sidebands discrete SR785 Dynamic Signal Analyzer 4 52 Marker Menu frequencies are identified by small triangular Sideband Markers The Marker Position Display can show the position of the Fundamental or of a single Sideband The Sideband Power is calculated within the Marker menu in display units and dB Only those sidebands within the measurement span which are identified by the Sideband Markers contribute to the Sideband Power Sideband Marker is only available for FFT measurements in the frequency domain The knob moves the Fundamental Marker of the active display whenever there is no pending entry Use Marker Max to move the Fundamental Marker to the peak of the graph The sideband identification works best if the fundamental frequency is a bin frequency If the fundamental is off bin then it is best to use the Flattop window to broaden all of the peaks Sideband Marker is not available for Correlation Octave or Swept Sine or Time Histogram measurement groups Band The Band Marker Mode defines two frequency bands in the display The Upper 2 band is delimited by dashed vertical markers and the Lower 1
250. bit 7 is set in the Serial Poll status before sending another command SR785 Dynamic Signal Analyzer 5 116 Data Transfer Commands Loading the Waterfall buffer loads data into the waterfall buffer and recalls the measurement parameters which were in effect when the waterfall buffer was saved The recalled parameters include items in the Frequency Display Setup Display Options Average Window User Math and Waterfall menus SR785 Dynamic Signal Analyzer Interface Commands 5 117 Interface Commands RST IDN LOCL i OVRM 7 i The RST command resets the SR785 to its default configurations The communications setup is not changed All other modes and settings are set to their default conditions and values This command takes some time to complete Do not send other commands on the same command line after RST Do not send another command until RST is complete Either wait a fixed amount of time approximately 12 seconds or use serial polling to wait for IFC to be set again in the Serial Poll status before sending more commands The IDN query returns the SR785 s device identification string This string is in the format Stanford_Research_Systems SR785 s n00001 ver007 In this example the serial number is 00001 and the firmware version is 007 The LOCL command sets the local remote state The parameter 1 selects LOCAL 0 REMOTE 1 or LOCAL LOCKOUT 2 The states duplicate the GPIB
251. c Signal Analyzer 4 62 Sideband Marker Menu Display Only those sidebands within the measurement span which are identified by the Sideband Markers contribute to the Sideband Power calculations The sideband identification works best if the fundamental frequency is a bin frequency If the fundamental is off bin then it is best to use the Flattop window to broaden all of the peaks Each display has its own Number Of Sidebands This entry field can be linked to both displays using the Link key Command SDBN d 1 Select the Harmonic and Sideband Display for the active display The marker display can read the position of the fundamental or any identified harmonic or sideband For sideband marker the value ranges from O fundamental to plus and minus the Number of Sidebands The first lower sideband is identified as 1 the first upper sideband is 1 etc The small square marker will move to the selected harmonic or sideband If the selection is not within the measurement span the marker will move to the highest or lowest measured frequency which will be reported as the marker position Each display has its own harmonic sideband display This entry field can be linked to both displays using the Link key Command HDSP d 1 Readout Mode Select the Readout Mode for the Harmonic and Sideband Marker of the active display Absolute Relative The Marker Position Display shows the amplitude of the Fundamental or a
252. c and Sideband Marker of the active display Absolute Relative The Marker Position Display shows the amplitude of the Fundamental or any identified Harmonic or Sideband in either Absolute units or Relative to the fundamental Relative Mode reports the amplitude of the selected harmonic or sideband relative to the fundamental The marker amplitude units are dBFundamental The frequency is always absolute Each display has its own Readout Mode This entry field can be linked to both displays using the Link key Command HRDO 7 d 1 This menu box displays the Total Harmonic Distortion THD of the active display The THD squared is the harmonic power sum of the squared magnitudes of the harmonics divided by the sum of the fundamental power plus the harmonic power Only those harmonics within the measurement span which are identified by Harmonic Markers contribute to the THD The THD is displayed in dB 20log THD and percent To measure THD N use the Band Marker Command HTHD d 1 Harmonic Power This menu box displays the Total Harmonic Power of the active display The harmonic power is the sum of the squared magnitudes of the harmonics identified with a Harmonic SR785 Dynamic Signal Analyzer 4 60 Harmonic Marker Menu Marker The result is shown in Vrms or dBVrms depending on the setting of dB Units To convert a value in Vrms to power square the result Command HPWR d SR785 Dynamic Signal Analyzer S
253. cate Memory Display the Memory Allocation menu Total Available 1000 Biks Capture Memory 500 Bik Waterfall Memory 500 Biks Arb Memory 0 Bliks Confirm Allocation c Total Available Total Available displays the total memory available for storage either 980 2004 or 4054 blocks depending upon the amount of installed memory Each block is 2 kPoints 2048 points The total of the Capture Waterfall and Arbitrary memory allocations cannot exceed the Total Available memory It may be necessary to decrease one allocation in order to increase another Command MMEM Capture Memory Capture Memory allocates memory blocks for the capture buffer The allocated Capture Memory sets the limit for the Capture Length Command MALC 1 j k Waterfall Memory Waterfall Memory allocates memory blocks for waterfall storage Command MALC 1 j k Arb Memory Arb Memory allocates memory blocks for the Arbitrary Source waveform The Arbitrary Source can also use the capture buffer as the output waveform Command MALC 1 j k SR785 Dynamic Signal Analyzer 4 146 Capture Menu Confirm Allocation Confirm Allocation places the new memory allocations into effect Exiting this menu without pressing lt Confirm Allocation gt will cancel any adjustments made in this menu Clear Allocation Clear Allocation clears the existing memory allocations in this menu The new allocations do not take effect unless lt Confi
254. cates memory blocks for the Arbitrary Source waveform The Arbitrary Source can also use the capture buffer as the output waveform Clear Allocation Clears the existing memory allocations in this menu Confirm Allocation Places the memory allocations in this menu into effect Exiting this menu without pressing lt Confirm Allocation gt will cancel any adjustments made in this menu Command MALC 1 j k Trace to Arb Copy the real part of a stored trace into the Arbitrary Waveform memory Select a Trace 1 5 and press Enter The Arb Length is set to 2 kpoints and the Arbitrary Waveform Source is set to the Arbitrary Buffer Only traces which contain FFT measurements can be copied to the Arbitrary memory In almost all cases the trace should contain a time record If the length of the trace is less than 2 kPoints 2048 points then the trace is repeated until 2 kPoints is reached This can cause discontinuities if the trace is not continuous from its end to its beginning If this source is measured with an FFT time record equal to the trace length in time then windowing should solve this problem SR785 Dynamic Signal Analyzer 4 82 Arbitrary Source Menu Only the real part of the trace is used Baseband time records are completely real and can be reproduced as an Arbitrary waveform Non baseband time records or complex traces do not reproduce well The amplitude of the Arbitrary Waveform is normalized to the maximum value in
255. cating that the measurement is not settled Once the 4th measurement is complete the display returns to full intensity since the measurements have completely settled time records If averaging is on changes which unsettle the measurement will restart the average Unsettled measurements are not included in the new average Averaging does not start until the measurement is settled When the time record increment ts less than 100 Settle is displayed instead of the number of averages below the graph to indicate that the unsettled measurements are not being averaged See also Real Time Bandwidth and Overlap If the Analyzer Configuration is Independent Channels each display can have its own Time Record Increment This entry field can be linked to both displays by using the Link key Command FOVL d x More This submenu selects additional averaging parameters off Trigger Avg Mode Time Record Return Overload Reject Select Overload Reject for both displays Off On When Overload Reject is On time records which contain points which were overloaded at the input are not included in the measurement average Whenever a time record is rejected the Reject indicator below the graph next to the average type and number turns on briefly This has no effect if Averaging is Off SR785 Dynamic Signal Analyzer Average Menus 4 113 When Overload Reject is Off all time records are part of the measu
256. center of the triggered time record The trigger delay is specified in time record bins at the current span Note that the windowed time record in DisplayB shows the signal at the center of the time record The amplitude of the windowed time record is not the same as the amplitude of the time record itself This is because the window functions have gain and attenuation at different parts of the time record The Hanning window is 2 0 at the center so the amplitude of the signal in the windowed time record is twice as large The Hanning Flattop BMH and Kaiser windows are not intended for use with narrow pulse signals They are used for signals which last the entire time record and normalized as such The Uniform and Force windows have no gain and should be used with pulsed signals such as this SR785 Dynamic Signal Analyzer 1 22 Triggering and the Time Record 9 Press Display Setup Press lt Measurement gt Select Time1 with the knob and press Enter Press Window Press lt Window gt Select Uniform with the knob and press Enter 10 Press Trigger Press lt Trigger Source gt Select Cont with the knob and press Enter Adjust the generator frequency to 255 Hz SR785 Dynamic Signal Analyzer Select the Display Setup menu Change the Measurement of DisplayB back to Time Record Timel is the un windowed time record Select the Window menu Change the window type for both displays Use
257. ch as View Scaling and Marker Functions may be changed Off Line The two displays can have different Display Update Modes This entry field can be linked to both displays using the Link key A single display may be taken Off Line while the other display is still Live This allows comparison of live results with a previous result This is unlike the Pause Cont key which pauses ALL measurements Command DISP d 1 Select the screen Display Format Single Dual or Overlay SR785 Dynamic Signal Analyzer X Axis Display Options Menu 4 47 In Single format the active display is shown Use the Active Display key to switch between DisplayA and DisplayB In Dual format DisplayA is always on top The Active Display key switches the active display from top A to bottom B In the Overlay format the inactive display is shown in half intensity video on the same graph as the active display The axes markers and menus still reflect the values for the active display Command DFMT 1 Select the X Axis Scale Type for the active display Linear Logarithmic Logarithmic scaling is only available for FFT measurements with frequency as the X axis Displaying a measurement with a time axis Time Record Capture will change the scaling to linear and disable this softkey Octave Analysis is always displayed on a logarithmic X axis The X axis type for Swept Sine measurements is set by the Sweep Type This softkey is
258. ch occur at different times For example echoes show up as peaks separated by the echo time Sine waves appear as sine waves in auto correlation and square waves appear as triangles Signals which do not repeat or are completely random such as noise appear only at t Q The definition of Auto Correlation depends upon the what type of averaging is selected in the Average menu Averaging Auto Correlation invFFT FFTuN FFTN RMS or Peak Hold Averaging Auto Correlation invFFT lt FFTuN FFTN gt Vector Averaging On Auto Correlation invFFT lt FFTuN gt lt FFTN gt where N is Channel 1 or 2 FFT is a windowed FFT FFTu is an un windowed FFT uniform window and invFFT is an inverse FFT Correlation is a real function and requires a baseband span real time record Non baseband time records do not preserve the original signal frequencies and thus do not yield the correct correlation A display which is measuring a single channel correlation will have its start frequency set to 0 Hz A correlation window is applied to the time record of one FFT in the computation This is because the FFT models the time domain as a single time record repeating itself over and over Computing the correlation over a t greater than half of the time record length will result in wrap around where the correlation starts to repeat itself To avoid this special windows which zero half of the time record are used The 0 T 2 window
259. chronous 1 e they are not related to the signal and do not occur at the signal frequency or its harmonics Examples include lighting fixtures motors cooling units radios computer screens etc If these noise sources are large they can determine the input range and hence the noise floor They can however be removed from the FFT spectrum by using triggering and vector averaging Since the noise signals are not phase coherent with the trigger and signals of interest they vector average to zero Some noise sources however are related to the signal source and if picked up in the signal will add or subtract from the actual signal and cause errors in the measurement A typical source of synchronous noise is a ground loop between the signal source and the analyzer Many of these noise sources can be minimized with good laboratory practice and experiment design There are several ways in which noise sources are coupled into the signal path Capacitive Coupling An AC voltage from a nearby piece of apparatus can couple to a signal path via a stray capacitance Although Csray may be very small the coupled noise may still be larger than a weak signal This is especially damaging if the coupled noise is synchronous with the signal Stray Capacitance Noise Source Signal Source Figure Chapter 2 3 Capacitive Coupling We can estimate the noise current caused by a stray capacitance by i aay dV dt OC stray V noise
260. ck 1 softkey merely selects which channel will be displayed Once a track measurement is done or paused data for each channel can be displayed without retaking any data Command OIBN D d 1 Track 2 Order Specifies the order associated with the Track 2 measurement If the entered value is not an integer multiple of delta order the SR785 will display the closest available order to the entered value Regardless of the order specified the SR785 always tracks all orders specified by the max order and delta order softkeys The Track 2 Order softkey merely selects which order will displayed Once a track measurement is done or paused any order track can be displayed without retaking any data Command O2TK d f SR785 Dynamic Signal Analyzer 4 22 Order Frequency Menu Input Channel Track 2 Specifies the input channel associated with the Track 2 measurement Regardless of the input channel specified the SR785 always tracks all orders specified by the max order and delta order softkeys for both input channels The Input Channel Track 2 softkey merely selects which channel will be displayed Once a track measurement is done or paused data for each channel can be displayed without retaking any data Command O2BN d 1 SR785 Dynamic Signal Analyzer Time Histogram Frequency Menu 4 23 Time Histogram Frequency Menu When the Measurement Group is Time Histogram this menu sets parameters related to the resol
261. command is valid only when the Measurement Group is Octave WVCT d i The WVCT command sets queries the Waterfall View Count for display d The parameter 1 is a number of records This command is not valid when the Measurement Group is Swept Sine WHIT d i The WHIT command sets queries the Waterfall Trace Height for display d The parameter 1 is a percentage 20 80 of the total display height This command is not valid when the Measurement Group is Swept Sine WANG d i The WANG command sets queries the requested Waterfall Angle for display d The parameter 1 is a signed integer number of degrees 75 75 The display will scroll as close to this angle as possible This command is not valid when the Measurement Group is Swept Sine WFST d i The WEST command sets queries the Waterfall Fast Angles for display d The parameter 1 selects Off 0 or On This command is not valid when the Measurement Group is Swept Sine WTHR d i The WTHR command sets queries the Waterfall Threshold for display d The parameter 1 1s a percentage of the full scale trace height This command is not valid when the Measurement Group is Swept Sine WHID d i The WHID command sets queries the Waterfall Hidden Lines for display d The parameter 1 selects Invisible O or Visible 1 This command is not valid when the Measurement Group is Swept Sine WREV d i The WREV command sets q
262. command to SR785 address WaitIFC serial poll until IFC set ok to continue KKKKKKKKKKKKKKKKKKKKKKKK KKK KKKKKEKKKKKKKKKEK KKK KKKKKKKKKKKKKKKKKKKKKKHEK void WaitIFC void serial poll until IFC bit7 set command done modify for your GPIB interface stb is serial poll byte char stb do spoll SR785 amp stb amp status while stb amp 128 IFC if stb amp 32 4 JA LE ESB Dit See there must be a command error in the Standard Event status word Handle command errors here TxGpib SR785 ESR clear the Standard Event status word GetGpib SR785 print ADEE error aT GetSpace KKEKKKRKKRK AAAA AAAA AAAA KKK KKK KK KKK KKK KKK KKK KKK KKK KKK KKK KKK KKK KKK KKK void GetSR785 char getcmd 1 query the SRIS5 for an answer getcmd is the query command string TxXSR785 getcemd send query command GetGpib SR785 get response into global recv string KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKEK KKK KKKKKEK KKK KKKKKRKKKKKKKKKKKKKKKKKEK void WaitAvg void routine to start a linear avg and wait until both displays are done int result avgdone SR785 Dynamic Signal Analyzer Example Program 5 135 avgdone 0 init avgdone status GetSR785 DSPS clear sticky bits in Display status word first TRSR LOS STRT start lin average measurement do GetSR785 DSPS result atoi recv read display status word avgdone avgdo
263. correlation over a t greater than half of the time record length will result in wrap around where the correlation starts to repeat itself To avoid this special windows which zero half of the time record are used The 0 T 2 window zeroes the second half of the time record and the T 4 T 4 window zeroes the first and last quarter of the time record The T 2 T 2 is a uniform window which should only be used on data which is self windowing lasts less than half of the time record Time Record Windowed Time Record These correlation group measurements are similar to their FFT group counterparts The major differences are 1 Because correlation is a baseband measurement the time records are never heterodyned and are therefore always real 2 Correlation uses a different set of windows than the FFT measurement group The Correlation windows which are described above are designed to zero half of the time record in order to eliminate wrap around error SR785 Dynamic Signal Analyzer 2 40 Correlation Capture The capture buffer may be used as a source of data for correlation measurements See Capture Buffer for more details The Capture measurement displays the contents of the capture buffer Correlation measurements can use this stored data as input data by choosing Playback as the Input Source in the Input menu User Function User Function displays the results of a user defined math function User Functions defined w
264. cquired If the SR785 Dynamic Signal Analyzer Status Indicators 3 19 Trigger Mode is Auto Arm the indicator returns to Trig wait after the time record is acquired If the Trigger Mode is Manual Arm then the indicator reads Arm wait while waiting for a manual arm command or keypress Run Pause Done Run indicates that the measurements of BOTH displays are running Whenever new data is available for a Live display the display will update Off Line displays do not update Pause indicates that the measurements of BOTH displays are paused Done indicates that single shot capture playback is finished Use the Start Reset and Pause Cont keys to control the measurements Analog Playback Analog indicates that the measurements of BOTH displays are taking their inputs from the Channel Input or Channel 2 Input Playback indicates that the measurements of BOTH displays are taking their inputs from the Capture buffers Real Time When the Measurement Group is FFT or Octave the Real Time indicator shows the actual time record increment for the measurements in progress If the displayed increment is 100 the start of the next time record is exactly one time record advanced from the start of the previous time record If the increment is 25 then the next time record starts 1 4 of a time record advanced from the start of the previous time record This is sometimes referred to as 75 overlap since th
265. curs This may occur if there is insufficient Arbitrary memory allocated Serial Poll until IFC bit 7 is set in the Serial Poll status before sending another command The CGET command uploads a Capture buffer to the host computer This command is valid only via the GPIB interface The parameter 1 selects Ch1 0 or Ch2 1 The parameter j selects upload the whole buffer 0 or just the playback portion 1 The uploaded data should be saved in its entirety by the host computer The saved data can be downloaded back to the SR785 at a later time using CPUT The CGET and CPUT commands allow a host computer to save and reload the Capture buffer without using disks The upload sequence is as follows SR785 Dynamic Signal Analyzer 5 114 Data Transfer Commands CPUT i WGET Host Send CGET 1 J Do NOT wait for IFC to be set in the Serial Poll status SR785 Returns n 4 byte binary long int which is the number of bytes needed to transfer the Capture buffer Host On receipt of n 4 byte binary long int executes a binary read from the SR785 of n bytes Expect EOI with the final byte of the transfer Serial Poll until IFC bit 7 is set in the Serial Poll status before sending another command The CPUT command downloads Capture buffer data to the SR785 This command is valid only via the GPIB interface The parameter 1 selects Ch1 0 or Ch2 1 After the download is complete the Capture Length will be set to the length
266. d Single channel analysis has twice the measurement bandwidth of two channel analysis Thus to increase the highest measured band use 1 channel analysis Set the highest band to 40 kHz This is the highest allowed band for 1 channel 1 3 octave analysis Select the Display Setup menu SR785 Dynamic Signal Analyzer 1 26 Octave Analysis Press lt Measurement gt Use the knob to select Oct ch2 and press Enter Press lt Measurement gt Use the knob to select Oct ch1 and press Enter 9 Press Input Press lt Input Config gt Press lt Ch1 A Wt Filter gt Use the knob to select On and press Enter Press Link Auto Scale A SR785 Dynamic Signal Analyzer Change the Measurement of both displays Remember in channel analysis both displays measure the same input Both displays now show the filter output on Ch2 Change the Measurement again Show the source output on Ch1 on both displays Select the Input menu Show the Input Configuration submenu Choose the Ch Input A Weighting filter Turn the A Wt filter On The Chl Awt indicator at the top of the screen is highlighted The hardware A Wt filter conforms to the ANSI standard and is commonly used in sound measurements This filter attenuates high and low frequencies according to how people hear and perceive sound The A Weighted spectrum is a bandpass centered around 2 kHz This concludes this measurement example You shoul
267. d If the base frequency is set to 102 4 kHz the sampling time ranges from 3 81uS to 2S in power of 2 increments If the base frequency is set to 100 kHz the sampling time ranges from 3 91uS to 2 048S in power of 2 increments The parameter f is a frequency real number of specified units related to the sampling time by the equation f 25 64 t The set command requires d 2 both displays The set command requires a display to be Live HLEN 7 d x lt samples records uS mS S gt The HLEN command sets queries the histogram length of display d The parameter x is the histogram length in the specified units This command is valid only when the Measurement Group is Time Histogram The set command requires the display d to be Live HBIN d i The HBIN command sets queries the number of histogram bins for display d The parameter 1 is related to the number of histogram bins by the equation Bins 2 1 2 The range of 1 is from 0 to 8 This command is valid only when the Measurement Group is Time Histogram The set command requires the display d to be Live FBAS 7 d i The FBAS command sets queries the Base Frequency of display d The parameter 1 selects 100 0 kHz 0 or 102 4 kHz 1 To set the Base Frequency d must be 2 both displays There is only one Base Frequency for both displays Changing the Base Frequency will affect all of the FFT and source frequency parameters The set command requires at
268. d The UNST command unsettles the measurement of display d The measurement is not actually perturbed by the UNST command The settling status is set to unsettled and the full settling time of the measurement is required before the status returns to settled The measurement is unsettled by changing any one of several measurement parameters For example changing the input range or FFT span will unsettle the measurement If the signal comes from an external source and is changed in such a way as to require the measurement to settle it is convenient to use the UNST command and wait for settling to finish This command is valid only when the Measurement Group is FFT or Octave SVTR d i The SVTR command saves display d to Trace 1 SR785 Dynamic Signal Analyzer RCTR d i SVRF d i RCRF d i PRNT PLOT DUMP ASCL d A1RG i A2RG i MRON d Front Panel Commands 5 103 The RCTR command recalls Trace 1 to display d If Trace 1 does not have data then an error occurs The SVRF command saves the Reference Display of display d to Trace 1 The RCRF command recalls Trace 1 to the Reference Display of display d If Trace 1 does not have data or is not compatible with the active display measurement an error occurs For example if Trace 1 is a time record it cannot be recalled into the Reference Display of an FFT measurement The PRNT command prints the screen using the selected Printer Type and Destination All o
269. d The parameter 1 selects Max 0 Min 1 or Mean 2 This command is only valid if the Marker Mode for display d is Normal MWID d i The MWID command sets queries the Normal Marker Width of display d The parameter 1 selects Spot 0 1 2 division 1 or 1 division 2 This command is only valid if the Marker Mode for display d is Normal MREL d i The MREL command sets queries the Normal Marker Relative Mode of display d The parameter 1 selects Off 0 Relative to Offset 1 Relative to Reference Display 2 or Relative to Other Display 3 This command is only valid if the Marker Mode for display d is Normal MROX d x The MROX command sets queries the X Offset for the Normal Marker of display d The parameter x is a real number in display units This command is only valid if the Marker Mode for display d is Normal MROY 7 d x The MROY command sets queries the Y Offset for the Normal Marker of display d The parameter x is a real number in display units This command is only valid if the Marker Mode for display d is Normal MXRL d i The MXRL command sets queries the X Rel Mode for the Normal Marker of display d The parameter 1 selects Absolute Off or Relative On This command is only valid if the Marker Mode for display d is Normal MRON d The MRON command sets toggles the Normal Marker between Marker Rel Off and Marker Rel to Offset This is similar to the Mar
270. d 2 is not allowed This command should always be sent before defining any limit segments Limit segments may not be defined or edited after the Measurement or Measurement Group is changed until LCLR clears the existing segments LMAX d i The LMAX command sets queries the Last Limit Segment Number for display d The parameter 1 is a last limit segment number from 0 to 199 The set command is not valid for d 2 both displays The LMAX command queries the last limit segment number The LMAX d i command sets the last limit segment number to 1 If i is greater than the current last limit segment number new entries are created up to line 1 These entries simply follow the last limit segment If the value of 1 is less than the last line number an error is returned To remove entries from the table use the LDLT command This command also sets Limit Segments to Show LSEG 7 d i j xO yO x1 y1 The LSEG command sets queries the Endpoints and Type of limit segment 1 for display d The parameter 1 selects the limit segment number from 0 to the last segment If 1 exceeds the last segment number as set by LMAX an error is reported SR785 Dynamic Signal Analyzer 5 88 Limit Test Commands LDLT d i LSFT d x The segments are defined separately for each display The set command is not valid for d 2 both displays The parameter j selects Upper 0 or Lower 1 limit The parameters xO and yO are the coordinat
271. d at the back of the waterfall lt Record to Trace gt saves the record selected by the marker to a Trace Use the knob without Alt to move the marker along the X axis within a record lt Slice to Trace gt saves a slice to a Trace A slice is the history of a single X position data at the marker X position from all stored records The Waterfall Display for each display can be selected separately This entry field can be linked to both displays by using the Link key Command WDSP d 1 Select the type of Waterfall Storage Off Continuous One Shot The two displays always have the same Waterfall Storage mode Waterfall storage is not available for Swept Sine measurements Storage Off does not store any measurements to waterfall memory and changes the Waterfall Display to a graphical scroll only Continuous storage adds measurement records to the waterfall memory until Pause Cont is pressed The last Total Count number of records are saved in memory and may be displayed One shot stores the Total Count number of measurement records and pauses the waterfall storage The first Total Count number of records are saved in memory Pause the measurements to scroll through the waterfall memory Waterfall memory must be allocated before waterfall storage may be used Linear Averaging If Waterfall Storage is On the waterfall buffer only stores the completed linear averages not each individual measurement Each time the
272. d below 0 Hz or above the FFT Base Frequency then the Start and End frequencies will be adjusted The two displays can have different Linewidths if the Analyzer Configuration is set to Independent Channels In this configuration no two channel measurements are allowed frequency response cross spectrum etc but the entry field can be linked or unlinked using the Link key If Analyzer Configuration is set to Dual Channel the field is automatically linked to both displays Command FSPN d f Acquisition Time Full Span Select the Acquisition Time of the active display The Acquisition Time is the time record length for the FFT FFT Resolution Span A numerically entered value is rounded to the nearest allowable Acquisition Time Changing the Acquisition Time will change the Span FFT Resolution Acquisition Time and Linewidth 1 Acquisition Time The Linewidth and Acquisition time are other ways to change the Span If the new frequency Span would extend below 0 Hz or above the FFT Base Frequency then the Start and End frequencies will be adjusted The two displays can have different Acquisition Times if the Analyzer Configuration 1s set to Independent Channels In this configuration no two channel measurements are allowed frequency response cross spectrum etc but the entry field can be linked or unlinked using the Link key If Analyzer Configuration is set to Dual Channel the field is automatically linked to both disp
273. d have a feeling for Octave measurements and how they are setup Capture 1 27 Capture This example investigates the Capture buffer using FFT measurements You will use the SR785 to capture a signal and then analyze it from memory Press System Press lt Preset gt Press Enter to confirm Preset Connect the Source Output to the Channel 1 A Input Press Source Press lt Sine gt Press lt Frequency 1 gt Press 1 0 2 4 select kHz with the knob and press Enter Press lt On gt Press Capture Press lt Allocate Memory gt Press lt Waterfall Memory gt Display the System menu Preset returns the unit to its default settings Preset requires confirmation to prevent accidental reset Wait until the self tests are completed Setup to analyze the source output Select the Source menu Choose Sine output Adjust the output Frequency Enter 1 024 kHz for the Frequency Enter the value with the numeric entry keys Select the units with the knob Enter the new value with the Enter key Turn the source on Select the Capture menu The data memory is allocated between Capture Waterfall Order Track and Arbitrary Waveform storage Memory is allocated in blocks Each block can store 2 kPoints The total number of blocks available is displayed in the lt Total Available gt menu box This number is for display only it cannot be changed from the menu Larger memory options up to
274. d in the form X0 Y0O X1 Y1 X2 Y2 Xn Yn If where Xn Yn are the last entries in the table index n Any table entry not within the current measurement span returns the value 1 0E 34 for both X and Y The DTRD d i command queries the X and Y values for line 1 only The data is returned X Y If If the table entry is not within the current measurement span the values 1 0E 34 are returned for both X and Y This command is valid only if the Data Table for display d is On and display d is the active display Use the ACTD command to select the active display Only the Data Table of the active display may be edited or queried SR785 Dynamic Signal Analyzer Limit Test Commands 5 87 Limit Test Commands LSON 7 d i The LSON command sets queries the Limit Segments Display for display d The parameter 1 selects Hide 0 or Show 1 LTST d i The LTST command sets queries the Limit Testing for display d The parameter 1 selects Off O or On 1 LALM 7 d i The LALM command sets queries the Limit Fail Alarm for display d The parameter 1 selects Off O or On 1 LFAL d The LFAL command queries the result of the most recently completed limit test of display d If the test passed O is returned If the test failed 1 is returned LCLR d The LCLR command clears the Limit Segments for display d All defined limit segments for display d are erased The limits for each display are cleared separately
275. d new records are added at the top back The display may not scroll fast enough to show every stored record in real time When the measurement is paused the display is redrawn with either the newest record in back normal or the oldest record in back reversed When paused every stored record which is visible in the display is shown The marker can access the data in any stored record and scroll the display through the entire waterfall buffer Waterfall display WITHOUT storage is simply a graphical display scrolling The marker is constrained to the most recent record Older records are only shown graphically their data has not been saved and may not be accessed in any way In this case the display updates and scrolls as quickly as possible The Waterfall menu configures both waterfall storage and display Waterfall displays are not available for Nyquist or Nichols Views or for Swept Sine measurements Waterfall Storage Waterfall records are stored in waterfall memory This memory is not retained when the power is off Use the Waterfall lt Memory Allocation gt menu to allocate memory between the capture buffer waterfall storage and the arbitrary source waveform Waterfall memory must be allocated before waterfall storage may be used SR785 Dynamic Signal Analyzer Waterfall Display 2 31 The SR785 can store waterfall measurements in the waterfall buffer in one of two ways depending on the setting of the lt Save Option gt softk
276. d relative to the trigger Power Spectrum The Linear Spectrum in the order measurement group is similar to the Power Spectrum measurment in the FFT measurement group except that the x axis is calibrated in orders instead of absolute frequency The power spectrum gives the power present in each spectral order no phase information is included Time Record The time record is not similar to the time record measurement in the FFT measurement groups Time Records in the fft group are measurements of the input signal at fixed time intervals In the Order measurement group time records are measurements of the input signal at fixed angular positions around the shaft Since the analyzer only samples the input at fixed time intervals the order time record must be calculated by combining the fixed interval sampling with information from the tachometer about where the shaft position was relative to the sampled data The x axis of the order time record is calibrated in revolutions the resolution and number of resolutions in the time record are determined from the Maximum Order and Delta Order softkeys Windowed Time Record The windowed time record shows the Time Record multiplied by the Window function Remember that in the order measurement group you should use the uniform window if the expected harmonics are integer multiples orders of the rotating machine speed SR785 Dynamic Signal Analyzer Order Analysis 2 57 RPM Profile The RPM profile
277. d the problem orders we can move to the second type of measurement where the amplitude of a specific order or set of orders is recorded as the machine speed is changed We may want to ramp the machine from startup to operating speed and track the behavior of the third order vibration The SR785 can perform both types of measurements by selecting a value for the Freq lt Tracking gt softkey When tracking is turned on the analyzer records the amplitude for each spectral order as a function of RPM Using the Freq lt Track Setup gt submenu a 2 dimensional plot of the amplitude of any order of either input channel can be generated Using RPM trigger arming the analyzer can be configured so that the tracked data points are acquired at fixed RPM intervals The tracking feature uses the SR785 s Tracking Waterfall memory Thus when tracking is turned on waterfall storage of spectra is not allowed If waterfall storage is necessary turn tracking off Order Measurement Setup Choose the Maximum RPM Minimum RPM Maximum Order and Delta Order to setup an Order measurement Maximum RPM affects the available range of Max Order the higher the selected Maximum RPM the lower the maximum order that can be selected The realtionship can be summarized as max Max RPM 60 e 40 000 Max Order Minimum Order does not affect the measurement at all 1t merely sets a default scaling for measurements whose x axis 1s calbrated in RPM such as Order Track
278. d units The available spans depend upon the FFT Base Frequency The set command changes the FFT Span to the available span closest to f The query command always returns the span in Hz This command is valid only when the Measurement Group is FFT or Correlation The set command requires display d to be Live FLIN d i The FLIN command sets queries the Resolution of display d when the measuremen group is FFT or Correlation The parameter 1 selects 100 0 200 1 400 2 or 800 3 lines FLIN does not change the Span This command is valid only when the Measurement Group is FFT or Correlation The set command requires display d to be Live FBAS 7 d i The FBAS command sets queries the FFT Base Frequency of display d The parameter 1 selects 100 0 kHz 0 or 102 4 kHz 1 To set the Base Frequency d must be 2 both displays There is only one Base Frequency for both displays Changing the Base Frequency will affect all of the FFT and source frequency parameters This command is valid only when the Measurement Group is FFT Correlation or Time Histogram The set command requires at least one display to be Live FSTR d f lt kHz Hz mHz wHz gt The FSTR command sets queries the FFT Start frequency of display d The parameter f is a frequency real number of the specified units Values of f which would cause the span to exceed the 0 to 102 4 100 0 kHz range cause an error This command is valid onl
279. dBV 10V SRT785 Ocap L10 120 C1 TXT Converting Files to Arbitrary Waveform Format 78C Usage SRT785 Oarb options infile outfile Allowed Input File Types ASCH Default Output File Extension 78C Arbitrary Waveform output options Bn Base Frequency n 0 for 100kHz n 1 for 102 4 kHz default Ln Length of Buffer n is number of kPoints default L2 Nn Sampling Frequency Sampling frequency 256 kHz 2 or 262kHz 2 depending on the base frequency Default is n 0 The input values are ASCII floating point numbers with a range of 1 0 These values represent the source voltage when the arbitrary source is on with an amplitude of 100 If the number of values found in the input file 1s less than the number of points specified with the Ln option the output file is zero padded SR785 Dynamic Signal Analyzer
280. dance Statistics 1 63 Continue the live measurement Note that the live measurement data rarely exceeds the reference graph Pause the live measurement again Change the Exceedance Percentage Enter 99 This level is exceeded 99 of the time The exceedance results are stored in Trace 2 Trace to Ref is an alternate function The alternate key functions are labeled below each key in this case the Link key Trace to Ref copies the data in a trace to the reference graph of the active display The reference graph is shown in half intensity In this case the reference graph is the level of each octave bin which is exceeded 99 of the time Loo This concludes this example Exceedance is a common measurement for environmental noise levels such as airports or highways Change the octave integration time and waterfall storage interval to optimize the measurement rate Use a larger waterfall buffer up to 2000 measurements per display for long monitoring times 1 64 Exceedance Statistics Chapter 2 Analyzer Basics In This Chapter Measurement Groups Analyzer Configuration What is an FFT Why Look At A Signal s Spectrum The FFT Analyzer Advantages And Limitations FFT Frequency Spans Full Span Spans Less Than Full Span Baseband Spans Starting the Span Above DC FFT Time Record Baseband Time Records Heterodyned Time Records The Time Record Display Why Use The Time Record Watch Out For Windowing FFT Win
281. data is available on the display The accumulation of the statistical quantities continues even when the Marker Statistics menu is not displayed The MSRS command resets and starts the accumulation of marker statistics The various quantities are reset to zero and the accumulation of marker statistics begins The MSAA command queries Max for the Display A Marker The MSIA command queries Min for the Display A Marker The MSEA command queries Mean for the Display A Marker The MSSA command queries Standard Deviation for the Display A Marker The MSAB command queries Max for the Display B Marker The MSIB command queries Min for the Display B Marker The MSEB command queries Mean for the Display B Marker The MSSB command queries Standard Deviation for the Display B Marker SR785 Dynamic Signal Analyzer 5 90 Exceedance Statistics Commands Exceedance Statistics Commands ESTR 7 i ESTP i EPCT 7 i EXCE d i The ESTR command sets queries the Exceedance Start Index for both displays The parameter 1 is a waterfall index 0 This command is not valid when the measurement group is swept sine The ESTP command sets queries the Exceedance Stop Index for both displays The parameter 1 is a waterfall index 0 Remember the records are numbered starting from 0 The last record is the number of stored records minus one The exceedance calculation can not proceed 1f the stop index is
282. de gt Use the knob to select One Shot and press Enter Press Start Reset Press lt Manual Trigger gt SR785 Dynamic Signal Analyzer Choose Start This means that a new measurement is started as soon as the previous average is complete In this case a new measurement is made every 8 ms regardless of triggering If we choose One Lin Avg then a measurement is made only when triggered Change the Power Bin Choose L Leq as the sound level bin Leq is a standard broad band sound measurement When we start the next measurement the result will be displayed as the last bin in the display and labeled E Select the Trigger menu Change the Trigger Source Choose Manual trigger We will start our measurement with a button press We could also use an external trigger Triggering on the signal itself requires the use of an external signal source Change the Triggered Source Mode This determines whether the source triggers only once on the first trigger after Start Reset or on every trigger Choose One Shot to trigger the noise burst only once at the start of the measurement Start Reset starts the measurement Since the measurement is triggered not Free Run nothing happens until the first trigger is received lt Manual Trigger gt supplies the first trigger The source outputs a single noise burst Trigd Source Mode 0ne Shot The display starts a continuous stream of octave measurements each linear
283. der The set command requires display d to be Live and the Force Exponential window to be selected FWTC d x The FWTC command sets queries the FFT Expo Window Time Constant for display d The parameter x is a percentage of the time record This command is valid only when the Measurement Group is FFT or Order The set command requires display d to be Live and the Force Exponential window to be selected TRWI i The TRWI command copies the real part of stored Trace 1 to the User window Trace 1 must contain stored data This command is valid only when the Measurement Group is FFT or Order WITR d i The WITR copies the window of display d to the real part of Trace 1 Trace 1 will have a length of 2048 points This command is valid only when the Measurement Group is FFT or Order WSYM d i The WSYM sets queries User Window Form for display d The parameter 1 selects Non Symmetric 0 or Symmetric 1 This command is valid only when the Measurement Group is FFT or Order and the window of display d is User SR785 Dynamic Signal Analyzer 5 80 Waterfall Commands Waterfall Commands WDSP 7 d i The WDSP command sets queries the Waterfall Display Mode for display d The parameter 1 selects Normal 0 or Waterfall 1 This command is not valid when the Measurement Group is Swept Sine WSTO d i The WSTO command sets queries the Waterfall Storage for display d The parameter 1 selects Off 0
284. disabled for the Octave Analysis Swept Sine Order and Time Histogram Measurement Groups The logarithmic scale does not affect the frequency bins of the FFT measurement The resolution is still linear The points are simply graphed with a logarithmic axis DC bins are not shown The two displays can be scaled differently This entry field can be linked to both displays using the Link key Command XAXS 7 d 1 RPM Frequency Grid Select the Frequency Axis Units for the active display Off On RPM frequency is only available for FFT measurements with frequency as the X axis If RPM Frequency is On frequency values will be converted to RPM If RPM Frequency is Off the values are displayed in Hz Command RPMF 1 Select the Grid for the active display On Off The grid is the set of dotted lines on the display which mark each scale division SR785 Dynamic Signal Analyzer 4 48 Display Options Menu The two displays have their own Grid This entry field can be linked to both displays using the Link key Command GRID d 1 Grid Div Select the number of Grid Divisions for the active display 8 10 12 15 Changing the number of Grid Divisions changes the vertical scaling Y div and leaves the display references unchanged If the view is polar the horizontal scaling X div is also changed Change the scaling in the Display Setup menu The two displays have their own number of Grid Divisions T
285. display B since Marker Stats was turned On or Reset This min value is updated whenever new data is available for Display B and does not update if Display B is not visible Command MSIB Mean Display B This menu box displays the mean value of the marker Y value for display B since Marker Stats was turned On or Reset This mean value is updated whenever new data is available for Display B and does not update if Display B is not visible Command MSEB Sid Dev Display B This menu box displays the standard deviation of the marker Y value for display B since Marker Stats was turned On or Reset This standard deviation is updated whenever new data is available for Display B and does not update if Display B is not visible Command MSSB SR785 Dynamic Signal Analyzer Exceedance Statistics Menu 4 159 Exceedance Statistics Menu Start Index Stop Index The Exceedance Statistics menu calculates exceedance centile statistics from Octave and FFT measurements stored in the waterfall buffer Exceedence calculation is only available when the waterfall buffer has been saved using the Active Measurement Only Save Option Exceedance Start Index Stop Index 100 ExceedancePct a0 Return Set the starting record in the waterfall buffer for the calculation of L exceedance centile The analysis starts at the start index and includes all records through the stop index Index 0 is the most recent record
286. display d The parameter 1 selects none 0 Ifrom2 1 or 2from1 2 This command is only valid if the Marker Mode for display d is Band BRAM d i The BRAM command queries the Band Ratio Mode for display d The parameter 1 selects 2 1 0 or 2 1 2 1 This command is only valid if the Marker Mode for display d is Band BPWR d i The BPWR command queries the Band Power for display d The parameter 1 selects Upper 0 or Lower 1 band power This command is only valid if the Marker Mode for display d is Band BRAT d i The BPWR command queries the Band Ratio for display d The parameter 1 selects percent 0 or dB 1 band ratio This command is only valid if the Marker Mode for display d is Band SR785 Dynamic Signal Analyzer 5 52 Marker Commands Marker Commands Frequency Damping MMCA d The MMCA command queries the Frequency Damping marker result The query returns two values in the form f g where f is the resonant frequency and g is the damping factor This command is only valid if the Marker Mode for display d is Frequency Damping SR785 Dynamic Signal Analyzer Source Commands 5 53 Source Commands SRCO i The SRCO command sets queries the Source On or Off The parameter 1 selects Off 0 or On 1 This command is not valid when the Measurement Group is Swept Sine STYP 7 i The STYP command sets queries the Source Type The parameter 1 selects Sine 0 Chirp 1 Noise 2 o
287. display must be paused or done with a 1 shot waterfall Waterfall display is not required to be on The save option must be set to Active Measurement Only The result is stored in a data trace and has the same measurement type as the waterfall measurements To view the result recall the trace to a display or reference graph Command EXCE d 1 SR785 Dynamic Signal Analyzer Curve Fit Menu 4 161 Curve Fit Menu Start Fit The Curve Fit Menu calculates best fit curve parameters from a measured frequency response function Synthesis of user entered curve parameters is also provided Curve Fit Start Fit Abort Fit Synthesize TbI 1 Synthesize TbI 2 Fit setup Return When start fit is pressed the analyzer begins the curve fitting process The SR785 will determine a fit to the data in the active display which must be part of the FFT or swept sine measurement group When determining the fit the analyzer uses the fit region and weighting specified in the fit setup submenu After the fit is determined the fit parameters are placed in curve Table 1 The curve in table 1 is then synthesized into whichever trace is specified by the table The non active display is taken off line and the trace with the fit data is displayed The fit parameters include the frequency scaling specified in curve table 1 For instance if the frequency scaling is set to 1000 a pole at 1 kHz will show up as a term s 1 in the pole zero display Com
288. displays but does not show the exact frequency of a bin For example for a 400 line FFT on 100 0 kHz base with a span of 97 66 Hz the first frequency bin is shown as 244 140625 mHz Exact Bin or 244 1 mHz Rounded The second bin is 488 28125 mHz Exact Bin and 488 3 mHz Rounded Command FFMT 1 SR785 Dynamic Signal Analyzer 4 198 System Preferences Menu Node Info Prompt Turns the node information prompt when saving files on or off Modal analysis programs require that a given spectrum cross spectrum or frequency response function transfer function be associated with information regarding the nodal degrees of freedom DOF When Node Info Prompt is set on the SR785 allows enty of DOF parameters when saving data using Trace to Disk or Display to Disk When the lt Trace to Disk gt or lt Display to Disk gt is initiated using a remote command the node info prompt will not be displayed however the information entered in the Node Info menu will still be saved with the disk file as long as the lt Node Info Prompt gt softkey is on The nodal DOF information is saved with the disk file and is used when translating SR785 files to Universal File Format UFF and other file formats used by popular modal analysis programs Command SVNI 1 SR785 Dynamic Signal Analyzer System Date Time Menu 4 199 System Date Time Menu 01 17 95 Return Time Set the System Time hh mm ss The System Time is ente
289. dowing In The Frequency Domain Uniform Hanning Flattop BMH Kaiser Force Exponential User Defined FFT Measurements Definitions FFT Spectrum Power Spectrum Time Record Windowed Time Record Orbit Cross Spectrum Frequency response Coherence Capture Buffer 2 4 2 6 2 6 2 6 2 7 2 8 2 8 2 8 2 9 2 9 2 10 2 10 2 10 2 11 2 11 2 11 2 12 2 12 2 12 2 13 2 13 2 13 2 14 2 14 2 14 2 16 2 16 2 16 2 16 2 17 2 17 2 18 2 18 2 18 2 19 2 19 2 1 User Function 2 20 Views 2 21 Log Magnitude 2 21 Linear Magnitude 2 21 Magnitude 2 21 Real Part 2 21 Imaginary Part 2 21 Phase 2 21 Unwrapped Phase 2 22 Nyquist Plot 2 23 Nichols Plot 2 23 FFT Averaging 2 24 RMS Averaging 2 24 Vector Averaging 2 24 Peak Hold Averaging 2 25 Linear Weighting 2 25 Waterfall Storage 2 25 Exponential Weighting 2 25 Real Time Bandwidth and Overlap 2 27 What is Real Time Bandwidth 2 27 Averaging Speed 2 27 Overlap Processing 2 27 Time Record Increment 2 28 Settling 2 28 Vector Averaging 2 29 Triggering 2 29 Waterfall Display 2 30 What is a Waterfall 2 30 Waterfall Storage 2 30 Waterfall Display 2 31 Capture Buffer 2 33 Input Sampling 2 33 Capture Fill 2 33 Capture Playback 2 34 Capture as the Arbitrary Source 2 35 The Source 2 36 Sine 2 36 SR78S5 Network Signal Analyzer 2 2 Analyzer Basics Two Tone Chirp Noise Arbitrary Windowing Source Trigger External Trigger Correlation Analysis What is Correl
290. e Band Ratio Chirp Amplitude Chirp Burst Percentage Capture Channels Upload Capture Buffer Capture Length Capture Mode Continue Capture Auto Pan Download Capture Buffer Capture Rate Source Display Capture Stop Capture Start D DBIN d j DBMR x DCLR d DDLT d i DDXW d x DELD DELF DFMT i DINS d i j DISP d i DMAX d i DNAM s DREFF d i DSPB d j DSPE i j DSPN d DSPS i DSPY d j DTBL d i DTRD d i DUMP DUMP E EDLY i x EFIT d EFSC 2 i x EGAN i x ETRC i j ENPL 2 i ENZE i EPCT i EPLY 2 i j k x EPOL 2 i j x y ERES i j x y ERNG 2 d i j ERRE i j ERRS i ESTP i ESTR i ESYN i d ETRC i j EUIL d i EUIM d i EUIU d s EU1V d x EU2L i EU2M i EU2U s EU2V x EWTT 2 i EWTU i EXCE d i 5 108 5 40 5 86 5 85 5 44 5 96 5 96 5 43 5 85 5 43 5 85 5 96 5 104 5 107 5 122 5 107 5 122 5 107 5 85 5 86 5 103 5 97 5 91 5 91 5 91 5 92 5 92 5 91 5 91 5 90 5 92 5 92 5 92 5 91 5 121 5 121 5 90 5 90 5 91 5 92 5 62 5 62 5 62 5 62 5 63 5 62 5 63 5 63 5 91 5 91 5 90 Index of Commands 5 13 Read Display d Bin Freq or Time dBm Reference Impedance Data Table Clear Data Table Delete d dx Window Delete Directory Delete File Display Format Data
291. e Marker Stats was turned On or Reset This max value is updated whenever new data is available for Display A and does not update if Display A is not visible Command MSAA Min Display A This menu box displays the minimum value of the marker Y value for display A since Marker Stats was turned On or Reset This min value is updated whenever new data is available for Display A and does not update if Display A is not visible Command MSIA Mean Display A This menu box displays the mean value of the marker Y value for display A since Marker Stats was turned On or Reset This mean value is updated whenever new data is available for Display A and does not update if Display A is not visible Command MSEA Std Dev Display A This menu box displays the standard deviation of the marker Y value for display A since Marker Stats was turned On or Reset This standard deviation is updated whenever new data is available for Display A and does not update if Display A is not visible Command MSSA Max Display B This menu box displays the maximum value of the marker Y value for display B since Marker Stats was turned On or Reset SR785 Dynamic Signal Analyzer 4 158 Marker Statistics Menu This max value is updated whenever new data is available for Display B and does not update if Display B is not visible Command MSAB Min Display B This menu box displays the minimum value of the marker Y value for
292. e The buffer will take 7 03 seconds to fill Since the Capture Mode is 1 Shot the capture stops once the buffer is full During this time Capture indicator is highlighted and the Capture Progress indicator shows how much of the buffer has been filled up to 100 After capture is complete the Capture indicator shows Cap Data indicating that the Capture buffer contains data Make DisplayB bottom the active display Select the Display Setup menu Change the measurement of DisplayB Choose Capturel to show the contents of the Chl Capture buffer Press lt Zoom gt Press 1 1 and Enter Unplug the signal from the Ch1 input Press Input Press lt Input Source gt Use the knob to select Playback and press Enter Press lt Playback Config gt Press lt Playback Length gt Press 1 8 0 0 and Enter Press lt Playback Mode gt Use the knob to select Circular and press Enter Capture 1 29 There are far too many points in the buffer to graph each one The graph shows the envelope of the data in this case Zoom in to show individual points Expand below the graph indicates that the graph has been graphically zoomed and does not show all of the data along the X axis Enter a zoom factor of 11 2 The display now shows the signal sine wave clearly The signal should disappear from the spectrum in DisplayA Select the Input menu Change the Input Source to measur
293. e DSPE i command sets the Display status enable register to the decimal value 1 0 65535 The DSPE 1 j command sets bit 1 0 15 to j O or 1 The DSPE command queries the value of the Display status enable register The DSPE 1 command queries the value 0 or 1 of bit 1 0 15 When a bit becomes set in BOTH the Display status word AND the Display status enable register bit 1 DISP of the Serial Poll status word is set This causes an SRQ if bit 1 in the Serial Poll enable register is set To clear a bit in the Display status word use DSPS The DSPS command queries the value of the Display status word The value is returned as a decimal number from 0 to 65535 The DSPS 1 command queries the value 0 or 1 of bit 1 0 15 DSPS clears the entire word while DSPS i clears just bit 1 The INPE 1 command sets the Input status enable register to the decimal value 1 0 65535 The INPE 1 jJ command sets bit 1 0 15 to j O or 1 The INPE command queries the value of the Input status enable register The INPE i command queries the value 0 or 1 of bit 1 0 15 When a bit becomes set in BOTH the Input status word AND the Input status enable register bit 2 INPT of the Serial Poll status word is set This causes an SRQ if bit 2 in the Serial Poll enable register is set To clear a bit in the Input status word use INPS The INPS command queries the value of the Input status word The value is returned as a decimal number from
294. e Display Setup menu Change the Measurement Group Choose the Octave group Both displays are now making Octave Analysis measurements Select the Source menu Turn the Source On Choose Noise as the source type Octave measurements are generally used to measure noise Change the type of noise Choose Pink noise Pink noise rolls off at 3dB per octave This maintains equal power per octave band and yields a flat octave spectrum 5 Press Average Press lt Power Bin gt Use the knob to select L and press Enter Press Auto Scale A 6 Press Waterfall Press lt Storage gt Use the knob to select One Shot and press Enter Press lt Total Count gt Press 1 0 0 Enter Press lt Save Option gt Use the knob to select Active Meas Only and press Enter Exceedance Statistics 1 61 Select the Average menu Note that this menu is changed in Octave group We will leave the averaging at its default 100 ms exponential time Change the Power Bin Choose L Leq as the sound level bin Leq is a standard broad band sound measurement The result is displayed as the last bin in the display and is labeled L Scale DisplayA to show the entire range of the data Select the Waterfall menu L is calculated from measurements stored in the waterfall buffer Select waterfall Storage Choose One Shot to fill the waterfall buffer once and stop Change the number of measurements to store in t
295. e I2AF command sets queries the Ch2 Anti Aliasing Filter Off On The parameter 1 selects Off O or On 1 The I2AW command sets queries the Ch2 A Weighting Filter Off On The parameter 1 selects Off O or On 1 The IAOQM command sets queries the Input Auto Offset Off On The parameter i selects Off 0 or On 1 SR785 Dynamic Signal Analyzer 5 62 Input Commands Transducer Parameter Commands EU1M d i The EUI1M command sets queries the Chl Engineering Units Mode for display d The parameter 1 selects Off 0 or On 1 The set command requires d 2 both displays EU1L d i The EU1L command sets queries the Chl Engineering Units Label for display d The set command requires d 2 both displays The parameter 1 selects the unit label i Label i Label 0 m s 8 kg l m s 9 lbs 2 m 10 N 3 in s 11 dyne 4 in s 12 Pas 5 in 13 bar 6 mil 14 USER 7 g EU1V d x The EU1V command sets queries the Chl Engineering Units per Volt scale for display d The set command requires d 2 both displays The parameter x is real number of EU Volt EU s per Volt EU1U d s The EU1U command sets queries the Chl User Label for display d The set command requires d 2 both displays The string s is the user label TDIC d i The TD2C command sets queries the Chl Transducer Conversion for display d The set command requires d 2 both displays The parameter 1 selects the units
296. e Memory sets the limit for the Capture Length Capture memory must be allocated before the capture buffer may be used SR785 Dynamic Signal Analyzer 4 140 Waterfall Menu Waterfall Order Memory Allocates memory blocks for waterfall storage and tracking orders Waterfall memory must be allocated before waterfall displays may be used Arb Memory Allocates memory blocks for the Arbitrary Source waveform The Arbitrary Source can also use the capture buffer as the output waveform Clear Allocation Clears the existing memory allocations in this menu Confirm Allocation Places the memory allocations in this menu into effect Exiting this menu without pressing lt Confirm Allocation gt will cancel any adjustments made in this menu Command MALC 1 j k More Display the More Waterfall menu Press lt Return gt or Waterfall for the main Waterfall menu Waterfall Trace Height Fast Angles Threshold 0 Hidden Lines Invisible Paused Drawing Normal Record to Trace Return Trace Height Set the Waterfall Trace Height for the active display 20 80 The Trace Height specifies the percentage of the display height occupied by the Y axis of a single record The View Count and the Trace Height determine the available scroll Angles Each display has its own Waterfall Trace Height This entry field can be linked to both displays by using the Link key Command WHIT d 1 SR785 Dynamic Signal
297. e active display Expand is shown in the display whenever it is expanded Expanding the X axis is a convenient way of examining closely spaced details in a display without changing the measurement Expansion is about the Marker Position whenever possible Use Pan to translate a zoomed display Zoom is not allowed when the X axis is logarithmic or when the View is polar Nyquist or Nichols plot The two displays can have different Zoom values when expanded This entry field can be linked to both displays using the Link key Command XZOM d 1 SR785 Dynamic Signal Analyzer 4 46 Display Options Menu Display Options Menu Display Format The Display Options menu configures the active display format Display Options Display Live Format Dual X Axis Linear RPM frequency Off Grid Grid Div Nyquist Grid Rectangular Phase Suppress 0 0000e 000 didx window 0 5 Select the Display Update of the active display Live Off Line A Live display updates continuously to show live measurement results as long as the measurement is not paused An Off Line display does not update The display shows a frozen measurement result or trace A display becomes Off Line whenever a trace is recalled to the display from disk or memory Since an Off Line display is showing old data its Measurement Window Frequency Span and Averaging may not be modified Only display related parameters su
