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2900 Manual_book

1. 15 3 Count Averaging Special Considerations a 15 3 Initiation of an Autostore byTime Sequence sse enne 15 3 Chapter 16 2900 MANUAL ERES cM EIE 15 3 Frequency Trigger Startseite anti sii ena ER Es 15 4 Conclusion of an Autostore byTime Sequence s s a 15 5 Disabling Autostore Dy l me 15 5 Data Storage Format t tee teet te ett eed egeta entra ENEE 15 6 Averaging Time Consideratons eene nennen nennen nnns nnne nens 15 6 EET Analysis ieiuna ee Deech deed dees 15 6 OCTAVE EE 15 7 Recall and Display of Autostored Data 15 7 Displaying Individ al Spectra iia rr e tenth er eon eae t e teda 15 8 G rSOP GO Ir O S e a Scat Sce a met toS o Ne 15 9 Display of Amplitude vs TIME eene enne 15 9 Leq Measurements in the vsTime Display Mode A 15 10 Changing the Displayed Frequency Band 15 11 Broadband Level versus Time ccceccescceeeeeeseeeeteeeeeeceeeeeeeeneeeeeeseneeeeeseseeeeeseenenneeseeeneneaes 15 11 SLM Data versus Time 15 11 Displaying the Same Frequency of Another Hecor 15 12 Displaying and Storing Leg MIN MAX SEL and Mx Spec Gpecha 2222 15 12 Deleting Autostore Records 5 2 cid deed e a i EE Peer Ee DUE aea eda 15 13 Averaging of Autostore by Time Records sse eene 15 13 Block Maximum of Autostored byTime RecordS AAA 15 14 Block Summation of Autost
2. 2 1 Softkey Menu Concepts ined dee Re Pe tite i C dt e e rp dedi 2 1 Analyzer Mode uuu usuy ege Pe ren ip TIME 2 1 SO MEN UE EE 2 2 sound Level Meter MOGeS reto e e hec a pr te e i tal 2 3 ShiTi Menus uo BSU 2 4 Sound Level Meter Operating 3 1 Sound Pressure Level Measurements Single Channel Sound Level Meter with Frequency Analysis SEM EA MOS uscite bostes s EE m teal EN n Ee 3 2 IE 3 2 Changing the Microphone Bias Voltage I 3 3 Changing the Microphone Input 3 3 Changing the SLM Analog Eiere 3 4 Selecting SLM and Frequency Analysis Weighting 3 4 VVarm p RU C 3 5 Alignment of the Microphone Boom and Microphone Preamplifier 3 5 Microphone Boom Alignment AA 3 5 SEM Standard veces PEE 3 6 IEG BD V1 e 3 6 ANSES1 4 1989 5 5 ru e e Ee X en dotato anre er KEE 3 6 Microphone Preamplifier Alignment essen enne 3 6 Free Field Measurements U U U U enne nennen nennen nnne nnns 3 7 Random Incidence Measurements A 3 9 ETfect or Windsereern e eoe iet ep eer exe ect e pen rp recette ter M d eed 3 10 Position Of Operator r diese tote tac ee LU SEL en ka ANN a de 3 11 Making a Sound Level Measurement eene eene nnne ns 3 11 Adjusting the Input Gain 5 2
3. 23 12 Storing Print Setups to Memory n aya nennen nnns 23 12 Recalling Print Setups from Memory a 23 13 Default Custom Printout Setups 2 n 23 13 Initiating Printing of a Custom Printout a 23 15 Chapter 24 Use of External Color Monitor for Display and Instrument Control 24 1 Hardware Considerations a 24 1 Activating the External Monitor 24 3 System Operation Using Pop Up Control Wimdow enn 24 4 Selecting the Number of Display Windows 24 5 System Operation Without the Control Wimdow nennen 24 5 Global Configuration Windows sse nennen inneren nnne en 24 5 Base Frequerncy EE 24 5 Selection of Analysis Tvpe entere nne sseoossasasassanonsasaaassononooe 24 6 Selection of Filter Type nn 24 6 Selection of Detector Type entere see ootsesanassanonoasasassanonone 24 6 Selection of Averaging Time 24 6 Selection of Master Display Type nennen nnne nnne nn 24 7 Selecting the Number of Analysis Channels U 24 8 Selecting the Number of Data Display Windows i s asi enn 24 8 Setting the Range Input Gain n 24 8 Selecting vsTime or vsTach Autostore emere 24 9 Running and Stopping the Analysis eene nnns 24 9 Individual Data Display Windows 24 9 DisplaysTypes iio teet t
