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Nor-840 User Manual - Campbell Associates

1. Press INPUT and select inout source Adjust the full scale setting GAIN 1 GAIN2 Press CAL and set the calibrator frequency Set the calibrator s output level Select Calibrate and press Enter to commence auto calibration Checking Residual Intensity Using the Nor 1254 Sound Intensity Calibrator After you have calibrated your sound in tensity system you may want to check for residual intensity By residual intensity we mean virtual in tensity appearing when both transducers microphones in most cases of a p p probe is exposed to the same sound field Any residual intensity present stems mainly from interchannel phase mismatch To do this you will need an intensity cali brator such as the Nor 1254 to be able to expose the two microphones to the same sound field simultaneously This cali brator is available separately The Nor 1254 is a two port calibration cou pler for phase and level calibration of sound intensity pairs When used with the Nor 840 the calibrator is connected to the noise generator output of the analyser The sound intensity calibrator Nor 1254 consists of a sound source supplying a well defined sound pressure field simultane ously to the diaphragms of the two meas urement microphones of the p p probe The microphones can be 4 or 4 the lat ter by means of an adaptor The microphones are inserted into the holes of the No
2. Input selection camel 1 Press INPUT and select input source 2 Microphone HP filter 2 26Hz Channel 2 Source 3 Charge LP filter 0 Off HP filter E 20Hz Adjust the full scale setting GAIN1 GAIN2 Fullscale channel 1 Fullscale dB 2 00e 08 Ju 4 Calibration Channel 1 Microphone Press CaL and set a the calibrator lech frequency Channel 2 Microphone L 27 3 8 iz evel 4 dB r 1k Sens Level E dB 2 00e 05 114 3 Calibrate Cal freq sik Pol Volt 280 eva 1 Microphone Set the sensitivity of 6 8 the microphone used e p until the sound 114 0 Calibrate Channel 2 Microphone pressure level is Sens Level indicated correctl ers a 2 22 05 114 0 Calibrate Calibration Setting the Sensitivity Input selection Channel 1 Press INPUT and select input source HP filter 2 20Hz Channel 2 Source 3 Charge LP filter 6 Off HP filter 2 20Hz Channel 1 Microphone Press Cat and set the sensitivity of the microphone used Calibrate 2 80e 85 Calibrate Cal freq ik Pol Volt 200 This method is in general not recom mendable since it does not take into account whether the microphone actually
3. Fulhscale channel 2 108 Fullscale Do not confuse the full scale setting and the full display setting The former defines the input amplifier gain and hence the overload margin for a given signal level while the latter is used to set the display to make the measured signal fit within the setting of the axis If you set the full scale setting to one of the three highest settings a small will warn you that the analyser is prone to overload 56 6 A 5 2 0 xf Hz 315 Note Autoranging is not available in any of the sound intensity modes Full Scale Setting The available full scale setting of a measurement is given as a combination of the input amplifier gain setting and the calibration setting The gain is set separately for each chan nel and is adjustable in steps of 5 dB Press GAIN1 GAIN2 to enter the menu The full scale setting controls the set ting of the input amplifiers However it has no influence on the vertical scale in the display The two extremes top and bottom of the vertical scale is control led by the top scale value which has its own dedicated key called the Y Max key The top scale setting is purely a display function having nothing to do with the input amplifier whatsoever Note that if you set the full scale set ting to a very high value you face the risk of having severe overload in the transducers without seeing any trace of it i
4. Calibration Channel 1 Microphone Sens Level A EE e G Unit dB Be Bees H Autocal c Hm a i Channel 2 Microphone Sens Level D J Unit dB e a Bowes K Autocal Fp Haa rr L Cal freq ik M Pol Volt 280 N Sensitivity of channel 1 Ch 1 units dB or engineering units Auto calibration level of channel 1 Sensitivity of channel 2 Ch 2 units dB or engineering units Auto calibration level of channel 2 Level of ch 1 measured with the selected time constant O dB level of ch 1 Initiate auto calibration of ch 1 Level of ch 2 measured with the selected time constant O dB level of ch 2 Initiate auto calibration of ch 2 Calibrator frequency Polarisation voltage setting When Using the Nor 216 Intensity measurements may also be made with the now discontinued p u probe Nor 216 The cable Nor 1460 must be used to connect the probe to the analyser Analysers with serial number 17857 and lower must undergo a minor hardware modification to be able to support the use of Nor 216 The probe type selection is made in the measurement setup menu The sensitivity of the velocity channel must be set 52 dB above the sensitivity that was used when the probe was used with the Nor 830 This means that you should key in 26 dB as the velocity sensitivity setting and not 26 dB as when used with the Nor 830 If you Change the 0 dB Reference level Lvl Flt Sgl READY
5. aa E Unit dB 1 dB 2 00e 05 futocal 114 6 Calibrate GB 7 000705 114 4 Calibrate Cal freq ik Pol Volt 280 Channel Sens Unit ae Autocal Press INPUT and select input source Press Cat and set the sensitivity of the microphone used This method is in general not recom mendable since it does not take into account whether the microphone actually works as it is Supposed to do Bearing in mind that the microphone itself is the most vulnerable part of the measurement chain this method obviously suffers from severe shortcomings Auto calibration Using a Sound Calibrator Insert microphone into calibrator Input selection Channel 1 Source 2 Microphone Channel 2 Source 3 Charge LP filter Off HP filter 2 2 Hz HP filter E 2 Hz Fullscale channel 1 Fullscale dB 4 Calibration Channel 1 Microphone Sens Level 25 7 39 1 Unit BdB 2 00e 05 Autocal ia i Calibrate Channel 2 Microphone Sens Level 27 3 0 4 Unit dB 2 8Ge 85 Autocal Calibrate 1 Cal freq PIS Pol Volt 5 Calibration Channel 1 Microphone Sens Level O Calibration Channel 1 Microphone
6. Auto calibration Using a Sound Calibrator 1 Insert microphone into calibrator Channel 1 Press INPUT and select inout source HP filter 2 2 Hz Channel 2 Source 3 Charge LP filter Off HP filter E 2 Hz Fullscale channel 1 Fullscale dB 2 00e 00 u 4 Calibration Channel 1 Microphone Adjust the full scale setting Gain 1 GAIN2 Press CaL and set sa et the calibrator Unit BdB AE frequency Calibrate Autocal ia i Channel 2 Microphone Sens Level 27 3 0 4 Unit dB 2 8Ge 85 ii 1 Autocal Calibrate Cal freq PIS Pol Volt O Calibration Channel 1 Microphone Set the calibrator s output level Sens Level 6 EET Select Calibrate and press ENTER tO commence auto calibration The Level Mode Measurement Setup Menus The measurement setup menu is used to set up essential measurement parameters The menu comes in two flavours one to cover the setup of single spectrum measure ments and another to cover that of the mul tispectrum level measurement To access the menu press the M Setup key If you alter the high pass filter setting of the input selection menu this will cause
7. Lyl Flt sgl oT OPPEO 125 IZ say H B6 40 218 9 Nov 1997 1la 4hi22 Che nth To get the spectral weighting function shown as a reference spectrum To get the measured spectrum shown weighted with the spectral weighting function preweighting To get the level of the weighted spectrum indicated as a bargraph _ Load the reference files you need as Load the reference files you need as Load the reference files you need as described on the previous page spread if applicable Skip this point if you are going to utilise preprogrammed spectral weighting functions only Press 2nd D Setup to produce the Reierence CUE Sero KAn Reference Curve Setup Level There are up to Set a display described on the previous page spread if applicable Skip this point if you are going to utilise preprogrammed spectral weighting functions only Press D Setup to produce the Display Setup menu Display Setup Channel 41 Chi Y unit Preweighting Curves 1 4 SPL 2 3 Networks described on the previous page spread if applicable Skip this point if you are going to utilise preprogrammed spectral weighting functions only Press D Setup to produce the Display Setup menu Display Setup Channel Preveight ing Curves 1 2 1 Leq 3 2 Max Networks two ref Curves offset i e gain for available for each each curve Set it display window
8. Reverberation calculation Excitation type 2 Impulse Backward integration mode 1 On Minimum distance to noise floor dB in Time reversal tet All registers are cleared Sampling frequency f MLS sequence period length T 64 000 Hz 32 000 Hz 16 000 Hz 2 048 s 4 096 s 8 192 s 16 384 s 32 768 S 65 536 s For reverberation time calculations the impulse response generated by the MLS process may be reversed in time to enable measurements of very short reverberation times Set the shown parameter field to On to activate this feature and back to Off to deactivate it Note that switching to MLS mode causes the analyser to reset it self completely This means that the contents of all registers will be deleted upon entering MLS mode Saving the Broadband Impulse Response on Disk Save Name 844sich sdf Path ciN Type Ketin ti PEE Jirectories Files ool 12 sdf LeFiMu test 644sichl sdf LeFiMu j boktst 4 ref laiid cfg To save the impulse response waveform on disk do as when storing any file on disk but set the Type to 4 Imp Resp Displaying the Signal to noise Ratio Columns in the numerical table 1 J61 Leg 2 06 Off 3 ar M amis S N M 5 14 S N N 6 aa OS synchresi7e The only extras provided by the MLS extension is ability to display the apparent S N ratio with and without MLS The options appear in the numerical table setting in the display setup me
9. f Hz 2k f Hz 2k Switch to view the AVRG register and press RT key to begin calculating the reverberation time You may save your captured sound decays on the hard disk or a diskette Observe that you do not need to calculate the reverbera tion time before you save the decays the calculation can in principle be applied to any multispectrum measurement those just ac quired as well as those stored However calculations made on non decaying signals will not yield meaningful results There are restrictions on the lower limit of reverberation times if the decay is to steep you will instead measure the impulse re sponse of the filters In the Appendices section of this manual there is a set of tables listing the minimum reverberation times allowed If your analyser is equipped with the op tional Maximum Length Sequence MLS extension you may utilise this mode s time reversal option which opens up for calcula tions of even shorter reverberation time val ues Averaging and Viewing the Calculated Values Most applications of reverberation time RT calculations call for averaging to rule out lo cal phenomena not representative for the measurement site as such Basically you have two ways of creating av eraged RT values viz by averaging several decays and then calculate the RT values or by averaging several individual RT values Although either method may be used lead ing insti
10. from sound calibrators microphones amp preamplifers via small handheld sound level meters to advanced yet portable real time analysers but also spectrum shapers building acoustics analysers and complete community Find us on the World Wide Web industry and airport noise monitoring systems Contact your local representative or the factory for http www sol no norsonic information on our complete range of instrumentation
11. Only one input can be selected at the time per channel but the two channels need not be set to the same type of in put source One of the channels may be set to Off but both channels cannot be set to Off at the same time If you set one channel to Off in the in put source menu the corresponding part of the calibration menu will be blank Observe that if you select sound inten sity for one of the channels the other channel will be set to the same mode au tomatically since sound intensity is a two channel measurement technique If you then change the setting of one of the channels the other will go back to the setting it had at the time intensity was Selected A lowpass filter will be activated when 3 Charge is selected The menu contains a highpass filter for each channel If you activate the highpass filter it will affect the setting of the lowest frequency band to be measured This setting is found in the measure ment setup menu The new setting will be the first centre frequency above that of the highpass setting provided the initial setting was lower than or equal to the highpass fil ter is set to If it was set to a higher value initially it will remain unaffected Note that although the input selection is a global setting affecting the entire instrument and all modes only the cur rent mode single spectrum or multi spectrum will be affected by the forced change of lower end frequency range s
12. gt O o ED Input Setup lt g s 5 Chapter 11 127 Technical Specifications Technical Specifications Technical Specifications The below specifications apply to all new models Due to continuous technological advances older versions of the analyser may have specifications that are slightly inferior In particular the storage capacity the hard disk size the battery capacity and the analyser s ability to suppress any effects of mechanical shocks have been significantly improved on newer units ANALOGUE INPUTS Number of channels Two Nor 840 is also available in single channel version Microphone inputs two 7 pin LEMO connectors B amp K type JJ0723 on request Preamplifier voltage 120 V 3 mA to each preamplifier Polarisation voltage 0 28 or 200V selectable 1 Direct inputs two BNC connectors Charge inputs two TNC connectors Intensity Input 18 pin LEMO connector Maximum input signals 120 VPEAK all inputs except charge Input impedance 1 MQ 200 pF all inputs INPUT AMPLIFIERS Amplifier gain 40dB to 70dB in 5dB steps Additional gain 0 10 dB with accuracy and resolution 0 1 dB for calibration purposes Measurement range 0 03mV 100Vrms Corresponds to SPL values from 30dB to 160dB with a microphone sensitivity of 50mV Pa Amplification error Max 0 2dB 20Hz 12 5kHz Frequency range AC output 0 1Hz 50kHz within
13. Period number of the last period to be printed multisoectrum only Making a Screendump 1 I 0 Setup 1 B Off RS 232 Remote Baudrate IEEE Remote IEEE Address Printer port Printer type 1 Parallel Port 4 HP DeskJet Formf eed imi a Off Press the I O key 1 0 Setup 1 Baudrate RS 232 Remote Off 9600 IEEE Remote IEEE Address Printer port Baudrate Printer type 2 Serial Port 1 9688 4 Formf eed uo En Y uj nj os oj oO oO oO gt oO gt cal Ea baal a o Set the orinter type 1 0 Setup 1 R5 232 Remote Baudrate Off 9688 IEEE Remote IEEE Address Off Printer port Printer type 1 Parallel Port 4 HP DeskJet Formf eed wj nj off Set Printer port to the printer s port 1 0 Setup 1 R5 232 Remot Baudrate e OFF 9688 IEEE Remote IEEE Address off Printer port Baudrate Printer type 9600 HP DeskJet Formf eed a uo N on oO wj eo nj os 3 oj pk a Be a o J ES off Set the if need baud rate ed Press PLot to produce a screen dump Making a PCX File of the Screendump Setup 1 0 RS 232 Remote Baudrate Off E 9688 IEEE Remote IEEE Address Printer port Printer type E Of f
14. Save Make Dir About abctool 12 sdf LeFiMu 97824 970901 12 24 Ww boktest 84 sicO1 sdf LeFiMu 403718 970901 12 28 W buildini boktst 4 ref 988 971110 13 57 chdd laiid cfg 970731 09 45 futo File Gen 1 0n Template boktst Select Exit and press Enter to leave the menu or select Save if you want to start using the feature immediately hydro00 Your number series will start from OO The first file will be named hydro0o hydro This number series will also start from OO as no starting number was specified hydro2 Again your number series will start from 0O as no starting number was specified starting number must be preceded by six alohanumeric characters to be recognised as a Starting number However the first file will appear as hydro200 which is the file number 00 of hydro2 hydro50 Now your number series will appear as if it starts from 50 The first file will be named hydro50 as it will be file number O of hydro5d hydro134 This time your number series will start from 34 but it will appear as if it starts from 134 hydro1 is here the common part the first file will therefore be hydro 134 When you do spatial averaging and want to retain the individual results or you make several related measurements for exam ple on large machinery you may want to save the measurements using file names with a common part for easy identifica tion later The Nor 840 offers the feature of auto mated generati
15. The menu comes in two flavours one to cover the setup of single spectrum meas urements and another to cover that of the multispectrum level measurement To access the menu press the M Setup key If you alter the high pass filter setting of the input selection menu this will cause the lower setting on the frequency range to be changed if the initial setting was lower than that of the new high pass filter setting If it was set to a higher value initially it will remain unaffected You may change the lower end setting of the frequency range in the measurement setup menu after having set the high pass filter in the input menu However if you set the frequency range to include fre quency bands below the high pass filter setting the readings of these frequency bands will be biased because of the high pass filter Note that changing the high pass filter set ting affects the measurement setup menu of the selected mode single spectrum or multispectrum only Other modes will not be affected and may hence yield biased data to avoid inconsistencies As long as the highpass filters of the two channels are set to the same cut off fre quency their influence on residual inten sity will be insignificant Multispectrum measurements consist of a series of consecutive measurements re ferred to as periods All periods will have the same duration specified in the meas urement setup menu and there is no loss 72 of data i
16. USER DOCUMENTATION Nor 840 Real Time Analyser A dual channel real time analyser designed to meet the most stringent demands Alongside with the more traditional 4 and s octave band analysis the analyser can also do optional fractional narrow band octave analysis FFI sound inten sity measurements reverberation time calculations and measure ments using maximum length se quence The analyser has a bright colour 10 LCD screen and the operator ac cesses the setups using dedicated ep ee e a front panel keys to open logical eg ae ee menus All setups are selected us SS PS ing only single level menus so 7 E a i I S A ZZ AS A _ there is no need to navigate through i multilevel menus LF 7 SNS CE aon s gt e oe e cra 1 gt gt v Dn ooo Soo SoooSo VOLUME Using the Nor 840 NN Norsonic Using the Nor 840 June 1998 edition Using the Nor 840 June 1998 Edition Editor Gustav Bernhard Ese Dipl Ing Page Design GRID Strategisk Design Oslo Text and Layout Gustav Bernhard Ese Production Notes This manual was created elec tronically on the Microsoft Windows NT 4 0 Workstation platform using Adobe PageMaker 6 51 Artworks were made with Adobe PhotoShop 4 and FreeHand 8 Proofs were made on HP LaserJet 4M and 4MV PostScript printers RIP and final printout were made at Allkopi H vik Norway We us
17. dition once again has been met Copy Copy the contents of a register to another register leaving the source register contents intact The contents of the destination reg ister will be overwritten except when the destination is the Average register Ctrl The same as the corresponding key on an MS DOS PC Cursor Select the graph cursor as the function con trolled by the Drar and the Prev amp Next keys D Setup Produce the Display setup menu Note that there is a separate display setup menu for each measuring mode Del Delete characters to the right of cursor whilst editing in a string field Dial Scroll through the valid states or values of a parameter including the position of the graph cursor Also used in scroll lists When applied to cursor and graph functions the function to be controlled for example Y range must be selected first Disk Store or retrieve data and set ups to and from the floppy disk DOS Enter the MS DOS mode and run the Nor 840 as an IBM compatible PC Requires MS DOS extension installed Edit In numerical tables values may be edited by the user Edit is used to enter this function End Move to the end of a menu however not inside a list field Inside a list field it is used to go to the end of the list Enter Confirm settings and selections as well as exit to menus Esc As the corresponding MS DOS key but also to leave a menu ignoring und
18. 2ND 7 Home and 2ND 1 END The table is no more than a numeric repre sentation of the data so the Z cursor and cursor alignment works even here Editing in the Tables You may edit tabulated values except the Last register Transfer data to another register before editing To start editing go to the line to edit and press 2nD Aux Epit Selected position is then shown highlighted Use the numerical keypad to key in the new value Terminate by Enter or abort editing with Esc Use Dia PRev amp Next and the 2np 9 PeUP 2ND 3 PGDN 2nD 7 Home and 2np 1 END to move up and down in the table Use Field cursor those pointing horizontally to move between columns Press 2np Aux Epit to deactivate function A Tabulated Example Int Flt Sgl STOPPED FrqlHz2 Ieg dB 24048 250 315 co he W wu DeAnna A A A N WUWU N OaanNm Lw dB co A m U w Deme A Nn u A A AN WBBM OAanNm Leg dB 9 MOOMMWOMMOMNAMAhNee WM 46 15 7368 6 May 1996 46 35 49 PICdB When You Edit in the Tables it looks like this Frglhe J Legi dB W N Ww N OU OWU DNU AOR NBO O oN N Ieg 1 1 1 1 1 1 l 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 The Noise Generator in Sound Intensity Mode The Menu for this Task The noise type is 1 White raise type Z Pink 3 BP filtered Noise seq 4 mpulse Bandwidth 5 BP filtered impulse 8 Mul
19. 3a E Parallel Port 4 HP DeskJet Formf eed a Of f Press the I O key 1 0 Setup 1 RS 232 Remote Baudrate off 5 9688 IEEE Remote IEEE Address a off 38 Printer port Baudrate Printer type 2 Serial Port 1 E 9688 4 HP DeskJet Formf eed off Set Printer port to File Screen dumps always use form feed on irrespective of your setting Press PLorT to generate the PCX fil e Making Screendumps Graphical printouts are available in the form of screendumps screenshots output to a printer or to file for later import to other software programs The generated file will be in PCX format which is a format recognised by most PC software programs Generated files will be saved in C the root directory and their names will be 840_XXXX PCX in which Xis a number 0 9 If no such file existed in advance the first file will be named 840_0000 PCX the next will be named 840_0001 PCX and so on You may have removed some of the PCX files that you have made earlier Free slots will then be available and they will be used when storing new PCX files However existing files will not be overwritten Use MS DOS commands to move the file s to a more suitable location Making Numerical Printouts Numerical or tabulated printouts are gen ae Making Numerical Printouts erated in a way quite similar to the
20. Applies when loading The names of the files in The Automatic file setups only the selected directory guessing feature will when activated propose the next file to be retrieved based on an alphabetic sorting of the file names Retrieving Stored Data Press HDD to enter the Load menu Select the file to be retrieved Use the About function if needed Select Load and press Enter or just press Enter from the Files scroll list When you retrieve stored measurements from the disk they are automatically trans ferred to the Aux register of the mode in which the measurement was originally made The analyser will switch to this mode and display the contents of this mode s Aux register Observe that the dis play settings of the analyser will be ap plied to the retrieved file This will include such things as the displayed functions which may cause your display to appear without graph if the display was set to dis play functions not contained in the re trieved file or if there is a severe mismatch between the retrieved levels and the cur rent top scale setting For FFT a beam finder feature is available see the FFT section of this manual for details Automatic File Guessing If you are going to retrieve several files one after the other you may set the ana lyser to suggest the next file to be retrieved This is achieved by setting the Auto File Guess to On in the Load menu The file proposed will be the next fi
21. DOS key 123 Duration lower limit level mode 17 Duration of measurement setting up in level mode 16 E Edit key 123 End key 123 Energy Spectral Density FFT mode 56 Enter key 124 Esc key 124 ESD FFT mode 56 Exponential window functions FFT mode 44 Export of data for spreadsheet use 119 Extended help level 8 level of on line help 8 Extensions installed displaying a list of 3 F F keys 124 Fast Fourier Transform See FFT FFT 42 auto correlation 53 averages indication of the number of 55 beam finder 58 calibration 48 cross correlation 53 cursor alignment 58 cursor functions 58 cursor icons 59 determinstic signals 56 differentiation of spectrum 57 display modes 54 displaying the weighted time function 57 displaying the window function 57 finding the graph 58 flattening the spectrum 57 frequency spans available 53 fundamentals 42 graduation cursor func tions 58 graduation range 59 harmonic cursor 59 integration factor 57 integration of spectrum 57 locating the graph 58 master cursor 58 noise generator 61 random signals 56 reference cursor 59 scaling cursor functions 58 scaling range 59 scaling the vertical axis 56 setting the full scale 47 setting up for zoom 53 slave cursor 58 spectral density 56 transient signals 56 trigger conditions 50 vertical axis scaling 56 Y axis scaling 56 zero pad 53 zoom 45 time spacing 45 using 45 FFT key 124 Field Selector keys 124 Fil
22. Define the setup position type of delimiter and the left margin Exit the menu Exporting Data for Spreadsheet Use 00 06 458 7 Jan 1998 12 15 53 1 Lvl Flt 5gl READY 13 1V x 9 5 2 0 8 8 31 5 125 508 fLH2 1 80 1 3 oct 1 8s F 5 Hz SkHz Trig Manual Cont End 0 00 08 Inpl Microphone Call 26 0 dBl 2 HP 1 q fInp2 Cal2 26 4 4adB2 2 ist HP2 63Hz 2 6 6 08 31 5 125 580 2k 0 5 f Hz 1 88 Set as active window t he window whose data are to be exported Directories Files 1 0 Setup 1 In the I O R5 232 Remote E Of f Baudrate 5 9600 setup IEEE Remote por menu set IEEE Address 2a Printer port Printer port 2 Serial Port 1 N Baudrate E 9688 to File Formf eed a off O Print to File Name l Print Path c Exit Mask trt Exporting Data for Spreadsheet Use Display Setup In the Display Channel 81 Chi v unit ke setup menu set mamans bea the Displayed col umns to display the functions needed for your spreadsheet 1 04 SPL 2 81 Leq 3 02 Max Ss 1 81 Lin 2 82 A 3 00 Off Columns in the numerical table 1 REET 2 a3 Min 3 02 Max 4 aa Off 5 aa off 6 aa Off Synchronize O Setup 4 Print Setup
23. This discontinuity is very steep and will appear as false frequency components and or incorrect levels in parts of the spectrum False and incorrect in relation to the signal itself of course there is nothing false about the process as such There is one way to avoid this and that is to ensure that the two extremes of the time buffer always have identical values The easiest value is 0 zero Therefore we force the value to become zero in both extremes of the time buffer By doing it gradually and smoothly we ensure that no abrupt transitions are in troduced This means that we put more emphasis or weight on some parts of the time buffer the middle part and less on oth ers the extremes The technique is therefore often referred to as time weighting or windowing If the signal contained in the time buffer is shorter than the buffer length no weighting will be needed To enter FFT mode press the FFT key There is no multisoectrum mode for FFT measurements The auto spectrum is calculated from the spectrum and its complex conjugate Im X f We use the two auto spectra and the cross spectrum to obtain the frequency response of the system In this way the phase relationship is maintained see text for details The time buffer is considered as one period of a periodic signal If the two extremes are not identical in amplitude a discontinuity not present in the input signal is created when the time buf
24. Whenever using microphones set the input source selection to Microphone Full scale setting is used to set the input am plifier gain so that you get the optimum use of the analyser s dynamic range Calibration is needed to ascertain that the values measured are accurate enough to serve their purpose Measurement mode selection refers to the selection between single spectrum and mul tispectrum measurements given that you already did select Level Measurement parameter settings are used to define the time constant the frequency range which functions to measure and the measurement duration For multispectrum measurements the number of periods the number of consecutive measurements should also be defined Trigger condition settings are used to define the start conditions of the measurement Should it start when hitting the Starr key Or should it start when the level exceeds a given threshold At a given moment in time Wii Should there be any delay from trigger un til the measurement actually starts Alto gether you have nine trigger condition al ternatives at your disposal To begin measuring press the Start key The data acquisition will then start as soon as the trigger condition is met and go on until the preset measurement time expires if left uninterrupted Pause You may pause the instrument at any instant during the measurement Press CONT to resume Prolong You may prolong a measurement if
25. extrapolate the results to 60 dB In the Nor 840 we specify the actual decay range over which the measurement took place by the annotation T and T An ideal sound decay will form a straight line when drawn in a coordinate system with logarithmic axes In reality however sound decays will always contain fluctuations Two problems will then immediately arise viz how to have the analyser accurately deter mine the initial level and when to start the calculation Noise Excitation With noise excitation the calculation starts at 5 dB below the mean level i e the La of the noise measured at the microphone po sition before the noise is switched off As long as the noise stays below this 5 dB line the L in the Fig the time elapsed is counted Once the level drops below a sec ond line the L in the Fig the counting is discontinued Should the level for any rea son again exceed the second line the count ing will be resumed and go on until the level once again drops below this line Likewise should the level exceed the first line any time after counting has started the counting will be discontinued until the level once again drops below this line 36 E The second line will be 25 dB below the ini tial level for T measurements and 35 dB below for T measurements leaving a meas urement range of 20 and 30 dB respectively To reduce the influence of fluctuations at the start and the end of the tim
26. most important part of this manual because it explains all the fundamentals from trans ducer connections and battery handling to the principles of menu handling and param eter setup Consequently if you are going to read just one section in this manual before you start using the analyser we strongly recommend that this should be the Getting Started sec tion The rest of the manual can then be consulted whenever required Observe the analyser s built in on line help function For each parameter field there is an associated help box This context sensi tive box is produced by pressing the HELP key and contains the valid ranges for the parameter together with a short description of its function Our main objective with this manual was to address your goals and needs Please let us know how well we succeeded NN imi Contents ooo co JIi FENN N 10 11 12 il 14 16 18 20 21 22 24 25 26 28 28 28 30 30 30 30 3l l 32 33 Getting Started Connecting Transducers Basic Concepts On the Use of the Menus Batteries Charging the Batteries The Battery Capacity Indicator Using the Menus Getting On line Help Making Level Measurements Level Mode Fundamentals Single Spectrum vs Multispectrum Selecting Input Source for Level Mode Measurements Full Scale Setting Calibrating for Level Mode Measure ments The Level Mode Measurement Setup Menus Trigger Conditions in Leve
27. sen maximum frequency the fax The reso lution of the spectrum is determined by the size of the transform i e the number of sam ples used to describe the time signal The Nor 840 has a 2048 samples time buffer which gives 1024 frequency lines evenly dis tributed over the range from 0 to the sam pling frequency Out of these 1024 lines we end up using 801 lines only since those af fected by the anti aliasing filter must be dis carded To be precise we use 800 lines 1 for DC In normal operation the DC is not used since the inputs of the Nor 840 are AC coupled but when zooming you will get 400 lines on each side of the zoom centre fre quency The line spacing is then given by Af f ax 800 or Af f 1024 sampling This leaves us with only one option if we want to increase the resolution correspond ing to a reduction of the Af and that is to increase the size of the transform However if we make a sacrifice we can still increase the resolution without increasing the transform We may increase the fre quency resolution but only within a corre spondingly smaller part of the original fre quency range at a time This is called zoom FFT What we actually do is that we shift by het erodyning and then low pass filter the part of the frequency range that we are going to look at more closely This means that the desired part of the spectrum hereinafter referred to as AF is shifted down in fre qu
28. the initial duration proved insufficient Merge You may merge the two channels of a dual channel measurement into a single channel measurement This feature is often used to save time when making measure ments involving spatial averaging Averaging In order to reduce the influence of extraneous noise measurements are of ten averaged together We have even in cluded an undo average function in case you make an average too much Serial analysis A multitude of real time ana lysers on the market have for some strange reason unknown to us been made without the ability to make serial frequency analysis From time to time you will prob ably encounter situations where an excita tion signal is needed but the source turns out be incapable of generating a sufficiently high output level However if you bandlimit the output signal you will normally be able to obtain an output with a higher level This can only be utilised if your analyser can do serial analysis i e one frequency band at the time The Nor 840 can do serial analy sis in manual as well as in automated scan ning mode All measurements made with the Nor 840 are either single spectrum or multi spectrum measurements irrespective of the measurement mode in which the measurement was made A multispectrum measurement is a record ing of successive measurements all hav ing the same duration The successive measurements are referred to as per
29. the lower setting on the frequency range to be changed if the initial setting was lower than that of the new high pass filter setting If it was set to a higher value initially it will remain unaffected You may change the lower end setting of the frequency range in the measurement setup menu after having set the high pass filter in the input menu However if you set the fre quency range to include frequency bands below the high pass filter setting the read ings of these frequency bands will be biased because of the high pass filter Note that changing the high pass filter set ting affects the measurement setup menu of the selected mode single spectrum or mul tispectrum only Other modes will not be affected and may hence yield biased data to avoid inconsistencies Multispectrum measurements consist of a series of consecutive measurements referred to as periods All periods will have the same duration specified in the measurement setup menu and there is no loss of data in between the periods You may set up your Nor 840 to capture the time profile of what goes on immediately before the trigger condition is met This is done by specifying that a certain number of 16 B the multispectrum periods shall apply to the situation before trigger Although this may sound like a violation of the causality requirement a brief look into how it is done will reveal that causality is indeed maintained Having set up for
30. two graphs with or without essential setup information A numerical listing of the acquired data may be substituted for any of the graphs to pro vide a tabulation of the results The two display halves referred to as the upper and lower windows respectively are completely independent of each other and may be set to show two unrelated functions or measurements if required However the two graphs must have been made in the same measurement mode e g FFT When Using the Menus Several Keys Apply in Addition to the Numerical Keypad DIAL turn clockwise to Use this key to move to the left Use this key to move up increase the value and counter clockwise to decrease PRev ious _ ete CURSORS T Use this key 10 move to the right key move one step towards lower values Use this key to move down Next key move one step towards higher values nth Connecting Microphones amp Transducers to the Analyser Assembling the Microphone System Microphone heating Polarisation voltage Sound intensity ee socket ae Line input Line input Channel 2 inputs Channel 1 inputs pale o M Always screw the microphone cartridge onto the preamplifier before you connect the preamplifier to the analyser Accelerometer Accelerometer The analyser can also l a input input be delivered with B amp K Screw only finger tight type connectors Micro