298. e d dx operator requires a smoothing aperture or window GrpDly is the group delay operator Group delay is simply d6 dw Use Display Options lt d dx Window gt to set the aperture This operator yields valid results for any complex operand which has a frequency x axis AWt is the A Weighting operator This filter is a software version of the input A Weight filter BWt and CWt are the software B Weighting and C Weighting operators The AWt BWt and CWt operators should only be used on operands with a frequency x axis All three filters conform to ANSI Standard S1 4 1983 Function String Move the cursor to the function equation window at the top of the screen Use the knob to move the highlighted cursor within the equation lt Delete gt will delete the highlighted term lt Operands gt and lt Operations gt will either insert or replace at the cursor Use lt Insert Replace gt to switch between insert and replace mode lt Backspace deletes the term before the cursor Insert Replace Toggle between insert and replace mode while editing a User Function equation If editing in insert mode Ins appears in the upper right corner of the edit window If editing in replace mode Rep appears SR785 Dynamic Signal Analyzer User Math Menu 4 129 When editing a User Function equation selecting lt Operands gt or lt Operations gt will insert or replace before the cursor location Delete
299. e decimal value 1 0 255 The SRE 1 j command sets bit 1 0 7 to j O or 1 The SRE command queries the value 0 255 of the serial poll enable register The SRE 1 command queries the value 0 or 1 of bit 1 0 7 When a bit becomes set in BOTH the Serial Poll status word AND the Serial Poll enable register an SRQ GPIB service request is generated The SRQ is cleared by performing a serial poll The bit in the Serial Poll status word which caused the SRQ must be cleared before this bit can cause another SRQ To clear this bit the condition which causes it to be set in the Serial Poll status word needs to be cleared For the INST DISP INPT IERR or ESB bits this is accomplished by clearing the enabled status bits in the Instrument Display Input Error or Standard Event status words by reading them The STB command queries the value of the Serial Poll status word The value is returned as a decimal number from 0 to 255 The STB 1 command queries the value 0 or 1 of bit 1 0 7 The value of bit 6 SRQ when read using STB returns 1 if a bit is set in BOTH the Serial Poll status word AND the Serial Poll enable register This is independent of serial polling and SRQ s Bit 6 is the SRQ bit only when serial polled STB has no effect on the value of the Serial Poll status word To clear a bit in the Serial Poll status the condition which causes it to be set must be cleared For the INST DISP INPT IERR or ESB bits
300. e feed pair For ASCII input the conversion utility expect values to be separated by any whitespace character with no leading header data Characters after the last expected data value are ignored SDF Files Standard Data Format or SDF is a file format supported by Hewlett Packard instruments and is designed to allow data sharing among various analyzers and external programs Many modal analysis programs for example accept SDF files The SR785 file conversion utilities can convert version 2 or 3 SDF files to SRS trace 78D files and can convert 78D files to SDF files Note that because of specific differences between HP analyzers and the SR785 it may not be possible to exactly convert all types of measurements Matlab MAT Files MATLAB is a popular program for doing mathematics and for the analysis of numeric data Although it easy to import ASCII data directly into MATLAB it is faster and more efficient to use the binary MAT File format The conversion utilities include the capability of directly converting a SR785 display file into a binary MAT File The MAT File format used by the conversion utilities is supported by MATLAB version 4 and version 5 Universal File Format The Universal File Format is a specification for an ASCII database capable of describing the geometry degree of freedom and measurement data used in structural analysis Most modal analysis programs are capable of importing measurement data formatted in Universa
301. e file name The volume label and sub directories are treated the same as actual files FREE The FREE query returns the number of bytes available on the disk SR785 Dynamic Signal Analyzer FRST FNXT FSAV d FRCLd SSAV SRCL i Disk Commands 5 95 The FRST query returns the first entry in the current directory The entire entry string is returned filename ext NNN m d y h m s where NNN file size m d y creation date and h m s creation time Use FRST to reset the catalog file pointer and then repeat FNXT to query the rest of the directory entries The FNXT query returns the next entry in the current directory The entire entry string is returned filename ext NNN m d y h m s where NNN file size m d y creation date and h m s creation time FNXT returns the string to signify that there are no more entries Use FRST to reset the catalog file pointer and then repeat FNXT to query the rest of the directory entries until is returned The FSAV command saves display d data to disk The file name is specified by FNAM and the directory is specified by FDIR The FRCL command recalls data from disk to display d Display d will be set Off Line The file name is specified by FNAM and the directory is specified by FDIR The SSAV command saves the instrument settings to disk The file name is specified by FNAM and the directory is specified by FDIR The SRCL command recalls the inst
302. e from the Capture buffer Choose Playback instead of the analog inputs The measurement now takes its input from the data stored in the Chl Capture buffer The signal reappears in the spectrum in DisplayA Only single channel measurements using Ch1 are allowed in this case there is no Ch2 data available Enter the playback configuration submenu You can choose to playback only a portion of the buffer if desired Choose the entire buffer by setting the Playback Length equal to the Capture Length Playback can be 1 Shot once through the buffer and stop or Circular repeat when finished Choose circular playback The indicator at the top of the display shows the current progress through the playback buffer uffer during playback DisplayB automatically pans to show the portion of the Capture buffer at the current playback position SR785 Dynamic Signal Analyzer 1 30 Capture 8 Use a BNC TEE to connect the source to both Ch1 and Ch2 A inputs Press Input Press lt Input Source gt Use the knob to select Analog and press Enter Press Display Setup Press lt Measurement gt Use the knob to select FFT ch2 and press Enter Press Capture Press lt Capture Channels gt Use the knob to select Ch1 Ch2 and press Enter Press lt Sampling Rate gt Use the knob to decrease the rate to 131 1 kHz and press Enter Press Start Capture 10 Disconnect the signal from both inputs
303. e generator setting and the distortion may be greater than normal Select the Source menu Choose Sine output Adjust the output Frequency Enter 1 024 kHz for the Frequency Enter the value with the numeric entry keys Select the units with the knob Enter the new value with the Enter key Turn the source on When the instrument is turned on the source is always off Setup the function generator for 1 024 kHz sine output SR785 Dynamic Signal Analyzer 1 8 Analyzing a Sine Wave 4 Press Auto Range Chl 5 Press Freq Press lt Span gt Use the knob to adjust the Span to 6 4 kHz and press Enter 6 Press Display Options Press lt Format gt Select Single with the knob and press Enter 7 Press Auto Scale A Press Marker Max 8 Use the knob to move the Marker around Take a look at some of the harmonics 9 Let s look at the fundamental only Press Span Down twice to decrease the Span to 1 6 kHz The Stop Frequency shown at the bottom right of the graph should read 1 6 kHz Press Marker Max SR785 Dynamic Signal Analyzer Let the analyzer automatically set the Input Range to agree with the signal either from the Source or function generator Note that the Chl Input Range readout at the top of the screen is displayed in inverse when Ch1 Auto Range is on Select the Frequency menu Adjust the FFT Span Set the Span to display the signal and its first few harmonics S
304. e histogram The x axis of the histogram represents the input amplitude range of the SR785 from negative full scale plus an overhead factor of 1 25 to positive full scale plus an overhead factor of 1 25 divided into a number of histogram bins given by the Bins softkey While the histogram is being acquired the input signal is sampled at intervals given by Sampling Time and the number of samples in each histogram bin is recorded If Repeat has been selected the histogram will restart automatically after finishing The x axis unit of the histogram measurement is volts indicating the voltage corresponding to each histogram bin while the y axis unit is counts indicating how many samples are in the bin If Engineering Units are turned on the x axis will be in the selected Engineering Units Time Record The Time Histogram Time Record measurement is similar to the FFT group time record The key difference is that while the FFT group time record 1s digitally filtered to eliminate aliases the Time Histogram group time record is unfiltered If the sample time is set to 1s the analyzer simply samples the input every second This allows examination of the input signal without the effects of additional filtering If desired the input anti aliasing filters can be turned off to present an even purer view of the input signal The number of samples in a time record is fixed at 1024 in the Time Histogram group Probability Density Function PDF
305. e limits only over the range of X values for which Limit Segments have been defined Segments do not have to cover the entire display span or connect with each other Only segments or the portions of segments within the measurement span are tested Limits outside the measurement span are ignored The test result is shown in the display to the left of the graph An audible alarm may be sounded when a test fails Display the Marker Statistics menu The Marker Statistics menu displays various statistics about the marker Y values including Mean Max Min and Standard Deviation When Marker Statistics are On the various statistical quantities are updated whenever new data is available on the display The accumulation of the statistical quantities continues even when this menu is not displayed Return to this menu to see the latest statistical values Exceedance Stats Curve Fit Display the Exceedance Statistics menu This menu is used to calculate L exceedance centile from Octave or FFT measurements stored in the waterfall buffer The calculation of L requires that the active display have records stored in the waterfall buffer The display must be paused or done with a 1 shot waterfall Waterfall display is not required to be on The save option must be set to Active Measurement Only to calcucalte exceedance L is the amplitude at each bin which is exceeded by n of the records in the waterfall L is a large amplitude exceeded only 1
306. e output file Separate fields with spaces default Separate fields with commas Separate fields with tabs Append to output file uff and ASCII outputs only 78D and 78W input files Specify Output Columns default is Cx v x X axis values v view shown when file was saved mag magnitude m2 magnitude squared r real part 1 imaginary part p phase u unwrapped phase Specify unit choices not all choices apply to all views pk rms pk or pp rms units peak units or peak to peak dB lin dB dBm dBSpl lin linear units deg deg rad degrees or radians Additional Options 78W input files only Wch Sn Rn Examples Specify display ch A or B Specify starting trace in waterfall buffer 0 is first trace Specify number of traces to extract 1 means extract to end of buffer default Convert the files DATAO 78D through DATA9 78D to ASCH Show the x axis values and the real and imaginary parts of the y values in the output files using rms values SRT785 Oasc Urms Cx r i DATA 78D Convert the 10th through 15th waterfall traces in WATER 78W to an ASCII file with magnitude squared data values only SRT785 Oasc S10 R6 Cmag2 WATER 78W An example of a 78D file converted with the default program options is shown below SR785 Dynamic Signal Analyzer Input File SRSO0O1 78D Measure Group FFT Measurement FFT 1 Num of extracted Points 401 Start Freq 0 Hz Span 102 4 kH
307. e record Poll the NEWA and NEWB New Data status bits in the Display Status word to determine when each time record has been acquired After accepting or rejecting the time record the display reverts back to showing the actual measurement This change does not set NEWA or NEWB but occurs upon receipt of the accept or reject command or after a Preview Time This command is valid only when the Measurement Group is FFT This command has no effect unless the previewed time records are displayed The PAVR command rejects the previewed time record The averages of both displays ignores the previewed time record Poll the NEWA and NEWB New Data status bits in the Display Status word to determine when each time record has been acquired After accepting or rejecting the time record the display reverts back to showing the actual measurement SR785 Dynamic Signal Analyzer 5 70 Average Commands This change does not set NEWA or NEWB but occurs upon receipt of the accept or reject command or after a Preview Time This command is valid only when the Measurement Group is FFT This command has no effect unless the previewed time records are displayed SR785 Dynamic Signal Analyzer Average Commands 5 71 Average Commands Octave OTYP d i The OTYP command sets queries the Octave Averaging Type for display d The parameter 1 selects Linear Time 0 Exponential Time 1 Peak Hold 2 or Equal Confidence 3 For 1 Channel
308. e rms averaged vector averaged peak hold averaged or instantaneous not averaged frequency response by adjusting the lt Display Avg gt softkey there s no need to acquire new data to look at a different averaging type You can control whether the SR785 calculates averaged quantities for measurements with the lt Compute Avgs gt Softkey If lt Compute Avgs gt is set to Yes the SR785 will compute averages for all measurements If lt Compute Avgs gt is No the SR785 will not compute any averages and all quantities diplayed will be instantaneous values RMS Averaging RMS averaging involves averaging the result of multiplying a complex quantity by the complex conjugate of another complex quantity For instance the RMS averaged FFT is defined as RMSAvg FFT1 V lt FFT1 FFT1 gt The precise definition of what RMS Averaging means for each measurement is given in the description of each measurement Baiscally since RMS averaging always involves averaging the square of a quantity RMS averaging reduces fluctuations in the data but does not reduce the actual noise floor squared values never cancel With a sufficient number of averages a very good approximation of the actual noise can be obtained Note that the definition given above always yields a real quantity whose phase is zero This is not true for all RMS averaged quantities computed by the SR785 however Both the rms averaged frequency response and the rms averaged cr
309. e separated by a time equal to 1 Capture Sampling Rate The corresponding start time relative to the start of the buffer is displayed as well Both channels playback starting at the Playback Start Command ISTR 1 Playback Length Select the Capture Playback Length in 2 kPoint 2048 points increments The Playback Length in points plus the Playback Start cannot exceed the Capture Length of the buffer The corresponding playback time is displayed as well Both channels playback the same Playback Length Command ILEN 1 Set Left Edge The active display must be a Capture Buffer measurement for this key to be active SR785 Dynamic Signal Anaylzer 4 98 Playback Input Menu Choose a Capture Buffer as the Measurement and use Zoom and Pan to show the region of interest Press lt Set Left Edge gt to set the Capture Playback Start to the marker position The Playback Length is not changed If the requested Start position plus the Playback Length in points exceeds the Capture Length of the buffer the Playback Length is reduced Set Right Edge The active display must be a Capture Buffer measurement for this key to be active Choose a Capture Buffer as the Measurement and use Zoom and Pan to show the region of interest Press lt Set Right Edge gt to set the Capture Playback Length to the marker position minus the Playback Start The Playback Start is not changed If the marker position is to the left of the Playback
310. e source length FFT time record noise source period or arbitrary source length This is useful when the source length is the same as the FFT time record length Do not use Ch1 or Ch2 input trigger since the output will not start until a trigger is received Source trigger outputs the source continuously over and over FFT time records are synchronized to the source start If a triggered source is selected Chirp Burst Chirp Burst Noise or Arbitrary the triggered FFT measurement phase is stable only if the input signals are derived from the Watch Out For Triggered Sources SR785 Dynamic Signal Analyzer 4 104 Trigger Menu source output Turn the source off or set it to Sine when making triggered measurements without the source Command STMD 1 RPM Time Arm Setup Select the RPM Time Arm menu to view and adjust parameters relating to RPM and Time arming Delta RPM Delta RPM Sense Abs Change Time Arm Step 100 ms Return C Start RPM Specify the threshold RPM for RPM arming Start RPM is only active if Start RPM On Off is On For the trigger to initially arm the RPM must exceed the threshold RPM if Delta RPM Sense is Increasing or must be below the threshold Gf Delta RPM Sense is Decreasing If Delta RPM sense is set to Abs Change the Start RPM is ignored Command TRSR f Start RPM On Off Activates the Start RPM threshold If Start RPM is set On the trigger will not be armed
311. e the backspace key lt or press Alt and turn the knob Press Alt again to return the keypad to normal mode You can not delete all of the entries in the table Command DDLT d 1 Clear Table Clear the Data Table for the active display The table is left with a single entry for the first bin in the display Command DCLR d SR785 Dynamic Signal Analyzer 4 152 Limit Testing Analysis Menu Limit Testing Analysis Menu The Limit Testing menu is used to edit the limits and display the limit test results for the active display Limit Segments Limit Beep Of Clear Limits C Limit Segments Display the Limit Segments in the active display Hide Show Hide turns off the Limit Segments in the display Limit testing may still be performed Show displays the Limit Segments in the display Choosing lt Edit Limits gt also sets this to Show Command LSON d 1 Limit Testing Limit Beep Turn Limit Testing for the active display On or Off Off turns off limit testing The limit segments are not affected On turns on limit testing Test results Pass Fail are shown in the display to the left of the graph Limit testing may not be turned on until there is at least one defined limit segment Command LTST 7 d 1 Turn the audible Limit Alarm for the active display On or Off Off turns off the alarm On turns on the alarm Limit tests which fail will sound an audible alarm SR785 Dynamic S
312. e top of the menu is turned on If the indicator reads DispA or DispB parameter entry or selection modifies only Display A or Display B If the indicator reads Link both displays are modified at once To change the Link indicator use the Link key When Link is activated the value of the parameter for the non active display will be made equal to the value of the parameter for the active display Buttons Lists Buttons are the simplest type of softkey Pressing a button performs the specified action Examples of buttons are lt Full Span gt lt Preferences gt and lt Display to Disk gt Buttons simply show a graphic button or arrow in their menu box Parameters with a list of possible selections display their current selection in their softkey menu box Examples of parameter lists are lt View gt lt Window gt and lt Trigger Source gt To make a new selection press the softkey to highlight its menu box The list of possible choices is displayed in the entry field at the top of the screen For example to change the View press Display Setup for the menu and then lt View gt 3rd softkey The lt View gt menu box will be highlighted and the View selections will be listed at the top of the screen Use the knob to make the desired selection If a vertical thermometer appears at the right of the entry field then the selection list is too long to display at one time The bright bar within the th
313. e two time records share 75 of a record The overlap is simply 100 minus the Time Record Increment If the displayed increment is 200 the start of the next time record is advanced from the start of the previous time record by 2 time records leaving a gap of record This means that the data between the two time records is not measured When the displayed increment is less than or equal to 100 the measurement is said to be real time All time points contribute to one or more measurements When the displayed increment is greater than 100 then the measurement is not real time and some time points do not contribute to a measurement If the indicator shows a value greater than the requested Time Record Increment it means that the measurement cannot be made with the requested increment but is running with the smallest increment possible Factors which affect the processor s ability to run real time include the measurement type averaging and source type See also Real Time Bandwidth and Overlap SR785 Dynamic Signal Analyzer 3 20 Status Indicators This indicator is replaced by the Capture Playback Progress indicator when capture playback is in progress This indicator is replaced by the Sweep Frequency indicator when the Measurement Group is Swept Sine This indicator is replaced by the RPM indicator when Show Tach is set to On in the input lt Tach Input gt submenu Sweep Frequency RPM The Sweep Freq
314. ear Spectrum The FFT spectrum is the basic measurement of an FFT analyzer It is simply the FFT of a time record The spectrum is a complex quantity it contains phase as well as amplitude information This is sometimes referred to as the linear spectrum The phase of the spectrum is meaningful only if the time record is triggered with a fixed relationship to the input signal If the signal 1s periodic as well the signal and trigger repeat then vector averaging can be used to reduce the noise level of the spectrum The vector averaged spectrum is still a complex quantity The precise definition of the FFT1 measurement for all averaging modes is as follows No Average FFT 1 FFT1 Vector Average FFT 1 lt FFT1 gt RMS Average FFT 1 V lt FFT1 FFT1 gt Peak Hold Average FFT 1 V MAX FFT1 FFT1 Power Spectrum The Power Spectrum is derived from the FFT spectrum by multiplying the spectrum by its complex conjugate The averaged power spectrum is a good approximation to the rms SR785 Dynamic Signal Analyzer Display Setup Menu 4 27 signal and noise amplitudes The power spectrum is a real quantity and contains no phase information The precise definition of the Power Spectrum 1 measurement for all averaging modes is as follows No Average Power Spectrum FFT1 FFT 1 Vector Average Power Spectrum lt FFT1 gt lt FFT1 gt RMS Average Power Spectrum lt FFT1 FFT I gt Peak Hold Average Power
315. ect the measurement for Display A Pressing Active Display once makes Display B active and allows you to select the measurement for Display B using the same menu Only those parameters which are associated with an individual display have differing values SR785 Dynamic Signal Analyzer 3 30 Status Indicators between the displays Parameters such as input configuration or source setup are instrument parameters and are not associated with a display When a display specific parameter is highlighted for modification the Link indicator next to the top of the menu is turned on If the indicator reads DispA or DispB parameter entry or selection modifies only Display A or Display B If the indicator reads Link both displays are modified at once To change the Link indicator use the Link key Parameter linking is a convenient way of changing both displays together For example Span and Start frequency may be linked while the Measurement is unlinked This allows the two displays to have different measurements over the same frequency span Since the Spans are linked changing the Span does not require separate entries for each display Command ACTD 7 1 Link The Link key is used to link and unlink display specific parameters to perform a function on both displays at once or to temporarily link the display markers When an unlinked display specific parameter is highlighted for modification the Link indicator nex
316. ect the Analysis menu Select the Exceedance Statistics menu The exceedance is calculated using the records in the waterfall buffer starting with the Start Index 0 is the most recent record and continuing through the Stop Index Total Count 1 Enter 99 to include records O through 99 100 total Pause the measurement Exceedance calculation requires that the active display be paused This ensures that the waterfall buffer is static and no new records will be added during the calculation The exceedance results are stored in a data trace The trace measurement is the same type as the waterfall measurements In this case the trace data for each bin is exceeded by only 1 Exceedance Pct of the records stored in the waterfall buffer Trace to Ref is an alternate function The alternate key functions are labeled below each key in this case the Link key Trace to Ref copies the data in a trace to the reference graph of the active display The reference graph is shown in half intensity In this case the reference graph is the level of each octave bin which is exceeded only 1 of the time Li Note that the exceedance is also calculated for the power bin Leq Press Pause Cont Press Pause Cont Press lt Exceedance Pct gt Press 9 9 Enter Press lt Calculate Excd gt choose Trace 2 with the knob and press Enter Press Alt Link choose Trace 2 with the knob and press Enter Excee
317. ected Constant The imaginary part is left unchanged and the magnitude and phase are updated Command USRC i x y Imaginary Part Enter a new value for the imaginary part of the selected Constant The real part is left unchanged and the magnitude and phase are updated Command USRC i x y Mag Enter a new value for the magnitude of the selected Constant The phase is left unchanged and the real and imaginary parts are updated Phase deg Enter a new value for the phase in degrees of the selected Constant The magnitude is left unchanged and the real and imaginary parts are updated Marker to Mag Copy the marker reading exactly as shown in the Marker Position Bar of the active display to the magnitude of the selected Constant No unit translation takes place Make sure that the units of the active display are correct before using this feature SR785 Dynamic Signal Analyzer Window Menu 4 131 Window Menu Window The Window menu allows the user to choose the window function for FFT measurements See Windowing in Chapter 2 for more information Window l Window Force Exp Channel 1 Window Force Channel 2 Window Exp Force Length 3 00026 ms Expo TC 50 00 Trace to Window Window to Trace Select the Window Function for the active display If the Analyzer Configuration is set to Independent Channels the two displays can have different Windows If the Analyzer Conf
318. ectory Display Measurement Measurement Group Center of FFT Span to Marker Center of FFT Span to Marker Marker Mode Move the Marker to the Minimum Frequency Damping Results Total Memory Available Normal Marker Relative Mode Query the Marker Bin Marker Tracking Query the Marker X Position SR785 Dynamic Signal Analyzer 5 16 Index of Commands MRKY d MRKZ d MRON d MROX d x MROY d x MSAA MSAB MSAO d i MSEA MSEB MSEK d i MSIA MSIB MSRS MSSA MSSB MWEL d i MWID d i MXRL d i N NAMP x NAVG d NAVG d NBUR x NOTE 1 j k l m s NPER x NTYP i O OIBN d i OITK d f O2BN d i O2TK d f OCHN d i OCNF d i ODLT d f OHIB d f OIMP d i OLAT 2 d i OLOB d f OMAX d f ONPT d i ORES d i ORMN d f ORMX d f OSTO d i OTIM d x OTRK d i OTYP d i OUTX i OVRM 7 i 5 45 5 46 5 103 5 47 5 47 5 89 5 89 5 89 5 89 5 89 5 47 5 89 5 89 5 89 5 89 5 89 5 45 5 47 5 47 5 56 5 68 5 71 5 56 5 99 5 56 5 56 5 35 5 35 5 35 5 35 5 30 5 71 5 34 5 30 5 71 5 72 5 30 5 34 5 34 5 30 5 34 5 34 5 35 5 71 5 34 5 71 5 100 5 100 SR785 Dynamic Signal Analyzer Query the Marker Y Position Marker Z Read Set Marker to Ref Nor
319. ed Chirp Burst Chirp Burst Noise or Arbitrary the triggered FFT measurement phase is stable only if the input signals are derived from the source output Turn the source off or set it to Sine when making triggered measurements without the source Trigger Auto Arm Trigger Source Ch 1 Trigger Level per Trigger Mode ee 7 09 TEs Slope a Rising Delay 1 Eeu Delay 2 ae Trigd Source Mode __ Continuous RPMiTime Setup ime Setup i Manual Arm eee Manual Trigger a R Trigger Mode Select the Trigger Arming Mode Auto Arm Manual Arm RPM Arm Time Arm The trigger must be armed before a trigger event will be recognized Auto Arm arms the trigger automatically whenever possible without waiting for an arming event The combination of Auto Arm Trigger Mode and the Continuous Trigger Source is often known as Free Run triggering since the analyzer will take data as quickly as possible In Manual Arm the trigger is armed only after lt Manual Arm gt is pressed or the TARM interface command is received Once the trigger is armed the next trigger event will trigger the measurement In RPM Arming the trigger is armed when the RPM passes through a start threshold and at fixed rpm increments thereafter In Time Arming the trigger is armed after a specified amount of time has elapsed The time interval is specified with the Time Arm Step softkey SR785 Dynamic Signal Analyzer Trigger Menu 4 101 Tr
320. ed lt If gt or carriage return lt cr gt on RS232 or a linefeed lt lf gt or EOI on GPIB No command processing occurs until a terminator is received Commands function identically on GPIB and RS232 whenever possible Command mnemonics beginning with an asterisk are IEEE 488 2 1987 defined common commands These commands also function identically on RS232 Commands may require one or more parameters Multiple parameters are separated by commas Multiple commands may be sent on one command line by separating them with semicolons There is no need to wait between commands The SR785 has a 256 character input buffer and processes commands in the order received If the buffer fills up the SR785 will hold off handshaking on the GPIB and attempt to hold off handshaking on RS232 Similarly the SR785 has a 256 character output buffer to store output until the host computer is ready to receive it If either buffer overflows both buffers are cleared and an error reported The present value of a particular parameter may be determined by querying the SR785 for its value A query is formed by appending a question mark to the command mnemonic and omitting the desired parameter from the command Values returned by the SR785 are sent as a string of ASCII characters terminated by a carriage return lt cr gt on RS232 and by a line feed lt lf gt on GPIB If multiple query commands are sent on one command line separated by semicolons
321. ed Source Mode Start Reset Source Type Save Nodal Information Reference to Trace Display d to Trace 1 Trace to Arb Manual Trigger Arm Download Trace i Ascii Download Trace i Ascii Trigger Average Mode Ch1 Transducer Convert Ch2 Transducer Convert Trigger Delay A Trigger Delay B Upload Trace i Buffer Upload Trace i Buffer Time Arm Increment Time Download Trace 1 Binary Download Trace 1 Binary Trigger Level Manual Trigger Trigger Arming Mode TONE i j TPUT i TPUT i TRCL i TRCL i TRDM i TRDR x TRSM i TRSR x TRWI i TSAV i TSLP i TSRC i U UNDB d 1 UNIT d UNPH d 1 UNPK d 1 UNST d USRC i x y USRE 1 J k USRH 1 J k USRO 1 J k USRR 1 j k USRS 1 J k USRT i J k V VIEW d i W WANG d i WAVA d WDSP d i WESB d i WESK 2 d i WEST d i WGET WGET WHID d i WHIT d i WITR d i WOSK d x WPUT WPUT WREV d i WSLC d i j WSTO d i WSYM d i WTHR d i WTOT d i WTRC 4 i j WVCT d i 5 106 5 112 5 112 5 96 5 96 5 67 5 67 5 67 5 67 5 79 5 96 5 66 5 66 5 40 5 40 5 40 5 40 5 30 5 77 5 74 5 74 5 74 5 74 5 74 5 74 5 39 5 81 5 80 5 80 5 80 5 80 5 81 5 114 5 114 5 81 5 81 5 79 5 80 5 115 5 115 5 81 5 82 5 80 5 79 5 81 5
322. ed at fixed time intervals The time record contains data which 1s processed to yield samples at equal positions around the shaft To graphically expand a region of the display use the Pan and Zoom functions in the Display Setup menu The capture buffer display will automatically pan as the capture fill and playback progress through the buffer During capture fill if the capture buffer contains more points than can be displayed points are skipped This speeds up the display update so that it keeps up with the real time capture but allows visual aliasing to occur Once capture is complete the display is redrawn showing the envelope of all points eliminating any visual aliasing effects User Functions A User Function displays the results of a user defined math function User Functions defined within the Order Measurement Group may include order measurement results Use the User Math menu to define a function SR785 Dynamic Signal Analyzer Display Setup Menu 4 37 A User Function may not be selected as the measurement if it uses a Trace which is empty or which contains data taken in a different Measurement Group See User Math Functions in Chapter 2 for more Measurement Time Histogram Histogram This is the basic measurement in the Time Histogram group The display shows a histogram of the number of samples found in some length of the input signal versus the amplitude of the sample The amplitude covers the entire input ra
323. ed is increased until the Max of Skips is reached This speeds up the sweep in regions where the response is Slowly changing 11 Press Source Press lt Auto Level Ref gt Select Channel 2 with the knob and press Enter Press lt Ideal Ref gt Press 1 0 select mV with the knob and press Enter Press Active Display Swept Sine Measurement 1 45 If successive points differ by more than the Slower Threshold on either input then the sweep returns to the earlier point and continues with no skipping This fills in the region where the response is rapidly changing The sweep continues from this point speeding up when allowed and slowing down when required Note that the sweep progress marker at the bottom of the graph changes speed through the notch Auto Resolution greatly shortens the measurement time while preserving the resolution where required Select the Source menu Change the Auto Level Reference Choose Channel 2 as the Auto Level Reference Change the Ideal Reference level Enter 10 mV Auto Level will try to maintain the Ch2 signal level at the Ideal Reference level by changing the source level at each point of the sweep The Max Source sets the largest source output allowed This is useful whenever the transfer function has substantial gain as well as attenuation or if a test requires a constant level within the device under test usually input or output In this case Auto
324. ed with signals which are exactly periodic in the time record such as a chirp or exact bin sine frequencies In the Order Analysis measurement group the uniform window can be used in situations where most of the harmonics of interest will be at integer multiples of the shaft rotation speed In this case these harmonics will fall on exact bin frequencies and will be most accurately reproduced with the uniform windows Hanning Flattop BMH The Hanning window is a commonly used window However it has an amplitude variation of about 1 5 dB for signals which are not at exact bin frequencies and provides only reasonable selectivity Its side lobes are very high and broad for off bin frequencies As a result the Hanning window can limit the performance of the analyzer when looking at signals close together in frequency and very different in amplitude The Hanning window is most often used in noise measurements since it has the lowest noise floor The Hanning window function 1s w L0 cos 27 for 1 0 N 1 and N number of time record points The Flattop window has the best amplitude accuracy of any window The amplitude variation is only about 0 02 dB for signals between exact frequency bins However the selectivity 1s worse Unlike the other windows the Flattop window has a very wide pass band and very steep rolloff on either side Thus signals appear wide but do not leak across the whole spectrum The Flattop window is the best
325. eform and displays the appropriate setup menu Watch Out For Triggered Sources If a triggered source is selected Chirp Burst Chirp Burst Noise or Arbitrary the triggered measurement phase is stable only if the input signals are derived from the source output Turn the source off or set it to Sine when making triggered measurements without the source Source oo Off s cn Sine Chirp Noise Arb Turn off the source output The output is held at 0 V If a triggered source is selected Chirp Burst Chirp Burst Noise or Arbitrary the phase of the measurement is relative to the source not the trigger Command SRCO 1 Turn on the source output The output is determined by the selected source type Command SRCO 1 Set the source output to Sine and display the Sine Setup menu The output is the sum of two tones sine waves plus the offset To generate a single tone set the amplitude of one of the tones to zero The frequencies should be exact bin frequencies of the FFT This eliminates windowing effects in the measured amplitude and phase SR785 Dynamic Signal Analyzer 4 68 Source Menu Chirp Noise The sine source is not triggered The output is always continuous Command STYP 1 Set the source output to Chirp and display the Chirp Setup menu The output is an equal amplitude sine wave at each frequency bin of the FFT spectrum This source is useful for measuring transf
326. elect the Display Options menu Choose a new Display Format Select the desired option from the displayed list and press Enter Single Display Format shows a single large graph Automatically scale DisplayA the active display to show the entire range of the measurement This moves the Marker to the maximum data point in the active display A The Marker should now be on the 1 024 kHz signal The Marker Position shown above the graph displays the frequency and amplitude of the signal The knob normally adjusts the Marker Position within the active display DisplayA in this case If a menu box is highlighted with a softkey the knob adjusts the selected parameter shown in the entry field at the top of the screen You can also use the Span Up and Span Down keys to adjust the Span This isolates the 1 024 kHz fundamental frequency You may notice that the spectrum takes a noticeable time to settle at this last span This is because the time record is 250 ms long Move the Marker to the peak Press Marker Center 10 Let s look at the signal distortion Press Freq Press lt Span gt Enter 1 2 8 select kHz with the knob and press Enter Press Auto Scale A 11 Let s measure some harmonics using the Marker Reference Press Marker Max Press Marker Ref Use the knob to move the Marker to the harmonics Press Marker Ref 12 Let s have the analyzer measure the distortion Press Ma
327. em menu Press lt Preset gt Press Enter to confirm Preset 2 Connect the Source Output to the filter input Connect the filter output to the Ch2 A Input 3 Press Source Press lt Noise gt Press lt On gt Press lt Type gt Select White with the knob and press Enter Press Auto Range Ch2 Press Display Setup Press lt Measurement gt Select FFT ch2 with the knob and press Enter Press Input Press lt Analyzer Config gt Preset returns the unit to its default settings Preset requires confirmation to prevent accidental reset Wait until the self tests are completed In this example only the filter output on Channel 2 is required Select the Source menu Choose Noise output The output is random noise Turn the source on Adjust the Noise Type This source is White Noise which extends over the entire 0 102 4 kHz frequency range Let the analyzer automatically set the Input Range to agree with the signal Note that the Input Range readouts at the top of the screen are displayed in inverse when Auto Range is on Select the Display Setup menu Change the Measurement of the active display A Choose FFT spectrum of Ch2 for the measurement in DisplayA top Both displays are independently measuring the filter output spectrum Select the Input Menu Change the way the input channels are used SR785 Dynamic Signal Analyzer 1 16 Linking Advanced Operation Select I
328. ement Each time the linear average is done the result is stored in the waterfall buffer and the average is reset and started over instead of stopping Each completed average counts as a single waterfall record Exponential Time New filtered data is weighted more than older data The exponential time constant is the Integration Time Averaging continues indefinitely While Exponential averaging is in progress the completed integration time is shown in the Horizontal Scale Bar below the graph The displayed time stops incrementing at the Integration Time while the averaging continues Exponential weighting reaches a steady state after approximately an integration time Once in steady state further changes in the average are detected only if they last for a SR785 Dynamic Signal Analyzer 2 44 Octave Analysis sufficient number of measurements Make sure that the integration time is not so large as to eliminate changes in the data which might be important Equal Confidence Equal confidence averaging is exponential averaging where the integration time is set for each band separately The integration times are set so that there 1s a 68 probability that the results are within the specified confidence level of the true mean for every band in the measurement There is a 96 probability that the results are within twice the confidence level in dB of the true mean The effect of equal confidence averaging is that higher frequency band
329. ent Groups Operations Use the knob to pick one of the displayed Operations and press Enter to place it in the equation at the cursor location The display then automatically switches to the Operands display To enter another operation instead press lt Operations gt again The available operations depend upon the current Measurement Group FFT Measurement Group FFTU FFT jomegat Te GrpDly AWH FFT FFTu FETC er SR785 Dynamic Signal Analyzer User Math Menu 4 127 Swept Sine Measurement Group Phase jJOmegat GrpDly Xf 1 X Order Measurement Group Phase X 1 X Arithmetic operations x combine operand terms on a point by point basis It is the user s responsibility to ensure that the operand terms have the correct X axis type and lengths in order to produce meaningful results View operations Mag Mag Phase Real Imag simply convert the complex operand array into the desired form Mag and Mag compute the magnitude V x y or magnitude squared x y with a real result Phase computes the phase tan y x unwrapped with a real result Real simply zeroes the imaginary part Imag zeroes the real part Conj Ln Exp and Sqrt are defined as follows Conj x jy X jy Conj x jy x Jy Ln x jy In r 38 Exp x jy exp x cos y jsin y Sqrt x jy y r e cos 0 2 jsin 0 2
330. ent in this instrument Use extreme caution whenever the instrument cover is removed Do not remove the cover while the unit is plugged into a live outlet This instrument may be damaged if operated with the LINE VOLTAGE SELECTOR set for the wrong AC line voltage or if the wrong fuse is installed Line Voltage Selection Line Fuse Line Cord Service Fan The SR785 operates from a 100V 120V 220V or 240V nominal AC power source having a line frequency of 50 or 60 Hz Before connecting the power cord to a power source verify that the LINE VOLTAGE SELECTOR card located in the rear panel fuse holder is set so that the correct AC input voltage value is visible Conversion to other AC input voltages requires a change in the fuse holder voltage card position and fuse value Disconnect the power cord open the fuse holder cover door and rotate the fuse pull lever to remove the fuse Remove the small printed circuit board and select the operating voltage by orienting the printed circuit board so that the desired voltage is visible when pushed firmly into its slot Rotate the fuse pull lever back into its normal position and insert the correct fuse into the fuse holder Verify that the correct line fuse is installed before connecting the line cord For 100V 120V use a 1 5 Amp fuse For 220V 240V use a 3 4 Amp fuse The SR785 has a detachable three wire power cord for connection to the power source and to a protective ground The exp
331. ent type and length to be loaded from the interface The loaded data simply takes the place of the stored trace data and assumes the measurement parameters Measurement Averaging Window Frequency span etc and length of Trace 1 TASC loads the actual complex data values in the trace NOT the data displayed in a particular view Remember views are simply different ways of showing the actual complex data A trace contains n complex points The value of n depends upon the type and length of the target trace N should be chosen equal to or less than the length of the target trace If the length is less than that of the target trace the remainder of the trace will be filled with zeros Each complex point is two floating point numbers representing the real and imaginary parts Thus the TASC command loads 2n floating point numbers in ASCI format The downloaded values are assumed to have the same units as the target trace Depending upon the trace measurement the values are assumed to be either unitless Volts or Volts See TLOD for more The download sequence is as follows Host Send TASC 1 n Do NOT wait for IFC to be set in the Serial Poll status SR785 Checks to make sure that Trace 1 has length n Returns 4 byte binary long int if OK to begin data transfer A return of 0 indicates that n is too large for Trace 1 Host On receipt of 1 4 byte binary long int executes a transfer to the SR785 of 2n ASCII floats The
332. ental lt 30 kHz lt 74 dBc fundamental gt 30 kHz 1 of setting 0 Hz to 102 4 kHz 0 1 Vpk to 5 Vpk high impedance load 0 V to 5 V max output 5 V ac dc 0 1 Vpk to 2 5 Vpk O V offset lt 80 dBc fundamental lt 30 kHz lt 74 dBc fundamental gt 30 kHz Continuous or Burst DC to 102 4 kHz or limited to analysis span lt 0 25 dB pk pk typical lt 1 0 dB pk pk max xiv Specifications Pink Noise Time Record Bandwidth Flatness Chirp Time Record Output Flatness Crest Factor Swept Sine Auto Functions Dynamic Range Offset Arbitrary Amplitude Range Record Length General Monitor Interfaces Hardcopy Disk Preamp Power Power Dimensions Weight Warranty 5000 rms averages Continuous or Burst DC to 102 4 kHz lt 2 0 dB pk pk 20 Hz 20 kHz measured using averaged 1 3 Octave Analysis Continuous or Burst Sine sweep across the FFT span 0 25 dB pk pk Amplitude 1 0 Vpk 1 94 5 77 dB Source Level Input Range and Frequency Resolution 145 dB 0 V to 5 V max output 5 V ac dc 5V 2M samples playback from Arbitrary Waveform memory or a Capture buffer 4M and 8M samples optional Variable output sample rate Monochrome CRT 800H by 600V resolution IEEE 488 RS232 and Printer interfaces standard All instrument functions can be controlled through the TEEE 488 and RS232 interfaces A PC XT keyboard input is provided for additional flexibili
333. entry field can be linked to both displays by using the Link key Command OTYP d 1 Linear Time The band filter outputs are equally weighted and averaged for an Integration Time While Linear averaging is in progress the integration time completed is shown in the Horizontal Scale Bar below the graph When the Integration Time has been completed the measurement stops and Done is displayed below the graph If the Done alarm is enabled an audible alert is also sounded Waterfall Storage If Waterfall Storage is On the waterfall buffer only stores the completed linear averages not each individual measurement When the measurement is free running Auto Arm Continuous Trigger each time the linear average is done the result is stored in the waterfall buffer and the average is reset and started over instead of stopping Each completed average counts as a single waterfall record SR785 Dynamic Signal Analyzer 4 116 Octave Average Menu When the measurement is triggered each linear average may be triggered as well Set the Linear Avg Mode to choose triggered averages or automatically reset averages Exponential Time New filtered data is weighted more than older data The exponential time constant 1s the Integration Time Averaging continues indefinitely While Exponential averaging is in progress the completed integration time is shown in the Horizontal Scale Bar below the graph The displayed time stop
334. eq_Resp Trace Trace Traces Traced Traces Order Measurement Group Time t Time 2 lt Spec 1 gt lt Spec 2 gt lt Pwr l gt lt Pwri2j gt Vee lt T1 gt Vec lt T2 gt Const Const Const3 Const4 Const5 SR785 Dynamic Signal Analyzer User Math Menu 4 125 Time Histogram Measurement Group Hist Hit POFA PDF CDF 1 CDF 2 Timet Time 2 Trace Trace Traces Traced Traced Operands are arrays of complex values real and imaginary They may be measurement results such as FFT 1 Time 1 or Oct 1 a Trace or a Constant An array which is real simply has zero for its imaginary parts The array length of an Operand is determined by the measurement length number of FFT lines length of time record number of octaves etc or Trace length length of the data which is stored in the Trace Constants assume the length of the user function Operands which are measurement results enclosed in angle brackets such as lt Freq Resp gt or lt Spec 1 gt are exactly the same as the normal measurements They are computed using whatever averaging is selected with the lt Display Average gt softkey They are computed from the input data real time Analog or capture Playback and use the frequency and windowing parameters from the menus Frequency domain measurements are amplitude calibrated time records are not FFT and Time record measurements are also triggered just like the normal measurements Operands
335. equal to the Linewidth If an entered End frequency is incompatible with the Span then it will be set to the closest allowed value SR785 Dynamic Signal Analyzer FFT Frequency Menu 4 11 This softkey also anchors the End frequency Adjusting the FFT Span will leave the End frequency unchanged Enlarging the frequency Span may change the End frequency if the new measurement would extend below 0 Hz or above 102 4 100 0 kHz If the measurement group is Correlation then the End frequency is always equal to the Span baseband The two displays can have different End Frequencies if the Analyzer Configuration is set to Independent Channels In this configuration no two channel measurements are allowed frequency response cross spectrum etc but the entry field can be linked or unlinked using the Link key If Analyzer Configuration is set to Dual Channel they field is automatically linked to both displays Command FEND d f SR785 Dynamic Signal Analyzer 4 12 Octave Frequency Menu Octave Frequency Menu When the Measurement Group is Octave Analysis this menu selects the number and spacing of frequency bands for the active display See Octave Analysis in Chapter 2 for a discussion about octave analysis fundamentals Frequency Frequency Highest Band 8 kHz kHz peee Band 20 Hz Hz DERRE Resolution eee FORE Hannan Channels 1 Channel Highest Band Set the Highest Band for the active display The limi
336. er Press Marker Max SR785 Dynamic Signal Analyzer Choose the Harmonic Marker for the active display Adjust the Number Of Harmonics for analysis Enter 10 harmonics Move the Marker to the peak fundamental Notice that Harmonic Markers little triangles appear on top of all of the harmonic peaks These indicate which data points are used in the harmonic calculations The harmonic calculations are displayed within the menu THD total harmonic distortion is relative to the fundamental Harmonic power is an absolute measurement of the harmonic power level This concludes this measurement example You should have a feeling for the basic operation of the menus knob and numeric entry marker movement and some function keys Measuring a Frequency Response Function 1 11 Measuring a Frequency Response Function This example investigates the frequency response of the test filter enclosed with this manual using FFT measurements You will use the SR785 source to provide a broad band chirp and both input channels to measure the input to and output from the device under test 1 Press System Press lt Preset gt Press Enter to confirm Preset 2 Use a BNC Tee to connect the Source Output to the filter input and the Chl A Input Connect the filter output to the Ch2 A Input 3 Press Source Press lt Chirp gt Press lt On gt Press Window Press lt Window gt Select Uniform with the knob and press En
337. er multiple of the rotation frequency It is derived from the Linear Spectrum by multiplying each point by its complex conjugate Time Record The order time record displays the amplitude of the input signal at equiangular sampling points around the machine shaft Note that strictly speaking this is not a time record the time at which the shaft reached any particular angular depends on the rotational speed of the shaft and is communicated to the analyzer via the tachometer input The number of time record points in each shaft revolution is equal to 5 12 times the setting of the Max Order softkey In the order measurement group the displayed time record will be averaged if averaging is On Windowed Time Record The order group Windowed Time Record shows the Time Record multiplied by the currently selected Window Function Remember that window functions prevent events which occur at the beginning and end of the time record from appearing in spectral measurements If this happens use a uniform window or adjust the trigger to move the event to the center of the time record SR785 Dynamic Signal Analyzer 4 36 Display Setup Menu Track The Order Track measurement is a two dimensional plot of the amplitude of a given order vs RPM The Track measurement can only be selected when Tracking is turned on in the Frequency menu The order and input channel displayed by the track measurement is selected with the Track Setup submenu The a
338. er 3 6 Horizontal Scale Bar The Horizontal Scale Bar is directly below the data graph When displaying spectral measurements with no horizontal expansion these values are the Start Center and Stop frequencies of the measurement The start and stop frequencies can be displayed in RPM instead of Hz using the RPM frequency softkey When displaying time records these values are the Start and End of the time record Below the X Axis labels the measurement view window and averaging are shown These parameters may be different for each display The Average Count shows the number of measurements averaged so far up to the programmed Number of Averages Settle is shown when the displayed measurement is not settled and is not added to the average Reject is shown when the Overload Reject is On and a measurement is not included in the average due to input overload For Swept Sine measurements the estimated Sweep Time is displayed instead of the Average Count This is the time to complete a sweep when no auto functions are selected no Source Auto Level no Auto Range no Auto Resolution This Sweep Time is simply the sum of the Settle and Integrate times for all points in the sweep To horizontally expand a graph use lt Pan gt and lt Zoom gt in the Display Setup menu When the display is expanded on the horizontal axis the graph labels reflect the displayed data not the actual measurement span or time Expanded displays show the
339. er a new value with the entry keys and press Enter lt Start Freq gt is an example of a numeric value Menus which show parameters specific to a single display show the parameters for the active display Use Active Display to change the active display SR785 Dynamic Signal Analyzer Screen Display 3 17 A softkey menu box which is shown in gray 1s not available in the current measurement Also the measurement softkeys for an Off Line display are shown in gray indicating that they may not be changed Each menu is described at length in Chapter 4 SR785 Dynamic Signal Analyzer 3 18 Status Indicators Status Indicators In addition to the data displays and menu boxes there are a number of status indicators which are displayed at the top of the screen Figure Chapter 3 9 Status Indicator Panel Input Ranges The Input Ranges for both inputs are displayed If the range is set manually the range indicator is on a normal background If Auto Range is On then the range is displayed on a highlighted background The input range is displayed in whatever units it was last entered in with the menu Overloads The input overload condition of the inputs are displayed to the right of their Input Ranges The overload indicator is a bar When the bar is 1 division long displayed faintly then the input signal is below half full scale When the bar is 2 divisions long displayed in black the input signal is above half full
340. er functions quickly Use Source Trigger for stable time records and phase The Uniform window should be used since individual frequencies are not present at all times in the time record The chirp is exactly periodic with the FFT time record so the Uniform window does not cause leakage problems This source is only available for the FFT and Correlation Measurement Groups The chirp frequency span and burst time record is linked to either DisplayA or DisplayB If the other display has a different span the chirp span will not be appropriate for that display The chirp source is triggered by External triggers Set the Trigd Source Mode to trigger once or with every trigger With the continuous Trigger the chirp repeats over and over Trigger Caution If the Chirp source is selected the triggered FFT measurement phase is stable only if the input signals are derived from the triggered source output Turn the source off or set it to Sine when making triggered measurements of external signals not the source Command STYP 1 Set the source output to Noise and display the Noise Setup menu The output is broadband noise This source is useful for estimating transfer functions quickly White noise provides equal amplitude per VHz White noise is useful in electronic applications Pink noise rolls off at 3 dB oct providing equal energy per octave Pink noise is preferred for octave analysis Burst noise is selected whenever the Burst
341. er than the A D converter itself The noise floor in this case is 300 nVrms VHz relative to 1 Vpk or 130 dBpk VHz relative to full scale All of this assumes that the signal input is driven from a low impedance and noiseless source Remember resistors have a Johnson noise equal to 0 13xVR nVrms VHz Even a 50 Q resistor has almost 1 nVrms VHz of noise A signal source impedance of 6 kQ has a Johnson noise equal to the SR785 s input noise To determine the overall noise of multiple noise sources take the square root of the sum of the squares of the individual noise figures For example a 6 kQ source impedance has 10 nVrms VHz of noise Added to the input noise the overall noise is 107 107 or 14 nVrms VHz Input Impedance The input impedance of the SR785 is 1 MQ If a higher input impedance is desired then the SR550 remote preamplifier must be used The SR550 has an input impedance of 100 MQ and is AC coupled above 1 Hz Anti aliasing Filter After all of the signal amplification there is an anti aliasing filter This filter is required by the signal digitization process According to the Nyquist criterion signals must be sampled at a frequency at least twice the highest signal frequency In this case the highest signal frequency is 102 4 kHz and the sampling frequency is 262 kHz so things are ok However no signals above 131 kHz can be allowed to reach the A D converter These signals would violate the Nyquist criterion and be under
342. erage Menu User Math Menu Window Menu Waterfall Menu Capture Menu Analysis Menu Data Table Analysis Menu Limit Testing Analysis Menu Marker Statistics Analysis Menu Exceedance Statistics Analysis Menu Curve Fit Menu Disk Menu Nodal Degree of Freedom Menu Recall Settings Menu Disk Buffers Menu Disk Upkeep Menu Output Menu System Menu System Remote Menu System Preferences Menu System Date Time Menu System Diagnostics Menu Edit Macro Menu Chapter 5 Programming Index of Commands Alphabetical List of Commands Introduction Command Syntax Frequency Commands Display Setup Commands Display Options Commands Marker Commands Source Commands Input Commands Trigger Commands Average Commands User Math Commands Window Commands Waterfall Commands Capture Commands Contents 4 100 4 107 4 107 4 115 4 119 4 122 4 131 4 135 4 143 4 147 4 150 4 152 4 156 4 159 4 161 4 167 4 171 4 174 4 177 4 182 4 184 4 191 4 194 4 196 4 199 4 200 4 203 5 2 5 12 5 21 5 25 5 28 5 37 5 43 5 45 5 53 5 60 5 66 5 68 5 74 5 78 5 80 5 83 V vi Contents Memory Allocation Commands 5 84 Data Table Commands 5 85 Limit Test Commands 5 87 Marker Statistics Commands 5 89 Exceedance Statistics Commands 5 90 Disk Commands 5 94 Output Commands 5 97 System Commands 5 100 Front Panel Commands 5 102 Data Transfer Commands 5 107 Interface Commands 5 117 Nodal Degree of Freedom Commands 5 118 Status
343. erages are still selected in the Average menu Both channels use the window selected in the Window menu Coherence is a unitless real quantity and varies from 1 0 perfect coherence to 0 0 no coherence Coherence measures the percentage of power in the response channel 2 which is caused by phase coherent with power in the reference or input channel 1 Ideally a coherence of 1 0 means that the corresponding frequency response is completely legitimate All of the response power came from power at the input If there is noise or other signals generated from within the device under test which is not related to the input signal it will result in a coherence of less than 1 0 Capture Buffer The capture buffer stores sequential time domain input data in memory See Capture later in this section for more details The Capture measurement displays the contents of the capture buffer The FFT and Octave Measurement Groups can use this stored data as input data by choosing Playback as the Input Source in the Input menu The capture buffer is often very long To graphically expand a region of the display use the Pan and Zoom functions in the Display Setup menu The capture buffer display can automatically pan with the capture fill or playback progress through the buffer During capture fill if the capture buffer accumulates points faster than they be displayed some points are not shown This speeds up the display update so that it keeps
344. erated using the lt Trace to Disk gt or lt Display to Disk gt softkeys or by using the TGET 1 remote command The display file contains both the trace data and a complete record of the instrument s setup when the trace was stored Buffers 78C and 78W Files The SR785 uses 4 user allocable buffers to store large amounts of data These are the Channel capture buffer the Channel 2 capture buffer the waterfall buffer and the arbitrary waveform buffer Capture and arbitrary waveform buffers have the same format and can be saved to disk as 78C files using the lt Buffer to Disk gt softkey or the AGET 1 and CGET 1 j commands Waterfall buffers have a different format and can be saved to disk as 78W files using the lt Buffer to Disk gt softkey or the WGET i command The conversion utility can convert ASCII files to 78C files and to convert both 78C and 78W files into ASCII files SR785 Dynamic Signal Analyzer 6 4 Supported External File Types Supported External File Types Five different file types are currently supported by the SR785 file conversion utilities ASCII Files ASCII files consist of plain ASCII text ASCII files written by the SR785 file conversion utility consist of an alphanumeric header with instrument setup information followed by a number of columns of data values Columns are separated by spaces TAB characters or commas depending on the output option selected Each line is terminated with a carriage return lin
345. eries the time A string of the form HH MM SS is returned The TIME i j k command sets the time to 1 0 23 hours j 0 59 minutes and k O 59 seconds The parameters 1 j and k must all be sent DATE 7 i j k The DATE command sets queries the System Date The DATE command queries the date A string of the form MM DD YY is returned The DATE 1 j k command sets the date to 1 1 12 month j 1 31 day and k 0 99 year The parameters 1 j and k must all be sent SR785 Dynamic Signal Analyzer 5 102 Front Panel Commands Front Panel Commands ACTD i The ACTD command sets the Active Display to display 1 The parameter 1 selects DisplayA 0 or DisplayB 1 Use the ACTD command to select the active display in the Single format In the Single format the inactive display is still accessible via commands STRT The STRT command starts the measurement Any average in progress is reset and started over If the measurement is paused STRT starts the measurement over This function is the same as pressing the Start Reset key PAUS If the measurement is already in progress PAUS pauses the measurement If the measurement is paused PAUS has no effect This function is similar to pressing the Pause Cont key CONT If the measurement is paused CONT continues the measurement If the measurement is running CONT has no effect This function is similar to pressing the Pause Cont key UNST
