TDS3AAM Advanced Analysis Application Module User Manual
Contents
1. outs ays values at and between the ions as X and Y read Polar Disp cursor posi read outs ays va lues at and between the ions as radius and angle Product Disp cursor and the two cursors ays product values of the active the difference vector of Ratio Disp ays ra io values of the active cursor and the difference vector of the two cursors 32 0 0 Origin The XY waveform origin is the 0 volt point of each source waveform Positioning both source wave form 0 volt points on the vertical center graticule places the origin in the center of the screen All actual measurements are referenced to the XY waveform s 0 0 origin and show the value of the active cursor Waveform Mode The Waveform mode uses cursors to measure the actual waveform data to determine X and Y values and units While in Waveform mode the XY cursors always lock onto the XY waveform and cannot be positioned off the XY waveform Graticule Mode The Graticule function does not connect screen cursor position to waveform data Instead the display is like a piece of graph paper where the values of the divisions are set by each channel s vertical scale The graticule cursor readouts display the XY value of the screen not the waveform data Because graticule cursors are not associated with waveform data the cursors are not locked to the XY waveform and can be positioned anywhere on the gra2. Bottom Side Description FFT Set FFT Sets the FFT signal source Source to Valid input sources are Ch 1 and Ch 2 2 channel instru ments Ch 1 through Ch 4 4 channel instruments and Ref 1 through Ref 4 all instru ments SetFFT Vert Sets the display vertical scale Scale to units Available scales are dBV RMS and Linear RMS Set FFT Sets which window function Window to Hanning Hamming Blackman Harris or Rectangular to apply to the source signal Refer to page 40 for more FFT window information Advanced FFT You can perform FFT analysis on arbitrary math expressions See Advanced Math Functions on page 24 for more information Linear RMS Scales A Linear scale is useful when the frequency component magnitudes are all close in value letting you display and directly compare components with similar magnitude values 13 dB Scales A dB scale is useful when the frequency component magnitudes cover a wide dynamic range letting you show both lesser and greater magnitude frequency components on the same display The dBV scale displays component magnitudes using a log scale expressed in dB relative to 1 Vrms where 0 dB 1 VRMS Or in source waveform units such as amps for current measurements FFT Analysis on Active or Stored Waveforms You can display an FFT waveform on any active signal periodic or one shot the last acquired signal or any signal stored in reference memory FFT Windows
3. DPO Math Functions The TDS3AAM application module adds the ability to perform dual waveform math on DPO waveforms The resulting DPO math waveform contains intensity or gray scale information that like an analog oscilloscope increases waveform intensity where the signal trace occurs most often This gives you more information about signal behavior To access the DPO math menu push the MATH front panel button and then push the DPO Math bottom button DPO Math Menu Bottom Side Description DPO Math Set 1stSource Selects the first source wave to form SetOperator Selects the math operator to or X Set 2nd Selects the second source Source to waveform Intensity Use the WAVEFORM INTENSITY front panel knob to control the overall waveform intensity as well as how long the waveform data persists on the screen 22 Acquisition Modes Changes to the acquisition mode globally affect all input channel sources except for DPO math thereby modifying any math waveforms using them For example with the acquisition mode set to Envelope a Chl Ch2 math waveform will receive enveloped channel 1 and channel 2 data which results in an enveloped math waveform Clearing Data Clearing the data in a waveform source causes a null waveform to be delivered to any math waveform that includes that source until the source receives new data 23 Advanced Math Functions The TDS3AAM application module lets you creat
4. Tektronix Phone 1 800 833 9200 Address Tektronix Inc Department or name if known 14200 SW Karl Braun Drive P O Box 500 Beaverton OR 97077 USA Web site www tektronix com Sales support 1 800 833 9200 select option 1 Service support 1 800 833 9200 select option 2 Technical E mail techsupport tektronix com support 1 800 833 9200 select option 3 1 503 627 2400 6 00 a m 5 00 p m Pacific time This phone number is toll free in North America After office hours please leave a voice mail message Outside North America contact a Tektronix sales office or distributor see the Tektronix web site for a list of Offices Contents Safety Summary 0 cece ee eee eee 2 TDS3AAM Overview cece cece eens 5 Installing the TDS3AAM Application Module 6 Accessing Advanced Analysis Menus 6 Measurement Functions 00c eeu eeeeees 8 FFT Math Functions 00e eee seen eaee 12 DPO Math Functions ccs eee eee 22 Advanced Math Functions ceeeeeeee 24 XY CUISOIS ocrni eg ee eld Ree nk eens 31 Appendix A FFT Concepts ee eens 40 Safety Summary To avoid potential hazards use this product only as specified While using this product you may need to access other parts of the system Read the General Safety Summary in other system manuals for warnings and cautions related to operating the system Preventing Electrostatic Damage CAUTION Electros