4. 4 25 DC G tp t cc 4 26 WO PortiGontroli usu a pent ad i d o l eiut c li 4 27 AlDYInputs 1 42 and EE 4 27 I O Channels 142 and 493 iecit etcetera dayad ii ons masak E rabo ayda epe utin 4 27 Frequency Domain Interface Trigger of I O Channel 3 4 28 Key A and Key B Control 4 29 Beeper Ettel eet di kont Yen die aou a ond a a a erae EO dte ee 4 30 Selecting the RS 232 Interface AAA 4 30 ant Aaner qoe 4 30 The Resets Men s eege gedet m kk 4 31 Remaining System SoftkeyS eene arama yaaa m enn nnne ns 4 32 Selection of Averaging Parameters J 5 1 Selecting Averaging Type ENEE 5 1 Accessing Averaging Menu l u u uu 5 1 Averaging Type Octave Filters n nn a 5 1 Averaging Typez EFT Filters u u dee Edge te Ee n eere i t HE Mr etu 5 2 Avera n TITIO tees tota ki cai an tB sk qhu EN 5 3 Averaging Time with Linear Types U 5 3 Averaging Time with Exponential Tvpes a 5 3 Averaging Time with Constant Confidence Type Octave Bandwidths Only 5 4 Averaging Time with Spectral Type Averaging FFT Bandwidths Only 5 4 Signal Averaging Considerations esee enne nnne ens nnne en 5 5 Stationary Signals seii pono 2 dati Het ee He a v HR nas 5 5 Time AVeraging MU 5 5 Linear Time
5. c 1 INITIAL Pink noise has equal energy per percentage bandwidth e g octave or 1 3 octave As with the sine generator the level is set using the softkey LEVEL E and entering a value between O and 9999 using the numeric keypad The keys lt ATTEN G and gt ATTEN H will produce attenuation or reduction in attenuation in 20 dB increments also as described for the sine generator When 1 3 octave digital filters have been selected the gener ator can also produce 1 3 octave bandlimited pink noise From the Broadband Pink Noise Menu the Bandlimited Pink Noise Menu shown in Figure 4 12 Bandlimited Pink Noise is accessed by pressing 18 A 2900 Instrument Setup Via The System Menu Autolevel Control Bandlimited Pink Noise 2900 Instrument Setup Via The System Menu 2900 MANUAL Figure 4 12 Bandlimited Pink Noise 3e 981 82 22 23 WIDE N OFF LEVEL Hote 1 3 OCT NOISE 20 8958 EXPONENTIAL Input 1_LINEAR 20 2 20 2 STOP 38 OCT 94 02 21 23 FILTER 854 2 56kHz 125 v Channel 1 of 1 NORMAL dz 97 2 2 167 1 PHONS 116 2 TACH 6 6 SPEED 4 6 0 H 600 H s a kHz dotted crsr INITIAL BOTH SOLID DOTTED As with the wideband pink noise the key LEVEL E is used to set the relative output level of the signal and the keys ATTEN G and gt ATTEN H are used to add and remove attenuation at all frequencies in increments of 20 dB The keys ALL I and NONE J are used to tur
6. enne nennen 20 12 Storage and Recall of Intensity Gpechra eere 20 13 Editing the JOB PART and AREA Names the surface Area value and the Note Field of a Stored Intensity SpeCtF lm s oot dete cie eie hy Su tede kuq usasqa uay REN RETURN kant pant 20 14 Power SumimaltlOn 2 2 5 ont aa p ec Eget rodea e ia m ee E t boda e n d aaah 20 15 Accessing Power Summation Men 20 15 Search Field CONCEDES s itor tte t n RUE et Ca HR HER RARE Pa e EO e eate a nar e 20 15 Manually Entering Labels into the Search Field 20 16 Entering Labels by Recalling Spectra essen 20 16 Performing a Power Summation sess enne enne 20 16 Storage of Power Spectra as Pei tie P e Ce Ain une de cere pent 20 17 Recall of Power Spectra I eene trennen sistere 20 17 Power Summation Example I eene 20 17 Three Level Search tete eei ee Reg ine ease E 20 18 Two Eevel Seatch ie ere cte e t Pato Sep nt aie Sit adi alate 20 18 Elle UE e EEN 20 18 Field Indicators Specified in the Standard ISO 9614 1 1993 E 20 19 Temporal Variability Indicator EI 20 19 Surface Pressure intensity Indicator F2 Negative Partial Power Indicator F3 and Field Non uniformity Indicator FA 20 20 Surface Pressure Intensity Indicator a 20 20 Negative Partial Power Indicator AA 20 2