346. erm before the cursor To edit a macro string use lt Macro String gt and the knob to move the flashing cursor within the string lt Delete gt will delete the highlighted term Menu Function Control and Number keys and lt Special Keys gt will either insert or replace at the cursor Use lt Insert Replace gt to switch between insert and replace mode lt Clear Macro gt will delete the entire string To increase CW or decrease CCW a knob event use lt Inc Knob Count gt and lt Dec Knob Count gt lt Cancel gt will discard any changes made in this menu and exit this menu lt Enter Macro gt will enter the new macro and exit this menu Pressing Enter while the cursor is in the macro string display also enters the macro and exits this menu SR785 Dynamic Signal Analyzer System Menu 4 193 Show Settings Show the instrument setup This key enters the Help system and displays the measurement setup and system settings Press 0 to exit Help Show Version Show the power on screen This screen shows the version number as well as the results of the power on tests The size of the installed data memory is also displayed 2 Ms 4 Ms or 8Ms SR785 Dynamic Signal Analyzer 4 194 System Remote Menu System Remote Menu Output To Output To OutputTo r PIB GPIB A Addos E 0 OverideREM m aud Rate 9600 bd bd ti ae lon ______8 bits bits PM None Return Select the Output
347. ermometer indicates the position within the complete list Use the knob to scroll through the entire list Choices shown in gray are not available in the current configuration When the correct choice is selected press Enter to change the parameter The menu box now shows the new selection and becomes un highlighted Many parameters require the Enter key to enter the new selection In these cases the Enter indicator next to the top of the menu will turn on while the selection is being made No change is made until Enter is pressed To cancel the operation press the same softkey again or another softkey to modify another parameter instead of Enter Some parameters do not require the Enter key to make the new selection valid lt Window gt is an example In this case moving through the list of windows with the knob changes the Window immediately and displays the selection in the highlighted menu SR785 Dynamic Signal Analyzer 3 26 Status Indicators box This allows the effect of various choices to be compared while making the selection Press Enter the same softkey another softkey or a menu key to un highlight the menu box when finished List selection may also be made using the numeric keys The choices are numbered 0 through 9 Press a number key to make a selection If Enter is not required the new selection immediately appears in the menu box If Enter is required the new selection appears when Enter is pressed
348. ers such as accelerometers convert a physical quantity such as acceleration into a voltage at the analyzer s input By assigning Transducer Units to an input measurements based upon the transudcer signal acceleration may be displayed in units of the actual physical quantity being measured velocity or displacement Transducer conversion is accomplished in the frequency domain by multiplying and dividing by jo which is equivalent to differentiating and integrating in the time domain The two input channels may have different transducer conversions Command TD1C s EU2U s SR785 Dynamic Signal Anaylzer Tachometer Input Menu 4 95 Tachometer Input Submenu This submenu sets parameters for the tachometer input The tachometer input is used in the Order Measurement Group to synchronize the analyzer to a rotating machine The tachometer input is also used by the trigger in the RPM Arming trigger mode Tach Input Tachinput_ Pulses per Rev eee Tach Trig Rng Trig Rng 2 V V Tach TachLewl 10 00 V FTachigiape rt Slope RISING Hold Off Enable Tach Hold Off Hold Off 2 ES Show Tach Ot tices eee eee Pulses per Rev Sets the number of tach pulses in each revolution of the device under test The allowed range is to 2048 Non integer values are allowed Command TAPR f Tach Trigger Range Tach Level Specify the range over which the tachometer input can be set to trigger SV 25V TT
349. ery small the resolution of the source amplitude may result in a Reference Channel signal which is not within tolerance of the Ideal Reference The Ideal Reference may be changed at any time during a sweep Command SSRF x Source Ramping Select the Source Ramping Mode Off On If Source Ramping is Off source level changes are made instantly If Source Ramping is On source level changes are made at the Source Ramp Rate Settling starts after the source amplitude reaches the desired level This prevents fast level changes from disturbing the device under test The swept sine source turns off whenever there are no measurements being made This is before the sweep is started at the end of a single sweep or while a sweep is paused If Source Ramping is Off the source shuts off instantly in these situations If Source Ramping is On the source will ramp off When the sweep is started or re started the source will ramp on for the first measurement Command SRMP 1 Source Ramp Rate Set the Source Ramp Rate 0 001 V s 500 V s The Source Ramp Rate is the rate at which the source amplitude changes when Source Ramping is On If Source Ramping is Off source amplitude changes are made instantly SR785 Dynamic Signal Analyzer Swept Sine Source Menu 4 85 Note that very slow ramp rates can add significantly to the sweep time especially if Auto Level is on and many changes to the source amplitude are required during the
350. es SDF Files Default Output File Extension 78D 78D output options Vxxx Specify firmware version of input file The firmware version can be found by pressing System lt Show Version gt Example Convert an SR780 file named OSR780 78D to an SR785 file named NSR785 78D SRTRANS 078d OSR780 78D NSR785 78D Converting Files to MATLAB Format Usage SRT785 Omat options infile outfile Allowed Input File Types 78D Files Default Output File Extension MAT MATLAB output options Gmname Name the MATLAB matrix mname The Matrix name defaults to the filename Cview1 view2 Specifiy Output Columns defualt is Cx v The MATLAB matrix will have as many columns as are specified with this option X x axis values v view shown when file was saved mag magnitude m2 magnutude squared r real part 1 imaginary part SR785 Dynamic Signal Analyzer Upk dB deg Example Using the File Conversion Utilities 6 9 p phase u unwrapped phase Specify unit choices not all choices apply to all views pk rms pk or pp rms units peak units or peak to peak dB lin dB dBm dBSpl lin linear units deg deg rad degrees or radians Convert an SR780 file named MYFILE 78D into a MAT file named M1 MAT containing a MATLAB array named datal with 2 columns containing the magnitude and phase of the input data SRT785 Omat Gdatal Cmag p MYFILE 78D M1 MAT Converting Files to Universal File Forma
351. es of the limit start X0 Y0 The parameters x1 and y1 are the coordinates of the limit end X1 Y 1 x0 y0 x1 and y1 are real numbers in the display units The LSEG d i command queries the endpoints and type of limit segment 1 The data is returned J f1 f2 yl y2 If The LSEG d 1 J xO yO x1 yl command sets the endpoints of segment 1 to xO yO and x1 yl and the type to Upper j 0 or Lower G 1 This command also sets Limit Segments to Show The LDLT command deletes Limit Segment Number 1 for display d The value of 1 may not exceed the last limit segment number The remaining segments are renumbered sequentially This command is not valid for d 2 both displays This command also sets Limit Segments to Show The LSFT command shifts all Limit Segments for display d The parameter x is real number The Y coordinates of all segments are shifted by x in display units This command is not valid for d 2 both displays This command also sets Limit Segments to Show SR785 Dynamic Signal Analyzer Marker Statistics Commands 5 89 Marker Statistics Commands MSAO d i MSRS MSAA MSIA MSEA MSSA MSAB MSIB MSEB MSSB The MSAO command sets queries the Marker Statistics On or Off for display d The parameter 1 selects Off 0 or On 1 The set command requires d 2 both displays When Marker Statistics are On the various statistical quantities are updated whenever new
352. eshold and Hidden Lines specifies whether portions of a record which are hidden behind other records will be shown The Paused Drawing mode determines how the display is drawn when the measurement is paused Normal displays the newest record at the top back Oldest at Top displays SR785 Dynamic Signal Analyzer 2 32 Waterfall Display the oldest record at the top back This is reversed from how the display is scrolled while the measurement is running A single record can be saved to a trace A time slice history of a single X from all stored records can also be saved to a trace SR785 Dynamic Signal Analyzer Capture Buffer 2 33 Capture Buffer Input Capture samples the analog inputs at a selected sample rate and stores the samples in memory Storage is continuous and real time without interruption in the data stream Triggering only starts the capture it does not synchronize individual time records Captured data can be used as the input for all measurement groups except Swept Sine The capture buffer can neither be filled nor measured while in the Swept Sine Measurement Group Use the Capture lt Memory Allocation gt menu to allocate memory between the capture buffer waterfall storage and the arbitrary source waveform Capture memory must be allocated before the capture buffer may be used Input Sampling The input data is always digitized at the maximum sample rate The maximum sampling rate is 262 1 kHz when the
353. estination and choose the Printer or Plotter Type in the Output menu Parallel Printer Connector Attach a parallel printer to the Printer port Use a standard printer cable Select the Centronics printer interface as the Output Destination and choose the Printer Type in the Output menu Preamp Connector This 9 pin D connector provides power and control signals to external preamplifiers such as the SR550 and SR552 The power connections are described below a in Voltage 20V 5V 20V Signal Ground Ground saan SR785 Dynamic Signal Analyzer 3 10 Rear Panel Connectors Using SRS Preamps When using either the SR550 or SR552 connect the power cable standard 9 pin D connectors from the preamp to the rear panel Preamp connector Use BNC cables to connect the A output from the preamp to the A input of either channel on the SR785 The B output from the preamp preamp ground may be connected to the B input on the SR785 In this case use A B as the Input Mode Be sure to twist the A and B cables together to reduce noise pick up The SR550 and SR552 are AC coupled above 1 Hz Do not use either preamp to measure signals below 1 Hz The SR785 does not compensate for the gain of the preamp Both preamps operate at their highest gain Measurements made by the SR785 need to be divided by the gain of the preamp The SR550 has a gain of 10 and the SR552 has a gain of 100 Tachometer Input Attach a tachometer to the rear panel
354. eters are changed to values incompatible with the Reference Display the reference display will be turned off Changing the display scale does NOT rescale the Reference Display This allows the live measurement display to be offset from the Reference Display by changing either Ymax Ymid or Ymin in the Display Setup menu To graph the Reference Display in the new display scale press Alt Snap Ref Link Display Ref toggles the Reference Display of both displays Command DREF d 1 SR785 Dynamic Signal Analyzer Status Indicators 3 37 Marker Center Marker Center sets the FFT Center frequency to the Marker frequency in the active display If the new Center frequency and Span conflict with the maximum measurement range 0 to 102 4 100 0 kHz then the Span is decreased to the largest span which allows the Marker frequency to be the center Link Marker Center adjusts the span of the active display and sets the Span of the inactive display to match Command MKCN d Marker Max Marker Max moves the Marker to the location of the maximum data value within the active display Marker Max only searches the data which is in the display If the maximum value occurs at more than one location then the one closest to the left edge is found If the Marker Mode in the Marker menu is Normal Marker Max centers the marker region around the maximum The Marker Seeks Mode chooses whether the Marker seeks the Maximum Minimum o
355. etup menu The SR785 calculates all the measurements in a given group simultaneously regardless of which measurements are actually being displayed When a measurement is paused or finished you can view the results of all measurements in the group without having to take new data The Measurement Group determines how the input data is processed In FFT group the input data is gathered into time records which are then transformed into spectra In Correlation group these spectra are transformed back into the time domain to yield auto and cross correlations In Time Histogram group the time records are processed to give a statistical description of the input signal In Octave group the data is passed through a parallel bank of filters and averaged In Swept Sine group the input data is processed to determine the spectral content at a single frequency by integrating over an exact number of source cycles Finally in the Order Analysis group the input data is processed together with information from a tachometer to give spectra corresponding to the revolutions of a rotating machine rather than a fixed sampling frequency The data processing in each group is governed by the parameters chosen in the menus For some menus the choice of the Measurement Group determines which parameters are shown in the menu The Frequency Average and Source menus have different sets of parameters in each group For other menus part or all of the menu is unavail
356. eturns the data in display d in binary format The parameter d selects Display A 0 or Display B 1 This command is only available with the GPIB interface The DSPB d jJ command returns the data value of bin j only The bins are numbered from 0 to length 1 The value is returned as a 4 byte IEEE float The DSPB d command returns all of the data in display d in binary format Do not serial poll for IFC bit 7 in the Serial Poll status after DSPB is sent IFC will NOT be set until the transfer is complete Send the command and then make the host computer a listener and the SR785 a talker The DSPB d returns 4 bytes per bin starting with bin 0 and continuing to bin length 1 There is no separation between data points No line feed follows the last data point instead EOI is asserted with the last byte The 4 bytes are an IEEE floating point number The returned data depends upon the display View and Units The data values are the same as if they were read with the marker In the case of a 2 D view Nyquist or Nichols two values per bin are returned 8 bytes per bin The first value is the Y axis value and the second is the X axis value In this case there are twice as many points returned The host interface must be capable of binary transfer 1 e accepting line feeds and carriage returns as data rather than terminators In addition the host program must read exactly the correct number of bytes 4xlength or 8xlength While a
357. ey If lt Save Option gt is set to All each time the SR785 stores a record it stores enough information to recreate every measurement in the current measurement group In this mode you can go back after the waterfall storage is complete and look not just at the measurement that was displayed while the waterfall was stored but at any measurement in the group Of course in this mode more waterfall memory is required to store each record If lt Save Option gt is set to Active Meas Only only the currently displayed measurement is stored so you can not go back later and change the measurement More waterfall records can be stored in this mode however The number of measurement records which are stored in waterfall memory is set by the Waterfall Total Count The maximum Total Count depends upon the allocated memory the type of measurement and the setting of lt Save Option gt as described above The amount of waterfall memory available for each display is always half of the allocated waterfall memory For example 500 blocks of allocated waterfall memory is allocated as 250 blocks for each display For 400 line FFT measurements This memory can store 250 measurement records from each display in waterfall memory in the Active Meas Only save mode If lt Save Option gt is switched to All the number of records for each display is reduced to 142 The rate at which measurement records are added to waterfall memory is set by the Waterfall Skip
358. ey such as Marker Max is pressed the function is performed on the active display If Link is pressed immediately before then the function is performed on both displays at once Link only affects the next key pressed If the next key is not a function key then it has no affect Linking affects each function differently See the function key definitions for more information SR785 Dynamic Signal Analyzer Status Indicators 3 31 When no parameter softkey is highlighted turning the knob adjusts the marker position in the active display If Link is pressed then the marker of the inactive display is linked to the active display and the knob moves both markers together Pressing a key will cancel this link If the key is a function key its function will be linked Print Screen The Print Screen hardkey allows you to print or plot the screen from any menu Configure printing and plotting in the Output menu and choose Print Plot or Dump Screen as the Hard Copy Button function to configure the Print Screen hardkey Pressing lt backspace will abort the printout No other front panel operations may be performed until printing is completed Command PRNT PLOT or DUMP Help Local Help Local provides on screen help for any key or softkey Press Help Local to enter the on line help system Press Help Local again for more information on the help system When a host computer places the unit in the REMOTE state no
359. ey entry to first pick a known selection and then use the knob to select an entry in the list relative to it For example to choose Capturel as the FFT Measurement press Display Setup lt Measurement gt 0 Enter lt Measurement gt select Capture with the knob Enter The first entry selects FFT 1 with the 0 key regardless of the current measurement The knob then selects a position in the list relative to FFT 1 When recording a macro remember that the macro is played back EXACTLY as recorded Thus do not start a macro with a softkey press since the menu which is displayed at playback may not be the one displayed when the macro was recorded Always start a macro with a menu key press if you want to change parameters within a menu SR785 Dynamic Signal Analyzer Chapter 4 Menus The SR785 has a menu driven user interface All operating parameters of the SR785 are grouped into 4 1 sixteen menus The Menu keys each display a menu of softkeys The softkeys at the right of the display change depending upon the displayed menu There are three types of softkeys buttons lists and numeric values A button performs a function such as lt Full Span gt A list presents a list of choices or options in the entry field at the top of the screen Use the knob to make a selection and press Enter lt Measurement gt is an example of a list A numeric value presents the current value in the entry field and awaits numeric entry Ente
360. f Set the Y Maximum top reference of the active display The top reference is the Y value of the top of the graph The top reference has the same units as the display When Y Max is changed the value of Y Min is kept fixed and Y mid and Y Div are adjusted The two displays can have different top reference values This entry field can be linked to both displays using the Link key Command YMAX d x Set the Y Midpoint center reference of the active display The center reference is the Y value of the center of the graph The center reference has the same units as the display The two displays can have different center reference values This entry field can be linked to both displays using the Link key When Y Mid is changed the value of Y Div is kept fixed and Y Max and Y Min are adjusted SR785 Dynamic Signal Analyzer Y Min Y Div Display Setup Menu 4 43 Command YMID 7 d x Set the Y Minimum bottom reference of the active display The bottom reference is the Y value of the bottom of the graph The bottom reference has the same units as the display The two displays can have different bottom reference values This entry field can be linked to both displays using the Link key When Y Min is changed the value of Y Max is kept fixed and Y mid and Y Div are adjusted Command YMIN d x Set the Y Division scale of the active display This value is the vertical scale of the graph T
361. f the noise burst The low frequency bands grow more slowly than the high frequency bands because their filters have longer time constants Pressing Alt removes the keypad and knob from the alternate mode The normal knob function moves the marker along the X axis of a single record Move the marker all the way to the right hand edge of the display The marker position should read L 49 12 Press Waterfall Press lt More gt Press lt Slice to Trace gt select Trace 1 with the knob and press Enter Press Active Display Press Alt Help Local select Trace 1 with the knob and press Enter Press Auto Scale B Use the knob to move the marker around in the waterfall slice DisplayB 13 Press Active Display Press Waterfall Press lt View Count gt Press 5 0 Enter Press lt Marker Z to gt Waterfall Display 1 39 The last bin in the octave display is the total sound level Leq as selected by lt Power Bin gt Select the Waterfall menu Show More of the Waterfall menu A waterfall slice is the time history of a single X axis location data at the marker X position from all stored records The slice data is stored in a trace Make the bottom display active DisplayB Trace to Display is an alternate function The alternate key functions are labeled below each key in this case the Help Local key Trace to Display recalls trace data to the active display Auto Scale
362. formation is stored with the 78D file and is available for use by external programs which convert the SR780 files into formats suitable for modal analysis programs Command RSNA s Response Number Enter the identification for the reference node For a frequency response function the response node is the node where the response is measured e g the node where the accelerometer or other detector is placed The number may be any integer The SR780 does not use the nodal degree of freedom information itself The information is stored with the 78D file and is available for use by external programs which convert the SR780 files into formats suitable for modal analysis programs Command RSNU 1 Response Direction Enter the direction associated with the response node 1 e the axis of the accelerometer or other measuring device Direction can be specified either along the X Y or Z axes for linear stimulus or as 0x 0y or 6z for angular measurements The SR780 does not use the nodal degree of freedom information itself The information is stored with the 78D file and is available for use by external programs which convert the SR780 files into formats suitable for modal analysis programs Command RSDR 1 SR785 Dynamic Signal Analyzer Nodal DOF Menu 4 173 Abort Save Press to abort the selected disk operation while in the nodal DOF information menu Continue Save Press when finished entering nodal DOF
363. g X axis Marker Source Input Trigger Average User Math Window Waterfall Capture Analysis Disk Output System Configure the markers Turns on and configures the source Configures the signal and tachometer inputs and select the input ranges Setup the trigger Turn averaging on and select the averaging type Define user math functions Select the measurement window Setup waterfall displays and storage Setup the time domain capture buffer Setup data tables and limit testing Store and recall data and settings to and from disk Configure the hardcopy output Configures the computer interfaces preferences and clock Diagnostics menu checks the instrument hardware Detailed descriptions of each menu are provided in the next chapter SR785 Dynamic Signal Analyzer Status Indicators 3 25 Entry Keys To modify or examine a parameter press the menu key which displays the appropriate softkeys Press a softkey to select highlight a parameter or function There are three types of softkeys or menu boxes buttons lists and numeric values The active display determines which display s parameters are shown in the menus Press Active Display to toggle between Display A and Display B parameters Only those parameters which are associated with an individual display have differing values between the displays When a display specific parameter is selected the Link indicator next to th
364. g takes place according to Averagey New Data 1 N Averagen N 1 N where N is the number of averages While Exponential averaging is in progress the number of averages completed is shown in the Horizontal Scale Bar below the graph The displayed number stops incrementing at the Number of Averages while the averaging continues SR785 Dynamic Signal Analyzer 2 26 FFT Averaging Exponential weighting reaches a steady state after approximately 5N measurements Once in steady state further changes in the average are detected only if they last for a sufficient number of measurements Make sure that the number of averages is not so large as to eliminate changes in the data which might be important SR785 Dynamic Signal Analyzer Real Time Bandwidth and Overlap 2 27 Real Time Bandwidth and Overlap What is Real Time Bandwidth The Real Time Bandwidth is the largest frequency span whose corresponding time record exceeds the time it takes to compute the FFT measurement At this span and narrower spans it is possible to compute the measurement for every time record without skipping any input data The spectra are computed in real time At spans larger than the real time bandwidth the measurement computations take longer than a time record The analyzer can not keep up and some input data must be ignored Data is lost between time records while the computations are in progress For FFT Resolutions greater than 100 lines the
365. ge of the display The value of O n x 360 deg which is closest to the phase of the previous bin is assigned to each bin n is an integer Single channel phase is relative to the center of the time record for Uniform BMH Hanning Flattop and Kaiser windows For Force and Exponential windows phase 1s relative to the start of the time record In general single channel phase is useful only when the time record is triggered in phase with the signal For two channel measurements the phase is relative between channel 2 and channel 1 Triggering is not always required for meaningful two channel phase measurements Phase Suppress sets the phase of small data values to zero This avoids the messy phase display associated with the noise floor Remember even a small signal has phase Set the Phase Suppress threshold in the Display Options menu SR785 Dynamic Signal Analyzer Views 2 23 Nyquist Plot The Nyquist Plot graphs complex measurement data as imaginary part along the Y axis versus real part along the X axis The graph is scaled linearly Adjacent frequency time points are connected by a line This view is generally meaningful only for measurements which have data at every frequency point such as chirp source or swept sine The Marker Position Bar shows the real and imaginary parts of each point as well as its frequency or time The marker moves sequentially through the frequency time points and can be linked to the freq
366. gger will be in effect and the next trigger event will start capture The Capture Progress indicator shows how much of the desired capture length has been filled If the Capture Mode is 1 Shot capture stops when the buffer is full Press Stop Capture to halt capture before the buffer is full If the Capture Mode is Continuous once capture is started it continues indefinitely and fills the capture buffer in a circular fashion In this case press Stop Capture to halt SR785 Dynamic Signal Analyzer 2 34 Capture Buffer capture with the most recently acquired data stored in the buffer Continuous Capture Mode is not available in the Order measurement group While capture is in progress the displays do not update unless the measurement is a Capture buffer Use Zoom and Pan to inspect a portion of the buffer The capture buffer display can automatically pan as the capture progresses through the buffer During capture if the capture buffer accumulates points faster than can be displayed some points are not displayed This speeds up the display update so that it keeps up with the real time capture data but allows visual aliasing to occur Once capture is complete the display is redrawn showing the envelope of all points eliminating any visual aliasing effects Capture Playback Captured data can only be played back in a measurement with the same maximum sampling rate Data digitized at 262 1 kHz can only be played back in FFT Group with the
367. ging parameters are the same for both displays Averaging successive measurements together improves accuracy and repeatability Averaging Compute Avgs Yes Averaging Type Linear Fix Len Avgs 10 Display Avg Vector More Avg Preview Manual Preview time Accept Reject Compute Averages Turns the computation of averages on and off If Compute Averages is off no averaged quantities will be computed or displayed Although this results in a slight improvement in the speed of some measurements for normal operation Compute Averages should be left On Some FFT measurements such as coherence have averaging as part of their definition If one of these measurements is selected Compute Averages will be forced On Command FAVG 7 d 1 SR785 Dynamic Signal Analyzer 4 108 Average Menus Averaging Type Select the Averaging Type weighting Choose Linear Fixed Length or Exponential Continuous The Start Reset key resets the current average and starts a new average The Pause Cont key pauses the average in progress Pressing Pause Cont again will continue the average from where it was paused If the Analyzer Configuration is Independent Channels each display can have its own Averaging Type This entry field can be linked to both displays by using the Link key Command FAVT d 1 Linear Fixed Length Weighting Linear weighting combines N Number Of Averages measuremen
368. gram Group m m SR785 Dynamic Signal Analyzer User Math Menu 4 123 Edit Function Function Operands f Function String R O D RURE i Repla i Operations ee Delete Ee Eq Cancel __ a Enter Eq A Operands Use the knob to pick one of the displayed Operands and press Enter to place it in the equation at the cursor location The display then automatically switches to the Operations display To enter another operand instead press lt Operands gt again The available measurement operands depend upon the current Measurement Group FFT Measurement Group Time 1 Time 2 FFT 1 FFT 2 lt Pwr F1 gt lt Pwr F2 gt Coherence i lt Cross Spec gt lt Freq Resp gt Vec lt F1 gt Vec lt F2 gt RMS lt F1 gt RMS lt F2 gt PeakHold lt F1 gt PeakHold lt F2 gt Rms lt xSpec gt Const1 Const2 Const3 Const4 Const5 SR785 Dynamic Signal Analyzer 4 124 User Math Menu Correlation Measurement Group Time 1 Time 2 Auto_Corr 1 Auto_Corr 2 FFU FFT 2 FFTu l FFTu 2 Vec lt Ful gt lt F1 Vec lt Fu2 gt lt F2 Vec lt Ful gt lt F2 Rms lt Ful F1 gt Rms lt Fu2F2 gt Rms lt Fu2F1 gt Const Const2 Const3 Const4 Const5 Octave Measurement Group Oct 1 Oct 2 Const Const Const3 Const4 Const5 Trace Trace Trace3 Traced Traced Swept Sine Measurement Group spec i Norm_Var 1 Norm_Var 2 Cross_Spec Fr
369. gt menu regardless of which interface received the query Use the OUTX command to select the correct interface at the beginning of every program Active Display and Linking Set commands which require a d parameter specify DisplayA 0 DisplayB 1 or Both Displays 2 without regard to the active display or any parameter linking Active display and linking are screen features which do not apply to interface commands Analyzer Configuration and Linking When the Analyzer Configuration is set to Dual Channel many commands that have a d display parameter require d be set to 2 both channels This reflects the fact that the two displays cannot have different frequency parameters in the dual channel configuration Command Context Errors Commands which perform softkey functions are not allowed unless the corresponding softkey function is allowed If the softkey is not available either shown in gray or not displayed at all then the corresponding set command is not allowed Be careful to send commands in the correct order to avoid context errors A good practice 1s to send the commands in the same order as programming the instrument using the softkeys SR785 Dynamic Signal Analyzer 5 28 Frequency Commands Frequency Commands FFT and Correlation FSPN 7 d f lt kHz Hz mHz wHz gt The FSPN command sets queries the FFT frequency Span of display d The parameter f is a real number representing the span in the selecte
370. h either the newest Normal or Oldest at Top Since this measurement is measuring a transient decay it is better to draw the oldest record at the top and the subsequent smaller amplitude records in the front This concludes this example There are many display parameters in the Waterfall menu which you should familiarize yourself with The transient response of any FFT or Octave measurement may be recorded in a waterfall buffer Using a slice will give a time evolution of a single X axis bin Swept Sine Measurement 1 41 Swept Sine Measurement This example investigates the test filter enclosed with this manual using Swept Sine measurements You will use the SR785 source to provide a sweeping sine source and both inputs to measure the input to and output from the device under test 1 Press System Press lt Preset gt Press Enter to confirm Preset 2 Use a BNC Tee to connect the Source Output to the filter input and the Ch1 A Input Connect the filter output to the Ch2 A Input Press Input lt Input Conifg gt Press lt Ch1 Input Range gt Press 2 select dB Vpk with the knob and Enter 3 Press Display Setup Press lt Measurements Group gt Select Swept Sine with the knob and press Enter 4 Press Freq Press lt Start gt Press 9 0 0 select Hz with the knob and press Enter Press lt Stop gt Display the System menu Preset returns the unit to its default settings
371. harmonics within the measurement span which are identified by the Harmonic Markers contribute to the THD calculations The harmonic identification works best if the fundamental frequency is a bin frequency If the fundamental is off bin then it is best to use the Flattop window to broaden all of the peaks Each display has its own Number Of Harmonics This entry field can be linked to both displays using the Link key Command HRMN d 1 Select the Harmonic and Sideband Display for the active display The Marker Position can display the Fundamental or any identified Harmonic or Sideband For Harmonic Marker the minimum is 0 Fundamental and the maximum is the Number Of Harmonics The second harmonic 2xfundamental is identified as 1 etc SR785 Dynamic Signal Analyzer Harmonic Marker Menu 4 59 For Sideband Marker the value ranges from 0 Fundamental to plus and minus the Number Of Sidebands The first lower sideband is identified as 1 the first upper sideband is 1 etc The small square marker will move to the selected harmonic or sideband If the selection is not within the measurement span the marker will move to the highest or lowest measured frequency which will be reported as the Marker Position Each display has its own Harmonic and Sideband Display This entry field can be linked to both displays using the Link key Command HDSP d 1 Readout Mode THD Select the Readout Mode for the Harmoni
372. hase and imaginary quadrature signals are measured yielding both magnitude and phase frequency responses SR785 Dynamic Signal Analyzer Swept Sine Measurements 2 51 The Integration Time is always an exact number of cycles at the source frequency This rejects signals which are at a different frequency such as noise and harmonics A long Integration Time results in a narrow detection bandwidth at the source frequency This improves signal to noise at the cost of longer measurement times This is similar to the linewidth of an FFT However in the FFT the linewidth is exactly related to the frequency span Span FFT Resolution In swept sine the Integration Time is independent of the frequency span Thus wide spans can be measured with narrow line widths The Integration Time is specified in both time and cycles of the source Times are converted to the next larger exact number of cycles The larger of the two specifications is used as the Integration Time A minimum of cycle or 15 6 ms is always measured To measure each point with the same linewidth set the Integration Cycles to 1 and the Integration Time to 1 linewidth To measure each point for a time inversely proportional to the frequency set the Integration Time to 15 6 ms and the Integration Cycles to the desired number Remember the detection bandwidth increases with frequency in this case the cycles get shorter which may result in increased detected noise at higher frequencies
373. he FNAM MYDATA DAT command sets the file name to MYDATA DAT DOS file name conventions must be followed 1 e file names are 8 characters or less with an optional extension of up to 3 characters If the extension is omitted the SR785 uses default extensions File access 1s to the current directory FDIR 7 s The FDIR command sets queries the Save Recall File Directory All save and recall disk operations use the directory specified by this command Be sure to use the FDIR s command before any file operation commands FDIR DIRNAME looks within the current directory for a sub directory called DIRNAME If it exists the current directory is changed to DIRNAME FDIR moves down a directory path one level at a time Use multiple FDIR commands to move down a directory path FDIR moves up one directory towards the root FDIR V sets the current directory to the root Only the last directory in the path is displayed in the menu box MDIR s The MDIR command creates directory s within the current directory For example the MDIR TODAY command creates the sub directory TODAY within the current directory DOS file conventions must be followed Use FDIR to set the current directory FXST s The FXST FNAME query returns a if the file FNAME exists in the current directory 0 is returned if there is no file or subdirectory named FNAME in the current directory Wild cards and are not allowed in th
374. he waterfall buffer Enter the Total Count for both displays 100 The Storage Interval is 100 ms A measurement snapshot is added to the waterfall buffer every Storage Interval so 100 measurements will take 10 s to complete The SR785 has two waterfall storage options for saving measurements All Means that all possible measurements for the currently selected measruement group will be stored in the waterfall buffer This option saves more measurements but each trace takes more space in the waterfall buffer so fewer traces will be available Active Meas Only means that only the currently selected measurement will be saved in the waterfall buffer To calculate exceedence statistics we must use the Active Measurement Only save option 1 62 Exceedance Statistics Press Start Reset 7 Press Analysis Press lt Exceedance Stats gt Press lt Stop Index gt Press 9 9 Enter Press Pause Cont Press lt Calculate Excd gt choose Trace 1 with the knob and press Enter 8 Press Alt Link choose Trace 1 with the knob and press Enter Start the measurement This resets the waterfall buffer New measurements are added to the waterfall buffer every 100 ms The number of records stored in the waterfall is shown in the Vertical Scale Bar and increments to 100 Because the waterfall storage is One Shot the waterfall buffer fills once 100 records No more records are added after 10 seconds Sel
375. he FFT Group A stored Trace can be recalled to the active display as Display data A Trace may be recalled to a display regardless of its associated Measurement Group When a Trace is recalled as Display data the Display becomes Off Line Since the Off Line display is showing static trace data its Measurement Window Frequency Span and Averaging may not be modified Only display related parameters such as View Scaling and Marker Functions may be changed Off Line A stored Trace can also be recalled to the active display as its Reference Display In this case the Measurement Group associated with the Trace must be the same as the Measurement Group of the active display either Live or Off Line A stored Trace may be used as an operand in a User Math Function In this case in order to display the User Function the Trace must contain data AND the Trace must have data stored from within the current Measurement Group For example an FFT User Function which uses Tracel cannot be chosen as a Measurement if Tracel is empty OR contains octave analysis data To preserve Trace data permanently save the Trace to disk A Trace may be recalled from a disk file or loaded from an interface If a User Function is displayed and it uses a Trace in its equation then that Trace cannot be changed to data from a different Measurement Group For example if an FFT User Function using Tracel is being displayed you cannot recall octave data from disk to Tracel
376. he FFT Measurement Group may include FFT measurement results Use the User Math menu to define a function A User Function may not be selected as the measurement if it uses a Trace which is empty or which contains data taken in a different Measurement Group See User Math Functions in Chapter 2 for more Measurement Correlation Select the Measurement of the active display when the Measurement Group is Correlation Each Measurement has an associated View Changing the Measurement changes the View to the View last used with the new Measurement Command MEAS d 1 The following Measurements are available in the Correlation Measurement Group Auto Correlation Auto correlation is a single channel measurement In the time domain it is a comparison of a signal x t with a time shifted version of itself x t t displayed as a function of q This is useful for detecting similarities which occur at different times For example echoes show up as peaks separated by the echo time Sine waves appear as sine waves and square waves appear as triangles Signals which do not repeat or are completely random for all time appear only at t 0 Averaging Auto Correlation invFFT FFTuN FFTN RMS or Peak Hold Averaging Auto Correlation invFFT lt FFTuN FFTN gt Vector Averaging On Auto Correlation invFFT lt FFTuN gt e lt FFTN gt where N is Channel 1 or 2 FFT is a windowed FFT FFTu is an un windowed FFT u
377. he FFT frequency Span of both displays by a factor of 2 This provides a way of adjusting the spans regardless of which menu is displayed The Span is adjusted with either a fixed start Center or End frequency depending upon which frequency was most recently anchored in the Frequency menu In Correlation group Span Up decreases the time window over which the correlation is computed but increases the time resolution In Octave group Span Up moves the octave measurement span of both displays up by an octave Span Up affects each display independently if their frequency parameters are unlinked Span Up has no affect for Swept Sine Order or Time Histogram measurements Link Span Up is the same as Span Up Command FSPN d 1 Span Down In FFT group Span Down decreases the FFT frequency Span of both displays by a factor of 2 This provides a way of adjusting the spans regardless of which menu is displayed The Span is adjusted with either a fixed Start Center or End frequency depending upon which frequency was most recently anchored in the Frequency menu In Correlation group Span Down inreases the time window over which the correlation is computed but decreases the time resolution SR785 Dynamic Signal Analyzer 3 36 Status Indicators In Octave group Span Down moves the octave measurement span of both displays down by an octave Span Down affects each display independently if their frequency para
378. he knob adjusts the vertical scale in a 1 2 5 10 sequence Knob adjustments set the Y Midpoint center reference to the current Marker X Position The Y Maximum and Y Minimum are adjusted to give the effect of vertical zooming Entering a scale numerically leaves the Y Min bottom reference unchanged The Y Max and Y Mid are adjusted If the View is Log Mag and lt dB Units gt are set Off then the graph will be logarithmically scaled In this case the box will display the total number of decades along the Y axis The two displays can have different vertical scales This entry field can be linked to both displays using the Link key Command YDIV d x X Center Polar Set the X Center of the active display when the View is Nyquist or Nichols plot The X Center is the X axis value at the center of the graph The X Center has the same units as the display The two displays can have different X Center values This entry field can be linked to both displays using the Link key Command XCEN 7 d x SR785 Dynamic Signal Analyzer 4 44 Display Setup Menu X Div Polar Set the X Division scale of the active display when the View is Nyquist or Nichols plot This value is the horizontal scale of the graph The knob adjusts the scale in a 1 2 5 10 sequence Changing the scale does not change the X Center location The X axis is scaled linearly and the scale is expressed in the display units The two displays c
379. he marker will move to the next peak in the display in the direction of the knob turn If no peaks are found the marker will remain in the same position Marker Position Bar 10 24 kHz 6 021 dBVpk Frequency Time or Bin Data value of Marker Number of Marker Figure Chapter 3 8 Marker Position Bar The Marker Position Bar is displayed above each graph The first value is the marker frequency time or bin number If the display is a waterfall the waterfall record number is also shown SR785 Dynamic Signal Analyzer 3 16 Screen Display The second value is the marker Y Position or data value For 2 D displays Nyquist or Nichols View X and Y values are both displayed If a value is preceded by a A delta symbol then the value is relative to a reference point or graph Use the Marker menu to configure a relative reading If N A appears instead of a value measurement data is not available This often occurs when a measurement with a long acquisition time is changed and new data is not yet available Ifa appears after a value the displayed value has not actually been measured but is interpolated from actual measured points This arises in Swept Sine sweeps with Auto Resolution On when some frequency points are not measured Active Display The active display is indicated by the highlighted Marker Position bar Use Active Display to toggle the active display Reference Graphs In addition to the data graph each dis
380. henever possible At lower frequencies DC coupling is required For small signals it is common that the DC offset of the signal exceeds the amplitude of the AC signal of interest In this case the input range may be limited to accommodate the large DC offset while sacrificing signal to noise in the measurement of the AC signal If the signal frequency exceeds 0 16 Hz use AC coupling if possible SR785 Dynamic Signal Analyzer 2 70 Intrinsic Noise Sources Intrinsic Random Noise Sources Random noise finds its way into signals in a variety of ways Good test design can reduce these noise sources and improve the measurement stability and accuracy There are a variety of intrinsic noise sources which are present in all electronic signals These sources are physical in origin Johnson Noise Every resistor generates a noise voltage across its terminals due to thermal fluctuations in the electron density within the resistor itself These fluctuations give rise to an open circuit noise voltage V noise rms 4kTRAP where k Boltzmann s constant 1 38x10 J K T is the temperature in Kelvin typically 300 K R is the resistance in Ohms and Af is the bandwidth in Hz Af is the bandwidth of the measurement usually the FFT linewidth Shot Noise Electric current has noise due to the finite nature of the charge carriers There is always some non uniformity in the electron flow which generates noise in the current This noise is
381. his entry field can be linked to both displays using the Link key Command GDIV 7 d 1 Nyquist Grid Select the type of grid for 2 dimensional Nyquist View graphs If this softkey is set to rectangular the Nyquist View is displayed with a rectangular grid In this case X Center Y Center Y div and X div are all individually adjustable If the grid is set to polar a polar grid is displayed In this case X center and Y center are fixed at 0 Y div is adjustable and gives the number of Y units in each radial spoke of the grid Command GDIV d 1 Phase Suppress Set the Phase Suppress Threshold for the active display 0 When the display View is Phase or Unwrapped Phase the phase of data points with a squared magnitude less than the threshold are displayed as zero This avoids the messy phase display associated with the noise floor Remember even a small signal has phase To display the phase of all points set the threshold to 0 0 To suppress the phase of signals below 60 dBV 1 0E 3 V set the threshold to 1 0E 6 V magnitude squared The two displays have their own Phase Suppress Threshold This entry field can be linked to both displays using the Link key Command PHSL d x SR785 Dynamic Signal Analyzer Display Options Menu 4 49 d dx Window Set the d dx Window for the active display as a percentage of the display length 0 0005 10 The percentage is converted to a number
382. his measurement group Spectrum The swept sine spectrum is simply the measurement of a single channel over a sweep The spectrum is complex it contains phase and amplitude information The phase is relative to the source and is stable but arbitrary Single channel phase is not generally meaningful The spectrum measures the actual signal level at the inputs If Source Auto Level is On then the spectrum will tend to be constant Use Frequency response to remove the effects of a changing source level SR785 Dynamic Signal Analyzer 2 50 Swept Sine Measurements Cross Spectrum The swept sine cross spectrum is a two channel measurement defined as Cross Spectrum conj Specl Spec2 The cross spectrum contains both magnitude and phase information The phase is the relative phase at each frequency between the two channels The magnitude is simply the product of the magnitudes of each spectrum Frequencies where signal is present in both spectra will have large components in the cross spectrum Frequency response The swept sine frequency response sometimes called frequency response is a two channel measurement defined as Frequency response Spec2 Specl The frequency response contains both magnitude and phase information The phase is the relative phase at each frequency between the two channels Frequency response measures the response of a network or device under test The reference channel 1 measures the signal a
383. hlighted term Menu Function Control and Number keys and lt Special Keys gt will either insert or replace at the cursor Use lt Insert Replace gt to switch between insert and replace mode lt Backspace deletes the term before the cursor Insert Replace Toggle between insert and replace mode while editing a macro string If editing in insert mode Ins appears in the upper right corner of the edit window If editing in replace mode Rep appears SR785 Dynamic Signal Analyzer 4 204 Edit Macro Menu When editing a macro string Menu Function Control and Number keys and lt Special Keys gt will insert or replace before the cursor Inc Knob Count To edit a knob event move the cursor to the macro string window at the top of the screen and move to the desired knob event displayed as lt Knob n gt lt Inc Knob Count gt will increase the knob count by which is the same as rotating clockwise one choice in a parameter list Dec Knob Count To edit a knob event move the cursor to the macro string window at the top of the screen and move to the desired knob event displayed as lt Knob n gt lt Dec Knob Count gt will decrease the knob count by which is the same as rotating counterclockwise one choice in a parameter list Delete Delete the highlighted term in a macro string To move the cursor in a macro string use lt Macro String gt and the knob Clear Macro Clear the entire macro string C
384. iables are defined as follows d display O DispA 1 DispB 2 Both Displays d 2 is not allowed for queries 1 J K l m integers X y real numbers f frequency in Hz S text string Commands to set values which may be different for each display require the d parameter These values must be queried separately for each display d 2 is not allowed for queries even if the parameter is linked All numeric variables may be expressed in integer floating point or exponential formats 1 e the number five can be either 5 5 0 or 0 5E1 Strings are sent as a sequence of ASCII characters Commands and Units Some parameters display a choice of units in the entry field when a numeric value is entered These same units can be sent in the corresponding command For instance when a numeric value is enterered for the span the following choice of units appears kHz Hz mHz wHz SR785 Dynamic Signal Analyzer 5 26 Remote Programming Likewise to set the span to 51 2 kHz one could send any one of these five equivalent commands FSPN 2 51200 FSPN 2 51 2 kHz FSPN 2 51200 Hz FSPN 2 51200000 mHz FSPN 2 5 12E10 uHz Actually it is only necesssary to send sufficient characters to uniquely identify the units from the list Thus FSPN 2 51 2 k would set the span to 51 2 kHz as well Regardless of the units used to set the parameter the analyzer almost always returns the result of queries in one unit So if the span were queried after any
385. ideband The maximum value of i plus or minus the Number of Sidebands 1 lt 0O is valid only for Sideband marker This command is only valid if the Marker Mode for display d is Harmonic or Sideband HRDO 7 d i The HRDO command sets queries the Harmonic and Sideband Marker Readout for display d The parameter 1 selects Absolute 0 or Relative to Fundamental 1 This command is only valid if the Marker Mode for display d is Harmonic or Sideband SPWR d i The SPWR command queries the Sideband Power for display d The parameter 1 selects dB Relative to Fundamental 0 or Vrms or dB Vrms 1 and is required This command is only valid if the Marker Mode for display d is Sideband SR785 Dynamic Signal Analyzer Marker Commands 5 51 Marker Commands Band BMKL 7 d i j The BMKL command sets queries the Band Left Bin for display d The parameter 1 selects Upper 0 or Lower 1 band and jJ is the bin number 0 is the most left and cannot exceed number of bins in the display This command is only valid if the Marker Mode for display d is Band BMKR 7 d i j The BMKR command sets queries the Band Right Bin for display d The parameter 1 selects Upper 0 or Lower 1 band and jJ is the bin number 0 is the most left and cannot exceed number of bins in the display This command is only valid if the Marker Mode for display d is Band BEXC d i The BEXC command queries the Band Exclusion for
386. ideband Marker Menu 4 61 Sideband Marker Menu This menu is displayed when the active display Marker Mode is Sideband Marker Marker Setup Marker Sideband Sideband Sep 4096 kHz 096 kHz Hade a Te Saard E CoE Fundamental Readout Mode Absolute ree Ratio 98 3 dB RMS SB PUSR 3 038 uYrms Sideband Separation Set the Sideband Separation for the active display The Sideband Marker identifies the carrier frequency with the Fundamental Marker solid vertical line and the number of sidebands with small triangular Sideband Markers The Sideband Separation determines the location of these Sideband Markers relative to the Fundamental Only those sidebands within the measurement span which are identified by the Sideband Markers contribute to the Sideband Power calculations Each display has its own Sideband Separation This entry field can be linked to both displays using the Link key Command SSEP d f Sidebands Select the Number Of Sidebands for the active display 1 50 The first upper sideband fundamental separation is identified as 1 the first lower sideband fundamental separation 1s 1 etc The Sideband Marker identifies the carrier frequency with the Fundamental Marker solid vertical line and the number of sidebands with small triangular Sideband Markers The Sideband Separation determines the location of these Sideband Markers relative to the fundamental SR785 Dynami
387. iggers are ignored unless measurements are started with Start Reset and the trigger is armed Triggers are ignored while paused For FFT Correlation Time Histogram and Order measurements the trigger triggers individual time records For octave and swept sine measurements the first trigger after arming starts the measurement and subsequent triggers are ignored Use Start Reset to reset the measurement and start again For FFT Correlation Octave and Time Histogram modes the trigger can be configured to trigger a group of linear averages instead of individual time records with the Trigger Avg Mode Softkey Command TMOD 1 Trigger Source Select the Trigger Source Cont Chl Ch2 External Ext TTL Source Manual Continuous trigger automatically generates a trigger as soon as the trigger is armed The combination of Auto Arm Trigger Mode and the Continuous Trigger Source is often known as Free Run triggering since the analyzer will take data as quickly as possible Ch1 or Ch2 internally trigger on the Chl or Ch2 input signal The trigger is detected after the anti aliasing filter Gf On External and Ext TTL trigger on the front panel Trigger Input External has a variable Trigger Level and Ext TTL triggers on TTL signals Manual triggers with lt Manual Trigger gt or an interface command Use Auto Arm Trigger Mode with Manual Trigger since unwanted triggers are not a problem External Ext TTL and Manual also
388. ignal Analyzer 5 32 Frequency Commands Frequency Commands Swept Sine SSTR d f lt kHz Hz mHz wHz gt The SSTR command sets queries the swept sine Start frequency of display d The parameter f is a frequency real number of specified units The range of f is 0 001 to 102 4E3 The set command requires d 2 both displays This command is valid only when the Measurement Group is Swept Sine The set command requires a display to be Live SSTP d f lt kHz Hz mHz wHz gt The SSTP command sets queries the swept sine Stop frequency of display d The parameter f is a frequency real number of specified units The range of f is 0 001 to 102 4E3 The set command requires d 2 both displays This command is valid only when the Measurement Group is Swept Sine The set command requires a display to be Live SSFR The SSFR command queries which sweep point was the most recently measured While a sweep is in progress SSFR returns values from O to the Number Of Points 1 After a sweep is started SSFR will not return 0 until the first point 1s measured This may take some time if Source Ramping is On or if the Settling Time is very long This command is valid only when the Measurement Group is Swept Sine SRPT d i The SRPT command sets queries the swept sine Repeat Mode of display d The parameter 1 selects Single Shot 0 or Continuous 1 The set command requires d 2 both displays This co
389. ignal Analyzer Clear Limits Edit Limits Limit Testing Analysis Menu 4 153 Command LALM d 1 Clear the Limit Segments for the active display All limit segments are cleared and Limit Testing is turned Off Command LCLR d Display the Edit Limits menu Press lt Return gt for the lt Limit Test gt menu Choosing this menu also Shows Limit Segments Edit Limits New Segment c Lait vile Tepi teop TERT Tt Return New Segment Add a new segment to the Limit Test for the active display The new segment starts at the end of the last existing segment This simplifies the building of a continuous limit table The new segment is also the Current Segment Command LMAX 7 d 1 Limit Type Select the Limit Type for the Current Segment Upper Lower Each segment is identified by small triangular arrow markers at the segment end points These markers are above the segment and point downwards for Upper limits They are below the segment and point upwards for Lower limits SR785 Dynamic Signal Analyzer 4 154 Limit Testing Analysis Menu Command LSEG d 1 J xO yO x1 y1 Segment Select the Current Segment for editing 0 n The limit Type and Start X0 YO and End X1 Y1 points for this segment are edited in this menu The Current Segment is identified by two triangular arrows located at the segment endpoints These arrows are above the Upper or below the Lower Limit Type markers Use lt
390. iguration is set to Dual Channel both displays use the same Window The following windows are available for FFT and Order measurements Command FWIN d 1 Uniform The time record is used with no windowing This window provides amplitude accuracy only for exact bin frequencies and very poor frequency selectivity This window is a poor choice for continuous signals In general this window is only useful when looking at transients which do not last the entire time record The uniform window may also be used with signals which are exactly periodic in the time record such as a chirp The uniform window is also useful in the order analysis measurement group when the harmonics of interest are integer multiples of the shaft rotation speed This guarantees that these order fall on exact bin frequencies Hanning The Hanning window is the most commonly used window However it has an amplitude variation of about 1 5 dB for off bin signals and provides only reasonable selectivity Its side lobes are very high and broad for off bin frequencies As a result the Hanning SR785 Dynamic Signal Analyzer 4 132 Window Menu window can limit the performance of the analyzer when looking at signals close together in frequency and very different in amplitude The Hanning window is most often used in noise measurements since it has the lowest noise floor Flattop The Flattop window has the best amplitude accuracy of any window Its off bin amplitude
391. information to continue the selected disk operation SR785 Dynamic Signal Analyzer 4 174 Recall Settings Menu Recall Settings Menu File Name Get Setting File Name MYFILE Current Directory Measurements Sources Analysis Inputs Triggers DRAM settings Gen System Macros Recall from Disk i Enter the save and recall Current File Name Turn the knob to bring up the file catalog display listing all files in the Current Directory with the extension 78 SR785 files Press Exp to display all files in the directory Choose a file name with the knob and press Enter to make it the Current File Name This file name is used for saving and recalling displays traces and settings Remember saving to this file will write over the existing file New file names are entered using the Alt key and the letters associated with each key Press Alt again to return to normal keypad operation DOS file name conventions must be followed File names are 8 characters or less with an extension ext of up to 3 characters Default extensions are automatically supplied if no extension is specified The default extensions should be used since the directory display assumes an extension appropriate for the current menu Command FNAM s Command FREE Command FXST s Command FRST Command FNXT Current Directory Enter the Current Disk Directory SR785 Dynamic Signal Analyzer Recall Sett
392. ing capture playback User Function User Function displays the results of a user defined math function User Functions defined within the Order Measurement Group may include order measurement results Use the User Math menu to define a math function A User Function may not be selected as the measurement if it uses a Trace which is empty or which contains data taken in a different Measurement Group SR785 Dynamic Signal Analyzer 2 58 Time Histogram Time Histogram Measurements Time and Histogram Measurements Time and Histogram measurements give a statistical picture of an input signal in the time domain only Histogram measurements answer questions such as How often is my signal between 1V and 1 1 V or What s the probability that my signal exceeds 5V Time and Histogram measurements are useful for characterizing noise as well as in many mechanical applications Measurements in the Time Histogram Group Time Records Histograms Probability Density Functions PDF Cumulative Density Functions CDF and Capture are the measurements available in the Time Histogram group Time Histogram measurements may be stored in the waterfall buffer and the Capture Buffer may be used as in input Histogram The Histogram displays the distribution of amplitudes found in the input signal over a time determined by the Histogram Length Histogram Length may be set in terms of the number of points in the histgoram or the length of time to acquire th