5. as part of a math expression The side menu button toggles between selecting the numeric field and selecting the scientific notation field E Use the general purpose knob to enter values in either field Push the COARSE front panel button to quickly enter larger numbers in the numeric field 28 Edit Math Units Controls The Edit Math Units screen provides controls and menu items to create custom units for math waveforms Whenever the oscilloscope cannot determine the horizontal or vertical units for a measure ment it displays the undefined unit character The user defined units function replaces the undefined horizontal or vertical unit character with the user defined vertical or horizontal unit for math waveforms only The following table describes the Edit Math Units controls Edit Math Units Controls Control Description General pur Selects highlights a character in the label list pose knob Up Arrow Selects the Vertical or Horizontal label in the Down Arrow unit label field OK Accept Closes the Edit Math Units screen and button displays the math menu Enter Charac Adds the selected character atthe cursor ter button position in the unit field Left Arrow Moves the unit label field cursor to the left or Right Arrow right 29 Edit Math Units Controls cont Control Description Back Space Erases the character to the left of the cursor button position Delete button
6. is a single shot transient signal make sure that the entire signal transient event and ringing or noise is displayed and centered on the screen 3 Push the Vertical MATH button to show the math menu If you are in the oscilloscope QuickMenu push the MENU OFF button then push the MATH button 4 Push the FFT screen button to show the FFT side menu 5 Select the signal source You can display an FFT on any channel or stored reference waveform 6 Select the appropriate vertical scale page 13 and FFT window page 43 7 Use zoom controls to magnify and the cursors to measure the FFT waveform page 16 17 FFT Example 1 A pure sine wave can be input into an amplifier to measure distortion any amplifier distortion will introduce harmonics in the amplifier output Viewing the FFT of the output can determine if low level distortion is present You are using a 20 MHz signal as the amplifier test signal You would set the oscilloscope and FFT parame ters as listed in the table FFT Example 1 Settings Control Setting CH 1 Coupling AC Acquisition Mode Average 16 Horizontal Resolution Normal 10k points Horizontal SCALE 100 ns FFT Source Chil FFT VertScale dBV FFT Window Blackman Harris 18 y AA A A A ACA A A i i i l l i J j j 1 A i i Di ii AIATATATSTET i V y y WV WV VV VY VOW WW 1 The first component at 20 MHz figur
7. menu Function button button button Area MEASURE Select More button until Cycle Area Measrmnt you display Area and measurement Cycle Area buttons See page 8 Measurement MEASURE Statistics To select Min Max or Statistics Mean Standard Devi ation See page 9 Measurement Functions Area and Cycle Area Measurements cont The TDS3AAM application module adds Area and Bottom Side Description Cycle Area Measurements to the Select Measurement Statistics OFF isables displaying statistical side menu list and adds a Statistics bottom button to the information with active measure Measurement menu To access these measurement menu ments items push the MEASURE front panel button iw Min Max J isplays minimum and maximum Area and Cycle Area Measurements readouts for each active measure ment readout Bottom Description Mean Displays Mean and Standard Select Voltage over time measurement Standard Deviation readouts for each active Measurmnt The arithmetic area over the entire Deviation measurement readout waveform or gated region mea n sured in vertical unit seconds for n is the number of measurement example voltseconds or amp se values used to calculate the mean conds and standard deviation values and ranges from 2 to 1000 Use the ENES V heimetc aes avectie a oly gute e value in increments of 1 fine cycle in the waveform or the first or 10 coarse The default value