7. 3 11 Overload IndiGatiOn 5 3 3 1 aa ERE SOT GIOI REEF ERU ete ui Ad 3 12 AUtOFANO ne DE 3 12 Measurement 6 5 AA e FAAR R RA R YARAR R YR aY AR aaa akril 3 12 Primary Indicator Range ll u ln ALA Re AAA a Okuyan enne nennen enn 3 14 Non linear DISTONNON s L E nt E RO E ea s 3 14 Selecting the Displayed Parameter 3 14 Frequency Analysis Display u a aasawa eene en nennen nennen 3 16 3 17 Sound Level Galibratot 5 1 t a tee 3 17 Calibration Procedure s ati ette hei m deber deleta 3 17 Effect of Microphone Extension Cable sse 3 19 Noise Floor Measurement and Proximity Message essen 3 19 2900 MANUAL Environmental Effects on SLM Measurements eene 3 20 Magnetic Ge WEE 3 20 Tempora teer mE 3 20 H midity ik CR 3 20 Temperature and Humidity Permanent Damage sese ene 3 21 Effect or Vibration EEN 3 21 Sound Pressure Level Measurements Dual Channel Sound Level Meter with Frequency Analysis SLM A Mode Two Microphones enne nensi nrnn rens inneren 3 22 SIC geet ama a ele ZA EE E 3 22 Sound Pressure Level Measurement Dual Channel Sound Level Meter with Frequency Analysis SLM A Single Microphone esent en thn nnns sinn tenen 3 23 Sound Pressure Level Measurements using the Wide Dynamic Range Sound Level Meter WDR SDM SUV uL 3 23 Accessing the WRD SLM Men aa asah
8. ERAN EVER za salam A 1 2900 MANUAL 16 Introduction 1 Introduction The Model 2900 Real time SLM performs two measurement functions simultaneously that of a Precision Sound Level Meter and that of a real time frequency analyzer As a digital sound level meter it simultaneously calculates the sound pressure level corresponding to the following detectors RMS Slow RMS Fast Impulse and Peak The Min and Max values of the Slow Fast and Impulse detectors over the measurement period are maintained At the same time it calculates both LEQ and SEL integrated values In certain versions of the Model 2900 such as delivered to German users the Min and Max values of the Impulse weighted sound level are replaced by the Taktmaximal Fast weighted 3 and 5 values As a real time analyzer it can perform single or dual channel frequency analysis using digital 1 1 and 1 3 octave band widths and FFT analysis using 100 200 400 or 800 line res olution When equipped with the optional OPT 80 Acoustic Intensity Module and using a Larson Davis intensity probe it can perform acoustic intensity measurements in both digi tal 1 1 and 1 3 octave and FFT filter formats Using digital filters it can generate statistics and Ln data using one or two channels In its autostore mode it can store spectra as fast as 400 spectra second to non volatile memory and subsequently display data in sel
9. J J J nnmnnn nne 7 1 Manual Control of Run Stop n a 7 1 Continuously Running Time Averaging n 7 1 Finite Length Time Averaging uu u u uya a ao aE TEAT ENa E ETE 7 2 Input Gal Control u EE 7 2 Manual GControl of Input Galri n uu a ntur Ferrero o e tite Re OE tenta 7 2 Offsetting Gain Between Channels enne enne ns 7 3 Autorange of Input Galn 2 deed lente ecd Hd dae dl bae a cv Ret dap ioe 7 3 Response Time of Digital Filters U U 7 4 Possible Overload Indication upon Resuming Analyse 7 4 Cursor Control m 8 1 Solid and Dotted Cursors Moving Independent 8 1 Solid and Dotted Cursors Moving Together 8 2 Harmonic CUrSOts c a a v ti e a anal atid a eoe udi bun te ede eae 8 2 Fixing Cursor POSITIONS tr aves eaten vette ERR eee FE REB stains eR vets 8 3 Selection of Units and Calibration J 9 1 elt 9 1 Accessing Units Menu EE 9 1 Creation of Unit NAMES nennen taa kaai daa haoin aE d ea etnies nnne nnns 9 1 Assignment of Unit Names nennen nnn R RK e nennen nennen nr enter nennen 9 2 Assignment of Integration or Differentiation nenne 9 2 1 1 and 1 3 Octave Integration and Differentiation 9 3 FFT Integration and Differentiation Operations