393. ingle or dual graph Menu prints the menu of softkeys Indicators prints the status indicators at the top of the screen All prints the entire screen image including the menu softkeys and status area Command PSCR 1 Vector Plotter Select the Vector Plotter type for the Vector Plot operation HPGL Postscript Vector Plot only plots the displayed graphs SR785 Dynamic Signal Analyzer 4 186 Output Menu HPGL is used for HPGL compatible plotters Postscript is used for Postscript compatible plotters or printers Postscript output to a disk file 1s a convenient way to import the screen plot to a PC application The Destination for all Plotter Types can be either an on line Interface or a Disk file Command PLTP 1 Destination This softkey selects the Print Plot or ASCH Dump Destination Disk File Centronics Serial GPIB Choose Disk File to output to a disk file All Bitmap Printer and Vector Plotter types can save to Disk File This is convenient for using a printer or plotter which is not connected to this unit or to import the screen image into a PC application Files are written to the Current Directory specified in the Disk menu Files are named SCRNXXXX EXT where XXXX is a 4 digit number which automatically increments starting at the File Start Number The EXT extensions are TXT ASCH Dump EFX Epson PCL HP Laser GIF GIF PCX PCX HPG HPGL EPS Postscript Centronics selects the parallel pri
394. ings Menu 4 175 Turning the knob will bring up the directory tree display which lists all of the sub directories on the disk Choose a directory with the knob and press Enter to make it the Current Directory A directory may be entered using the Alt key and the letters associated with each key Press Alt again to return to normal keypad operation An error results if the entered directory does not exist New directories are created with lt Make Directory gt Command FDIR s Measurements Sources Analysis Include the Frequency Display Setup Display Options Marker Average Window User Math Waterfall and Capture menu settings in the recall This may invalidate current Analysis menu settings Command SRCL 1 Include the Source menu settings in the recall Command SRCL 1 Include the Analysis menu settings in the recall Do not recall Data Tables and Limits unless Measurements are also recalled This is because the analysis parameters are defined for specific frequency Spans and Views Command SRCL 1 Inputs Triggers Include the Input and Trigger menu settings in the recall Command SRCL 1 DRAM settings Include the memory allocation Capture Arbitrary Source or Waterfall settings in the recall Command SRCL 1 SR785 Dynamic Signal Analyzer 4 176 Recall Settings Menu General System Include the System and Output menu settings in the recall Command
395. input rate so only every other point is saved Thus the original 102 4 kHz span is represented by a time record with half as many points and half the sampling rate and the same duration How can this be The complex time record has half as many points as the baseband real time record with the same span and resolution This is because the negative frequency part of the spectrum is kept in the heterodyned case You can think of the real and imaginary parts of the complex time record as completely independent data streams each at half of the original sample rate and each with half of the original span Together they represent the original span with the original number of samples and the original time record length Digital filtering and down sampling is used to narrow the span of the heterodyned data This zooms in around the heterodyne frequency span center The first digital filter reduces the sample rate by 2 to 131 kHz but does not reduce the span The second digital filter cuts off at 25 6 kHz and reduces the sample rate by 2 again The number of points in the time record is NOT halved again this only happens at the first filter due to the splitting of the real time record into two parts real and imaginary The new time record must have twice the original duration and thus half of the original span This results in a 51 2 kHz 25 6 kHz span centered at 51 2 kHz The time record SR785 Dynamic Signal Analyzer FFT Time Record
396. ints are complex For an octave measurement the imaginary parts are all zero transmit mta listen 10 amp status make SR785 a listener pc a talker for i 0 i lt 33 i download 33 octave bins Sprinter emda DATA 216 gt OCtredl if real part transmit cmd amp status Sprinter cmd DATA Sit My eCbimag imacinary part transmit cmd amp status last bin is the total power bin sprinti cmd DATA S14 M octreal 33 gt real part Of total power bin transmit cmd amp status sprint tr enda DATA ali END yO Oy imag part of total power bin transmit lt cmd status gt last value terminate with EOL WaitIFC serial poll until IFC set ok to continue printi done wi TXSR785 RCTR 1 5 recall Trace 5 to DisplayB to view the new data KKKKKKKKKKKKKKKKKKKKKKKRKKKKKKKKKKKKKKKKKKEKKKKKKKKKKKK xxxxx Define a User Function define Funcl Oct 1 Traced TROR 7857 TUSRO 1 36 5 5 2 05 SfSe Oet Cl Ss Cdivide S Traces TSR 189D MEAS 0737 2 DisplayA measures UserFuncl TXSR785 YMAX 0 40 Change the top graph scale Funel is Oct 1 normalized by Traces The amplitudes are approximately O dB The Total Power bin is calculated from the sum of the octave bins in the function it is not normalized to Trace5 LE FSCLE end of main program KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK KKK KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK
397. ions are retained at power down Macros are saved to disk with the instrument settings Use Macro Rec Alt Pause Cont to start recording a macro Use the knob to select which macro 0 9 will be recorded and press Enter Press the desired sequence of keys The instrument responds to these keys while the macro is being recorded Press End Rec Alt Stop Capture to stop recording the macro To play a recorded macro press Play Macro AIt Start Reset choose the desired macro with the knob and press Enter To edit a recorded macro use System lt Edit Macro gt Choosing From Lists Menus The knob is normally used to pick an entry from a list However knob movements are recorded as movement relative to the starting position This leads to ambiguity when using the knob in a macro Playing the macro will have different results depending upon the starting state of the instrument Thus using the knob within a macro to choose a parameter is not recommended To choose a parameter from a list the numeric keys should be used instead of the knob while recording a macro The list choices are numbered 0 through 9 Press a number key to make a selection and Enter if required For example to select the Hanning window press Window lt Window gt 2 Enter since Hanning is entry number 2 If the parameter list has more than 10 choices FFT Measurement for example then the knob must be used In this case use a numeric k
398. is softkey is only active 1f the selected window is Force Exponential Command W2FE 1 Force Length Expo TC Set the Force Window Length The maximum value that can be entered is the length of the FFT time record Points in the time record up to the Force Length are unmodified Points in the time record past the Force Length are zeroed Choose Force Exponential as the window before setting the Force Length Command FWEL d 1 Set the Expo Window Time Constant as a percentage of the FFT time record 5 1000 This is the point where the window function reaches 1 e Choose Force Exponential as the window before setting the Expo Time Constant Command FWTC d 1 SR785 Dynamic Signal Analyzer 4 134 Window Menu Trace to Window Copy a stored data trace real part only to the User window Use the knob to pick a trace which already contains data and press Enter To see the effects of the new window the User window must be selected The trace data is interpolated if necessary in order to provide the window function with the correct number of points The trace length is mapped to the entire window length The User window may be used with time records of any length Command TRWI d 1 Window to Trace Copy the current window of the active display to the real part of a stored data trace Use the knob to pick a trace and press Enter lt Window to Trace gt always stores a trace with 2048 points Thi
399. is on the measurement is paused after the average is completed unless triggered or waterfall storage is on Press Start Reset to take another average Triggering If the analyzer is waiting for a trigger the Trig Wait indicator at the top of the screen is on If the measurement is not meant to be triggered make sure the Trigger Mode is Auto Arm and the Trigger Source continuous If the measurement is meant to be triggered make sure that the correct Trigger Source is selected and the Trigger Level is appropriate for the trigger signal SR785 Dynamic Signal Analyzer 1 6 Getting Started Check that the Trigger Mode is set to Auto Arm If the Trigger Mode is Manual Arm then the analyzer will only trigger once and then wait for the next Manual Arm command Scaling and Ranging Check that the inputs are not completely overloaded by using Auto Range Ch1 and Auto Range Ch2 Scale the display to show the entire range of the data with Auto Scale A and Auto Scale B Local Make sure that the analyzer is not in the REMOTE state where the computer interfaces have setup the instrument and locked out the front panel Press the Local Help key to restore local control Reset If the analyzer still seems to function improperly turn the power off and turn it back on while holding down the lt backspace key This will reset the analyzer into the default configuration The analyzer should power on running and taking measurement
400. ished by selecting the Force Exponential Window The Force Exponential window is actually two windows either of which can be applied to either input channel The Force window is uniform over the beginning of the time record and sets the remainder of the time record to its average value This method minimizes sepectral artifacts caused by zeroing the remainder of the time record The force length is user specified This window is used to isolate impulsive signals such as impact excitations from noise and other oscillations later in the time record The Exponential window attenuates the time record with a decaying exponential time constant This window is often used in impact testing on the response channel to remove oscillations which last longer than the time record When the Force Exponential window is selected and the analyzer is in the Dual Channel configuration the choice of which window is applied to which input channel is made by the lt Channel 1 Window gt and lt Channel 2 Window gt softkeys When the analyzer is in the Independent Channels configuration these softkeys govern which window is applied to the measurement in the two displays User Defined The User window is any function that the user provides The User window is copied from a stored trace using lt Trace to Window gt The trace may contain display data or be loaded from disk or via the computer interface SR785 Dynamic Signal Analyzer FFT Windowing 2 15 Remember
401. isplay B 1 The ENPL command sets queries the number of poles in the fitting function The parameter j is the number of poles between 0 and 20 The ENZE command sets queries the number of zeros in the fitting function The parameter j is the number of zeros between 0 and 20 The EWTU command sets queries the type of weighting used for fitting The parameter j specifies Uniform 0 Coherence 1 or User 2 The EWTT command sets queries the trace which will be used if user weighting is selected The parameter j is the trace number 1 5 ERNG d i j EDLY i x EFSC 7 i x The ERNG command sets queries the fit range The parameter d is the display number The parameters 1 and j are the starting and stopping bin numbers for the fit range The EDLY command sets queries the delay value associated with one of the curve tables The parameter 1 selects curve table 1 0 or curve table 2 1 The parameter x is the delay in seconds The EFSC command sets queries the frequency scaling for one of the curve tables The parameter 1 selects curve table 1 0 or curve table 2 1 The parameter x is the frequency scaling value SR785 Dynamic Signal Analyzer 5 92 Curve Fit Commands EGAN 7 i x The EGAN command sets queries the gain for one of the curve tables The parameter 1 selects curve table 1 0 or curve table 2 1 The parameter x is the gain value ETRC i j The ETRC command sets q
402. isplays We want both displays on a log x axis Note that the linkage indicator at the top of the screen changes from DispA to Link Measuring a Frequency Response Function 1 13 Select Log with the knob and press Enter Let s show phase response on DisplayB bottom Press Active Display Press Display Setup Press lt Measurement gt Select lt Freq Resp gt with the knob and press Enter Press lt View gt Select Phase with the knob and press Enter Press Auto Scale B 10 Let s link the Markers together Press Active Display Press Marker Press lt Width gt Select Spot with the knob and press Enter 11 Press Link and use the knob to move the marker Press Enter Log scale is acommon way to display filter response functions Note that both displays now have log x axes The two displays have separate Measurements Make DisplayB the active display The active display has its Marker Position Bar above the graph highlighted Select the Display Setup menu The setup of DisplayB the active display is now shown in the menu Adjust the Measurement of DisplayB Choose Frequency Response also The measured data is a set of complex values which can be viewed in a number of different ways Choose Phase View to show the phase of the transfer function Scale DisplayB to show the entire phase transfer function Make DisplayA top the active display Select the Mar
403. ithin the Correlation Analysis Measurement Group may include correlation measurement results Use the User Math menu to define a math function SR785 Dynamic Signal Analyzer Octave Measurements 2 41 Octave Analysis What is Octave Analysis An FFT measurement measures the power within equally divided frequency bins Octave measurements use logarithmic frequency bands whose widths are proportional to their center frequencies The bands are arranged in octaves with either 1 3 or 12 bands per octave 1 1 1 3 or 1 12 octave analysis Octave analysis measures spectral power closer to the way people perceive sound that is in octaves 1 3 octave analysis with A weighting is the most common measurement for acoustics and sound To make an octave measurement the input data passes into a bank of parallel digital filters The filter center frequencies and shapes are determined by the type of octave analysis either full 1 1 1 3 or 1 12 octave and comply with ANSI S1 11 1986 Order3 Type 1 D The output from each filter is rms averaged to compute the power and displayed as a bar type graph This is a real time measurement of the power within each band and is the only available octave measurement Since the bands are spaced logarithmically octave graphs always have a logarithmic X axis In addition to the octave bands the sound level is also measured and displayed as the last band in the display Exponential averaged sound power is calculated
404. itions Input Status Word Bit Name 0 LOW 1 1 HLF1 2 OVLI 3 HIV1 4 ARGI 5 7 unused 8 LOW2 9 HLF2 10 OVL2 11 HIV2 12 ARG2 13 15 unused Set when Input has fallen below half full scale Input has exceeded half full scale Input has exceeded full scale Input has exceeded 35 dBV Input range switched to 34 dBV Input has AutoRanged Input2 has fallen below half full scale Input2 has exceeded half full scale Input2 has exceeded full scale Input2 has exceeded 35 dBV Input range switched to 34 dBV Input2 has AutoRanged These status bits do not necessarily reflect the current input status The Input status bits stay set until read by INPS They are also cleared by the CLS command Use INPE to set bits in the Input status enable register To read the current input overload condition use INPC Error Status Word Bit Name 0 OUTE 1 DSKE 2 FLTE 3 RAME 4 ROME 5 VIDE 6 HELPE 7 DSDE 8 DSPE 9 DSRE 10 CALO 11 CALI 12 CAL2 13 15 unused Set when An output error has occurred Print Plot or Dump A disk error has occurred A math error has occurred RAM memory test fails ROM memory test fails Video memory test fails Help memory test fails DSP data memory test fails DSP program memory test fails DSP DRAM memory test fails DSP calibration memory fails Ch1 calibration memory fails Ch2 calibration memory fails The Error status bits stay set until read by ERRS They are also cleared by the CLS comma
405. itmap Printer type and Destination All other operations are disabled until printing is completed The PRTP command sets queries the Bitmap Printer type The parameter 1 selects a type below Printer Type Epson FX HP PCL HP Small PCL PCX 2 bit file GIF file PCX 8 bit file MBWNrR Oo The PSCR command sets queries what portion of the screen to print The parameter 1 selects Graphs Only 0 Menu Only 1 Status Indicators Only 2 or All 3 This only affects printing Plotting only plots the display graphs SR785 Dynamic Signal Analyzer 5 98 Output Commands PBRI i The PBRI command sets queries the print density of highlighted areas The parameter 1 selects White 0 6 1 12 2 25 3 50 4 or Black 5 PDIM 7 i The PDIM command sets queries the print density of normal areas The parameter 1 selects White 0 6 1 12 2 25 3 50 4 or Black 5 PBLK 7 i The PBLK command sets queries the print density of black text The parameter 1 selects Black 0 or White 1 PGRF 7 i The PGRF command sets queries the graph print mode The parameter 1 selects Black on White 0 or White on Black 1 PLOT The PLOT command plots the graph displays using the selected Vector Plotter type and Destination All other operations are disabled until plotting is completed PLTP i The PLTP command sets queries the Vector Plotter type The parameter 1 selects HPGL 0 or
406. its marker display Each display has its own Marker Tracking This entry field can be linked to both displays using the Link key Command MRKR d 1 Select the Marker Mode of the active display Normal Harmonic Sideband Band Choosing the Marker Mode also configures the rest of this menu FFT and Order measurement groups can use any Marker Mode Octave measurement group can use Normal and Band modes only Correlation Swept Sine and Time Histogram measurement groups can only use Normal mode Each display has its own Marker Mode This entry field can be linked to both displays using the Link key Command MKMD d 1 SR785 Dynamic Signal Analyzer Marker Menu 4 51 Normal The Normal Marker Mode defines a Marker Region between two solid vertical lines The Width may be set to a single point Spot or 1 2 Normal or 1 wide grid division The Marker is a small square which Seeks the Max Min or Mean of the data within the Marker Region When seeking Max or Min the Marker is located at the max or min data point This allows peaks and valleys in the display to be easily read by the Marker Position display above the graph When the Marker Seeks the Mean the X position is the center of the Marker Region and the Y position is the Mean of the data within the region When a Spot Marker is used the Marker is confined to a single X axis location Use Marker Max or Marker Min to move the Marker to the maximum
407. ive ORES 7 d i The ORES command sets queries the Octave Resolution of display d The parameter 1 selects 1 1 0 1 3 1 or 1 12 2 octave analysis Changing the resolution may change the values of the Highest and Lowest Band for display d For 1 Channel octave analysis the set command requires d 2 This command is valid only when the Measurement Group is Octave The set command requires display d to be Live OCHN 7 d i The OCHN command sets queries the Octave Channels The parameter 1 selects 1 0 or 2 1 channel octave analysis This command is valid only when the Measurement Group is Octave The set command requires both displays to be Live UNST d The UNST command unsettles the measurement of display d The measurement is not actually perturbed by the UNST command The settling status is set to unsettled and the full settling time of the measurement is required before the status returns to settled The measurement is unsettled by changing any one of several measurement parameters For example changing the input range or FFT span will unsettle the measurement If the signal comes from an external source and is changed in such SR785 Dynamic Signal Analyzer Frequency Commands 5 31 a way as to require the measurement to settle it is convenient to use the UNST command and wait for settling to finish This command is valid only when the Measurement Group is FFT Correlation or Octave SR785 Dynamic S
408. kHz then the source output will contain aliases In this case be sure to limit the measurement bandwidth to the sampling rate 2 56 to eliminate the effect of these aliases on the measurement The amplitude of the arbitrary output depends upon the amplitude of the captured data relative to the Input Range during capture If the captured data was 100 of the Input Range then an output amplitude of 100 will be 1 Vpk SR785 Dynamic Signal Analyzer 2 36 The Source The Source Sine The SR785 source provides a variety of test signals which allow the SR785 to measure the response of electronic mechanical and acoustic devices without the need for an external generator In many cases the SR785 source is better than an external source since it is synchronous with the input sampling A low distortion sine wave for general purpose gain distortion and signal noise measurements The sine source is synchronous with the FFT 1 e sine waves can be generated at exact bin frequencies of the FFT This can eliminate windowing effects in the measured amplitude and phase Two Tone Chirp Noise Two low distortion sine waves can be generated simultaneously for intermodulation distortion tests IMD Each tone has independent frequency and amplitude settings The Chirp source provides an equal amplitude sine wave at each bin of the displayed spectrum For a 400 point FFT the output is the sum of 400 discrete sine waves The phases of each sine
409. ked to the frequency of the other display Real measurement data such as baseband time record have zero phase This view is entirely along the Y axis Display the Units submenu Press lt Return gt for the main Display Setup menu Choices in the units submenu are limited to those which are appropriate for the current Measurement and View For instance dB units may not be selected when the view is Real Part Settings in the units submenu are associated with the Measurement and View Changing Measurements or Views may change the settings within the Units submenu SR785 Dynamic Signal Analyzer Units dB Units Pk Units Display Setup Menu 4 41 This display only menu box shows the units of the active display The units will depend upon the measurement the view the Transducer Parameter settings and the settings of the lt dB Units gt lt Pk Units gt lt PSD Units gt lt Phase Units gt and lt dBm Ref Imped gt softkeys Determines whether a Log Mag view will be shown in dB decibel units If off no decibel conversion will be performed If set to On the measurement results will be converted to decibels relative to the underlying units of the display If the view is Log Mag and dB Units is off the graph will be shown with a logarithmic y axis If dB units is on the graph will be shown with a y axis linear in dbs Setting this softkey to dBm will convert measurement results to decibels relative to 1 mW The volt
410. ker Ref key MRON operates on a single display d 2 is not allowed If Marker Rel is Off MRON d sets the Normal Marker offsets X and Y to the current marker position and sets the Marker to Relative to Offset relative marker readings SR785 Dynamic Signal Analyzer 5 48 Marker Commands If Marker Rel is Relative to Offset MRON d sets the Marker Rel to Off absolute marker readings MRON d returns 0 if Marker Rel is Off and 1 if Marker is Rel to Offset This command is only valid if the Marker Mode for display d is Normal SR785 Dynamic Signal Analyzer Marker Commands 5 49 Marker Commands Harmonic HRMN 7 d i The HRMN command sets queries the Number of Harmonics for display d The parameter i is a number of harmonics from 1 to 100 This command is only valid if the Marker Mode for display d is Harmonic HDSP d i The HDSP command sets queries the Harmonic and Sideband Marker Display for display d For Harmonic Marker 1 0 selects the Fundamental 1 1 selects 2xFundamental etc The maximum value of 11s the Number of Harmonics For Sideband Marker i 0 selects the Fundamental i 1 selects the first lower sideband i 1 selects the first upper sideband The maximum value of i plus or minus the Number of Sidebands 1 lt 0O is valid only for Sideband marker This command is only valid if the Marker Mode for display d is Harmonic or Sideband HRDO 7 d i The HRDO command sets queries the
411. ker Width of the active display Spot Normal Wide The Normal Marker Mode defines a Marker Region between two solid vertical lines The Width may be set to a single point Spot or 1 2 Normal or 1 Wide grid division The Marker is the small square which Seeks the Max Min or Mean of the data within the Marker Region Each display has its own Normal Marker Width This entry field can be linked to both displays using the Link key SR785 Dynamic Signal Analyzer Rel X Rel Normal Marker Menu 4 55 Command MWID d 1 Select the Normal Marker Rel Mode of the active display Off Relative Reference Display Other Display The Marker Position display above the graph shows the X position frequency or time and the Y value amplitude of the Marker A relative reading is preceded by a A delta symbol The X position may be shown absolute or relative in all cases as selected by lt X Rel gt When Rel is Off the absolute marker position is displayed Relative calculates the marker position relative to the Marker Offset X Rel Y Rel The Marker Offset location if it is within the display is marked by a small flag shaped symbol Reference Display calculates the marker position relative to the Reference Display The X position is absolute and the Y position is offset by the Reference Display value at the X position Ref Disp is only available if the Reference Display is On Other Display calculates the marker positi
412. ker menu Adjust the Marker Width of DisplayA Change the Marker Width to Spot The Link key links the two display markers together This allows simultaneous readout of Transfer Function Magnitude top and Phase bottom Pressing any key removes the linkage between the markers SR785 Dynamic Signal Analyzer 1 14 Measuring a Frequency Response Function To permanently link the Markers go to the Marker menu Press Marker Press lt Marker gt Select Link with the knob and press Enter Move the Marker with the knob SR785 Dynamic Signal Analyzer Select the Marker menu Adjust the Marker Type Linked Markers move together Since we changed the DisplayA Marker to Linked moving the DisplayA Marker moves the DisplayB Marker If DisplayB is active moving its Marker does not move the DisplayA Marker To do this change the DisplayB Marker Type to Linked also This concludes this measurement example You should have a feeling for the basic operation of two channel measurements and the use of Active Display Linking Advanced Operation 1 15 Linking Advanced Operation This example investigates the test filter enclosed with this manual using FFT measurements You will use the SR785 source to provide a broad band source and both displays to measure the output of the device under test Display parameter linking and function linking will be explored in greater detail 1 Press System Display the Syst
413. key enters the new parameter value or selection When selecting from a list of choices with the knob Enter will enter the new selection When entering a numeric value Enter will enter the new value Whenever the Enter indicator at the top of the screen is on Enter is required to enter the new choice or entry Indicates that the ALTERNATE keypad is in use The ALTERNATE keypad uses the alphabetic legends printed below each key To enter the ALT mode press the ALT key once Pressing the keys will now enter alphabetic characters into the active entry field The O 9 lt and ALT have the same function in the ALTERNATE keypad In ALTERNATE mode the knob moves the waterfall marker along the Z axis To return to the normal keypad press the ALT key again GPIB RS232 This indicator shows RS232 if the interface responses are directed to the RS232 serial port This indicator shows GPIB and the GPIB address if the interface responses are directed to the GPIB port Use lt Output To gt in the System lt Remote gt menu to select the appropriate interface Comm Error SRQ Comm is displayed when the computer interface is idle RS232 flashes when there is activity on the RS232 interface GPIB flashes when there is activity on the GPIB interface ERR flashes whenever a computer interface error occurs such as illegal command or out of range parameter is received
414. l File Format The SR785 file conversion utilities include the capability of converting SR785 display files into Universal File Type 58 Function at Nodal DOF data sets SR780 78D Files The file conversion utility will accept SR780 78D files anywhere a SR785 78D file can be used This allows you to convert your old SR780 files to the SR785 format The file conversion utility however will not write SR780 files as output nor will it accept SR780 78C or 78W files as input SR785 Dynamic Signal Analyzer Using the File Conversion Utilities 6 5 Using the File Conversion Utility The disk supplied with the SR785 contains the conversion utility SRTRANS EXE There is no installation required simply copy to the program to your hard disk The program has a number of options some of which are generally applicable and some of which are specific to certain output file types In the following discussion of the program options text in brackets indicates optional parameters and text in italics indicates that the text should be replaced by the indicated parameters when using the program Using SRTRANS Usage SRT785 options infile outfile Infile specifies the file to be converted Wildcard file characters and are accepted Outfile specifies the name of the output file If no name is supplied the program creates an output file with the same name as the input file and an extension appropriate to the output file type Universal Option
415. l not be appropriate for that span Burst Chirp is a percentage of the Source Display FFT time record length Command CSRC 1 SR785 Dynamic Signal Analyzer Noise Source Menu 4 75 Noise Source Menu Amplitude Type The Noise Source menu is used to configure the noise source Source Off C On C Sine Chirp Noise E i Arb Amplitude 500 0 mV Type Type BL Vhite White Burst Burst 100 100 000 Source lt gt Display Source Period Display A 100 ms Set the peak Amplitude of the noise output The source output will overshoot this amplitude by as much as 100 a small percentage of the time Because of the nature of noise the peak amplitude is not perfectly defined Command NAMP x Select the Type of noise output White Pink Bandlimited White or Pink White Noise White noise provides equal noise density V VHz from 0 to above 102 4 kHz regardless of the measurement bandwidth of the displays The spectrum of white noise appears flat in an FFT spectrum The power spectral density PSD remains constant at all spans Pink Noise Pink noise rolls off at 3 dB oct providing equal energy per octave and extends beyond 102 kHz The spectrum of pink noise appears flat in octave analysis SR785 Dynamic Signal Analyzer 4 76 Noise Source Menu Burst BandLimited White Bandlimiting restricts the noise bandwidth to the measurement span of the Source Display Bandlimited noise is available on
416. l of 4n bytes are transferred Assert EOI with the final byte of the transfer Serial Poll until IFC bit 7 is set in the Serial Poll status before sending another command The TGET command uploads a Trace buffer to the host computer This command is valid only via the GPIB interface The parameter 1 selects a Trace 1 5 Trace 1 must contain data The uploaded data should be saved in its entirety by the host computer The saved data can be downloaded back to the SR785 at a later time using TPUT The TGET and TPUT commands allow a host computer to save and reload a trace buffer without using disks TGET uploads trace information as well as trace data TPUT restores the trace type length and other attributes as well as the data The upload sequence is as follows Host Send TGET 1 Do NOT wait for IFC to be set in the Serial Poll status SR785 Returns n 4 byte binary long int which is the number of bytes needed to transfer the Trace buffer Host On receipt of n 4 byte binary long int executes a binary read from the SR785 of n bytes Expect EOI with the final byte of the transfer Serial Poll until IFC bit 7 is set in the Serial Poll status before sending another command SR785 Dynamic Signal Analyzer 5 112 Data Transfer Commands TPUT i The TPUT command downloads Trace buffer data to the SR785 This command is valid only via the GPIB interface The parameter i selects a Trace 1 5 Trace 1 does not need to alread
417. lable as operators in User Math functions Input Transducer Units Transducers such as accelerometers or microphones convert a physical quantity such as acceleration or pressure into a voltage at the analyzer s input By assigning Transducer Units to an input measurements based upon the transducer signal may be displayed in units of the actual physical quantity being measured such as m s or Pascals Transducer Units require a transducer which 1s linear over the frequency range of interest Measurements of inputs which are assigned units of acceleration velocity or displacement may be displayed with any of these three units using Transducer Convert in the Display Options menu SR785 Dynamic Signal Analyzer 2 68 Input Connections Input Connections In order to achieve the best accuracy for a given measurement care must be taken to minimize the various noise sources which can be found in the laboratory With intrinsic noise Johnson noise 1 f noise or input noise the signal source must be designed with these noise sources in mind These noise sources are present regardless of the input connections The effect of noise sources in the laboratory such as motors signal generators etc and the problem of differential grounds between the signal source and the analyzer can be minimized by careful input connections There are two basic methods for connecting a voltage signal to the analyzer the single ended connection is
418. lar 1 This command is valid only when the Input Source is Playback The ISPD command sets queries the Capture Playback Speed The parameter 1 selects Normal 0 or Every Frame 1 This command is valid only when the Input Source is Playback SR785 Dynamic Signal Analyzer 5 66 Trigger Commands Trigger Commands TMOD 7 i TSRC i The TMOD command sets queries the Trigger Arming Mode The parameter 1 selects Auto Arm 0 Manual Arm 1 RPM Arm 2 or Time Arm 3 The TSRC command sets queries the Trigger Source The parameter 1 selects Continuous 0 Chl 1 Ch2 2 External 3 External TTL 4 Source 5 or Manual 6 TLVL x lt V mV ChU gt TSLP 7 i The TSRC command sets queries the Trigger Level The parameter x is the trigger level in the specified units The query command returns two values in the form f where f is the trigger level and j is the index into the list of units The ChU Unit are equivalent to EUs if EUs are turned on for the active display otherwise ChU are equivalent to Volts The TSRC command sets queries the Trigger Slope The parameter 1 selects Rising 0 or Falling 1 TDLA 7 x lt s ms us gt The TDLA command sets queries the Trigger Delay 1 The parameter x is the delay in the specified units This command is valid only when the Measurement Group is FFT or Correlation TDLB 7 x lt s ms us gt TARM STMD 7
419. lay which determines the burst time record FFT time record and the bandwidth for bandlimited noise and chirp FFT Span There is a single Source Display for both Chirp and Noise outputs Changing this entry for one type of source also changes it for the other Select which display sets the bandwidth for bandlimited noise Burst Noise is a percentage of the Source Display FFT time record length SR785 Dynamic Signal Analyzer Noise Source Menu 4 77 The noise output is continuous for Octave Analysis Command CSRC 1 Source Period Set the Burst Period for noise in Octave group 4 ms 1ks In Octave and Order group the burst period is not linked to a display but is specified in time by the Source Period The burst output is present for a Burst percentage of the Source Period Triggering When the burst percentage is less than 100 the burst noise source is triggered by External triggers Set the Trigd Source Mode to trigger once 1 Shot or with every trigger Continuous In the 1 Shot case the burst source only triggers on the first trigger after Start Reset This same trigger starts the measurement and waterfall In the Continuous case the source triggers on every trigger with a minimum trigger period set by the Source Period Source trigger outputs a noise burst every source period Free Run Trigger Mode outputs a noise burst every source period Do not use Ch1 or Ch2 input trigger since the output will not start
420. lays Command FSPN d f Set the FFT Span of both displays to the FFT Base Frequency 102 4 100 0 kHz The Linewidth Acquisition Time Start frequency and Center frequency are set to 256 250 Hz 3 906 4 00 ms 0 0 Hz and 51 2 50 0 kHz respectively SR785 Dynamic Signal Analyzer FFT Frequency Menu 4 9 FFT Lines Select the FFT Resolution of the active display 100 200 400 800 lines Changing the FFT Resolution does not change the Span Instead the Acquisition Time is changed FFT Resolution Span Fewer lines means wider linewidths poorer resolution but faster measurements More lines means narrower linewidths better resolution but slower measurements The various FFT resolutions are summarized below FFT Frequency Resolution Resolution Time Record 100 lines Span 100 100 Span 200 lines Span 200 200 Span 400 lines Span 400 400 Span 800 lines Span 800 800 Span The two displays can have different number of Lines if the Analyzer Configuration is set to Independent Channels In this configuration no two channel measurements are allowed frequency response cross spectrum etc but the entry field can be linked or unlinked using the Link key If Analyzer Configuration is set to Dual Channel they field 1s automatically linked to both displays Command FLIN d 1 Base Frequency Select the FFT Base Frequency 102 4 kHz 100 0 kHz The Base Frequency sets the Full Span bandwidth for FFT and Co
421. lect Ch2 with the knob and press Enter Press lt Ch2 Coupling gt Select AC with the knob and press Enter 10 Press Freq Press lt Auto Resolution gt Select On with the knob and press Enter SR785 Dynamic Signal Analyzer When Auto Range is on the Input Range is optimized at each frequency point in the sweep If the signal is overloaded the range moves up If the signal is below half scale the range moves down This optimizes the input signal to noise at each point separately and can dramatically improve the S N of measurements with a large dynamic range Measurements in excess of 140 dB of dynamic range are possible with swept sine This notch filter is only 60 dB deep and does not actually require Auto Range for a clean measurement Note that the Ch2 Input Range changes as the sweep moves through the notch following the filter output signal Auto Range increases the sweep time Select the Input Configuration submenu Select Ch2 Input Configuration Change the Input Coupling for Ch2 Choose AC coupling This eliminates the DC offset from the source and allows Auto Range on Ch2 to cover the entire allowable input range Select the Frequency menu Change the Auto Resolution mode Choose Auto Resolution on If successive points differ by less than the Faster Threshold on both Chl and Ch2 then the sweep starts to skip points Each successive time this threshold is met the number of points skipp
422. les into formats suitable for modal analysis programs Command RFNA s Reference Number Enter the identification for the reference node For a frequency response function the reference node is the node where the stimulus is applied The number may be any integer The SR780 does not use the nodal degree of freedom information itself The information is stored with the 78D file and is available for use by external programs which convert the SR780 files into formats suitable for modal analysis programs Command RFNU 1 SR785 Dynamic Signal Analyzer 4 172 Nodal DOF Menu Reference Direction Enter the direction associated with the reference node 1 e the direction of the stimulus Direction can be specified either along the X Y or Z axes for linear stimulus or as 0x 0y or 8z direction for angular stimulus The SR780 does not use the nodal degree of freedom information itself The information is stored with the 78D file and is available for use by external programs which convert the SR780 files into formats suitable for modal analysis programs Command RFDR 1 Response Name Enter a descriptive name for the response node For a frequency response function the response node is the node where the response is measured e g the node where the accelerometer or other detector is placed The name may be up to six characters long The SR780 does not use the nodal degree of freedom information itself The in
423. less than half of the time record SR785 Dynamic Signal Analyzer 4 32 Display Setup Menu Capture The capture buffer stores sequential time domain data in memory See Capture in Chapter 2 for more details The capture measurement displays the contents of the capture buffer FFT measurements can use this stored data as input data by choosing Playback as the Input Source in the Input menu The capture buffer often stores many time records To graphically expand a region of the display use the Pan and Zoom functions in the Display Setup menu The capture buffer display will automatically pan as the capture fill and playback progress through the buffer During capture fill if the capture buffer contains more points than can be displayed points are skipped This speeds up the display update so that it keeps up with the real time capture but allows visual aliasing to occur Once capture is complete the display is redrawn showing the envelope of all points eliminating any visual aliasing effects To measure from a region of the buffer set the Playback Start and Length in the Input lt menu The capture data is filtered and down sampled according to the capture Sample Rate Only baseband data data bandwidth starts at DC are captured The capture buffer resembles a digital oscilloscope display Signals at frequencies above 1 2 56 times the sample rate have been filtered out The capture buffer is not a continuous representation
424. line number an error is returned The parameter j is the X axis bin number of line i Bin O is the leftmost bin in the display If there is no bin j in the display an error occurs This command is valid only if the Data Table for display d is On and display d is the active display Use the ACTD command to select the active display Only the Data Table of the active display may be edited or queried The DDLT command deletes line number 1 The value of 1 may not exceed the last line number in the table The remaining lines are renumbered sequentially The Data Table can not be erased completely The last remaining line may not be deleted This command is valid only if the Data Table for display d is On and display d is the active display Use the ACTD command to select the active display Only the Data Table of the active display may be edited or queried SR785 Dynamic Signal Analyzer 5 86 Data Table Commands DCLR d DTRD d i The DCLR command clears the Data Table for display d The Data Table can not be erased completely The last remaining line may not be deleted This command is valid only if the Data Table for display d is On and display d is the active display Use the ACTD command to select the active display Only the Data Table of the active display may be edited or queried The DTRD command queries the Data Table measurement results for display d The DTRD d command queries the entire table The data is returne
425. linear average is done the result is stored in the waterfall buffer and the average is reset and started over instead of stopping Each completed average counts as a single waterfall record Command WSTO d 1 Select whether the analyzer should store all the measurements in the current measurement group or only the currently displayed measurements SR785 Dynamic Signal Analyzer Total Count Waterfall Menu 4 137 When All is selected the SR785 stores all the measurements in the current measurement group to the waterfall buffer This allows later viewing of any measurement but uses up more space in the waterfall buffer When Active Measurement Only is selected the SR785 stores only the currently selected measurement for each display This takes less space in the waterfall buffer and allows a higher value for Total Count but only allows the currently selected measurements to be displayed Command WFSB d 1 Set the Total Count number of records to store in the waterfall memory for the active display The maximum Total Count depends upon the allocated memory and the setting of Save Option gt For example if 500 blocks of allocated waterfall memory are allocated and the lt Save Option gt is set to Active Measurement each display will store 250 400 line FFT measurements If lt Save Option gt is changed to Save All the buffer will be able to hold only 142 measurements Changing frequency resolution may reduce the
426. ll be zero padded If N is too large the extra points will be ignored Command TLOD i n Choose which data buffer Ch1 capture Ch2 capture Arbitrary Waveform or Waterfall to save to or load from disk Buffers which have no allocation may not be chosen Only the capture buffers specified by lt Capture Channels gt may be chosen Ch1 capture and Ch2 capture are saved and recalled separately Both can be recalled into a buffer configured for Chl Ch2capture channels SR785 Dynamic Signal Analyzer 4 180 Disk Buffers Menu Interval The waterfall buffers for both displays are saved together all stored waterfall records for both displays are saved If one display has waterfall storage off then no data is saved for that display Capture and Arbitrary files are compatible Data saved from a capture buffer can be loaded into the arbitrary waveform buffer and vice versa Choose to save the entire data buffer or only the playback portion Capture or Arbitrary Waveform All stored waterfall records for both displays are saved This only affects the saving of data to disk When a buffer 1s loaded from disk the buffer is configured to be exactly the length of the recalled data Disk to Buffer Load binary data from the Current File in the Current Directory into the selected data buffer This function only recalls files made using lt Buffer to Disk gt The selected buffer Capture Arbitrary Waveform or Waterfall must have sufficie
427. lowly varying potentials This source of noise is typically at very low frequency since the temperature generally changes slowly This effect is large on the scale of many signals 10 s of uV and can be a problem for low frequency measurements especially in the mHz range Some ways to minimize thermocouple effects are 1 Hold the temperature of the signal source or detector constant 2 Use a compensation junction i e a second junction in reverse polarity which generates an emf to cancel the thermal potential of the first junction This second junction should be held at the same temperature as the first junction SR785 Dynamic Signal Analyzer Curve Fitting and Synthesis 2 75 Curve Fitting and Synthesis Often the frequency response measurements made in the FFT and Swept Sine measurement groups need to be compared to a theoretical model of the device s behavior This comparison is the job of Curve Fitting and Synthesis In curve fitting the analyzer extracts the best fit parameters of a linear frequency response function from a measured frequency response function In Curve Synthesis the analyzer transforms a set of frequency response parameters into an SR785 frequency response measurement which can be compared with the measured data Curve Tables Both curve fitting and curve synthesis use the SR785 s two Curve Tables The curve tables allow entry and editing of frequency response parameters in one of three formats polynomial pole
428. ltage card position and fuse value Disconnect the power cord open the fuse holder cover door and rotate the fuse pull lever to remove the fuse Remove the small printed circuit board and select the operating voltage by orienting it so that the desired voltage is visible when pushed firmly back into its slot Rotate the fuse pull lever back into its normal position and insert the correct fuse into the fuse holder Line Fuse Verify that the correct line fuse is installed before connecting the line cord For 1O0V 120V use a 1 5 Amp fuse For 220V 240V use a 3 4 Amp fuse IEEE 488 Connector The 24 pin IEEE 488 connector allows a host computer to control the SR785 via the IEEE 488 GPIB instrument bus The GPIB Address of the unit is set in the System lt Remote gt menu A GPIB plotter with HPGL compatible graphics may be connected to the IEEE 488 port In this case the SR785 will control the plotter to generate plots of the display graphs Select GPIB as the Output Destination and set the Plotter Address and Type in the Output menu Serial RS232 Connector The RS232 interface connector is configured as a DCE transmit on pin 3 receive on pin 2 The Baud Rate Parity and Word Length are set in the Setup lt Remote gt menu To connect the SR785 to a PC serial adapter which is usually a DTE use a straight through serial cable A serial plotter or printer may be connected to the RS232 port Select the Serial interface as the Output D
429. lters also called the power spectrum The spectrum gives a stable reading of the rms signal amplitudes and noise levels within each band RMS averaging results in a real spectrum and there is no phase information Capture The capture buffer stores sequential time domain data in memory See Capture in Chapter 2 for more details The Capture measurement displays the contents of the capture buffer Octave measurements can use this stored data as input data by choosing Playback as the Input Source in the Input menu The capture buffer is often very long To graphically expand a region of the display use the Pan and Zoom functions in the Display Setup menu The capture buffer display will automatically pan as the capture fill and playback progress through the buffer During capture fill if the capture buffer contains more points than can be displayed points are skipped This speeds up the display update so that it keeps up with the real time capture but allows visual aliasing to occur Once capture is complete the display is redrawn showing the envelope of all points eliminating any visual aliasing effects To measure from a region of the buffer set the Playback Start and Length in the Input menu The capture data is filtered and down sampled according to the capture sample rate Only baseband data data bandwidth starts at DC are captured The capture buffer resembles a digital oscilloscope display Signals at frequencies above 1
430. lution Resolution Time Record 100 bins Span 100 100 Span 200 bins Span 200 200 Span 400 bins Span 400 400 Span 800 bins Span 800 800 Span Starting the Span Above DC Using digital filtering alone requires that every span start at DC Frequency shifting is accomplished by heterodyning Heterodyning is the process of multiplying the incoming signal by a sine and cosine wave The resulting spectrum is shifted by the heterodyne frequency If we incorporate heterodyning with our digital filtering we can shift any frequency span so that it starts at DC The resulting FFT yields a spectrum offset by the heterodyne frequency When this spectrum is displayed the frequencies of the X axis are the original frequencies of the signal Heterodyning allows the analyzer to compute zoomed spectra spans that start at frequencies other than DC The digital processor must filter and heterodyne the input in real time to provide the appropriate filtered and down sampled time record at all spans and center frequencies SR785 Dynamic Signal Analyzer 2 10 FFT Time Record FFT Time Record The FFT operates on time records A time record is simply a sequence of data samples The duration of the time record is the FFT resolution span There are two types of time records those corresponding to baseband spans starting at DC and those corresponding to zoomed spans not starting at DC Zoomed time records are heterodyned frequency shifted and do NOT contain the i
431. ly 5N measurements Once in steady state further changes in the average are detected only if they last for a sufficient number of measurements Make sure that the number of averages is not so large as to eliminate changes in the data which might be important SR785 Dynamic Signal Analyzer Average Menus 4 109 When used with peak hold averaging this weighting mode is known as Continuous averaging This means that new measurements are continually being compared to the current maximum to determine the new peak Number of Averages Set the Number Of Averages for the active display 2 32767 The Number Of Averages specifies the number of measurements for Linear Fixed Length averages or the weighting of new data in Exponential Continuous averages The Start Reset key resets the current average and starts a new average The Pause Cont key pauses the average in progress Pressing Pause Cont again will continue the average from where it was paused Changing the Number Of Averages does not start averaging If the Analyzer Configuration is Independent Channels each display can have its own Number of Averages This entry field can be linked to both displays by using the Link key Command FAVN d 1 Display Average Select the type of averaging for the measurement displayed on the active display None RMS Vector Peak Hold Note that when Compute Averages is On the SR785 always computes the non averaged rms averaged
432. ly for the FFT and CorrelationMeasurement Group Command NTYP 1 Set the Burst Percentage of the noise 0 1 100 In FFT group the noise waveform is output for a percentage of the FFT time record of the display selected as the Source Display In Octave group the burst period is not linked to a display but is specified in time by the Source Period For a continuous output use 100 burst Triggering When the burst percentage is less than 100 the burst noise source is triggered by External triggers Set the Trigd Source Mode to trigger once 1 Shot or with every trigger Continuous In the 1 Shot case the burst source only triggers on the first trigger after Start Reset This same trigger starts the measurement and waterfall In the Continuous case the source triggers on every trigger with a minimum trigger period set by the time record of the Source Display FFT Correlation Time Histogram or the Source Period Octave Order Source trigger outputs a noise burst every source period or FFT time record The FFT time records are synchronized to the burst Free Run Trigger Mode outputs a noise burst every source period Do not use Ch1 or Ch2 input trigger since the output will not start until a trigger is received Command NBUR x Source Display Select the Source Display DisplayA DisplayB The Source Display only applies for the FFT and Correlation Measurement Groups The Source Display is the disp
433. m memory Press lt Return gt for the lt Memory Test gt menu Display the Disk Drive Test screen Continuing with this test will destroy any data on the disk currently in the drive Remove the data disk and insert a scratch disk This test will check the controller format the disk and perform a read write check on the disk The entire test takes about 2 minutes Press lt Begin gt to start the test When the test reaches the Disk Changed Sensor Out phase remove the disk and then insert it again SR785 Dynamic Signal Analyzer 4 202 System Diagnostics Menu Press lt Return gt for the lt Diagnostics gt menu Serial Number Reset the internally stored serial number after replacing the DSP board The serial number which is reported on the power on screen and in the GPIB identification string is stored in the calibration ROM on the DSP board Do not use this function unless the DSP board has been replaced After replacing the DSP board enter the unit serial number shown on the rear panel and use lt Program S N gt to store the serial number permanently Press lt Return gt for the lt Diagnostics gt menu Program S N Reset the internally stored serial number after replacing the DSP board The serial number which is reported on the power on screen and in the GPIB identification string is stored in the calibration ROM on the DSP board Do not use this function unless the DSP board has been replaced After replacing the D
434. m to the input power spectrum a technique called the tri spectral average Coherence The coherence function is a two channel measurement defined as Coherence Mag RMSAveg CrossSpec Pwrl Pwr2 Averaging 1s always On and the Averaging Modes are defined by the measurement above The Type and Number Of Averages are still selected in the Average menu Coherence is a unitless real quantity and varies from 1 0 perfect coherence to 0 0 no coherence Coherence measures the percentage of power in the response channel 2 which is caused by phase coherent with power in the reference or input channel 1 Ideally a coherence of 1 0 means that the corresponding Frequency Response is completely legitimate All of the response power came from power at the input If there is noise or other signals generated from within the device under test which is not related to the input signal it will result in a coherence of less than 1 0 Capture The capture buffer stores sequential time domain data in memory See Capture in Chapter 2 for more details The capture measurement displays the contents of the capture buffer FFT measurements can use this stored data as input data by choosing Playback as the Input Source in the Input menu The capture buffer often stores many time records To graphically expand a region of the display use the Pan and Zoom functions in the Display Setup menu The capture buffer display will automatically
435. mal Marker X Offset Normal Marker Y Offset Marker Max A Read Marker Max B Read Marker Statistics On Marker Mean A Read Marker Mean B Read Normal Marker Seeks Mode Marker Min A Read Marker Min B Read Reset Marker Statistics Marker Std Dev A Read Marker Std Dev B Read Marker Move Waterfall to record 1 Normal Marker Width Normal Marker X Rel Mode Noise Amplitude Averages Completed Octave Averages Completed Noise Burst Percentage Display Note Noise Source Period Noise Type Track 1 BNC Track 1 Order Track 2 BNC Track 2 Order Octave Channels Octave Confidence Level Delta Order Octave Highest Band Octave Power Bin Octave Linear Average Mode Octave Lowest Band Max Order Track Points Octave Resolution Min RPM Max RPM Track Storage Mode Octave Average Time Order Tracking Octave Average Type Output Remote Interface Overide Remote P PAUS PAVA PAVO d i PAVR PAVT 2 d x PBLK i PBRI i PCIC 2 i PDIM i PDST i PFIL 2 i PGRF i PHSL d x PLAY i PLGD i PLMK i PLOT PLOT PLTA 2 i PLTP i PLTR i PLTX 2 i POUT 2 i PRNT PRNT PRTP i PSCR D i PSDU d i R RCRE d i RCTR d i REFY d j RFEDR i RFNA s RFNU i RPMF i RSDR i RSNA s RSNU i S SLAM x S1FR f S2AM x S2FR f SARS 2 d i SAVR 2 i SBRI 2 i SCON i
436. mand EFIT d Synthesize Table 1 and 2 Synthesizes the curve in table 1 or 2 into a trace The frequency range and resolution over which the synthesis is performed is determined by the active display which must be part of the FFT or swept sine measurement group When the synthesis is complete the data in the active display is replaced by the trace containing the synthesis SR785 Dynamic Signal Analyzer 4 162 Curve Fit Menu The synthesis uses the frequency scaling specified in the curve table being synthesized For instance if the frequency scaling is set to 1000 the term s 1 in the curve table will produce a pole at kHz in the synthesized frequency response Command ESYN 1 d Table Turns the curve table display on and off When the curve table display is on you can use the edit table menu to modify poles zeros residues polynomial coefficients overall gain delay or frequency scaling SR785 Dynamic Signal Analyzer Fit Setup Menu 4 163 Fit Setup Submenu Fit setup Number Poles Number Zeros 4 Weighting User Weighting Trace Set Fit Rgn C Return Number Poles Specifies the number of poles to use in the fit 0 20 The analyzer will compute the best fit to the data in the active display using the specified number of poles Each complex pole is actually a member of a complex conjugate pair and counts as 2 poles Command ENPL 1 Number Zeros Specifies the number of zer
437. marker X position in absolute units Each display has its own X Rel Mode This entry field can be linked to both displays using the Link key Command MXRL d 1 SR785 Dynamic Signal Analyzer Normal Marker Menu 4 57 Marker X to Sends the marker to the X position specified by the Target softkey The target position is entered in the current units of the x axis If the exact x value specified is not available the marker will be sent to the closest available X value Target Specifies the X position the marker will be sent to with the Marker X to button The target is entered in the current units of the x aaxis If the exact x value specified is not available the marker will be sent to the closest available X value SR785 Dynamic Signal Analyzer 4 58 Harmonic Marker Menu Harmonic Marker Menu Harmonics Display This menu is displayed when the active display Marker Mode 1s Harmonic Marker Setup Marker Harmonics 3 Display Fundamental Readout Mode Absolute THD 0 00737 RMS Harm Power 18 44 u Vrms Set the Number Of Harmonics for the active display 1 100 The second harmonic 2xfundamental is identified as 1 etc The Harmonic Marker identifies the fundamental frequency with the Fundamental Marker solid vertical line and the number of harmonics with small triangular Harmonic Markers The Marker Position Display can read the Fundamental or a single Harmonic Only those
438. me is 1 Sxbandwidth for each band in the measurement The bandwidth of an octave filter 1s given by 1 Bandwidth Center Frequency x 22n where n 1 3 or 12 octave 92n Settle is shown below the graph while settling takes place Bands which are un settled are displayed at half intensity in the graph When Waterfall Storage is selected records are not added to the waterfall buffer while octavebands are still settling SR785 Dynamic Signal Analyzer Swept Sine Measurements 2 47 Swept Sine Measurements A swept sine measurement is basically a sine sweep which steps through a specified sequence of frequency points At each point the source maintains a constant frequency and the inputs measure signals only at this frequency After each measurement point is complete the source then moves to the next point in the sequence Unlike the FFT which measures many frequencies at the same time a swept sine source measures the frequency response a single frequency at a time Why Use Swept Sine Frequency response can be measured using the FFT However if the frequency response has a large variation within the measurement span then the FFT may not be the best measurement technique It s limitation comes from the nature of the chirp source that must be used The FFT measures the response at all frequencies within the span simultaneously thus the source must contain energy at all of the measured frequencies In the time record
439. measurement is a two dimensional plot showing RPM on the x axis and time on the y axis Orbit The orbit measurement is a two dimensional plot of the Channel 2 time record vs the Channel time record The orbit measurement is often used in shaft balancing applications Track The Order Track measurement is a two dimensional plot of the amplitude of a given order vs RPM The Track measurement can only be selected when Tracking is turned on in the Frequency menu The order and input channel displayed by the track measurement is selected with the Track Setup submenu The amplitude recorded in the track is the Linear Spectrum and contains both amplitude and phase information Since the tracking feature uses the memory allocated to the Waterfall Order buffer the waterfall buffer is not available for waterfall storage when tracking is enable Capture The capture buffer may be used as a source of data for order measurements See Capture Buffer for more details The Capture measurement displays the contents of the capture buffer Order measurements can use this stored data as input data by choosing Playback as the Input Source in the Input menu In the order analysis measurement group the capture buffer must store information about the tachometer input as well as the signal inputs Therefore only capture buffers that were taken while the analyzer is in the order measurement group may be used as a source of data for order measurements dur
440. med with respect to the X axis bin number not the x axis values For example to convert d dx to d df for a linear frequency display divide by the frequency spacing of the bins In the case where the X axis is logarithmic the function needs to correct for ddlogx dx The d dx operator requires a smoothing aperture or window GrpDly is the group delay operator Group delay is simply d6 dw Use Display Options lt d dx Window gt to set the aperture This operator yields valid results for any complex operand which has a frequency x axis AWt is the A Weighting operator This filter is a software version of the input A Weight filter BWt and CWt are the software B Weighting and C Weighting operators The AWt BWt and CWt operators should only be used on operands with a frequency x axis All three filters conform to ANSI Standard S1 4 1983 User Function Limits User Functions and Constants are defined in the User Math menu Only the 5 functions within the current Measurement Group are available for editing in this menu Editing a function which is currently being displayed is allowed In this case Traces which do not contain compatible measurements are not allowed as operands User Functions have a maximum length of 31 operators plus operands User Functions cannot use another User Function as an operand SR785 Dynamic Signal Analyzer Signal Inputs 2 65 Signal Inputs The Input Range on the SR785 va