8. Deletes the character at the cursor position in the unit label field Clear button Clears erases all characters in the current unit field Horizontal or Vertical MENU OFF Closes the Edit Math Units screen and returns button to the previous menu without applying the user defined units Math Expression Example The following expression calculates the energy in a waveform where Ch1 is in volts and Ch2 is in amps Intg Ch1xCh2 Taking an Area measurement on the resulting waveform displays the waveform power value 30 XY Cursors The TDS3AAM application module adds XY and XYZ waveform measurement cursors These cursor functions are part of the Cursor menu You must display an XY waveform DISPLAY gt XY Display gt Triggered XY or Gated XYZ in order to access the XY cursor menu items The following figure shows XY cursors in Waveform mode with polar readouts FFS 1 48 1 11r diin CE 31 XY Cursor Menu Bottom Function Side Off Description Turns XY cursors off Waveform Graticule Turns waveform or graticule cursor modes on Use the front panel SELECT button to select which cursor to move the active cursor Use the general purpose knob to move the active cursor Mode Independent Sets cursors to move independently Tracking Sets cursors to move together when the reference cursor is selected Readout Rectangular Disp cursor posi
9. Four FFT windows Rectangular Ham ming Hanning and Blackman Harris let you match the optimum window to the signal you are analyzing The Rectangular window is best for nonperiodic events such as transients pulses and one shot acquisitions The Hamming Hanning and Blackman Harris windows are better for periodic signals Refer to page 43 for more information on FFT windows 14 Positioning the FFT Waveform Use the Vertical POSI TION and SCALE knobs to vertically move and rescale the FFT waveform FFT and Acquisition Modes Waveforms acquired in Normal acquisition mode have a lower noise floor and better frequency resolution than waveforms acquired in Fast Trigger mode due to the higher number of wave form samples Do not use Peak Detect and Envelope modes with FFT Peak Detect and Envelope modes can add significant distortion to the FFT results Waveforms with DC Waveforms that have a DC compo nent or offset can cause incorrect FFT waveform compo nent magnitude values To minimize the DC component choose AC Coupling on the waveform Reducing Random Noise To reduce random noise and aliased components in repetitive waveforms set acquisi tion mode to average 16 or more acquisitions However do not use acquisition averaging if you need to resolve frequencies that are not synchronized with the trigger rate Measuring Transients For transient impulse one shot waveforms use the oscilloscope trigger controls to cent
10. OFF Closes the Edit Expression screen and returns button to the previous menu without changing the math expression Expression List The following gives more information on the expression list items Expression List Menu item Description Ch1 Ch4 Specifies a waveform data source Refl Ref4 FFT Intg Executes a Fast Fourier Transform integra Diff tion or differentiation operation on the expression that follows The FFT operator must be the first left most operator in an expression All these operations must end with a right parenthesis 27 Expression List cont Menu item Description Period Executes the selected measurement operation on the waveform active or reference that CycleArea follows All these operations must end with a right parenthesis Varl Var2 Adds the user defined variable to the expres sion t xX Executes an addition subtraction multiplica tion or division operation on the following expression and are also unary use to negate the expression that follows 0 Parentheses provide a way to control evaluation order in an expression The comma is used to separate the from and to waveforms in Delay and Phase measurement operations 1 0 E Specifies a numeric value in optional scientific notation User Defined Variables This feature lets you define two variables such as math constants that you can then use
11. Peak Amplitude High Low Max Mini Mean CycleMean Rms CycleRms Area CycleAreat VARI VAR2 er 3 1234H67890 25 Edit Expression Screen Menu item Description Expression Location in expression field where the next cursor expression element is entered Expression Area that displays the entered expression field elements up to a maximum of 127 characters Expression list The list of available elements Use the general purpose knob to select an element You can only select elements that are syntactically correct for the current math expression Non selectable elements are grayed out Refer to page 27 for more expression element information Edit Expression Controls The Edit Expression screen provides controls and menu items to create math expres sions The following table describes the Edit Expression controls Edit Expression Controls Control Description General pur Selects highlights an element in the expres pose knob sion list Enter Selec Adds the selected element to the expression tion button field You can also use the front panel SELECT button 26 Edit Expression Controls cont Control Description Back Space Erases the last entered element from the button expression field Clear button Clears erases the entire expression field OK Accept Closes the Edit Expression screen and button displays the math expression waveform MENU