10. ne E nennen eene 10 5 Creating a User Weighting Curve from a Measured Spectrum 10 5 RER ee EE 10 6 Storing the Active Register into Storage Heglsters sss 10 6 Recalling from Storage Registers eene 10 7 ele Huis HS ET 10 7 Subtract n Be isters ot ET e Sat UD Ret tus 10 7 Storage of User Curve Records 10 7 Recall of User GUrV8s uie ce dude en ed ea ca cU dte Sn eov i ae ARZU 10 8 Exiting from the Setuser aeaaeae e ran aag nennen nennen sistens nnns nennt 10 8 Trigger Functions E 11 1 Time domain Triggering EE 11 1 Trigger Level 2 n ede eee eee eot adie e e den 11 1 Trigger Slapesz s e metere UT ee m e dee tete t dT ae A m EN erit 11 2 leie RE 11 2 EU IER RE ET 11 4 Arming and HERE o 1419 ET 11 4 Frequency Domain Trggertmg eee 11 4 Selecting Trigger Frequency enne nnne nnne trennen nennen 11 5 Selecting the Trigger Criterion eene enne nnne nnns 11 5 Selecting the Trigger Level iiie nitet ER ra oak en kay t E bor p e ep uda 11 6 Frequency Domain Trigger Setup for the SLM Mode sese 11 6 Arming and MRT DEEN 11 6 Life ugeet ul E 11 7 Storage and Recall of Instrument Setups 12 1 Labeling and Assigning Softkeys n nnns nnne 12 2 Changing 2900 Setup from 5 sse 12 2 Reset of User defined 5 2 eese nennen enn
11. o o o o o o n ELE EXPONENTIAL 1 64 PREAMP LINEAR 16 26kHz RESET 02 JAN 96 06 40 08 T d FILTER 10 0kHz L73 TRIG v Channel 1 of 2 NORMAL dz 23 7 Ze 48 4 6 bees PHONS 61 8 LOC TACH 6 6 SPEED 6 6 l fi eee ee NOE A dotted crsr FILES 16 2 The Tacho parameters are set from the Tacho Menu shown in Figure 16 2 Tachset Menu which is accessed from the Autostore Menu by pressing TACHSET K Figure 16 2 Tachset Menu 32 E 85 26 33 t scale t sPan t amin t amax cal SLOPE _ X AVE 05 STORE SLOPE PL 6 60068 ONENTIAL 1 8 AMP 188 Hz HP P 62 JAN 96 05 i FILTER 829 808 Hz Channel 1 of 2 NORMAL A 56 4 J PHONS 70 8 TRCH 5184 6 SPEED 0 0 dotted crsr Autostore by Tach Tach Speed Scaling 2900 MANUAL Autostore by Tach Example Example Example The pulse train signal pulses sec applied to each of the hardware inputs TACH and SPEED is detected by the 2900 as a frequency Hz For example if the signal input to the TACH input represented a single pulse per revolution of a shaft the units of TACH as read by the 2900 would be shaft speed in Hz rev sec Often one would prefer other units such as RPM and also there may be more than a single pulse per revolution In the Model 2900 the pulse rate is multiplied by a user define
12. 12 92 snuey Aayyos 62 42 1 o r E Z pu sfouueyo U99A 19q YINAS Jo on eA UT 10 N PAPS x 7 n o 1 kia o qe SOS DES lqe 9 qe IAN UNA sonsnejs eLOA SODSnevjs lqe3 52051 015 po e2o1 SIIN H Ol VETO 4 ACTH d IVLS A Dl Nvas ap a HINLL S V JAO NO o q 3 sonsrejs sow WN p y s XIIjeul XIineu sonsnejs yo xngeursonsnejs SOnsneg 8801 Wouj CID 1S9 m r piuun sonsuejsjosow Juey oprindwuy s s yepdn Joy 830 Sursn MELIPONA oun 135 S SZ IMFI n yy SISAIEUN PILPUBIS JO c cc IMIT n yy Ae dsiq WIS Wouj nuoJA Sonses 82 92 snu W Aayyos d Daat t 19331 0 3uipuodso1109 ndug W TVANVIN t T SSLL enue A VAS yc gc FTANDII O 440 N Wav da Jossip kouonbaln 1o so1nv ue SurMo o Ho um uLreos onewomy 3 y s 1 A ados MmaJo1s II lt t 1 10s4no 10 EL 1983811 1099 9S S SZ SANBL nu lN srsApeuy prepuegi1s wouj nusp 1933111 A u nb kni 62 92 snu W Aayyos 91 Z m k O SA TIJ t nuoJA 5914 SS V D atou 1 PIPI JON WPT S SZ IMFI MWAN SIS JEUY pIEpuLIS JO c cc MIZI 92 42 FJANDII VC Sc 1 814 IN SALH t nuoJA 19331 kouanbalj SS V q ospu t 16 92 omar M LASHOVL 11 H V L