31. works as it is Supposed to do Bearing in mind that the microphone itself is the most vulnerable part of the measurement chain this method obviously suffers from severe shortcomings Auto calibration Using a Sound Calibrator Insert microphone into calibrator Input selection Channel 1 Source 2 Microphone Channel 2 Source 3 Charge LP filter a off HP filter E 2 Hz HP filter 2 2 Hz Fullscale channel 1 Fullscale ee dB 2 00e 00 Calibration Channel 1 Microphone Sens Level 25 7 39 1 Unit dB E dB 2 08e 85 ae Calibrate Channel 2 Microphone Sens Level 27 3 0 4 Unit dB E dB 2 08e 85 Autocal 114 3 Calibrate Cal freq Pol Volt 280 Calibration Channel 1 Microphone Sens 25 7 Unit i Level 6 8 dB 2 e 85 Calibrate Channel 2 Microphone Sens Level 27 3 2 3 Unit dB 1 dB 2 08e 5 Autocal 114 8 Calibrate Cal freq ik Pol Volt 200 Calibration Channel 1 Microphone Sens 25 7 Level 6 8 Unit dB 1 dB 2 0 e 85 futocal Channel 2 Microphone Sens Level 27 3 2 3 Unit dB 1 dB 2 08e 85 Autocal 114 8 Calibrate Cal freq ik Pol Volt 200 P
32. 0 31 5 f Hz 77 18 D Creating Spectral Weighting Functions from Measurements Creating a spectral weighting function from a measurement Select the register In the display setup in which the menu Saleen iie measurement or the aa EE function whose retrieved file Y unit L spectrum is to serve resides EU T ie as spectral weighting Preweighting aa off Curves Example Last or function Aux register etwarks This is done by ea St ee I selecting this Columns in the numerical table function as the One Bei leo e pii 2 Max to appear in column 4 aa Off 5100 Off 6 faa ofr 4 in the numerical i Synchronize D Setup table see also the Tip below Press Cory HDD Set Type to Reference Save Name Name jboktst 4 ref Path c networks Path c networks Mask Mask T Type fi Measurement Type Directories Files Directories 782 940418 15 23 5453 960821 14 37 1972 940418 15 23 10731 960821 14 37 578 940602 09 34 5008 960821 14 37 1408 940602 09 36 sumf_24 ref 9854 960821 14 37 82 Hels futo File Gen Auto File Gen 1 On Template boktst Template j boktst Proceed as when storing measurements on disk Tip for power users Once your measurement has been made and the display setup menu has been set up with the function you want just p
33. 0 5dB 0 05Hz 100kHz within 3dB High Pass filters 3dB 3 pole Butterworth set at 0 5Hz or 16Hz all inputs Low Pass filter 3dB 3 pole Butterworth selectable at 2 kHz charge inputs only Hum and Noise Microphone inputs Measured with preamplifier type 1201 and 18 pF microphone equivalent FSD 50dB calibration 26 0dB re 1V HP filter set to 0 5Hz 0 8 5Hz lt 20dB 6 3 20Hz lt 12dB 25 100Hz lt 7dB 125 315Hz lt 0dB 400 3150Hz lt 4dB 4 20kHz lt 0dB Lin network lt 15dB A network lt 10dB Hum and Noise Line inputs Measured with Line input short circuited to ground FSD 50dB HP filter set to OFF calibration 26 0dB re 1V 0 1 25Hz lt 30dB 31 5 100Hz lt 25dB 125 400Hz lt 20dB 500 1600Hz lt 15dB 2 5kHz lt 10dB 6 3 20kHz lt 5dB Lin network lt 3dB A network lt 0dB Hum and Noise Charge inputs Measured with alnF capacitor connected to the Charge input HP filter set to OFF Calibration 240dB re 1V implying that 180dB 1nC FSD 140dB 0 1 250Hz lt 5 6x10 C 315 1250Hz lt 7x10 C 1 6 10kHz lt 18x107 C 12 5 20kHz lt 32x107 C Lin network lt 100x10 C A network lt 100x106 C ANALOGUE OUTPUTS Wideband outputs two BNC connec tors The output signal comes directly from the input amplifiers Output level 10Vpeak 1 0Vrms corresponds to full scale deflection on display Outputs are short circuit proof to gro
34. 13 2V 6 00 88 088 26 Sep 1997 13 18 43 Yeu 173 act 1 88 F 16Hz 16kH2 0 5 2 6 8 8 31 5 125 588 2k 8k LA IA f Hz J 88 an indication is provided nth Calibration Using a Sound Calibrator Insert BE opoe Input selection Channel 1 Source 2 Microphone Channel 2 Source 3 Charge LP filter Off HP filter E 2 Hz HP filter 2 2 Hz Fullscale channel 1 Fullscale dB 4 Calibration Channel 1 Microphone Sens Level 25 7 39 1 Unit BdB 1 dB 2 88e 85 ji 114 0 Calibrate Channel 2 Microphone Sens Level 27 3 0 4 Unit dB 2 8 e 85 i TE 114 6 Calibrate Cal freq Pol Volt 280 Calibration into calibrator Press Input and select input source Adjust the full scale setting GAIN1T GAIN2 Press Cat and set the calibrator frequency Set the sensitivity of the microphone used until the sound pressure level is indicated correctly Calibration Setting the Sensitivity Input selection Channel 1 Source 2 Microphone Channel 2 Source 3 Charge LP filter 0 Off HP filter 2 20Hz HP filter 2 20Hz Calibration Channel 1 Microphone Sens
35. 4 Haik information used to acquire the measurement surrounded by the thick frame The register whose contents is displayed Title field lower display window The graph cursor Time profile period number Spectral weighting bargraphs multispectrum measurements only If you set the full scale deflection to one of the three highest settings a small x will warn you that the analyser is prone to overload The Sound Intensity Mode Display Setup Menu This setup menu controls the type of func tions values measured e g leq or Imax to be displayed the scaling of the axes and the layout of the numerical table There is one setup menu for each display window and one set of setup menus for the single spectrum mode and another for the multispectrum mode i e one set of two menus for each mode These two sets of setup menus are com pletely independent of each other while you can copy the display setup of the up per window to the lower window and vice versa you cannot copy between the sin gle spectrum and the multispectrum modes Press D Setup to produce the Display Setup menu Displayed Curves The sound intensity is shown on a bipolar basis For convenience the origin will be suppressed when a combination of Y range and Y max does not allow the origin to be included Similarly a very low Y max set ting may set the vertical datum the lower end of the scale to a value below O dB You may also set the ana
36. T xX Hz 1000 00 1000 dB Auto spectrum 16 8 18 0 63H2 30 8 AT 12508 09 X Hz 1000 00 Dual display without setup information Lv1l FFT Sgl STOPPED 13 1 685 7 Oct 1997 12 46 36 dB Chi LAST 125 paftute spectrum Y 85 0 185 84 85 04 65 684 45 0 9 og 15625 00 F XLHz 1900 00 JB 38 8 Auto spectrum 16 8 18 8 30 8 T 15625 00 X Hz 1000 00 a numerical printout dB Ch2 LAST 30 0 futo spectrum ya Sia ri 1 2Z2OD DEV 50 0 0 00 15625 08 XIHzl 1000 0 Single display active window with condensed setup information Lvl FFT Sgl STOPPED 13 1 685 7 Oct 1997 12 46 28 8Hz 25888 GHz Input Cal dB HP Line 26 8 2 48e 85 2 Hz Line 26 0 2 00e 05 63Hz Trig Amplitude End 18000 Ch1 Ch2 dB Ch2 LAST 30 0 Auto spectrum Veo asics rar ZoD DEV 758 85 a0 15625 08 E X Hz 1000 00 Note The data of the active window will be the only set of data printed out when you make nth Function displayed Measurement mode Vertical axis scaling unit Full scale setting is higher than present top scale setting Top scale setting Selected cursor function Full scale setting is higher than present top scale setting Selected cursor
37. Top scale 13 vs full scale 13 Top scale value changing the 40 Top off charging of the battery 5 Transducers connecting to the analyser 2 sockets 2 Transfer functions for sinusoidal signals FFT mode 42 Transient signals FFT mode 56 Trig key 126 Trigger conditions FFT mode 50 intensity FFT mode 77 fractional octave mode 74 intensity mode 74 level mode 18 Two microphone probe for sound intensity meas urements 65 Type key 126 U Undo average level mode 22 Upper frequency level mode 16 User key 126 User register 106 User defined window func tions FFT mode 44 V Values to record multispectrum level mode 17 Velocity based probe for sound intensity measurements 65 Vertical axis scaling FFT mode 56 intensity mode 82 level mode 28 Vertical graduation changing the 40 Voltage indication battery 5 W W1 8 used in spectral weighting functions 101 Weighted time function FFT mode 57 Weighting functions applied to sound decays 37 creating your own 98 White noise setting noise generator V1 S level mode 33 Whole body spectral weighting network Window 3 Window function displaying 57 Window functions proper use of FFT mode 44 X X axis scaling FFT mode 57 X min key 126 Y Y axis scaling FFT mode 56 Y max key 126 Y range key 126 Z Z axis cursor intensity mode 84 level mode 30 Z cursor 2nd Cursor key 126 Zero pad FFT mode 53 Zero pad setting Intensity FFT mode 76 Zoom FF
38. Vie and 24 Oci bands Lower and upper end of the frequency bands to be measured Measurement Setup Measurement pe Turns the serial measurement on or off Good for situations with high background noise and for retakes of certain frequency bands Measurement duration Lower limit 10 ms amp 1 oct bands 20 ms 1 2 oct bands 40 ms oct bands Upper limit is 100 hours when specifying 99h 59m 59s 1000ms Optional must be ordered separately nth The Multispectrum Measurement Setup Menu is an just extension of the single spectrum setup menu Number of periods to be measured Lower limit is bandwidth dependent see the Note on this page Upper limit is as for single spectrum This is now the period length not the total duration Number of periods before trigger Time constant Bandwidth Lower frequenc Serial measurement periods periods b trigger Max of periods Total time Values to Leq record Min SEL Up to six functions can be logged as L t Options The max are On Off No of periods available The total depends on measurement the amount duration is calculated of free for you as the product memory of the No of periods available and the period length In multispectrum mode the Nor 840 can be set up to record a number of spectra before trigger When you have set up the Nor 840 to recor
39. also X axis spanwidth Harmonic cursor is not operating in fractional octave modes Z Setup Cursor alignment Reference cursor Step one step towards higher values Note that the Y axis is left unaffected by this swopping since the level in both cases will be the same RMS or Peak values always in dB To move along the X axis irrespective of whether this represents time or frequency press CURSOR and then use the DIAL or the Prev amp Next keys To move in the Z direction again irrespec tive of what it represents press 2ND CURSOR and do as for cursor movements along the X axis A small icon in the display will indi cate that Z cursor is selected 3D Cursor Functions Measured data acquired in multispectrum mode may also be displayed as a three di mensional graph For obvious reasons this feature does not apply to the single spec trum mode To activate this feature make a multi spectrum measurement set the column 1 of the Displayed curves in the Display Setup menu to one of the functions actually meas ured and press the 2ND LF LT keys If you fail to set up a function actually meas ured all you Il see will be an empty floor and no graph The graph is always drawn so that the peri ods most recently acquired appear to be clos est to you Use the Lr Lr to flip the X and Z axis Whilst the graph is being drawn the Tyre key is used to select the next display type The CuRSOR with or
40. built in hard disk drive must be ordered separately The storing procedure treats hard disk and floppy disk as variations on the same theme The advantage of this is that the hard disk and the floppy disk then both are treated as external storage media If for example your analyser is hooked up to a LAN Local Area Network such as a Novell or NT Server network together with other computers you will normally have access to several hard disks in addition to those in your analyser All these disks will then appear as disks available for storing and retrieving alongside with the built in ones and they are all treated in the same way If the measurement has been given a title the eight first characters ignoring any spaces will be suggested as file name The File Extension sdf Regardless of what extension name you append to a measurement file it will automatically be replaced by sdf This means that even if you specify no extension at all the sdf extension will still be appended by the analyser This is done to make measurement files easier to locate upon file retrieval Saving a Measurement on Any Disk Select the register where the data currently reside for example the Average register press AVERAGE to select this register Save Name boktst4 sdf Save Path c Exit Mask R Make Dir Type k Measurement Pbout Directories Files 12 sdf LeFiMu 97824 970901 12 24 N 84 sic l sdf LeFiMu 403718
41. ch 2 The type of function displayed will be given by what you have specified in column 1 of the Columns in the numerical table field of the Display Setup menu Should Column 1 be set to 0 Off the ana lyser will search for the first activated func tion and use that for the two curves in stead The A and Linear spectral weighting networks are true spectral weighting functions in the sense that they are separate measurement filter bands All other spectral weighting functions are applied as postprocessing features only This means that if you synthesise e g a B weighting curve and fail to apply a full bandwidth to your measurement by measuring 50 3150Hz only for example the B weighted values will normally deviate from those obtained with a true spectral weighting filter band The only way to make them similar is to apply your function to measurements When applying spectral weighting functions other than A and Linear see above the term maximum values become meaningless since we have no information on when Tip using a full bandwidth Tip the maximum level occurred Tip Numerical tabulated printouts will contain the functions set active in the numerical table part of the Display setup menu only Make sure that the functions here are functions measured otherwise your printout will contain one or more empty columns nth The Menu for this Task there is one independent menu for each of the two display
42. default is activated it also controls the trigger condi tion setting and the range of frequency bands activated Minimising Background Noise You may specify a signal to noise ratio re quirement for your measurement to mini mise any possible influence from the back ground noise level This is called the minimum distance to the noise floor and serves to avoid that a sudden increase in the background noise level causes the reverberation time to seem longer than it actually is If the minimum distance to noise floor re quirement has been violated a warning will be produced In the numerical table a will appear next to every frequency band af fected The minimum distance to the noise floor can be set to anything in the range 0 30dB both extremes included Resolution is 0 1 dB Although some International Standards such as the ISO 60 354 requires a minimum distance of 15 dB a fairly tough requirement actually a minimum distance of 5 to 10 dB will suffice in most cases Default setting is 5 dB nth Noise Excitation Impulse Excitation Weighting function Weighting function A triangular weighting function is applied to the the counting of time elapsed to minimise the effect of fluctuations in the extremes Some Vital Terminology Start of calculation L UUWI YI End of calculation Minimum distance to noise floor Hmann An OSN LAL 2 o waa so Background noise level noi
43. following we are always referring to the contents of time buffers Auto Spectrum It can be shown that the spectrum cal culated will be complex i e it will con 42 tain real and imaginary values This is just a function of the moment of obser vation Let X f be the complex spectrum of the signal x t and X f its complex conju gate The product G f X f x X will then be real maintaining the am plitude the length of the complex vec tor of the X f We have thus obtained a signal whose amplitude is independ ent of the moment of observation This spectrum the G f is called the auto spectrum of the x t Cross Spectrum Let x t and y t denote the two input signals to a dual channel FFT analyser Let X f and Y f denote the correspond ing spectra The product G f X x Y is then called the cross spectrum of x t and y t By taking the complex conju gate of one of the two the only phase information present will be the phase difference between the two signals Again we have escaped the dependence of the moment of observation Frequency Response Functions Assume that we have a system with one input and one output Let x t denote the input time signal y t the output time signal and X f and Y f the correspond ing spectra The following relationship exists Y H x X in which H f stands for the frequency response function the transfer function for
44. function 56 0 A ae Displayed channel s Measurement status Battery voltage No of averages made Graph value level at cursor position Date and time of day Lv1 FFT So8 STOPPED 131 1V a65 7 Oct 1997 12 42 13 Ue field upper Aut t y eer If the two time weighting windows function are not set to the same this setting appears in reverse video gt Amplitude Continuous Measurement setup information used to acquire the measurement i Auto spectrum ete surrounded by the thick frame H HE xs Hz J 166e 44 The register whose content is displayed Title field lower display window H SEOD 12506 A EN The graph cursor Graph cursor position Highest frequency displayed Scaling unit for the spectrum displayed If you set the full scale deflection to one of the three highest settings Hz 1864 84 a small x will warn you that the analyser is prone to overload The FFT Mode Display Setup Menu This setup menu controls how the acquired data are to be displayed There is one setup menu for each display window he two are completely independ ent of each other You can however copy the display setup for one of the windows to the other by the click of a button the same way as you do in fractional octave band mode Pres D Setup to produce the display setup menu A Few Words on Functions Some of the functions available are based on single channel measurements while
45. functions other than A and Linear see above the term maximum values become meaningless since we have no information on when Tip using a full bandwidth Tip the maximum level occurred Tip Numerical tabulated printouts will contain the functions set active in the numerical table part of the Display setup menu only Make sure that the functions here are functions measured otherwise your printout will contain one or more empty columns nth The Menu for this Task there is one independent menu for each of the two display windows Up to three set of curves graphs may be shown simultaneously Which functions to show is defined here Choose between Off Leg leq Lw Seo SUL Pl In multisoectrum mode only the functions actually recorded will provide graphs There are up to four bargraphs located to the right of the spectrum in the display Select which ones to appear among A Lin SumAT SumB SumC SumL or W1 W8 The contents of the numerical table is determined by the setup of these parameter fields Both the numerical display and the numerical output printout is affected by this setup The options to select from are the same as those applying to the displayed curves plus N Leq and N leq Display Setup Time cursor Preweighting Curves synchronize XO Setup W1 W8 denotes the spectral weighting function you can make yourself either by keying in the gain attenuatio
46. in dB or absolute Select the spectral units as you like weighting Changing one will change the other Synchronize O Setup Synchronize O Setup functions to be used as reference accordingly curves Example shows W1 and W3 Exit the menu Set Preweighting to the spectral weighting function required Example shows W3 Exit the menu Set any number of the networks to the spectral weighting functions required up to four simultaneously Exit the menu Chapter 8 106 Memory Handling Fundamentals 108 Storing a Measurement on Disk 109 Autonumbering Files Stored Consecutively 110 Disk Handling Tools 111 Retrieving Stored Measurements 112 Storing Instrument Setups 113 Retrieving Instrument Setups Memory Handling Memory Handling Fundamentals The Nor 840 can store measured data as well as measurement setups A fully equipped Nor 840 has four registers and two external although built in storage media For simplicity we refer to all these as memory locations The registers are called Last Average Aux and User while the storage media are the floppy disk and the optional hard disk There is one set of registers for each meas urement mode of the analyser as shown to the right The registers are not nonvolatile i e their contents are not retained if the ana lyser is switched off The following restrictions apply e The Last register is reserv
47. input amplifiers However it has no influence on the vertical scale in the display The two extremes top and bottom of the vertical scale is control led by the top scale value which has its own dedicated key called the Y Max key The top scale setting is purely a display function having nothing to do with the input amplifier whatsoever Full Scale Setting If you are uncertain about which gain setting to use there is an autoranging feature available The autoranging is separate for each channel and is activated by pressing 2ND GAIN1 GAIN2 Once activated the instrument will set the full scale to maximum and wait for three seconds to let the analogue cir cuitry settle The analyser will then measure the SPL twenty times at 100 msec intervals Five decibels will be added to the highest SPL detected and the result will be rounded off upwards to the nearest standard gain setting Note that if you set the full scale setting to avery high value you face the risk of having severe overload in the transduc ers without seeing any trace of it in the analyser simply because the analyser input isn t overloaded For example a 1 2 microphone with a sensitivity of 5 0mV Pa will distort severely more than 3 total harmonic distortion when exposed to levels above 135 dB A To warn you about this the three highest settings provide an asterisk in the display Calibrating for Level Mode Measurements The Nor 8
48. is met you may set up the analyser to do so How ever this applies to multispectrum measurements only and it is not done in the trigger setup menu but in the mul tispectrum measurement setup menu The trigger condition menu is accessed by pressing 2ND START The nine trigger conditions available and how they work can be seen on the right part of this page spread The Menu for this Task The condition for trigger Trigger Setup Trigger condition KARIERE Trigger type Trigger delay Insert a delay from trigger condition is fulfilled until the measurement actually starts Options are 0 60 000ms Not used in this version If you select Clock as trigger condition extra parameter fields will appear Trigger condi Trigger type Trigger delay Trigger Setup tion KEHAS Mate M D H M 5 ms If you select level related trigger conditions extra parameter fields will appear Trigger Setup Trigger condition PIRES esa Jas e Jre ot om Trigger tupe Trigger Setup Trigger condition PEHA S A S ea Jas k Jre pr on e Trigger delay Trigger Setup Trigger condition ESASTAN ena Jas k Je are or Trigger type Trigger delay Trigger Setup Trigger condition EE RMII ST aRtslsteer ena Je Te Je ar chi Trigger tupe Trigger delay ms nth Manual as trigger condition Level exceeds as trigger condition Level above as t
49. just press the Pause or the Stop key To resume measuring press the Cont key If the measurement was halted prematurely paused pressing Cont will cause the in strument to resume the measurement and go on until the preset measurement dura tion expires On the other hand if the Cont key is pressed after a measurement has ended successfully i e the preset duration has expired the measurement will be prolonged by a another period equal to the preset duration In the latter case the total duration will be the sum of the two durations provided the measurement was not terminated prema turely during the prolongation The Tools for this Task amp gt t2 F l Page Up 10 M Home Cy a N 10 E3 3D O End age Dn nsert 2 Tee P DUE Display Enter Z curs V Y Z Setup ieva meme FFT f amp Trig u S Setup U Set ae A lt Control 7 Control 4 Q W Harm Autoseq oa The measurement control keys Pressing Causes Start Pause Stop Cont Cont after the measurement end condition is met the measurement to begin as soon as the trigger condition is met an ongoing measurement to be temporarily halted an ongoing measurement to be terminated the measurement to be resumed If left uninterrupted the measurement will then go on until the measurement end condition is met the measurement to be resumed If left unin
50. master will go on until it reaches its extreme end To spot when this occurs watch the period number in each display window If the cursor alignment was active at the time you stored a setup file a cfg file and you put this on a floppy disk naming the file 840 cfg Iinitialising the analyser with this floppy will cause the cursor alignment function to be set active as a part of the initialisation Tip Do not confuse top scale and full scale The top scale is purely a display control More 3D If the X axis represents the frequency the Z axis will represent the time and vice versa Use LF LT to Swop indicating the top of the vertical axis while the full scale controls the input amplifier gain settings Changing the latter will delete the Last register contents Scaling and Graduation Range Y axis 20 40 60 80 or 100 dB across the vertical scale or in a 1 2 5 sequence when set to engineering units KeaaxiS Se 14 lee i 2 1 4 amp 1 ane S T applies to time displays only not the fractional octave spectrum displays The Numerical Table Data measured or retrieved can be shown either as graphs or tabulated To switch e tween these two ways of presenting the data press the Num key The contents of the table is determined by the Display Setup menu You navigate in the table by means of the DIAL Prev amp Next and the 2ND 9 PGUP 2ND 3 PGDN 2ND 7 Home and 2NpD 1 END The table is no more
51. multiple spectra as meas urement mode Size Not supported in this version Start Start a measurement The data acquisition will not start until the preset trigger condi tion has been met Stop Stop an ongoing measurement Resume by pressing CONT Tab Applies to MS DOS mode Title Key in a measurement title up to 10 lines 40 characters each Trig Access the Trigger condition menu Type Switch between different display modes User Provides access to the User register X min Select the left most point of the horizontal axis as the function controlled by the DIAL and the Prev amp Next keys Y max Y range Z cursor 2nd Cursor Select the vertical axis top scale value asthe Select the vertical axis range as the function Select the graph cursor of the time axis when function controlled by the Diar and the Prev controlled by the Drar and the Prev amp Next displaying the frequency spectrum and of the amp Next keys keys frequency axis when displaying a time his tory profile The selection will be a function controlled by the Dral and the Prev amp Next keys Applies to multispectrum mode only Move Cc Page Up 10 Setup lt AvLa D G setup J etup gt N 0 5 seooo O ize E It H 3D O Insert etup B000 GG gt 005 Memory Display Enter Z curs ez Z E gt Control i Control Trig T Analyse PIR O Te ca Setup U Record EB easuremen Control i l gt c O
52. multispectrum mode we calculate short time Leq values as usual from the impulse response as if it were a regular impulse measured by the analyser in conventional multispectrum mode Therefore the MLS extension acts as a shell on the top of the rest of the analyser The rest of the analyser is happily ignorant about how the signal measured was generated The Fig above shows an impulse example the impulse has been squared and converted to the dB domain A noise density can be determined from the background noise measured between t and t Since the noise density is the same all along the time axis we are now able to de termine the noise contents in the signal for all values of t This means that we are able to determine the true signal to noise ratio for the impulse response itself In addition since practically all the signal energy is located to the left of t in the Fig and since the noise is distributed evenly along the time axis this method exhibits a signficant improvement in the signal to noise ratio Why Simply because the signal remains concentrated while the noise is spread out This means that the MLS method makes it possible to make measurements with sig nal to noise ratios hitherto unusable The snag is that you trade requirements for dynamics for requirements for more time spent but in extreme cases you will still ap preciate it Would you like to read more A more detailed di
53. numerical keypad 2 using the Prev amp Next keys Z parameter fields 6 using detailed description of principles 6 overview 2 Merging two channels into one 21 Microphone heating socket 3 Input sockets 2 system assembling cable pre amplifier and cartridge 3 M MLS 90 autocorrelation 90 background level correc tions 92 impulse response 90 saving on disk 93 setting up S N ratio 94 system analysis 90 time reversal 93 time smearing 90 Move memory handling 106 Move key 124 Multi key 124 Multi sine noise generator in FFT mode 61 87 Multispectrum level mode 11 principles in level mode 17 N Next key 124 Noise excitation for reverberation time measurements 36 Noise floor in reverberation time measurements 37 Noise generator and serial scan level mode 22 features level mode 33 intensity mode 87 level mode 33 used in FFTmode 61 Nor 1254 intensity calibrator 70 Nor 216 using with NOR 840 68 Normal help level 8 level of on line help 8 Num key 125 FFT 60 Numerical prinouts 118 Numerical tables editing intensity mode 86 level mode 32 FFT 60 intensity mode 82 level mode 28 navigating in intensity mode 86 level mode 32 O Observation time FFT mode 56 On line help 8 Operating the analyser 2 Operating principles 2 Options installed displaying a list of 3 Output level noise generator level mode 33 Overload margin warning of reduced 13 Overwriting an existing file 108 P P I index checking for 7
54. oth ers require dual channel measurements to become meaningful The two auto spectra and the correspond ing auto correlations work with single chan nel measurements all the others require dual channel measurements to work The correlation functions require zero pad activated and the weighted time function and the weighting window both require one measurement to be made first and that the number of averages is set to no more than 1 Displaying the Time Window Function The Nor 840 offers you the option of dis playing the selected time window function and the effect this has on the contents of the time signal buffer This however requires that you make one measurement first and that you set the number of averages to 1 Since the analyser does not support time synchroneous aver aging enhanced time this is required to make the time buffer contents meaningful 6 E A description of how to display the time window function is given at the lower right part of this page spread Optimum Scaling of the Spectrum The range of window functions available in the Nor 840 FFT extension gives the ana lyser the ability to analyse a wide variety of signal types The multitude of degrees of freedom that an FFT analyser provides generates many pit falls which must be avoided The shape of the window function and the frequency span of the measurement determine the noise bandwidth of the filters and the analysis time r
55. pe um unit 1 ola 2 Units Lim l s Y axis unit 3 Units log Integr factor ch 1 Make the other display setup integr Factor dho X axis setting Options are 1 Line ear 2 Log arithmic Spectrum scaling unit HB Options are 1 PWR 2 RAMS 3 RSD 4 ESD See text for details re a EE Integration factor E et ae Options are 1 10 j 2 10 ja 3 1 4 jo 103 5 105 00 Need to Flatten the Spectrum Meet the Integration Factor The display setup menu enables you to perform an integration or differentiation of the FFT spectrum Applications for this feature include conversion from acceleration to velocity and displacement as well as vice versa but also to make the spectrum fit better within the display range Note the gain attenuation factor of 10 which has been included to make the processed graph fit within the display range Double integration will then have an integration factor of 10 Do not forget to take this into account when you evaluate the results The feature is a display feature only It has no effect on the measured data whatsoever To display the selected windows function or the time function weighted with the selected windows function Measurement Setup Display Setup Lv1 FFT Sgl ENDED 13 1V 1 8 Oct 1997 12 39 06 1 zoom E 0n Function pr Auto spe
56. per second Once a started measurement is terminated the display will freeze to show the data acquired during the measurement The data acquisition is still active however running in the background but data are discarded and not retained To return to the the acquisition show and then discard process press CLEAR Last or change any of the measurement parameters Pressing Causes uninterrupted the measurement will then go on until the preset number of averages is reached the measurement to begin as soon as the trigger condition is met an ongoing measurement to be temporarily halted an ongoing measurement to be terminated the measurement to be resumed If left Cont the measurement to be resumed If left uninterrupted the measurement will then go on until the preset number of averages is reached The total number of averages made will be the sum of the two measurements after the measurement end condition is met Once the Nor 840 has been set up to your requirements it is ready to make measure ments To begin measuring press the Start key The data acquisition will start as soon as the trig ger condition is met If you have set up a trigger delay the acquisition will not begin until a the trigger condition has been met and b any delay subsequently elapsed The measurement will if left uninter rupted go on until the preset number of averages has been reached You may halt the measurem
57. pressing the corresponding key and then press the Help key In addition the help system can be used to provide you with warnings whenever you are about to jeopardise measured or stored data and whenever you make an attempt to perform something illegal in the current state or mode You can set the amount of help text and warnings supplied in accordance with your demands To set the help level press 2ND Herr and then select the help level required You have three levels to choose from Lim ited Normal and Extended Irrespective of the help level setting your Nor 840 will always provide system error information and general information such as Calculating Printing Averaging etc Limited will then provide no information further to what is always provided irrespec tive of the help level setting This applies even to situations where jeopardising com mands are about to be executed Normal will in addition provide information like Overwriting existing file No file se lected Cancel all changes Measure ment parameters have been changed etc wherever applicable Extended will in addition provide messages like Number entered contains illegal char acters etc wherever applicable Lv1 Flt Sgl READY 15 1 4 66 64 08 22 Sep 1997 14 44 15 170 Setup 1 E ar OC Printer Port 1 Parallel Port 2 Serial Port 1 3 Serial Port 2 4 File a The measurement result
58. recording of periods be fore trigger the instrument will start to ac quire data once you press the Start key However the acquired data are put in a circular buffer having a length exactly matching the number of periods before trigger When the buffer gets full the oldest data are overwritten In this way the buffer will always contain the latest periods acquired Once the trigger condition is met the con tents of the circular buffer will be the time profile required This is then retained while the measurement goes on as usual Note that to make this work properly the time elapsed between the Start key is pressed and the trigger condition met must be equal to or grater than the product periods before trigger x period duration which expresses the total time to be spent on the pretrigger time profile recording If the trigger moment comes before this only the periods recorded so far will be shown while the rest of the periods will be set to Zero Note that in order to make this work the trigger condition cannot be set to manual For obvious reasons the above situation ap plies to multispectrum measurements only The single spectrum mode should be con sidered as a collapsed multispectrum meas urement where the number of spectra is one The Single Spectrum Measurement Setup Menu Set the time constant Options are Vie 8 a2 11S 2 4 6 16seconas and Filter bandwidth Options are 1 1s
59. s minimum reverberation time nth limits will be significantly reduced com pared to the conventional methods Time reversal is set up in the reverbera tion time setup menu which appears slightly redesigned when MLS is active Entering and Quitting MLS Mode Press 2ND ANALYSE to produce this dialogue box Select mode Analyser Setup MLS Master Instrument Mode Spotting Unlinearities ml aal 14 AM W HN j i ity WN p Pe e Lata ia Nb hale asd E a a ka aa leds LALAKAS A Pe Unlinearities tend to show up as spikes in the noise part of the impulse response Shown here are two measurements both 10 averages The left was made with loud speaker amplifier working in their linear regions the right while the loudspeaker was severely overloaded Period Length of the MLS Signal Is Bandwidth dependent The MLS sequence length is fixed to 21 1 samples It is possible to change the period duration needed for inter alia RT measurements T by changing the sampling frequency f When changing fs we must satisfy the Nyquist sampling theorem the upper frequency band will therefore determine the sampling frequency as follows Uppermost frequency band f 12 500 20 000 Hz 6 3800 10 000 Hz 3 150 5 000 Hz 1 600 2 500 Hz 600 1 250 HZ 0 17630 Hz 8 000 Hz 4 000 Hz 2 000 Hz Time Reversal in Reverberation Mode