12. Transform FFT waveform analysis m Waveform area and cycle area measurements m Measurement statistics Adds min max or mean standard deviation readouts to displayed measurements m XY waveform cursors Installing the TDS3AAM Application Module Refer to the TDS3000 amp TDS3000B Series Application Module Installation Instructions for instructions on installing and testing your TDS3AAM Advanced Analy sis application module Accessing Advanced Analysis Menus The TDS3AAM Advanced Analysis module adds Area Cycle Area and statistical measurement functions to the Measure menu and FFT DPO math and Advanced Math functions to the Math menu and XY cursors to the Cursor menu To access the Advanced Analysis func tions use the following table Accessing TDS3AAM Functions Accessing TDS3AAM Functions cont Push Push front bottom panel menu Push side menu Function button button button FFT MATH FFT To select waveform source vertical scale and FFT window See page 12 DPO Math MATH DPO Math To select waveform sources and operator See page 22 Math MATH Advanced To create a math ex waveform Math pression define a expressions variable value define units and display the math expression See page 24 XY Cursors CURSOR Function To select Waveform XY cursor you must be in XY display mode to see this menu See page 31 Push Push front bottom panel menu Push side
13. User Manual TDS3AAM Advanced Analysis Application Module 071 0946 00 TMUN NUN UE TT TU TET 071094600 Copyright Tektronix Inc All rights reserved Tektronix products are covered by U S and foreign patents issued and pending Information in this publication supercedes that in all previously published material Specifications and price change privileges reserved Tektronix Inc P O Box 500 Beaverton OR 97077 TEKTRONIX TEK TEKPROBE and Tek Secure are registered trademarks of Tektronix Inc DPX WaveAlert and e Scope are trademarks of Tektronix Inc WARRANTY SUMMARY Tektronix warrants that the products that it manufactures and sells will be free from defects in materials and workmanship for a period of one 1 year from the date of shipment from an authorized Tektronix distributor If a product proves defective within the respective period Tektronix will provide repair or replacement as described in the complete warranty statement To arrange for service or obtain a copy of the complete warranty statement please contact your nearest Tektronix sales and service office EXCEPT AS PROVIDED IN THIS SUMMARY OR THE APPLICABLE WARRANTY STATEMENT TEKTRONIX MAKES NO WARRANTY OF ANY KIND EXPRESS OR IMPLIED INCLUDING WITHOUT LIMITATION THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE IN NO EVENT SHALL TEKTRONIX BE LIABLE FOR INDIRECT SPECIAL OR CONSEQUENTIAL DAMAGES Contacting
14. alue means that the delta cursor is below the reference cursor on the Y axis X Y The actual X and Y values of the active selected cursor At The time from the reference cursor to the delta Waveform cursor A negative value means that the delta Mode cursor is earlier in the waveform record than the reference cursor t The time from the trigger point to the active cursor Waveform A negative value means that the active cursor is Mode earlier in the waveform record than the trigger point The following is an example of Rectangular readouts in Waveform mode AX 1 43V X 140mV AY 2 14V Y 480mV At 660ns t 1 6lus 35 Polar Readouts The Polar readout displays the following information Ar A0 The radius and angle from the reference cursor to the delta cursor r 8 The radius and angle from the XY waveform origin to the active selected cursor At The time from the reference cursor to the delta Waveform cursor A negative value means that the delta Mode cursor is earlier in the waveform record than the reference cursor t The time from the trigger point to the active cursor Waveform A negative value means that the active cursor is Mode earlier in the waveform record than the trigger point The following is an example of Polar readouts in Wave form mode Ar 2 90V r 1 27V A0 32 6 0 179 At 4 20uUs t 8 36us 36 The following figure shows an example o
15. e a custom math waveform expression that can incorporate active and reference waveforms measurements and or numeric constants To access the Advanced Math menu push the MATH front panel button and then push the Advanced Math bottom button Advanced Math Menu Bottom Side Description Advanced Edit Displays a screen in which you Math Expression can create or edit the expres sion that defines the math waveform See page 25 VAR1 VAR2 Assigns numeric values to two n nnnn variables You can use these E nn variables as part of an expres sion Push the side menu button to select between the base n nnn and the exponent nn field Use the general purpose knob to enter values Define Units Displays a screen in which you can enter user defined unit labels These labels replace the unknown readout value 24 Advanced Math Menu cont Bottom Side Description Advanced Display Displays the current advanced Math cont Expression math expression on the grati cule Edit Expression Screen The Edit Expression screen lets you create arbitrary math expressions Refer to page 26 for a description of the Edit Expression controls Expression Expression Expression cursor field list y l Y chi Ch2 Ch3 cha 4 Refl Ref2 Ref3 Ref4 FFT Intg Diff Period Freq Delay Rise Fall Burstwidth Phase PosDutyCycle NegDutycycle Poswidth Negwidth PosOverShoot NegOverShoot Peak