441. ment Group is FFT Correlation or Order The set command requires display d to be Live W1FE i The WIFE command sets queries the window which will be applied to Channel 1 when the main window selection is Force Exponential If the Analyzer Configuration is set to Independent Channels the command sets queries the window which will be applied to the measurement in Display A The parameter 1 selects Force Window 0 or Exponential Window 1 This command is valid only when the Measurement Group is FFT or Order The set command requires display d to be Live and the Force Exponential Window to be selected W2FE i The W2FE command sets queries the window which will be applied to Channel 2 when the main window selection is Force Exponential If the Analyzer Configuration is set to Independent Channels the command sets queries the window which will be applied to the measurement in Display B The parameter 1 selects Force Window 0 or Exponential Window 1 This command is valid only when the Measurement Group is FFT or Order The set command requires display d to be Live and the Force Exponential Window to be selected FWEL 7 d x lt s ms us gt The FWFL command sets queries the FFT Force Window Length for display d The parameter x is the duration of the force window in the specified units SR785 Dynamic Signal Analyzer Window Commands 5 79 This command is valid only when the Measurement Group is FFT or Or
442. ments which differ by more than the Faster Threshold on EITHER channel but less than the Slower Threshold on BOTH channels maintain the present sweep speed Generally the Slower Threshold should be set to less than half of the smallest desired feature size relative to the region before the feature A good rule is to set the Slower Threshold at twice the Faster Threshold Command SSLO D d 1 SR785 Dynamic Signal Analyzer Order Frequency Menu 4 19 Order Frequency Menu Max RPM Min RPM Max Order When the Measurement Group is Order this menu sets parameters related to which orders the SR785 will compute and track These parameters govern the measurements on both displays See Order Analysis in Chapter 2 for a discussion about order measurement fundamentals Frequency Max ARF M 6e 004 Min RPM 30 hax Order g i o IF Track Setup _ gt Delta Order a Set the maximum rotational speed allowed during order measurements The maximum rpm can take on a value between that specified by Min RPM and a value calculated from the Max Order by the formula max Max RPM 60 40 000 Max Order Selecting a lower Max RPM will allow calculation of higher orders Command ORMX d f This parameter does not affect the way order measurements are calculated by the SR785 It merely provides a default lower value by which to scale measurements whose x axis 1s RPM such as RPM profiles and Tracked Orders Co
443. meters are unlinked Span Down has no affect for Swept Sine measurements Order measurements or Time Histogram measurements Link Span Down is the same as Span Down Command FSPN d 1 Marker Ref Marker Ref toggles the Marker Rel Mode in the Marker menu between Off and Relative for the active display If Marker Rel is Off Marker Ref sets Marker Rel to Relative and sets the X Rel and Y Rel Marker Offsets to the current Marker Position Subsequent marker readings are relative to this offset The relative Marker Position values are preceded by a A delta symbol The Marker Offset location within the display is marked by small flag shaped symbols If Marker Rel is Relative Marker Ref sets Marker Rel to Off and the Marker Position is absolute Marker Ref has no affect if the Marker Rel Mode is not Off or Relative Link Marker Ref toggles the Marker Rel Mode of both displays Command MRON d Display Ref Display Ref toggles the Reference Display within the active display If the Reference Display is off Display Ref loads the Reference Display with the current display data The Reference Display is graphed in half intensity This allows comparison of new data with the stored Reference Display Set the Marker Relative to Reference Display in the Marker menu to read the Marker Position relative to the Reference Display Press Display Ref again to turn off the Reference Display If display param
444. mic Signal Analyzer KEYP i Front Panel Commands 5 105 The KEYP command performs the same function as pressing key 1 in the table below key lt Softkey 1 gt top lt Softkey 2 gt lt Softkey 3 gt lt Softkey 4 gt lt Softkey 5 gt lt Softkey 6 gt lt Softkey 7 gt lt Softkey 8 gt lt Softkey 9 gt lt Softkey 10 gt bottom Freq Display Setup Display Options Marker Source Input Trigger Average User Math Window Waterfall Capture Analysis Disk Output System AutoScale A AutoScale B Span Up Span Down AutoRange Ch1 AutoRange Ch2 Marker Max Marker Min Marker Ref Display Ref Marker Center Show Setup Start Reset Pause Cont Start Capture Stop Capture Active Display Link Print Screen 40 34 35 36 41 42 43 44 49 50 51 52 57 58 59 60 37 45 53 61 38 46 54 62 39 47 55 63 17 25 18 26 19 27 20 SR785 Dynamic Signal Analyzer 5 106 Front Panel Commands Help Local 28 Alt 7 Backspace 6 Exp 5 0 29 1 21 2 22 3 23 4 13 5 14 6 15 7 2 8 3 9 4 30 31 Enter l Brighter 56 Dimmer 48 KNOB i The KNOB command simulates turning the knob The parameter 1 selects counter clockwise 0 or clockwise 1 TONE i j The TONE command makes an audible tone The parameter 1 is the duration in 5 ms increments and j selects a note from 0 to 66 Sequential TON
445. mmand ORMN d f Specifies the maximum order 1 e multiple of the rotational speed calculated by the SR785 Allowed values are between 3 and 200 Choosing a higher Max Order will limit the allowed range of Max RPM Command OMAX d f SR785 Dynamic Signal Analyzer 4 20 Order Frequency Menu Delta Order Tracking Track Setup Sets the resolution for order spectra The value may range between Max Order divided by 400 and 1 0 Choosing a smaller value for Delta Order higher resolution increases the time it takes to acquire an order spectrum Command ODLT d f Turns order tracking on and off When tracking is On the Track and Track2 measurments become available in the order measurement group The Track measurements are plots of the amplitude of one particular order as a function of RPM Because track measurements use the memory allocated to the waterfall buffer you cannot use waterfall storage while Tracking is on Command OTRK 7 d 1 Displays the track setup submenu This submenu displays parameters which define the Track1 and Track2 measurements Continuous Track 1 Order i 1 Input Channel Ch 1 Track 2 Order Ch2 Return Input Channel Track Points Sets the number of points for track measurements When the specified number of points have been acquired the measurement will either stop or wrap around depending on the setting of the track storage softkey A track meas
446. mmand is valid only when the Measurement Group is Swept Sine The set command requires a display to be Live SSTY d i The SSTY command sets queries the swept sine Sweep Type of display d The parameter 1 selects Linear 0 or Logarithmic 1 The set command requires d 2 both displays This command is valid only when the Measurement Group is Swept Sine The set command requires a display to be Live SARS 7 d i The SARS command sets queries the swept sine Auto Resolution Mode of display d The parameter 1 selects Off 0 or On 1 The set command requires d 2 both displays SR785 Dynamic Signal Analyzer Frequency Commands 5 33 This command is valid only when the Measurement Group is Swept Sine The set command requires a display to be Live SNPS 7 d i The SNPS command sets queries the swept sine Number Of Points of display d The parameter 1 is a number of points from 10 to 2047 The set command requires d 2 both displays This command is valid only when the Measurement Group is Swept Sine The set command requires a display to be Live SSKP 7 d i The SSKP command sets queries the swept sine Maximum Number Of Skips of display d The parameter 1 is a maximum number of skips from 2 to 200 The set command requires d 2 both displays This command is valid only when the Measurement Group is Swept Sine The set command requires a display to be Live SFST d x The SFST command set
447. mplitude recorded in the track is the Linear Spectrum and contains both amplitude and phase information Since the tracking feature uses the memory allocated to the Waterfall Order buffer the waterfall buffer is not available for waterfall storage when tracking is enable RPM Profile The RPM profile measurement is a two dimensional plot showing RPM on the x axis and time on the y axis Orbit The order Orbit measurement is a two channel measurement whose real part is the real part of Time Record Ch1 and whose imaginary part is the real part of Time Record Ch2 Orbit is normally displayed with the Nyquist View Time2 vertical vs Time horizontal Orbit measurements are often used in the order measurement group for shaft balancing Capture The capture buffer stores sequential time domain data in memory See Capture in Chapter 2 for more details The capture measurement displays the contents of the capture buffer Order measurements can use this stored data as input data by choosing Playback as the Input Source in the Input menu In the order measurement group the capture buffer stores tachometer information as well as input data Therefore only a capture buffer which was taken while the instrument was in the order group can be used as a source of playback data for order measurements Note that in order group the data in the capture buffer will not look like the data in the order time record The capture buffer contains data sampl
448. n 5 28 Output Commands 5 97 Frequency Commands Octave 5 30 System Commands 5 100 Frequency Commands Swept Sine 5 32 Front Panel Commands 5 102 Frequency Commands Order Analysis 5 34 Data Transfer Commands 5 107 Frequency Commands Time Histogram 5 36 Interface Commands 5 117 Display Setup Commands 5 37 Nodal Degree of Freedom Commands 5 118 Display Options Commands 5 43 Status Reporting Commands 5 120 Marker Commands 5 45 ne Word Definition 124 Marker Commands Normal 5 47 Slate tr ore DENNIMKONS 9 Marker Commands Harmonic 5 49 Example Program 5 129 Marker Commands Sideband 5 50 Marker Commands Band 5 51 Marker Commands Frequency Damping 5 52 Source Commands 5 53 Sine Source Commands 5 54 Chirp Source Commands 5 55 Noise Source Commands 5 56 SR785 Dynamic Signal Analyzer 5 2 Index of Commands Index of Commands Variables d display O DisplayA 1 DisplayB 2 Both i J K 1 m integers X y real numbers f frequency in Hz S text string Frequency FFT and Correlation Measurement Group FSPN d f 5 28 FFT Frequency Span FLIN d 1 5 28 FFT Resolution FBAS d 1 5 28 FFT Base Frequency FSTR d f 5 28 FFT Start Frequency FCTR d f 5 28 FFT Center Frequency FEND d f 5 29 FFT End Frequency UNST d 5 29 Unsettle Measurement Frequency Octave Measurement Group OHIB d f 5 30 Octave Highest Band OLOB d f 5 30 Octave Lowest Band ORES d 1 5 30 Octave
449. n An error results if the entered directory does not exist New directories are created with lt Make Directory gt Command FDIR s Display to Disk Save the active display data to the Current File in the Current Directory If the Current File has no specified extension the default extension 78D is used The measurement frequency span averaging and window are stored with the data in order to preserve the integrity of the data when recalled Command FSAV d Disk to Display Recall data from the Current File in the Current Directory to the active display The active display will be set to Off Line when data is recalled to it The display will not update with live measurement results until the Display is set back to Live in the Display Options menu The measurement frequency span averaging and window are recalled with the data and cannot be changed These menus are shown in gray and reflect the settings or values for the last Live measurement Parameters which pertain to the display of the data such as scale and view may be changed in the Display Setup and Display Options menus SR785 Dynamic Signal Analyzer Disk Menu 4 169 When the Display is returned to Live the measurement frequency span averaging and window all return to the settings in effect before the data was recalled and the live measurement returns to the display Command FRCL d Settings to Disk Save the instrument settings to the Curren
450. n Octave Swept Sine Order and Histogram For example to define FFT User Function 3 as FFT 1 FFT 2 the command USRE 3 10 1 20 is used If the function cannot be entered a command execution error occurs Operand Operation Token Valid in Groups Mag 101 F C O S Or H Conj 102 F C O S Or H Real 103 F C O S Or H Imag 104 F C O S Or H Ln 105 F C O S Or H Exp 106 F C O S Or H FFT 107 F C Or FFT u 108 F C Or IFFT 109 F C Or Sqrt 110 F C O S Or jOmega 113 F C S Phase 114 F C O S Or H Mag 115 F C O S Or H AWt 116 F C O S Or BWt 117 F C O S Or CWwt 118 F C O S Or d dx 119 F C O S Or GrpDly 120 F C O S X 1 X 121 F C O S Or SR785 Dynamic Signal Analyzer n yx FFT Group Operands Time 1 Time 2 FFT 1 FFT 2 lt Pwr 1 gt lt Pwr 2 gt lt Coherence gt lt CrossSpec gt lt Freq Resp gt Vec lt F1 gt Vec lt F2 gt RMS lt FI1 gt RMS lt F2 gt PeakHold lt F1 gt PeakHold lt F2 gt RMS lt CrossSpec gt Correlation Group Operands Time 1 Time 2 Auto_Corr 1 Auto_Corr 2 X_Corr 3 5 6 20 21 22 23 14 15 70 71 pe 24 25 26 21 28 29 67 20 21 64 65 73 User Math Commands 5 75 F C O S Or H F C O S Or H F C 0O S Or H F C O S Or H F C O S Or H F C O S Or H SR785 Dynamic Signal Analyzer 5 76 User Math Commands FFT 1 22 FFT 2 23 FFTu 1 30 FFTu 2 31 Vec lt Ful gt lt F1 gt 32 Vec lt Fu2 gt lt F2 g
451. n addition the host program may need to check that these operations executed without error In these cases after the command is sent the status should be queried When using the GPIB interface serial polling may be used to check the IFC bit in the Serial Poll status while an operation is in progress After the IFC bit becomes set signaling the completion of the command then the IERR bit may be checked to verify successful completion of the command If the RS232 interface is used or serial polling is not available then the STB query command may be used to read the Serial Poll status word However STB NEVER returns the IFC bit set since STB is itself a command Since the SR785 processes one command at a time status queries will not be processed until the previous operation is finished Thus a response to a status query in itself signals that the previous command is finished The query response may then be checked for various errors For example the command line FSAV 0 ERRS lt If gt will save the DisplayA data to disk and return the Error Status word when finished The Disk Error bit may be checked to make sure that the FSAV Display to Disk command completed without error Since the FSAV command may take a long time to execute it 1s important that the host computer interface does not time out while waiting for the response to the ERRS query In the case where the host interface times out before the ERRS response the host
452. n algorithm known as the Fast Fourier Transform or FFT The resulting spectrum shows the frequency components of the input signal The original digital time record comes from discrete samples taken at the sampling rate The corresponding FFT yields a spectrum with discrete frequency samples or bins In fact the spectrum has half as many frequency bins as there are time points Remember Nyquist s theorem Suppose that you take 1024 samples at 262 kHz It takes 3 9 ms to take this time record The FFT of this record yields 512 frequency points but over what frequency range The highest frequency will be determined by the period of 2 time samples or 131 kHz The lowest frequency is just the period of the entire record or 1 3 9 ms or 256 Hz The output spectrum thus represents the frequency range from DC to 131 kHz with 512 points spaced every 256 Hz SR785 Dynamic Signal Analyzer Measurement Groups 2 7 Advantages And Limitations The advantage of this technique is its speed The entire spectrum takes only 3 9 ms to measure The limitation of this measurement is its resolution Because the time record is only 3 9 ms long the frequency resolution is only 256 Hz Suppose the signal has a frequency component at 380 Hz The FFT spectrum will detect this signal but place part of it in the 256 Hz bin and part in the 512 Hz bin One way to measure this signal accurately is to take a time record that is 1 380 Hz or 3 846 ms long with 1024 evenly spaced
453. n the Current Directory with the extension 78 SR785 files Press Exp to display all files in the directory Choose a file name with the knob and press Enter to make it the Upkeep File Name This file may be erased with lt Del File gt New file names are entered using the Alt key and the letters associated with each key Press Alt again to return to normal keypad operation DOS file name conventions must be followed File names are 8 characters or less with an extension ext of up to 3 characters Command DNAM 7 s Current Directory Enter the Current Disk Directory Turning the knob will bring up the directory tree display which lists all of the sub directories on the disk Choose a directory with the knob and press Enter to make it the Current Directory A directory may be entered using the Alt key and the letters associated with each key Press Alt again to return to normal keypad operation An error results if the entered directory does not exist SR785 Dynamic Signal Analyzer Disk Upkeep Menu 4 183 New directories are created with lt Make Directory gt Command FDIR s Make Directory Make a new directory on the disk Enter a directory name with the Alt key The new directory will be created in the Current Directory Command MDIR s Del File Delete the Disk Upkeep File from the Current Directory Make sure that the file and directory are correct before pressing this key Command
454. n the shields does not translate into signal noise since the shields are ignored The shields in this case are grounded by 50 Q since they are being used as signal shields When using two cables it is important that both cables travel the same path between the signal source and the analyzer Specifically there should not be a large loop area enclosed by the two cables Large loop areas are susceptible to magnetic pickup Common Mode Signals Common mode signals are those signals which appear equally on both center and shield A or both A and B A B With either connection scheme it is important to minimize both the common mode noise and the common mode signal If the signal source floats at a non zero potential the signal which appears on both the A and B inputs will not be perfectly canceled The common mode rejection ratio CMRR specifies the degree of cancellation For low frequencies the CMRR of 90 dB indicates that the common mode signal is canceled to part in 30 000 Even with a CMRR of 90 dB a 1 V common mode SR785 Dynamic Signal Analyzer Input Connections 2 69 signal behaves like a 3 uV differential signal The CMRR decreases by about 6 dB octave 20 dB decade starting at around 1 kHz AC vs DC Coupling The signal input can be either AC or DC coupled The AC coupling high pass filter passes signals above 160 mHz 0 16 Hz and attenuates signals at lower frequencies AC coupling should be used at frequencies above 160 mHz w
455. nd Use ERRE to set bits in the Error status enable register Bits 7 12 are set by the power on tests Bits 3 5 are set in the System lt Diagnostics gt SR785 Dynamic Signal Analyzer Example Program 5 129 Example Program Using Microsoft C with the GPIB interface A To successfully interface the SR785 to a PC via the GPIB interface the instrument interface card and interface drivers must all be configured properly To configure the SR785 the GPIB address must be set in the System lt Remote gt menu The default address is 10 use this address unless a conflict occurs with other instruments in your system The SR785 will be set to GPIB address 10 whenever a reset is performed power on with the backspace key down Make sure that you follow all of the instructions for installing the GPIB card The GPIB card cannot be simply unpacked and put into your computer To configure the card you may need to set jumpers and switches on the card to set the I O address and interrupt levels Refer to your manual for more information Capital Equipment Corp CEC488 GPIB Card The CEC488 card contains its low level drivers in ROM The card address needs to be set so as not to conflict with other devices in your computer The software interface uses a header file and a link library There is no initialization required for the drivers Use the TEST488 program to test the card installation Use TRTEST to communicate directly from the keyboard
456. nd is valid only when the Measurement Group is Order The set command requires a display to be live ODLT d x The ODLT command sets queries delta order for display d The parameter x is delta order a real number The range of f 1s between Max Order 400 and 1 The set command requires d 2 both displays This command is valid only when the Measurement Group is Order The set command requires a display to be live OTRK 7 d i The OTRK command sets queries tracking for display d The parameter 1 selects Off 0 or On 1 The set command requires d 2 both displays This command is valid only when the Measurement Group is Order The set command requires a display to be Live ONPT d i The ONPT command sets queries number of points in a track measurement for display d The parameter 1 is the number of points The set command requires d 2 both displays This command is valid only when the Measurement Group is Order The set command requires a display to be Live SR785 Dynamic Signal Analyzer Frequency Commands 5 35 OSTO d i The OSTO command sets queries the track storage mode for display d The parameter 1 selects Continuous 0 or One Shot 1 The set command requires d 2 both displays This command is valid only when the Measurement Group is Order The set command requires a display to be Live O1TK 7 d x The OITK command sets queries the order associated with the track 1 me
457. nd press Enter 4 Press Freq Press lt Lowest Band gt Use the knob to select 50 Hz and press Enter 5 Press Source Press lt On gt Press lt Noise gt Press lt Type gt SR785 Dynamic Signal Analyzer Display the System menu Preset returns the unit to its default settings Preset requires confirmation to prevent accidental reset Wait until the self tests are completed Setup to analyze the source output Select the Display Setup menu Change the Measurement Group Choose the Octave group Both displays are now making Octave Analysis measurements Select the Frequency menu Change the lowest band in the display Select 50 Hz as the lowest band The lowest band places a limitation on the minimum integration time Raising this lowest band allows shorter integration times Select the Source menu Turn the source on Choose Noise as the source type Octave measurements are generally used to measure noise Change the type of noise Use the knob to select Pink and press Enter Press lt Burst gt Press 9 6 Enter 6 Press Average Press lt Averaging Type gt Use the knob to select Linear Time and press Enter Press lt Integration Time gt Use the knob to select 8 ms and press Enter Press lt Linear Avg Trig gt Waterfall Display 1 35 Choose Pink noise Pink noise rolls off at 3dB per octave This maintains equal power per octave band and yields a flat
458. nd the full settling time of the measurement is required before the status returns to settled The measurement is unsettled by changing any one of several measurement parameters For example changing the input range or FFT span will unsettle the measurement If the signal comes from an external source and is changed in such a way as to require the measurement to settle it is convenient to use the UNST command and wait for settling to finish This command is valid only when the Measurement Group is FFT or Octave SR785 Dynamic Signal Analyzer 5 30 Frequency Commands Frequency Commands Octave OHIB 7 d f lt kHz Hz mHz wHz gt The OHIB command sets queries the Highest Band in the Octave measurement of display d The parameter f is a frequency real number in the specified units The Highest Band is specified to the nearest octave For 1 Channel octave analysis the set command requires d 2 This command is valid only when the Measurement Group is Octave The set command requires display d to be Live OLOB d f lt kHz Hz mHz wHz gt The OLOB command sets queries the Lowest Band in the Octave measurement of display d The parameter f 1s a frequency real number in the specified units The Lowest Band is specified to the nearest octave For 1 Channel octave analysis the set command requires d 2 This command is valid only when the Measurement Group is Octave The set command requires display d to be L
459. ndependent Chan 7 Press Freq Press lt Span gt Use the knob to adjust the Span to 12 8 kHz and press Enter Press lt Span gt again Press Link Use the knob to adjust the Span to 3 2 kHz and press Enter 8 Press Average Press lt Display Avg gt Select RMS with the knob and press Enter SR785 Dynamic Signal Analyzer In this example we ll want to set separate frequency spans for the two displays To do that the analyzer must be in the Independent Channels mode In the default Dual Channel mode the span is the same for both channels but dual channel measurements are allowed Select the Frequency menu The menu shows the frequency parameters for the measurement in DisplayA active display Highlight the Span Note that the Link indicator at the top of the screen turns on This indicates that the highlighted parameter Span is linked to both displays Changing a linked parameter affects both displays at once Narrow the Span of both displays to show the filter notch at 1 kHz noisy of course Highlight the Span again Pressing Link toggles parameter linking off The Link indicator now shows DispA indicating that this menu box adjusts the span for DisplayA only Change the Span of DisplayA to 3 2 kHz The Span of DisplayB remains at 12 8 kHz The SR785 allows the two displays to have differing Spans and Start frequencies in the Independent Channels mode Many parameters affect
460. ne result amp 0x0202 Check for AVGA and AVGB status bits until both have occurred Remember they may not be set together in the same query Do MOt check Tor both an the same query while avgdone amp 0x0202 0x0202 both AVGA and AVGB have occurred KKKKKKKKKKKKKKKKKKKKKKKRKKKKKKKKKEKKKKKKKKKRKKKKKKKKKKKKKKKKKKEKKKKKKKKHEK double GetData int disp int bin coutine to move the display marker to a bin and return the data value move the marker in display disp to bin Sprint tend MBIN sda Oda sp bain TxSR785 cmd sprintf cmd DSPY d d disp bin read the data value at bin GetSR7 85 cmd return atof recv return the value as a double KKKKKKKKKKKKKKKKKKKKKKKEKKKKKKKKKRKKKKKKKKKRK KKK KKKKKEKKKKKKKKKKKKKKKKKKEK Af void GetSpace void Wait for space key char ch while kbhit getch clear the keyboard buffer prince lt nxSpace gt Le continue lt O gt bo GULE Vy do ch char getch if ch q ch Q exit 0 exit while ch continue peri 0 an KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKEKKKKKKKKKEKKKKKKKKKKKKKKKKKKKKKKKKKKKK SR785 Dynamic Signal Analyzer 5 136 Example Program SR785 Dynamic Signal Analyzer Chapter 6 File Conversions In This Chapter Why File Conversion 6 2 SR785 File Types 6 3 78D Files 6 3 Buffers 78C and 78W Files 6 3 Supported External File Types 6 4 ASCII Files
461. ne heterodyne and FFT Signals in phase with cosine result in real data signals in phase with sine result in imaginary data The real and imaginary parts represent data 90 degrees out of phase Phase Phase view graphs the phase of the measurement data The phase is a four quadrant quantity defined as 9 arctan y x where y is the imaginary part and x is the real part and x is positive If x is negative an additional 180 deg is added to the phase Phase is graphed linearly from 180 7 to 180 m degrees radians To show unwrapped phase choose the Unwrapped Phase view Real measurement data such as baseband time record have zero imaginary part The phase is zero for all points Single channel phase is relative to the center of the time record for Uniform BMH Hanning Flattop and Kaiser windows For Force and Exponential windows phase is relative to the start of the time record In general single channel phase is useful only when the time record is triggered in phase with the signal For two channel measurements the phase is channel 2 relative to channel 1 Triggering is not generally required for meaningful two channel phase measurements Phase suppress sets the phase of small data values to zero This avoids the messy phase display associated with the noise floor Remember even a small signal has phase Set the phase suppress threshold in the Display Options menu The FFT can be thought of as a set of bandpass filters
462. ng the frequency axis of a single record SR785 Dynamic Signal Analyzer lt Manual Trigger gt supplies the first trigger The source outputs a single noise burst Trigd Source Mode One Shot The display starts a continuous stream of octave measurements each linear averaged for 8 ms and each starting when the previous average 1s complete Linear Avg Mode Continuous 50 averaged measurements are stored in the waterfall buffer starting with the trigger The first 96 ms 12 measurements are during the triggered noise burst The remaining measurements are taken after the noise burst turns off and measure the decay response or reverberation The number of records stored in the waterfall is shown in the Vertical Scale Bar as wf 50 Alt knob moves the marker in the Z direction time axis in the waterfall display This scrolls the display to show earlier measurement record When the keypad and knob are in the alternate mode the alternate key functions labeled below each key are in effect The waterfall records are numbered starting with O the most recent measurement in the back In this case we stored 50 records so the earliest record is number 49 The marker Z position is displayed next to the marker frequency in the Marker Position Bar above the graph It should read 49 when you have scrolled all the way to the beginning of the buffer Notice how the first few records show the spectrum growing at the start o
463. nge of the analyzer PDF The PDF or probability density function is a normalized version of the histogram The value of the PDF for a given voltage V multiplied by a small voltage interval AV is the probability that a sample of the signal will fall between V and V AV CDF The CDF or cumulative density function is the integral of the probability density function The CDF at a given voltage is the probability that a sample of the input signal will be below that voltage Time The time record in the time histogram measurement group shows the value of the input signal sampled at intervals specified by lt Sample Time gt softkey Unlike the FFT time record the histogram time record 1s not filtered as the sampling frequency is decreased and may contain aliased signals While this is important for the frequency domain measurements in the FFT measurement group it is not a consideration in time histogram group where the goal is to represent the original signal as closely as possible Capture The capture buffer stores sequential time domain data in memory See Capture in Chapter 2 for more details The capture measurement displays the contents of the capture buffer Time Histogram measurements can use this stored data as input data by choosing Playback as the Input Source in the Input menu The capture buffer often stores many time records To graphically expand a region of the display use the Pan and Zoom functions in the Display
464. niform window and invFFT is an inverse FFT SR785 Dynamic Signal Analyzer Display Setup Menu 4 31 Correlation is a real function and requires a baseband span real time record Non baseband time records do not preserve the original signal frequencies and thus do not yield the correct correlation The Start Frequency is always set to 0 in the Correlation Measurement Group A window is applied to the time record of the first FFT in the computation This 1s because the FFT models the time domain as a single time record repeating itself over and over Computing the correlation over a t greater than half of the time record length will result in wrap around errors where data starts to repeat itself To avoid this special windows which zero half of the time record are used The 0 T 2 window zeroes the second half of the time record and the T 4 T 4 window zeroes the first and last quarter of the time record The T 2 T 2 is a uniform window which should only be used on data which is self windowing lasts less than half of the time record Cross Correlation Cross correlation is a two channel measurement which is only available when the Input lt Analyzer Conig gt softkey is set to Dual Channel In the time domain it is a comparison of a signal x t with a time shifted version of another signal y t t displayed as a function of t This is useful for measuring time delays between two common signals The definition of Cross Cor
465. nk indicator next to the top of the menu reads either DispA or DispB whichever is the active display Parameter entry or selection modifies only the active display To change which display will be modified press Active Display When a linked parameter is highlighted the Link indicator reads Link Parameter entry or selection modifies both displays at once To link or unlink a parameter highlight the parameter softkey and press the Link key If the Link indicator is shown in gray then the parameter linking may not be changed SR785 Dynamic Signal Analyzer Enter ALT Status Indicators 3 21 The availability of linking and unlinking is affected by the setting of the Analyzer Configuration softkey For instance if Analyzer Configuration is set to Independent Channels Span may be unlinked and the two displays set to have different spans If Analyzer Config is set to Dual Channel however the span softkey will always be linked since Dual Channel measurements such as frequency response require both channels to have the same span Parameter linking is a convenient way of changing both displays together For example Span and Start frequency may be linked while the Measurement is unlinked This allows the two displays to have different measurements over the same frequency span Since the Spans are linked changing the Span does not require separate entries for each display When modifying a parameter the Enter
466. nob and press Enter to make it the Current File Name This file name is used for saving and recalling displays traces and settings Remember saving to this file will write over the existing file New file names are entered using the Alt key and the letters associated with each key Press Alt again to return to normal keypad operation DOS file name conventions must be followed File names are 8 characters or less with an extension ext of up to 3 characters Default extensions are automatically supplied if no extension is specified The default extensions should be used since the directory display assumes an extension appropriate for the current menu If the filename specified ends in a sequence of digits the filename will be incremented any time a save to disk operation is performed For instance if SRS001 78D is shown in the menubox it will be incremented to SRSOO2 78D after a save operation is performed SR785 Dynamic Signal Analyzer 4 168 Disk Menu Command FNAM 7 s Command FREE Command FXST s Command FRST Command FNXT Current Directory Enter the Current Disk Directory Turning the knob will bring up the directory tree display which lists all of the sub directories on the disk Choose a directory with the knob and press Enter to make it the Current Directory A directory may be entered using the Alt key and the letters associated with each key Press Alt again to return to normal keypad operatio
467. not be adjusted for an Off Line display SR785 Dynamic Signal Analyzer 1 52 User Math Functions User Math Functions This example measures the group delay of the test filter enclosed with this manual using User Math Functions You will use the SR785 source to provide a broad band source and both displays to measure the output of the device under test 1 Press System Press lt Preset gt Press Enter to confirm Preset 2 Use a BNC Tee to connect the Source Output to the filter input and the Ch1 A Input Connect the filter output to the Ch2 A Input 3 Press Source Press lt On gt Press lt Chirp gt Press Window Press lt Window gt Select Uniform with the knob and press Enter 4 Press Auto Range Chl Press Auto Range Ch2 5 Press Freq Press lt Span gt SR785 Dynamic Signal Analyzer Display the System menu Preset returns the unit to its default settings Preset requires confirmation to prevent accidental reset Wait until the self tests are completed In this instrument transfer function is defined as Ch2 response over Ch1 reference Thus Ch monitors the filter input source output and Ch2 measures the response of the device under test Select the Source menu Turn on the source Choose Chirp output The output is an equal amplitude sine wave at each frequency bin of the FFT spectrum Select the Window menu Adjust the FFT Window function The Chirp source req
468. nput signal at its original frequencies Baseband Time Records Baseband time records are very simple to understand They represent the input signal passed through low pass filters At full span the signal has passed through the analog anti aliasing filter The sample rate 1s 262 kHz To get the time records for narrower spans the data is digitally filtered and down sampled At a given FFT resolution each time the span is halved the bandwidth of the time record is halved and the sampling rate is halved The length of the time record in seconds doubles Heterodyned Time Records Zoomed time records are more complicated Heterodyning is a complex operation The input points are multiplied by cos t and sin at to yield a real and an imaginary part is 2m times the span center frequency The real and imaginary parts of each point are orthogonal You can think of the complex time record as two separate records one real and one imaginary The input signal is frequency shifted or heterodyned This moves signals at the span center to DC and frequencies below span center to negative frequencies If the span center is at 51 2 kHz the input range from 0 to 102 4 kHz is shifted to 51 2 kHz to 51 2 kHz This data is then passed through a low pass filter which cuts off at 51 2 kHz This results in a 51 2 kHz 102 4 kHz useable span centered at 51 2 kHz The output data only requires a sampling rate of 131 kHz instead of the original 262 kHz real
469. ns Command HBIN d 1 SR785 Dynamic Signal Analyzer 4 24 Time Histogram Frequency Menu Base Frequency This softkey sets the allowed values of the sampling time If set to 100 kHz the fundamental sampling rate of the instrument is 256 kHz and the allowed sampling times will be multiples of the reciprocal of this frequency 3 91us If set to 102 4 kHz the the fundamental sampling rate of the instrument is 262 144 kHz and the allowed sampling times will be multiples of the reciprocal of this frequency 3 814us Command FBAS d 1 Repeat When repeat is set off the SR785 computes a single histogram and stops If repeat is on the analyzer will automatically acquire new histograms continually as each one is finished This can be useful for analyzing signals which change slowly with time Command HRPT d i SR785 Dynamic Signal Analyzer Display Setup Menu 4 25 Display Setup Menu The Display Setup menu allows the user to choose the Measurement View and Display Scaling for the active display Display Setup Measure gii FT FFTi 1 ___ beg Mag _ Log Mag Ye kh 160 7 Pan i Zoom x1 Measurement Group Select the Measurement Group for both displays FFT Correlation Octave Analysis Swept Sine Order Time Histogram To choose a specific measurement choose the Measurement Group then select a Measurement The FFT Measurement Group uses the Fast Fourie
470. ns use the knob to choose a function and press Enter Only the 5 User Functions within the current Measurement Group may be edited The current definition of the functions is displayed as the knob moves through the list Edit Function Display the Edit Function menu to edit the selected User Function Press lt Cancel gt to exit back to the main User Math menu To enter an equation use lt Operands gt and lt Operations gt and the knob to select operands and operations lt Backspace deletes the term before the cursor To edit an equation use lt Func String gt and the knob to move the flashing cursor within the equation lt Delete gt will delete the highlighted term lt Operands gt and lt Operations gt will either insert or replace at the cursor Use lt Insert Replace gt to switch between insert and replace mode lt Clear Eq gt will delete the entire equation lt Cancel gt will discard any changes made in this menu and exit this menu lt Enter Eq gt will enter the new function equation and exit this menu The new User Function definition is used immediately if it is being displayed Command USRF i k 1 m FFT Group Command USRR i k l m Correlation Group Command USRO i j k 1 m Octave Group Command USRS 7 1 j k 1 m Swept Sine Group Command USRT 1 j k 1 m Order Group Command USRH 7 1 J k 1 m Time Histo
471. ns 2N floating point numbers The values are linearly scaled usually with units of Vpk The first value in the file is N followed by the real part of the first point then the imaginary part of the first point etc Each value is delimited by a comma white space tab or carriage return Traces which are entirely real should store 0 0 as the imaginary part of every point The value of N depends upon the type and length of the target trace N should be picked at least as large as the number of points displayed in the trace If N is specified too small the trace will be zero padded If N is too large the extra points will be ignored For example the ASCII file for a 400 line FFT might be 400 0 000 0 500 1 000 1 500 2 000 2 500 399 000 399 500 where 0 000 0 500 is the first complex data point and 399 000 399 500 is the 400th data point SR785 Dynamic Signal Analyzer Disk Buffers Menu 4 179 To read this file into a trace a 400 line FFT must first be stored in the trace This can be done using lt Display to Trace gt or lt Disk to Trace gt Loading the ASCII file into the trace then replaces the trace data with the data from the disk file Command TASC 1 n Load Trace Data binary Buffer Load binary data from the Current File in the Current Directory into a Trace This is a way to import calibration data from a file into a trace The trace can then be used in a user function to calibrate live measurements
472. ns n 4 byte binary long int which is the number of bytes needed to transfer the Arbitrary buffer SR785 Dynamic Signal Analyzer APUT CGET i j Data Transfer Commands 5 113 Host On receipt of n 4 byte binary long int executes a binary read from the SR785 of n bytes Expect EOI with the final byte of the transfer Serial Poll until IFC bit 7 is set in the Serial Poll status before sending another command The APUT command downloads Arbitrary Waveform buffer data to the SR785 This command is valid only via the GPIB interface After the download is complete the Arbitrary Length will be set to the length of the download The download data must be data which was originally uploaded by AGET in its entirety The AGET and APUT commands allow a host computer to save and reload the Arbitrary buffer without using disks The download sequence is as follows Host Send APUT Do NOT wait for IFC to be set in the Serial Poll status SR785 Returns 1 4 byte binary long int when OK to begin binary transfer to the SR785 A return of O indicates that there is no Arbitrary Waveform memory allocated Host On receipt of 1 4 byte binary long int executes a binary transfer to the SR785 of n bytes as uploaded using AGET Asserts EOI with the final byte of the transfer SR785 Receives n bytes and the EOL If an error is detected during transfer the Arbitrary buffer reverts to the empty state and a command execution error oc
473. nsity Function CDF Capture User Function Trace Storage User Math Functions What is a User Function Measurement Groups and Traces Operands X Axis Operations User Function Limits Signal Inputs Manual Range Auto Range Input Noise Input Impedance Anti aliasing Filter A Weighting Filter Input Transducer Units Input Connections Single Ended Connection A Differential Connection A B Common Mode Signals AC vs DC Coupling Intrinsic Random Noise Sources Johnson Noise Shot Noise 1 f Noise Total Noise External Noise Sources Capacitive Coupling Inductive Coupling Resistive Coupling Ground Loops Microphonics Thermocouple Effects 2 56 2 56 2 57 2 57 2 57 2 57 2 57 2 58 2 58 2 58 2 58 2 58 2 58 2 59 2 59 2 59 2 60 2 61 2 61 2 61 2 61 2 62 2 63 2 64 2 65 2 65 2 65 2 65 2 66 2 66 2 67 2 67 2 68 2 68 2 68 2 68 2 69 2 70 2 70 2 70 2 70 2 70 2 71 2 71 2 72 2 73 2 73 2 74 Curve Fitting and Synthesis Curve Tables Polynomial Pole Zero Pole Residue Frequency Scale Delay Trace Curve Fitting Weighting Curve Synthesis 2 75 2 75 2 75 2 75 2 75 2 76 2 76 2 76 2 76 2 77 2 77 Analyzer Basics 2 3 SR785 Dynamic Signal Analyzer 2 4 Analyzer Basics Measurement Groups The SR785 is organized into six Measurement Groups FFT Correlation Octave Analysis Order Analysis Time Histogram and Swept Sine Choose the Measurement Group in the Display S
474. nt Screen Press lt Return gt for the Output menu Command NOTE 1 j k l m s Edit ANote A Note prere X position a 0 eere Y position EE Diy ee T Yes Text String ABC Return C Text X Position Adjust the horizontal position of the Note with the knob Command NOTE 1 j k 1 m s Text Y Position Adjust the vertical position of the Note with the knob Command NOTE 1 j k l m s SR785 Dynamic Signal Analyzer 4 188 Output Menu Display Select which display the Note appears in 0 DisplayA 1 DisplayB Command NOTE 1 j k l m s Visible Make the Note visible Yes visible No invisible Command NOTE 1 j k l m s Text String Enter the Note text Use the AIt key to enter the note text Command NOTE 1 j k l m s File Start Number Set the Starting File Number for printing plotting or dumping to Disk X XXX up to 4 digit integer All Bitmap Printer and Vector Plotter types can save to Disk This is convenient for using a printer which is not connected to this unit or to import the screen image into a PC application Files are written to the Current Directory specified in the Disk menu Files are named SCRNXXXX EXT where XX XX is a 4 digit number which automatically increments starting at the File Start Number Command PFIL 1 SR785 Dynamic Signal Analyzer Colors Output Menu 4 189 Display the Hardcopy Colors menu
475. nt memory allocated before loading from disk Load Arbitrary Waveform A saved Arbitrary or Capture file may be loaded into the Arbitrary Waveform buffer The Arb Src Length will be set to the length of the disk data Load A Capture Buffer A saved Arbitrary or Capture file may be loaded into a Capture buffer If the disk data has the same Capture Length and Sampling Rate as shown in the current Capture menu the data is simply loaded into the selected channel s buffer In the case of Ch1 Ch2 capture loading one channel does not disturb the contents of the other channel s buffer If either the length or sampling rate is different from the current Capture menu they are changed to the length and sampling rate of the disk data In the case of Ch1 Ch2 capture loading Ch1 Ch2 capture will zero the Ch2 Ch1 capture buffer if the capture length or sampling rate is changed by this operation To recall both capture channels configure lt Capture Channels gt for Chl Ch2 Both files must contain the same length buffers with the same sampling rate Use lt Buffer gt to choose either Chl or Ch2 and load the appropriate disk file to the buffer This will set the capture length and sampling rate according to the recalled disk file Then use lt Buffer gt to choose the other channel and load the other disk file to the buffer Since the existing Capture Length and Sampling Rate are already compatible this operation does not zero the first capt
476. nt to be accepted added to the average or rejected not added to the average based upon the input time records This is useful for rejecting bad time records from corrupting an averaged measurement Command PAVA Reject Reject the displayed preview time record and do not add the measurement to the average Average Preview allows each individual measurement to be accepted added to the average or rejected not added to the average based upon the input time records This is useful for rejecting bad time records from corrupting an averaged measurement Command PAVR SR785 Dynamic Signal Analyzer Octave Average Menu 4 115 Octave Average Menu When the Measurement Group is Octave Analysis this menu sets the averaging parameters for the active display Averaging Averaging Type Exp Time Integration Time 100 ms Peay feed eve ee A ea lE Power Bin Total Linear Avg Trig One Lin Avg Averaging Type Select the Averaging Type for the active display Linear Time Exponential Time Peak Hold Equal Confidence Choosing Peak Hold also sets the Power Bin to Peak Octave measurements are always rms averaged to measure the power in each band The Start Reset key resets the current averages and starts the measurement over The Pause Cont key pauses the measurement Pressing Pause Cont again resets the averages and starts the measurement over The Averaging Type of each display can be selected separately This
477. ntained in the curve table These values are placed in the trace corresponding to the synthesized curve table Finally the active display is taken Off Line and the synthesized trace is displayed on the active display Synthesis is only allowed when the active display is in the FFT or Swept Sine measurement group SR785 Dynamic Signal Analyzer 2 78 Curve Fitting and Synthesis SR785 Dynamic Signal Analyzer 3 1 Chapter 3 Operation In This Chapter AWt 3 18 E Switch ArmWait Trig wait Trig Acquire 3 18 PA T i Run Pause Done 3 19 Hardware Reset 3 3 Soft Reset 34 Analog Playback 3 19 E i Real Time 3 19 Video Display 3 4 K d 34 Sweep Frequency 3 20 pa i RPM 3 20 Softkeys 3 4 Knob 3 5 Capture Progress 3 20 Di i Dy 35 No Cap Cap Data 3 20 REE j Link 3 20 Front Panel Connectors 3 6 Enter 3 21 Ch1 Signal Inputs 3 6 ALT 3 21 Ch2 Signal Inputs 3 6 GPIB RS232 3 21 Trigger Input 3 6 Comm Error 3 21 Source Output 3 6 SRQ 3 21 PC Keyboard Connector 3 6 Local Remote LOCK 3 22 3 22 Rear Panel Connectors 3 8 NREN Power Entry Module 3 8 Keypad 3 23 IEEE 488 Connector 3 9 Serial RS232 Connector 3 9 Normal and Alternate Keys 3 23 Parallel Printer Connector 3 9 Menu Keys 3 24 Preamp Connector 3 9 Using SRS Preamps 3 10 Entry Keys 3 25 Buttons 3 25 Tachometer Input 3 10 Start Input 3 10 eae oe P Numeric Values 3 26 Screen Display ae Control Keys 3 28 Displays 3 11 Data Graph 3 12 Start Reset 3 28 Vertical Scale Bar 3 13 aes ee
478. nter interface Most dot matrix printers use this Serial selects the RS 232 serial interface Some plotters and printers use this GPIB selects the IEEE 488 interface Most HPGL plotters use this Command PDST 1 GPIB Control Choose the GPIB Controller Host or SR785 Choose SR785 if there are no other controllers attached to the GPIB interface This is typically the case where only a plotter is attached to the SR785 Choose Host if there is host computer which is in control This is the case where both the SR785 and the plotter are controlled by a host computer The host is responsible for issuing the PLOT command to the SR785 and then making the plotter a listener and the SR785 a talker The plotter commands will then be transferred from the SR785 to the SR785 Dynamic Signal Analyzer Output Menu 4 187 plotter The host can periodically untalk the SR785 and serial poll the SR785 via the Instrument Status to determine when the plot is finished Command PCIC 1 GPIB Address Edit A Note Enter the GPIB Address for a GPIB plotter or printer 0 30 If an HPGL plotter is used with the GPIB interface this GPIB Address must agree with the actual address of the plotter Command PLTA 1 Select a Note to edit 0 7 and press Enter to display the Edit Note menu A Note is a text annotation within a display graph Notes are visible only within this menu and may be printed or plotted with the graph using Pri
479. ntry field and awaits numeric entry Enter a new value with the entry keys and press Enter lt Start Freq gt is an example of a numeric value Alt Keys Knob The Alt key is a special key which has no meaning by itself but instead modifies the meaning of another keypress or knob turn Pressing the Alt key toggles the state of the ALT indicator at the top of the screen Pressing a control key while the ALT indicator is lit selects the alternate function labeled underneath the key instead of the normal function Turning the knob when ALT is lit affects the way the markers move in the waterfall data tables and other displays The knob normally moves the markers within the displays If a parameter has been highlighted by its softkey the knob adjusts the parameter List parameters are most easily modified with the knob Numeric parameters may also be adjusted with the knob Knob list selections are referenced in parenthesis like Hanning SR785 Dynamic Signal Analyzer 1 4 Getting Started Help Enter the on screen help system by pressing Help Local Help on any hardkey or softkey is available simply by pressing the key Press 1 for the Help Index Press 0 to exit the help system and return to normal operation SR785 Dynamic Signal Analyzer Getting Started 1 5 Things To Watch Out For If the analyzer is on but doesn t seem to be taking data there are a number of things to check Start Press the Start
480. number of averages below the graph to indicate that the unsettled measurements are not being averaged Vector Averaging Be sure to select 100 Time Record Increment if you are interested in vector averaged measurement results Vector averaged results will be incorrect if anything besides 100 Time Record Increment is used because the phase of each time record will not be the same Triggering If the measurement is triggered then Time Record Increment is ignored Time records always start with the trigger with the specified Trigger Delays The analyzer must use the Continuous Trigger Source to use overlap processing SR785 Dynamic Signal Analyzer 2 30 Waterfall Display Waterfall Display What is a Waterfall Waterfall displays show multiple measurement results records in a single display New records are added at the top of the display and older records scroll off the bottom of the display This gives a time history of the measurement An example is shown below dBVpk OHz 51 2 kHz FFT chi Log Mag Kaiser NoAvg Figure Chapter 2 1 Waterfall Display Waterfall Storage saves measurement records in waterfall memory The number of records which may be stored depends upon the allocated memory and the type of measurement The rate at which records are put into memory is programmable Waterfall display WITH storage shows only records which are stored in waterfall memory While the measurement is running the display scrolls down an
481. number of exact cycles The actual number of integration cycles is the larger of the Integration Time in cycles and the Integration Cycles The integration time is always a minimum of 1 cycle or 15 625 ms To measure each point for the same amount of time constant detection bandwidth set the Integration Cycles to 1 and the Integration Time to the desired time The Integration Time should be greater than 1 cycle of the lowest frequency in the sweep Changes made to the Integration Time during a sweep take effect immediately The estimated sweep time is displayed in the Horizontal Scale Bar This time is simply the sum of the Settle and Integrate times for all points in the sweep Auto functions Source Auto Level Auto Range Auto Resolution will change the actual sweep time Command SITM d x Integration Cycles Set the number of Integration Cycles 1 32767 At each frequency point the inputs measure the signal at the source frequency This is done by multiplying the input data by the source sine and cosine wave and averaging the results over an integration time The actual integration time is always an exact number of cycles at the source frequency This rejects signals which are at a different frequency such as noise and harmonics A long integration time results in a narrow detection bandwidth at the source frequency This improves signal to noise at the cost of longer measurement times The integration time is an exact
482. nvolving square waves or impulses removing the filter can remove ringing and improve the accuracy of the time record The specifications apply only if the filter is On Command II AF 7 1 Command I2AF 7 1 Select the A Weighting Filter for the selected input Off On The AWt indicator at the top of the screen shows AWt in bright whenever the A Weighting filter is On The A Weighting filter simulates the hearing response of the human ear and is often used with Octave Analysis measurements The input A Weighting filter conforms to ANSI standard 1 4 1983 A B and C Weighting functions are also available as operators in User Math functions Command I1AW 7 1 Command I2AW 7 1 Select the AutoRange Mode for the selected input Up Only Tracking This mode only applies when Ch1 Auto Range is On In Up Only only overload causes the Input Range to change The Input Range only moves up In Tracking Mode the Input Range moves up for overloads and down when the signal falls below half scale Some signals such as low frequency noise can cause the Input Range to oscillate Do not use Tracking Mode in these cases Auto Range responds to all frequencies present at the input except those attenuated by AC coupling or the anti aliasing filter not just those within the measurement span Command I1AR 1 Command I2AR 1 SR785 Dynamic Signal Anaylzer 4 92 Transducer Parameter Menu Transducer
483. ny identified Harmonic or Sideband in either Absolute units or Relative to the fundamental Relative Mode reports the amplitude of the selected harmonic or sideband relative to the fundamental The marker amplitude units are dBFundamental The frequency is always absolute Each display has its own Readout Mode This entry field can be linked to both displays using the Link key Command HRDO d 1 Sideband Ratio This menu box displays the Sideband Ratio of the active display The sideband power is the sum of the squared magnitudes of the sidebands Only those sidebands within the SR785 Dynamic Signal Analyzer Sideband Marker Menu 4 63 measurement span which are identified by Sideband Markers contribute to the calculation The Sideband Ratio in dB is 10log sideband power fundamental power sideband power Command SPWR d 1 RMS Sideband Power This menu box displays the Sideband Power of the active display The Sideband Power is the sum of the squared magnitudes of the sidebands Only those sidebands within the measurement span which are identified by Sideband Markers contribute to the calculation The result is shown in Vrms or dBVrms depending on the setting of dB Units To convert a value in Vrms to power square the result Command SPWR d 1 SR785 Dynamic Signal Analyzer 4 64 Band Marker Menu Band M Modify Band arker Menu This menu is displayed when the active display Marker Mode is Band Ma
484. ny time during the sweep as well Source Auto Level and Ramping The source amplitude parameters for a swept sine measurement are set within the Source menu Normally the source amplitude is maintained at a constant level at all frequencies during the sweep This usually works best for frequency responses which are mostly attenuating and have little or no gain Simply set the source amplitude such that the device under test is not overloaded anywhere in the sweep Source Auto Level will adjust the source amplitude to maintain a constant level called the Ideal Reference at the Channel or Channel 2 input This is useful whenever the frequency response has substantial gain as well as attenuation Suppose the frequency response of the device under test has 30 dB of gain at one point and 80 dB of loss at another point and overloads at an input or an output of 1 0 V If a constant source level is used it must be set to avoid overload during the gain portion of the sweep This requires a level of 30 dBV When the sweep reaches the attenuation region the output signal will drop to 110 dBV While this is still measurable it may not be optimum With Auto Level the source can try to maintain an Ideal Reference of 1 0 V at the output of the device under test input of Channel 2 while not exceeding 1 0 V at the device input Where the gain is 30 dB the source level is 30 dBV and where the attenuation is 80 dB the source level increases to the Maxim
485. o not contain data The Arbitrary waveform memory can be loaded via the computer interfaces from a disk file or from a stored trace The Capture buffer is filled by capturing an input signal The Arbitrary source can play a portion of memory starting at a specified point The output sampling rate can also be specified The amplitude of the source is set relative to 1 V up to a maximum of 5 V Triggering The Arbitrary source is triggered by External triggers Set the Trigd Source Mode to trigger once 1 Shot or with every trigger Continuous In the 1 Shot case the source only triggers on the first trigger after Start Reset This same trigger starts the measurement and waterfall This is useful when the source length is very long compared to the measurement time This allows a sequence of many measurements to be triggered at the start of a single playback of a long source In the Continuous case the source triggers on every trigger with a minimum trigger period set by the Arbitrary Source Length This is useful when the source length is the same as the FFT time record length Source trigger outputs the source continuously over and over The FFT time records are synchronized to the source start Continuous Trigger outputs the source continuously over and over Do not use Ch1 or Ch2 input trigger since the output will not start until a trigger is received SR785 Dynamic Signal Analyzer 4 70 Source Menu Trigger Caution
486. of an FFT measurement Command RCRF d 1 Display to Trace Alt Print Screen Display to Trace saves the active display s measurement data to a Trace buffer Select a Trace 1 5 with the knob and press Enter to save the display data to the Trace A stored trace can be recalled to a Display or Reference Display used in a User Math Function saved to disk or copied to the Arbitrary Waveform buffer SR785 Dynamic Signal Analyzer Status Indicators 3 33 Command SVTR d 1 Trace to Display Alt Help Local Trace to Display recalls Trace data to the active display Select a Trace 1 5 with the knob and press Enter to recall the Trace data to the active display The active display will be set to Off Line when data is recalled to it The display will not update with live measurement results until the Display is set back to Live in the Display Options menu The measurement frequency span averaging and window are recalled with the data and cannot be changed These menus are shown in gray and reflect the settings or values for the last Live measurement Parameters which pertain to the display of the data such as Scale and View may be changed in the Display Setup and Display Options menus When the Display is returned to Live the measurement frequency span averaging and window all return to the settings in effect before the data was recalled and the live measurement returns to the display C
487. of display bins minimum of 1 and the aperture is 2 times this number plus 1 The aperture is used in the calculation of d dx and group delay in user math functions Larger windows result in smoother graphs with less x axis resolution Derivative calculations are not available in Octave Analysis measurements and this menu box cannot be changed The two displays have their own d dx Window The same function may viewed in the two displays with different d dx windows This entry field can be linked to both displays using the Link key Command DDXW 7 d x SR785 Dynamic Signal Analyzer 4 50 Marker Menu Marker Menu Marker Mode The Marker menu configures the display markers Marker functions such as Harmonic Distortion Sideband Power or Band Analysis are available in this menu Marker Setup F Marker Setup Marker E odes Normal Select the Marker Tracking of the active display Off On Track Link Off turns the Marker off It may be desirable to do this before printing the display On turns the Marker on Use the knob whenever no entry is pending to move the Marker Region Track automatically moves the Marker position to the maximum point in the display For Normal Marker minimum tracking is also available by choosing Minimum for the Marker Seeks selection Link moves the Marker Region in the other display with the Marker Region in this display The marker setup of the other display still configures