60. sinusoidal signals If we multiply both sides of the equa tion by X f the equation now yields x xY HG X Kw x XD which should be recognised as G f H f x G 6 giving H f Gv H f XX Similarly it can be shown that H f Gw H A and that Gold H P x Gf Are there cases where the three ways of estimating the frequency response yield different results The answer to this is clearly yes The latter of the three clearly stands out being based as it is on the two auto spectra and hence it contains no phase information H f tends to be preferable when the extraneous noise in the system occurs predominantly at the output of the sys tem while H f on the other hand is preferable when the noise is predomi nantly at the input of the system Both the H f and the H f are available as selectable functions in the FFT extension of the Nor 840 nth Time Weighting Windows The FFT process assumes that the time record buffer contains one period of a periodic signal Although this is in gen eral not true for the signals we re meas uring on it is a requirement needed to make the FFT work Now if the two extremes of the time buffer have very different amplitude connecting the end of one buffer to the beginning of the next because of this artificial periodicity which is needed will introduce a discontinuity not present in the original signal see Fig to the right for details
61. t is the instantaneous pressure and i t is the instantaneous particle velocity of the sound field Sound pressure is a scalar quantity having magnitude only while the sound particle velocity is a vector quantity having both magnitude and direction The magnitude of the intensity can be meas ured in one particular direction for example the x direction in which case I 7 Jt 0a in which the uy denotes the instantaneous sound particle velocity in the x direction The subscript X of I is normally not writ ten so the intensity component is denoted I only In the rest of this manual the symbol I should be interpreted as the intensity level along the axis of the sound intensity probe unless explicitly stated otherwise G4 E From the above follows that a sound inten sity probe must be able to measure the par ticle velocity as well as the sound pressure of the sound field The sound intensity level is referred to the value L 10 2 W m The equivalent continuous sound intensity level can then be expressed as I Lolog l dB Lo Sound power may be calculated directly from the intensity values provided that you have information on the area over which the in tensity was measured The sound power may then be expressed as Ly 1 10logS dB in which S is the area in m The following annotation is used through out this section of the manual SIL Sound Intensity Level Ig Equvivalent
62. the presentation of the meas ured functions and values you may adjust the horizontal and vertical axes graduations X RANGE and Y RANGE respectively the vertical axis top scale value Y Max and the horizontal axis minimum value X MiIN The Cursor Control Keys X min cursor defines the lower end of the displayed X axis Z axis Cursor moves the graph cursor along the Z axis X axis Cursor moves the graph Cursor along lt A Zurs V ihe K axis Cursor WwW Y max cursor controls the top scale value Yange curso 2 4 defines the vertical graduation and thereby also Y axis spanwidth Y Step one step towards smaller values Use the DIAL to scroll through the valid settings Z axis Cursor In multispectrum mode the measured data can be represented by a three dimensional matrix having level frequency and time as the three dimensions If the display is set to display a spectrum the X axis will be the frequency axis the Y axis will be the level axis and the Z axis will be the time axis You may also display the time profile for a certain frequency band e g the 3150Hz 1 3 octave band or the A weighted value In this case the X axis becomes the time axis and the Y axis remains the level axis while the Z axis now becomes the frequency axis To switch between time and frequency as X axis use the Lr LT key X range cursor defines the horizontal graduation and thereby
63. two measured sound pressures the mean sound pressure and the particle velocity from the pressure gradient are calculated in the direction of a line joining the two mi crophones centres see Fig below In this way we obtain both the magnitude and the direction of the sound intensity The p u probe on the other hand is based on a somewhat different principle As a practical example we will take a look at the now discontinued intensity probe Nor 216 which consisted of two sets of transduc ers a microphone for the sound pressure and a sound velocity transducer for detect A p p probe example the Nor 240 ing the particle velocity directly The velocity transducer utilised the interac tion between an ultrasonic wave and the audio sound field that we want to measure The ultrasonic wave will travel faster in an airflow in the same direction as the sound propagation and slower in an airflow of the opposite direction Two pairs of ultrasonic transmitters and re ceivers were placed in antiparalel close to each other The particle velocity of the sound field then acted as an oscillating airflow with the direction changing in accordance with the frequency of the sound field By com paring the phases of the two received ultra sound signals the difference inthe transmis sion velocity was determined This was a di rect indicator for the sound particle velocity A p u probe example the Nor 216 x di
64. use Op tions are Parallel port Serial port 1 Serial port 2 and File Determines the position of the setup Options are Top Bottom None Single spectrum version Multisoectrum version Left margin can be set in number of charac ters Note that this will be font dependent and applicable to printer outputs only AS 232 Remote Baudrate IEEE Remote Printer port Off gt Parallel Port Printer type Formf eed 4 HP DeskJet Set Formfeed to On to have one printout per page only Set to Off to have the next printout appear im mediately below the previous one Page printers like the HP DeskJet and LaserJet series must have Formfeed set to On ce Print Setup Setup position Rae Delimiter Left margin Print Setup Start period End period Setup position Left margin Set this to Standby to al low parallel IEEE IEC interface Communication and to Off to save batter ies when you are not us ing the interface Select an address in the range 0 30 to be used as bus identifier for the NOR 840 select printer tyoe Op tions are Canon BJ 10E Diconix 150 160 Epson FX HP DeskJet HP LaserJet Proprinter and PostScript Delimiters are needed when the file is to be imported to a spread sheet Options are Tab Comma Semicolon pe riod and Spaces Period number of the first period to be printed multisoectrum only
65. way Se ees cu screendumps are made However a few a Oom differences exist a e A numerical printout will be made of ee the data associated with the active win a dow only T e The printout will be of parameters set T T to On in the numerical table ne nee an ene e Only the activated spectral weighting be exported functions wil be printed a Ok Consider the Formfeed eem E The formfeed function is activated from the I O I Setup menu press the I O key When active every new printout will ap Set Printer port to Set the Baud rate pear on anew page Page printers like the the printer s port if needed HP DeskJet and LaserJet series must have the form feed activated Otherwise the paper may get stuck or some lines may O e not print When the formfeed function has been deactivated a new printout will appear immediately below the previous set Formfeed On or Off and the number of lines per page Exit the menu HP DeskJet 66 Press Print to generate the numerical printout Wii In the Display setup menu set the Displayed col umns to display the functions needed for your numerical printout IEEE Address Set the Printer type Define the period in terval multi spec trum only
66. without 2Np the X MIN and the X RANGE are used to select the cursor function to which the DIAL and the PREV amp Next keys apply However these step con trol keys will not cause response until the graph has been redrawn completely nth When the keys Y Max Y RANGE 2ND X RANGE and 2ND Y RANGE are pressed prior to using the step control keys any display update in progress will be aborted and a new update started Cursor Alignment In dual display mode the graph cursors X axis cursors of the two windows may be aligned with each other and moved together in either direction Press 2ND Rer to align cursors To deactivate press again press Type or change to another measurement mode e g single spectrum or intensity The master cursor will be the cursor of the active window the one surrounded by the thick frame The two display windows must contain data acquired with the same filter bandwidth e g 1 3 octave bands but they need not display data in identical domains i e one can show data with time as X axis while the other shows frequency as X axis The contents of the two windows need not belong to the same measurement Reference Cursor The reference cursor is used to investigate the difference between two points on a graph To activate the reference cursor select CURSOR to move the graph cursor to your ref erence point then press Rrr and use the DIAL or Prev amp Next to move the graph c
67. work all the reponses are time shifted so that they seem to occur si multaneously and summed together nth A very convenient algorithm already exists for this purpose known as the Hadamard transform Synchronous Averaging Normally an MLS measurement consists of several periods each containing 2 1 im pulses All the periods are averaged together to form one period of 2 1 time synchro nously averaged impulse responses The Hadamard transform will now time shift all the 2 1 impulse responses back to the ori gin and calculate the averaged impulse re The excitation signal is a train of impulses with amplitude 1 or 1 ie they are equal in magnitude and normalised to a certain value e g 0 775V 1 The train of impulse responses After the Hadamard transformation all the impulse responses have been time shifted back to origin summed and properly scaled to yield a single impulse response The squared impulse response obtained with MLS The t is where the noise starts to dominate while and t are used to determine the noise energy h t sponse This broadband AC impulse re sponse is then fed to the filters of the Nor 840 to obtain an impulse response for each fractional octave band Note that the MLS ex tension applies to Level mode of the Nor 840 only Single vs Multispectrum In single spectrum mode we calculate the mean signal energy to get the Leq while in
68. 0 intensity mode 70 minimum requirements 71 P p probe for sound intensity measurements 65 P p probes and trigger conditions 74 82 P u probe for sound intensity meas urements 65 Page Dn key 125 Page Up key 125 Parameter field editing 7 in menus 6 indication of selected field 6 Particle velocity 64 calculated from the pres sure gradient 65 Pause effect of pressing intensity mode 78 level mode 20 Pause key 125 PCX files generated from screendumps 117 Period length in level mode a definition 11 Periods before trigger level mode 17 in level mode a definition 11 max number of level mode 17 Personalising the instrument setup 112 Phase relationship maintaining between input and output FFT mode 43 Pink noise setting noise generator level mode 33 Plot key 125 Power FFT mode 56 Power Spectral Density FFT mode 56 Power supply 4 connecting 4 Pressure gradient probe for sound intensity meas urements 65 Pressure velocity probe for sound intensity meas _ W urements 65 Prev key 125 Preweighting used with spectral weight ing functions 102 Principles of operation 2 Print key 125 Printer type selection 116 Printing 116 Printouts making 116 numerical 118 Probes for sound intensity meas urements 65 PSD FFT mode 56 Pseudorandom noise noise generator level mode 33 PWR FFT mode 56 R Random noise noise generator level mode 33 Random signals FFT mode 56 Record key 125 Rectang
69. 1 1424 13 Oct 1997 13 26 22 of the reference point The difference in level between the present cursor position and the reference point The difference in frequency between the present cursor position and the reference point The Harmonic Cursor dB Eee X Hz 1281 25 The level and frequency DN i AX H2 1 7593 75 Ch2 LAST uto spectrum r t r Z2ZoOD o ie a 15625 80 Lyl FFT Sgl ENDED 1024 13 Oct 1997 13 26 46 dB Harmonics overtones The fundamental frequency 8 indicating the top of the ver gain settings Changing the Ch2 LAST Auto spectrum Y 91 4 r t r PAE Z2oOD ou fe a 8 08 15625 80 X Hz 1281 25 Do not confuse top scale and full scale The top scale is purely a display control tical axis while the full scale controls the input amplifier latter will delete the Last register contents The Numerical Table in FFT Mode Data measured or retrieved from the disk may also be shown tabulated To switch between graphic and numerical presentation use the Num key The table is merely a numeric representa tion of the data Ly l FFT 5gl Auto spectrum Hz 1844 1431 1862 YIdE T H 1 H 5 aa pH a ou 1 4 5 a 9 aid H H Ae 5 J 1 H H Ee Wii The Numerical Table Is Merely a Numeric Representation of the Data ST FFED 12 94 6
70. 12 28 WN boktst 4 ref 988 971110 13 57 laiid cfg 978731 09 45 Auto File Gen 1 On Template jboktst To save it under a new name move up to Name and key in the file name Press Enter twice or move to Save and then press Enter to save the file Setting up for Autonumbering Sav Name PERSEA Save Path c Exit Mask E Make Dir surel About LeF iMu 97824 970901 12 24 N c l sdf LeFiMu 403718 970901 12 28 W ta4 ref 988 971114 13 57 cf 4 970731 49 45 to File Gen mn Template Save Name boktst 4 sdf Bave Path c Exit Mask Make Dir Type 1 Measuremen t About Directories Files abctool 12 sdf LeFiMu 97824 970901 12 24 Ww boktest 84 sicO1 sdf LeFiMu 403718 970901 12 28 N boktstQ4 ref 988 971110 13 57 chdd laiid cfg 970731 09 45 futo File Gen 1 0n Template ERE In the Template field key in the common part of the file name up to six alphanumeric characters Key in the starting number of your number series at the end of the common name Examples of File Autonumbering Autonumbering Files Stored Consecutively Save Name boktsta4 sdf Save Path c Exit Mask Make Dir e Measurement Pbout rectorie Files 12 sdf LeFiMu 97824 970901 12 24 Ww 84 sicOl sdf LeFiMu 403718 970901 12 28 W boktst 4 ref 988 971110 13 57 laiid cfg 970731 09 45 Auto File Gen PERMU
71. 2 Comma Bo Print Setup Start period e End period Eo e Setup position iz Top E Delimiter 2 Comma Bo In the Print setup menu define the period interval multi setup position and delimiter Delimiter Left margin Left margin Press PRINT to enter the Print to file menu Select directory and key in the file name Select Print and press ENTER Your measurements may be exported for use in spreadsheet programs or wordprocessors and page layout programs However the data needs to be exported in a format read able for these programs Some applications tends to prefer certain file name extensions to be able to import the data correctly The exported data are in ASCII format making the extension txt the obvi ous choice for many applications Although modern versions of the most popular spreadsheet programs are quite tol erant there may still be programs demand ing certain delimiters to be able to sort the data correctly Many table editors still seem to be without options on this Therefore the NOR 840 offers the possibility to specify the type of delimiter You may choose between tabulator comma semicolon and space Chapter 10 122 The Front Panel Keys in Alpha betic Order Front Panel Keys The Front Panel Keys in Alphabetic Order The following contains a list of all the front panel keys in alphabetic order 1 amp 2 2nd Avrg Comb
72. 315Hz 12 16 0 40mz 51l 0 5S0HZ 5 A7 ez 160 037 12 5kiz 16060 03 l kHz 172 037 20kHz The file must start with this line typed exactly as shown Some lines have been removed for clarity Comments may appear everywhere provided they are preceded by a semicolon Must always be present and located here i e after the line 840 and before the line Data However the internal order of appearance of these items is not important Type Is always Reference Bandwidthis 1 1 1 3 1 12 or 1 24 octave band Dataformat IS dB Lin ear values or Sec onds for reverberation time measurements This line tyoed exactly as shown must appear exactly where shown There must be a value coefficient for each frequency band all the way from 0 1 Hz to 20 kHz both extremes included e g 18 for 1 1 octaves and 54 for 1 3 octave bands etc Note When you use Dataformat dB neither attenuation nor amplification entered as O zero Amplification is entered as a positive dB value and attenuation as a negative When you use Dataformat Lin neither attenuation nor amplification entered as 1 one Amplification is entered as a gain factor gt 1 and positive and attenuation as an attenuation factor lt 1 and positive Loading a Spectral Weighting Function into the Analyser Thotoo le fomtiie tac Once generated a reference file may be ap plied as spectral weighting function to an
73. 36 5 l 7 4 37 7 l 315 l8 2 two rel il ABk 4 4 0 4 ated l SHH sr A a 45 1 l 634 fet r g 46 7 l AHH sz H 18 5 44 6 l Ik 23 4 Viet 41 5 l 1 25k 23 r 12 6 41 3 l 1 6k 21 4 lat So l ak 19 4 5 4 Iga il 2 5k 23 6 15 5 44 6 l Jalok 23 6 Ir r 44 5 l Ak 34 9 34 4 41 7 l H A6 40 166 22 Sep 199 13 85 59 Che USER The Noise Generator in Level Mode The Menu for this Task The noise type is Generator set up 1 White oise type 2 Pink 3 BP filtered Noise seq 4 Impulse Bandwidth 5 BP filtered impulse Lets the generator span or follow the measurement When set to 1 On and Start is pressed the noise generator will be turned on before the measurement is started and switched off after the measurement has ended The noise sequence can be either 7 Ran dom or 2 P seudo Ra ndom 1 Broadband Extra field to define bandwidth when applicable see below Set the noise generator output level in dB re 1V Range 40 0 dB to 0 0 dB in 0 1 dB steps Generator set up Noise type 3 BP filtered Noise seq 1 Ran Bandwidth 2 1 3 octave Attenuation dB Synchronization If you select bandpass filtered noise you must specify the filter bandwidth 1 or 3 octave bands Generator set up Noise type 2 Pink Noise seq Bandwidth Attenuation dB Synchronization If you select pink noise you must
74. 40 with a suitable microphone and pream plifier such as the Nor 1220 1225 1230 and Nor 1201 corresponds to the Sound Meter Level Standards IEC 60651 Type 1 IEC 60804 Type 1 and ANSI S 1 4 1983 Type 1 Type 0 with suitable micro phones MAINS ADAPTOR Nor 329A Mains input 93 130 Vac US version or 198 250 Vac 50 60 Hz Output 13 2 Voc 135 Wmax HF noise at input and output Approved in accordance with CISPR 14 Protection Short circuit proof thermal protection protected against over and undervoltage Enclosure class IP 20 Dimensions 192x109x53 5 mm 7 6x4 3x2 1 inches Weight 0 85kg 1 9 lb BATTERY PACK Nor 330A Battery capacity 5Ah gives approxi mately 2 5 hours of continuous operation with two microphones preamplifiers Charging time 2 hours Weight 3 3 kg 7 3 Ib BATTERY PACK Nor 332 Battery capacity 10Ah gives more than 7 hours of contiuous operation with two microphones preamplifiers Charging time 16 hours Weight 6 2 kg 13 7 lb All specifications subject to change without further notice NN Norsonic Declaration of Conformity We Norsonic AS Gunnersbratan 2 Tranby Norway declare under our sole responsibility that the product Real Time Analyser NOR 840 FROM SERIAL NUMBER 18711 including mains adaptor 329A battery pack 330A or 332A to which this declaration relates is in conformity with the following standards or other normative documents Performance complying
75. 40 is calibrated by means of a sound or vibration calibrator and the cali bration menu Although you may calibrate by just keying in the sensitivity we always recommend that you use a calibrator This is the only way to ensure proper operation of the en tire measuring chain including the transducer s If you are going to use the instrument for vibration measurement it may be conven ient to change the 0 dB level to obtain dB readings easy to compare with other vi bration measurements Check with rel evant Standards and conventions to find suitable or commonly used 0 dB levels Note that if you set the 0 dB level to a value different from 2x10 the selected setting will appear in reverse video on the screen as shown in the lower Fig to the right Half of this menu may occasionally appear blank This will take place whenever the corresponding input channel has been set to Off If you Change the 0 dB Reference Level Lvl Flt Sgl READY 13 2V 6 00 88 088 26 Sep 1997 13 18 43 A 1 3 oct 1 8s F 16Hz Ny tt aag Wyre HLT TITRE I 16kH2 TETEEEEET Tea J TH f ALANTI ne PEELE ELE LEE M 0 5 2 6 68 86 31 5 125 588 2 f Hz J 88 0 5 2 6 68 8 31 5 125 588 2k 8k LA Al f Hz J 88 an indication is provided The Tool for this Task ZH 0001 O porni paad da 2 on 5 a D oS ae 9 fS S Norsonic offers three diffe
76. 64 14 Oct 1997 12 42 36 Ch2 LAST The Menu for this Task The Noise Generator in FFT Mode The noise type is 1 White aise Type Zink 3 BP filtered Noise seq 4 mpulse Bandwidth 5 BP filtered impulse 8 Multi sine Lets the generator span the measurement When set to 1 On and START is Generator set up 1 Broadband Attenuation dB The noise sequence can be either 7 Ran dom or 2 P seudo Ra ndom Extra field to define bandwidth when applicable see below Set the noise generator output level in dB re 1V pressed the noise generator will be turned on before the measurement is started and switched off after the measurement has ended Range 40 0 dB to 0 0 dB in 0 1 dB steps Generator set up Noise type 3 BP filtered Noise seq 1 Ran Bandwidth 2 1 3 octave Attenuation dB Synchronization If you select bandpass filtered noise you must specify the filter bandwidth 4 or amp octave bands Generator set up Noise type 2 Pink Noise seq Bandwidth Attenuation dB Synchronization If you select pink noise you must specify whether broadband 20 20 000 Hz or limited 100 5 000 Hz shall be used This icon appears in the status line of the display when the noise generator is running The Nor 840 comes with a powerful noise generator built in To access the setup menu press 2ND GEN T
77. 8 A 12s 2 46 e seconds and Lower and upper end of the frequency bands to be measured Filter bandwidth Options are 1 1 1 3 Wi2Z ana 1 24 octaves Probe type Option p p Or p u H M 5 ms a Area for Lw Probe type Spacer mm Amb Press Spacer when Temperature using p p probe Options Amb 1 0 200 0mm temperature Options 20 to 50 C Area for sound power Options 0 1 100 0 m Amb pressure Options 50 0 150 0 kPa Measurement duration Lower limit 10 ms amp 4 oct bands 20 ms 2 oct bands 40 ms 24 oct bands Upper limit is 100 hours when specifying 99h 59m 59s 999ms Optional must be ordered separately nth The Multispectrum Measurement Setup Menu is just an extension of the single spectrum setup menu Number of periods Lower limit depends on to be measured bandwidth and functions active see the Note on this page Upper limit is as for single spectrum This is now the period length not the total duration Number of periods before trigger Measuxement Setup a 0S E 2 173 octave Upper frequenc Time cons Bandwidth Lower frequen Probe type K SiL Up to six functions can Une ier be logged as NO ou L t Options panoa are On Off available depends on The total measurement the amount duration is calculated for of fr
78. 84asicBl sdf LeFiMu 403718 970981 12 28 W util boktst 4 ref 988 971118 13 57 winsic winsic_b a fert Setup select 1 All futo File Guess 1 On Select the setup file Note f a setup file is stored on a floppy disk under the name of 840 cfg and this floppy disk is inserted in the disk drive before the analyser is switched on the analyser will pick 97824 970901 12 24 Ww 403718 970901 12 26 N 988 971118 13 57 403718 978731 09 45 c Setup select 1 All futo File Guess 1 On Set the mask to Cfg if required O i i Name 12 sdf Path c rectories Files 12 sdf LeF im 97824 978981 12 24 W 848sicBl sdf LeFiM 403718 970901 12 28 W boktst 4 ref 988 97111 13 57 laiid cfg 403718 978731 89 45 ect 1 All Auto File Guess 1 On Select Load and press Enter or press Enter on the file in the Files scrolling list window up this setup and configure itself accordingly during start up Retrieving Instrument Setups A setup file is retrieved in the same way as a measurement file However its extension is always cfg Set the mask to cfg to mask out all other files than the configuration files if needed Observe the ability to personalise your ana lyser upon start up by having the setup file stored on a floppy disk the name of the setup file must be 840 cfg see note below and the article on the left page of this page spread Th
79. 970901 12 28 W boktst 4 ref 988 971110 13 57 laiid cfg 970731 09 45 futa File Gen I On Template baktst select the required disk drive press ENTER Save Path c Exit Directories Files LeFiMu 97824 970901 12 24 W 84 sicOl sdf LeFiMu 403718 978981 12 25 W boktst 4 ref 988 971118 13 57 laiid cfg 978731 89 45 Auto File Gen 1 On TOFT To overwrite an existing file select that file to make the name appear in the Name parameter field and press ENTER Path c irectories Files abctool 12 sdf boktest buildini LeFiMu d44sicl sdf LeFiMu boktst 4 ref chdd laiid cfg checkit Jos622 enm msdos5 88 fluto File Gen 1 Template Press Copy HDD Save Name boktsta4 sdf Save Path c Erit Mask Make Dir Type Measurement Pbout Directories Files 12 sdf LeFiMu 84 sicOl sdf LeFiMu boktst 4 ref laiid cfg 97824 978981 12 24 Ww 403718 970901 12 28 N 988 971110 13 57 978731 89 45 fluto File Gen 1 On Template boktst Position the cursor on the required directory and press Enter to produce a list of the contents of the selected directory Save Name ISEGER Save Path c Eat Mask E Make Dir Type ie Measurement About Directories Files 12 sdf LeFiMu 97824 970901 12 24 N 84asic l sdf LeFimMu 403718 970981
80. A whenever the level is above the threshold transition is the keyword as soon as START IS pressed Level drops below as trigger condition External as trigger condition Level below as trigger condition m wv transition is the keyword whenever the level is below the threshold grounding pin 23 on digital I O will do it Noise off as trigger condition Noise on as trigger condition Clock as trigger condition when you switch off the internal generator at a specific moment in time when you switch on the internal generator _KA The Sound Intensity Measurement Setup Menus FFT Analysis Sound intensity measurements can also be made with FFT technique as an alternative to the more conventional fractional octave method The measurement setup menu is identical to the FFT measurement setup menu with the exception of two extra lines added to provide probe definition Automated sound power calculations can not be made with FFT based sound inten sity For details on aspects of setting up for FFT measurements not covered here see the sec tion Making FFT Measurements The Menu for this Task The zoom span frequency range Options available can be found in the FFT section of this manual Lower frequency as calculated with the selected setting Time weighting window function Chie Zero pad On or Off Spacer when u
81. Continuous Sound Intensity Level L Sound Power Level Direction is indicated as follows 23 6 equals a positive intensity of 23 6 dB re 10 W m nth Sound Intensity Probes Traditionally two types of sound intensity probes used to be around viz the p p probe and the p u probe The p p probe the two microphone probe uses the sound pressure from two closely spaced microphones to calculate the sound particle velocity by applying Newton s sec ond law mass x acceleration force gt ee rad P F S aap also called Euler s Relation in which p is the density of the air and u is the particle ve locity In one direction x we have Ou __ op ot ox Since the pressure gradient is proportional to the particle acceleration the particle ve locity can be obtained by integrating the pressure gradient with respect to time u Pa p dx For practical cases the pressure gradient is approximated by measuring the sound pressures p and p at two closely spaced points and dividing the pressure differ ence p p by the microphone separation distance Ax The estimate for the particle velocity _ in the x direction will then be A 1 u z P p at This is an approximation but it is valid for separation distances much smaller than the examined wavelengths of the sound field A practical probe can therefore be designed using two closely spaced microphones From the
82. E f Hz 1 68 T f Hz 1 68 Type Single display Dual display without setup information with condensed setup information Lvl Flt 5gl READY 13 2V 60 00 00 000 30 Sep 1997 13 83 14 Lvl Flt 5gl READY 13 2V 60 00 00 000 38 Sep 1997 13 03 08 1 3 oct_ 1 8s F 16Hz 16kHz Trig Manual End 99 59 59 408 Input Cal AdB HP Chi Microphone 25 7 2 0 0e 05 Ch2 Microphone 27 3 2 00e 05 63Hz dB Chi LAST 1gs amSPL __41 9 Leg N 1 25 0 5D i p e S 0 125 5 2 0 f Hz 1 88 dB Ch2 LAST 1 E5 hee oe eo eek he ete ee bee eee So Ge RE 45 845 6 eee E 25 07 6 125 8 5 2 8 0 31 5 125 500 2k 8k LA 2 0 8 0 31 5 125 500 LA E f Hz 1 88 T f Hz 1 88 Note The data of the active window will be the only set of data printed out when you make a numerical printout nth l Overload is occurring now here ch 1 First function displayed Cursor alignment activated Displayed channel s Measurement status Play s Battery voltage Measurement duration Measurement mode Noise generator activated Date and time of day Vertical axis scaling unit Title field upper display window HSH sep 1337 Lli 22153 Top scale setting Full scale setting No of averages made Measurement was 1 3 act overloaded 1 8s F LHz Spectral weighting of 2AkHz the displayed eae spectrum 5A 31 5 125 SPA Measurement setup Selected cursor Period 145 p 0A A0 Tete information used to func
83. Mode Display Cursors 60 The Numerical Table in FFT Mode 61 The Noise Generator in FFT Mode si a AN y vs aN Making FFT Measurements Fast Fourier Transform Fundamentals Fast Fourier Transform FFT is a means of calculating the spectrum of a time function It is a digital process using a signal s amplitude at discrete moments in time to produce the corresponding spectrum which also will consist of dis crete frequency lines a non continuous spectrum A time buffer consisting of 2048 sam ples representing the time history of a signal is acquired The length in sec onds of the buffer and thereby also the spacing between the time samples de pends on the upper frequency of the analysis The higher the upper fre quency the shorter the time buffer length will be measured in seconds It will however always consist of 2048 samples The FFT process generates 2048 fre quency lines based on the 2048 line time buffer Out of these 2048 lines only 1024 are unique and distributed evenly over the frequency range used Furthermore out of these 1024 unique lines we use 801 lines since those af fected by the anti aliasing filter of the analyser must be discarded To be pre cise we use 800 lines 1 for DC In nor mal operating mode the DC line is not in use since the analyser is AC coupled It is however used in zoom mode When we talk about time signals in the
84. One or two windows with or without annotation and setup information Each window may indi vidually present data from selectable channel and selectable parameter s as a numerical table as a level vs frequency graph or as a level vs time graph Displayed level range 20 40 or 80dB User selectable Graduation 0 1dB 0 8dB depending on selected format Numeric graduation 0 1dB Numerical range 99 9dB to 199 9dB MEMORY Internal storage Up to 10 000 full frequency single channel spectra Depends on No of channels employed as well as registers parameters and frequency range range used Volatile memory Floppy disk 1 44 Mbyte 31 2 floppy drive Ms DOs compatible format Capacity approximately 250 single spectrum measurements or 100 multi spectrum measurements 1000 periods each Hard disk optional 2 1 Gbyte hard disk MS bos compatible format Capacity approximately 391 000 single spectrum measurements or 153 000 multispectrum measurements 1000 periods each DIGITAL INTERFACES Control Almost any setting or any data read out may be made using the digital interfaces See also Remote Control Commands separate booklet TEEE 488 Meets the IEEE Standard 488 1978 RS 232C three Meets the RS 232C Standard for normal serial interfaces with handshakes Printer Graphic screen dumps or numeric tables may also be printed out using the Centronics parallel interface SIGNAL GENERATOR Outp
85. S Resolution 0 1dB in accordance with IEC 60651 and IEC 60804 Type 0 as well as ANSIS 1 4 1983 Type 0 Reference range 40 120dB in accord ance with IEC 60651 60804 and ANSI S 1 4 1983 Primary indicator range 50 120dB with CF _ 3 50 110 at CF_10 in accordance with IEC 60651 type 0 and ANSI S 1 4 1983 type 0 Linearity range 75 dB in accordance with IEC 60804 type 0 Pulse range 78 dB in accordance with IEC 60804 type 0 Reference frequency 1000Hz Reference SPL 114 0dB SPL Accuracy 20Hz to 12 5kHz measured at reference range 5dB above to 60 dB below FSD lt 0 2 dB 60 dB to 70 dB below FSD lt 0 4dB 70 dB to 80 dB below FSD lt 1 0dB Time constants Selectable in a binary sequence from is sec to 8 sec plus I mpluse The s sec as F ast the 1 sec as S low and the I mpulse are in accordance with IEC 60651 Type 0 and ANSIS 1 4 1983 Type 0 Integration period 4 msec to 100 hours with lmsec resolution Crest factor capability 10 dB crest factor margin at FSD increasing to 90 dB at 80 dB below FSD Overload detector The overload detector operates in accordance with IEC 60651 IEC 60804 and ANSIS 1 4 1983 standards The overload detection starts at 10dB PEAK above FSD DISPLAY Display type 10 bright backlit double twisted monochrome LCD screen or optional back lit 10 4 VGA colour screen Resolution 640 horiz x 480 vert pixels VGA standard Display formats
86. T See also FFT setting up 53 Wi 00 07 790 12 I Sens Level el Completely Revised Expanded amp Up to Date Unit dB fi dB 2 ade a5 Autocal 14 0 Calibrate bee aa Your approach to the Nor 840 documentation depends on what you want to do and how much you already know The User Documentation has been designed to help you get more benefits from all the analyser s features in less time than ever before Need a quick start guidance Read the Getting Started section This part of the manual outlines in just a few pages all the fundamentals needed to start using the analyser from the hardware of battery handling to the software of menu handling Need in depth knowledge about a certain topic The concept provides detailed information at a glance All the related information is compiled and presented on a single page or a page spread Need to know the correct procedure for setting the analyser up The order of appearance of the topics reflects the recommended sequence Looking for certain topic The extensive index provides the keywords you need Book Level Beginning v Some experience v Intermediate Pearce Tutorial v How to v Reference J NN Norsonic P O Box 24 N 3420 Lierskogen Norway Tel 47 3285 8900 Fax 47 3285 2208 norsonic online no Norsonic AS supplies a complete range of instrumentation for acoustics
87. VO Setup menu 116 Icons for cursors in FFT mode 59 used for cursors 31 85 IEEE adress setting 116 Impulse excitation for reverberation time measurements 36 Impulse noise noise generator level mode 33 Impulse response MLS 90 saving on disk MLS 93 Index key 124 Information fields in menus 6 Initialising the analyser with your personal setup 112 Input amplifiers gain setting in level mode 13 Input key 124 Input source selection level mode 12 sensitivity setting in level mode 14 FFT mode 46 intensity mode 66 level mode highpass filter 12 Insert key 124 Installed options displaying a list of 3 Instrument setup initialising the instrument with a personalised 112 retrieving 113 storing 112 Integr key 124 Integration of spectrum FFT mode 57 Intens key 124 Intensity 64 and sound power 64 calibration 68 checking for residual 70 equivalent level 64 full scale setting 67 fundamentals 64 indication of direction 64 input source selection 66 level 64 magnitude 64 measurement setup menu FFT mode 76 fractional octave mode 72 minimum requirements for P I index 71 multisine noise generator 87 noise generator 87 Nor 1254 intensity calibra tor 70 P I index 70 setting zero pad 76 specifying the sound power area 72 trigger conditions FFT mode 77 fractional octave mode 74 using Nor 216 68 Intensity mode 3D cursor 84 active window 80 cursor alignment 84 cursor icons 84 display cursors 84 display modes 80 disp
88. able to 800 20 18 26 20 19 16 the left 1000 20 18 26 20 19 16 1200 20 18 ao 20 te 1o Checking P I Index for Probe Nor 840 1600 20 18 26 20 19 16 2000 20 18 26 20 19 16 Mount the probe and enter intensity 2500 20 18 26 20 19 fe mode Set 25 mm as spacer length 3150 20 18 26 20 19 16 in the measurement setup menu 4000 20 18 26 20 19 16 Connect the noise generator to the 5000 20 18 26 20 19 16 Nor 1254 Set the input selectors of 6300 20 18 26 20 19 16 the Nor 840 to those used with your p p probe Select pink or red white noise if available and adjust the output level to about 5 dB Note We recommend an electrical P I index of 30 dB or better when checking probe alone Set FSD so that the SPL level is about 10 dB below FSD to get an Note Long averaging times are necessary e g to determine a P I index of 20 dB 50 Hz optimum signal to noise ratio the averaging time must be at least four minutes Start a measurement Use the display setup menu to set up Tip Reproducing measured values for intensity probe P I indices greater than 25 the display to show the P I index i approximately has proven to be very difficult Very small phase changes are likely to directly See the left table for produce significant variations in the P I index minimum requirements The Sound Intensity Measurement Setup Menus Fractional Octave Analysis The measurement setup menu is used to set up essential measurement parameters