16. e label 1 is the source signal fundamental frequency The FFT wave form also shows a second order harmonic at 40 MHz 2 and a fourth order harmonic at 80 MHz 3 The pres ence of components 2 and 3 indicate that the system is distorting the signal The even harmonics suggest a possible difference in signal gain on half of the signal cycle 19 FFT Example 2 Noise in mixed digital analog circuits can be easily observed with an oscilloscope However identifying the sources of the observed noise can be difficult The FFT waveform displays the frequency content of the noise you may then be able to associate those frequen cies with known system frequencies such as system clocks oscillators read write strobes display signals or switching power supplies The highest frequency on the example system is 40 MHz To analyze the example signal you would set the oscilloscope and FFT parameters as listed in the following table FFT Example 2 Settings Control Setting CH 1 Coupling AC Acquisition Mode Sample Horizontal Resolution Normal 10k points Horizontal SCALE 4 00 us Bandwidth 150 MHz FFT Source Chil FFT VertScale dBV FFT Window Hanning 20 Note the component at 31 MHz figure label 1 this coincides with a 31 MHz memory strobe signal in the example system There is also a frequency component at 62 MHz figure label 2 which is the second harmonic of the strobe signal 21
17. er the waveform pulse information on the screen 15 Zooming an FFT Display Use the Zoom button along with horizontal POSITION and SCALE controls to magnify and position FFT waveforms When you change the zoom factor the FFT waveform is horizontal ly magnified about the center vertical graticule and vertically magnified about the math waveform marker Zooming does not affect the actual time base or trigger position settings NOTE FFT waveforms are calculated using the entire source waveform record Zooming in on a region of either the source or FFT waveform provides more display resolution but will not recalculate the FFT waveform for that region Measuring FFT Waveforms Using Cursors You can use cursors to take two measurements on FFT waveforms magnitude in dB or signal source units and frequency in Hz dB magnitude is referenced to 0 dB where 0 dB equals 1 Vrms Use horizontal cursors H Bars to measure magnitude and vertical cursors V Bars to measure frequency 16 Displaying an FFT Waveform Do these steps to display an FFT waveform 1 Set the source signal Vertical SCALE so that the signal peaks do not go off screen Off screen signal peaks can result in FFT waveform errors 2 Set the Horizontal SCALE control to show at least five waveform cycles Showing more cycles means the FFT waveform can show more frequency components provide better frequency resolution and reduce aliasing page 45 If the signal
18. f how the oscilloscope calculates the difference vector from the radius and angle values of the two cursors The following figure shows how the oscilloscope determines polar angle values XY origin or reference cursor for A measurements 180 0 180 37 Product Readouts The Product readouts displays the following information AX x AY The product of the difference vector s X component multiplied by the difference vector s Y component XX Y The product of the active cursor s X value multiplied by the active cursor s Y value At The time from the reference cursor to the delta Waveform cursor A negative value means that the delta Mode cursor is earlier in the waveform record than the reference cursor t The time from the trigger point to the active cursor Waveform A negative value means that the active cursor is Mode earlier in the waveform record than the trigger point The following is an example of Product readouts in Waveform mode AX xX AY 7 16VV Xx Y 1 72VV At 4 68us t 8 84us 38 Ratio Readouts The Ratio readouts displays the follow ing information AX AY The ratio of the difference vector s Y component divided by the difference vector s X component X Y The ratio of the active cursor s Y value divided by the active cursor s X value At The time from the reference cursor to the delta Waveform cursor A negative value means