488. of the above commands were sent the analyzer would return 51200 It is never necessary to send a unit string with a set command Each command has a default unit which it will use if no units are sent with the value The default units are also the units used when the analyzer responds to queries Some commands must identify the units in which queries are responded to Examples would be the source amplitude and input range commands which can return values in dB and linear units In these cases the response to the query is in the form f j where f is the actual floating point return value and j is the index into the list of units which uniquely identifies the units of f These commands are identified in the individual command description In the detailed command descriptions lists of allowed units are indicated in angle brackets lt gt Within the list the default units are listed surrounded by square brackets For instance for the above command the allowed unit list would be written as lt kHz Hz mHz wHz gt Help The detailed command list is available on screen by pressing Help Local to enter the help system Press 4 to show the command list Commands are also cross referenced in the help about each key SR785 Dynamic Signal Analyzer Remote Programming 5 27 Things to Remember Output Interface RS232 or GPIB All responses are directed to the interface selected by lt Output To gt in the System lt Remote
489. of the download The download data must be data which was originally uploaded by CGET in its entirety The CGET and CPUT commands allow a host computer to save and reload the Capture buffer without using disks The download sequence is as follows Host Send CPUT 1 Do NOT wait for IFC to be set in the Serial Poll status SR785 Returns 1 4 byte binary long int when OK to begin binary transfer to the SR785 A return of 0 indicates that there is no Capture memory allocated Host On receipt of 1 4 byte binary long int executes a binary transfer to the SR785 of n bytes as uploaded using CGET Asserts EOI with the final byte of the transfer SR785 Receives n bytes and the EOI If an error is detected during transfer the Capture buffer reverts to the empty state and a command execution error occurs This may occur if there is insufficient Capture memory allocated Serial Poll until IFC bit 7 is set in the Serial Poll status before sending another command The WGET command uploads the Waterfall buffer to the host computer This command is valid only via the GPIB interface SR785 Dynamic Signal Analyzer WPUT Data Transfer Commands 5 115 The uploaded data should be saved in its entirety by the host computer The saved data can be downloaded back to the SR785 at a later time using WPUT The WGET and WPUT commands allow a host computer to save and reload the Waterfall buffer without using disks The upload sequence is
490. of the input signal The data is sampled and has a time resolution of I sample rate High frequency signals will appear distorted in the time record However ALL of the spectral information up to 1 2 56 times the Sample Rate is preserved by the Nyquist theorem as long as the value of each sample is accurate Amplitude calibration is performed in the frequency domain Hence the captured time data amplitudes are not calibrated User Functions A User Function displays the results of a user defined math function User Functions defined within the Correlation Measurement Group may include correlation measurement results Use the User Math menu to define a function A User Function may not be selected as the measurement if it uses a Trace which is empty or which contains data taken in a different Measurement Group See User Math Functions in Chapter 2 for more Measurement Octave Analysis Select the Measurement of the active display when the Measurement Group is Octave Analysis Each Measurement has an associated View Changing the Measurement changes the View to the View last used with the new Measurement SR785 Dynamic Signal Analyzer Display Setup Menu 4 33 Command MEAS d 1 The following Measurements are available in the Octave Analysis Measurement Group Octave Spectrum The octave spectrum is the basic measurement of octave analysis It is simply the rms averaged outputs from the parallel bank of octave fi
491. oise floor at full span is about 100 dBV Thus the dynamic range of this measurement is roughly 70 dB pass band to noise floor Vector averaging in this case improves the dynamic range to about 80 dB The swept sine sweep measures each frequency alone thus optimizing each frequency point individually This measurement was taken using Auto Range to adjust the input range at each frequency for the best signal to noise When the frequency is in the stop band the return signal to Channel 2 is 80 dBV or less The input range of Channel 2 is adjusted to 50 dBV for these frequencies eliminating the noise floor limitation The depth of the zero in the response as well as the shape of the stop band are clearly resolved SR785 Dynamic Signal Analyzer Swept Sine Measurements 2 49 Swept Sine Measurement Setup The advantages of the swept sine are apparent in the above comparison The real usefulness of this technique is that all of the optimizations can be automated in the SR785 To make a swept sine measurement select Swept Sine as the Measurement Group This makes both displays swept sine measurements Capture and Waterfall are unavailable in the Swept Sine group The sweep frequency parameters are set in the Frequency menu The settling and integration time for each point is set in the Average menu The source amplitude is set in the Source menu Simply press the Auto Range Ch1 and Auto Range Ch2 keys to turn on Auto Ranging
492. oldoff time long enough to prevent retriggering for each tach pulse Command TAHO 1 Tach Hold Off Show Tach Specify the interval during which the tachometer input is prevented from triggering when tachometer hold off is enabled For a noisy tachometer signal the tachometer holdoff time should be set long enough so that the tachometer triggers only once for each pulse on the tachometer input Command TAHD f Specifies whether the RPM corresponding to the tachometer input should be displayed in the RPM indicator location When the measurement group is Order Show Tach is always On Likewise if the trigger mode is RPM Arm Show Tach is always on If Show Tach is off the indicator is displayed in the same position as the RPM indicator Command TASH 1 SR785 Dynamic Signal Anaylzer Playback Input Menu 4 97 Playback Submenu This menu sets the parameters for capture playback Playback Config Playback Start Pt 0 os Playback Length i 488 kPts ch Wit ey fe kit A mak an ed feule Heel Tete hau te a Tene Feel a Ga IIEEEELLEEEEIOREEELLLLLPLPLPLPPPPPLLLELLLLLLLLLLLPPPLLLLEELLE Wet I et je I eee pel peed ate ARE PS TSE ke CIRI te te i Playback Mode 1 Shot Playback Speed Normal Return i Playback Start Select the Capture Playback Start position within the capture buffer The start position is specified as a bin number or individual point position The bins ar
493. om the active display again Select the Display Options menu Make DisplayB live again Choose Live to return the live measurement to DisplayB SR785 Dynamic Signal Analyzer 1 50 Saving and Recalling 6 Put a blank 1 44MB 3 5 disk into the disk drive Press Disk Press lt Disk Upkeep gt Press lt Format Floppy gt and press Enter to confirm Press lt Return gt Press Active Display Press lt File Name gt Press Alt Press D A T A 1 Enter Press lt Display to Disk gt Press lt Display to Disk gt Press Active Display Press lt File Name gt SR785 Dynamic Signal Analyzer Let s save DisplayA to a disk file Use a blank disk if possible otherwise any disk that you don t mind formatting will do Make sure the write protect tab is off Select the Disk menu Choose the Disk Upkeep menu Make sure that the disk does not contain any information that you want This function requires a confirmation Go ahead and confirm Formatting takes about a minute Go back to the main Disk menu Make DisplayA top the active display again We are going to save DisplayA to disk We need a file name Alt lets you enter the letter characters printed below each key The number and backspace keys function normally ALT is highlighted at the top of the screen when the Alternate keys are in use Enter a file name any legal DOS file name up to 8 characters
494. ommand RCTR d 1 SR785 Dynamic Signal Analyzer 3 34 Status Indicators Function Keys Auto Scale A Auto Scale A automatically sets the vertical scale of Display A to show the entire range of the data Horizontal scaling is not affected Auto scale only operates on the data which is displayed on the graph If the graph is expanded data corresponding to frequency or time bins which are not shown do not figure in the auto scaling calculations Link Auto Scale A auto scales Display A and sets the vertical scale of Display B to match Display A Command ASCL d Auto Scale B Auto Scale B automatically sets the vertical scale of Display B to show the entire range of the data Horizontal scaling is not affected Auto scale only operates on the data which is displayed on the graph If the graph is expanded data corresponding to frequency or time bins which are not shown do not figure in the auto scaling calculations Link Auto Scale B auto scales Display B and sets the vertical scale of Display A to match Display B Command ASCL d Auto Range Ch1 Auto Range Ch1 toggles Channel 1 Input Ranging between Manual and Auto In Manual Ranging the Input Range is set within the Input lt Input Config gt submenu In Auto Range the Input Range is adjusted automatically according to the Chl AutoRange Mode also in the Input menu In Up Only Auto Range only overloads cause the range to change In Tracking Auto Range the
495. on relative to the other display s marker position The marker offset is just the marker position of the other display This is generally valid only if the two displays have a similar measurement Pressing Marker Ref changes from Off to Rel and sets the Marker Offset to the current Marker Position Marker Ref again changes from Rel back to Off Marker Ref does not change the other modes Each display has its own Normal Marker Rel Mode This entry field can be linked to both displays using the Link key Command MREL d 1 Set the X Offset for the Normal Marker of the active display When the Marker Rel Mode is Relative the marker position is calculated relative to the Marker Offset X Rel Y Rel The Marker Offset location if it is within the display is marked by a small flag shaped symbol The Marker Offset has no associated units The relative calculation simply subtracts the Marker Offset in the display units from the absolute marker position Changing the display units invalidates the Marker Offset Re enter the Marker Offset or use Marker Ref to reset the Marker Offset in the new units SR785 Dynamic Signal Analyzer 4 56 Normal Marker Menu Y Rel X Rel Pressing Marker Ref changes from Off to Rel and sets the Marker Offset to the current Marker Position Marker Ref again changes from Rel back to Off Each display has its own Normal Marker X Offset This entry field can be linked to both display
496. ontinuity in the input data has propagated through the digital filters and a complete new time record has been acquired If the time record increment is 100 unsettled measurements are not displayed After a change is made which unsettles the measurement new data is not displayed until the filters are settled and a complete time record has been acquired If the measurement is running with a time record increment less than 100 and the measurement is unsettled unsettled measurements may be displayed New data is displayed after the filters are settled and a portion of the new time record has been acquired For example if the time record increment is 25 3 measurements are made before a complete new time record has been acquired These first 3 measurements have time records which contain data from before AND after the measurement was unsettled These unsettled measurements are displayed in half intensity indicating that the SR785 Dynamic Signal Analyzer Real Time Bandwidth and Overlap 2 29 measurement is not settled Once the 4th measurement is complete the display returns to full intensity since the measurements have completely settled time records If averaging is on changes which unsettle the measurement will restart the average Unsettled measurements are not included in the new average Averaging does not start until the measurement is settled When the time record increment is less than 100 Settle is displayed instead of the
497. order is real part of point 0 imag part of point O real part of point 1 imag part of point 1 etc Each ASCII float is delimited by a comma space tab or carriage return NOT EOI Assert EOI with the final byte of the transfer Serial Poll until IFC bit 7 is set in the Serial Poll status before sending another command The ALOD command loads binary data into the Arbitrary Waveform buffer This command is valid only via the GPIB interface The parameter n specifies the number of points to be loaded and must be a multiple of 2048 The Arbitrary Waveform buffer must already have sufficient memory allocated After the load is complete the Arbitrary Length will be n points SR785 Dynamic Signal Analyzer TGET i Data Transfer Commands 5 111 Each point is a 4 byte IEEE float number and range from 1 0 to 1 0 A value of 1 0 is output at 100 amplitude as 1 Volt The data should not exceed this range The download sequence is as follows Host Send ALOD n Do NOT wait for IFC to be set in the Serial Poll status SR785 Checks to make sure that the Arbitrary buffer has sufficient length Returns 1 4 byte binary long int if OK to begin data transfer A return of O indicates that n is too large for the buffer Host On receipt of 1 4 byte binary long int executes a binary transfer to the SR785 of n 4 byte IEEE floats The order is point 0 point 1 etc Each 4 byte float is transmitted least significant byte first A tota
498. os to use in the fit 0 20 The analyzer will compute the best fit to the data in the active display using the specified number of zeros Each complex zero is actually a member of a complex conjugate pair and counts as 2 poles Command ENZE 1 Weighting Specifies the type of weighting to use when performing the fit Auto User When Auto weighting is selected the analyzer computes an appropriate weighting function for the type of data being fit Live FFT data displays will be weighted with the Coherence funtion Live Swept Sine data are weighted with the normalized variance of channel 2 Off line displays including synthesized traces and recalled data are weighted uniformly When User weighting is selected the analyzer uses data in one of the 5 traces to weight the fit The trace used is selected with the Weighting Trace softkey The length of the trace being used must match the length of the display being fit Only the real part of the trace data is used SR785 Dynamic Signal Analyzer 4 164 Fit Setup Menu Command EWTU 7 1 Weighting Trace Selects which trace 1 5 will be used to weight the fit when User Weighting is selected Command EWTT 1 Set Fit Region Selects the region of the active display which will be fit When the Fit Setup menu is entered a band at the bottom of the graph displays the fit region The position of the band can be adjusted using the knob The width of the band can be adjusted by
499. ose real part is the real part of Time Record Ch1 and whose imaginary part is the real part of Time Record Ch2 Orbit is normally displayed with the Nyquist View Time2 vertical vs Time horizontal For baseband spans the time records are entirely real and the Nyquist view of the Orbit measurement is a Lissajous figure Cross Spectrum The cross spectrum sometimes called cross power spectrum is a two channel measurement defined as No Average Cross Spectrum FFT1 e FFT2 Vector Average Cross Spectrum lt FFT1 gt lt FFT2 gt RMS Average Cross Spectrum lt FFT1 FFT2 gt Peak Hold Average Cross Spectrum MAX FFT2 y lt FFT1 FFT1 gt In these definitions the brackets lt gt represent averaging the real and imaginary part of the enclosed quantity either linearly or exponentially as described below The cross spectrum contains both magnitude and phase information The phase is the relative phase at each frequency between the two channels Vector averaging can be used to eliminate signals which do not have a constant phase relationship between the two channels In this case triggering may not be required for vector averaging The magnitude is simply the product of the magnitudes of each spectrum Frequencies where signals are present in both spectra will have large components in the cross spectrum Frequency response The frequency response sometimes called transfer function is a two channel measurement
500. osed metal parts of the instrument are connected to the outlet ground to protect against electrical shock Always use an outlet which has a properly connected protective ground Do not attempt to service or adjust this instrument unless another person capable of providing first aid or resuscitation is present Do not install substitute parts or perform any unauthorized modifications to this instrument Contact the factory for instructions on how to return the instrument for authorized service and adjustment The fans in the SR785 are required to maintain proper operation Do not block the vents in the chassis or the unit may not operate properly SR785 Dynamic Signal Analyzer Contents Safety and Preparation For Use 1 Contents iii Table of Figures vii Features 1X Specifications xi Chapter 1 Getting Started General Installation 1 2 Front Panel Quick Start 1 3 Things To Watch Out For 1 5 Analyzing a Sine Wave 1 7 Measuring a Frequency Response Function l 11 Linking Advanced Operation 1 15 Triggering and the Time Record 1 19 Octave Analysis 1 23 Capture 1 27 Waterfall Display 1 34 Swept Sine Measurement 1 41 Saving and Recalling 1 47 User Math Functions 1 52 Limit Testing 1 56 Exceedance Statistics 1 60 Chapter 2 Analyzer Basics Measurement Groups 2 4 What is an FFT 2 6 FFT Frequency Spans 2 8 FFT Time Record 2 10 FFT Windowing 2 12 FFT Measurements 2 16 Views 2 21 FFT Averaging 2 24 Real Time Bandwidth and Overla
501. oss spectrum are complex quantities whose phase is not necessarily zero Vector Averaging Vector averaging computes the average of the real part X and imaginary part Y of a measurement according to VecAvg X Y lt X gt lt Y gt ie the Vector average of a complex quantity is the complex quantity formed by the average of its real and imaginary parts independantly Linear averaging computes the equally weighted mean of X and Y over N measurements Exponential averaging weights new data more than old data and yields a continuous moving average SR785 Dynamic Signal Analyzer FFT Averaging 2 25 Since signed values are combined in the mean random signals tend to average to zero This reduces the noise floor since random signals are not phase coherent from measurement to measurement Only signals with a constant phase have real and imaginary parts which repeat from time record to time record and are preserved Vector averaging can substantially improve the dynamic range of a measurement as long as the signals of interest have stable phases For single channel measurements vector averaging requires a trigger The signal of interest MUST be phase synchronous with the trigger to have a stable phase For a two channel measurement the phase is relative between Channel 2 and Channel 1 As long as the signals of interest have stable relative phases triggering is not required for vector averaging Triggering is still required to isol
502. ot have a constant phase relationship between the two channels In this case triggering 1s not required for vector averaging The magnitude is simply the product of the magnitudes of each spectrum Frequencies where signal is present in both spectra will have large components in the cross spectrum Frequency Response The Frequency Response sometimes called transfer function is a two channel measurement which ratios the spectrum of Ch 2 to the spectrum of Ch 1 Frequency Response measures the response of a network or device under test The reference channel 1 measures the signal at the input to the device and the response channel 2 measures the device output The result is the complex Frequency Response of the device The definition of frequency response depends on the type of averaging which is displayed No Average Freq Response FFT2 FFT 1 Vector Average Freq Response lt FFT2 gt lt FFT1 gt RMS Average Freq Response RMSAvs cross spectrum power spectrum 1 SR785 Dynamic Signal Analyzer Display Setup Menu 4 29 Freq Response lt FFT1 e FFT2 gt lt FFT1 e FFTI gt Peak Hold Average Freq Response MAX FFT2 V lt FFT1 FFT1 gt Both the RMS averaged and Vector averaged frequency response contains both magnitude and phase information The phase is the relative phase at each frequency between the two channels The RMS averaged frequency response is computed by taking the ration of the cross spectru
503. ote interface settings power the unit on with the backspace key held down Command RST Remote Display the System lt Remote gt interface menu Remote interface parameters should not be altered while the computer interface is active Press lt Return gt or System for the System menu Preferences Display the System lt Preferences gt menu Press lt Return gt or System for the System menu SR785 Dynamic Signal Analyzer 4 192 System Menu Date Time Display the System lt Date Time gt menu Press lt Return gt or System for the System menu Diagnostics Display the System lt Diagnostics gt test menu Press lt Return gt or System for the System menu Macro Use the knob to pick one of the ten Macros to edit and press Enter All macros may be edited including those which have not been recorded See Macros in Chapter 3 for more Edit Macro Display the Edit Macro menu to edit the selected macro Press lt Cancel gt to exit back to the main System menu It is generally easier to record a macro than it is to enter it in this menu Use this menu to edit existing macros See Macros in Chapter 3 for more To enter a macro string enter Menu Function Control and Number keys by simply pressing the desired key these keys do not have their normal effect in this menu Use lt Special Keys gt and the knob to select lt Softkeys gt and Enter lt Backspace deletes the t
504. ove the frequency resolution However a large amount of the sweep time will be spent measuring points between the features of interest This is where Auto Resolution can save measurement time while preserving resolution Auto Resolution is specified by three parameters the Faster Threshold the Slower Threshold and the Maximum Step Size As with all frequency parameters these are set within the Frequency menu SR785 Dynamic Signal Analyzer 2 52 Swept Sine Measurements Auto Resolution examines the measurements of successive frequency points If the newest measurement is within the Faster Threshold of the previous measurement for BOTH channels then the sweep will take larger steps skipping frequency points Each successive time this threshold is met the step size is increased until the Maximum Step Size is reached This speeds up the sweep in regions where the response is flat varies less than the Faster Threshold If a measurement differs from the previous measurement by more than the Slower Threshold for EITHER channel then the sweep returns to the previously measured point and moves to the very next frequency point in the sweep with no skipping The sweep continues from this point speeding up if allowed and slowing down when required This fills in skips in the sweep which vary by more than the Slower Threshold Measurements which differ by more than the Faster Threshold on EITHER channel but less than the Slower
505. oves the Waterfall Marker of display d to record 1 in the Z axis Record O is the most recent record in the display The marker of each display must be moved separately d 2 is not allowed This command is valid only if display d is a Waterfall and the measurement is paused This command is not valid if the Marker of display d is Off The MRKX command queries the time frequency or bin number of the marker position in display d The returned value is always the absolute position of the marker even when the on screen marker is relative The returned value has the same units as the first value shown in the Marker Position Bar This command is not valid if the Marker of display d is Off The MRKB command queries the marker bin number of display d The value returned is the bin number of the marker Bin 0 is the left most bin in the display SR785 Dynamic Signal Analyzer 5 46 Marker Commands MRKY d MRKZ d MKMX d MKMN d MKCN d This command is not valid if the Marker of display d is Off The MRKY command queries the vertical axis data value at the marker position of display d The returned value is always the absolute position of the marker even when the on screen marker is relative This command is not valid if the Marker of display d is Off The MRKZ command queries the Z position at the marker position of display d If the display is a 2 D display Nyquist or Nichols view MRKZ queries the horizontal
506. ower Spectrum 2 Time Time 2 Windowed Time 1 Windowed Time 2 Orbit Coherence Cross Spectrum Frequency Response Capture Buffer 1 Capture Buffer 2 FFT User Function 1 FFT User Function 2 FFT User Function 3 FFT User Function 4 FFT User Function 5 ONAN BWNRK OK pee LO OANA NBWNK CO SR785 Dynamic Signal Analyzer 5 38 Display Setup Commands I 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 4 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 SR785 Dynamic Signal Analyzer Correlation Group Measurement Auto Correlation 1 Auto Correlation 2 Cross Correlation Time 1 Time 2 Windowed Time 1 Windowed Time 2 Capture Buffer 1 Capture Buffer 2 Correlation Function 1 Correlation Function 2 Correlation Function 3 Correlation Function 4 Correlation Function 5 Octave Group Measurement Octave Octave 2 Capture Capture 2 Octave User Function 1 Octave User Function 2 Octave User Function 3 Octave User Function 4 Octave User Function 5 Swept Sine Group Measurement Spectrum Spectrum 2 Normalized Variance 1 Normalized Variance 2 Cross Spectrum Frequency Response Swept Sine User Function 1 Swept Sine User Function 2 Swept Sine User Function 3 Swept Sine User Function 4 Swept Sine User Function 5 Order Group Measurement Linear Spectrum 1 Linear Spectrum 2 Power Spectrum 1 Power Spectrum 2 Time 1 58 59 60 61 62 63 64
507. p 2 27 Waterfall Display 2 30 Capture Buffer 2 33 The Source 2 36 Correlation Analysis 2 38 Octave Analysis 2 41 Swept Sine Measurements 2 47 Order Analysis 2 55 Time Histogram Measurements 2 58 Trace Storage 2 60 User Math Functions 2 61 Signal Inputs 2 65 SR785 Dynamic Signal Analyzer iV Contents Input Connections 2 68 Intrinsic Noise Sources 2 70 External Noise Sources 2 71 Curve Fitting and Synthesis 2 75 Chapter 3 Operation Overview 3 3 Front Panel Connectors 3 6 Rear Panel Connectors 3 8 Screen Display 3 11 Status Indicators 3 18 Keypad 3 23 Normal and Alternate Keys 3 23 Menu Keys 3 24 Entry Keys 3 25 Control Keys 3 28 Function Keys 3 34 Macros 3 38 Chapter 4 Menus Frequency Menus 4 7 FFT Frequency Menu 4 7 Octave Frequency Menu 4 12 Swept Sine Frequency Menu 4 15 Order Frequency Menu 4 19 Time Histogram Frequency Menu 4 23 Display Setup Menu 4 25 Display Options Menu 4 46 Marker Menu 4 50 Normal Marker Menu 4 54 Harmonic Marker Menu 4 58 Sideband Marker Menu 4 61 Band Marker Menu 4 64 Frequency Damping Marker Menu 4 66 Source Menus 4 67 Sine Source Menu 4 7 Chirp Source Menu 4 73 Noise Source Menu 4 75 Arbitrary Source Menu 4 78 Swept Sine Source Menu 4 83 Input Menu 4 87 Input Configuration Menu 4 89 Transducer Parameter Menu 4 92 Tachometer Input Menu 4 95 Playback Input Menu 4 97 Trigger Menu Average Menus FFT Correlation and Order Average Menu Octave Average Menu Swept Sine Av
508. pan as the capture fill and playback progress through the buffer During capture fill if the capture buffer contains more points than can be displayed points are skipped This speeds up the display update so that it keeps up with the real time capture but allows visual aliasing to occur Once capture is complete the display is redrawn showing the envelope of all points eliminating any visual aliasing effects To measure from a region of the buffer set the Playback Start and Length in the Input menu The capture data is filtered and down sampled according to the capture Sample Rate Only baseband data data bandwidth starts at DC are captured The capture buffer resembles a digital oscilloscope display Signals at frequencies above 1 2 56 times the sample rate have been filtered out SR785 Dynamic Signal Analyzer 4 30 Display Setup Menu The capture buffer is not a continuous representation of the input signal The data is sampled and has a time resolution of I sample rate High frequency signals will appear distorted in the time record However ALL of the spectral information up to 1 2 56 times the Sample Rate is preserved by the Nyquist theorem as long as the value of each sample is accurate Amplitude calibration is performed in the frequency domain Hence the captured time data amplitudes are not calibrated User Functions A User Function displays the results of a user defined math function User Functions defined within t
509. pared to the original data in the active display SR785 Dynamic Signal Analyzer Curve Fitting and Synthesis 2 77 Weighting Because the quality of the measured frequency response function is not uniform over the entire region to be fit it is sometimes necessary to weight the input data when performing the fit The analyzer can weight the fit in one of three ways Uniform weighting weights all parts of the fit region uniformly Coherence weighting uses the calculated coherence function or normalized variance in the case of swept sine measurements to weight the data Coherence is a measure of the signal to noise ratio of the measured frequency response function In regions of high signal to noise the value of the coherence function will be near In regions of low signal to noise the coherence function will be less than 1 Coherence weighting is not available for Off Line displays User weighting allows the user to specify the weighting function The analyzer uses whatever data is found in the real part of the specified weighting trace to determine the weighting Curve Synthesis The curve table is synthesized when the user presses the Synthesize Table 1 or Synthesize Table 2 softkeys The analyzer first looks at the active display to determine the frequency range over which the synthesis occurs Then the SR785 calculates the complex frequency response function corresponding the curve parameters frequency scale delay and gain settings co
510. percentage is less than 100 The burst noise source is triggered by External triggers Set the Trigd Source Mode to trigger once or with every trigger With Free Run Trigger Mode the burst repeats over and over In FFT group the noise bandwidth and burst time record is linked to either DisplayA or DisplayB If the other display has a different span the source may not be appropriate for that display Since the signal is random windows are always required when making FFT measurements using the noise source SR785 Dynamic Signal Analyzer A Arbitrary Source Menu 4 69 In Octave group the burst period is not linked to a display but is specified in time The bandwidth is always full bandwidth Trigger Caution If the Noise source is selected and the Burst is less than 100 the triggered FFT measurement phase is stable only 1f the input signals are derived from the triggered source output Turn the source off or set it to Sine when making triggered measurements of external signals not the source Command STYP 1 Set the source output to Arbitrary and display the Arbitrary Setup menu The Arbitrary source plays a waveform stored in memory The waveform can be either Capture buffer or the Arbitrary Waveform memory Use the lt Memory Allocation gt menu to allocate memory between the capture buffer waterfall storage and the arbitrary source waveform The Capture buffers may not be selected as the Arbitrary source if they d
511. phase Linear averaging computes the equally weighted mean over N measurements Exponential averaging weights new data more than old data and yields a continuous moving average RMS averaging reduces fluctuations in the data but does not reduce the actual noise floor squared values never cancel With a sufficient number of averages a very good approximation of the actual noise floor can be measured Vector Averaging For a simple FFT measurement the definition of the Vector average measurement is Vector Avg FFT lt X gt j lt Y gt Where X and Y are the real and imaginary parts of the instantaneous FFT measurements and the lt gt angle brackets indicate either linearly weighted or exponentially weighted averaging over N FFT records For other measurements the definition of the vector averaged measurement depends upon the measurement Vector averaging is often called time averaging since vector averaging in the frequency domain yields the same value as taking the FFT of the averaged input time record Linear averaging computes the equally weighted mean of X and Y over N measurements Exponential averaging weights new data more than old data and yields a continuous moving average Since signed values are combined in the mean random signals tend to average to zero This reduces the noise floor since random signals are not phase coherent from measurement to measurement Signals with a constant phase have real and imaginary parts
512. play can also show a reference graph The reference graph is a graph of a stored Reference Display and is drawn in half intensity This allows comparison of live measurement data with a stored Reference Display The Reference Display data is copied from the current display data using Display Ref or loaded from a data Trace with Trace to Ref Set the Marker Relative to Reference Display in the Marker menu to read the Marker Position relative to the Reference Display Press Display Ref again to turn off the Reference Display Changing the display scale does NOT rescale the Reference Display This allows the live measurement display to be offset from the Reference Display by changing either Ymax Ymid or Ymin in the Display Setup menu To graph the Reference Display in the new display scale press Alt Snap Ref Menu Display The softkey menu boxes define the functions of the softkeys to the right of the screen Related functions and parameters are grouped into menus Pressing each of the Menu keys displays a different set of menu boxes There are three types of softkeys buttons lists and numeric values A button performs a function such as lt Full Span gt A list presents a list of choices or options in the entry field at the top of the screen Use the knob to make a selection and press Enter lt Measurement gt is an example of a list A numeric value presents the current value in the entry field and awaits numeric entry Ent
513. points x 4 bytes point WaitIFC serial poll until IFC set ok to continue printf Sd bytes readin length actual number of bytes read print a few points from the spectrum for 37 1 lt 44 gt Ft foriner bin Sd RE CBVok n 1 xBute i 54 PEIRCE Ui KKKKKKKKKKKKKKKKKKKKKKKRK KKK KKKKKRKKKKKKKKKKKKKKKKKKKKK PX Sees Mien Ont LIMIE Testing sae ew E Thon Oo be DR Oe first clear any existing limits for DisplayA TORS TLMAX O72 J Jima tialive 2 seqments TRORTSS VLSEG 04 07 05 1 2 00328 35 90 05 102 4h 3y 9050 s 77 upper segment TRSR OS TESEG 05 1 071 2883 90 078 96h3 90 lt 0 ys upper segment SR785 Dynamic Signal Analyzer 5 132 Example Program TORT Oo CULES Oye seem Orr Tes rae x xx kx take a new measurement prune WVAWo Sed ie ies WaitAvg peinet donen GetSR785 LFAL 0 read limit test result Prints LEME Test TY if atoi recv 0 printf pass else printf fail BENCE ATRN KKKKKK clean up TxSR785 LCLR 0 jelear limits turn off testing TXSRTSS TFAVG 270 3 7 CUE avg Ofri KKEKKKKKKRKKKKKKRKKKKKKRKKKKR KEKE KKK KRKKKRKKEKEKKKEKRKEKK KKK KKK IKHK LR REECE TOA Cie Arbitrary waver orm DUIISrT 2e rere 7 construct a normalized ramp of 2048 points each point is a 4 byte IEEE float between 1 0 and 1 0 for 1 0 i lt 2048 i txBuftf i float i 2048 F This section
514. ponents by their relation to the speed of the rotating machine rather than their absolute frequency For instance if we identify a potentially troublesome vibration component at 3 times the rotation speed during a baseline test of a machine at 120 RPM all we really care about is that the vibration is at 3rd order not that it s at 6Hz That way we can compare the results to the 3rd order vibration level in some future test without having to worry about getting the machine to run at exactly 120 RPM again In the Order Analysis measurement group the SR785 calculates spectra whose x axis is in orders i e multiples of the machine speed To do this it requires information about the speed and postition of the machine s shaft This is provided by a tachometer input which provides a signal at fixed positions relative to the shaft rotation With the SR785 all the traditional measurements of rotating machinery analysis including order maps rpm profiles run up and run down plots can be easily made without any additional equpment Order Spectra and Order Tracking Two types of measurement are typically made with rotating machinery The first looks at the input amplitude as a function of order This type of measurement is similar to the standard FFT except that the x axis is calibrated in orders instead of in absolute frequency Typically a measurement of the order spectrum is first performed to identify orders for further study Once we ve identifie
515. program must wait before sending the ERRS query Interface ommands like their keyboard equivalents may not take effect immediately if the analyzer is paused or finished with a set of linear averages If the display is paused or Done and a command is sent to change a frequency parameter the menu will reflect the new parameter querying the parameter with a command will return the new parameter but the new parameter does not take effect until Start ist pressed or the STRT command is sent You should always send STRT after a series of setup commands to ensure that the new parameters are in effect Data Synchronization Changing measurement parameters often invalidates the display data For example changing FFT spans or resolution requires some time before new data taken with the new span or resolution is available Another example is changing the FFT average mode while averaging is on In this case the average is re started and some time is required before a new average is completed For these types of commands simply waiting for IFC to be set does not ensure that the display data reflects the operation just completed Before querying or saving the display data the Display Status word needs to be queried until either NEW AVG or STL is set SR785 Dynamic Signal Analyzer 5 24 Remote Programming indicating new data is available average completed or new settled data is available This will ensure that the display data has been updated
516. r Arbitrary 3 When the Measurement Group is Swept Sine the Source Type may not be changed and this command is not valid SR785 Dynamic Signal Analyzer 5 54 Source Commands Sine Source Commands S1FR f lt kHz Hz mHz wHz gt The SIFR command sets queries the Frequency of Sine Tone The parameter f is a frequency in the specified units The query command always returns a value in Hz This command is valid only when the Source Type is Sine S1AM x lt mVpk mVpp mVrms Vpk Vrms dBVpk dBVpp dBVrms gt The S1AM command sets queries the Amplitude of Sine Tone 1 The parameter x is a real number of the specified units The query returns two numbers of the form y 1 where y is a real number and 1 is an index indicating the units This command is valid only when the Source Type is Sine SOFF x lt mV V gt The SOFF command sets queries the Offset of the Sine Source The parameter X is areal number of the specified units The query returns two numbers of the form y i where y is a real number and 1 is an index indicating the units This command is valid only when the Source Type is Sine S2FR f lt kHz Hz mHz wHz gt The S2FR command sets queries the Frequency of Sine Tone 2 The parameter f is a frequency in the specified units The query command always returns a value in Hz This command is valid only when the Source Type is Sine S2AM x lt mVpk mVpp mVrms Vpk Vrms
517. r Function the Trace must contain data AND the Trace must have data stored from within the current Measurement Group For example an FFT User Function which uses Trace cannot be chosen as a Measurement if Tracel is empty OR contains octave analysis data If a User Function is displayed and it uses a Trace in its equation then that Trace cannot be changed to data from a different Measurement Group For example if an FFT User Function using Tracel is being displayed you cannot recall octave data from disk to Tracel Changing Measurement Groups and storing Traces may make User Functions unavailable because of the above restrictions In this case store Trace data within the current Measurement Group before selecting the User Function as the measurements Operands Operands are arrays of complex values real and imaginary They may be measurement results such as FFT 1 Time 1 or Oct 1 a Trace or a Constant An array which is real simply has zero for its imaginary parts The array length of an Operand is determined by the measurement length number of FFT lines length of time record number of octaves etc or Trace length length of the data which is stored in the Trace Constants assume the length of the user function Operands which are measurement results enclosed in angle brackets such as lt Freq Resp gt or lt Spec 1 gt are exactly the same as the normal measurements They are SR785 Dynamic Signal Analyzer 2 62 User Ma
518. r Max B Read Marker Min B Read Marker Mean B Read Marker Std Dev B Read Exceed Start Index Exceed Stop Index Exceed Centile Calculate Exceedance Start Fit Synthesis Number Poles Number Zeros EWTU 1 EWTT 1 ERNG d 1 J EDLY 1 x EFSC 1 x EFSC 1 x EGAN 1 x ETRC 7 1 j ETRC 1 J EPLY 1 j k x EPOL 1 x y EZER 1 J x y ERES 14 x y Disk FNAM 7 s FDIR s MDIR s FXST s FREE FRST FNXT FSAV d FRCL d SSAV SRCL i TSAV i TRCL i DNAM s DELF DELD Output POUT i PDST i PFIL i DUMP PRNT PRTP i PSCR i PBRI i PDIM i PBLK i PGRF i PLOT PLTP i PLTA i PCIC i PLTX i PLGD i PLTR i PLMK i NOTE 1 j k 1 m s 5 91 5 91 5 91 5 91 5 91 5 91 5 92 5 92 5 92 5 92 5 92 5 92 5 92 5 94 5 94 5 94 5 94 5 94 5 95 5 95 5 94 5 95 5 95 5 95 5 96 5 96 5 96 5 96 5 96 5 97 5 97 5 97 5 97 5 97 5 97 5 97 5 98 5 98 5 98 5 98 5 98 5 98 5 98 5 98 5 98 5 98 5 98 5 98 5 99 Index of Commands Weighting Weighting Trace Fit Range Table Delay Table Frequency Scale Table Frequency Scale Table Gain Table Trace Table Item Query Polynomials Poles Zeros Residues Save Recall File Name Save Recall Directory Make Directory File Exist Disk Free Space Reset Disk Catalog Read
519. r Mean of the data within the Marker Region For Harmonic or Sideband markers Marker Max moves the Fundamental Marker to the location of the maximum Marker Max has no affect on Band markers Link Marker Max moves the Marker to the location of the maximum within both displays Command MKMX d Marker Min Marker Min moves the Marker to the location of the minimum data value within the active display Marker Min only searches the data which is in the display If the minimum value occurs at more than one location then the one closest to the left edge is found If the Marker Mode in the Marker menu 1s Normal Marker Min centers the Marker Region around the minimum The Marker Seeks Mode chooses whether the marker seeks the Maximum Minimum or Mean of the data within the Marker Region For Harmonic or Sideband markers Marker Max moves the Fundamental Marker to the location of the minimum Marker Max has no affect on Band markers Link Marker Min moves the marker to the location of the minimum within both displays Command MKMN d Show Setup Show Setup enters the Help system and displays the measurement setup and system settings Press 0 to exit Help and return to the measurement displays SR785 Dynamic Signal Analyzer 3 38 Status Indicators Macros Keypad Macros A sequence of front panel key presses can be recorded and played as a macro There are 10 macros which may be defined Macro definit
520. r Transform FFT to compute the frequency spectrum of finite time records The Correlation Measurement Group calculates the time domain auto and cross correlation of signals The Octave Analysis Measurement Group measures the power within logarithmically spaced frequency bands covering up to 11 octaves The Swept Sine Measurement Group uses the sine source to sweep a frequency range making optimized measurements at discrete frequency points along the way The Order Measurement Group makes spectrum and time measurements which are synchronized to the rotation of a rotating machine The Time Histogram Measurement Group calculates histograms and statistical parameters of the input signal SR785 Dynamic Signal Analyzer 4 26 Display Setup Menu The choice of Measurement Group changes the Frequency Average and Source menus Command MGRP d 1 Measurement FFT Select the Measurement of the active display when the Measurement Group is FFT Each Measurement has an associated View Changing the Measurement changes the View to the View last used with the new Measurement The two displays generally have different Measurements This entry field can be linked to both displays using the Link key Measurements which are listed as 2 channel may only be selected if lt Analyzer Config gt is set to Dual Channel Command MEAS d 1 The following Measurements are available in the FFT Measurement Group FFT Lin
521. r a new value with the entry keys and press Enter lt Start Freq gt is an example of a numeric value Some parameters can have different values or settings for each display In these cases the menu shows the values or settings for the active display Press Active Display to toggle the active display and show the values or settings for the other display lt Measurement gt is an example of such a parameter Use Link to link a parameter to a single display or to both displays at once A Help for any key or softkey is available on screen by pressing Help Local Simply press any key for help about that key or function Press 0 to exit help In This Chapter Frequency Menus FFT Frequency Menu Span Linewidth Acquisition Time Full Span FFT Lines Base Frequency Start Frequency Center Frequency End Frequency Octave Frequency Menu Highest Band Lowest Band Octave Resolution Octave Channels 4 7 4 7 4 7 4 8 4 8 4 8 4 9 4 9 4 9 4 10 4 10 4 12 4 12 4 13 4 13 4 14 Swept Sine Frequency Menu Start Stop Repeat Type Auto Resolution Number of Points Maximum Step Size Faster Threshold Slower Threshold Order Frequency Menu Max RPM Min RPM Max Order Delta Order Tracking Track Setup 4 15 4 15 4 15 4 16 4 16 4 16 4 17 4 17 4 17 4 18 4 19 4 19 4 19 4 19 4 20 4 20 4 20 SR785 Dynamic Signal Analyzer 4 2 Menus Track Points 4 20 Normal Marker Menu 4 54 S
522. r status word AND the Error status enable register bit 3 IERR of the Serial Poll status word is set This causes an SRQ if bit 3 in the Serial Poll enable register is set To clear a bit in the Error status word use ERRS The ERRS command queries the value of the Error status word The value is returned as a decimal number from 0 to 65535 The ERRS 1 command queries the value 0 or 1 of bit 1 0 15 ERRS clears the entire word while ERRS 1 clears just bit 1 The INSE 1 command sets the Instrument status enable register to the decimal value 1 0 255 The INSE 1 jJ command sets bit 1 0 7 to j 0 or 1 The INSE command queries the value of the Instrument status enable register The INSE 1 command queries the value 0 or 1 of bit 1 0 7 When a bit becomes set in BOTH the Instrument status word AND the Instrument status enable register bit 0 INST of the Serial Poll status word is set This causes an SRQ if bit O in the Serial Poll enable register is set To clear a bit in the Instrument status word use INST SR785 Dynamic Signal Analyzer 5 122 Status Reporting Commands INST i The INST command queries the value of the Instrument status word The value is returned as a decimal number from 0 to 255 The INST 1 command queries the value 0 or 1 of bit 1 0 7 INST clears the entire word while INST i clears just bit 1 DSPE 7 i j DSPS i INPE 7 i j INPS i INPC i Th
523. rameter 1 selects Independent Channels 0 or Dual Channels 1 The I1MD command sets queries the Chl Input Mode The parameter 1 selects A single ended 0 or A B differential 1 The I1GD command sets queries the Chl Input Grounding The parameter 1 selects Float 0 or Ground 1 The I1CP command sets queries the Ch1 Input Coupling The parameter 1 selects DC 0 AC 1 or ICP 2 l11RG x lt dBVpk dBVpp dBVrms Vpk Vpp Vrms dBEUpk dBEUpp dBEUrms EUpk EUpp EUrms gt A1RG i I1AR 2 i 11 AF 7 i The I1RG command sets queries the Chl Input Range The parameter x is the full scale input range in the specified untis If the exact input range specfied is not available the closest available input range will be used The query command returns a value of the form x j where x is the value and j is the index into the list of units If Chl AutoRange is On the I1RG i command will turn Chl AutoRange Off and the set the Chl Range to f The AIRG command sets queries the Chl AutoRanging Off On The parameter 1 selects Off Manual 0 or On AutoRanging 1 If 1 1 and Chl AutoRange is already On a new AutoRange is performed The I1AR command sets queries the Chl AutoRange Mode The parameter 1 selects Up Only 0 or Tracking 1 The I1 AF command sets queries the Chl Anti Aliasing Filter Off On The parameter 1 selects Off O or On 1 SR785 Dynamic Signal Analyzer IAW 2
524. rces Command TSLP 1 Set the Trigger Delay for Chl or Display A depending on the Analyzer Configuration The Trigger Delay applies only to FFT and Correlation measurements When the Analyzer Configuration is Dual Channel the delay setting affects the Chl input When the Analyzer Configuration is Independent Channels the delay setting affects the measurement displayed in Display A The triggered time record does not have to start with the trigger event The time record can start before the trigger negative delay or after the trigger positive delay A delay of O starts the time record at the trigger The Trigger Delay does not apply if the Trigger Source is Continuous The trigger delay can range from 8 000 to 100 000 times the underlying FFT sample rate When a large trigger delay is used the display may update more slowly since the acquisition time for each record time record length plus trigger delay is noticeably long Command TDLA 1 Set the Trigger Delay for Chl or Display A depending on the Analyzer Configuration The Trigger Delay applies only to FFT and Correlation measurements SR785 Dynamic Signal Analyzer Trigger Menu 4 103 When the Analyzer Configuration is Dual Channel the delay setting affects the Ch2 input When the Analyzer Configuration is Independent Channels the delay setting affects the measurement displayed in Display B The triggered time record does not have to start with the t
525. reLength 500 kPts ch Sampling Rate 262 1 kHz Allocate Mem View Header Capture Channels Select which inputs to capture Ch1 Ch2 Chl Ch2 Choose either input or both inputs Capturing a single input limits playback to measurements of a single input Capturing both inputs allows playback of all measurements but the Capture Length will be half as long as for a single input When the measurement group is order Capture Channels is always set to Ch1 Ch2 Turn off Auto Offset during capture to avoid interrupting the input signal Command CCHN 1 Capture Mode Select the Capture Mode 1 Shot Continuous Press Start Capture to begin storing data in the capture buffer If the Capture Mode is 1 Shot capture stops when the buffer is full Press Stop Capture to halt capture before the buffer is full If the Capture Mode is Continuous once capture is started it continues indefinitely and fills the capture buffer in a circular fashion In this case press Stop Capture to halt capture with the most recent data in the buffer Continuous capture is not allowed in the order measurement group SR785 Dynamic Signal Analyzer 4 144 Capture Menu Command CMOD 1 Capture Length Set the Capture Length in 2 kPoint 2048 points increments Memory is allocated in blocks Each block is 2 kPoints Thus 500 blocks of capture memory allows a maximum Capture Length of 1000 kPoints for a single input and a
526. red as hours minutes seconds and all entries are 6 digits 24 hour format is used Enter sets the new time or press this softkey again to abort the entry Command TIME 1 Date Set the System Date mm dd yy The System Date is entered as month day year and all entries are 6 digits Enter sets the new date or press this softkey again to abort the entry Command DATE 1 SR785 Dynamic Signal Analyzer System Diagnostics Menu Keypad Keyboard Knob A it R 232 Printer i 31004 Program SIN Kill AutoOff C Return C Keypad Test Display the Keypad Test screen The test screen is a map of the keypad Press each key until all keys are marked When all of the keys are marked the test 1s completed successfully Turn the knob to abort this test and return to the lt Diagnostics gt menu Keyboard Test Display the Keyboard Test screen Characters typed on an attached PC keyboard PC XT or 8088 mode required are displayed on the test screen If the displayed characters are accurate then the keyboard interface is functioning correctly If not check that the keyboard is in the correct mode Many keyboards have a switch on the bottom to select PC XT 8088 or AT 80286 mode Turn the knob to abort this test and return to the lt Diagnostics gt menu Knob Test Display the Knob Test screen A circle with a marker is displayed Select one of the 4 speeds displayed in the menu
527. reen Indicators And Queues To assist in programming the SR785 has 4 interface indicators which are displayed at the top of the screen The RS232 gpib indicator shows RS232 if the interface responses are directed to the RS232 serial port and gpib and the address if the interface responses are directed to the GPIB port The comm indicator flashes RS232 when there is activity on the RS232 interface and GPIB when there is activity on the GPIB interface ERR flashes whenever a computer interface error occurs such as illegal command or out of range parameter is received The REM indicator is on whenever the SR785 is in a remote state front panel locked out The SRQ indicator is on when the SR785 generates a service request SRQ stays on until a GPIB serial poll is completed To help find program errors the SR785 can display the interface buffers on the screen This screen 1s accessed by lt View Qs gt in the System lt Remote gt menu The last 256 characters received and transmitted by the SR785 are displayed SR785 Dynamic Signal Analyzer 5 22 Remote Programming Command Format Communications with the SR785 uses ASCII characters Commands may be in either UPPER or lower case A command to the SR785 consists of a four character command mnemonic with optional arguments if necessary and a command terminator The command arguments and terminator may be separated by spaces The terminator must be a linefe
528. relation depends upon the Average Mode selected in the Average menu Averaging Cross Correlation invFFT FFTu2 FFT1 Peak Hold or RMS Averaging On Cross Correlation invFFT lt FFTu2 FFT1 gt Vector Averaging On Cross Correlation invFFT lt FFTu2 gt lt FFT1 gt where FFT 1 is the windowed FFT of Channel 1 and FFTu2 is the un windowed FFT uniform window of Channel 2 Correlation is a real function and requires a baseband span real time record Non baseband time records do not preserve the original signal frequencies and thus do not yield the correct correlation A display which is measuring a single channel correlation will have its start frequency set to 0 Hz A display which measures cross correlation will set the start frequency of both displays to O Hz A correlation window is applied to the time record of the first FFT in the computation This is because the FFT models the time domain as a single time record repeating itself over and over Computing the correlation over a t greater than half of the time record length will result in wrap around errors where data starts to repeat itself To avoid this special windows which zero half of the time record are used The 0 T 2 window zeroes the second half of the time record and the T 4 T 4 window zeroes the first and last quarter of the time record The T 2 T 2 1s a uniform window which should only be used on data which is self windowing lasts
529. rement Group is Swept Sine and Auto Level Reference is Chl or Ch2 SR785 Dynamic Signal Analyzer Source Commands 5 59 SSLL x The SSLL command sets queries the Swept Sine Reference Lower Limit The parameter x is a ratio in dB from 0 1 to 30 0 dB This command is valid only when the Measurement Group is Swept Sine and Auto Level Reference is Chl or Ch2 SMAX x lt mV V dBVpk gt The SMAX command sets queries the Swept Sine Maximum Level The parameter x is the maximum level in the specified units The query returns two numbers of the form y 1 where y is a real number and 1 is an index indicating the units This command is valid only when the Measurement Group is Swept Sine and Auto Level Reference is Chl or Ch2 SOFF x lt mV V gt The SOFF command sets queries the Offset of the Swept Sine Source The parameter x is a real number of the specified units The query returns two numbers of the form y 1 where y is a real number and 1 is an index indicating the units This command is valid in the swept sine measurement group SR785 Dynamic Signal Analyzer 5 60 Input Commands Input Commands ISRC 7 i LINK i I1MD 2 i 11GD i l1CP 7 i The ISRC command sets queries the Input Source The parameter 1 selects Analog 0 or Capture 1 Capture is not valid when the Measurement Group is Swept Sine The LINK command sets queries the Analyzer Configuration The pa
530. rement average Overloads can greatly disturb the average so be certain that the correct Input Range is used Command FREJ d 1 Trigger Average Mode Selects the triggering mode for FFT Correlation and Time Histogram measurements Time Record Start Average Normally when Trigger Average Mode is set to Time Record each trigger triggers a single time record in each of these measurement groups So if the Averaging Type is set to Linear and the Number of Averages is set to 50 50 triggers will be required to complete the average When Trigger Average Mode is set to Start Average the first trigger will trigger the first time record and subsequent time records will be acquired as quickly as possible until the linear average is complete In the above example only one trigger would be required to acquire all 50 time records and complete the average Command TAVM 7 d 1 Average Preview Select Average Preview for both displays Off Manual or Timed When averaging is on Average Preview allows each individual measurement to be accepted added to the average or rejected not added to the average based upon the input time records This is useful for reyecting bad time records from corrupting an averaged measurement When Average Preview is Manual each input time record is displayed after it is acquired Choose lt Accept gt or lt Reject gt to either use or ignore the measurement based upon the displayed time record
531. rements require the Force window for the excitation channel and the Exponential window for the response channel Use the lt Channel 1 Window gt and lt Channel 2 Window gt softkeys to select which channel to apply the force and exponential windows to User Defined The User window is any function that the user provides The User window is copied from a stored trace using lt Trace to Window gt The trace may contain stored data or may be loaded from disk or via the computer interface Remember window functions have a great deal of impact on the resulting FFT spectrum A poorly designed window can result in significant measurement errors SR785 Dynamic Signal Analyzer Window Menu 4 133 Correlation Windows When the measurement group is Correlation the available windows are 1 2 T 2 This is a uniform window which should only be used on data which is self windowing lasts less than half of the time record 0 T 2 This window zeroes the second half of the time record T 4 T 4 This window zeroes the first and last quarter of the time record Octave Swept Sine and Time Histogram measurements do not use windows Channel 1 Window Selects whether the Force or Exponential window is applied to the Channel 1 input This softkey is only active 1f the selected window is Force Exponential Command W1FE 1 Channel 2 Window Selects whether the Force or Exponential window is applied to the Channel 2 input Th
532. remove the portions of the new record which are behind older records This cleans up a waterfall display by removing intersecting lines If records at the front of the waterfall are obscuring details hidden behind them reverse the waterfall direction Each display has its own Waterfall Hidden Line Mode This entry field can be linked to both displays by using the Link key Command WHID d 1 Paused Drawing Set the waterfall display direction for a paused measurement Normal Oldest at Top While the measurement is running the waterfall display scrolls down and the newest record is added to the top back of the waterfall SR785 Dynamic Signal Analyzer 4 142 Waterfall Menu When the measurement is paused the waterfall is redrawn with either the newest record at the top Normal or reversed Oldest at Top If records at the front of the waterfall are obscuring details hidden behind them reverse the waterfall direction Each display has its own Paused Drawing Mode This entry field can be linked to both displays by using the Link key Command WREV d 1 Record to Trace Save a single record or measurement from the waterfall to a Trace lt Record to Trace gt saves the record selected by the marker to a Trace Choose a Trace with the knob and press Enter to complete the operation A stored trace can be recalled to a Display or Reference Display used in a User Math Function saved to disk or copied
533. rences Menu Key Click Alarms Alarms Volume Done Volume Audible Overload Screen Saver Screen Saver Delay Frequency Format Node Info Prompt System Date Time Menu Time Date System Diagnostics Menu Keypad Test Keyboard Test Knob Test RS232 Printer Test String to RS232 SR785 Dynamic Signal Analyzer 4 195 4 195 4 196 4 196 4 196 4 196 4 196 4 197 4 197 4 197 4 197 4 198 4 199 4 199 4 199 4 200 4 200 4 200 4 200 4 200 4 201 String to Printer Memory Test System RAM System ROM Video RAM Help ROM Disk Test Serial Number Program S N Kill AutoOff Edit Macro Menu Special Keys Macro String Insert Replace Inc Knob Count Dec Knob Count Delete Clear Macro Cancel Enter Macro 4 201 4 201 4 201 4 201 4 201 4 201 4 201 4 202 4 202 4 202 4 203 4 203 4 203 4 203 4 204 4 204 4 204 4 204 4 204 4 204 Frequency Menu 4 7 Frequency Menus The Measurement Group determines which Frequency menu is displayed This menu sets the frequency parameters for the measurement A set of parameters is stored for each group FFT Frequency Menu Span When the measurement group is FFT or Correlation this menu sets the frequency span and location for the active display 51 2 kHz Line Width 128 Hz Acquisition Time 7 81 ms Full Span 102 4 kHz Start Freq 0 Hz Center Freq i 25 6 kHz End Freq FFT Lines 51 2 kHz Select the FFT Span of the
534. ress lt Return gt or Disk for the main Disk menu The Disk Buffers menu loads traces from disk files It also loads and saves Capture Arbitrary Source and Waterfall data buffers to disk Disk Upkeep Display the Disk Upkeep menu Press lt Return gt or Disk for the main Disk menu The Disk Upkeep menu allows files to be deleted directories to be created and removed and disks to be formatted SR785 Dynamic Signal Analyzer Nodal DOF Menu 4 171 Nodal Degree of Freedom Menu The nodal DOF menu appears after lt Display to Disk gt or lt Trace to Disk gt is selected if the lt Node Info gt softkey in the System lt Preferences gt menu is set to on The nodal DOF menu allows entry of descriptive paramters relating to the nodal DOFs which will be saved with the file and available to external programs which convert the files to formats usable by modal analysis programs Node Information Reference Name NODE1 Reference Num Ref Direction Response Name NODE2 Response Num Resp Direction Abort Save Continue Save Reference Name Enter a descriptive name for the reference node For a frequency response function the reference node is the node where the stimulus is applied The name may be up to six characters long The SR780 does not use the nodal degree of freedom information itself The information is stored with the 78D file and is available for use by external programs which convert the SR780 fi
535. ries from a maximum of 34 dBV full scale to a minimum of 50 dBV full scale A signal which exceeds the current input range will cause the OverLoad indicator to appear at the top of the screen A signal which exceeds the maximum safe range 35 dBVpk will turn on the Hi V indicator and set the range to 34 dBV The Input Range is displayed in dBV The maximum and minimum range equivalents are tabulated below Max 34dBVpk 31 dBVrms 50 1 Vpk 35 4 Vrms Min 50dBVpk 53 dB Vrms 3 16 mVpk 2 24 mVrms Manual Range The fixed Input Range is specified in the Input menu Signals that exceed the range will overload and become distorted Signals which fall to a small percentage of the range will lose dynamic range Auto Range The Input Range can be set to automatically correct for signal variations Use the Auto Range Ch1 and Auto Range Ch2 keys to toggle Auto Ranging On and Off Specify either Normal or Tracking Auto Range in the Input menu When Normal Auto Ranging is On and an overload occurs the Input Range is increased so that the signal no longer overloads If the signal decreases the input range is not adjusted You must take care to ensure that the signal does not fall dramatically after pushing the Input Range to a very high insensitive setting Tracking Auto Range moves the Input Range up when an overload occurs and down when the signal falls below half full scale Auto Range is always Tracking for swept sine measurements