89. ad For p p probes the trigger condition you define will be applied to the mean sound pressure level i e 4 p t p t For all other probes or configurations the trigger condition will be applied to the SPL of channel 1 The correspond ing time constant is defined in the meas urement setup menu The condition for trigger The Menu for this Task Trigger Setup Trigger condition KARIERE Trigger type Trigger delay Insert a delay from trigger condition is fulfilled until the measurement actually starts Options are 0 60 000ms Not used in this software version If you select Clock as trigger condition extra parameter fields will appear Trigger Setup Trigger condition KERAS i M D H M 5 Eo po e ee e iih Trigger type Trigger delay If you select level related trigger conditions extra parameter fields will appear Trigger Setup Trigger condition PIRES esa Jas e Jre ot om Trigger tupe ms Trigger delay Trigger Setup Trigger condition PEHA S A S sa dB 1 Hz 1 Chi Trigger type Iz Continuous edt i Trigger delay Trigger Setup Trigger condition ESASTAN ee Joe pe e p e ne eh Trigger Setup Trigger condition PESA S r E ena Je Te Je ar chi Trigger tupe Trigger delay ms nth Manual as trigger condition Level exceeds as trigger condition Level above as trigger condition W M
90. al display without setup information with condensed setup information Int Flt Sgl STOPPED 13 1V 06 00 15 738 6 May 1998 08 32 29 Int Flt Sgl STOPPED 13 1 6 46 15 738 6 May 1998 48 32 22 1 3 oct 1 8s F 20Hz i 2 kHz Trig Manual End 08 00 35 000 Input Cal dB HP This is an example showing how the t Chi Intensity 25 3 2 00e 05 2 Hz Ch2 Intensity 24 9 2 00e 05 2 Hz dB LAST a h a 89 0 SIL 13 1 SPL 19 8 N 1 appears in the display Note that yo 80 0 ER ean A r fCH2 1k Bleq t 28 2 mPI 18 7 Oleg 38 9 N 1 a TTT T T T T T T T 6 125 AS 2 50 BHB 31 5 125 Sea 2k 8k LA 31 5 125 588 2k 8k LA f Hz 1k T f Hz 1k Note The data of the active window will be the only set of data printed out when you make a numerical printout Mth Cursor alignment activated Measurement status Measurement mode Vertical axis scaling unit Top scale setting Full scale setting is higher than the top scale setting Selected cursor function Full scale setting Suppressed origin First function displayed Selected cursor function Graph cursor position 56 6 A S 2 0 xf Hz 315 Battery voltage Measurement duration Date and time of day Title field upper display window 16 4 No of averages made ly o Oct l s F 2HHz 2HkHz gt Manual Hl Measurement setup H 5 2
91. arded as a sub set of FFT as such The FFT based intensity trigger condition setup menu is identical to the fractional oc tave based trigger condition menu However for obvious reasons some of the trigger con ditions available with fractional octaves be come meaningless when working with FFT The trigger conditions shown here are those applying to FFT based intensity The trigger condition menu is accessed by pressing 2ND START For a view of how the menu looks turn to the article Trigger Conditions in FFT Mode of the section Making FFT Measurements Measurement Controls Once the Nor 840 has been set up to your requirements it is ready to make measure ments To begin measuring press the Start key The data acquisition will start as soon as the trig ger condition is met If you have set up a trigger delay the acquisition will not begin until a the trigger condition has been met and b the delay subsequently elapsed The measurement will if left uninter rupted go on until the measurement end condition is met You may halt the measurement temporarily and then resume the measurement later You may also stop the measurement prematurely by pressing the Stop key The instrument does not discriminate be tween pausing and termination with respect to resuming a halted measurement There fore to pause the instrument just press the Pause or the Stop key To resume measuring press the Cont key If
92. asurement setup menu and is Measurement Setup 2 1 8s F 2 1 3 octave Time constant Bandwidth multispectrum mode single spectrum as Upper frequency ek dit Lower frequency ste Serial measurement H M S ms Measurement period accessible in well as in Serial measurement is activated here Options are 0 Off 1 0n and 2 Scan Note When using the serial analysis function for retakes you will have to enter the Tip measurement setup menu to activate the serial analysis function However you must make no other changes in this menu Neither must you make any changes to the input calibration nor the gain setting menus Any changes made in these menus will cause the analyser to erase the data already acquired If you have set the help level to Limited you will not even be notified about the erasure of data Once you select serial analysis the noise generator will automatically switch to pink bandpass filtered noise If this is unsatisfactory you may use the generator setup menu to change the setting When you later deactivate the serial analysis function the noise generator will switch back to the noise type it was set to initially Note that the other generator setup parameters will not be reset instead the new settings will be retained When a serial analysis measurement is running in serial scan mode and it is stopped prematurely by you the measurement will go on for another
93. asurements 64 65 66 67 68 70 72 74 76 T7 78 79 80 82 84 85 85 86 87 Sound Intensity Fundamentals Sound Intensity Probes Selecting Input Source for Sound Intensity Measurements Full Scale Setting Calibrating for Sound Intensity Measurements Checking Residual Intensity Using the Nor 1254 Sound Intensity Calibrator The Sound Intensity Measurement Setup Menus Fractional Octave Analysis Sound Intensity Trigger Conditions Fractional Octave Analysis The Sound Intensity Measurement Setup Menus FFT Analysis Sound Intensity Trigger Conditions FFT Analysis Measurement Controls Assigning a Title to Your Measurement A Tour of the Sound Intensity Mode Display The Sound Intensity Mode Display Setup Menu The Sound Intensity Mode Display Cursors Cursor Alignment Reference Cursor The Numerical Table The Noise Generator in Sound Intensity Mode Sound Intensity Fundamentals Intensity measurements are useful for the study of many sound propagation and trans mission phenomena Simultaneous obser vation of sound pressure and sound particle velocity can be used to determine the mag nitude and direction of the energy propaga tion Sound intensity is a vector quantity defined as the average rate of flow of acoustic en ergy through a unit area perpendicular to the direction of the wave propagation With mathematics l n t ii t dt Wim in which p
94. ating from scratch 100 ref files 100 valid range for coefficients 100 Spectral weighting functions 98 apply to display intensity mode 82 level mode 28 applying to a measure ment 102 bargraph representation 102 created from a measure ment 99 dataformat 100 functions to choose from 101 loading into analyser 101 preweighting 102 reference curve 102 use of index key 101 Spectrum types level mode 11 Spectrum flattening FFT mode 57 Spectrum scaling FFT mode 56 Spreadsheet export of data for spreadsheet use 119 Start effect of pressing intensity mode 78 level mode 20 Start key 125 Status bar 3 Stop effect of pressing intensity mode 78 level mode 20 the hard disk 3 Stop key 125 Storage media 106 Storing measurements 108 SumA 98 intensity mode 82 level mode 28 SumB 98 intensity mode 82 level mode 28 SumC 98 intensity mode 82 level mode 28 Sumf spectral weighting network 98 SumL 98 Swapping the contents of the chan nels 107 Synchronisation noise generator level mode 33 System analysis MLS 90 T Tab key 125 Temp warning battery pack 4 Template for autonumbering files while storing 109 Time axis in level mode 11 Time axis scaling intensity mode 82 level mode 28 Time constant setting level mode 16 Time smearing MLS 90 Time weighting FFT mode 43 Time window function FFT mode 56 Title and autonumbering 109 of measurement intensity mode 79 level mode 25 Title key 126 Time reversal MLS 93
95. ause the slave cursor to stop at its extreme end while the master will go on until it reaches its extreme end To spot when this occurs watch the period number in each display window If the cursor alignment was active at the time you stored a setup file a cfg file and you put this on a floppy disk naming the file 840 cfg Iinitialising the analyser with this floppy will cause the cursor alignment function to be set active as a part of the initialisation Tip Do not confuse top scale and full scale The top scale is purely a display control indicating the top of the vertical axis while the full scale controls the input amplifier gain settings Changing the latter will delete the Last register contents More 3D If the X axis represents the frequency the Z axis will represent the time and vice versa Use LF LT to Swop Scaling and Graduation Range Y axis 20 40 60 80 or 100 dB across the vertical scale or in a 1 2 5 sequence when set to engineering units KeaaxiS Se ae lee i 21l 4 amp 1 ane S T applies to time displays only not the fractional octave spectrum displays The Numerical Table Data measured or retrieved can be shown either as graphs or tabulated To switch e tween these two ways of presenting the data press the Num key The contents of the table is determined by the Display Setup menu You navigate in the table by means of the DIAL Prev amp Next and the 2ND 9 PGUP 2ND 3 PGDN
96. be used with or without external power External power is fed to the unit either directly or via the battery box In the latter case batteries will be recharged while the analyser is available for normal use The LEMO connector of the power supply fits in the socket of the battery box as well as in the socket on the rear panel of the analyser and nowhere else The battery pack contains a battery charger and the batteries will therefore be charged as long as power is received from the power sup ply The battery box is equipped with eight LED lamps indicating the status of the batteries The power supply of the Nor 840 The Battery Box is Detachable Fuse Label with LED lamp indicators is on this side of the battery box socket LEMO connector Battery m ri box gy re Security locks The label with the LED lamp indicators Charging is finished and the battery pack is ready for use Batteries are being charged Ambient temperature is outside allowable range for charging Battery capacity is 80 100 60 80 40 60 20 40 0 20 READY CHARGE TEMP WARNING 100 60 40 20 0 BATTERY CHECK NN Norsonic Type Serial No LEMO socket accepting the cable from the power supply Battery capacity meter Type No and Serial No Press here to activate the battery capacity meter nth Charging the Batteries Once you plug the cable from th
97. buffer length will be 32 ms in the initial 25 kHz situa tion and 512 ms in the zoom situation Zoom FFT in the Nor 840 The zoom FFT should be used as follows 1 Start by specifying a centre frequency e g 10 416 Hz and a zoom frequency span 1 of 8 preset zoom factors 2 Since the FFT analysis is an 801 line proc ess you ll get 400 lines on each side of the specified centre frequency 3 The centre frequency must be chosen so that the entire span is contained within the frequency range Example A centre frequency of 1000 Hz and a span of 3 125 Hz is not possible However the analyser keeps track of this and adjusts the zoom factor i e the span whenever a conflicts arises 4 Based on your selections the analyser will display the corresponding upper and lower frequency of your zoomed fre quency range The zoom feature is located in the measure ment setup menu Selecting Input Source for FFT Measurements The Nor 840 has four different types of signal input sockets These are accessed via the input menu Press the Input key to produce this menu Only one input can be selected at the time per channel but the two channels need not be set to the same type of in put source One of the channels may be set to Off but both channels cannot be set to Off at the same time If you set one channel to Off in the in put source menu the corresponding part of the calibration menu will be blank Obser
98. cale setting GAIN1T GAIN2 Fullscale channel 1 Fullscale dB 2 00e 00 u 4 Calibration Channel 1 Microphone Sens Level Press CaL and set a the calibrator 1 dB 2 08e 85 frequency ji 114 0 Calibrate Channel 2 Microphone Sens Level 27 3 0 4 Unit dB 2 8 e 85 i TE 114 6 Calibrate Cal freq Pol Volt 280 Calibration Set the sensitivity of the microphone used eee until the sound pressure level is indicated correctly Calibration Setting the Sensitivity 1 Input selection Channel 1 Press INPUT and select input source HP filter 2 20Hz Channel 2 Source 3 Charge LP filter 0 Off HP filter 2 20Hz Calibration Channel 1 Microphone Press CAL and set the renee sensitivity of the a e microphone used 114 6 Calibrate Sens GB 7 000705 114 4 Calibrate Cal freq ik Pol Volt 280 Channel Sens Unit ae Autocal This method is in general not recommended since it does not take into account whether the microphone actually works as it is Supposed to do Bearing in mind that the microphone itself is the most vulnerable part of the measurement chain this method obviously suffers from severe shortcomings
99. ct This can easily be overcome by setting the second half of the time buffer to zero By doing this we introduce another error but this error is known and can be compensated for which is done of course There are eight predefined frequency spans available for zooming Span Af 12925 00070000 Hz 31 2000 HZ Zale S00 OOOO tmz 15 6250 iz 3 E 250 0000 Hz NZS Hz 4 3 125 0000 Hz 3 9063 Hz De e2 5000 lz T953 Ia 6 roi 2500 Hz 0 9766 HZ T 390 6250 Hz 0 4883 Hz 6 I9 S 2S HZ 0 2441 Hz The Menu for this Task ZoomiOn or Off When zoom is activated the centre frequency must be keyed in here Legal range is 97 66 24 902 34 The zoom span frequency range Options are listed at the bootom of this Measurement Se page Lower frequency as Centre frequency Upper frequency as calculated with the Span calculated with the selected setting bawer frequency Upper frequenc selected setting 884 55 Hz msa fe Time weighting window function ch Time weighting 1 wfe up x t2fi__ zt3fi__s window function Extra fields appearing Window Channel 2 3 Exponentiai ch 2 averages Displacement when user defined nee cae Time constant defines weighting is applied the width of the exponential window function in ms Start of exponential window relative to start of time record buffer a Number of frequency ea window spectrum averages to be selected given in made Options are 1 99 999 ms Zero
100. ctrum 4 Ch1 LAST Centre frequency 1200 00 Start Channel faz Ch2 ae Weighted time Y 3 94e 88 Span 390 625 Hz Function coordinates fi Magnitude 5 00 Lower frequency Upper frequency x axis EE Lin 2 88 884 69 Hz 1195 31 Hz Spectrum unit fi PWR o a N i Window Channel 1 4 User def Y axis unit E dB 5 88 we kup krep jrih ora indow Channel 2 Integr factor ch i 1 pe lt a 53 Displacement aa Jms Tc 16 00 Jms Integr factor ch 2 EE eres 1 umber of averages as paar ot average E ae 2 Weighting window Y 8 62e 81 Zero pad a off a m l z In the measurement setup Press the Start key In the display setup menu menu set the windows select Weighting window 5 functions as required and or Weighted time as Xims 1 19 89 the number of averages to 1 displayed function Example showing Weighted time top and Weighting window bottom The FFT Mode Display Cursors The Nor 840 has an extensive set of cursor functions However some apply to certain situations only All the cursor controls are located around the DuL To operate a cursor you start by selecting the type of cursor and then use the Du or Prev amp Next A small icon appears in the display to tell you which cursor func tion has been activated Scaling and Graduation To optimise the presentation of the meas ured functions and values you may adjust the horizontal and vertical axes graduations X RANGE and Y RANGE respectively the vert
101. d a part of the periods before trigger the acquisition of data starts upon pressing the Start key The data are stored in a circular buffer whose length exactly matches the number of periods to be recorded before trigger When the buffer gets full the oldest data are overwritten Thus the buffer will always contain the latest periods acquired Once the trigger condition is met the circular buffer will be retained containing the periods before trigger while the data acquisition will go on as normal Note that the trigger condition must be set to something different from manual to make this feature work gt Note The lower limit for the period length i multisoectrum mode is bandwidth dependent 4 ms 1 amp 3 oct bands 10 ms 112 oct bands and 20 ms 124 oct bands If more than one function is set active the lower limits are 10 ms 4 amp 4 oct bands 20 ms 1 2 oct bands and 40 ms 724 oct bands Note The time constant Ves is too short to produce meaningful results when measuring in 1 24 oct bands this combination of settings has therefore been disabled and cannot be selected Switching to a less narrow analysis bandwidth or a longer time constant will restore valid combinations Tip In multisoectrum mode the number of periods available depends on the amount of free memory available However if you can do with fewer functions logged simultaneously or with a more narrow range of
102. d come back to analyser mode the analyser will need to read the linked files This will take time particularly when the files are stored on floppy disk You may not want this whenever you are not using the reference files This is when to use the Clear links feature of the Index list Applying a Spectral Weighting Function to a Measurement Applying a spectral weighting function SWF to a measurement can be done in three ways in the NOR 840 An SWE may be used as e Spectral weighting function showing the measured spectrum weighted by the spec tral weighting function in the NOR 840 referred to as preweighting e Bargraph indicating the total level of the spectrally weighted spectrum e As a reference curve indicating how the measured spectrum looks compared to a certain reference The three options are independent of each other the very same spectral weighting function may appear in all three positions at the same time The application of spectral weighing func tions is a display matter only It does not af fect the measurement as such in any way There are two types of spectral weighting functions preprogrammed and customised The preprogrammed functions are e SumA SumB SumC and SumL which are spectral weighting functions that can be used to calculate the weighted value based on the frequency range actually measured For frequency ranges smaller than the standards define for the A B and C cu
103. described on the previ ous page or from scratch i e by keying in the value for each frequency band However you may start by generating a ref erence file from a measurement and later modify this file manually To synthesise a reference spectrum entirely from scratch you will need a text editor such as NotePad which is included with Win dows or a wordprocessor program such as Microsoft Word or WordPerfect from Corel If your NOR 840 is equipped with the MS DOS extension any text editor installed here may be used Follow the guidelines given here and save the file as ASCII text The file must be given the extension ref Observe that a reference file is made for a certain bandwidth only and cannot be used with other bandwidths than the one it was designed for There is no need for any kind of END state ment in the file Valid Ranges for the Coefficients Dataformat dB 327 to 327 Dataformat Lin O to 2 4e16 2 4x10 Dataformat Sec 0 to 327 An example of a synthesised reference file A B C D WO A 840 This file describes a weighting network for the NOR 840 comments are preceded by line length must not exceed 80 characters Type Reference Bancwi dth 1 3 may also be 1 1 or 1 12 or 1 24 DabakOuman ds May also be lin OO E O 1OHZ Data 2 Sez GHZ 36 007 0 1 3 k 99 el 2T Or On Soe 99a 0 OZ 20 01 0 25mz 16 05 0
104. disk and main tain the autostore function do as follows 1 Create and save your setup in the direc tory to be used for autonumbering 2 Copy by means of MS DOS the setup file onto the floppy disk Remember to name it 840 cfg Storing a Setup Set up the analyser as required Remember to include display setups noise generator setup I O and other settings applicable to your situation If setup for more than one mode Is to be stored be sure to set up all modes fluto File Gen 1 On Template boktst Press Copy HDD and select the directory in which the setup shall be stored tote pors Key in the setup s file name Set Type to Cur to store the setup of the current mode only or to All to store the setups of all the modes Press Enter twice or move to Save and then press Enter to save the file Loading a Stored Setup Load Name 12 sdf ath c orii ile bctool 12 sdf LeFiM 97824 970901 12 24 N boktest 840sic l sdf LeFiM 403718 978981 12 28 W buildini boktst84 ref 988 971118 13 57 hdd laiid cfg 403718 978731 89 45 heckit dos622 nm dos5 88 Setup select futo File Guess 1 On Press HDD to produce the Load menu Load Name laiid cfg Path ci Directories Files Load Exit About test 12 sdf LeFiMu 97824 970901 12 24 N tmp
105. do this by using the al Av La Average less Last function ijl ult Press 2ND Come to activate this function Note There is only one level of undo i e you cannot repeatedly use the undo key to undo previous mergings Assigning a Title to Your Measurement The Menu for this Task 2nd Tip Title of the LAST register Enter the text here The analyser will enter aloha mode upon entering this menu so you won t have to press ALPHA first This is an example showing how the text appears in the display Note that you must use the Enter key to make the e fit within the borders To exit the menu you must use the FIELD CURSOR to move to this field and then press ENTER and here is how Ly1 Flt Sgl READY 13 2V 00 00 00 000 26 Sep 1997 13 16 88 the text appears in C AST This i hi cess peep the display Note how the text has Pa been truncated ed Only the text 16kHz written inside the ig Manual dotted field Continuous appears in the f Hz 1 88 End 16 68 48 088 display when exiting the menu The text is the same for the upper and lower window since they belong to the same measurement This is an exfamp appears in the d If automatic file name generation has been set to off and a title is present the eight first characters of the title ignoring any spaces will be proposed as file name when storing the acquired data You may assi
106. e configuration file will affect the instru ment measurement as well as the display setups of the modes one or all of them that were specified when the setup file was gen erated Chapter 9 116 Hardcopy Fundamentals 117 Making Screendumps 118 Making Numerical Printouts 119 Exporting Data for Spreadsheet Use Ni Hardcopy Fundamentals Hardcopies or printouts are available in two formats as graphical i e screendumps or numerical i e a tabulation of values In addition you may choose to either direct the output to a printer or to a file There are two menus needed for this the I O Setup I menu which controls to which port the printout is to be directed the baud rate etc and the print setup menu which allows you to specify numerical printout details The graphical outputs are available as screendumps only thus no setup menu will be needed for these To access the I O Setup I menu press the I O key To access the Print Setup menu press 2ND PRINT The Menus for this Task Wii Set this to Standby to enable serial commu nication and to Off to save batteries when you are not using the interface The baudrate expresses the bit transmission rate in baud bits per second Select between 300 1200 2400 4800 9600 and 19200 baud Select whether printing shall be to a physical printer or to a file When printing to a physical printer you must specify which port to
107. e measurement a triangular weighting function is applied to the decay More emphasis is then applied to the middle part of the decay and less to its extremes Impulse Excitation For impulse excitation the calculation starts at 5 dB below the maximum level measured As long as the sound level stays below the 5 dB line the time elapsed is counted un til the level is 25 dB below maximum level measured for T measurements and 10 dB further down 35 dB altogether for T measurements The main difference between the noise and the impulse excitation calculation method lies thus in the way the initial 5 dB level is determined Level Mode Is Used for Acquisition Although the RT Mode is a separate meas urement mode it uses the multispectrum Level Mode to acquire the decays Rever beration times can be calculated on the ba sis of level mode measurements only FFT and Sound Intensity won t work As a separate measurement mode the RT Mode has its own set of registers of course independent of the Level Mode registers The RT calculation procedure is based on ex citation type information Level Mode multispectrum period length information and the preset requirement for minimum distance to the noise floor see below Hence the RT Mode becomes unusable without the multispectrum Level Mode yet it has influence on the setup of the multi spectrum measurement via the period length setting and when Revert to
108. e name title based on measure ment 25 79 Files deleting 110 retrieving 111 Filter key 124 Filter out file names in memory handling 107 Fiter bandwidth setting up level mode 16 Flattening the spectrum FFT mode 57 Formfeed nth activating 116 considerations 118 Frequency axis in level mode 11 Frequency Response Functions 42 Frequency scan level mode 22 Frequency spans available FFT mode 53 Front panel keys Keyboard 122 Full scale vs top scale 13 Full scale deflection See Full scale setting Full scale Setting FFT mode 47 autoranging 13 indication in FFT mode 55 intensity mode 67 level mode 13 Function coordinates FFT mode 57 Fundamentals of level mode 10 G Graduation cursors FFT mode 58 Gain autoranging input amplifi ers in level mode 13 input amplifiers setting in level mode 13 Gainl key 124 Gain2 key 124 Gen key 124 Graduation cursor intensity mode 84 level mode 30 Graduation range FFT mode 59 Graph locating it in FFT mode 58 H H1 FFT mode 42 H2 FFT mode 42 Hadamard transform MLS 91 Hand arm spectral weighting network 98 Hanning window functions FFT mode 44 Hard disk forcing it to stop 3 Hardcopies making 116 Harm key 124 Harmonic cursor FFT mode 59 HDD key 124 Help level 8 setting the 8 on line 8 Help key 124 Highpass filter input source selection level mode 12 Highpass filter setting intensity mode 66 Home key 124 Horizontal axis scaling FFT mode 57 I I O key 124
109. e power supply into the battery pack charging will commence irrespective of whether the pack is connected to the Nor 840 or not The power supply supplies enough power to let you run the instrument while the bat teries are being charged The yellow LED lamp denoted CHARGE will illuminate and stay lit as long as the charging goes on When the batteries become fully charged the yellow LED lamp will extinguish and the green READY lamp will illuminate instead If the temperature should fall outside the al lowable range for charging any ongoing charging will immediately be suspended and the TEMP WARNING lamp will illuminate in lieu of the green READY or yellow CHARGE lamps This is a safety measure to protect the batteries from damage It is not likely that you will encounter this under normal conditions but it may occur if the charger is left on i e connected for a prolonged time after the battery has been fully charged Top off charging will go on for approxi mately 10 hours after the batteries are re ported to be fully charged This will further increase the amount of energy in the bat teries During top off charging the internal temperature in the batteries will increase and sometimes exceed the maximum permitted level Typically this will occur if you initiate charg ing repeatedly without allowing the batter ies to cool in between Therefore you should leave the power supply connected to the mains
110. ecific moment in time when you switch on the internal generator when you switch off the internal generator Note t may sound strange that a time signal s amplitude could be expressed in decibels After all time signals are occasionally negative sinusoids for instance tend to be negative for half the period and the logarithm of negative figures fails to exist However the analyser employs the same technique as the one used in Intensity mode viz to split the negative and the positive part of the signal and then treat them separately In this way the decibel term retains its meaningfulness Wii The FFT Measurement Setup Menu FFT mode supports single spectrum meas urements only no multi spectrum meas urements can be made with FFT The Nor 840 makes all measurements with 67 overlap i e all measurements made with Hanning weighting will be in real time in dual channel mode and all the way up to 25 kHz The measurement setup menu is accessed by pressing the M SerTUP key What is Zero pad The FFT process assumes that the time buffer contains one period of a periodic signal When computing correlation functions these artificial periodic signals are displaced relative to each other and a circular correlation effect will appear This is because the end of one signal period will overlap the beginning of the next period The estimated correlation function will thus be incorre
111. ectrum summing up what took place dur ing the measurement or it can consist of a series of consecutive measurements all of the same duration In the latter case you will be able to produce a time profile of your measurement by looking into a single fre quency band at the time to see how the level of this frequency band changes as a func tion of time Using only one spectrum to document what went on is referred to as a single spectrum measurement while the Starts from Level Mode Always Lv1 Flt Sgl READY 13 2V 4 00 080 080 36 Sep 1997 13 82 54 0 5 2 6 8 8 31 5 125 588 2k f Hz 1 88 eee ill Pettitt lh a a aiaiai Manilii ioiii diie 2 0 68 6 31 5 125 508 2k 8k LA 8 5 A LHe 1 80 When you switch on the instrument it will always come up in Level mode To switch to Level mode from any other mode press the LeveL key followed by SINGLE or MULTI other method is referred to as multispectrum measurement More information about this can be found in the article Single Spectrum vs Multispectrum on the next page Whenever you are going to set up the in strument for a level vs frequency measure ment you need to set the following e Input source selector e Full scale setting e Calibration e Measurement mode e Measurement parameters e Trigger conditions Input source selection is used to activate the input terminal to which the transducer is connected
112. ed Palatino and Helvetica typefaces in this manual Norsonic is a registered trademark of Norsonic AS Windows is a registered trademark of Microsoft in the US and other countries All other brand or prod uct names are trademarks or registered trademarks of their respective companies Every effort has been made to supply complete and accurate information However Norsonic AS as sumes no responsibility for the use of nor for the consequential damages of the use of this informa tion and or the instrumentation described herein Furthermore Norsonic AS assumes no responsibil ity for any infringement of the intellectual property rights of third parties wherever applicable which would result from such use Norsonic AS reserves the right to amend any of the information given in this manual in order to take ac count of new developments If you wish to communicate with us please feel wel come Our address is Norsonic AS P O Box 24 N 3420 Lierskogen Norway Tel 47 3285 8900 Fax 47 3285 2208 e mail norsonic online no Copyright Norsonic AS 1992 97 All rights reserved hank you for choosing Norsonic The real time analyser Nor 840 has ben de signed to give you many years of safe reli able operation Your approach to the Nor 840 documenta tion depends on what you want to do and how much you already know The manual has been divided into eleven sections plus index Each section provides differen
113. ed for measure ments only Data can be copied from but not to this register i e data cannot be transferred to the Last register they have to come directly from a measurement e Data retrieved from any of the storage me dia enters the Aux register From there they can be copied everywhere except to the Last register e Averaging is done in the Average register only e All registers share a common register pool A large amount of data stored in one mode may use so much register capacity that the storage capacity in other modes are seriously affected Otherwise they are completely independent e Register contents are preserved when switching to another measurement mode However switching to MLS mode will clear all registers There is one register per instrument mode Level Filter Single Level Filter Multi Reverberation Time Intensity Filter Single Moving Data Between Memory Locations Intensity Filter Multi Fast Fourier Transform Hard Disk f Floppy i Disk The general command sequence is lt SOURCE gt lt COMMAND gt lt DESTINATION gt SOURCE iS where the data reside CommanD is Move Copy or ComBIiNE while DESTINATION is the location to which the data will be moved or copied BEFORE AFTER LEGEND Source Dest Command SOURCE Avra User Aux oje CJ E O gt 0 x No contents empty Ole O fa O r Ss Q amp Olle cm ko Rey nee The commands Move and Combi
114. ed to show the battery energy level as accurately as possible However the battery capacity will actually increase for batteries used correctly i e not exposed to repeated short duration charging see the article on this page for more on this but the capacity indicator will not automatically be made aware of the increase in capacity To teach the capacity indicator the relationship between the actual energy level and maximum capacity we recommend that you once a month or once every second month charge the batteries completely switch on the analyser and leave it on running solely on batteries until the 0 indicator starts blinking Then you should connect the power supply to the battery pack and recharge the batteries The capacity indicator will now show the actual energy levels Using the Menus Your Nor 840 is a menu driven instrument Each menu is activated by a dedicated key on the front panel There are no submenus A menu contains several parameter fields to control the parameter settings and some times also information fields You have three ways to set a parameter Method 1 The Prev and Next keys are used to scroll through the legal range of settings in the best resolution available Use PREV to move towards lower values and NExT to wards higher When you reach the end of a range the value will overscroll Method 2 The Dia is used to scroll through the legal range of settings in a much faster way than wi
115. ed with your calibration set ting and then measures the linear level which is a separate measuring channel independent of your frequency range set ting twenty times It then picks out the maximum level re corded adds 5dB and then sets the full scale deflection to the nearest legal value above this value It must be set separately for each channel This means that you do not have to have the full scale deflection of both channel 1 and channel 2 set by means of autoranging You may just as well have one set by auto ranging and the other set manually Autoseq Not supported in this version Aux As one of the four independent volatile registers of the Nor 840 All files retrieved from disk end up in this register When you retrieve a file you will overwrite the current contents of the Aux register There is one Aux register for each measure ment mode Hence the Aux register of the multi spectrum mode is not the same reg ister as the Aux register of the single spec trum mode or the reverberation mode op tional However they all share a common memory pool Which means that if one of the Aux registers contains a large amount of data this may affect the amount of free memory available for the Aux registers in the other modes Av La 2nd Comb As an undo function when you have merged a data set contained in the Last register with the contents of the Average register It should be read as Ave
116. ee you as the product of the memory No of periods and the available period length Functions and features not explained here is explained in the single spectrum setup menu to the left In multisoectrum mode the Nor 840 can be set up to record a number of spectra before trigger When you have set up the Nor 840 to record a part of the periods before trigger the acquisition of data starts upon pressing the Start key The data are stored in a circular buffer whose length exactly matches the number of periods to be recorded before trigger When the buffer gets full the oldest data are automatically overwritten Thus the buffer will always contain the latest periods acquired Once the trigger condition is met the circular buffer will be retained containing the periods before trigger while the data acquisition will go on as normal Note that the trigger condition must be set to something different from manual to make this feature work gt Note The lower limit for the period length in multispectrum mode is bandwidth dependent 4 ms 1 amp 3 oct bands 10 ms 12 oct bands and 20 ms 7 24 oct bands If more than one function is set active the lower limits are 10 ms 71 amp Y3 oct bands 20 ms 1 12 oct bands and 40 ms 24 oct bands Tip In multisoectrum mode the number of periods available depends on the amount of free memory available However if you can do with fewer funct