19. form so that the start and stop values are close to each other reducing FFT waveform discontinuities This results in an FFT waveform that more accurately represents the source signal frequency components The shape of the window determines how well it resolves frequency or magnitude informa tion 41 Source waveform Waveform record With windowing 42 Point by point multiply Window function Hanning Source waveform after windowing FFT Window Characteristics The FFT application module provides four FFT win dows Each window is a trade off between frequency resolution and magnitude accuracy What you want to measure and your source signal characteristics help determine which window to use Use the following guidelines to select the best window FFT Window Characteristics FFT Window Characteristics Best for measuring Blackman Best magnitude Predominantly single fre Harris worstatresolving quency waveforms to look frequencies for higher order harmonics Hamming Better frequency Sine periodic and narrow Hanning poorer magnitude band random noise accuracy than Rectangular Transients or bursts where Hamming has the signal levels before and slightly better fre quency resolution than Hanning after the event are signifi cantly different 43 FFT Window Characteristics cont FFT Window Characteristics Rectangular Best frequency worst magnit
20. is cycle in the gated region mea 32 sured in vertical unitseconds for example volt seconds or amp se PA i Waveform Polarity For area calculation the waveform area above ground is positive the waveform area below ground is negative Waveform Clipping For best results make sure that all input waveforms do not extend beyond the top or bottom graticules of the display referred to as clipping the waveform Using clipped waveforms with measure ment or math functions can result in incorrect values Area The following equation shows the algorithm for calculating the waveform area for the entire record or gated region If Start End then return the interpolated value at Start Otherwise End Area Waveform t dt Start Cycle Area The following equation shows the algorithm for calculating the waveform area for a single cycle in the record or gated region If StartCycle EndCycle then return the interpolated value at StartCycle Otherwise EndCycle CycleArea Waveform t dt StartCycle 10 Min Max Min Max displays a minimum and maximum measurement readout directly below each active mea surement The following is an example of a Min Max readout Ch1 Freq 15 98 MHz Min 15 81MHz Max 16 17MHz Mean Standard Deviation Mean Standard Deviation displays a mean U and standard deviation O readout directly below each active measurement The mean and standard deviation values are running calcu
21. lations which means that the current calculation incorporates the results of previous calculations The following is an example of a Mean Standard Deviation readout Ch1 Freq 15 98 MHz u 15 99MHz o 82 92kHz Screen Readouts The Min Max and Mean Standard Deviation readouts display directly below the waveform measurements in an area normally used for measure ment qualifier text such as Low resolution If you suspect the measurement turn off statistics to see if the oscilloscope displays any qualifier text 11 FFT Math Functions The TDS3AAM application module adds FFT Fast Fourier Transform measurement capabilities to the oscilloscope The FFT process mathematically converts the oscilloscope time domain signal repetitive or single shot acquisition into its frequency components providing spectrum analysis capabilities Being able to quickly look at a signal s frequency components and spectrum shape is a powerful research and analysis tool FFT is an excellent troubleshooting aid for m Testing impulse response of filters and systems m Measuring harmonic content and distortion in systems m Identifying and locating noise and interference sources m Analyzing vibration m Analyzing harmonics in 50 and 60 Hz power lines The application module adds the FFT functions to the Math menu To access the FFT math menu items push the MATH front panel button and then push the FFT bottom button 12 Math FFT menu
22. ppear at their proper frequency If the increased number of frequency components shown on the screen makes it difficult to measure individual components use the Zoom button to magnify the FFT waveform You can also use a filter on the source signal to band width limit the signal to frequencies below that of the Nyquist frequency If the components you are interested in are below the built in oscilloscope bandwidth settings 20 MHz and 150 MHz set the source signal bandwidth to the appropriate value Push the Vertical MENU button to access the source channel bandwidth menu 46