536. rigger event The time record can start before the trigger negative delay or after the trigger positive delay A delay of O starts the time record at the trigger The Trigger Delay does not apply if the Trigger Source is Continuous The trigger delay can range from 8 000 to 100 000 times the underlying FFT sample rate When a large trigger delay is used the display may update more slowly since the acquisition time for each record time record length plus trigger delay is noticeably long Command TDLB 1 Trigd Source Mode Set the trigger mode for the source 1 Shot Continuous The Chirp Burst Chirp Burst Noise and Arbitrary sources are all triggered sources This box is unavailable if the source is not a triggered source When the trigger is set to Auto Arm Continuous the source is output continuously and this menu box is ignored Triggering The triggered sources are triggered by External triggers In the 1 Shot case the source only triggers on the first trigger after Start Reset This same trigger starts the measurement and waterfall This is useful when the source length is very long compared to the measurement time or many measurements are required to determine the response to a single source output This allows a sequence of many measurements to be triggered at the start of a single triggered source output In the Continuous case the source triggers on every trigger with a minimum trigger period set by th
537. rker Press lt Mode gt Analyzing a Sine Wave 1 9 This sets the span Center Frequency to the Marker Position for the active display The signal will be at the center of the span Further adjustments to the span will keep the center frequency fixed Select the Frequency menu Adjust the Span You can also use the numeric keypad to enter the span Enter the 12 8 kHz span numerically Note that the Center Frequency is no longer 1 024 kHz This is because a 12 8 kHz span cannot be centered below 6 4 kHz without starting at a negative frequency Adjust the graph scale and reference to display the entire range of the data This key can be used at any time Move the Marker to the fundamental peak Set the Marker Offset or Reference to the amplitude of the fundamental The Marker Position above the graph now reads relative to this offset 0 dB This is indicated by the A in front of the Marker Position reading A small flag shaped symbol is located at the screen location of the reference The Marker Position shows the distortion peaks relative to the fundamental Pressing Marker Ref again removes the Marker Offset and returns the Marker to absolute readings Select the Marker menu Adjust the Marker Mode SR785 Dynamic Signal Analyzer 1 10 Analyzing a Sine Wave Select Harmonic with the knob and press Enter Press lt Harmonics gt Use the knob to adjust the Number Of Harmonics to 10 and press Ent
538. rker Setup n Marker On Mode Band Modify Band Upper Band Exclude none Band Ratio Mode 2 fy 2 958 Vrms Band Ratio 7 67 22 3 dB Select the Upper 2 or Lower 1 Band Marker to modify Use the knob to move the selected band Use Alt knob to re size the selected band The Marker Position display above the graph shows the left and right limits of the selected band and the Band Power The Band Power is the sum of the squared magnitudes of all frequencies within the band shown in Vrms The label 1 or 2 preceding the Marker Position display denotes Lower or Upper Band Marker Command BMKL d 1 or BMKR d 1 3 Band Exclude Select Band Exclusion for the Band Marker in the active display none 1from2 2from1 None means that the two bands are independent and include all bins within their left and right limits lfrom2 means the bins in band 1 Lower are excluded from the band 2 Upper power The region where the two bands overlap is not included in band 2 Upper 2from1 means the bins in band 2 Upper are excluded from the band 1 Lower power The region where the two bands overlap is not included in band 1 Lower For example to measure THD N use the Lower 1 band to define a small region around the fundamental and the Upper 2 band to define the total bandwidth of interest SR785 Dynamic Signal Analyzer Band Marker Menu 4 65 Exclude Ifrom2
539. rm Allocation gt is pressed View Header View information about the capture buffer data Auto Pan Set Auto Pan On or Off Auto Pan On automatically pans zoomed capture buffer displays to keep up with capture fill and playback The measurement must be a capture buffer and the display needs to be Zoomed in order for this to have any effect During capture fill this keeps the capture display showing the new points being added to the buffer During playback this keeps the capture display showing the points which are currently being measured Off leaves the display Pan to that set in the Display Setup menu Command CPAN 7 1 SR785 Dynamic Signal Analyzer Analysis Menu 4 147 Analysis Menu Data Table Limit Test Analysis Data Table gt Limit Test Marker Stats Exceedance Stats Display the Data Table menu for the active display The Data Table reports the Y data values for user specified X coordinates For example the entries could be a set of harmonic frequencies which need monitoring Each display has its own Data Table though only the table associated with the active display is shown at any time If the Display Format is Dual the active display s Data Table is in the inactive display s location If the Display Format is Single or Overlay the Format is first changed to Dual To generate a report of the measurement the active display Data Table may be printed Choose ASCII Dump for
540. rrelation measurements All spans are derived from the base frequency by dividing by powers of 2 102 4 kHz is commonly used and has an advantage at narrow spans where even bin frequencies of 1 Hz 0 5 Hz etc are available 100 0 kHz has even bin frequencies of 1000 Hz 500 Hz etc at wide spans Changing the FFT Base Frequency affects ALL of the FFT frequency parameters as well as the source frequency All FFT measurements on BOTH displays use the same Base Frequency Command FBAS d 1 Start Frequency Set the Start frequency of the active display FFT span The Start frequency is the lowest frequency in the measurement span The knob adjusts the Start frequency in steps equal SR785 Dynamic Signal Analyzer 4 10 FFT Frequency Menu to the Linewidth If an entered Start frequency is incompatible with the Span then it will be set to the closest allowed value This softkey also anchors the Start frequency Adjusting the FFT Span will leave the Start frequency unchanged Enlarging the frequency Span may change the Start frequency if the new measurement would extend below O Hz or above 102 4 100 0 kHz If the Measurement Group is Correlation then the Start frequency is always 0 Hz baseband The two displays can have different Start Frequencies if the Analyzer Configuration is set to Independent Channels In this configuration no two channel measurements are allowed frequency response cross spectrum etc but the ent
541. rument settings from disk The individual bits of integer 1 determine which parameter groups are recalled bit Parameter Group 0 Measurements 1 Sources 2 Analysis 3 Inputs Triggers 4 DRAM Settings 5 General System 6 Macros If a bit is 0 the corresponding group IS NOT recalled If a bit is 1 the corresponding group IS recalled To determine the value of 1 start with 1 0 For each bit which is 1 add 2 raised to the bit number For example SRCL 127 recalls all groups SRCL 17 recalls only the Measurements 2 1 and DRAM Settings 2 16 SR785 Dynamic Signal Analyzer 5 96 Disk Commands TSAV i TRCL i DNAM 7 s DELF DELD The TSAV command saves Trace i data to disk The file name is specified by FNAM and the directory is specified by FDIR The TRCL command recalls data from disk to Trace 1 The file name is specified by FNAM and the directory is specified by FDIR The DNAM command sets queries the Upkeep File Name The Delete File function will destroy this file Be sure to use the DNAM s command before any file delete command For example the DNAM MYDATA DAT command sets the file name to MYDATA DAT DOS file name conventions must be followed 1 e file names are 8 characters or less with an optional extension of up to 3 characters The extension is NOT automatically supplied File access 1s to the current directory The DELF command deletes the file specified by the Upkeep File Name from the c
542. ry part The sampling rate is always half of the equivalent baseband span Some points to remember 1 The time record is not a continuous representation of the input signal The data is sampled and has a time resolution of 1 sample rate High frequency signals will appear distorted in the time record However ALL of the spectral information is preserved by the Nyquist sampling theorem as long as the value of each sample is accurate 2 Averaging does not affect the time record Averaging is performed on the FFT spectrum and not on the time data 3 Amplitude calibration is performed in the frequency domain Hence the time record amplitudes are not calibrated 4 A triggered time record will always jitter by 1 sample This jitter is removed in the computation of the phase of the spectrum relative to the trigger Averaged and calibrated time records can be obtained using a User Math function using inverse FFT Windowed Time Record The FFT operates on windowed time records The window function is applied to the time record immediately before the FFT Most window functions taper off to zero at the start and end of the time record If a transient signal occurs at the start of the time record the corresponding windowed time record and FFT may not show anything because the window function reduces the transient to zero SR785 Dynamic Signal Analyzer 2 18 FFT Measurements Orbit The Orbit measurement is a two channel measurement wh
543. ry field can be linked or unlinked using the Link key If Analyzer Configuration is set to Dual Channel they field 1s automatically linked to both displays Command FSTR d f Center Frequency Set the Center frequency of the active display FFT span The Center frequency is the center of the measurement span The knob adjusts the Center frequency in steps equal to the Linewidth If an entered Center frequency is incompatible with the Span then it will be set to the closest allowed value This softkey also anchors the Center frequency Adjusting the FFT Span will leave the Center frequency unchanged Enlarging the frequency Span may change the Center frequency if the new measurement would extend below O Hz or above 102 4 100 0 kHz If the Measurement Group is Correlation then the Center frequency is always equal to Span 2 baseband The two displays can have different Center Frequencies if the Analyzer Configuration is set to Independent Channels In this configuration no two channel measurements are allowed frequency response cross spectrum etc but the entry field can be linked or unlinked using the Link key If Analyzer Configuration is set to Dual Channel they field is automatically linked to both displays Command FCTR 7 d f End Frequency Set the End frequency of the active display FFT span The End frequency is the highest frequency in the measurement span The knob adjusts the End frequency in steps
544. ry other point is kept as part of the time record The result is a time record of 1024 points sampled at 131 kHz to make up an 7 8 ms record The FFT processor operates on a constant number of points and the resulting FFT will yield 400 bins from DC to 51 2 kHz The resolution or linewidth is 128 Hz 1 7 8 ms This process of halving the sample rate and span can be repeated by using multiple stages of digital filtering The SR785 can process a 400 bin spectra with a span of only 195 3 mHz and a time record of 2048 seconds if you have the patience However this filtering process only yields baseband measurements frequency spans which start at DC SR785 Dynamic Signal Analyzer FFT Frequency Spans 2 9 Baseband Spans Some points to remember are 1 The FFT resolution number of frequency bins in the spectrum determines the number of points required in the time record 2 The duration of the time record determines the frequency resolution of the spectrum spacing of frequency bins in the spectrum 3 The sampling rate determines the frequency span of the spectrum Nyquist s theorem The sampling rate is the number of points in the time record divided by the duration of the time record The SR785 allows FFT resolutions of 100 200 400 or 800 bins not counting DC Changing the resolution does not change the span instead the time record length is changed The various FFT resolutions are summarized below FFT Frequency Reso
545. s Oxxx Output File Type asc ASCII default 78d 78D SR785 display file sdf HP SDF v3 File mat MATLAB binary file uff Universal File Format cap capture buffer 78C file arb arbitrary waveform buffer A Append to output file uff and ASCII outputs only Efilename Specify error log file Default is Esrslog txt J Append to logfile Default is replace logfile Help For Help on options pertaining to a specfic output file specify the ouput file type with no input file e g srtrans Oasc Frequently used program options may be kept in a file named SRT785 INI in the current directory The INI file is scanned for options before the command line options are processed Converting Files to ASCII Usage SRT785 Oasc options infile outfile Allowed Input File Types 78D Files 78C files 78W files Default Output File Extension ASC ASCII Output Options D Data only in output no descriptive header SR785 Dynamic Signal Analyzer 6 6 Using the File Conversion Utilities H1 H2 Pn Fstring KO K1 K2 A Additional Options for Cview1 view2 Upk dB deg Header Only Standard Header default Header Only Exhaustive Header The exhaustive header contains a list of all of the instrument settings Output n points per line default is P1 Data Format String default is F 14 6e This is a standard C language printf format specifier which determines the format of numbers in th
546. s SR785 Dynamic Signal Analyzer Analyzing a Sine Wave 1 7 Analyzing a Sine Wave This measurement investigates the spectrum of a 1 024 kHz sine wave You will use the SR785 source to provide the sine signal or you can use a function generator capable of providing a 1 024 kHz sine wave at a level of 100 mV to 1 V such as the SRS DS345 The actual settings of the generator are not important since you will be using the SR785 to measure and analyze its output 1 Press System Display the System menu Press lt Preset gt Press Enter to confirm Preset 2 Connect the Source Output to the Channel 1 A Input Or connect a function generator s output to the Ch1 A Input of the analyzer Press Source Press lt Sine gt Press lt Frequency 1 gt Press 1 0 2 4 select kHz with the knob and press Enter Press lt On gt Or turn on the generator set the frequency to 1 024 kHz and the amplitude to approximately 1 Vrms Preset returns the unit to its default settings Preset requires confirmation to prevent accidental reset Wait until the self tests are completed Setup to analyze the source output The input impedance of the analyzer is 1 M2 The generator may require a terminator Many generators have either a 50 or 600 Q output impedance Use the appropriate feedthrough termination if necessary In general not using a terminator means that the output amplitude will not agree with th
547. s a percentage of the time record length If the increment is 100 the start of the next time record is exactly one time record advanced from the start of the previous time record If the increment is 25 then the next time record starts 1 4 of a time record advanced from the start of the previous time record This is sometimes referred to as 75 overlap since the two time records share 75 of a record The overlap is simply 100 minus the Time Record Increment When the Time Record Increment is less than or equal to 100 the measurement is said to be real time All time points contribute to one or more measurements If the increment 1s 200 the start of the next time record is advanced from the start of the previous time record by 2 time records leaving a gap of 1 record This means that the data between the two time records is not measured When the Time Record Increment is greater than 100 then the measurement is not real time and some time points do not contribute to a measurement The actual time record increment for the measurements in progress is displayed in the Real Time indicator in the status area below the Input Ranges If the indicator shows a value greater than the requested Time Record Increment it means that the measurement cannot be made with the requested increment but is running with the smallest increment possible Factors which affect the processor s ability to run real time include the measurement
548. s queries the swept sine Faster Threshold of display d The parameter x is a level from 0 01 to 3 0 dB The set command requires d 2 both displays This command is valid only when the Measurement Group is Swept Sine The set command requires a display to be Live SSLO d x The SSLO command sets queries the swept sine Slower Threshold of display d The parameter x is a level from 0 05 to 6 0 dB The set command requires d 2 both displays This command is valid only when the Measurement Group is Swept Sine The set command requires a display to be Live SR785 Dynamic Signal Analyzer 5 34 Frequency Commands Frequency Commands Order Analysis ORMX d x The ORMX command sets queries the maximum RPM for display d The parameter x is the maximum rpm a real number The set command requires d 2 both displays This command is valid only when the Measurement Group is Order The set command requires a display to be live ORMN 7 d x The ORMN command sets queries the minimum RPM for display d The parameter x is the minimum rpm a real number The set command requires d 2 both displays This command is valid only when the Measurement Group is Order The set command requires both displays to be Live OMAX d x The OMAX command sets queries the maximum order for display d The parameter x is the maximum order a real number The set command requires d 2 both displays This comma
549. s are allowed Dual channel measurements such as frequency response or orbit cannot be selected Dual Channel allows selection of all measurements both single and dual channel However in Dual Channel mode the two displays always have the same frequency parameters SR785 Dynamic Signal Anaylzer 4 88 Input Menu When the measurement group is Swept Sine or Order the Analyzer Configuration 1s always set to Dual Channel Command LINK 1 Auto Offset Enable Auto Offset input calibration Off On When Auto Offset is On the analyzer will periodically perform an input offset calibration This involves internally grounding both inputs and correcting their DC offsets This only takes a second However the measurements will need to settle again after an offset calibration To avoid disrupting a lengthy measurement turn Auto Offset Off A warning message is displayed 15 seconds before an Auto Offset calibration is performed Pressing lt backspace will abort the scheduled calibration Command IAOM 7 1 SR785 Dynamic Signal Anaylzer Input Configuration Menu 4 89 Input Configuration Submenu Channel Input Mode Grounding Channel Chi Ch1 Input Mode A Ch1 Grounding Float Ch1 Coupling Ch1 Input Range 2 dBVpk Ch1 AA Filter i Chi A Wt Filter off Ch1 AutoRange Return Selects which input channels will be affected by the input configuration submenu Chl Ch2 Both When
550. s corresponds to the longest possible time record 800 line baseband Using this trace in User Math requires attention to the lengths of other operands in any user function Command WITR d 1 Window Form Select the Window Form of the User window Non Symmetric Symmetric This softkey only affects the User window Use Symmetric if the User window is centered or symmetric in the time record Phase will be measured relative to the center of the time record Uniform Hanning Flattop BMH and Kaiser windows are all symmetric Use Non Symmetric if the User window is non symmetric Phase will be measured relative to the start of the time record Force and Exponential windows are non symmetric Command WSYM d 1 SR785 Dynamic Signal Analyzer Waterfall Menu 4 135 Waterfall Menu Display The Waterfall menu configures the waterfall displays Waterfall displays are not available for Nyquist or Nichols Views or Swept Sine measurements Waterfall Display Normal Storage off Save Option Skip View Count Angle Marker Z to Allocate Mem More Select the Normal or Waterfall Display for the active display Waterfall Display only applies to FFT and Octave measurements Waterfall displays are not available for Nyquist or Nichols Views or Swept Sine measurements Normal Display only shows the results of a single measurement Waterfall Display WITHOUT storage is simply a graphical display scrolling
551. s have shorter time constants and lower frequency bands have longer time constants This is very noticeable in the update of the display Peak Hold Peak Hold displays the peak output from each band filter The peak detection continues indefinitely Sound Level Measurement The last bin in an octave display shows one of many types of sound level measurement Leq Leq exponential time averaged power is computed according to ANSI S1 4 1983 It is computed from real time low pass filtered input data not from the octave band outputs The bandwidth of Leq is DC 100kHz for 1 octave channel and DC 50kHz for 2 channels To measure Leq set the Averaging Type to Exponential and the Power Bin to L When the Averaging Type is Exponential or Linear the exponential time constant for Leq is the Integration Time Leq power is always an exponential average Standard measurements use either 125 ms Fast or 1000 ms Slow Note that the lowest octave band places a limit on the averaging time The standard time constants may not be available if the octave measurement extends to low frequency bands If the Averaging Type is Equal Confidence Leq has the same confidence level as the octave measurement If the Averaging Type is Peak Hold Leq is not available The last bin in the measurement displays the Leq sound level The last bin is labeled either L for uniform weighting or LA if the input A Weighting filter is on In a User Math function
552. s incrementing at the Integration Time while the averaging continues Exponential weighting reaches a steady state after approximately an integration time Once in steady state further changes in the average are detected only if they last for a sufficient number of measurements Make sure that the integration time is not so large as to eliminate changes in the data which might be important Equal Confidence Equal Confidence averaging is exponential averaging where the integration time is set for each band separately The integration times are set so that there is a 68 probability that the results are within the specified Confidence Level of the true mean for every band in the measurement There is a 96 probability that the results are within twice the Confidence Level in dB of the true mean The effect of Equal Confidence averaging is that higher frequency bands have shorter time constants and lower frequency bands have longer time constants This is very noticeable in the update of the display Averaging continues indefinitely Peak Hold Peak Hold displays the peak output from each band filter The peak detection continues indefinitely Choosing Peak Hold also sets the Power Bin to Peak Integration Time Set the Integration Time for the active display 4 ms 1 ks in 4 ms increments The Integration Time affects Linear Time Exponential Time and Peak Hold averaging The minimum Integration Time is determined by the Lowest B
553. s menu Go to the Limit Testing menu Select Limit Segments Show the segments The two segments defined earlier are still available This concludes this example Limit testing is a powerful tool for repetitive tests In an automated test environment limit segments are usually downloaded from a host computer The SR785 performs the limit testing in real time and the results are queried by the host computer 1 60 Exceedance Statistics Exceedance Statistics This example is intended to familiarize the user with calculating exceedance centile statistics La Ly 1s calculated from measurements stored in the waterfall buffer L is the amplitude at each bin which is exceeded by n of the records in the waterfall The SR785 simultaneously calculates L at all frequencies in the spectrum L is commonly used to characterize environmental noise levels Press System Press lt Preset gt Press Enter to confirm Preset Connect the Source Output to the Channel 1 A Input Press Display Setup Press lt Measure Group gt Select Octave with the knob and press Enter Press Source Press lt On gt Press lt Noise gt Press lt Type gt Use the knob to select Pink and press Enter Display the System menu Preset returns the unit to its default settings Preset requires confirmation to prevent accidental reset Wait until the self tests are completed Setup to analyze the source output Select th
554. s one measurement per time record and waits and does nothing until the next time record is complete The update rate is one measurement per time record With narrow spans this is quite slow With overlap processing the analyzer does not wait for the next complete time record before computing the next measurement Instead it uses data from the previous time record as well as data from the current time record to compute the next measurement This speeds up the update rate Remember most window functions are zero at the start and end of the time record Thus the points at the ends of the time record do not contribute much to the FFT With overlap these points are re used and appear as middle points in other time records This is why overlap effectively speeds up averaging and smoothes out window variations SR785 Dynamic Signal Analyzer 2 28 Real Time Bandwidth and Overlap Typically time records with 50 overlap provide almost as much noise reduction as non overlapping time records when RMS averaging is used When RMS averaging narrow spans this can reduce the measurement time by 2 Time Record Increment The Time Record Increment is how far the start of each time record is advanced between measurements as a percentage of the time record length If the increment is 100 the start of the next time record is exactly one time record advanced from the start of the previous time record no overlap If the increment is 25 then the next
555. s using the Link key Command MROX d x Set the Y Offset for the Normal Marker of the active display Enter a new offset numerically or adjust it with the knob When the Marker Rel Mode is Relative the marker position is calculated relative to the Marker Offset X Rel Y Rel The Marker Offset location if it is within the display is marked by a small flag shaped symbol The Marker Offset has no associated units The relative calculation simply subtracts the Marker Offset in the display units from the absolute marker position Changing the display units invalidates the Marker Offset Re enter the Marker Offset or use Marker Ref to reset the Marker Offset in the new units Pressing Marker Ref changes from Off to Rel and sets the Marker Offset to the current Marker Position Marker Ref again changes from Rel back to Off Each display has its own Normal Marker Y Offset This entry field can be linked to both displays using the Link key Command MROY d x Set the X Rel Mode for the Normal Marker of the active display Off On When the Marker Rel Mode is Relative to the Marker Offset or Relative to the Other Display the marker Y value is shown relative to the offset or other display Choose On to show the marker X value relative to the offset or other display as well Choose Off to show the absolute marker X value This is useful when making relative amplitude measurements while still needing to read the
556. sampled The result of this undersampling is to make these higher frequency signals appear as lower frequencies in the digital data stream Thus a signal at 175 kHz would appear below 102 4 kHz in the digital data stream and be detected in the spectrum To avoid this undersampling the analog signal is filtered to remove any signals above 160 kHz when sampling at 262 kHz signals above 160 kHz will appear below 102 kHz This filter has a flat pass band from DC to 104 kHz so as not to affect measurements in the operating range of the analyzer The filter rolls off from 104 kHz to 160 kHz and achieves an attenuation above 160 kHz of at least 90 dB Amplitude variations and phase shifts due to this filter are calibrated out at the factory and do not affect frequency domain measurements SR785 Dynamic Signal Analyzer Signal Inputs 2 67 For time domain measurements the anti aliasing filter limits the rise time of the signal and causes ringing To eliminate these effects in the time record the anti aliasing filter can be removed from the signal path However the spectrum of this time record may contain alias frequencies A Weighting Filter The A Weighting filter may be inserted after the anti aliasing filter The A Weighting filter simulates the hearing response of the human ear and is often used with Octave Analysis measurements The input A Weighting filter conforms to ANSI standard S1 4 1983 A B and C Weighting functions are also avai
557. samples Then the signal would land all in one frequency bin But this would require changing the sampling rate based upon the signal which you haven t measured yet This is not a practical solution Instead the way to measure the signal accurately 1s to lengthen the time record and change the span of the spectrum SR785 Dynamic Signal Analyzer 2 8 FFT Frequency Spans FFT Frequency Spans Full Span Full span is the widest frequency span corresponding to the fastest available sampling rate In the SR785 this is DC to 131 kHz using a sampling rate of 262 kHz Because the signal passes through an anti aliasing filter at the input the entire frequency span is not useable The filter has a flat response from DC to 102 4 kHz and then rolls off steeply from 102 4 kHz to 156 kHz The range between 102 4 kHz and 131 kHz is therefore not useable and the actual displayed frequency span stops at 102 4 kHz There is also a frequency bin labeled 0 Hz or DC For a time record of 1024 samples 3 9 ms this bin actually covers the range from 0 Hz to 128 Hz the lowest measurable frequency and contains the signal components whose period is longer than the time record not only DC So our final displayed spectrum contains 401 frequency bins The first covers 0 128 Hz the second 128 384 Hz and the 401st covers 102 272 102 528 kHz Spans Less Than Full Span The duration of the time record determines the resolution of the spectrum What happens if we
558. scale but not overloaded When the bar is 4 divisions long displayed brightly the input signal exceeds full scale and is overloaded This also sounds the audible overload alarm Once an overload occurs the outline of the overload bar remains in the indicator The overload outline indicates that the input has overloaded since the measurement was started This is important when the measurement is linearly averaged and an overload occurs during the average Pressing Start Reset restarts the measurement and erases this overload outline Whenever an input greater than 57 V is detected at the input the overload indicator displays HighV on a bright background The analyzer immediately switches to 34 dBV range to protect the input circuitry Any attempt to change the input will not be allowed until the input signal 1s reduced to a safe level Input Configurations AWt The Input Mode and Coupling for both inputs are displayed If the coupling is DC or AC the coupling indicator is on a normal background If ICP coupling is selected then ICP is displayed on a highlighted background The A Weighting filter status for both inputs are displayed If the A Weighting filter is ON then AWT is displayed on a highlighted background ArmWait Trig wait Trig Acquire This indicator reads Trig wait while waiting for a trigger Once triggered the indicator flashes Trig and then displays Acquire while the time record is being a
559. se holder Line Fuse Verify that the correct line fuse is installed before connecting the line cord For 1O0V 120V use a 1 5 Amp fuse For 220V 240V use a 3 4 Amp fuse Line Cord The SR785 has a detachable three wire power cord for connection to the power source and to a protective ground The exposed metal parts of the instrument are connected to the outlet ground to protect against electrical shock Always use an outlet which has a properly connected protective ground Power Switch The power switch is on the rear panel Turn the unit on by depressing the upper half of the power switch The green power LED on the front panel indicates that the unit is powered Screen Brightness If the screen is too dark or too bright adjust the brightness using the Brighter and Dimmer buttons below the softkeys below right of the display Do not set the brightness higher than necessary Fan The fans in the SR785 are required to maintain proper operation Do not block the vents in the chassis or the unit may not operate properly SR785 Dynamic Signal Analyzer Getting Started 1 3 Front Panel Quick Start There are two types of front panel keys which are referenced in this section Hardkeys are those keys with labels printed on them Their function is determined by the label and does not change Hardkeys are referenced by brackets like this Hardkey Softkeys are the ten gray keys along the right edge of the screen Their function is labeled b
560. seful for resolving adjacent peaks or improving signal to noise They should not be used for accurate amplitude measurements except for signals at exact bin frequencies If the filter is wide then frequencies farther from each exact bin will contribute to the bin amplitude making the signal peaks very wide However off bin frequencies are not attenuated These windows should be used for accurate amplitude measurements rather than good frequency resolution Windowing allows the FFT to accurately measure signals at frequencies which are not exact frequency bins The different types of windows trade off selectivity amplitude accuracy and noise floor The SR785 offers many types of window functions Uniform no windowing Flattop Hanning Blackman Harris BMH Kaiser Force Exponential and User Defined windows Uniform The Uniform window is actually no window at all The entire time record is used with equal weighting A signal will appear in a single frequency bin in the spectrum if its frequency is exactly equal to a frequency bin It is exactly periodic within the time record If its frequency is between bins it will leak into every bin of the spectrum These two cases also have a great deal of amplitude variation between them up to 4 dB SR785 Dynamic Signal Analyzer FFT Windowing 2 13 In general this window is only useful when looking at transients which do not last the entire time record The Uniform window may also be us
561. sible FOR USE BY QUALIFIED PERSONNEL ONLY USE CORRECT FUSE STANFORD RESEARCH SYSTEMS MADE IN U S A 7 00545 720 revB IEEE 488 STD PORT PUL Ea e NG 48 66Hz 1 5A 100 120V 75A 220 240V RS232 DCE PRINTER PORT Figure Chapter 3 2 Rear Panel Power Entry Module The power entry module is used to fuse the AC line select the line voltage and block high frequency noise from entering or exiting the instrument The SR785 has a detachable three wire power cord for connection to the power source and to protective ground The exposed metal parts of the instrument are connected to the outlet ground to protect against electrical shock Always use an outlet which has a properly connected protective ground Caution A This instrument may be damaged if operated with the LINE VOLTAGE SELECTOR set for the wrong AC line voltage or if the wrong fuse is installed Do not attempt to service or adjust this instrument while it is plugged into a live outlet Line Voltage Selection The SR785 operates from a 100V 120V 220V or 240V nominal AC power source having a line frequency of 50 or 60 Hz Before connecting the power cord to a power SR785 Dynamic Signal Analyzer Rear Panel Connectors 3 9 source verify that the LINE VOLTAGE SELECTOR card located in the rear panel fuse holder is set so that the correct AC input voltage value is visible Conversion to other AC input voltages requires a change in the fuse holder vo
562. since the previous operation Remember these status bits are only reset when read The status word needs to be cleared before waiting for the desired bits to become set For example to change the span and wait until new data is available a program might use the following procedure send CLS FSPN 0 6400 STRT CLS clears all status words FSPN changes the span of DisplayA to 6 4 kHz STRT starts the measurement with the new span query DSPS DSPS reads the Display Status until NEWA and STLA are set NEWA amp STLA indicates new settled data is available at the new span Command Context Errors Commands which perform menu softkey functions are not allowed unless the corresponding softkey function is allowed If the softkey is not available in the current context either shown in gray or not displayed at all then the corresponding set command is not allowed In general softkeys are disabled for two reasons the function is specifically not allowed in the current measurement context or the function is only applicable for certain measurement groups For example FFT lt Start Frequency gt is grayed when the measurement is full span The FSTR set command is not allowed in this situation However the FSTR query command is still allowed An example of group specific parameter are the commands which set Swept Sine parameters These set commands are not allowed unless the measurement group is Swept Sine just like the menu
563. sing the Hanning window while DisplayA is still using the BMH window So far we have unlinked measurement parameters Frequency Span Averaging and Window type affect the actual measurements within the displays Most analyzers do not allow these measurement parameters to be unlinked Display parameters such as Scaling Views Units and Marker functions are usually unlinked However linking them can be a convenient way to adjust graph parameters together with a minimum of key presses Select the Display Setup menu Enter the Units Select between peak rms and peak to peak units Link the Pk Units parameter default is unlinked Both displays Units become dBVrms with a single parameter entry The Pk Units remain linked until unlinked with the Link key Return to the Display Setup Menu SR785 Dynamic Signal Analyzer 1 18 Linking Advanced Operation Press lt Y Max gt Press Link Press 1 0 and press Enter Press Auto Scale A Press Link and then Auto Scale A 12 Press Link and use the knob to move the Marker Both Markers move together when linked Press Enter Press Marker Min Press Link then Marker Min SR785 Dynamic Signal Analyzer Let s change the Top Reference of the graphs Link the Y Max parameter default 1s unlinked Change the Top Reference of both graphs to 10 dBVrms with a single entry Change the scale of DisplayA to center the data Another simple
564. sistance of ground connections 3 Removing sources of large ground currents from the ground bus used for small signals 4 Measure the signal relative to the source ground using two cables A B Set the Input Grounding to Float Microphonics Not all sources of noise are electrical in origin Mechanical noise can be translated into electrical noise by microphonic effects Physical changes in the signal source or cables due to vibrations for example can result in electrical noise over the entire frequency range of the analyzer For example consider a coaxial cable connecting a signal source to the analyzer The capacitance of the cable is a function of its geometry Mechanical vibrations in the cable translate into a capacitance that varies in time typically at the vibration frequency Since the cable is governed by Q C V taking the derivative we have C dV dt V dC dt dQ dt i Mechanical vibrations in the cable which cause a dC dt will give rise to a current in the cable This current affects the measured signal Some ways to minimize microphonic signals are SR785 Dynamic Signal Analyzer 2 74 External Noise Sources 1 Eliminate mechanical vibrations near the signal path 2 Tie down cables carrying sensitive signals so they do not move 3 Use a low noise cable that is designed to reduce microphonic effects Thermocouple Effects The emf created by junctions between dissimilar metals can give rise to many microvolts of s
565. specific display Command EU1V x EU2V x EUs at Marker Calculate the EU Volt scale factor for either the selected input based upon the marker reading in the active display Enter the desired calibrated value for the marker reading in the display units The active display measurement must be a single channel measurement and Engineering Units must be On This feature is normally used for the input channel which is being measured in the active display In this case the active display marker reading changes to the calibrated value SR785 Dynamic Signal Anaylzer 4 94 Transducer Parameter Menu However you can use this feature for the other input channel In this case the active display is not affected but other measurements based upon the other input are affected User Label Enter the User Label for the selected input Engineering Units Use the ALT keys for alphabetic entry to enter a user defined name for the engineering units The displayed units change from Volts to the User Label when Engineering Units are On and USER is chosen for the EU Label Note that this softkey applies to an input channel unlike most softkeys which apply to a specific display Command EU1U s EU2U s Transducer Convert Select the Transducer Conversion for the selected input Transducer conversion only has an effect for measurements of inputs with Transducer Units of acceleration velocity or displacement Transduc
566. st Chirp and Burst Noise Source trigger aligns the start of the time record with the start of the burst output Source trigger only applies to FFT and Correlation measurements External Trigger For Chirp Burst Chirp Burst Noise and Arbitrary the External trigger can trigger the source output The source can trigger on only the first trigger or on every trigger after a measurement is started as selected in the Trigger menu The measurements are triggered normally in either case SR785 Dynamic Signal Analyzer 2 38 Correlation Correlation Analysis What is Correlation Analysis Correlation is a time domain measurement which reveals similarities and periodicities within a signal autocorrelation or between two signals cross correlation Although a time domain measurement the SR785 computes correlation measurements by transforming input data into the frequency domain processing it and retransforming back to the time domain Correlation Measurements Correlation Analysis is a Measurement Group Choose the Measurement Group within the Display Setup menu The available measurements are Auto Correlation Cross Correlation Time Record Windowed Time record Capture Buffer and User Function Auto Correlation Auto correlation is a single channel measurement In the time domain it is a comparison of the signal x t with a time shifted version of itself x t t displayed as a function of Tt This is useful for detecting similarities whi
567. st band in the octave graph Exponential averaged sound power Leq is calculated according to ANSI 1 4 1983 Type 0 Broadband Impulse and Peak measurements are made according to IEC 651 1979 Type 0 Exponential averaged power Leq Impulse I and Peak P power are computed from real time input data These are broadband measurements and are not computed from the octave bands The band limited Total T power is computed from the octave bands Each display has its own Power Bin This entry field can be linked to both displays by using the Link key Command OIMP 7 d 1 Linear Average Trigger Choose how linear averaged octave measurements behave when triggered One Lin Avg Start The Linear Avg Mode only applies for linear averaging when the Trigger Mode and Trigger Source are not Auto Arm and Continuous respectively When the measurement is triggered the Linear Average Mode determines how the measurement restarts One Linear Average means that each trigger starts anew measurement SR785 Dynamic Signal Analyzer 4 118 Octave Average Menu Start means that the next measurement starts immediately after the previous measurement finishes Only the first measurement after Start Reset is started with a trigger This mode is useful for measuring reverberation where the first measurement is triggered with the noise burst use the Burst Noise source with 1 Shot Trigd Source Mode and subsequent measurements follow continuously
568. stants for the Peak measurement are defined by the IEC standard The Integration Time and Confidence Level are ignored by the Peak calculation Peak power is always an exponential average The last bin in the measurement displays the Peak sound level The last bin is labeled Pe In a User Math function the P bin is treated the same as the other octave bins with the exception of the A B and C weighting operators These operators do not change the P bin Total Power Total power T is computed from the sum of the measured octave bands The bandwidth is set by the Highest and Lowest Bands of the octave measurement To measure Total Power set the Power Bin to T Total Power is available for all Averaging Types The last bin in the measurement displays the Total Power The last bin is labeled as follows Label Frequency Weighting T uniform weighting TA A Wt input filter Ta A Wt User Math Tb B Wt User Math Tc C Wt User Math Tu undefined SR785 Dynamic Signal Analyzer 2 46 Octave Analysis Tu is shown whenever more than one type of weighting exists in the measurement In a User Math function the octave bins are operated on and then summed to provide the T bin The T bin is computed after the function is evaluated Settling Time When an octave measurement or input is changed a settling time is required for the change to propagate through the octave filters and the measurement becomes valid again This settling ti
569. sweep Also the source ramps up when the sweep is started and ramps off when paused This causes a delay before the first point 1s measured Command SRAT x Reference Upper Limit Set the Reference Upper Limit 0 1 dB 30 0 dB This parameter is adjustable only if Auto Level Reference is set to Channel 1 or Channel 2 When Auto Level is on the Ideal Reference is the signal level the source will try to maintain at the Reference Channel The Reference Upper and Lower Limits are the allowable tolerances for the Reference Channel The source level is changed only if the reference channel measures an input which exceeds the Ideal Reference by more than the Upper Limit or which is less than the Ideal Reference by more than the Lower Limit In cases where the reference channel input must be limited the Ideal Reference plus the Upper Limit must be less than or equal to this limit If the required source amplitude is very small the resolution of the source amplitude may result in a Reference Channel signal which is not within tolerance of the Ideal Reference The Reference Upper Limit may be changed during a sweep Command SSUL x or SSLL x Reference Lower Limit Set the Reference Lower Limit 0 1 dB 30 0 dB This parameter is adjustable only if Auto Level Reference is set to Channel 1 or Channel 2 When Auto Level is on the Ideal Reference is the signal level the source will try to maintain at the Reference Channel
570. t 33 Rms lt FulF1 gt 34 Rms lt Fu2F2 gt 35 Rms lt Fu2 gt lt F1 gt 69 Octave Operands Oct 1 36 Oct 2 37 Swept Sine Operands Spec 1 38 Spec 2 39 Norm Var 1 40 Norm Var 2 41 Cross Spectrum 74 Freq Resp 0 75 Order Operands Time 1 42 Time 2 43 lt Spec 1 gt 60 lt Spec 2 gt 61 lt Pwr 1 gt 62 lt Pwr 2 gt 63 Vec lt Time 1 gt 44 Vec lt Time 2 gt 45 Time Histogram Operands Histo 1 48 Histo 2 49 PDF 1 50 PDF 2 5 CDF 1 52 CDF 2 53 Time 1 20 Time 2 2I Operands for All Groups Trace1 1 Trace2 2 Trace3 3 Trace4 4 Trace5 5 Constl 6 SR785 Dynamic Signal Analyzer User Math Commands 5 77 Const2 7 Const3 8 Const4 9 Const5 10 J 11 USRC i x y The USRC command sets queries the real and imaginary parts of User Constant i The parameter 1 selects a User Constant from to 5 The parameters x and y are floating point values for the real and imaginary parts SR785 Dynamic Signal Analyzer 5 78 Window Commands Window Commands FWIN d i The FWIN command sets queries the FFT Window for display d The parameter 1 selects a window below 1 Window 0 Uniform 1 Flattop 2 Hanning 3 BMH 4 Kaiser 5 Force Exponential 6 User 7 T 2 T 2 Correlation only 8 0 T 2 Correlation only 9 T 4 T 4 Correlation only The Correlation windows may be selected only if display d is a live Correlation measurement This command is valid only when the Measure
571. t 4 MAV The interface output buffer is not empty 5 ESB An enabled bit in the Standard status word is set 6 SRQ An SRQ has occurred serial poll or an enabled bit in the this status word is set STB 7 IFC No command execution is in progress The INST DISP INPT IERR and ESB bits are set whenever any bit in both their respective status words AND enable registers is set Use the INSE DSPE INPE ERRE and ESE commands to set the enable register bits The INST DISP INPT IERR and ESB status bits are not cleared until ALL enabled status bits in the Instrument Display Input Error and Standard Event status words are cleared by reading the status words or using CLS Use serial poll or STB to read the Serial Poll status Use SRE to set bits in the Serial Poll enable register Using STB to Read the Serial Poll Status The Serial Poll status word is NOT cleared by reading the status using STB A bit stays set as long as the status condition exists This is true even for bit 6 SRQ Bit 6 will be set whenever the same bit in the Serial Poll status word AND Serial Poll enable register is set This 1s independent of whether a serial poll has occurred to clear the service request Using Serial Poll to Read the Serial Poll Status Except for SRQ a bit in the Serial Poll status word is NOT cleared by serial polling the status word A bit stays set as long as the status condition exists When reading the status using a serial poll the SRQ
572. t Usage SRT785 Ouff options infile outfile Allowed Input File Types 78D Files Default Output File Extension UFF UFF output options Mrinodename Mrnn Mrdk Msinodename Msnn Msdk CONN NAN BWN KF ODO ps pa VD N e Reference node name Reference node number Reference node direction see table below Response node name Response node number Response node direction Node Direction id s Scalar Z Y X 0 0 0 SR785 Dynamic Signal Analyzer 6 10 Using the File Conversion Utilities Converting Files to Capture File Format 78C Usage SRT785 Ocap options infile outfile Allowed Input File Types ASCH Default Output File Extension 78C Capture output options Bn Base Frequency n 0 for 100kHz n 1 for 102 4 kHz default Ln Length of Buffer n is number of kPoints default L2 Nn Sampling Frequency Sampling frequency 256 kHz 2 or 262kHz 2 depending on the base frequency Default is n 0 In Full Scale Input Range in dBV Default is n 0 The input values are ASCII floating point numbers The numbers represent values in volts and must not exceed the full scale input range set with the In option If the number of values found in the input file is less than the number of points specified with the Ln option the output file is zero padded Example Convert the ASCII floating point values found in the file C1 TXT into a 10 kpoint capture file with an input range of 20
573. t Capture Press Display Ref Press Auto Scale A 5 Press Alt Print Screen Use the knob to select Trace 3 and press Enter Press Span Up twice to return to full span Press Active Display Press Alt Help Local SR785 Dynamic Signal Analyzer Select the Display Setup menu Change the top reference for the graph Set the middle reference to 400 dBV Note that the live data is graphed with the new vertical reference but the reference graph did not move This allows the reference graph to be offset from the live data so it is visible Snap Ref is an alternate function The alternate key functions are labeled below each key in this case the Start Capture key Snap Ref redraws the reference graph with the current display scaling Pressing Display Ref again turns off the reference graph The reference graph data is lost To save the reference graph transfer the reference graph to a trace before turning it off The trace may be saved to disk Scale the graph appropriately again Display to Trace is an alternate function This function saves the current data in the active display to a trace Store the display in Trace 3 There are 5 traces available for data storage They can store the results of any measurement other than capture buffer They can be viewed as complex arrays of data which can be viewed like any other measurement data Change the live measurement Make DisplayB bottom ac
574. t File in the Current Directory If the Current File has no specified extension the default extension 78S is used The entire instrument setup is stored to the file Portions of the setup may be excluded from the recall Command SSAV Recall Settings Display the Recall Settings menu Choose the portions of the setup to recall from the Current File in the Current Directory The recalled settings become effective immediately Press Disk again to return to the main Disk menu Command SRCL 1 Trace to Disk Save Trace data to the Current File in the Current Directory If the Current File has no specified extension the default extension 78D is used Select a Trace 1 5 with the knob and press Enter to save it to disk Only traces which currently have data in them may be selected To save a display to a Trace use Display to Trace AIt Print Screen Command TSAV 1 Disk to Trace Recall data from the Current File in the Current Directory to a Trace If the Current File has no specified extension the default extension 78D is used Select a Trace 1 5 with the knob and press Enter to recall from disk to the Trace The recalled data will replace any data presently stored in the Trace A stored trace can be recalled to a Display or Reference Display used in a User Math Function or saved to disk Command TRCL 1 SR785 Dynamic Signal Analyzer 4 170 Disk Menu Buffers Display the Disk Buffers menu P
575. t auto ranging has the largest impact on extending the dynamic range of a swept sine measurement It is also the simplest optimization to setup and use Simply press the Auto Range keys to turn on Auto Ranging Auto Ranging always tracks the input signals during a swept sine measurement At each frequency point each input range is adjusted to keep the signal within 6 dB of full scale if possible If the input is overloaded then the range is increased until the overload is removed Auto Ranging increases the measurement times whenever an input range is changed This is especially true when the signal drops below 6 dBfs In order to detect this under range condition the measurement must be made for the entire integration time At low SR785 Dynamic Signal Analyzer Swept Sine Measurements 2 53 frequencies this can add a significant amount of sweep time Overloads can be detected at any time during the integration time and thus ranging up requires less time For smooth frequency responses where successive measurement points do not differ by more than 6 dB auto ranging does not add substantially to the sweep time while increasing the dynamic range dramatically In some cases especially at very low frequencies it might be better to set the range manually to avoid increasing an already long sweep time Auto Ranging is set for each channel separately and can be turned on and off during the sweep The manual input range can be changed at a
576. t channel unlike most softkeys which apply to a specific display Command EUIM 7 1 EU2M i SR785 Dynamic Signal Anaylzer Transducer Parameter Menu 4 93 EU Label Choose the Engineering Units Label for the selected input The displayed units change from Volts to the EU Label when Engineering Units are On Choose USER for the user defined User Label Input units of acceleration m s in s or g velocity m s or in s and displacement m or in may be converted in the frequency domain using Transducer Convert For example the FFT of an input configured for an accelerometer with Engineering Units of m s may be displayed in displacement meters using Transducer Convert The two inputs may have different EU Labels For instance 1f Ch2 has EU Label set to m s and Ch1 has EU Label set to dyne then the units of the frequency response measurement will be m s7 dyne Note that this softkey applies to an input channel unlike most softkeys which apply to a specific display Command EUIL 1 Command EU2L 1 EU Volt Set the Engineering Units per Volt scale factor for the selected input This factor is used to scale the display units from Volts to Engineering Units when Engineering Units are On The displayed units change from Volts to the EU Label The EU scale factor may be entered in EU V V EU or dB EU V Note that this softkey applies to an input channel unlike most softkeys which apply to a
577. t the entry operation and leave the value unchanged Use the knob to select the kHz units When the entry value is correct and the correct units are selected press Enter to change the span to the new value Entries may be made in exponential form using the Exp key The entry above may be made by pressing 1 2 8 Exp 3 and selecting the Hz units Numeric entry always requires Enter to enter the new value Some menu boxes have Marker as one of the units choices If Marker is selected as the units the analyzer ignores the numeric keys pressed and substitutes the current marker value in the entry field If no menu box is highlighted pressing a numeric entry key automatically selects the most recently modified parameter within the menu and begins numeric entry This is convenient when a measurement requires a single parameter within a menu or menus to be modified repeatedly SR785 Dynamic Signal Analyzer Status Indicators 3 27 In general numeric parameters may also be adjusted with the knob In this case knob adjustment must be made before any numeric entry is started Enter 1s not required to enter the new value Changes are effective immediately while the value is being adjusted Press Enter the same softkey another softkey or a menu key to un highlight the menu box when finished Some entry fields allow only knob adjustment or only numeric entry SR785 Dynamic Signal Analyzer 3 28 Status Indicators
578. t the frequency to 256 Hz the pulse width to 100 us and the amplitude to 1V These settings only need to be approximate Make sure that the DC level of the output is near OV Connect the generator output to the Chl A input of the analyzer 3 Press Input Press lt Input Config gt Press lt Ch1 Input Range gt Press 1 5 Select Vpk with the knob Now press Enter 4 Press Active Display Press Display Setup Press lt Measurement gt Display the System menu Preset returns the unit to its default settings Preset requires confirmation to prevent accidental reset Wait until the self tests are completed The input impedance of the analyzer is 1 MQ The generator may require a terminator Many generators have either a 50 or 600 Q output impedance Use the appropriate feedthrough termination if necessary In general not using a terminator means that the output amplitude will not agree with the generator setting Select the Input master menu Select the input configuration submenu Choose an input range that doesn t overload Set the input range to about 1 5 Vpk The channel linput range indicator at the top of the unit now should read 1 58 Vpk the closest allowed input range to the value you entered Adjust the pulse amplitude to that no overloads occur Let s change the Measurement for DisplayB Make DisplayB the active display Select the Display Setup menu Change the Measurement of the
579. t the input to the device and the response channel 2 measures the device output The result is the complex frequency response of the device Normalized Variance Normalized variance is a single channel swept sine measurement similar to the coherence measurement of the FFT measurement group The normalized variance is an indication of the signal to noise ratio after integration over the specified number of cycles is performed Normalized variance like coherence has a value between 0 and 1 A value of 1 indicates that all noise has been removed from the signal Values less than one indicate that there is noise remaining Increasing the Integration Time or Integration Cycleswill move the variance closer to 1 User Function User Function displays the results of a user defined math function User Functions defined within the Swept Sine Measurement Group may include swept sine measurement results Use the User Math menu to define a math function A User Function may not be selected as the measurement if it uses a Trace which is empty or which contains data taken in a different Measurement Group See User Math later in this section for more Averaging Settling and Integration At each frequency point in a swept sine measurement the inputs measure the amount of signal at the source frequency This is done by multiplying the input data by sin ot and cos t and averaging the results over an Integration Time As with the FFT real in p
580. t to the top of the menu reads either DispA or DispB whichever is the active display Parameter entry or selection modifies only the active display To change which display will be modified press Active Display When a linked parameter is highlighted the Link indicator reads Link Parameter entry or selection modifies both displays at once To link or unlink a parameter highlight the parameter and press the Link key If the Link indicator is shown in gray then the parameter linking may not be changed If linking is available the value of the parameter for the non active display will be made equal to the value of the parameter for the active display Parameter linking is a convenient way of changing both displays together For example Span and Start frequency may be linked while the Measurement is unlinked This allows the two displays to have different measurements over the same frequency span Since the Spans are linked changing the Span does not require separate entries for each display The availability of parameter linking is affected by the setting of the lt Analyzer Configuration gt softkey If Analyzer Configuration is set to Independent Channels parameters such as span may be linked an unlinked for the two displays If lt Analyzer Configuration gt is set to Dual Channel these parameters will always be linked See Chapter 2 for a description of how Analyzer Configuration works When a function k
581. ta Half Intensity Data Graph Unsettled measurement data is graphed in half intensity Once the measurement becomes settled the graph returns to full intensity FFT and Octave measurements are unsettled when the frequency span or resolution is changed and when the input signal path is changed gain filters etc The measurement is not settled again until the discontinuity in the input data has propagated through the digital filters and for FFT s a complete new time record has been acquired FFT measurements running with a Time Record Increment less than 100 overlapped time records display unsettled measurements in half intensity SR785 Dynamic Signal Analyzer Screen Display 3 13 Octave measurements show unsettled octave bins in half intensity Each octave bin is displayed in half intensity until it 1s settled The settling time of each bin is related to the 1 center frequency and the lowest bins take the longest time to settle Vertical Scale Bar Display Label and Type A Live AO Y Max Top Reference dBin ispk No Anti Alias Filter Warning 90 Y Div Vertical Scale dBidiv ae No AA Filter Limit Test Result Pass 3 wf 100 Y Min Bottom Waterfall Storage Count 7 160 dBinispk The Vertical Scale Bar is at the left of the data graph for each display The display name either A or B is at the top left corner The display type Live Done Off Line or Preview is next to the display name
582. ta values in the trace NOT the data displayed in a particular view Remember views are simply different ways of showing the actual complex data A trace contains n complex points The value of n depends upon the type and length of the target trace N should be chosen equal to or less than the length of the target trace If the length is less than that of the target trace the remainder of the trace will be filled with zeros The download sequence is as follows Host Send TLOD 1 n Do NOT wait for IFC to be set in the Serial Poll status SR785 Checks to make sure that Trace 1 has length n Returns 4 byte binary long int if OK to begin data transfer A return of 0 indicates that n is too large for Trace 1 Host On receipt of 1 4 byte binary long int executes a binary transfer to the SR785 of 2n 4 byte IEEE floats The order is real part of point 0 imag part of point 0 real part of point 1 imag part of point 1 etc Each 4 byte float is transmitted least significant byte first A total of 8n bytes are transferred Assert EOI with the final byte of the transfer Serial Poll until IFC bit 7 is set in the Serial Poll status before sending another command The TASC command loads ASCH data into Trace 1 The parameter 1 selects Trace 1 through 5 This command is valid only via the GPIB interface SR785 Dynamic Signal Analyzer 5 110 Data Transfer Commands ALOD n The target Trace 1 must already store data of the measurem