117. ency to make it appear as if it were a sig nal spanning from 0 Hz to 0 AF Hz The signal can now be analysed as if it were a signal with a low upper frequency having a higher resolution Af Example Assume an initial frequency range of 25 kHz This gives a Af equal to 31 25 Hz How the Zoom FFT Terms Relate to Each Other Define the zoom area by entering the centre frequency and then select the zoom factor As the Fig shows the span must be chosen so that half its width is less or equal to the centre frequency chosen Otherwise the span would contain negative frequencies The zoom process shifts the zooms range by means of heterodyning and low pass filtering Thus the zoom analysis becomes similar to an analysis with a lower upper frequency limitation centre frequency span centre frequency The time buffer will not become meaningful for the zoom FFT analysis case Zoom FFT since 25 000 800 31 25 If we now decide to make a 16 times zoom over a selected range the bandwidth will be 25 000 16 1562 5 Hz and the resolution will be 1 95 Hz Since the bandwidth will be analysed using all the 2048 time samples the time buffer length when measured in terms of seconds will increase to 16 times the non zoomed length Why Simply because time and fre quency is related through Af x T 1 in which Af is the frequency resolution and T is the time buffer length For the above example the time
118. enever applicable the instru ment and measurement setup information Only one window is active i e responds to cursor movements etc at the time The active window has a thick frame surround ing it Use the vertical pointing arrows of the FIELD SELECTOR keys to go between the win dows In each window you may set such display parameters as horizontal and vertical gradu ation the vertical top scale and the horizon tal datum the lower end of the scale as well as move the graph cursor Observe that the alterations possible in the display have no effect on the measured or recalled data as such only the appearance of the data will be affected Use Type to switch between the display modes The Four Display Modes Dual display with setup information Single display active window Int Flt 5Sgl STOPPED 13 1V 06 00 15 738 6 May 1998 66 31 56 Int Flt 5Sgl STOPPED 13 1 60 00 15 738 6 May 1998 48 32 14 dB LAST BSIL H 12 8 OSPL 18 5 N 1 80 0 i 3 oct 60 8 1 8s F 20Hz 2 kHz 40 0 ig Manual Cont inuous 20 0 E a e a n a a a 0 5 2 80 8 0 31 5 125 f Hz 1k End 80 00 35 000 Intensity Bleg 26 2 mPI This is an examp appears in the d 80 0 METTEN T T t T T T T T T 0 5 2 0 8 80 31 5 125 588 2k 8k LA 125 58a 2k Bk LA f Hz 1k T f Hz 1k Type Single display Du
119. ent or vice versa or the upper display may show a graph while the lower shows a tabulation of the very same data etc When you select any of the two dual func tion displays with or without setup infor mation the screen will consist of an upper and a lower part which we may call win dows plus whenever applicable the instru ment and measurement setup information Only one window is active i e responds to cursor movements etc at the time The active window has a thick frame surround ing it Use the vertical pointing arrows of the FIELD SELECTOR keys to go between the win dows In each window you may set such display parameters as horizontal and vertical gradu ation the vertical top scale and the horizon tal datum the lower end of the scale as well move the graph cursor Observe that the alterations possible in the display have no effect on the measured or recalled data as such only the appearance of the data will be affected Use Tyre to switch between the display modes The four display modes Dual display with setup information Lv1 FFT Sgl STOPPED 13 1 685 7 Oct 1997 12 46 13 Single display active window Lv1 FFT Sgl STOPPED 13 1V 685 7 Oct 1997 12 46 21 dB Chi LAST 125 8 Auto spectrum Y 85 8 P W 105 84 2 GHz 25088 Hz 85 8 User def ay 65 84 ig Amplitude 45 0 Continuous 7 0 00 12508 00
120. ent Setup a an R 2 1 3 octave Upper frequency Time constant Bandwidth Lower frequency es je Serial measurement A Off periods oll periods b trigger Max of periods 32000 Total time Values to Leq Jl On record a ac m h h The keys for these tasks Page Up Home Inside a Parameter Field Use INSERT to edit a string without overwriting the contents When INSERT is operated the cursor will appear at the end of the current field Inside a parameter field whilst editing in the string field Use alphanumeric characters ASCII 32 127 to enter the contents Use Insert to toggle between insert and overwrite Use lt or Prev to move cursor left Use or Next to move cursor right Use Diat to move the cursor in either direction Use Home to go to the start of the string and Enp to go to end of the string Use Esc to exit string field ignoring undoing all changes Use Enter to leave string field putting changes into effect Use DeL to delete characters to the right of the cursor and Bksp F12 to delete characters to the left of the cursor The field Cursors The Next key Getting On line Help The Nor 840 comes with an on line help system providing explanation of the func tion of an activated menu and legal ranges for the menu s parameter settings To display the on line help text for a given menu produce the menu by
121. ent temporarily and then resume the measurement later You may also stop the measurement prematurely by pressing the Stop key The measurement will go on until the time buffer has been filled up and the corresponding spectrum calculated The instrument does not discriminate be tween pausing and termination with respect to resuming a halted measurement There fore to pause the instrument just press the Pause or the Stop key To resume measuring press the Cont key If the measurement was halted prematurely paused pressing Cont will cause the in strument to resume the measurement and go on until the preset number of averages has been reached On the other hand if the Cont key is pressed after the preset number of averages has been reached the measurement will be prolonged by a another set of averages equal to the pre set number of averages In the latter case the total number of averages will be the sum of the two measurements pro vided the measurement was not terminated prematurely during the prolongation F A Tour of the FFT Mode Display There are four display modes in the Nor 840 two single function and two dual function modes When we say function display rather than channel display this is because in dual func tion display mode the two display halves are completely independent The upper display may show what you just measured while the lower may show a graph of a stored measurem
122. equired Consequently you must apply cor rect units when scaling the frequency spec tra acquired To be able to determine what will be the optimum scaling of a given spectrum you must first evaluate what type of signal you are measuring on The signals can in general be divided into three types deterministic random and transient A fundamental difference here will be the du ration of the signal the determinstic and the random signal types are both continuous while the transient type of signal is not A transient signal is in this part of the manual considerd to be a signal which starts and ends at zero amplitude within the time buffer length The complete signal should be analysed in units of energy Stationary continuous signals on the other hand should not be measured in terms of energy since the amount of energy measured will be directly proportional to the measurement duration Therefore power which is energy per time unit is a better choice Continuous signals are either random or de terministic The former type will have a con tinuous spectrum while the latter has a a spec trum consisting of lines a line spectrum A continuous spectrum should be analysed in terms of spectral density i e the meas ured level should be divided by the frequency unit Hz that is This is because the meas ured level will be proportional to the filter analysis bandwidth at a relatively flat part of t
123. es for a better overall signal to noise ratio The signal is red in the lower end and white in the upper end of the spectrum making it look like a NY when viewed using a logarithmic frequency scale The frequency at which the spectrum changes from red to white is the geometric mean of the frequency range of the measurement which you set in the measurement setup menu for example 50 10 000 Hz The geometric mean on a linear scale corresponds to the arithmetic mean on a logarithmic scale so what we actually do is that we divide the frequency range in two halves and let the lower part the left part in the Nor 840 display use red noise and the upper part the right part in the display use white Your Nor 840 comes with a powerful noise generator built in To access the setup menu press 2ND GEN In MLS mode the generator can be set up to supply white noise whose level will in crease by 3 dB per octave when viewed us ing fractional octave filters red noise which will decrease by 3 dB per octave when viewed in a similar manner or a combina tion of the two called red white noise The main purpose of the red white noise is to boost the extremes of the spectrum to obtain a better overall signal to noise ra tio Once the generator has been properly set up and the setup menu exited press GEN to activate the generator and again to deacti vate Chapter 7 98 Spectral Weighting Function Fundamentals 99 Creat
124. etting The reason why the other modes are not affected is that otherwise measured data not stored would be deleted to avoid in consistencies However this means that if you make a measurement in any other mode with out modifying the lower end setting of the frequency range the frequency bands in the vicinity of the highpass fil ter cutoff frequency will be biased due to the presence of the highpass filter In the current mode you may change the setting of the lowest frequency band to be measured to the value of your liking after the highpass filter has been acti vated The change is made inside the measure ment setup menu for the current mode Should you again modify the highpass filter setting and set it to a higher value in Hz the same will take place again provided the lower end setting is lower or equal to the highpass filter cutoff fre quency Otherwise it will be left unaf fected If you decide to modify the lower end keep in mind that the above biasing of the lower frequency bands will apply to the current mode as well The highpass filter cutoff frequency stated is the 0 5 dB frequency point not the usual 3 dB frequency point Wii The Menu for this Task Input source selection ch 1 Options are Off Line Microphone Charge Intensity Highpass filter ch 1 18 dB oct Options are Off 0 63 Hz 20 HZ Values are the 0 5 dB points Input selection Ch 1 settin
125. even when not using the Nor 840 or you should only connect it to mains when charging is really needed The Battery Capacity Indicator The capacity indicator or fuel gauge pro vides an indication of the remaining energy in the battery pack When the Nor 840 is off and no charging takes place the remaining energy level is checked by pressing the BAT TERY CHECK button When the battery pack is being charged or the analyser is operating the capacity indi cator remains illuminated Checking the battery capacity could be worthwhile before going on in situ meas urement sessions and is therefore strongly recommended Battery voltage indication ENDED Lyl Flt 5gl Note Tip H 00 06 156 22 Sep 1997 16 56 51 When the battery voltage drops below 11V the battery voltage will appear in reverse video on the screen A message warning you will also appear If you are running an MS DOS program when this happens the LCD screen will start to flash to inform you about the battery condition No other warning will be given Once the voltage drops below 10 5V a message will inform you that the analyser is about to shut itself down Any ongoing activities will be aborted and autosave initiated as soon as the voltage gets too low to run the analyser The Nor 840 does not discriminate between batteries and mains Any power supply voltage drop will be considered as a battery failure The battery capacity indicator has been adjust
126. f the two dual func tion displays with or without setup infor mation the screen will consist of an upper and a lower part which we may call win dows plus whenever applicable the instru ment and measurement setup information Only one window is active i e responds to cursor movements etc at the time The active window has a thick frame surround ing it Use the vertical pointing arrows of the FIELD SELECTOR keys to go between the win dows In each window you may set such display parameters as horizontal and vertical gradu ation the vertical top scale and the horizon tal datum the lower end of the scale as well as move the graph cursor Observe that the alterations possible in the display have no effect on the measured or recalled data as such only the appearance of the data will be affected Use Type to switch between the display modes The Four Display Modes Dual display with setup information Single display active window Lv1 Flt Sgl READY 13 2V 0 00 00 000 36 Sep 1997 13 82 54 Lv1 Flt Sgl READY 13 2V 0 00 00 000 36 Sep 1997 13 03 02 dB Chl LAST mSPL i OMax 42 3 105 0 SPL 39 3 Leg Max N 1 BW 1 3 oct TC 1 8s F io 16Hz 1 16kHz 85 84 Trig Manual Continuous 25 0 2 6 8 8 31 5 125 588 2k 8k LA 0 5 2 0 8 0 31 5 125 500 LA
127. fact that we do apply a weighting to the signal will influence its shape However the alterations intro duced are well controlled and can to some extent be compensated for For example the amplitude of the windows is calculated so that the energy contents of the signal remains the same after the window has been applied Guidelines for the Use of Windows In general the following guidelines are recommended for proper use of win dows For the analysis of continuous signals Rectangular weighting should only be ap plied when analysing special sinusoidal signal i e multi sine signals having frequencies coinciding with the lines in the FFT spectrum and no frequency components elsewhere Hanning weighting is a general purpose weighting function and is in general the 44 E recommended window for continuous signals Since the Nor 840 does all the analysis using 67 overlap when Hanning is applied no loss of data will occur Rectangular and User defined cannot be recommended for continuous signals For the analysis of transient signals Rectangular weighting is the general pur pose window for this application pro vided that the transient is shorter than the time buffer length User defined weighting may be used for short impulses and transients mainly to improve the signal to noise ratio and for gating purposes Exponential weighting should be applied to transients that do not decay suffi ciently withi
128. fers are artificially put after each other By multiplying the X f by its complex conjugate we remove the influence from the moment of observation i e the phase of the signal For cross spectrum the product X f x Y f will produce a vector whose phase is identical to the difference between the phases of the two vectors and again we have removed the influnce of the moment of observation To avoid the discontinuities at the extremes of the time buffer Fig lower left the amplitude at the extremes are forced to identical values zero The time buffer contents is multiplied by es a time window aa oe here shown bipolar to ee ae Clarify and the result is zero at the extremes There are many different windows functions around but Hanning with the shape of a cosine is the most commonly encountered More about FFT Windowing Functions As described in the article on the previ ous page spread the FFT process as sumes that the contents of the time buffer is one period of a periodic signal In order to avoid introducing signal components not present in the original signal the two extremes must be set to the same value thus avoiding discontinuities at the extremes For practical reasons this value is always set to 0 The process of time weighting the time buffer contents is also called windowing since we change the window through which we observe the signal Obviously the
129. frequency bands the free memory available can be spent on what you really need The number of periods available will be doubled if the number of functions logged is halved Likewise it will be doubled if the frequency range is halved Therefore we recommend that you consider your needs before you set up the analyser Is the time domain resolution you have chosen appropriate or is it overkill drowning you in data If you can get away with for instance half the time resolution i e doubling the period length you will be able to cover the same total duration with only half the number of periods So maybe you could keep that many functions activated after all B 7 Trigger Conditions in Level Mode There are separate trigger setups for each of the two modes one for the sin gle spectrum mode and another for the multispectrum mode In this way the two modes are kept apart a feature that comes in handy when making build ing acoustics measurements with the Nor 840 The menu contains context sensitive el ements if you select trigger conditions related to level extra parameter fields will appear to let you define what level in which channel and which frequency band to serve as the trigger condition Likewise if you select clock as trigger condition extra fields will appear to let you define the time of trigger Note that if you want to record the time profile of what takes place immediately before the trigger condition
130. gn a title to your measurement This may help you keep track of what was measured and where The title is assigned to the contents of the current register of the current mode If you move or copy the contents of the current register a copy of the title follows the meas ured data If you assign a title to the Last register and let it remain unchanged all following meas urements will acquire the very same title since the title is assigned to the contents of the Last register whatever that may be We therefore recommend that you consider updating this title regularly to make it mean ingful If you change to another measurement mode the currently selected register of the new mode will acquire the same title as the same register of the previous mode unless that register of the new mode had a title al ready and it was empty in beforehand To access the Title menu press 2ND M SETUP A Tour of the Level Mode Display There are four display modes in the Nor 840 two single function and two dual function modes When we say function display rather than channel display this is because in dual func tion display mode the two display halves are completely independent The upper display may show what you just measured while the lower may show a graph of a stored measurement or vice versa or the upper display may show a graph while the lower shows a tabulation of the very same data etc When you select any o
131. gs T HP filter Channel 2 Source Ch 2 settings Input source selection G 2 Highpass filter ch 2 Lowpass filter 18 dB Oct Only when Charge selected Options are Off 1 4 kHz 0 5 dB point If a channel is set to Off in this menu the corresponding part of the Calibration menu will appear blank The Menu for this Task There is one menu per channel J Fuliscale channel 1 channel 1 Fullscale 18a dB 2 00e 00 Abert Hb 2 00e 00 u The full scale setting of the channel in dB The corresponding setting in absolute units Fulkscale channel 2 TA lt 2 2 00 00 Ju Fullscale dB Do not confuse the full scale setting and the full display setting The former defines the input amplifier gain and hence the overload margin for a given signal level while the latter is used to set the display to make the measured signal fit within the setting of the axis If you set the full scale setting to one of the three highest settings a small x will warn you that the analyser is prone to overload 50 6 A 5 2 0 xf Hz 315 The available full scale setting of a meas urement is given as a combination of the input amplifier gain setting and the cali bration setting The gain is set separately for each chan nel and is adjustable in steps of 5 dB Press GAIN1 GAIN2 to enter the menu The full scale setting controls the set ting of the
132. gue sockets These sockets are located on the analogue socket panel Connect as follows e Microphones are connected to the Mic socket e Accelerometers should be connected to the Acc socket e Line drive accelerometers accelerom eters with built in conditioning amplifier are normally connected to the Mic socket via a special adaptor gt E e Line level signals are fed to the Nor 840 via the Line input e Intensity probe output signals are fed to the analyser via the Intensity probe socket On the Use of the Menus The Nor 840 is menu driven but unlike computer operating systems with a graphi cal user interface such as Microsoft Win dows all menus are accessed from dedi cated keys Inside a menu use the FIELD Cursor keys to navigate between the parameter fields You have three ways of setting a parameter e by using the DIAL to scroll through the available settings e by using the Prev amp Next keys e by keying in a numerical value Even parameters that you do not normally associate with numerals have been assigned a value to enable quick setting Example If you key in 1 the Input source menu the input source will be set to Line input If you key in 2 it will be set to Mic ete Note that when you enter numerical val ues the analyser s keys are in alphanumeric mode This means that values like 10 con veniently can be entered as 10e 6 The display can be set up to show one or
133. he CURSOR with or without 2Np the X MIN and the X RANGE are used to select the cursor function to which the Diar and the Prev amp Next keys apply However these step con trol keys will not cause response until the graph has been redrawn completely nth When the keys Y Max Y RANGE 2ND X RANGE and 2ND Y RANGE are pressed prior to using the step control keys any display update in progress will be aborted and a new update started Cursor Alignment In dual display mode the graph cursors X axis cursors of the two windows may be aligned with each other and moved together in either direction Press 2ND Rer to align cursors To deactivate press again press Type or change to another measurement mode e g single spectrum or intensity The master cursor will be the cursor of the active window the one surrounded by the thick frame The two display windows must contain data acquired with the same filter bandwidth e g 1 3 octave bands but they need not display data in identical domains i e one can show data with time as X axis while the other shows frequency as X axis The contents of the two windows need not belong to the same measurement Reference Cursor The reference cursor is used to investigate the difference between two points on a graph To activate the reference cursor select CURSOR to move the graph cursor to your ref erence point then press Rrr and use the DIAL or Prev amp Next t
134. he selected file The path to it like in MS DOS Mask if applicable File type Directory column Tools for saving Name Emmas eel Save 12 sdf LeFiMu 644 sichl sdf LeFimMu boktst 4 ref laiid cfg Save Save leaving without saving Exit making new directories 988 971118 ae a 978731 89 45 and for providing more information File column about the Auto File Gen file tmp selected Ui Tools for automatic generation of file names Use the FieLD SELEcToR keys to go between the parameter fields However inside the directory or file column use Prev Next or the Dia Although this is in strict accordance with the operating principles of the Nor 840 it may seem strange to some at first glance The Wildcard Is used to Example Det Asterisk Question mark 7 Display all Nor 840 measurement and setup files but no other files Represent a whole word or a group of characters including no characters at all Represent a single character pcx will display all files with the extension ocx such as ole pcx arne pcx However ar e pcx will display files like are pcx arne pcx arveee pcx ar e pcx will display files like arne pcx arve pcx but not files like avre pcx arpve pcx Storing a Measurement on Disk A fully equipped analyser will contain a built in floppy disk drive comes as stand ard on all models and a
135. he generator can be set up to supply white noise whose level will increase by 3 dB per octave when viewed using fractional octave filters but it looks flat when viewed using FFT because of its linear frequency axis pink noise which looks flat in the fractional octave domain but with a level decreasing by 3dB per frequency doubling when viewed using FFT bandpass filtered 4 or 7 3 octave bands only impulse 4 or s oc tave bands only and bandpass filtered im pulse 4 or s octave bands only For the bandpass filtered signals the fre quency band is determined by the current graph cursor position Once the generator has been properly set up and the setup menu closed press GEN to activate the generator and again to deacti vate What Is Multi sine Multi sine is a complex signal consisting of sinusoids The frequency components of this signal coincides with the lines of the FFT spectrum Hence there is no signal energy outside these lines Such a signal can be shown to have a periodicity equal to the time buffer length This means that rectangular weighting can be applied without introducing discont inuities at the extremes In addition the phase of each of the sinusoids has been adjusted to give a crest factor much lower than that of conventional noise approximately 1 3 a single sinusoid has a crest factor of 1 4142 i e V2 or the same as 3 GB i Chapter 5 Making Intensity Me
136. he measured functions if you set them to functions not measured no curve will be displayed However when you select Ch1 and Ch2 only the first the left most setting will be applied to the display The settings of the two others will be ignored Two curves will be displayed one for each channel Which function the curves show will de pend on the curve specified in parameter field 1 of the Curves setup in the Display Setup menu Should this parameter field be set to 0 Off the analyser will search for the first activated function and use that for the two curves instead The Numerical Table The Display Setup menu is also used for set ting up the functions to appear in the nu merical table The table consists of six columns If you set e g three columns to display the same func tion this function will appear three times in the table In addition to the functions available for graphical display the table also offers the option of displaying the number of averages made within each filter band the average counter Note that if you select Ch1 and Ch2 as dis played curves the analyser will override your table setup The number of columns with non zero con tents will always be five leaving the rightmost column empty The contents of these five columns will be ch 1 data ch 2 data the arithmetic difference between the contents of column 1 and 2 the average counter for ch 1 and finally the average counter from
137. he spectrum The measured line spectra amplitude will provided the the analysis bandwidth is suf ficiently narrow to separate the individual components be independent of the filter bandwidth The Nor 840 detects the RMS value of the signal The FFT extension offers the follow ing scalings Root Mean Sqare RMS VPWR Power PWR RMS Power Spectral Density PSD PWR Bandwidth and Energy Spec tral Density ESD PSD x Observation time We recommend the following e Scale in RMS or PWR when analysing pe riodic determinstic signals e Scale in PSD when analysing stationary random signals e Scale in ESD when analysing transients e Sometimes signals are a combination of periodic and random e g sinusoids in noise the RMS or PWR should then be used for scaling the sinusoidal compo nents the lines in the spectrum and PSD for the continuous part of the spectrum since this is originating from a random type of signal nih The Menu for this Task Function coordinates Function to be displayed Options are 01 Auto spectrum 02 Cross spectrum 03 Coherence 04 Fra response H1 05 Frg response H2 06 Weighted time 07 Weighting window 08 Auto corr 09 Cross corr Which channel Options are Ch 1 Ch 2 Options are 1 Magnitude 2 Phase 3 Real part 4 Imaginary part ung tion Channel k i Function coordinates Vertical axis scaling unit X axis Options are
138. he total measurement duration will be the sum of the durations of the two measurements The Menu for this Task Tip Title of the LAST register fit within the borders This is an example showing how the text appears in the display Note that you must use the Enter key to make the e Assigning a Title to Your Measurement Enter the text here The analyser will enter aloha mode upon entering this menu so you won t Int Flt Sgl STOPPED This is an examp N 1 Jappears in the g 1 3 oct 1 8s F 28Hz 28kHz ig Manual Continuous Intensity This is an exfamp appears in the d have to press ALPHA first To exit the menu you must use the FIELD CURSOR to move to this field and then press ENTER and here is how the text appears in the display Note how the text has been truncated Only the text written inside the dotted field appears in the display when exiting the menu The text is the same for the upper and lower window since they belong to the same measurement If automatic file name generation has been set to off and a title is present the eight first characters of the title ignoring any spaces will be proposed as file name when storing the acquired data You may assign a title to your measurement This may help you keep track of what was measured and where The title is assigned to the contents of the current register of the current mode If
139. her frequency band Change the horizontal graduation Change the horizontal datum lower end of scale Change the top scale value Change the vertical graduation Switch between display modes Switch between display of RT related and multisoectrum related graphs Switch between display of a decay and RT vs frequency Display a tabulation of the calculated reverberation time values Wii Calculating RT Before Averaging Press RT key to calculate multisoectrum measurement 4 Move tha microphone y and repeat 0 080 until sufficient Copy result to Avrg number of register averages is reached Do this Select as cursor function Select as cursor function Select as cursor function Select as cursor function Select as cursor function Press the key a number of times until the required display mode is reached Press the key No new calculation will be made until changes are made in the Reverberation calculation menu Press the key Press the key Chapter 4 42 Fast Fourier Transform Fundamentals 43 Time Weighting Windows 45 Zoom FFT 46 Selecting Input Source for FFT Measurements 47 Full Scale Setting 48 Calibrating for FFT Measurements Is Done in Level Mode 50 Trigger Conditions in FFT Mode 52 The FFT Measurement Setup Menu 53 Measurement Controls in FFT Mode 54 A Tour of the FFT Mode Display 56 A Few Words on Functions 58 The FFT
140. horizontal graduation and thereby also X axis spanwidth Harmonic cursor is not operating in fractional octave modes Z Setup Cursor alignment Reference cursor Step one step towards higher values Note that the Y axis is left unaffected by this swopping since the level in both cases will be the same RMS or Peak values always in dB To move along the X axis irrespective of whether this represents time or frequency press CURSOR and then use the DIAL or the Prev amp Next keys To move in the Z direction again irrespec tive of what it represents press 2ND CURSOR and do as for cursor movements along the X axis A small icon in the display will indi cate that Z cursor is selected 3D Cursor Functions Measured data acquired in multispectrum mode may also be displayed as a three di mensional graph For sound intensity func tions only positive values can be shown To activate this feature make a multi spectrum measurement set the column 1 of the Displayed curves in the Display Setup menu to one of the functions actually meas ured and press the 2ND Lr LT keys If you fail to set up a function actually meas ured all you ll see will be an empty floor and no graph The graph is always drawn so that the peri ods most recently acquired appear to be clos est to you Use the Lr Lr to flip the X and Z axis Whilst the graph is being drawn the Tyre key is used to select the next display type T
141. ical axis top scale value Y Max and the horizontal axis minimum value X MIN The Cursor Control Keys X min cursor defines the lower end of the displayed X axis X axis Cursor moves the graph cursor along the X axis 2nd Y max Beam finder A Y range the top scale value Y range cursor Beam Finder Locating the Graph Sometimes the mismatch between the top scale setting and the values of the graph is so significant that no graph is shown in the display What to do Enter the beam finder A term borrowed from the world of oscilloscope technology where it was often difficult to tell which way to adjust the top scale to get the graph within the display If you press 2ND Y Max the top scale value is changed by the analyser so that the graph appears in the display The Y Max and Y RANGE may then be used to refine the view as usual In particular when using the integration dif ferentiation features of the display setup menu your graph may vanish from the screen although we have tried to compen Y range cursor defines the vertical graduation and thereby also Y axis spanwidth Harmonic cursor Z curs V Y Z locates the graph and adjusts Y max to display it Y max cursor controls _ E Cursor alignment defines the vertical graduation and thereby also Y axis spanwidth aoa Step one step towards smaller values Reference cursor y Use the Diat to scroll step one step t
142. if you set the full scale deflec tion to a very high value you face the risk of having severe overload in the transducers without seeing any trace of it in the analyser simply because the analyser input isn t overloaded For ex ample a microphone with a sensi tivity of 50mV Pa will distort severely more than 3 total harmonic distor tion when exposed to levels above 135 dB A To warn you about this the three highest settings provide an aster isk in the display Calibrating for FFT Measurements Is Done in Level Mode The calibration for FFT level measure ments must be carried out in Level mode Press LEVEL to switch to Level mode g Calibration The Tool for this Task The Menu for this Task ea Channel 1 Microphone Although you may calibrate by just key ores ene ing in the sensitivity we always recom A E G mend that you use a calibrator This is D Unit BdB the only way to ensure proper operation B H of the entire measuring chain including ae o a r the transducer s 9 c TE 3 Channel 2 Microphone If you are going to use the instrument Be oe Level for vibration measurement it may be 3 D J convenient to change the 0 dB level to Unit BdB obtain dB readings easy to compare with Z K utocal other vibration measurements Check F with relevant Standards and conven tions to find suitable or commonly used Aia ran M 0 dB levels Pol Volt 200 N Note tha
143. ine a dual channel measurement into a single channel measurement The function works on the contents of the Average regis ter only What it actually does is that it merges the contents of the two channels and puts the result of the merging into channel 1 leaving channel 2 empty The merging is an averaging on energy basis 1 lt 52 2nd Last Swap the contents of the two measuring channels 10 Not supported in this version 10 Not supported in this version 2nd Use this key to access all functions printed in orange colour on the front panel When the keyboard is set to alpha mode for ex ample when keying in a measurement title the 2ND key works as the Suirr key on a PC keyboard to key in capital letters 3D 2nd Lf Lt Three dimensional display of multispectrum measurements Align 2nd Ref Align the cursors of the upper and lower dis play windows Alpha Default On whenever appropriate Alt The same way as the same MS DOS key is used i e it requires the MS DOS extension to work Analyse Enter the analysis part of the Nor 840 as op posed to the DOS key which is used to en ter the MS DOS mode applies to units equipped with the MS DOS extension only Auto 2nd Gain1 2nd Gain2 Perform input autoranging as an alternative to setting the full scale deflection manually What it does is that it sets the full scale de flection to the maximum level available closely connect
144. ing Spectral Weighting Functions from Measurements 100 Creating Spectral Weighting Functions from Scratch 101 Loading a Spectral Weighting Function into the Analyser 102 Applying a Spectral Weighting Function to a Measurement Generating Spectral Weighting Functions Spectral Weighting Function Fundamentals The NOR 840 lets you define your own spectral weighting functions These can be directly based on an actual measurement or they can be keyed in by you This feature applies to fractional octave modes only Your analyser comes with the following set of predefined spectral weighting functions as standard e SumA SumB SumC and SumL are spec tral weighting functions used to calculate the weighted value based on the fre quency range actually measured For fre quency ranges smaller than the standards define for the A B and C curves the value calculated will differ from what the value would be if measured with a sepa rate A B or C filter network For L inear the same will apply if significant amounts of energy exist in the signal outside the measured frequency range e Hand arm Whole Body X Y Whole Body Z and Whole Body Combined e Sumfis a sum of the energy of all the fre quency bands measured with flat or no weighting There is a difference between linear and flat Linear is defined as no spectral weighting between 20 Hz and 20 kHz and SumL is defined similarly This means tha