23. tatic discharge ESD can damage components in the oscilloscope and its accessories To prevent ESD observe these precautions when directed to do so Use a Ground Strap Wear a grounded antistatic wrist strap to discharge the static voltage from your body while installing or removing sensitive components Use a Safe Work Area Do not use any devices capable of generating or holding a static charge in the work area where you install or remove sensitive components Avoid handling sensitive components in areas that have a floor or benchtop surface capable of generating a static charge Handle Components Carefully Do not slide sensitive components over any surface Do not touch exposed connector pins Handle sensitive components as little as possible Transport and Store Carefully Transport and store sensitive components in a static protected bag or container Manual Storage The oscilloscope front cover has a convenient place to store this manual TDS3AAM Overview This section provides an overview of the TDS3AAM Advanced Analysis application module features and describes how to access the advanced analysis functions You can do the following analysis tasks with the TDS3AAM application module m DPO Math m Arbitrary math expressions Allow you to create waveforms using math operations on active and reference waveforms waveform measurements up to 2 user definable variables and arithmetic expressions m Fast Fourier
24. that the delta Mode cursor is earlier in the waveform record than the reference cursor t The time from the trigger point to the active cursor Waveform A negative value means that the active cursor is Mode earlier in the waveform record than the trigger point The following is an example of Ratio readouts in Wave form mode AY AX 1 22VV Y X 1 10VV At 4 68ms t 8 84ms 39 Appendix A FFT Concepts This appendix provides more information on FFT operation and theory FFT Windows The FFT process assumes that the part of the waveform record used for FFT analysis represents a repeating waveform that starts and ends at or near zero volts in other words the waveform record contains an integer number of cycles When a waveform starts and ends at the same amplitude there are no artificial discontinuities in the signal shape and both the frequency and ampli tude information is accurate A non integral number of cycles in the waveform record causes the waveform start and end points to be at differ ent amplitudes The transitions between the start and end points cause discontinuities in the waveform that introduce high frequency transients These transients add false frequency information to the frequency domain record 40 Time domain YT waveform la Waveform record Discontinuities Waveform seen by FFT Without windowing Applying a window function to the source waveform record changes the wave
25. ticule All readout types Polar Rectangular Product and Ratio are available in both Waveform and Graticule cursor modes However no time readouts are displayed in Graticule mode because the cursors are not measuring the waveform record 33 Turning XY Cursors Off To turn off the XY cursors push the front panel CURSOR button and then push the Cursor Function Off side menu button Reference and Delta Cursors Both Waveform and Grati cule modes use two XY cursors a reference cursor H and a delta cursor All difference A measurements are measured from the reference cursor to the delta cursor Switching Between XY and YT Display You can switch between XY and YT display mode to see the location of the Waveform cursors in the YT waveform The wave form record icon at the top of the graticule also shows the relative cursor positions of the Waveform cursors in the waveform record Waveform Sources You can use XY cursors on active acquisitions single sequence acquisitions and reference waveforms You must store both XY source waveforms in order to recreate an XY waveform The X axis wave form must be stored in Ref1 34 Rectangular Readouts The Rectangular readouts display the following information AX AY The X and Y difference from the reference cursor to the delta cursor A negative X value means that the delta cursor is to the left of the reference cursor on the X axis A negative Y v
26. ude resolution This is essentially the same as no win dow Best for measuring Transients or bursts where the signal levels before and after the eventare nearly equal Equal amplitude sine waves with frequencies that are very close Broadband random noise with a relatively slow varying spectrum 44 Aliasing Problems occur when the oscilloscope acquires a signal containing frequency components that are greater than the Nyquist frequency 1 2 the sample rate The fre quency components that are above the Nyquist frequen cy are undersampled and appear to fold back around the right edge of the graticule showing as lower frequen cy components in the FFT waveform These incorrect components are called aliases Nyquist frequency 0 Hz 1 2 sample rate y Frequency y aa frequencies pi Aliased frequencies a E 45 To determine the Nyquist frequency for the active signal push the ACQUIRE menu button The oscilloscope displays the current sample rate on the bottom right area of the screen The Nyquist frequency is one half of the sample rate For example if the sample rate is 25 0 MS s then the Nyquist frequency is 12 5 MHz To reduce or eliminate aliases increase the sample rate by adjusting the Horizontal SCALE to a faster frequency setting Since you increase the Nyquist frequency as you increase the horizontal frequency the aliased frequency components should a
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