583. teed FFT and Octave 145 dB Swept Sine Includes spurs harmonic and intermodulation distortion and alias products Excludes alias responses at extremes of span lt 80 dB Single tone in band lt 80 dB Two tones in band each lt 6 02 dBfs lt 80 dBfs lt 80 dBfs Single tone outside of span lt 0 dBfs lt 1 Mhz 100 dBfs typical Input grounded Input Range gt 30 dBV Hanning window 64 RMS averages lt 30 dBfs FFT with Auto Cal On 0 2 dB excluding windowing effects 0 05 dB dc to 102 4 kHz Transfer Function measurement both inputs on the same Input Range RMS averaged 3 0 deg relative to External TTL trigger 50 dBfs to 0 dBfs freq lt 10 24 kHz Center of frequency bin DC coupled For Uniform Blackman Harris Hanning Flattop and Kaiser windows phase is relative to a cosine wave at the center of the time record For Force and Exponential windows phase is relative to a cosine wave at the beginning of the time record 0 5 deg dc to 51 2 kHz 1 0 deg dc to 102 4 kHz Transfer Function measurement both inputs on the same Input Range Vector averaged SR785 Dynamic Signal Analyzer Specifications Signal Inputs Number of Inputs Full Scale Input Range Maximum Input Level Input Configuration Input Impedance Shield to Chassis Maximum Shield Voltage AC Coupling CMRR ICP Signal Conditioning A weight Filter Crosstalk Input Noise Trigger Input
584. ter 4 Press Auto Range Chl Press Auto Range Ch2 5 Press Freq Press lt Span gt Display the System menu Preset returns the unit to its default settings Preset requires confirmation to prevent accidental reset Wait until the self tests are completed Frequency Response is defined as Ch2 response divided by the Chl reference Thus Chl monitors the filter input source output and Ch2 measures the response of the device under test Select the Source menu Choose Chirp output The output is an equal amplitude sine wave at each frequency bin of the FFT spectrum Turn the source On Select the Window menu Adjust the FFT Window function The Chirp source requires the use of the Uniform window since not all chirp frequency components are present at all points in the time record The chirp 1s exactly periodic with the FFT time record and does not leak with the uniform window Let the analyzer automatically set the Input Ranges to agree with the signals Note that the Input Range readouts at the top of the screen are displayed in inverse when Auto Range is on Select the Frequency menu Adjust the FFT Span SR785 Dynamic Signal Analyzer 1 12 Measuring a Frequency Response Function Use the knob to adjust the Span to 6 4 kHz and press Enter 6 Press Display Setup Press lt Measurement gt Select Freq Resp with the knob and press Enter Press Auto Scale A 7 Press M
585. th Functions X Axis computed using whatever averaging is selected with the lt Display Average gt softkey They are computed from the input data real time Analog or capture Playback and use the frequency and windowing parameters from the menus Frequency domain measurements are amplitude calibrated time records are not FFT and Time record measurements are also triggered just like the normal measurements Operands which are measurement results which are not enclosed in angle brackets such as FFT 1 or Timel represent unaveraged instantaneous versions of the measurement Operands which contain an explicit averaging type such as Vec lt F1 gt or PeakHold lt F2 gt always are averaged according to their indicated type regardless of the setting of the lt Display Average gt softkey Octave and Swept Sine measurements are always averaged measurements Use the Average menu to set the averaging parameters FFT 1 and FFT 2 are the FFT of the Chl and Ch2 inputs These operands use the window chosen in the Window menu for the display which is measuring the function FFTu 1 and FFTu 2 are un windowed FFT s of the Chl and Ch2 inputs Correlation operands such as RMS lt FuleF1 gt are used to compte the RMS and Vector averaged auto and cross correlation measurements The Fu refers to the un windowed FFT See the descriptionof the Correlation measurements for exact definitions of the correlation measurements in terms of these operands
586. the Output lt Hard Copy Button gt and use Print Screen Data Table x coordinates are saved to disk with the instrument settings A Data Table with coordinates defined in the frequency domain will revert to bin locations if the measurement is changed to the time domain and vice versa Data Tables are generally only applicable for the domain time or frequency and span in which they were originally defined Display the Limit Test menu for the active display Limit Testing tests the measurement results against a set of defined Limit Segments When display data exceeds a Limit Segment at any point the test fails Each display has its own set of Limit Segments Limit Segments are saved to disk with the instrument settings A Limit Segment is defined as the line between the pair of points X0 Y0 and X1 Y 1 The segment values between the endpoints are calculated for the displayed span A segment may be defined as either an Upper or Lower limit Measurement data which is greater than an Upper limit or less than a Lower limit cause the test to fail Limit Segments are defined for the current View Changing the View invalidates the Limit Segments and limit testing is not available in the new View Either return to the SR785 Dynamic Signal Analyzer 4 148 Analysis Menu Marker Stats original View or define new segments in the new View Limit testing is not available for Nyquist or Nichols views Measurement data is compared with th
587. the Trace The largest trace value is considered full scale 100 amplitude 1V Be sure to set the Play Rate to the appropriate value to reproduce the frequencies in the trace correctly Command TARB 1 SR785 Dynamic Signal Analyzer Swept Sine Source Menu 4 83 Swept Sine Source Menu The Source menu sets the source amplitude parameters when the Measurement Group is Swept Sine See Swept Sine in Chapter 2 for a discussion about swept sine measurement fundamentals Source O Auto Level Ref ____ Channel 1 ideal etn at Ref 100 0 mV Source Ramping Lainie 1 VIS Ref Upper Limit IB 1000 0 mV Offset Max Source oe 0 MV Auto Level Reference Amplitude Select the Auto Level Reference mode Off Channel 1 Channel 2 Auto Level Off maintains the source amplitude at a constant level at all frequencies during the swept sine sweep This usually works best for transfer functions which are fairly flat Auto Level Channel 1 or 2 will adjust the source level to maintain a constant level called the Ideal Reference at the Channel or Channel 2 input Generally this is useful for frequency response functions with substantial gain as well as attenuation Input Auto Ranging is turned on for both inputs when Auto Level is on Whenever Auto Level is used the measurement MUST be frequency resonse The Auto Level Reference Channel determines which input will be maintained at the Ideal Reference Level This is
588. the Uniform window which is the correct window for this measurement Select the Trigger menu Change the Trigger Mode The continuious trigger source triggers measurements as fast as the analyzer can go If the generator is set to 256 Hz pulse rate the signal will drift slowly in the time record This is because the SR785 time records are exactly 1 256 Hz 3 90625 ms long 400 lines at full span and the analyzer is running in real time no missed data The drift in the time record is because the analyzer and the generator are using different time bases The time record is now unstable and the pulse moves through the entire time record The spectrum in DisplayA is mostly unaffected since the Uniform window allows the pulse to be anywhere in the time record Only when the pulse is not entirely within the time record is the spectrum disturbed This concludes this measurement example You should have a feeling for triggered time records and the effect of windowing on the resulting FFT Octave Analysis Octave Analysis 1 23 This example investigates the test filter enclosed with this manual using Octave measurements You will use the SR785 source to provide a broad band source and both displays to measure the output of the device under test Refer to Octave Analysis in Chapter 2 for more about Octave Analysis measurements 1 Press System Press lt Preset gt Press Enter to confirm Preset 2 Use a BNC
589. the amplitude of each component for a specified peak amplitude The input dynamic range of the measurement is reduced when using the chirp source Command CAMP x Set the Burst Percentage of the chirp 0 1 100 The chirp waveform is output over a percentage of the FFT time record of the display selected as the Source Display Burst is only available for the FFT Measurement Group For a continuous output use 100 burst with continuous Trigger Source or Source Trigger Source Trigger will synchronize the FFT time record with the chirp waveform SR785 Dynamic Signal Analyzer 4 74 Chirp Source Menu With External Trigger the chirp waveform is triggered along with the FFT time record Set the Trigd Source Mode to Continuous to trigger the source with every time record Do not use Ch1 or Ch2 input trigger since the output will not start until a trigger is received Command CBUR 7 x Source Display Select the Source Display DisplayA DisplayB The Source Display only applies for the FFT Measurement Group The Source Display is the display which determines the burst period FFT time record and the bandwidth for bandlimited noise and chirp FFT Span There is a single Source Display for both Chirp and Noise outputs Changing this entry for one type of source also changes it for the other Select which display sets the time record and frequency span of the chirp If the other display has a different span the chirp wil
590. the displays separately Linking is a convenient way to adjust the two displays together and keep their settings the same The default settings link many measurement parameters such as frequency and averaging together as found in many other instruments Select the Average menu Select the averaging mode to display The SR785 always computes all the averaging modes when lt Compute Avgs gt is set to Yes The lt Display Avg gt softkey selects which averaging mode is currently displayed Select RMS Averaging for both displays Press lt Avgs gt Press Link Press 2 0 and press Enter Press Active Display Press Window Press lt Window gt Press Link Select Hanning with the knob and press Enter 10 Press Display Setup Press lt Units gt Press lt Pk Units gt Press Link Select rms with the knob and press Enter 11 Press lt Return gt Linking Advanced Operation 1 17 Change the Number Of Averages for DisplayA Unlink the Number Of Averages DispA is shown on the Link indicator Change the Number Of Averages for DisplayA to 20 instead of 2 DisplayA will average for 10 times as many measurements as DisplayB and be quite a bit smoother Let s change the Window for DisplayB Make DisplayB the active display Select the Window menu The windows are linked by default Unlink the Window type DispB is shown as the Link indicator DisplayB is now u
591. the reference node The name may be up to 6 characters long RFNU i The RFNU command sets queries the number of the reference node RSDR i The RSDR command sets queries the response node direction The parameter 1 specifies the direction according to the following table SR785 Dynamic Signal Analyzer RSNA s RSNU 7 i OA Nn BWNRK OK ps pa O Ne Node Direction 0 Z 0 Y 0 X Scalar no direction X Y Z 0 X 0 Y 0 Z Nodal DOF Commands 5 119 The RSNA command sets queries the name of the reference node The name may be up to 6 characters long The RSNU command sets queries the number of the reference node SR785 Dynamic Signal Analyzer 5 120 Status Reporting Commands Status Reporting Commands CLS PSC i The Status Word definitions follow this section The CLS command clears all status registers The enable registers are not changed The PSC command sets the value of the power on status clear bit If i 1 the power on status clear bit is set and all status registers and enable registers are cleared on power up If i 0 the bit is cleared and all enable registers are stored at power down The status registers are cleared and the enable registers are restored to their stored values on power up This allows a service request to be generated at power up SRE i j STB i The SRE 1 command sets the Serial Poll enable register to th
592. the waterfall buffer A large View Count is a good way to display an overview of the entire buffer in order to identify a region of interest Remember View Count is strictly a display parameter it does not affect the actual storage of waterfall records The View Count and the Trace Height determine the available scroll Angles Each display has its own Waterfall View Count This entry field can be linked to both displays by using the Link key Command WVCT d 1 Set the requested Waterfall Scroll Angle for the active display Waterfall displays show multiple measurement results records in a single display New records are added at the top of the display and older records scroll off the bottom of the display When the Scroll Angle is 0 the older records scroll straight down When the Scroll Angle is negative the older records shift left as they scroll down When the Scroll Angle is positive they shift right as they scroll down SR785 Dynamic Signal Analyzer Waterfall Menu 4 139 The View Count and the Trace Height determine the available scroll angles When Fast Angles is On the available scroll angles are limited to those which scroll faster due to the graphics architecture This menu box sets the requested scroll angle The display scrolls at the allowed angle closest to the requested angle When adjusted with the knob only available angles are selected Each display has its own Waterfall Scroll Angle This entry field c
593. ther operations are disabled until printing is completed The PLOT command plots the screen using the selected Plotter Type and Destination All other operations are disabled until plotting is completed The DUMP command dumps the data in the active display in ASCII format to the selected Destination Interface or Disk The data 1s written f y x cr with the data for each point on a single line f is the frequency or time value y is the y axis value and x is the x axis value if necessary The ASCL command AutoScales display d This is the same as pressing the Auto Scale A or Auto Scale B keys The displays are AutoScaled separately d 2 is not allowed The AIRG command sets queries the Chl AutoRanging Off On The parameter 1 selects Off Manual 0 or On AutoRanging 1 If i 1 and Chl AutoRange is already On a new AutoRange is performed The A2RG command sets queries the Ch2 AutoRanging Off On The parameter 1 selects Off Manual 0 or On AutoRanging 1 If i 1 and Ch2 AutoRange is already On a new AutoRange is performed The MRON command sets the Normal Marker offsets X and Y to the current marker position and sets the Marker Relative to Offset f Marker Rel was Off This is similar to the Marker Ref key This command is only valid if the Marker Mode for display d is Normal SR785 Dynamic Signal Analyzer 5 104 Front Panel Commands MKMX d MKMN d MKCN d DREF d i SNAP d SBRI i SCON
594. this 1s accomplished by clearing the enabled status bits in the Instrument Display Input Error or Standard Event status words by reading them SR785 Dynamic Signal Analyzer Status Reporting Commands 5 121 ESE i j ESR i The ESE 1 command sets the Standard Event enable register to the decimal value 1 0 255 The ESE 1 j command sets bit 1 0 7 to j O or 1 The ESE command queries the value 0 255 of the status word enable register The ESE 1 command queries the value 0 or 1 of bit 1 0 7 When a bit becomes set in BOTH the Standard Event status word AND the Standard Event enable register bit 6 ESB of the Serial Poll status word is set This causes an SRQ if bit 6 in the Serial Poll enable register is set To clear a bit in the Standard Event status word use ESR The ESR command queries the value of the Standard Event status word The value is returned as a decimal number from 0 to 255 The ESR 1 command queries the value 0 or 1 of bit 1 0 7 ESR clears the entire word while ESR 1 clears just bit 1 ERRE i ERRS i INSE 7 i j The ERRE 1 command sets the Error enable register to the decimal value 1 0 65535 The ERRE 1 j command sets bit 1 0 15 toj O or 1 The ERRE command queries the value 0 65535 of the error status enable register The ERRE 1 command queries the value 0 or 1 of bit 1 0 15 When a bit becomes set in BOTH the Erro
595. tion Interface or Disk Other front panel operations are disabled until plotting 1s completed Pressing backspace will abort the operation Command PLOT SR785 Dynamic Signal Analyzer Output Menu 4 185 ASCII Dump Dump the data in the active display in ASCII format to the selected Destination Interface or Disk The data is written f y x cr with the data for each point on a single line f is the frequency or time value y is the y axis value and x is the x axis value if necessary Other front panel operations are disabled until the dump is completed Pressing backspace will abort the operation Command DUMP Bitmap Printer Select the Bitmap Printer type for the Bitmap Print operation Epson FX HP PCL HP Small PCL PCX 2 bit GIF PCX 8 bit Epson FX is used for Epson compatible dot matrix graphics printers HP PCL and HP Small PCL are used for HP LaserJet or InkJet compatible printers HP PCL is a full page printout and HP Small PCL 1s half page The PCX and GIF types are bit mapped file formats Choose one of these if you want to print to a disk file and import the image into a PC application The Destination for all Bitmap Printer types can be either an on line Interface or a Disk file Command PRTP 1 Bitmap Area Select the portion of the screen for the Bitmap Print operation Graphs Menu Indicators All Vector Plot only plots the displayed graphs Graphs prints the graph areas This is a s
596. tive Trace to Display is an alternate function This function recalls trace data to the active display Press Enter to select Trace 3 Press Display Setup Press lt Ymax gt Press 8 0 and Enter Press Active Display Press Active Display Press Display Options Press lt Display gt Use the knob to select Live and press Enter Saving and Recalling 1 49 Only Trace 3 contains data at this time Only Trace 3 may be selected DisplayB now shows the data stored in Trace 3 The display is labeled Off Line in its upper left corner indicating that it is showing static data Select the Display Setup menu Note that the Measurement Group and Measurement menu boxes are shown in gray This indicates that these parameters may not be changed for the active display In this case the active display contains stored data so the measurement parameters cannot be changed Other measurement parameters such as averaging and window type are also not allowed to be changed when the active display is Off Line Change the graph scale of DisplayB The view and scale of DisplayB can be changed of course These parameters simply change the way the stored data is graphed Move the graph down Make DisplayA top the active display Note that the Measurement Group and Measurement menu boxes are not gray This is because these parameters may be adjusted for the live measurement in DisplayA Make DisplayB bott
597. to Displa fee Scale B Range Ref y ch 2 L N N Mae Center P A a Ej T 0 Si Down Wy wy xy ZA a Display Fre i Options Display tu s Trigger Of DE OG d DIDIE Water a a O no gt oO D TA i Figure Chapter 3 10 Front Panel Keypad Normal and Alternate Keys The normal key definitions are printed on each key In addition many keys also have alternate definitions printed below them Press the Alt key once to enter the ALT keypad mode The ALT screen indicator is on indicating that the alternate key definitions are in use Use the alternate keys to enter alphabetic characters and to access secondary functions The 0 9 L L J lt Exp and Alt keys have the same definition in both modes Press Alt again to return to the normal keypad if necessary SR785 Dynamic Signal Analyzer 3 24 Status Indicators Menu Keys All operating parameters of the SR785 are grouped into sixteen function menus The menu keys select a menu of parameters to display next to the ten softkeys The softkeys either choose a submenu or select a parameter and place it in the entry field at the top of the screen for numeric entry or knob adjustment The menus are listed below Freq Display Setup Set the frequency span parameters for measurements Select the measurement type view units and scale Display Options Select the display format grid user units and lo
598. to be converted to Label m s m s m in s in s in mil NYA MN BWNR CO SR785 Dynamic Signal Analyzer Input Commands 5 63 EU2M d i The EU2M command sets queries the Ch2 Engineering Units Mode for display d The set command requires d 2 both displays The parameter 1 selects Off O or On 1 EU2L d i The EU2L command sets queries the Ch2 Engineering Units Label for display d The set command requires d 2 both displays The parameter 1 selects the unit label 1 Label 1 Label 0 m s 8 kg l m s 9 lbs 2 m 10 N 3 in s 11 dyne 4 in s 12 Pas 5 in 13 bar 6 mil 14 USER 7 g EU2V d x The EU2V command sets queries the Ch2 Engineering Units per Volt scale for display d The set command requires d 2 both displays The parameter x is real number of EU Volt EU s per Volt EU2U d s The EU2U command sets queries the Ch2 User Label for display d The set command requires d 2 both displays The string s is the user label TD2C d i The TD2C command sets queries the Ch2 Transducer Conversion for display d The set command requires d 2 both displays The parameter 1 selects the units to be converted to Label m s m s m in s in s in mil NYA NN BWNrR CO SR785 Dynamic Signal Analyzer 5 64 Input Commands Tachometer Input Commands TAPR 7 x TARG i TALV x TASL i TAHO 7 i TAHD 7 x TASH 7 i
599. torage 4 21 Seeks 4 54 Track 1 Order 4 21 Width 4 54 Input Channel Track 1 4 21 Rel 4 55 Track 2 Order 4 21 X Re 1 4 55 Input Channel Track 2 4 22 Y Rel 4 56 i 4 Time Histogram Frequency Menu 4 23 lig l Marker X to 4 57 Sample Time 4 23 Tarcet 4 57 Histogram Length 4 23 8 Bins 4 23 Harmonic Marker Menu 4 58 Base Frequency 4 24 Harmonics 4 58 Repeat 4 24 Display 4 58 R M 4 5 Display Setup Menu 4 25 sie 7 THD 4 59 Measurement Group 4 25 aimoie oner 4 59 Measurement FFT 4 26 Measurement Correlation 4 30 Sideband Marker Menu 4 61 Measurement Octave Analysis 4 32 Sideband Separation 4 61 Measurement Swept Sine 4 34 Sidebands 4 61 Measurement Order 4 35 Display 4 62 Measurement Time Histogram 4 37 Readout Mode 4 62 View 4 38 Sideband Ratio 4 62 Units 4 40 RMS Sideband Power 4 63 oe Hpo Band Marker Menu 4 64 dB Units 4 41 Modify Band 4 64 Pk Units 4 41 i Band Exclude 4 64 PSD Units 4 42 Band Ratio Mode 4 65 Phase Units 4 42 Band Power 4 65 dBm Reference Impedance 4 42 Band Rati 4 65 Y Max 4 42 PIERE Y Mid 4 42 Frequency Damping Marker Menu 4 66 Y Min 4 43 Calculate 4 66 Y Div 4 43 Frequency 4 66 X Center Polar 4 43 Damping Ratio 4 66 X Div Pol 4 44 m Source Menu 4 67 Y Center Polar 4 44 Source Off 4 67 Y Div Polar 4 44 Source On 4 67 Pan 4 44 Zoom 4 45 Sine FOI Chirp 4 68 Display Options Menu 4 46 Noise 4 68 Display 4 46 Arbitrary 4 69 F t 4 46 l ae Sine Source Menu 4 71 X AXIS 4
600. ts are voltage inputs with 1 MQ 50 pF input impedance The Input Coupling is either DC or AC The Input Mode may be single ended A or differential A B The A and B connector shields are common and grounded to the chassis by 1 MQ 0 01 uF Float or 50 Q Ground The shields should never exceed 4V Do not apply more than 50 V to either input If the input exceeds 57 V the input range will be set to 34 dBV to protect the input from damage and the HighV overload status is set The input range can not be changed while HighV is detected For two channel measurements such as Frequency Response Channel 2 is the response output from the device under test Trigger Input When the Trigger Source is External or Ext TTL the Trigger input triggers the measurement The input impedance is 1 MQ and the minimum pulse width is 25 ns The Trigger Level is adjustable from 5V to 5V with either Positive or Negative Slope The minimum trigger amplitude is 100 mV The trigger input should not exceed 5V Source Output The Source can output either Sine Two Tone Chirp Noise or Arbitrary waveforms The output impedance is less than 5 Q and is capable of driving a 50 Q load The output is ground referenced PC Keyboard Connector An IBM PC or XT compatible keyboard may be attached to the keyboard connector Most keyboards have a switch on the back to select PC XT or 8088 mode The SR785 can be controlled from this keyboard according to the table below
601. ts for the Highest Band are determined by the Octave Resolution and the number of Octave Channels 1 Octave Channel 1 1 Octave 125 mHz 32 kHz 1 3 Octave 160 mHz 40 kHz 1 12 Octave 190 mHz 12 34 kHz 2 Octave Channels 1 1 Octave 125 mHz 16 kHz 1 3 Octave 160 mHz 20 kHz 1 12 Octave 190 mHz 6 17 kHz The total power of all measured bands is displayed as a filled in band at the right side of the graph The exact band center frequencies are calculated according to the ANSI standard The displayed frequencies are sometimes rounded to even values for a simpler display The measurement may span 1 to 11 octaves Increasing the Highest Band will also increase the Lowest Band if necessary to keep the measurement span at 11 octaves The two displays can have different Highest Bands if the Analyzer Configuration is set to Independent Channels If Analyzer Configuration is set to Dual Channel they field is automatically linked to both displays Command OHIB 7 d f SR785 Dynamic Signal Analyzer Octave Frequency Menu 4 13 Lowest Band Set the Lowest Band for the active display The limits for the Lowest Band are determined by the Octave Resolution 1 1 Octave 125 mHz 1 3 Octave 100 mHz 1 12 Octave 100 mHz The exact band center frequencies are calculated according to the ANSI standard The displayed frequencies are the ANSI nominal center frequencies The measurement may span
602. ts with equal weighting in either RMS or Vector averaging While Linear averaging is in progress the number of averages completed is shown in the Horizontal Scale Bar below the graph When the Number Of Averages has been completed the measurement stops and Done is displayed along the y axis of the graph If the Done alarm is enabled an audible alert is also sounded When used with peak hold averaging this weighting mode is known as Fixed Lenth averaging This means that a fixed number N of measurements are compared to determing the peak Waterfall Storage If Waterfall Storage is on the waterfall buffer only stores the completed linear averages not each individual measurement Each time the linear average is done the result is stored in the waterfall buffer and the average is reset and started over instead of stopping Each completed average counts as a single waterfall record Exponential Continuous Weighting Exponential weighting weights new data more than old data For RMS and Vector averaging weighting takes place according to the formula Average N New Data 1 N Average N 1 C N 1 N where N is the Number Of Averages While Exponential averaging is in progress the number of averages completed is shown in the Horizontal Scale Bar below the graph The displayed number stops incrementing at the Number of Averages while the averaging continues Exponential weighting reaches a steady state after approximate
603. tween operands and operators Use the knob to highlight the desired box and press Enter to insert the selection into the function string at the top of the screen Choose FFT 2 as the first operand This is the FFT of Ch2 and is identical to the normal measurement We are going to define a transfer function FFT2 FFT 1 As soon as the operand is entered the display switches to show operations Choose the divide operation next The display switches back to operands You can choose another operation instead by pressing lt Operations gt Choose FFT 1 as the denominator of the transfer function SR785 Dynamic Signal Analyzer 1 54 User Math Functions Press lt Function String gt Use the knob to move the insertion point to the beginning of the function highlight FFT2 Press lt Operations gt Use the knob to highlight GrpDly and press Enter Press lt Enter Eq gt Press Display Setup Press lt Measurement gt Use the knob to select FFTUsrFn2 and press Enter Press lt View gt Use the knob to select Real Part and press Enter Press Auto Scale A SR785 Dynamic Signal Analyzer This key moves the marker to the function string at the top of the screen This allows you to delete terms and insert new ones Move to the start of the string by highlighting the first term FFT 2 Ins above the function string indicates that new terms will be inserted before the highlighted term
604. ty Print to dot matrix and HP LaserJet InkJet compatible printers Plot to HPGL or Postscript plotters Print Plot to RS232 or IEEE 488 interfaces or to disk file Additional file formats include GIF PCX and EPS 3 5 inch DOS compatible format 1 44 Mbytes capacity Storage of data setups and hardcopy Power connector for SRS preamplifiers 70 Watts 100 120 220 240 VAC 50 60 Hz 17 W x 8 H x 22 D 56 Ib One year parts and labor on materials and workmanship Chapter Getting Started These example measurements are designed to acquaint the first time user with the SR785 Dynamic Signal Analyzer They provide a foundation for understanding how to use the SR785 For a more complete overview of the instrument and its capabilities refer to the Analyzer Basics and Operation sections of this manual 1 1 Many of the examples use the test filter enclosed with this manual The filter is a simple twin tee 1 kHz passive notch filter This filter provides an interesting frequency response for these measurements In This Chapter General Installation Caution Line Voltage Selection Line Fuse Line Cord Power Switch Screen Brightness Fan Front Panel Quick Start Hardkeys lt Softkeys gt Alt Keys Knob Help Things To Watch Out For Start Live Display Narrow Span Low Detection Frequency Averaging Triggering Scaling and Ranging Local Reset DOOOMAAAaAaA PBPwoOwWWWOW YHNMNMDPNDNYNN ee ee i b i b
605. ue These are the most recent characters which have been received by the SR785 Commands which have already been executed are shown in normal text Commands which have not yet been executed are shown with a bright background Command errors are shown in inverse text The lower half of the screen is the Transmit Queue These are the most recent characters which have been placed in output buffer Characters which have already been sent over the interface are shown in normal text Characters which are waiting to be sent are shown with a bright background Press any key to exit from this display SR785 Dynamic Signal Analyzer 4 196 System Preferences Menu System Preferences Menu Key Click Alarms Preferences Key Click Alarme On Alarms Volume Noisy Done Volume o Noisy Audible Overload On Screen Saver On Screen Saver Delay 10 m Frequency Format Exact Bin Node Info prompt st Returm J Turn the Key Click on or off Command KCLK 7 1 Turn the system Alarm messages On or Off Command ALRM 7 1 Alarms Volume If Alarms Volume is set to Quiet alarm messages have no accompanying sound If Alarms are set to Noisy alarm messages are accompanied by an audible alarm Set system Alarms to Off for no alarm message at all Command ALRT 1 Done Volume If Done Volume is set to Noisy an audible alarm is sounded when a measurement is done or completed For ex
606. ue This affects the calculation of phase for display d DDXW d x The DDXW command sets queries the d dx Window of display d The parameter x is a percentage of the display width This affects the calculation of d dx and group delay for user math functions in display d SR785 Dynamic Signal Analyzer Marker Commands 5 45 Marker Commands MRKR d i The MRKR command sets queries the Marker Tracking of display d The parameter 1 selects Off 0 On 1 Track 2 or Link 3 MKMD d i MBIN d i MWFL d i MRKX d MRKB d The MKMD command sets queries the Marker Mode of display d The parameter 1 selects Normal 0 Harmonic 1 Sideband 2 Band 3 or Frequency Damping 4 All modes are allowed in the FFT and Order measurement groups Harmonic Sideband and Frequency Damping are not allowed in Octave measurement group Harmonic Sideband Band and Frequency Damping are not allowed in the Swept Sine Time Histogram or Correlation measurement group The MBIN command moves the Marker or Marker Region of display d to bin 1 Bin Q0 is the left most bin in the display The marker of each display must be moved separately d 2 is not allowed A Spot marker will move to bin 1 A marker region will be centered on bin 1 if possible The Normal marker will still seek the Max Min or Mean within the region This command is not valid if the Marker of display d is Off The MWFL command m
607. uency indicator shows the current frequency during Swept Sine sweeps Ramping is displayed if the source level is currently ramping This indicator replaces the Realtime indicator when the Measurement Group is Swept Sine The RPM indicator displays the rotational speed of the device under test based on information from the tachometer input The rotational speed is calculated from the freqeuency of pulses arriving at the tachometer input and the setting of the Pulses per Revolution softkey This indicator replaces the Real time indicator when the Measurement Group is Order or when Show Tach is set to On Capture Progress During capture fill the Capture Progress indicator shows how much of the capture buffer has been filled During capture playback this indicator shows the playback progress through the playback portion of the buffer This indicator replaces the Real time indicator when capture or playback is in progress No Cap Cap Data Link The Capture indicator shows the status of the Capture buffer No Cap indicates that the Capture buffer is empty Input playback from Capture is not allowed Arbitrary source playback from Capture is also not allowed Capturing indicates that capture is in progress The capture progress is shown in the Real Time indicator position Cap Data indicates that the Capture buffer contains data for playback When an unlinked display parameter is being entered or modified the Li
608. uency of the other display Real measurement data such as baseband time record have zero imaginary part This view is entirely along the X axis Nichols Plot The Nichols Plot graphs complex measurement data as log magnitude along the Y axis versus unwrapped phase along the X axis The Y axis is logarithmic and the X axis is linear Adjacent frequency time points are connected by a line This view is generally meaningful only for measurements which have data at every frequency point such as chirp source or swept sine The marker readout shows the log magnitude and phase of each point as well as its frequency or time The marker moves sequentially through the frequency time points and can be linked to the frequency of the other display Real measurement data such as baseband time record have zero phase This view is entirely along the Y axis SR785 Dynamic Signal Analyzer 2 24 FFT Averaging FFT Averaging Averaging successive measurements together improves accuracy and repeatability For measurements computed from multiple spectra averaging is performed on measurement results or individual spectra depending upon the measurement definition Time records are not averaged Just as the SR785 computes all measurements in a given measurement group simultaneously all averaging variants of any measurement are also computed simultaneously For instance if a frequency response measurement is paused or finished you can look at th
609. ueries the Waterfall Paused Drawing for display d The parameter 1 selects Normal Newest at Top 0 or Reversed Oldest at Top 1 This command is not valid when the Measurement Group is Swept Sine WTRC d i j The WTRC command saves waterfall record j 0 is most recent is next etc from display d to Trace 1 1 5 SR785 Dynamic Signal Analyzer 5 82 Waterfall Commands This command is valid only when the measurement is paused with waterfall storage on If there is no record J then an error occurs WSLC d i j The WSLC command saves the waterfall time slice of bin j 0 is left most on x axis from display d to Trace 1 1 5 This command is valid only when the measurement is paused with waterfall storage on If there is no bin j then an error occurs SR785 Dynamic Signal Analyzer Capture Commands 5 83 Capture Commands CCHN 7 i CMOD i CLEN i CRAT i CPAN 7 i CSTR CSTP The CCHN command sets queries the Capture Channels The parameter 1 selects Chl 0 Ch2 1 or Ch1 Ch2 2 This command is invalid it the source is arbitrary playback from the capture buffer or if the measurement group 1s Swept Sine The CMOD command sets queries the Capture Mode The parameter 1 selects 1 Shot 0 or Continuous 1 This command is invalid it the source 1s arbitrary playback from the capture buffer or if the measurement group is Swept Sine The CLEN command sets queries the C
610. ueries the trace associated with one of the curve tables The parameter 1 selects curve table 1 0 or curve table 2 1 The parameter j is the trace number from to 5 EITM i j The EITM command sets queries the number of items associated with a specific table format for one of the curve tables The parameter 1 selects curve table 1 0 or curve table 2 1 The parameter j selects the type of item as Zeros 0 Poles 1 Residues 2 Numerator Polynomial 3 or Denominator Polynomial 4 This command will switch the table format to the specified representation beforing return the number of items EPLY 7 i j k x The EPLY command sets queries the polynomial coefficients for one of the curve tables The parameter 1 selects curve table 1 0 or curve table 2 1 The parameter j selects the numerator polynomial 1 or the denominator polynomial 0 The parameter k selects which polynomial coeffiecient will be set queried from 0 up to the number of items in the list The parameter x is the actual coefficient This command will change the specified table format to polynomial EPOL i j x Ly The EPOL command sets queries the poles for one of the curve tables The parameter 1 selects curve table 1 0 or curve table 2 1 The parameter j selects which pole will be set queried from O up to the number of items in the list The parameter x is the real part of the pole The optional parameter y is the imaginary part if an
611. uires a display to be Live SITM 7 d x lt ks s ms gt The SITM command sets queries the Swept Sine Integration Time for display d The parameter x is an integration time from 0 016 to 1000 seconds The set command requires d 2 both displays This command is valid only when the Measurement Group is Swept Sine The set command requires a display to be Live SICY 7 d i The SICY command sets queries the Swept Sine Integration Cycles for display d The parameter 1 is a number of cycles from to 32767 seconds The set command requires d 2 both displays This command is valid only when the Measurement Group is Swept Sine The set command requires a display to be Live SR785 Dynamic Signal Analyzer 5 74 User Math Commands User Math Commands USRF 7 i j k USRR i j k USRO i j k USRS i j k USRT i j k USRH i j k a ae Ee Ce The USRF USRR USRO and USRS USRT and USRH commands define query the user functions for the FFT Correlation Octave Swept Sine and Time Histogram Measurement Groups The parameter 1 selects a function number from to 5 The parameters jJ k l are integers which are tokens for the available operands and operations The tokens are listed below The letters F C O and S Or and H indicate in which measurement groups each token is valid FFT Correlatio
612. uires the use of the Uniform window since not all chirp frequency components are present at all points in the time record The chirp 1s exactly periodic with the FFT time record and does not leak with the uniform window Let the analyzer automatically set the Input Ranges to agree with the signals Note that the Input Range readouts at the top of the screen are displayed in inverse when Auto Range is on Select the Frequency menu Adjust the FFT Span Use the knob to adjust the Span to 6 4 kHz and press Enter 6 Press User Math Press lt Function gt Use the knob to select FFTUsrFn2 and press Enter Press lt Edit Fn gt Press lt Operands gt Use the knob to highlight FFT 2 and press Enter Use the knob to highlight divide and press Enter Use the knob to highlight FFT 1 and press Enter User Math Functions 1 53 Set the Span to display the filter notch at 1 kHz The top display A is measuring the filter input and should show a fairly flat spectrum The bottom display B is measuring the filter output and should show a deep notch Both displays are measuring absolute signal levels Select the User Math menu Choose one of the five user functions available in the FFT measurement group Select Function to edit Show the Edit Function menu The display shows the available operands for this function Use lt Operands gt and lt Operations gt to switch the display be
613. um Source Level 1 0 V in this case The actual signal output from the device under test varies from 0 dBV to 80 dBV instead of 0 dBV to 110 dBV in the constant level case Varying the source level narrows the range of the output signals This avoids overloads when there is gain and increases the output signal to noise when there is attenuation Source Auto Level requires input Auto Ranging to be on This is because the non reference channel should follow all of the source changes In the above example the source changes by 30 dB at Channel 1 There are five important parameters to set when using Auto Level The Auto Level Reference Channel determines which input will be maintained at the reference level This is usually the device under test output Channel 2 In cases where the device under test is not driven directly from the source output the device input Channel 1 may be the reference The Ideal Reference is the level the source will try to maintain at the Reference Channel This is determined by the limitations of the device under test or may simply be the desired signal level at which the test is run The Maximum Source Level is the largest allowed source amplitude This is limited by the SR785 source output or the device under test input range The Reference Upper and Lower limits are the allowable tolerances for the Reference Channel The source level is changed only if the reference SR785 Dynamic Signal Analyzer 2 54 Swept Sine Me
614. unction Octave This is the basic measurement of octave analysis It is simply the rms averaged outputs from the parallel bank of octave filters also called the power spectrum The spectrum gives a stable reading of the rms signal amplitudes and noise levels within each band RMS averaging results in a real spectrum and there is no phase information The number of Octave Channels limits the measurement choices of both displays If 2 Octave Channels are selected then both inputs may be measured The Measurements of both displays are independent The Highest Band for all Octave Resolutions is decreased by 2 in this case If 1 Octave Channel is selected then only one input may be analyzed If both displays are making an octave measurement they must both use the same input and frequency range Changing the input or frequency range of the active display will change the other display if necessary Choosing 1 Octave Channel may change the current measurements so that both displays use the same input Capture The capture buffer stores sequential time domain data in memory See Capture Buffer for more details The Capture measurement displays the contents of the capture buffer Octave measurements can use this stored data as input data by choosing Playback as the Input Source in the Input menu The capture buffer is often very long To graphically expand a region of the display use the Pan and Zoom functions in the Display Setup menu
615. ure buffer Load the Waterfall Buffer A saved Waterfall file may be loaded into the Waterfall buffer SR785 Dynamic Signal Analyzer Disk Buffers Menu 4 181 Loading a Waterfall file loads data into the waterfall buffer and recalls the measurement parameters which were in effect when the waterfall buffer was saved The recalled parameters include items in the Frequency Display Setup Display Options Average Window User Math and Waterfall menus If the file contains records from both displays data is recalled for both displays The Waterfall Storage is set to Recalled Recalled simply means that the waterfall displays contain data which did not come from the two inputs but rather from disk Command APUT 1 Command CPUT 1 J Command WPUT Command TPUT 1 Buffer to Disk Save binary data from the selected data buffer to the Current File in the Current Directory Use lt Interval gt to select the playback portion or entire buffer Command AGET 1 Command CGET 1 Command WGET Command TGET 1 SR785 Dynamic Signal Analyzer 4 182 Disk Upkeep Menu Disk Upkeep Menu File Name MYFILE Current Directory Make Directory A_DIR Del File Del cur Dir File Name Enter the File Name for Disk Upkeep Keeping this file name separate from the save recall file name makes it harder to erase a file accidentally Turn the knob to bring up the file catalog display listing all files i
616. urement is a two dimensional plot of the amplitude of a particular order vs rpm with time as the parameter Individual points in the measurement can be taken continuously or at specified time or rpm intervals using Time arming and RPM Arming Command ONPT d 1 SR785 Dynamic Signal Analyzer Order Frequency Menu 4 21 Storage Determines the storage mode for track measurements If Storage is set to One Shot the track measurement will end after the specified number of points have been acquired If Storage is set to continuous the measurement will not stop but the new data will overwrite the oldest data Command OSTO d 1 Track 1 Order Specifies the order associated with the Track 1 measurement If the entered value is not an integer multiple of delta order the SR785 will display the closest available order to the entered value Regardless of the order specified the SR785 always tracks all orders specified by the max order and delta order softkeys The Track 1 Order softkey merely selects which order will displayed Once a track measurement is done or paused any order track can be displayed without retaking any data Command OITK d f Input Channel Track 1 Specifies the input channel associated with the Track 1 measurement Regardless of the input channel specified the SR785 always tracks all orders specified by the max order and delta order softkeys for both input channels The Input Channel Tra
617. urrent directory The file name is specified by DNAM and the directory is specified by FDIR The DELD command deletes the current directory The directory must be empty otherwise no action is taken If the directory is deleted the current directory 1s changed to the directory one level closer to the root The current directory is specified by FDIR SR785 Dynamic Signal Analyzer Output Commands 5 97 Output Commands POUT 7 i PDST 7 i PFIL 7 i DUMP PRNT PRTP 7 i PSCR 7 i The POUT command sets queries the Print Screen hardkey assignment The parameter 1 selects Bitmap Print 0 Vector Plot 1 or ASCII Dump 2 The PDST command sets queries the Print Plot Dump Destination The parameter 1 selects Disk File 0 Centronics Printer Port 1 RS232 Serial Port 2 or GPIB Port 3 The PFIL command sets queries the Disk File Start Number Print Plot Dump to disk automatically numbers the disk file names starting with the File Start Number The parameter 1 is an integer up to 4 digits The PFIL command queries the next file number to be used The DUMP command dumps the data in the active display in ASCII format to the selected Destination Interface or Disk The data 1s written f y x cr with the data for each point on a single line f is the frequency or time value y is the y axis value and x is the x axis value if necessary The PRNT command prints the screen using the selected B
618. ution and number of points in the histograms These parameters govern the measurements on both displays See Time Histogram Analysis in Chapter 2 for a discussion about time histogram measurement fundamentals 3 81 us Sample Time Histogram Length Base Freq 102 4 kHz epeat Sample Time Sets the sampling interval for time records and histograms in the Time Histogram measurement group The allowed sampling times depend on the setting of the base frequency softkey If the base frequency is 102 4 kHz the allowed sampling times range from 3 81us to 2s in powers of 2 If the base frequency is 100 0 kHz the allowed sampling times range from 3 91us to 2 048s in powers of 2 Command SPAN d 1 Histogram Length Bins Sets the number of points in each histogram The number of points can be specified in samples records each record is 1024 samples or in seconds When the specified number of samples records or seconds has been reached the histogram will update If repeat is on the SR785 will begin accumulating a new histogram at the end of the prior histogram Command HLEN 7 d f Sets the number of histogram bins along the x axis Values from 4 to 1024 in power of 2 increments are allowed The x axis display for histogram measurements ranges from 1 25 times the input range to 1 25 times the input range The resolution of the histogram is the therefore 2 5 times the input range divided by the number of bi
619. vailable Memory The MALC command automatically confirms the allocation SR785 Dynamic Signal Analyzer Data Table Commands 5 85 Data Table Commands DTBL d i The DTBL command sets queries the Data Table for display d The parameter 1 selects Off 0 or On 1 If the Data Table is On for both displays use the ACTD command to select the active display Only the Data Table of the active display may be edited or queried DMAX d i DINS d i j DDLT d i The DMAX command sets queries the Data Table Length for display d The parameter 1 is a last line number in the table up to 199 The DMAX command queries the last line number in the table The DMAX d i command sets the last line number in the table to 1 If 1 is greater than the current last line number new entries are created up to line 1 These new entries use the current marker position as their X position If the value of 1 is less than the current last line number an error is returned To remove entries from the table use the DDLT command This command is valid only if the Data Table for display d is On and display d is the active display Use the ACTD command to select the active display Only the Data Table of the active display may be edited or queried The DINS command sets queries the X Axis bin number for line number 1 in the Data Table for display d The parameter 1 selects the line number If the value of 11s greater than the last
620. variation is about 0 02 dB However the selectivity is worse Unlike the other windows the Flattop window has a very wide pass band and very steep rolloff on either side Thus signals appear wide but do not leak across the whole spectrum The Flattop window is the best window to use for accurate amplitude measurements BMH The BMH window has reasonable off bin amplitude accuracy about 0 8 dB and much lower side lobes than the Hanning window Thus it has very good selectivity and very little broadening of non bin frequencies The BMH window is a good window to use for measurements requiring a large dynamic range Kaiser The Kaiser window has the lowest side lobes and least broadening for non bin frequencies This makes this window the best for selectivity The off bin amplitude variation is the same as the BMH about 0 8 dB The Kaiser window is the best window to use for measurements requiring a large dynamic range Force Exponential The Force window is uniform over the beginning of the time record and zero over the remainder The force length is user specified This window is used to isolate impulsive signals such as impact excitations from noise and other oscillations later in the time record The Exponential window attenuates the time record with a decaying exponential time constant This window is often used in impact testing on the response channel to remove oscillations which last longer than the time record Many impact measu
621. vector averaged and peak hold averaged version of all measurements simultaneously The Display Average softkey only determines which version of the measurement is currently displayed You can change Display Average to view a different average of the current measurement without retaking any data Some measurements such as coherence have their own unique averaging mode In these cases the Display Average softkey is ignored The Start Reset key resets the current average and starts a new average The Pause Cont key pauses the average in progress Pressing Pause Cont again will continue the average from where it was paused Each display has its own Display Average This entry field can be linked to both displays by using the Link key Command FAVM d 1 RMS Averaging For a simple FFT measurement the definition of the RMS averaged measurement is RMS Avg FFT lt conj FFT FFT gt lt X Y gt SR785 Dynamic Signal Analyzer 4 110 Average Menus Where X and Y are the real and imaginary parts of the instantaneous FFT measurements and the lt gt angle brackets indicate either linearly weighted or exponentially weighted averaging over N FFT records For other measurements the definition of the RMS averaged measurement depends upon the measurement In the above example the RMS averaged FFT is real and has zero phase In general however rms averaged measurements have real and imaginary parts and have non zero
622. very Time Record playback displays the measurement result for every captured time record Since the data is stored in memory Every Time Record playback is not limited by real time considerations For example 1 second of capture contains 256 full span FFT time records In this case all 256 time records are measured AND displayed The display still updates at 8 Hz so playback takes about 32 seconds to complete If the time records are overlapped there may be more than 256 measurements to display and playback will take even longer When the measurement time records are very long narrow spans the time to process and display each measurement is much less than the real time record length Since the data is already available in the capture buffer Normal Speed playback means waiting unnecessarily for a real time record to elapse between updates In this case Every Time Record playback displays the measurements of all captured time records much faster than Normal Speed real time playback When the playback is in Octave Group playback is always Normal Speed The Capture Progress indicator at the top of the screen shows the playback progress through the buffer Both channels playback with the same Playback Speed Command ISPD 7 1 SR785 Dynamic Signal Anaylzer 4 100 Trigger Menu Trigger Menu A The Trigger menu configures the Trigger Mode Source Level and Delay Watch Out For Triggered Sources If a triggered source is select
623. with the SR785 If TRTEST doesn t work then your programs will not run The example is written using the CEC library routines National Instruments GPIB Card You must run the program IBCONPF to configure the resident GPIB driver for your GPIB card Please refer to the National Instruments manual for more information For example the following options should be set with IBCONF Device Name SR785 Device Address 10 EOS Character OAh linefeed Terminate Read on EOS Yes Once all the hardware and GPIB drivers are configured use IBIC Use IBWRT and IBRD to send to and receive from the SR785 If you cannot talk to the SR785 via IBIC then your programs will not run To modify the example to use a National Instruments card modify the routines where indicated Other GPIB cards You need to setup and configure your card according to your manual The example program points out the routines which are interface dependent Your card should have functions equivalent to those used in the example SR785 Dynamic Signal Analyzer 5 130 Example Program KKKKKKKKKKKKKKKKKKKKKEKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK Example program using Microsoft C v7 0 and the Capital Equipment Corp CEC488 GPIB interface card To use another interface card modify the GPIB subroutines where indicated The SR785 is Assumed to be at address 10 default Link this object file with ieee488 lib or the library
624. wo channel phase measurements Phase Suppress sets the phase of small data values to zero This avoids the messy phase display associated with the noise floor Remember even a small signal has phase Set the Phase Suppress threshold in the Display Options menu Watch Out For Triggered Sources If a triggered source is selected Chirp Burst Chirp Burst Noise or Arbitrary the triggered measurement phase is stable only if the input signals are derived from the source output Turn the source off or set it to Sine when making triggered measurements without the source Watch Out For Phase Errors The FFT can be thought of as a set of bandpass filters each centered on a frequency bin The signal within each filter shows up as the amplitude of each bin If a signal s frequency is between exact FFT frequency bins the filters cause phase errors Because these filters are very steep and selective they introduce very large phase shifts for signals not exactly on a frequency bin Use the SR785 source to generate exact bin frequencies whenever possible Unwrapped Phase Unwrapped Phase view graphs the phase of the measurement data as a continuous function without wrapping around at 180 degrees This view is generally meaningful only for measurements which have data at every frequency point such as chirp source or Swept sine The phase 8 is calculated for each point as in the wrapped Phase view The wrapping starts at the left ed
625. wo numbers of the form y 1 where y is a real number and 1 is an index indicating the units This command is valid only when the Source Type is Noise The NT YP command sets queries the Noise Type The parameter 1 selects Bandlimited White 0 White 1 or Pink 2 This command is valid only when the Source Type is Noise The NBUR command sets queries the Noise Burst Percentage The parameter x is a percentage from 1 to 100 This command is valid only when the Source Type is Noise and the Measurement Group is FFT or Time Histogram NPER 7 x lt ks s ms gt CSRC i The NPER command sets queries the Noise Burst Source Period The parameter x is a time from 4 ms to 1 ks This command is valid only when the Source Type is Noise and the Measurement Group is Octave or Order The CSRC command sets queries the Source Display The parameter 1 selects DisplayA 0 or DisplayB 1 This command is valid only when the Source Type is Chirp or Noise and the Measurement Group is FFT SR785 Dynamic Signal Analyzer Source Commands 5 57 Arbitrary Source Commands AAMP 7 x ARAT 2 i ASRC i ASTR i ALEN i TARB i The AAMP command sets queries the Arbitrary Source Amplitude The parameter x is a percentage of full scale 1V This command is valid only when the Source Type is Arbitrary The ARAT command sets queries the Arbitrary Source Playback Rate The parameter 1 0
626. y of the pole This command will change the specified table format to pole zero EZER i j x Ly The EZER command sets queries the zeros for one of the curve tables The parameter 1 selects curve table 1 0 or curve table 2 1 The parameter jJ selects which zero will be set queried from O up to the number of items in the list The parameter x is the real part of the zero The optional parameter y is the imaginary part Gf any of the zero This command will change the specified table format to pole zero ERES i j x Ly The ERES command sets queries the residues for one of the curve tables The parameter 1 selects curve table 1 0 or curve table 2 1 The parameter j selects which residue will be set queried from 0 up to the number of items in the list SR785 Dynamic Signal Analyzer Curve FitCommands 5 93 The parameter x is the real part of the residue The optional parameter y is the imaginary part if any of the residue This command will change the specified table format to pole residue ECLR i The ECLR command clears one of the curve tables The parameter 1 selects curve table 1 0 or curve table 2 1 SR785 Dynamic Signal Analyzer 5 94 Disk Commands Disk Commands FNAM 7 s The FNAM command sets queries the Save Recall File Name All save and recall disk operations use the name specified by this command Be sure to use the FNAM s command before any file operation commands For example t
627. y a menu box displayed on the screen next to the key Softkey functions change depending upon the menu and instrument configuration Softkeys are referenced as the lt Softkey gt Hardkeys The keypad consists of four groups of hardkeys keys with printed labels The ENTRY keys are used to enter numeric parameters which have been highlighted by a softkey The MENU keys select a menu of softkeys Pressing a menu key will change the menu boxes which are displayed next to the softkeys Each menu presents a group of similar or related parameters and functions The CONTROL keys start and stop data acquisition toggle the active display and link parameters and functions These keys are not in a menu since they are used frequently and within any menu The FUNCTION keys perform common functions such as Auto Scale and Auto Range These keys can be accessed at any time lt Softkeys gt The SR785 has a menu driven user interface The Menu keys each display a menu of softkeys The softkeys are at the right of the video display and have different functions depending upon the displayed menu There are three types of softkeys buttons lists and numeric values A button performs a function such as lt Full Span gt A list presents a list of choices or options in the entry field at the top of the screen Use the knob to make a selection and press Enter lt Measurement gt is an example of a list A numeric value presents the current value in the e
628. y contain data The download data must be data which was originally uploaded by TGET in its entirety The TGET and TPUT commands allow a host computer to save and reload a Trace buffer without using disks The download sequence is as follows Host Send TPUT 1 Do NOT wait for IFC to be set in the Serial Poll status SR785 Returns 1 4 byte binary long int when OK to begin binary transfer to the SR785 Host On receipt of 1 4 byte binary long int executes a binary transfer to the SR785 of n bytes as uploaded using TGET Asserts EOI with the final byte of the transfer SR785 Receives n bytes and the EOI If an error is detected during transfer the Trace buffer reverts to the empty state and a command execution error occurs Serial Poll until IFC bit 7 is set in the Serial Poll status before sending another command AGET i The AGET command uploads the Arbitrary Waveform buffer to the host computer This command is valid only via the GPIB interface The parameter 1 selects upload the whole buffer 0 or just the playback portion 1 The uploaded data should be saved in its entirety by the host computer The saved data can be downloaded back to the SR785 at a later time using APUT The AGET and APUT commands allow a host computer to save and reload the Arbitrary buffer without using disks The upload sequence is as follows Host Send AGET 1 Do NOT wait for IFC to be set in the Serial Poll status SR785 Retur
629. y when the Measurement Group is FFT The set command requires display d to be Live Since correlation is always a baseband measurement this command is not valid when the measurement group is correlation FCTR 7 d f lt kHz Hz mHz wHz gt The FCTR command sets queries the FFT Center frequency of display d The parameter f is a frequency real number of the specified units Values of f which would cause the span to exceed the 0 to 102 4 100 0 kHz range cause an error SR785 Dynamic Signal Analyzer Frequency Commands 5 29 This command is valid only when the Measurement Group is FFT The set command requires display d to be Live Since correlation is always a baseband measurement this command 1s not valid when the measurement group is correlation FEND d f lt kHz Hz mHz wHz gt UNST d The FEND command sets queries the FFT End frequency of display d The parameter f is a frequency real number of the specified units Values of f which would cause the span to exceed the 0 to 102 4 100 0 kHz range cause an error This command is valid only when the Measurement Group is FFT The set command requires display d to be Live Since correlation is always a baseband measurement this command 1s not valid when the measurement group is correlation The UNST command unsettles the measurement of display d The measurement is not actually perturbed by the UNST command The settling status is set to unsettled a
630. z FFT Lines 400 Window BMH Averaging Mode Vector Averaging Type Exp Cont Number of Avg 250 Overload reject Off RPrRrRWAONRFRFRRAION X Hz Mag dBVpk LVOOOOUE TOO Sees seca ud OU0O0STUZ Soulo9995e 0 1 120000e 02 7 247395et01 S6o0000E702 O 415229er01 sUZ4000ET0Sy L 30905 lEeh0Z s20 00006F03 143946116F02 MO26000GTOS SLaZzsSloyceroz SOU000ETOZ 6s lo9995e701 120000e 02 7 247395e 01 6S0000E 02 9 41522967 0 1 U2Z4000ET03 L 307905 LEF0Z lt 20 00006703 La 9460 L LEFU v396000ET0S A LI ger etc Converting Files to SDF Using the File Conversion Utilities 6 7 Usage SRT785 Osdf options infile outfile Allowed Input File Types 78D Files Default Output File Extension DAT For input files which contain nodal degree of freedom informat the following SDF Output Options can be used to change the DOF parameters Mrnn Mrdk Msnn Msdk OMANANINNMNBWN KF O pe fk o Reference node number Reference node direction see table below Response node number Response node direction Node Direction id s Scalar Z Y X 6 0 SR785 Dynamic Signal Analyzer 6 8 Using the File Conversion Utilities 12 0 Example Convert all the 78D files in the current directory to SDF files with the same name and a DAT extension SRTRANS Osdf 78D Converting Files to 78D Format Usage SRT785 O78d options infile outfile Allowed Input File Types 78D Fil

SR785 User`s Manual - Stanford Research Systems

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