145. iods periods b trigger Information field ax of periods 32HHH Total time A He a2 Hdg Information fields appear to provide information only they Be w Leg ee Wie cannot be accessed Min e Off SPL e Off by you SEL Off Peak JA Off Information field names Parameter field names Menus are context sensitive i e some parameter fields appear when applicable only nih Navigating Through the Menu and Inside a Parameter Field Navigating Through the Menu Use T to move to the nearest possible field above the current field If none is available current position is maintained Use J to move to the nearest possible field below the current field If none is available current position is maintained Use lt to move to the previous field in the horizontal plane If none is available it will move one field up If at the beginning of the menu overscroll wraparound will take place Use to move to the next field in the horizontal plane If none is available current position is maintained If at the end of the menu overscroll wraparound will take place Use Home to move to the beginning of the menu However not inside a list field Use Esc to exit a menu ignoring all changes Use Enter to leave amenu putting changes made into effect The numerical keypad The 2nd function is used to access the secondary functions of some of the keys The Dial Prev ious key Fa Measurem
146. iods and the duration of each pe riod is referred to as the period length The period length can be set to anything be tween 4 msec and 100 hours If more than one function is to be measured e g Lig and SPL simultaneously the lower i MAX limit is 10 msec time axis Single Spectrum vs Multispectrum At any rate the maximum number of pe riods in a single multispectrum measure ment is limited by the amount of free memory available in combination with the number of functions to be measured si multaneously Single spectrum measurements are multi spectrum measurements with the number of periods available fixed to one The sin gle spectrum mode appears for conven ience only The primary application of the single spectrum mode is general level or intensity analysis while multispectrum mode is used principally to obtain time profile information such as capturing sound decays for reverberation time analy sis frequency axis Multispectrum measurements permit the inspection of the time profile of a given frequency band or spectral weighting network To further extend the overview you may set up the analyser to capture data before the trigger condition is met to be able to study what takes place immediately before the trigger condition is fulfilled Upon a successful multispectrum meas urement you may inspect the time profile for a given frequency band or spectral weighting function as well as inspect the e
147. ions logged simultaneously or with a more narrow range of frequency bands the free memory available can be spent on what you really need The number of periods available will be doubled if the number of functions logged is halved Likewise it will be doubled if the frequency range is halved Therefore we recommend that you consider your needs before you set up the analyser Is the time domain resolution you have chosen appropriate or is it overkill drowning you in data If you can get away with for instance half the time resolution i e doubling the period length you will be able to cover the same total duration with only half the number of periods So maybe you could keep that many functions activated after all _ FA Sound Intensity Trigger Conditions Fractional Octave Analysis There are separate trigger setups for each of the two modes one for the sin gle spectrum mode and another for the multispectrum mode In this way the two modes are kept apart If you want to record the time profile of what takes place immediately before the trigger condition is met you may set up the analyser to do so However this ap plies to multispectrum measurements only and it is not done in the trigger setup menu but in the multispectrum measurement setup menu The trigger condition menu is accessed by pressing 2ND START The nine trigger conditions available and how they work can be seen on the right part of this page spre
148. ique of maximum length sequence MLS is based on a few well known facts These are e The measurement object is excited by means of impulses Any deformation time smearing of the impulses recorded at the output side of the measurement object originates from what the measurement object did to these impulses Repeated excitation is used to average out background noise Applies to System Analysis The MLS technique is used for system analy sis and not signal analysis Signal analysis deals with signals while system analysis aims at revealing system specific properties Properties which are independent of the sig nal used to excite the system As system analysis requires knowledge about both the stimulus and the response of a sys tem to be able to characterise it is will always be atwo or more channel analysis You can not make system analysis with only one chan nel measuring the stimulus only will tell you nothing about the response and hence how the system behaves Likewise measuring the response only will leave the stimulus un known and again no system information will be revealed Nevertheless MLS is applied to reverberation time measurements with great succes How come it may be applied to such measure ments After all reverberation time measure ments are single channel measurements Ac cording to the above they should belong to the signal analysis type of measurements rather than the system analysis ty
149. l Mode Measurement Controls Merging Dual Channel Data to Obtain Single Channel Data Serial Level Analysis Averaging a Measurement too Far Assigning a Title to Your Measure ment A Tour of the Level Mode Display The Level Mode Display Setup Menu Displayed Curves The Numerical Table The Level Mode Display Cursors Scaling and Graduation Z axis Cursor 3D Cursor Functions Cursor Alignment Reference Cursor The Numerical Table The Noise Generator in Level Mode 35 36 36 36 36 38 39 40 40 40 41 42 42 42 42 43 44 aoe 45 45 46 47 48 50 52 53 54 50 56 Making Reverberation Time Measurements Noise Excitation Reverberation Time Measurement Fundamentals Impulse Excitation Level Mode Is Used for Acquisition Minimising Background Noise Setting up for Decay Captures Calculating the Reverberation Time Averaging and Viewing the Calcu lated Values Applying the Schroder Method Viewing the Calculated Values Making FFT Measurements Fast Fourier Transform Fundamen tals Auto Spectrum Cross Spectrum Frequency Response Functions Time Weighting Windows More about FFT Windowing Functions Guidelines for the Use of Windows Zoom FFT Zoom FFT in the Nor 840 Selecting Input Source for FFT Measurements Full Scale Setting Calibrating for FFT Measurements Is Done in Level Mode Trigger Conditions in FFT Mode The FFT Measurement Setup Menu Measurement Controls in FFT Mode A Tou
150. lay setup menu 82 displayed curves 82 explanation of symbols used in display 81 graduation 84 numerical tables 82 reference cursor 84 scaling 84 time axis scaling 82 title of measurement 79 used as basis for file name 79 vertical axis scaling 82 z axis cursor 84 Intensity probes 65 L Last key 124 Last register 106 Level of on line help setting the 8 Level key 124 Level mode 3D cursor 30 active window 26 basic concepts 10 calibration using a sound calibra tor 15 cursor alignment 30 cursor icons 30 display cursors 30 display modes 26 display setup menu 28 displayed curves 28 explanation of symbols used in display 27 filter bandwidth setting up 16 Ly frequency axis 11 frequency range 16 graduation 30 highpass filter input source selection 12 input source selection 12 lower frequency 16 measurement setup menus 16 multispectrum principles 17 noise generator features 33 noise generator and serial scan 22 numerical tables 28 period length 11 periods a definition 11 periods before trigger 17 reference cursor 30 retaking frequency bands 22 scaling 30 sensitivity of input source 14 sequential analysis 22 sequential measurement setting up for 16 serial analysis 22 serial measurement setting up for 16 setting up the noise generator 33 time axis 11 time axis scaling 28 time constant setting 16 title of measurement 25 used as basis for file name 25 trigger conditions 18 trigger delay 18 undo a
151. le in the alphabet every time you press the Disk or the HDD key An obvious application for this will be when retrieving files with names gener ated by means of the autonumbering fea ture described in the article Autonum bering Files Stored Consecutively on the pre vious page spread but it may just as well be applied to any set of files The alphabetic order is such that the file AAO1 will appear before AAO2 the file A1A before A1B and the file 001 before OOA etc Storing Instrument Setups You may want to store your favourite setups to save work the next time you use your ana lyser Setups are used to configure the analyser A setup file is therefore a configuration file using the extension cfg as the obvious iden tifier This extension will be appended by the analyser When storing you must indicate whether the configuration file shall comprise all the measurement modes of the instrument or just the mode currently active If you store a setup file on a floppy disk un der the name 840 cfg and insert this floppy disk in the disk drive before turning on the analyser the analyser will pick up this setup file and use it to configure the instrument as specified in the setup file If you are going to use the automatic file generation you must store your setup file in the directory where you want to have your autonumbered files stored If you want to initialise the analyser with a setup file stored on a floppy
152. ling and Graduation To optimise the presentation of the meas ured functions and values you may adjust the horizontal and vertical axes graduations X RANGE and Y RANGE respectively the vertical axis top scale value Y Max and the horizontal axis minimum value X MiIN The Cursor Control Keys X min cursor defines the lower end of the displayed X axis Z axis Cursor moves the graph cursor along the Z axis X axis Cursor moves the graph Cursor along lt A Zurs V ihe K axis Cursor WwW Y max cursor controls the top scale value Yange curso 2 4 defines the vertical graduation and thereby also Y axis spanwidth Y Step one step towards smaller values Use the DIAL to scroll through the valid settings Z axis Cursor In multispectrum mode the measured data can be represented by a three dimensional matrix having level frequency and time as the three dimensions If the display is set to display a spectrum the X axis will be the frequency axis the Y axis will be the level axis and the Z axis will be the time axis You may also display the time profile for a certain frequency band e g the 3150Hz 1 3 octave band or the A weighted value In this case the X axis becomes the time axis and the Y axis remains the level axis while the Z axis now becomes the frequency axis To switch between time and frequency as X axis use the Lr LT key X range cursor defines the
153. ll be the case when using NExT and Prev Turn clockwise to move towards higher values and counter clockwise to move towards lower values When you reach the end of a range the value will overscroll Method 3 For purely numerical values the value to enter will be the parameter setting itself Parameter fields with a limited number of settings also have a number associated with each setting If you key in this number the parameter will be set to the correspond ing state immediately Some parameters have a two digit number of choices Values below 10 should then be keyed in as OX in which OSX 9 Note that the keyboard is in alohanumeric mode when accepting numerical inputs This means that numbers like 10 may be conveniently entered by pressing 10e 6 i e using the letter e as in scientific computer notation A Menu Example to enter a menu press the corresponding key There is a number associated with each setting of the parameter If the number of selections available exceeds 10 a two digit number is used The parameter field selected is shown with reverse video Menu title ere Medsursgent Setup Time constant See l s F Bandwidth 173 octave Lower frequency Hz ok Hz Parameter fields differ Serial measurement Off from the information H M me fields by the look of the Measurement period field borders Ld ol 5 ra T T 5 a z i o Z T 5 D cc Parameter field un per
154. lyser to display sound pressure related functions such as SPL and Leq Note that these will be shown symmetrically about the frequency axis to make comparisons between sound pressure and sound intensity easy to do For p p probes the sound pressure level is the mean sound pressure level i e p t p t For all other types of probes the SPL will be taken from channel 1 The Numerical Table The Display Setup menu is also used for set ting up the functions to appear in the nu merical table The table consists of six columns If you set e g three columns to display the same func tion this function will appear three times in the table In addition to the functions available for graphical display the table also offers the option of displaying the number of averages made within each filter band the average counter The A and Linear spectral weighting networks are true spectral weighting functions in the sense that they are separate measurement filter bands All other spectral weighting functions are applied as postprocessing features only This means that if you synthesise e g a B weighting curve and fail to apply a full bandwidth to your measurement by measuring 50 3150Hz only for example the B weighted values will normally deviate from those obtained with a true spectral weighting filter band The only way to make them similar is to apply your function to measurements When applying spectral weighting
155. mal No measurement title specified Bandwidth 1 24 oct Time constant 1 6s F Lower frequency 48 Hz Upper frequency 468 1 Hz Measurement start Tue 22 Apr 1997 15 40 10 Measurement duration 66 48 01 446 Period length 60 00 00 0280 Total number of periods 72 Trigger condition Manual Channel 1 Channel 2 Input Line Input Line Calibration 26 8dB Calibration 26 8dB Ref Level dB 2 88e 5 Fullscale 95dB High pass filter Off Ref Level dB 2 88e 5 Fullscale 18 dB High pass filter Off The About field of the Save and Load menus provide additional file information What Is SDF All measurement files are stored as SDF files in the analyser The abbreviation SDF stands for Standard Data Format a format designed by Hewlett Packard HP The advantage of using the SDF format is that there are quite a few SDF utility programs available and these may be used to extract postprocess and otherwise manipulate data stored in the Nor 840 For details on Hewlett Packard SDF utility programs contact your local HP dealer Creating a Directory 1 Neme boktet04 edf ath c Name boktst 4 sdf math cN Save Nene KOSOLA Path Mask Measurement Press Copy HDD Go to the directory in which you want to create a subdirectory Move u
156. mode 42 Auto calibration FFT mode 48 level mode 14 Autocorrelation MLS 90 Autonumbering files stored consecutively 109 Autoranging full scale deflection in level mode 13 Input amplifiers in level mode 13 Autoseq key 122 Aux key 122 Aux register 106 Av La 2nd Comb key 122 Average register 106 Averages indication of the number of FFT mode 55 Averaging decays 40 Avrg key 123 B Background level corrections MLS 92 Background noise considera tions for reverberation time 36 Background noise level 36 Backlight turning off and on 3 Bandwidth noise generator level mode 33 Bargraph indication used with spectral weight ing functions 102 Basic concepts level mode 10 of instrument operation 2 Batteries See Battery Battery capacity 4 charging 5 checking the condition 4 low voltage indication in analyser mode 5 in DOS mode 5 mounting 4 optimising accuracy of condition read out 5 top off charging 5 voltage indication 5 Baud rate 116 Beam finder FFT mode 58 BNL 36 BP filtered noisenoise genera tor level mode 33 C Cal key 123 Calibration auto calibration level mode 14 changing the 0dB level level mode 14 doing an auto calibration level mode 15 half of menu is blank 14 intensity mode 68 level mode 14 Index menu 14 menu level mode 14 sensitivity setting level mode 14 using a sound calibrator level mode 15 Capacity battery pack 4 Channel swapping the two 107 Charging battery 5 top off 5 Clea
157. mode 84 level mode 30 Scaling range FFT mode 59 Scaling the spectrum FFT mode 56 Scan level mode 22 Schroeder method 40 Screendumps making 117 making a PCX file 117 Sdf as file extension 108 Sensitivity of input source level mode 14 Sensitivity setting FFT mode 48 Sequential analysis level mode 22 noise generator mode level mode 22 Sequential measurement setting up for level mode 16 Sequential scan level mode 22 Serial analysis level mode 22 Serial measurement setting up for level mode 16 Serial scan level mode 22 Setup 2nd Analyse key 125 2nd Autoseq key 125 2nd Gen key 125 2nd Help key 125 2nd Plot key 125 2nd Print 125 2nd Record key 125 2nd RT key 125 2nd User key 125 Setup menu reverberation time meas urements 38 Setups of the instrument nth retrieving stored 113 Signal to noise considerations for rever beration time 36 Single channel data merged from dual 21 Single key 125 Single spectrum level mode 11 Size key 125 Sockets accelerometer 2 line drive 2 with built in conditioning amplifier 2 analogue 2 input 2 intensity probe 2 Nor 216 2 Nor 240 2 p p type 2 p type 2 two microphone 2 line level 2 microphone 2 Sound calibrator calibrating in level mode 15 Sound calibrator calibration FFT mode 48 Sound intensity See Intensity Sound power 64 level 64 specifying the area 72 Source memory handling 106 Spectral density FFT mode 56 Spectral weighting cre
158. n values of each frequency band or by converting a measurement to a weighting curve Time axis scaling Applies to multispectrum measurements only select between Periods Relative time since trigger and Absolute time date and time of day The displayed graph can be shown spectrally weighted Options are A B C L W1 W8 There is one display setup menu for each of the two windows the upper and the lower window Instead of going to the other window and set up the display you can apply the same setup to the other window by moving the cursor to this field and then exit the menu by pressing ENTER The term SumA denotes the A weighted value calculated from the measured spectrum while the A as such is a true A weighting filter applied to the measurement as an independent measurement channel The two may differ for two reasons round off differences in the digital calculation process normally small deviations and if the frequency range of the measured spectrum is limited see the tip on the left side of this page spread The Sound Intensity Mode Display Cursors The Nor 840 has an extensive set of cursor functions However some apply to certain situations only All the cursor controls are located around the DuL To operate a cursor you start by selecting the type of cursor and then use the Du or Prev amp Next A small icon appears in the display to tell you which cursor func tion has been activated Sca
159. n between the periods You may set up your Nor 840 to capture the time profile of what goes on immedi ately before the trigger condition is met This is done by specifying that a certain number of the multispectrum periods shall apply to the situation before trigger A more exhaustive explanation of this can be found in the article The Level Mode Measurement Setup Menus of the section Making Level Measurements and in the il lustrations to the extreme right of this page spread Specifying Area for Sound Power The surface area for sound power calcula tions is set up in this menu Normally you would set up the area before you make your measurement However for conven ience we have added the option of chang ing the area even after you made your measurement This applies to the contents of Last register only To utilise this post measurement feature press the M Setup key after the measure ment and change the Area for Lw Change nothing else Press ENTER to exit the menu as usual Based on the keyed in area the sound power is calculated for that particular sur face When you transfer these data to the Average register to average them with power data from other surfaces the effect of the surface area is implicitly taken into account Thus the use of surface parts with non identical areas will represent no prob lem The Single Spectrum Measurement Setup Menu Set the time constant Options are 1 16 1
160. n the analyser simply because the analyser input isn t overloaded For ex ample a 4 microphone with a sensi tivity of 50mV Pa will distort severely more than 3 total harmonic distor tion when exposed to levels above 146 dB A To warn you about this the three highest settings provide an aster isk in the display Calibrating for Sound Intensity Measurements Intensity calibration should be carried out in Level mode calibrating each part of the transducer separately This applies to both p p and p u probes You may want to check the system for residual intensity Turn page for a description of this Although you may calibrate by just key ing in the sensitivity we always recom mend that you use a calibrator This is the only way to ensure proper operation of the entire measuring chain including the transducer s If you are going to make non main stream intensity measurements e g in volving one microphone and one accel erometer it may be convenient to change the 0 dB level of the relevant channel to obtain dB readings easy to compare with other vibration measure ments Check with relevant Standards and conventions to find suitable or com monly used 0 dB levels Note that if you set the 0 dB level to a value different from 2x10 the selected setting will appear in reverse video on the screen as shown in the lower Fig to the right The Menu for this Task Cal Q num Se ey be SE HE ES
161. n the time buffer length Hanning weighting can be applied to transients much longer than the time buffer length For frequency response measurements User defined weighting when the input signal is impulsive Exponential weighting for the response of the system when excited with an im pulse provided that the system is lightly damped For zoom analysis Hanning weighting should be used instead Hanning weighting should be used in both channels when a random excita tion of the system is made Rectangular weighting should be applied only when multi sine signals having fre quencies coinciding with the lines in the FFT spectrum are used Wii Thw Window Functions Available a Rectangular no weighting at all b Hanning weighting which is a shifted cosine function starting and ending on O t 0 100 c User defined which is a cosine tapered rectangular window T I i I o 1 2 3 t 0 100 The four T values indicate the start and stop of the tapering in of the time buffer length If T 0 T T 50 and T 100 the window becomes a Hanning window and if T T 0 while T T 100 it becomes a rectangular window d Exponential window d Displacement 0 T 100 The position and size of the exponential window is given by its displacement relative to the origin 0 and its time constant t The FFT process normally produces a spec trum covering a range from 0 to some cho
162. nce files are generated from intensity measurements For intensity measurements the spectral weighting function will be shown symmetri cally about the frequency axis The bandwidth of a spectral weighting func tion must be the same as the bandwidth of the spectrum to which it shall be applied Apart from that no restriction applies a spectral weighting function generated in multispectrum intensity mode may just as well be used in level single spectrum mode In multispectrum mode the actual spectral weighting function will be the function set in column No 1 of the numerical table for the period No currently displayed in the ac tive window Hence regardless of whether the spectral weighting function was gener ated in single or multispectrum mode the result will be a single spectral weighting function always This article describes how to create spectral weighting functions directly from an actual measurement How to apply a spectral weighting function to a measurement is described on the following pages Creating Spectral Weighting Functions from Scratch A spectral weighting function can be applied to a spectrum to show the effect of the weighting to provide the weighted level or to serve as a reference spectrum to which the current measurement is compared The spectral weighting function is generated from a reference file The reference file is made either directly from a measurement as
163. ncy line present in both graphs the slave s cursor will move immediately to that line nth Time functions can be aligned with time functions only Reference Cursor The reference cursor is used to investigate the difference between two points on a eraph To activate the reference cursor select CuRSOR to move the graph cursor to your reference point then press Rer and use the Dia or Prev amp Next to move the graph cur sor to a point elsewhere on the graph The distance vertically and horizontally between the two points will now be shown in the active window Harmonic Cursor The harmonic cursor is used to indicate any possible harmonic relationships present in the recorded spectrum The harmonic cursor is activated by press ing the Harn key The harmonic cursor will not appear when ever the graph cursor frequency cursor is located close to the lowest frequency in a baseband unzoomed measurement The reason is simply that all you ll get when ac tivating the harmonic cursor from this po sition is a screen covered with cursors scaling and Graduation Range Y axis 20 40 60 80 or 100 dB across the vertical scale or in a 1 2 5 sequence when set to engineering units Keaxis 13 14 12 1 1 amp 1 4 1 ana 8 1 The Icons Show the Type of Cursor Selected A X min ASB 1G ADAFE The Reference Cursor E Graph cursor B X range C Y max D Y range Lv1 FFT Sgl ENDED 13
164. nd preamplifiers can be checked with the Nor 1254 The IEC 61043 Standard contains require ments to sound intensity measurement equipment We recommend that you read through that Standard The Menu for this Task Sensitivity channel 1 Sensitivity channel 2 The sound intensity level The SIL O dB level ihe ore Cal freq O cB level The sound pressure level as used in Calibrator intensity frequency calculations the mean of the SPLs of the two microphones The sound intensity calibrator Nor 1254 nth Minimum P I index dB requirements for 25 mm microphone separation from IEC 61043 1993 Checking P Index for the Nor 840 Enter Intensity mode Set spacer Band centre Probe Nor 840 Nor 840 Probe length to 25 mm in the measurement frequency setup menu Hz Class1 Class2 Classi Class2 Class1 Class2 Connect the noise generator to both 50 13 i 19 le 12 6 line inputs Be sure to set both inputs 60 14 8 20 14 13 7 to Line 80 15 9 21 15 14 8 l me 400 16 10 99 16 45 9 Select pink noise or red white if available 25 17 11 Ze I7 16 10 160 18 iz 24 18 ve mt Start a measurement 200 19 12 25 19 18 12 250 20 14 26 20 19 12 Use the display setup menu to set up le gt F a P gt T A aan pene een gue ay Ue Ze ae Ie i 300 Beis eae ore a P I index of 500 20 He 26 20 19 16 at least 29 dB Minimum 630 20 18 26 20 19 16 requirements are listed in the t
165. ne apply to the registers only they do not apply to any of the external storage media i e the disks Tip __ If the contents of one register makes storing in other registers difficult not enough free memory clear some of the registers to make space Remember to go to the corresponding measurement mode first Save the contents on disk if needed before clearing nth Swopping Measurement Channel Contents Press 2np followed by Last to swop the contents of channel 1 and channel 2 Note that the swop takes place in the Last register only Clearing a Specific Measurement Channel Leaving the Other Intact To clear the contents of a specific measurement channel of any register Last register included press e CLEAR 1 lt REGISTER NAME gt to clear the contents of channel 1 of that register e CLEAR 2 lt REGISTER NAME gt to Clear the contents of channel 2 of that register Clearing a Register 1 Go to the mode whose register is to be cleared for example the intensity multisoectrum mode 2 Press Cear followed by the name of the register to be cleared for example the Aux register Masking out File Names If your hard disk contains many different kinds of files it may be useful to mask out other files than those applying to your present task To do this use wildcards A wildcard acts a substitute for a name a part of a name or an extension Navigating in the Memory Handling Menus Name of t
166. nk noise which looks flat in the fractional octave domain but with a level decreasing by 3dB per frequency doubling when viewed using FFT bandpass filtered 4 or 7 3 octave bands only impulse 4 or s oc tave bands only and bandpass filtered im pulse 4 or s octave bands only For the bandpass filtered signals the fre quency band is determined by the current graph cursor position Once the generator has been properly set up and the setup menu closed press GEN to activate the generator and again to deacti vate What Is Multi sine Multi sine is a complex signal consisting of sinusoids The frequency components of this signal coincides with the lines of the FFT spectrum Hence there is no signal energy outside these lines Such a signal can be shown to have a periodicity equal to the time buffer length This means that rectangular weighting can be applied without introducing discont inuities at the extremes In addition the phase of each of the sinusoids has been adjusted to give a crest factor much lower than that of conventional noise approximately 1 3 a single sinusoid has a crest factor of 1 4142 i e V2 or the same as 3 dB _ Fy Chapter 6 90 Maximum Length Sequence Fundamentals 92 MLS Measurement Principles and Features 94 Setting up for MLS Measurements 95 The Noise Generator in MLS Mode Maximum Length Sequence Maximum Length Sequence Fundamentals The techn
167. ntire amount of acquired data as a three dimensional plot with selectable viewing angle The two modes the single spectrum mode and the multispectrum mode are completely independent of each other and have separate measurement setups This makes building acoustics measurements with the Nor 840 particularly easy as the setups for sound reduction measurements single spectrum and sound decay cap tures multispectrum may be defined in beforehand and will continue to be kept apart so that you won t have to define them again on site However the above segregation does not include global settings such as input se lection gain and calibration settings To go from the single spectrum mode to the multispectrum mode press MULTI and to go the other way press SINGLE Since the two modes are independent of each other going between the modes will have no effect on acquired but not yet saved data Each of them has its own part of the memory However they share a common memory pool if one of them is particularly large this may affect the amount of memory available to the other mode Note that the instrument will not accept that you switch between the two during a measurement You cannot measure in more than one mode at the time Selecting Input Source for Level Mode Measurements The Nor 840 has four different types of signal input sockets These are accessed via the input menu Press the INPUT key to produce this menu
168. ntrance key to intensity mode Last As one of the four independent volatile registers of the Nor 840 Measured data end up in this register Data can be transferred from but not to this register Level Select level as opposed to sound intensity as measurement mode Lf Lt Select between spectrum and time history profile of a multi spectrum mode measure ment M Setup Access the Measurement setup menu Note that there is a separate menu for each meas urement mode Move Move data from one register to another Note that the source register will be empty and des tination register contents will be overwritten once this command has been executed Multi Select Multi multiple spectra as opposed to Single one spectrum only as measure ment mode Next Scroll through a parameter s values or the cursor s valid positions in the smallest steps available towards increasing values Num Produce a tabulation of acquired or retrieved values as opposed to displaying a graph Page Up Page Dn Move page wise up amp down in a scroll list Pause Temporarily halt an ongoing measurement Use Cont to resume Plot Produce a screendump which is written to the selected device printer disk nth Prev Scroll through a parameter s values or the cursor s valid positions in the smallest steps available towards decreasing values Print Produce numerical printouts Record Not suppor
169. nu Annotation used is S N M for the S N ratio with MLS and S NN ior Normal without MLS For multispectrum measurements the feature is not available while for reverberation time measurements S N M is the only ratio available Setting up for MLS Measurements The MLS technique can be used with Level mode single spectrum or multispectrum and with Reverberation time mode You enter MLS mode by pressing 2ND ANa LYSE Select MLS To return to normal or conventional mode press 2ND ANALYSE again and select Normal Alternatively you may switch the analyser off When you switch it on again it will en ter conventional single spectrum Level mode Any data not stored will then be lost however Entering MLS Mode Analyser Setup Master Instrument Mode MLS The status bar of the analyser shows the word MLS in reversed video to warn you Lyl Flt Mlt READY 13 4 6 06 66 888 19 Jun 1995 11 57 57 few 1 3 oct 1 8s F gt 5 Hz idea i i yer Pee ee ae 6 5 2 0 8 8 31 5 125 508 riod f Hz 1k Period 5 2 0 8 0 31 5 125 509 2k 8k LA f Hz 1k Per iod 8 The Menu for this Task Lowest frequency band in the measurement Duration of each short time Leq period multispectrum only Key in the required signal to noise ratio here A warning will be produced if the requirement is not met The channel and frequency band of the lowest S N ratio encoun
170. o move the graph cursor to a point elsewhere on the graph The refer ence point will now be stated in a line in serted in the active window The Icons Show the Type of Cursor Selected es ew De ae a 3D Cursor Functions Lyl Flt Mlt STOPPED 12 9 4 00 07 798 12 Mar 1997 10 01 05 dB Leq 64 2 Chi LAST e M flH21 168 Period 117 To rotate graph around the Y axis the level axis press 2ND Y RANGE and use PREV amp Next or the DIAL Origin of rotation is not origin but a point exactly in the middle of the XZ time frequency plane To rotate the graph around the X axis press 2NnD X RANGE and use Prev amp Next or the DIAL Prev amp Next step size is 0 03 radians Remember to set the column 1 in the Display Setup menu to a function actually measured to get a graph Only positive intensity values are shown A X min E Graph cursor B X range F Z cursor C Y max G Y axis rotation 3D D Y range H X axis rotation 3D Cursor Alignment The master cursor is always the cursor of the active window surrounded by the thick frame The two displays must contain data with identical filter bandwidth e g 3 octave bands but one can show spectrum while the other shows time profile The cursor will never move outside the master cursor s range but if the period range of the master cursor window exceeds that of the other window moving the graph cursor will c
171. o repetitive No delay e Measurement to end at measurement time e Lower freq to 50 Hz Upper to 10 kHz e Values to record to Leg only e Follow cursor to Disabled e Minimum dist to noise floor to 5 dB e Time constant to F e Period length to the same value as Max RT expected but in msec In addition for Impulse excitation e Trigger to Level above 30 dB below full scale setting at1 kHz in ch 1 ch 2 if ch 1 is Set to Off e Backwards integration mode to On In addition for noise excitation e Synchronisation to Off e Trigger by Noise Off e Noise generator to Pink and Ran dom e Excitation time to half the setting of the Maximum RT expected The Menus for this Task Maximum reverberation time expected Options 4 8 16 and 32 seconds Excitation type noise or impulse Reverberatson calculathyon Maximum RT expected Excitation type Revert to default Backward integratign mode Minimum distancg noise floor 76 Revert to the default See Backward integra tion mode On Off Impulse excitation only When using noise excitation the noise gen erator on time for the internal noise gen erator must be specified in seconds Reverberatinn calculation Maximum AT expected Excitation type 1 Noise default Excitation time Minimum distance to noise floor dB The minimum distance to the noise floor serves to minimise the influence
172. od e J ee ee _ p20 Set Serial Make no other changes Move cursor to the lower end of the frequency band interval to be measured again Press START to measure again without affecting the frequency bands to be retained g Measurement will stop when the upper frequency band as defined by the Measurement setup menu is reached or Stop is pressed Scan selected If set to On move to another frequency band and repeat Use PAUSE and Cont as usual B 23 Averaging a Measurement too Far Merging measurements by averaging them together is needed in order to minimise the influence of spurious unwanted signals Now what if you get a bit carried away and average your most recent measurement with measurements made previously before you realise that doing so is going to ruin your entire measurement sequence Since this is indeed not an unknown prob lem most people will do this sooner or later the Nor 840 has been furnished with an undo average function For data security reasons the functions Copy and Combine are identical when applied to the average register so the method de scribed applies to both functions The Procedure Assume you just averaged the contents of the Average register with a measurement result that shouldn t at all be merged with the Average register contents tha Mi You can un
173. of 6 dB should do fine for most level measure ment purposes while a minimum of 40 dB should be used with RT measurements See also Setting up for MLS measurements for more on this Making MLS Measurements MLS measurements are made in the same way as measurements are made in conven tional Level mode The MLS has been put as a Shell on the top of Level mode prepar ing the measured data so that Level mode can make use of them directly In this way no reconfiguration of the Level mode is needed and no deep user knowledge of the MLS process is needed either Just set up the analyser as you would do for a Level measurement The only difference is as already mentioned that you may specify a required signal to noise ratio The measurement is started in the usual manner the only extraordinary now is that the analyser runs through a complete MLS signal period to ensure that the actual meas urement takes place after steady state con ditions have been established If you pause the instrument before the pre set number of averages has been reached you may resume the measurement as usual However you may also enter the measure ment setup menu during the pause and change the number of averages required Make no Corrections for Background Level Note that the MLS method compensates for the background noise by itself Do not in troduce any further compensation which you may be used to with conventional meas u
174. of the background noise Wii Setting up for the Capture ource HP filter 2 2 Hz Channel 2 Source 3 Charge LP filter 0 Off HP filter E 2 Hz Fullscale channel 1 Fullscale dB 2 00e 08 u Reverberation calculation Maximum RT expected E 4s Excitation type Revert to default Excitation time 2 Minimum distance to Ea noise floor dB Enter Level multisoectrum mode Press INPUT to select input source if applicable Adjust full scale deflection if needed GaINn1 GAIN2 Press 2nD RT select excitation method and adjust the other settings as required Viewing the Decay The straight line appears for your information only the slope cannot be changed by the user However you may edit the values Enter Level multi spectrum mode and set up inputs full scale etc Lv1l Flt Mlt READY Calculating the Reverberation Time 0 060 03 200 Tue 11 Jan 1994 10 20 52 Bleg 983 9 OMax 16 Start the measure ment Switch on the noise generator noise ex citation selected If you activated revert to default the gen erator will start by it self If impulse excitation was selected gener ate the impulse Transfer the ac quired data to the AVRG register clear it before using it the first time move the microphones and make another meas urement Repeat for as long as needed
175. oing all changes made to the menu F keys As the corresponding MS DOS keys F12 displays information about the Nor 840 soft ware version and stops the hard disk FFT Enter FFT mode Field Selector keys Select a parameter field inside a menu PA Filter Select fractional octave bands as measure ment mode as opposed to FFT Gain1 Gain2 Produce the menu for setting the full scale deflection of the corresponding measure ment channel Gen Switches the built in noise generator ON OFF Harm In FFT mode use this function to reveal any harmonic relations in the signal investigated HDD Store or retrieve data and set ups to and from the optional hard disk but can also be used to store and retrieve data to and from the floppy disk Help Activate the Help function Home Move to the beginning of a menu however not inside a string field Inside a string field it is used to go to the beginning of the string word value as well as the top line inside a list box such as the files list in the Save menu I O Access the I O set up menu controlling such things as remote control ports baud 124i rate IEEE address printer port and printer type Index List the paths to where user defined weight ing networks are stored Input Produce the Input source menu Insert Toggle between Insert and Overwrite in a string field Integr Not supported in this version Intens E
176. oms you will normally need to make spatial averaging in order to obtain representative data This will require several measurements If you only need single channel data anyway why not measure in dual channel mode merge the data and thus cut the time spent by almost half Serial Level Analysis The Nor 840 is basically a parallel analyser i e it measures in all the activated filter bands simultaneously However there are situations where the broadband output of your noise excitation may be too low to get a signal to noise ra tion high enough for your requirements Enter the serial analysis function This func tion turns the Nor 840 into a serial or se quential frequency analyser If you limit the bandwidth of the signal source output signal and combine this with serial analysis you will get a higher signal level at the expense of a more narrow sig nal bandwidth The function may also be used to polish spectra already acquired if some of the fre quency bands yield unsatisfactory results these may be retaken without affecting the rest of the frequency band results The serial function is a good idea to make use of when you do not have sufficient signal to noise ratio because of limited noise source output level or too high background noise level you need to retake a single frequency band ora row of frequency bands The Menu for this Task The feature is found in the Me
177. on of file names differing from each other by their last two digits only Examples of such file names would be hy dro00 hydro01 hydro02 hydro99 To make use of the feature just store the measurement as usual and accept the file name suggested by the analyser The next time a measurement is stored the last two digits will have been incremented If this next file already exists it will still be sug gested but if you have set the Help level to 2 or 3 you will be prompted to confirm whether the existing file is to be overwritten or not If the measurement has been given a title and the Auto File Gen is set to On was Off the six first characters ignoring any spaces will be suggested as a file name template In the Template field the eight first characters will appear but the last two will be replaced by the number series in the file name Disk Handling Tools Getting File Information Imagine that you are searching for a particular file and do not know exactly which file or that you would like to increase the amount of free disk space available on the hard disk or a floppy disk In order to avoid removing valuable files you ll often need additional information about the files Extended file information is available via the About parameter field This poarameter field is accessible from both the Save and the Load menu File Information Measurement mode Lyl Flt Mlt Master Instrument Mode Nor
178. owards through the legal settings higher values sate somewhat for this by applying a multi plication factor of 10 to this function Cursor Alignment In dual display mode the graph cursors X axis cursors of the two windows may be aligned with each other and moved together in either direction Press 2ND Rer to align cursors To deactivate press again press Tyre or change to another measurement mode e g Level or Intensity The master cursor will normally be the cur sor of the active window the one sur rounded by the thick frame However if the frequency axis of one of the window s charts is set to logarithmic scal ing while the other isn t the chart set to logarithmic frequency axis will always be come master If you try to force it to behave otherwise it will either make the logarithmic window active first attempt or switch the alignment off second attempt If the frequency range of the master s graph exceeds that of the slave s the slave s will stop at its end while the master s cursor will go on when moving the cursor along the fre quency axis If the frequency range of the master s graph is smaller than that of the slave s the cursor will refuse to move outside the master s fre quency range The slave s cursor will not move if the mas ter s cursor is positioned at a line not present in the slave s graph However once the mas ter s cursor is moved to a freque
179. p to Name and key in the name of the new directory Move to Make Dir and press ENTER Wii Deleting a Directory zm Press vE E Copy HDD File Gen Tem ate boktet Nene boktstd4 caf Er Go to the directory _ o pee e sa removed o File Gen I On Make sure that the directory is output empty i e containing se or NO files Press the DeL key to remove the directory Deleting a File Press Copy HDD to produce the Save menu or just HDD to produce the Load menu Go to the file to be deleted Press DEL Retrieving Stored Measurements The Menu for This Task Select a file name by scrolling The date and through the list of files of the time of day the Retrieve the directory selected file was generated selected file The path in the MS DOS sense of The file size Close the the word to the menu without directory or file Themed rement saving a file CUmemuly selected mode of the file If you want to i aca cancel all selections press Esc key You may Nae 2 sdf gt define a F thac mask to i Get more mask out Mask o information irrelevant Directories about the file file types i selected 403718 970901 12 28 Y 988 971118 13 57 q The logo Directory a indicates that selected the file is a valid measurement Setup select Auto File Guess 1 On file
180. pad On or Off Zero pad a Off Tip The effect the selected window function has on the time signal as well as the look of the selected window function itself can be displayed but you need to make one measurement first see The FFT Display Setup Menu for details Tip f the two channels are not set up with identical window functions the setting of ch 2 will appear in reverse video in the display see A Tour of the FFT Mode Display for details Would you like to read more A brief discussion of zoom and FFT windows functions is presented in the beginning of this section of the manual An exhaustive presentation can be found in Bendat J S and Piersol A G Engineering applications of correlation and spectral analysis John Wiley and Sons Inc 1980 ISBN 0 471 05887 4 Measurement Controls in FFT Mode The Tool for this Task Setup amp K Move _ C etul 142 F Page Up 10 I M Home ee G Setup J N 10 vm ac jj H K 3D 0 End age Dn nsert ac L p DD Memory Display 2 edie Enter Control Register Control oie N H itle Trig Q T N gaan aa a L X ANG Setu S Setup U p easuremen ZA Control The measurement control keys Once you enter the FFT mode you will note that the display is continuously updated How fast an update depends on the complexity of the function displayed For auto spectra the refresh rate is about 10 times
181. pe 90 E The clue here is that we know the stimulus it is impulse or noise excitation and we make use of this knowledge Therefore we actually have two channels For impulse excitations we assume that the impulse is so close to a perfect impulse that we skip the measurement of it but we still make use of it For noise excitations the only requirement is that we excite the measured frequency bands with a noise whose level is sufficiently high above the background noise level to generate decays that work Hence we do not need to measure the stimulus in this case either with the exception of the initial level to determine when to stop calculating The same thinking applies to MLS meas urements also Since we know the stimulus we can concentrate on the response and MLS becomes a single channel analysis al beit system analysis A Train of Impulses The noise generator of the Nor 840 has been designed to output a very special signal when used with the MLS extension The sig nal consists of a train of impulses each of the same amplitude normalised to 1 but with the polarity varying in a certain pat tern ie the amplitude is then 1 or 1 The spectrum of the MLS signal looks like white noise but it doesn t have the statisti cal properties of a white noise signal since the amplitude is either 1 or 1 and there fore not Gaussian distributed The autocorrelation of this train of impulse
182. phone AC out AC out Microphone input input l l To force the hard disk to stop turning to reduce the noise emission from the Nor 840 press the function key F12 To turn off the display backlight to save Navigating in the Displ e a eae ue waste oe battery power press 2NnD F12 Status bar Repeat to turn back on toggle function U Lvl Flt 5gl READY 00 00 0088 31 Aug 1994 09 56 44 Use these keys pei to go between eee the windows a Which extensions are installed in my analyser f 5 Hz Thick ae Press F12 to produce the below picture Unconditional d Ess f BS 2 6 8 8 31 5 125 pints enotes the active lt gt Serial no 18682 window Version 2 42 OSP1 RAM 32K FLASH 1 gt 2MB FLASH z gt not present 6 5 2 0 8 8 31 5 125 CPU gt 406 Lower fiHz1 ik Setup information FPL gt present i for active window Uptions HIN Qual channel D05 Noise generator Reverberation Narrowband Intensity MLS FFT Demo The active window will respond to your cursor movements etc poprat Gor 199227 orsoni ae the inactive will not unless cursor alignment is activated Batteries If the battery pack is charged you won t need external power The standard battery pack permits two hours of use before re charging is needed but battery packs with higher capacity are also available The bat tery pack is located inside the detachable battery box Your Nor 840 may
183. ps Making Numerical Printouts Consider the Formfeed Exporting Data for Spreadsheet Use Front Panel Keys The Front Panel Keys in Alphabetic Order Technical Specifications Technical Specifications Declaration of Conformity Index Index of this Volume Chapter 1 Connecting Transducers Batteries Using the Menus o 0 A PP Getting On line Help jee ne re aus een OO Getting Started Basic Concepts Your portable Nor 840 real time analyser is easy to use once you have understood the operating principles All setups and the control of the analyser are made by pressing dedicated keys which in turn open dedicated menus All these menus are single level menus so you do not have to navigate through multi level menus There is no special initialisation process re quired before the first time you use your Nor 840 The battery pack may not be fully charged so you may have to hook up the analyser to the mains via the separate power supply Otherwise your analyser is ready for use im mediately Turn to the next page spread for more information on the batteries Before you start using the analyser we rec ommend that you read through the Basic Concepts this section that is of the manual to get a good understanding of the working principles of your real time analyser Nor 840 Connecting Transducers Microphones and other transducers are con nected to the analyser s analo
184. r 1254 as shown in the photo below right The noise generator of the Nor 840 is connected to the BNC socket For a sound pressure level of approxi mately 110 dB SPL the generator should supply approximately 300 mVrms The electrical input signal to the Nor 1254 should never exceed 1 Vrs The Nor 1254 can be used in two modes viz as a P I index calibrator or as an in tensity particle velocity calibrator cf the user documentation for the Nor 1254 In the P I index mode the two micro phones are exposed to exactly the same sound field so that the difference in phase response between the two can be deter mined In the intensity particle velocity calibration mode the sound pressure signal fed to one of the microphones is phase shifted rela tive to the signal fed to the other The phase shift is introduced by inserting an acoustic resistor in the coupler between the two microphones P I Index Measurement Procedure Before you attempt to measure the P I in dex of your probe you should check that the phase match of your analyser is suffi cient This is done by feeding the same electrical signal from the noise generator of the analyser to the two inputs and then read the difference between the sound pressure level and the sound intensity level the P I index When it has been assured that the P I in dex of the analyser is large enough the intensity probe consisting of the sound intensity microphone pair a
185. r 840 has been designed for This setting is found in the measurement setup menu The new setting will be the first centre fre quency above that of the highpass setting provided the initial setting was lower than or equal to what the highpass filter is set to If it was set to a higher value initially it will remain unaffected Although the input selection is a global set ting affecting all modes only the current mode single spectrum or multispectrum will be affected by the forced change of lower end frequency range setting Otherwise measured data not stored would have to be deleted to avoid inconsistencies However this means that if you make a measurement in any other mode without modifying the lower end setting of the fre quency range the frequency bands in the vi cinity of the highpass filter cutoff frequency will be biased due to the presence of the highpass filter In the current mode you may change the setting of the lowest frequency band to be measured to the value of your liking after the highpass filter has been activated The change is made inside the measurement setup menu for the current mode Should you again modify the highpass filter setting and set it to a higher value in Hz the same will take place again provided the lower end setting is lower or equal to the highpass filter cutoff frequency Otherwise it will be left unaffected If you decide to modify the lower end keep in mind that
186. r key 123 Clearing register 107 the contents of a channel 107 Comb key 123 Combine memory handling 106 Complex conjugate FFT mode 42 Cont key 123 Continue effect of pressing intensity mode 78 level mode 20 Continuous See Trigger conditions level mode Copy memory handling 106 Copy key 123 Creating a directory 110 Cross spectrum FFT mode 42 Ctrl key 123 Cursor alignment FFT mode 58 intensity mode 84 level mode 30 Cursor icons FFT mode 59 intensity mode 85 level mode 31 Cursor key 123 Cursors FFT mode 58 intensity mode 84 level mode 30 D D Setup key 123 Dataformat spectral weighting func tions 100 Datum changing the horizontal 40 Decay of sound in rooms 36 Default mode when switching on 10 Del key 123 Deleting a directory 110 a file 110 Delimiter specification 116 Destination memory handling 106 Deterministic signals FFT mode 56 Dial key 123 Differentiation of spectrum FFT mode 57 Directories creating 110 deleting 110 Discontunities of time buffer FFT mode 43 Disk 1 stopping the hard disk 3 Disk key 123 Display backlight 3 explanation of symbols intensity mode 81 level mode 27 Display modes FFT mode 54 intensity mode 80 level mode 26 Display setup menu intensity mode 82 level mode 28 Display window 3 active window 3 indicating which window setup information 3 inactive window 3 Displayed curves intensity mode 82 level mode 28 Distance to noise floor 36
187. r of the FFT Mode Display A Few Words on Functions Displaying the Time Window Function The FFT Mode Display Setup Menu 63 64 65 66 67 68 70 70 72 72 74 76 77 78 79 80 82 82 Optimum Scaling of the Spectrum The FFT Mode Display Cursors Scaling and Graduation Beam Finder Locating the Graph Cursor Alignment Reference Cursor Harmonic Cursor The Numerical Table in FFT Mode The Noise Generator in FFT Mode Making Intensity Measurements Sound Intensity Fundamentals Sound Intensity Probes Selecting Input Source for Sound Intensity Measurements Full Scale Setting Calibrating for Sound Intensity Measurements Checking Residual Intensity Using the Nor 1254 Sound Intensity Calibrator P I Index Measurement Procedure The Sound Intensity Measurement Setup Menus Fractional Octave Analysis Specifying Area for Sound Power Sound Intensity Trigger Conditions Fractional Octave Analysis The Sound Intensity Measurement Setup Menus FFT Analysis Sound Intensity Trigger Conditions FFT Analysis Measurement Controls Assigning a Title to Your Measure ment A Tour of the Sound Intensity Mode Display The Sound Intensity Mode Display Setup Menu Displayed Curves nih 82 84 84 84 84 85 85 86 87 89 90 90 90 90 90 91 91 Ja 92 J2 J2 92 J2 J2 92 94 95 97 98 The Numerical Table The Sound Intensity Mode Display Cursors Scaling and Grad
188. rage less Last There is only one level of undo i e you can not repeatedly hit the Av La to undo previ ous mergings Avrg As one of the four independent volatile registers of the Nor 840 Merging in the sense of averaging on energy basis can only nth take place in this register To merge two sets of data place one in the Average register and copy the other into this register or use the Combine function To avoid unintended erasure of data the copy and combine functions have been made identical for the Average register Cal Enter the Calibration menu of the Nor 840 Clear Clear the contents of a register Comb Merge the dataset contained in one register with a dataset contained in another When a dataset is combined with the con tents of the Average register with the Aver age register as destination the merging will be an energy based averaging of the levels of the overlapping frequency bands while at the same time retaining the levels of the non overlapping frequency bands Single spectrum only Cont Resume a paused or halted measurement If the measurement was interrupted before it terminated hitting Conr will cause the measurement to be resumed and go on un til the Measurement end condition has been met If the measurement terminated by itself hit ting Cont will cause the instrument to pro long the measurement period and go on measuring until the Measurement end con
189. rection Microphone 2 Microphone spacer Microphone 1 Ultrasound transmitter Ultrasound acca receiver Condenser microphone x direction Ultrasound Ultrasound transmitter receiver Selecting Input Source for Sound Intensity Measurements The Nor 840 has four different types of sig nal input sockets These are accessed via the input menu Press the Nput key to produce this menu Only one input can be selected at the time per channel but the two channels need not be set to the same type of input source This opens up for non mainstream intensity measurements for example intensity meas urements using a microphone and an accel erometer Observe that when you select sound inten sity for one of the channels the other chan nel will be set to the same mode automati cally since sound intensity is a two channel measurement technique If you then change the setting of one of the channels the other will go back to the setting it had at the time intensity was selected A lowpass filter will be activated when 3 Charge is selected There is a highpass filter for each channel If you activate this it will affect the setting of the lowest frequency band to be measured The highpass filters are laser trimmed to maintain maximum phase accuracy Together with the choice quality components used this ensures a stable phase response throughout the temperature range your No
190. rements Leaving the MLS Mode To leave the MLS mode press 2ND ANALYSE and select Normal Alternatively switching the analyser off will also cause the instrument to leave the MLS mode Saving the Impulse Response on Disk The broadband impulse waveform may be stored on disk The file cannot be read back into the analyser but any PC the optional of the Nor 840 itself included equipped HP s SDF utilities or similar software will be able to make use of it Details to the right Display Features The only extras provided by the MLS ex tension is ability to display the apparent S N ratio with and without MLS These are of course theoretical considerations serving to provide information on what you gain from using MLS compared to tra ditional methods The S N options appear in the numerical table setting in the dis play setup menu Annotation used is S N M for the S N ratio with MLS and S N N for Normal without MLS For mul tispectrum measurements the feature is not available while for reverberation time measurements S N M is the only ratio available Time Reversal The MLS process generates an impulse which is fed to the analyser s Level mode and analysed there as if it were any meas ured impulse However since the impulse is stored in the RAM of the analyser it may be reversed in time played backwards before it is presented to the Level mode The advantage of doing this is that the analyser
191. rent sound calibrators all available separately to cover the requirements of the IEC 942 class OL class 1 and class 2 The model shown here is our class 1 calibrator the Nor 1251 The calibrator is shown at approximately 50 of actual size Note th adaptor designed to permit use of 1 as well as microphone cartridges The Menu for this Task cal u m g QO W ae E A ee eS Calibration Channel 1 Microphone Sens Level a EEN s HG Unit BdB B fie Bae H Autocal cme e i Channel 2 Microphone Sens Level D J Unit A dB e a Bow K Autocal p iae Fatsbrete L Cal freq ik M Pol Volt 280 N Sensitivity of channel 1 Ch 1 units dB or engineering units Auto calibration level of channel 1 Sensitivity of channel 2 Ch 2 units dB or engineering units Auto calibration level of channel 2 Level of ch 1 measured with the selected time constant O dB level of ch 1 Initiate auto calibration of ch 1 Level of ch 2 measured with the selected time constant O dB level of ch 2 Initiate auto calibration of ch 2 Calibrator frequency Polarisation voltage setting nth Calibration Using a Sound Calibrator 1 Insert EE ope into calibrator Input selection camel 1 Press INPUT and select input source HP filter 2 20Hz Channel 2 Source 3 Charge LP filter Off HP filter E 2 Hz Adjust the full s
192. ress Copy ReF lt Slot No gt in which lt Slot No gt is 1 8 You will now have generated a file whose file name is 840ref_x in which x is 1 8 located in the directory c 840ref root directory on the a drive for units without hard disk Each successive slot will overwrite an existing ref file Tip The function whose spectrum is to serve as spectral weighting function is taken from column 1 in the numerical table setup display setup menu If column 1 is set to Off the analyser will search the columns for activate functions The first active found will then be used Tip When you use the above method the analyser generates a file similar to the one described overleaf a synthesised reference file With a text editor or word processor you may therefore open an existing reference file regardless of how it was made from a measurement as here or synthesised as described overleaf and edit it ad ibitum Remember to save it as an ASCII file A spectral weighting function can be applied to a spectrum to show the effect of the weighting to provide the weighted level or to serve as a reference spectrum to which the current measurement is compared The spectral weighting function is generated from a reference file The easiest way to generate a reference file is by using an actual measurement A reference file can be made from any type of measurement but the direction informa tion is not retained when refere
193. ress INPUT and select input source Adjust the full scale setting GAIN 1 GAIN2 Press CAL and set the calibrator frequency Set the calibrator s output level Select Calibrate and press Enter to commence auto calibration Trigger Conditions in FFT Mode There are separate trigger setups for each of the measurement modes of the Nor 840 Hence the FFT mode has a trigger setup menu of its own The menu contains context sensitive el ements if you select trigger conditions related to amplitude extra parameter fields will appear to let you define what amplitude and which polarity in which channel to serve as the trigger condition Likewise if you select clock as trigger condition extra fields will appear to let you define the time of trigger The trigger condition menu is accessed by pressing 2ND START The six trigger conditions available in the FFT and how they work can be seen on the right part of this page spread The Menu for this Task Insert a delay from trigger condition is fulfilled until the measurement actually starts Options are from minus 67 of the time buffer length rounded off to the nearest ms and up to 60 000 ms Trigger type Trigger delay Trigger channel Chil Trigger Setup Trigger condition KLEE Interchannel delay 4 48908 eel EDED The condition for trigger Available trigger type is Continuous only i e trigger cond met once will cause a con
194. rigger condition W MA whenever the level is above the threshold transition is the keyword as soon as START IS pressed Level drops below as trigger condition External as trigger condition Level below as trigger condition m wv transition is the keyword whenever the level is below the threshold grounding pin 23 on digital I O will do it Noise off as trigger condition Noise on as trigger condition Clock as trigger condition when you switch off the internal generator at a specific moment in time when you switch on the internal generator _ Ef Measurement Controls Once the Nor 840 has been set up to your requirements it is ready to make measure ments To begin measuring press the Start key The data acquisition will start as soon as the trig ger condition is met If you have set up a trigger delay the acquisition will not begin until a the trigger condition has been met and b the delay subsequently elapsed The measurement will if left uninter rupted go on until the measurement end condition is met You may halt the measurement temporarily and then resume the measurement later You may also stop the measurement prematurely by pressing the Stop key The instrument does not discriminate be tween pausing and termination with respect to resuming a halted measurement There fore to pause the instrument
195. rves the value calculated will differ from what the value would be if measured with a separate A B or C filter network For L inear the same will apply if significant amounts of energy exist outside the meas ured frequency range The customised functions are of three types e Hand arm Whole Body X Y Whole Body Z 102i and Whole Body Combined Comes as standard with the analyser located in the directory c networks e Sumf which is a sum of the energy of all the frequency bands measured with flat or no weighting Comes as standard with the analyser located in the directory c networks e Your own reference files Note the difference between linear and flat Linear is defined as no spectral weighting at all but only between 20 Hz and 20 kHz and SumL is defined similarly This means that for vibration measurements the L and SumL networks are hardly usable at all Therefore a flat spectral weighting network has been introduced spanning the entire frequency range from 0 1 Hz to 20 kHz This spectral network is available in synthesised form only and thus named Sumf Before you can utilise a spectral weighting function the corresponding reference file must be loaded into the analyser This is described on the previous page Customised spectral weighting functions may be applied in three ways as reference curves as preweighting and as a bargraph representing the weighted level of the measured spectrum
196. s is an impulse at tT 0 ie again a sort of white noise look alike When making sound insulation measure ments the impulses are fed to a loudspeaker placed in the sending room Of course loud speakers are far from ideal any loudspeaker no matter how high end it may be will in evitably distort the impulses However for most practical purposes the room will distort the impulses to such an extent that what the loudspeaker and the microphone for that sake does is without significance The Impulse Response The distorted impulse is called the impulse response of the room since it expresses the way the room responds when excited with an impulse When we excite the room with a train of impulses we will end up with a train of impulse responses as well It can be shown that the impulse response the frequency response of a system is related through the Fourier transform They form a pair in which both express exactly the same information but in different domains viz time and the frequency domain respec tively The Nor 840 MLS excitation signal consists of period each containing 2 1 impulses equidistantly spaced along the time axis The impulse frequency is a function of the high est frequency band employed in a measure ment Time shift and Summation Now comes the clue each impulse response is captured retained by the analyser and then summed with the next impulse response to arrive To make this
197. s will be written to a DOS ASCII file when pressing the lt Print gt button A dialogue box for the DOS path and filename will then appear on the screen Printing to a printer is available with selection 1 3 0 5 f Hz 88 To access the help level Help set up setup press 2ND HELP Help and security level Start by setting the help level to Extended and then proceed to Normal as you get more skilled and experienced Leave the Limited setting to true expert users only Chapter 2 10 Level Mode Fundamentals 11 Single Spectrum vs Multisoectrum 12 Selecting Input Source for Level Mode Measurements 13 Full Scale Deflection 14 Calibrating for Level Mode Measurements 16 The Level Mode Measurement Setup Menus 18 Trigger Conditions in Level Mode 20 Measurement Controls 21 Merging Dual Channel Data to Obtain Single Channel Data 22 Serial Level Analysis 24 Averaging a Measurement too Far 25 Assigning a Title to Your Measurement 26 A Tour of the Level Mode Display 28 The Level Mode Display Setup Menu 30 The Level Mode Display Cursors 32 The Numerical Table 33 The Noise Generator in Level Mode Making Level Measurements Level Mode Fundamentals The level mode is the basic measurement mode in the Nor 840 With this mode you can make measurements of the level vs fre quency in octave bands or fractional octave bands Your measurement can yield a single sp
198. scussion of the MLS can be found in O H Bjor and B Winsvold Deterministic Excitation Signals Reduces Statistical Soread and Extraneous Noise Contamination in Sound Transmission Measurements Proceedings of Inter Noise 94 pp 1469 1474 Note The measured levels have already been corrected for the apparent background noise This follows from the algorithm itself No further corrections must be made MLS Measurement Principles and Features The differences between a conventional measurement and an MLS measurement are few but significant This article will elabo rate somewhat on the practical aspect of these differences The MLS mode works with Level mode only it cannot be used with other modes Setting It All Up Although the MLS can find its way through extraneous noise much better than conven tional methods can the method will still ben efit from a high noise generator output level Hence we advise you to set it as high as possible but be sure to check that the loud speaker power amplifier combination works well within its linear region Unlinearities are best spotted by making an MLS multispectrum measurement and then investigating the noise part of the impulse response for spikes cf the examples in the Fig on this page spread Apart from the parameter settings required for any Level mode measurement you may also specify the signal to noise S N ratio needed As a general rule an S N ratio
199. se floor With noise excitation the calculation starts at 5 dB below the mean level i e the Leq of the noise measured at the micro phone position before the noise is switched off With impulse excitation the calculation starts at 5 dB below the max level detected As long as the noise stays below this 5 dB line the Et ie lle ne wiine elapsed is counted Once the level drops below a second line the L in the Fig the counting is dis continued Should the level for any reason again exceed the second line the counting will be resumed and go on until the level once again drops below this line Likewise should the level exceed the first line any time after counting has started the counting will be discontinued until the level once again drops below this line Setting up for Decay Captures You may either use a single channel for re verberation time RT measurements or you may use both channels and later combine the results into one channel The latter lets you cover twice as many microphone posi tions and thereby reduce significantly the time spent on creating spatial averages of the RT If you prefer to use one channel only for your RT measurements you should turn off the channel you won t be using You can do this in the Input menu Revert to Default will irrespective of excitation type set e Bandwidth to s octave bands e No of periods to 1000 200 before trigger e Trigger t
200. sing p p probe Options 71 0 200 0 mm Zoom On or Off Measurement Sstup zoom Span 25000 Hz ower frequency oa Je Upper frequenc 25888 48 Hz Window anne Rectangular 1 Rectangur r Window Channel 2 Number of averages Zero pad a tf f Probe tupe Spacer mm Amb Press Temperature Amb pressure Options 50 0 150 0 kPa Wii When zoom is activated the centre frequency must be keyed in here Legal range is 97 66 24 902 34 Upper frequency as calculated with the selected setting Time weighting window function Ch 2 ba E frequency spectrum averages to be made Options are 1599099 Probe type Option p p or p u Amb temperature Options 20 to 50 C Manual as trigger condition Sound Intensity Trigger Conditions FFT Analysis Amplitude as trigger condition as soon as START IS pressed Clock as trigger condition at a specific moment in time External as trigger condition grounding pin 23 on digital I O will do it specify amplitude level and polarity Noise on as trigger condition A when you switch on the internal generator Noise off as trigger condition when you switch off the internal generator The trigger conditions of FFT based inten sity are the same as those applying to other FFT mode measurements In fact the FFT based intensity should be reg
201. specify whether broadband 20 20 000 Hz or limited 100 5 000 Hz shall be used This icon appears in the status line of the display when the noise generator is running The Nor 840 comes with a powerful noise generator built in To access the setup menu press 2ND GEN The generator can be set up to supply white noise whose level will increase by 3 dB per octave when viewed using fractional octave filters pink noise which looks flat in the frac tional octave domain bandpass filtered 1 or 3 octave bands impulse and bandpass filtered impulse For the bandpass filtered signals the fre quency band is determined by the current graph cursor position Once the generator has been properly set up and the setup menu closed press GEN to activate the generator and again to deacti vate Chapter 3 36 Reverberation Time Measure ment Fundamentals 38 Setting up for Decay Captures 39 Calculating the Reverberation Time 40 Averaging and Viewing the Calculated Values Making Reverberation Time Measurements Reverberation Time Measurement Fundamentals Reverberation time RT is defined as the time it takes for the sound pressure level in a room to decay by 60 dB when no more sound is fed into the room However the presence of background noise will normally prevent you from measuring a full 60 dB decay The normal circumvention is then to measure decays of 20 or 30 dB and
202. stead of determined by the setup of these going to the other window and set up parameter fields Both the numerical the display you can apply the same display and the numerical output setup to the other window by moving printout is affected by this setup The the cursor to this field and then exit options to select from are the same as the menu by pressing ENTER those applying to the displayed curves The term SumA denotes the A weighted value calculated from the measured spectrum while the A as such is a true A weighting filter applied to the measurement as an independent measurement channel W1 W8 denotes the spectral weighting function you The two may differ for two reasons round off differences in the digital can make yourself either by keying in the gain attenuation calculation process normally small deviations and if the frequency values of each frequency band or by converting a range of the measured spectrum is limited see the tip on the left side measurement to a weighting curve of this page spread The Level Mode Display Cursors The Nor 840 has an extensive set of cursor functions However some apply to certain situations only All the cursor controls are located around the DuL To operate a cursor you start by selecting the type of cursor and then use the Du or Prev amp Next A small icon appears in the display to tell you which cursor func tion has been activated Scaling and Graduation To optimise
203. t for vibration measurements the L and SumL networks are hardly usable at all Therefore a flat spectral weighting net work has been introduced spanning the entire frequency range from 0 1 Hz to 20 kHz This spectral network is available in synthesised form only and thus named Sumf Applications Customised spectral weighting functions can be used as follows e As reference curves e As a spectral weighting function applied to the displayed function display pre weighting As a bargraph displayed to the right of the frequency spectrum representing the combined level of the measured frequency bands when the spectral weighting is ap plied In this way more than one spectral weighting can be applied to the very same measurement Hence the same spectral weighting func tion may appear in three places in the dis play at the same time if you so wish Apply with Care Synthesised spectral weighting functions will not always work as a true substitute for the real thing One example is the already mentioned A B and C weightings Failure to apply the synthesised versions to a full range meas urement will yield results inconsistent with what you would get using true separate fil ters of the same type Another example is the application of spec tral weighting to vibration measurements The accelerometers output signal is accel Customised spectral weighting functions may be applied in three ways as reference cur
204. t if you set the 0 dB level to a Norsonic offers three different sound value different from 2x10 the selected calibrators available separately to cover the requirements of the IEC 942 settin ill appear in reverse video on al P y K class OL class 1 and class 2 The model the screen as shown in the lower Fig to Sensitivity of channel 1 herh shown here is our class 1 calibrator the the right Nor 1251 Note the adaptor designed to Ch 1 units dB or engineering units Half of this menu may occasionally ap permit the use of 1 as well as Auto calibration level of channel 1 pear blank This will take place when microphone cartridges Sensitivity of channel 2 ever the corresponding channel input Ch 2 units dB or engineering units has been set to Off Auto calibration level of channel 2 Qe il eG 0s Press the FFT key to return to FFT mode If You Change the 0 dB Reference Level Lvl FFT Sgl READY 13 1V a of Oct 1997 08 45 39 Level of ch 1 measured with the selected time constant O dB level of ch 1 Initiate auto calibration of ch 1 ST Level of ch 2 measured with the selected time constant O dB level of ch 2 Initiate auto calibration of ch 2 69 E XLHz1 6258 31 Calibrator frequency A a AR an indication is Polarisation voltage setting nth Calibration Using a Sound Calibrator Insert microphone into calibrator
205. t information Some places informa tion has been copied from other sections but adapted to let you have all the relevant information there and then thus avoiding unecessary page riding Depending on your requirements and your familiarity with technical acoustics as such you may find that you use some parts of the manual often and others not at all The manual describes a fully equipped in strument Your version may not have all the described optional extensions installed The extensions may however be installed as a Finding the Information You Need retrofit at any time in any analyser The idea of offering future expansion is a fundamen tal part of our business concept The manual s structure is well suited for ref erence purposes but beginners should note that the order of appearance of the manu al s topics is neither arbitrary nor alphabetic Instead we have sorted the topics in an or der reflecting the natural flow of work when dealing with a specific task For example the section Making Level Measurements starts with a discussion on general measurement aspects then proceeds through the complete measurement preparation procedure in the recommended order before an outline is provided on how to actually make the meas urement and on the display tools you have at your disposal For your convenience we have prepared an extensive index please use it We consider the section Basic Concepts as the
206. ted in this version Ref Used to visualise the difference between a level at one point of a graph and another point at the same graph For spectra the dis play will indicate level difference and fre quency difference for time profiles level vs time the display will indicate level differ ence and time difference Also used to insert a spectrum into the ref erence spectral weighting list the W1 W8 RT Calculate the reverberation time based on a multispectrum measurement Setup 2nd Autoseq Not supported in this version Setup 2nd Help Set the HELP level the amount of warnings you get when data are about to be jeopard ised Setup 2nd Record Not supported in this version Setup 2nd Gen Set up the noise generator such as the noise type output level etc Setup 2nd Plot Not supported in this version Setup 2nd RT Set up the basis for the reverberation time calculation such as type of excitation dis tance to background noise etc Setup 2nd Analyse Select Master Instrument Mode i e normal or MLS mode applies to units with MLS extension installed only Setup 2nd User Set real time clock Clock will be set to indi cated time when Enter is pressed Setup 2nd Print Define variables for the numerical print out such as Start amp End period Multispectrum only margin and data delimiter Single Select Single one spectrum only as op posed to Multi
207. ten seconds or until the preset measurement duration expires whichever comes first nth Making a Serial Measurement Measurement Setup Set Serial Time constant 02 1 8s F Bandwidth E octave measurement to Lower frequency Upper frequency ie Hz 16k Hz HOR Serial measurement fiz On H M S ms Measurement period e Jee ee e22 Move cursor to the frequency band to be measured Press START to measure the level of the selected frequency band Move graph cursor and repeat if required Use Pause and Cont keys as usual Making a Serial Scan Measurement Setup Set Serial Time constant fez ves F Bandwidth 2 1 3 octave measurement to Lower frequency Upper frequency 16 H 16k Hz AAS Cam Serial measurement H M 5 ms Measurement period a Move cursor to the lower end of the frequency band interval to be measured Press Start to measure the levels of the frequency band interval Measurement will stop when the upper frequency band as defined by the Measurement setup menu is reached or Stop is pressed Use PAUSE and ConT as usual Retaking Frequency Band s Measurement Setup Time constant 02 1 8s F Bandwidth 2 1 3 octave measurement to Lower frequency Upper frequency eI E ee 1 0n or 2 Scan Serial measurement fiz On F H M S ms Measurement period e Jee ee e22 z Serial measurement 2 Scan H M S ms Measurement peri
208. tered Key in the number of averages required Filter bandwidth Required 5 N ratio Measured S N ratio In channel eBasurement time Highest frequency band in the measurement Number of short time Leq periods allowed in the measurement with the present length of the MLS period determined by the highest frequency band and the period length set by you The analyser cannot estimate the S N ratio until you make your first measurement Hence the question marks This field is later used to display the lowest S N ratio encountered The total measurement time Averages x MLS period length Note When switching to MLS mode the contents of all the registers will be cleared The Noise Generator in MLS Mode The Menu for this Task 2nd The noise type is A ser ue The noise sequence is 1 White reso ne always set to 6 Red 2 P seudo Ra ndom 7 Red white Noise seq when the noise generator Bandwidth is used with MLS set the noise generator aa eta E output level in dB re 1V Synchronization a Off a Range 40 0 dB to 0 0 dB Lets the generator span in 0 1 dB steps the measurement With MLS the synchronisation is always set to ON This icon appears in the status line of the display when the noise generator is running Red white Noise Cut off Frequencies The red white noise is a combination of the two noise types to boost the spectrum extrem
209. terrupted the measurement will then go on until the measurement end condition is met The total measurement duration will be the sum of the durations of the two measurements Merging Dual Channel Data to Obtain Single Channel Data measurements Clear Average Make a dual register f channel OW AYO Move the transducers Copy measurement to Average register j Make another Copy measurement measurement to Average register 0 When all Merge the the measurements two channels have been successfully made go to the Average register Sometimes when making measurements that require averaging you may not need dual channel data Instead of switching off the second chan nel try using the 1 amp 2 function 2ND AVRG key sequence This function takes the data contained in channel 2 out of this channel and merges them with the contents of channel 1 The method used is energy based averaging The merged data end up in channel 1 Channel 2 will be left empty Note that the function works with the Av erage register only Do not operate the 1 amp 2 function until all of your measurements have been successfully merged as two channel data in the Average register This is a function that can save you a lot of time When e g you are measuring in ro
210. than a numeric repre sentation of the data so the Z cursor and cursor alignment works even here Editing in the Tables You may edit tabulated values except the Last register Transfer data to another register before editing To start editing go to the line to edit and press 2nD Aux Epit Selected position is then shown highlighted Use the numerical keypad to key in the new value Terminate by Enter or abort editing with Esc Use Dia PRev amp Next and the 2np 9 PeUP 2ND 3 PGDN 2nD 7 Home and 2np 1 END to move up and down in the table Use Field cursor those pointing horizontally to move between columns Press 2np Aux Epit to deactivate function Wii A Tabulated Example Ly1l Flt Mlt ENDED a 13 2V 00 00 10 000 1 Oct 1997 11 66 46 Period 5 Chl LAST FrqlHz2 Leg dB Min dB Max dB N Leq 1 25k gn 1 3 oct 1 88 F 2 5k Hz 3 15k Ak 2 kHz aa ig Manual 8k f Hz 1k Periods Leg dB When You Edit in the Tables it looks like this Here the upper window has been set to display L f of a multispectrum measurement while the lower shows L t of the very same might as well be from two different measurements We have activated the cursor alignment so that the two tables have the same period of the same frequency band shown highlighted Lvl Flt 5gl ENDED FegiHez Legi dB Mint dE Ma dE N Leg HE 153 9 4 5
211. the above biasing of the lower frequency bands will apply to the current mode as well The highpass filter cutoff frequency stated is the 0 5 dB frequency point not the usual 3 dB frequency point Tip Wii The Menu for this Task Input source selection ch 1 Options are Off Line Microphone Charge Intensity When set to Intensity the other channel is also set to Intensity automatically Highpass filter ch 1 18 dB oct Options are Off 0 63 Hz 20 HZ Values are the 0 5 dB points Input selection CHI settings T HP filter Channel 2 Source Ch 2 settings Input source selection CA 2 Highpass filter ch 2 Lowpass filter 18 dB Oct Only when Charge selected Options are Off 1 4 kHz 0 5 dB point Always set the two highpass filters to the same cut off frequency By doing so you ensure that any interchannel phase mismatch is without significance with respect to intensity measurements Note his is not the place where you enter intensity mode that is done by pressing INTENSITY FILTER SINGLE Or INTENSITY FiLteR Mutt Probe selection p p or p u probe is done in the measurement setup menu The Menu for this Task There is one menu per channel JL Fuliscale channel 1 channel 1 Fullscale ioa dB 2 00e 00 Aet AA 2 00e 00 u The full scale setting of the channel in dB The corresponding setting in absolute units
212. the measurement was halted prematurely paused pressing Cont will cause the in strument to resume the measurement and go on until the preset measurement dura tion expires On the other hand if the Cont key is pressed after a measurement has ended successfully i e the preset duration has expired the measurement will be prolonged by a another period equal to the preset duration In the latter case the total duration will be the sum of the two durations provided the measurement was not terminated prema turely during the prolongation The Tools for this Task amp gt t2 F l Page Up 10 M Home Cy a N 10 E3 3D O End age Dn nsert 2 Tee P DUE Display Enter Z curs V Y Z Setup ieva meme FFT f amp Trig u S Setup U Set ae A lt Control 7 Control 4 Q W Harm Autoseq oa The measurement control keys Pressing Causes Start Pause Stop Cont Cont after the measurement end condition is met the measurement to begin as soon as the trigger condition is met an ongoing measurement to be temporarily halted an ongoing measurement to be terminated the measurement to be resumed If left uninterrupted the measurement will then go on until the measurement end condition is met the measurement to be resumed If left uninterrupted the measurement will then go on until the measurement end condition is met T
213. ti sine Lets the generator span the measurement When set to 1 On and START is Generator set up 1 Broadband Attenuation dB The noise sequence can be either 7 Ran dom or 2 P seudo Ra ndom Extra field to define bandwidth when applicable see below Set the noise generator Cia output level in dB re 1V pressed the noise generator will be turned on before the measurement is started and switched off after the measurement has ended Range 40 0 dB to 0 0 dB in 0 1 dB steps Generator set up Noise type 3 BP filtered Noise seq 1 Ran Bandwidth 2 1 3 octave Attenuation dB Synchronization If you select bandpass filtered noise you must specify the filter bandwidth 4 or amp octave bands Generator set up Noise type 2 Pink Noise seq Bandwidth Attenuation dB Synchronization If you select pink noise you must specify whether broadband 20 20 000 Hz or limited 100 5 000 Hz shall be used This icon appears in the status line of the display when the noise generator is running The Nor 840 comes with a powerful noise generator built in To access the setup menu press 2ND GEN The generator can be set up to supply white noise whose level will increase by 3 dB per octave when viewed using fractional octave filters but it looks flat when viewed using FFT because of its linear frequency axis pi
214. tinuous recording of spectra until measurement is ended Insert a delay between the two channels Good for compensation for propagation delay Range 0 1 of the time buffer length Resolution equals the time buffer sample spacing select trigger channel Options are ch 1 ch 2 If you select Clock as trigger condition extra parameter fields will appear If you select Amplitude as trigger condition extra parameter fields will appear Trigger Setup Trigger condition ERM EEan 1 26e 82 Trigger Setup Trigger condition ZEEMiminie 5 er Br ee fe fee l Continuous Trigger type Trigger type Trigger delay Trigger delay E a Interchannel delay 8 0000 ms Interchanngl delay 8 08000 i lt Specify the polarity of the signal and the level of the amplitude see the right half of this page spread for more on this You may specify in dB or units If you set one the other will be set to the corresponding value Specify time of trigger here as month day of month and time of day nth Manual as trigger condition Amplitude as trigger condition External as trigger condition as SOON as START IS pressed specify amplitude level and polarity grounding pin 23 on digital VO will do it Clock as trigger condition Noise on as trigger condition Noise off as trigger condition at a sp
215. tion acquire the measurement surrounded by the thick frame Full scale setting is higher than the top The register whose scale setting contents is displayed 31 4 125 SAA Period 145 Title field lower display window Zk ok H 5 2 4 f0H2Z15315 a Selected cursor function The graph cursor Graph cursor position Time profile period number Spectral weighting bargraphs multispectrum measurements only 56 6 A S 2 0 xf Hz 315 If you set the full scale deflection to one of the three highest settings a small x will warn you that the analyser is prone to overload The Level Mode Display Setup Menu This setup menu controls the type of func tions values measured e g Leq or Lmax to be displayed the scaling of the axes and the layout of the numerical table There is one setup menu for each display window and one set of setup menus for the single spectrum mode and another for the multispectrum mode i e one set of two menus for each mode These two sets of setup menus are com pletely independent of each other while you can copy the display setup of the up per window to the lower window and vice versa you cannot copy between the sin gle spectrum and the multispectrum modes Press D Setup to produce the Display Setup menu Displayed Curves The display can show up to three curves simultaneously These three curves may be set to show any of t
216. tutions such as the PTB in Germany recommend the averaging of decays rather than the averaging of individual RT values Applying the Schroder Method If you use impulse excitation the method of decay averaging lets you apply the backward integration method aka the Schroder method as an afterthought without destroying the original data Press 2ND followed by RT and set the Back ward integration mode to 1 On You will be warned that the RT data register will be cleared Hence you must press the RT key to again calculate the RT values The values calculated now will be with the back ward integration method employed This afterthought works both ways of course If you did use the backward integra tion method you may also recalculate the RT without this method by changing the 1 On to 0 Off Viewing the Calculated Values Once the reverberation time has been cal culated you have several options available to get an optimum view of the reverbera tion time values see table for details 40 E Averaging Decays Before Calculating RT ha Copy result to Avrg multisoectrum measurement register Move O microphone A and repeat amp until a Go to the sufficient Avrg 3 number of register averages is reached Press RT key to calculate To achieve this View the decay and RT profile of anot
217. uation Z axis Cursor 3D Cursor Functions Cursor Alignment Reference Cursor The Numerical Table The Noise Generator in Sound Intensity Mode Maximum Length Sequence Maximum Length Sequence Funda mentals Applies to System Analysis A Train of Impulses The Impulse Response Time shift and Summation Synchronous Averaging Single vs Multispectrum MLS Measurement Principles and Features Setting It All Up Making MLS Measurements Make no Corrections for Background Level Leaving the MLS Mode Saving the Impulse Response on Disk Display Features Time Reversal Setting up for MLS Measurements The Noise Generator in MLS Mode Generating Spectral Weighting Functions Spectral Weighting Function Funda mentals 98 98 100 101 102 105 106 108 109 110 111 11i 112 113 115 116 117 118 118 119 121 122 127 128 129 Applications 133 Apply with Care 133 Creating Spectral Weighting Func tions from Measurements Creating Spectral Weighting Func tions from Scratch Loading a Spectral Weighting Function into the Analyser Applying a Spectral Weighting Function to a Measurement Memory Handling Memory Handling Fundamentals Storing a Measurement on Disk Autonumbering Files Stored Con secutively Disk Handling Tools Retrieving Stored Measurements Automatic File Guessing Storing Instrument Setups Retrieving Instrument Setups Making Hardcopies Hardcopy Fundamentals Making Screendum
218. ul scale channel 2 108 dB z oabroo Do not confuse the full scale setting and the top scale setting The former defines the input amplifier gain and hence the overload margin for a given signal level while the latter is used to set the display to make the measured signal fit within the setting of the axis If you set the full scale deflection to one of the three highest settings a small will warn you that the analyser is prone to overload x i Ve Hoe a SCH2 J 16ee ae Note Autoranging is not available in FFT mode Full Scale Setting The available full scale deflection of a measurement is given as a combination of the input amplifier gain setting and the calibration setting The gain is set separately for each chan nel and is adjustable in steps of 5 dB Press GAIN1 GAIN2 to enter the menu The full scale deflection controls the set ting of the input amplifiers However it has no influence on the vertical scale in the display The two extremes top and bottom of the vertical scale is control led by the top scale value which has its own dedicated key called the Y Max key The top scale setting is purely a display function having nothing to do with the input amplifier whatsoever To keep you informed about the present setting of the full scale deflection a small arrow is used as full scale deflection in dicator see A Tour of the FFT Mode Dis play for details Note that
219. ular window functions FFT mode 44 Red noise cut off frequencies 95 noise generator in MLS mode 95 Red white noise 95 Ref files spectral weighting func tions 100 Vv S Ref key 125 Reference cursor FFT mode 59 intensity mode 84 level mode 30 Reference curve used with spectral weight ing functions 102 Reference curves creating your own 98 Reference spectrum offset spectral weighting func tions 103 Register clearing the contents 107 Register contents are not preserved when switching to MLS 106 Register pool memory handling 106 Register structure memory handling 106 Removing a directory 110 a file 110 Residual intensity checking for 70 Retaking frequency bands level mode 22 Retrieving stored measurements 111 Reverberation time a definition 36 background noise consid erations 36 calculating 39 excitation alternatives 36 setup menu 38 viewing the decay 39 Reverberation time measure ments applying the Schroeder method 40 averaging values 40 time reversal MLS 93 viewing the calculated values 40 Revert to default 36 what it does 38 RMS FFT mode 56 Root Mean Square FFT mode 56 RT key 125 S S N ratio entering required MLS 94 MLS 91 recommended for MLS measurements 92 Save cursor cursor alignment 58 Scaling time axis intensity mode 82 level mode 28 vertical axis intensity mode 82 level mode 28 Scaling and graduation cursors FFT mode 58 Scaling cursor intensity
220. und and output current is in excess of 10 mA Output impedance Max 10Q ANALOGUE TO DIGITAL CONVERTER Converter type Sigma delta with 64 times oversampling Sampling rate 64 kHz 15 625 msec FILTERS AND NETWORKS Anti aliasing filter Combined analogue and digital low pass filter Passband ripple lt 0 1 dB Stopband attenuation gt 75 dB above 1 3 x cut off frequency Phase matching error lt 0 1 for 10Hz 5kHz lt 1 0 for 0 1Hz 20kHz Digital filters 6 pole IIR filters for and 3 octave bands The s octave centre frequencies are set with the factor 10 Frequency range dual channel 0 125 16000Hz for i1 octave bands centre frequency 0 1 20000Hz for s octave bands centre frequency Filter response The and s octave filters meet the requirements from IEC nth 61260 class 0 ANSI S 1 11 1986 Type 1D order III Weighting networks The true A and Lin networks fulfill the requirements of TEC 60651 Type 0 and ANSI S 1 4 1983 Type 0 for precision sound level meters Lin netw response 25 16 000Hz 0 3dB 17 8 22 300Hz 3dB Calculated networks A B C and Lin networks as well as up to four user defined networks may be calculated as a sum of the frequency bands within the selected frequency limitations SOUND INTENSITY Compliance The sound intensity option complies with IEC 61043 class 1 and ANSI S1 9 1996 class 1 LEVEL DETECTOR Detector type Digital true RM
221. ursor to a point elsewhere on the graph The refer ence point will now be stated in a line in serted in the active window The Icons Show the Type of Cursor Selected A X min es Ge De ee a 3D Cursor Functions Lyl Flt Mlt STOPPED 12 9 4 00 07 798 12 Mar 1997 10 01 05 dB Leq 64 2 Chi LAST e M flH21 168 Period 117 To rotate graph around the Y axis the level axis press 2ND Y RANGE and use PREV amp Next or the DIAL Origin of rotation is not origin but a point exactly in the middle of the XZ time frequency plane To rotate the graph around the X axis press 2NnD X RANGE and use Prev amp Next or the DIAL Prev amp Next step size is 0 03 radians Remember to set the column 1 in the Display Setup menu to a function actually measured to get a graph E Graph cursor B X range F Z cursor C Y max G Y axis rotation 3D D Y range H X axis rotation 3D Cursor Alignment The master cursor is always the cursor of the active window surrounded by the thick frame The two displays must contain data with identical filter bandwidth e g 3 octave bands but one can show spectrum while the other shows time profile The cursor will never move outside the master cursor s range but if the period range of the master cursor window exceeds that of the other window moving the graph cursor will cause the slave cursor to stop at its extreme end while the
222. ut BNC connector Output impedance lt 10Q 10mA Signal types Random or Pseudo Random noise Spectra White Pink octave or s octave noise Repetition rate Approximately 28 minutes corresponding to 0 00006Hz spectral line separation Filters The and octave filters meets the requirements from IEC 1260 class 1 and ANSI S 1 11 1986 Type 1D Output level Selectable in 1dB steps in the range 0 to 60 dB re 1VRMs GENERAL Power requirements 30W 11 15 Vbc Dimensions 34x21x35 cm 13 4x8 3x13 8 inches WxHxD without battery case Weight 9 7 kg 21 4 lb without batteries 12 3 kg 27 1 lb with Battery Case Nor 330A Warm up time lt 30sec for 0 1dB accu racy When used with condenser microphones no calibration should take place until polarisation voltage has settled approximately 2 minutes Enclosure class IP20 IP40 with closed front cover ENVIRONMENTAL Temperature range Storage 20 to 70 C gradient 15 C hour 4 to 158 F gradient 59 F hour Operating 5 to 55 C gradient 15 C hour 41 to 131 F gradient 59 F hour Temperature drift lt 0 002 dB C without microphone Relative humidity 5 90 provided no condensation for storage and 8 80 for operation Vibration 5m s operation 50m s storage Shock 100G 11msec half sine wave for operation and 200 G for storage transport OVERALL PERFORMANCE The overall performance of the Nor 8
223. ve that if you select sound inten sity for one of the channels the other channel will be set to the same mode au tomatically since sound intensity is a two channel measurement technique If you then change the setting of one of the channels the other will go back to the setting it had at the time intensity was selected A lowpass filter will be activated when 3 Charge is selected The menu contains a highpass filter for each channel The highpass filter cutoff frequency stated is the 0 5 dB frequency point not the usual 3 dB frequency point The Menu for this Task Input source selection ch 1 Options are Off Line Microphone Charge Intensity Highpass filter ch 1 18 dB oct Options are Off 0 63 Hz 20 Hz Values are the 0 5 dB points Input selection Ch 1 settings HP filter Channel 2 Source Che2 settings Input source selection Clima Highpass filter ch 2 Lowpass filter 18 dB Oct Only when Charge selected Options are Off 1 4 kHz 0 5 dB point Note f a channel is set to Offin this menu the corresponding part of the Calibration menu will appear blank The Menu for this Task There is one menu per channel LE Fullscale channel 1 channel 1 Fullscale jaa dB 2 88280 Gey Ha 2 88e 88 u The full scale setting of the channel in dB The corresponding setting in absolute units Fullscale F
224. verage 22 upper frequency 16 vertical axis scaling 28 Z axis cursor 30 Level scaling FFT mode 56 Lf Lt key 124 Limited help level 8 Line input socket 2 Loading stored measurements 111 Lower frequency level mode 16 M M Setup key 124 Making a directory 110 Mask in memory handling 107 Masking out file names 107 Master cursor cursor alignment 58 Maximum Length Sequence See MLS Measurement duration setting up level mode 16 Measurement setup menu FFIT mode 52 Intensity mode FFT mode 76 fractional octave mode 72 Memory handling autonumbering files while storing 109 clearing a channel 107 clearing a register 107 creating directories 110 deleting directories 110 deleting files 110 getting more file informa tion 110 masking out unwanted file names 107 moving data between locations 106 overwriting an exisiting file 108 removing directories 110 retrieving files 111 retrieving setups 113 storage media 106 storing measurements 108 storing setups 112 swopping channel contents 107 template for autonumbering files 109 the file extension sdf 108 the registers 106 use of wildcards 107 using parts of the title as filename 108 Menus calibration level mode 14 context sensitivity 6 editing a parameter field 7 indication of selected field 6 information fields 6 measurement setup level mode 16 navigating through 7 operating principles 2 nth using the Dial 2 using the Field cursor 2 using the
225. ves as preweighting and as a bargraph representing the weighted level of the measured spectrum Wii eration Sometimes velocity or displacement is required either because standards or conventions require it or simply because you may want a flatter spectrum fitting better within the display range available Integra tion of spectra is very simple in the fractional octave domain an integration of a spectrum simply corresponds to multiplying the level in pascals of each frequency band by 1 27rf or by adding 20log 1 2mf to the level in dB to each frequency band The frequency to be used should then be the centre frequency of each frequency band This works fine for stationary RMS signals However the procedure cannot be applied to peak signals or to transients as both these phenomena involve the need for informa tion on when things occurred i e phase re lationships to be calculated correctly Hence spectral weighting functions must always be applied with great care Also it is of vital importance to observe the need for sufficient measuring time To yield valid results your measurement must have a duration long enough to provide the fre quency resolution needed The BT product must of course be at least 1 but the higher the better a BT product of 5 or more is pref erable Lv1 F1t Sgl STOPPED 12 9 60 00 08 210 9 Nov 1997 15 48 22 dB Ch2 LAST N 1 9B gaf Legq 6 4 10
226. windows Defines the channel whose contents are to be displayed Select between ch 1 ch 2 ch 1 ch 2 ch 2 ch 1 ch 1 and ch 2 ch1 ref1 ch2 ref1 ch1 ref2 ch2 ref2 chi ref1 ch2 ref1 chi ref2 and ch2 ref2 Type of unit to be used for the vertical axis Select between dB and absolute engineering units Time axis scaling Applies to multispectrum measurements only select between Periods Relative time since trigger and Absolute time date and time of day Display Setup Up to three set of curves graphs may SS _ _ be shown simultaneously Which Channel functions to show is defined here Y unit Choose between Off Leg Max Min SPL SEIL In multispectrum mode only the functions actually recorded will provide graphs Time cursor Periods The displayed graph can be shown spectrally weighted Options are A B C L W1 W8 Preweighting Gi Gi i E i q4 SPL z Bl etworks it oO uu Az Max Gl 5 vn ow oN 2 H2 A 3 88 Off There are up to four bargraphs located to the right of the spectrum in the Ha Off display Select which ones to appear Columns in e numerical table among A Lin SumAT SumB SumC 2 SumL or W1 W8 ak SIA Off 6 l Off There is one display setup menu for each of the two windows the upper synchronize Ossetup The contents of the numerical table is and the lower window In
227. with IEC 60651 type 0 IEC 60804 type 0 IEC 61043 class 1 IEC 61260 class 0 ANSI S1 4 1983 type 0 ANSI S1 11 1986 order 3 type 1D ANSI S1 9 1996 class 1 EMC EN 50081 1 EN 50082 1 Safety EN 61010 1993 for portable equipment and pollution category 2 This product has been manufactured in compliance with the provisions of the relevant internal Norsonic production standards All our products are tested individually before they leave the factory Calibrated equipment traceable to national and interna tional standards has been used to carry out these tests This Declaration of Conformity does not affect our warranty obligations Tranby May 1998 Dag The declaration of conformity is given according to EN 45014 and ISO IEC Guide 22 Norsonic AS P O Box 24 N 3420 Lierskogen Norway Symbols 162 2nd Last key 122 1254 intensity calibrator 70 216 using with NOR 840 68 2nd Gain2 key 122 2nd key 122 3D 2nd Lf Lt key 122 3D cursor intensity mode 84 level mode 30 A About getting more file informa tion 110 Absolute units setting full scale setting in 67 Acc input sockets 2 Accelerometer connecting 2 Acoustic energy flow 64 Active window intensity mode 80 level mode 26 Align 2nd Ref key 122 Alpha key 122 Alt key 122 Analogue input sockets 2 socket panel 2 Analyse key 122 Analyser default mode when switching on 10 when switching on 10 Anti aliasing filter FFT mode 42 Auto key 122 Auto spectrum FFT
228. y Press HDD to e e E fractional octave measurement using the produce the Name wbcomb12 ref Load same filter bandwidth as the file itself does load menu Path c networks Exit vask about The first step when you are going to apply Locate the file ar a a spectral weighting function to a measure to be loaded L aen sas ment is to load the corresponding refer 92 948418 15 24 463 968621 Su 2 a n d Hipage tat ea Altogether the analyser can hold 14 spec numerical keypa 796 940418 15 23 tral weighting functions simultaneously out to load the fil i rate o lip omb 13 5122 of which 6 are predefined and the remain Een acie a 1 t e T7 ing 8 are entirely at your disposal ence file into the analyser These 14 spectral weighting functions are Off none Lin A SumA SumB SumC SumL and W1 W8 You may have as many spectral weighting functions as you like on the hard disk or Example By pressing 5 followed by Enter in the above menu the selected file will appear as W5 a floppy disk but only eight of them may be used simultaneously These are denoted W1 ll 1 W8 Wz W3 Wg W5 This list of which files ws o OO E rs a A function number is available by pressing e the INDEx key Note The analyser uses links instead of importing the reference file This saves memory However every time you exit to MS DOS mode an
229. you move or copy the contents of the current register a copy of the title follows the meas ured data If you assign a title to the Last register and let it remain unchanged all following meas urements will acquire the very same title since the title is assigned to the contents of the Last register whatever that may be We therefore recommend that you consider updating this title regularly to make it mean ingful If you change to another measurement mode the currently selected register of the new mode will acquire the same title as the same register of the previous mode unless that register of the new mode had a title al ready and it was empty in beforehand To access the Title menu press 2ND M SETUP A Tour of the Sound Intensity Mode Display There are four display modes in the Nor 840 two single function and two dual function modes When we say function display rather than channel display this is because in dual func tion display mode the two display halves are completely independent The upper display may show what you just measured while the lower may show a graph of a stored measurement or vice versa or the upper display may show a graph while the lower shows a tabulation of the very same data etc When you select any of the two dual func tion displays with or without setup infor mation the screen will consist of an upper and a lower part which we may call win dows plus wh

Nor-840 User Manual - Campbell Associates

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