13. 62 92 snu W Aayyos Vb e S e JANDII d 40 3 IO 4 do 8 en eA Jews AT A o um n ds punoisyorq WOOY SUTAT H PSI umaj2eds punoisyoeq uoo SurAr yi Aejdsiaq OlcSscemsu gICc Sc m n N FATAIDRA IN 404108 VII Las r OSI I WLSV tunnoodg p sn yoolq ep eugop o nUoJA ssoooy pue WOOY SurAro2os Aeydsiqq uoo oounog Ke dsiqq shay punorsyorg pue suone no e 10 o 0 Somog PM s o dnour prepue1s 199195 4 09121 3 euunjo q oejns 0 ou 8 AN V ON t t t t MWAN 0914 Ur uroow SUARA Ur UODDIed JO min d JABIPE JO umno d s JABINO 1 1 JO umupodg JABIYE T T JO SS920V JO 9um oA s y BOTY 99RJINS IUA Suney M ojen eAq Sunew AN 91enpeAq Sunew IN 91enpeAq S SZ AIS NUN SISAIEUNV pyepuejs y wouj NUJ N SUOOY v2 GZ snu W Aayyos glz sz 44n l4 I YT t SSe J UOTSSTU SUEAL punog pue uorssruisuei p r1 en eAg SS017 Uone os pedu platy pu ounsso1q punog edw pozi puuioN SSe UOISSTUISUEJ punog pue SSETO UODETOS 9SION PIZI JEWIJON UOTETOS STON pue SSO T UOISSIUISUEI 9JEn UA pue uononpaY SION SION INAJ pezi eurioN Npe VIZ SZ 2314 NUI suioos n wouj DU TN WALLS V GZ GZ snuey Aoyyos 12 92 FTANDII Aa a 2unssouq punos UTSTEVV uonoojojq p
14. Storing and Recalling Non Autostore Data From the record listing depending on the record type the highlighted record can be recalled and displayed by pressing KEEP H This will produce the message KEEP record and exit on the right of the screen To abort the procedure press NO C To continue the recall procedure press YES A The analyzer setup will be configured to that which was active at the time 13 5 2900 MANUAL that data record was stored and the corresponding Analysis Menu will be displayed along with the data stored in the data record The word KEEP is used to indicate that the analyzer setup configuration will be kept to that recalled from the data record Only records having the form of spectra or time waveform blocks can be recalled and displayed from the Files Menu as described here The following types of records cannot be recalled in this manner vsRPM Trace Ln Trace Ln Table User Curves Setups Units Data Macros Data Print Setup Class Setup and Field Indi cators When the 2900 is not in the Files Menu stored records can be recalled from the active memory file using the RECALL hardkey as described later in this chapter Storage of Normal Non autostored Data to Internal Memory Storage of Data Blocks Record Classification We refer to the storage mode of the 2900 as normal unless the autostore mode of storage is active In the normal mode of storage the displayed data block i
15. Control of Display Formats Cross Channel Normalization and Use of Key Macros 19 5 2900 MANUAL 19 6 Press one of the following keys to obtain the full screen range as indicated below Table 19 1 Vertical Scales Log Full Display Range Linear Full Display Range Normalized Display Range 10 20 40 80 100 to 87 5 100 to 75 0 100 to 50 100 to 0 0 12 to 0 12 0 25 to 0 25 0 50 to 0 50 1 00 to 1 00 Display of frequency domain functions will be either log or linear 1 The Normalized display range is used for display of time domain functions such as autocorrelation cross correla tion coherence coherent output power time weighted time and averaged time After this is done note that the value of the full scale on the display remains the same but that the numbers below are reduced as a result of the decrease in the display range When the displayed amplitude range is made less than the dynamic range of the measurement the resolution seen on the screen is increased but the entire valid range of the mea sured data can no longer be seen at one time For example when the displayed amplitude range is decreased from 80 dB to 20 dB only the upper 20 dB of the data will be visible on the screen This conflict is resolved by offsetting the position of the dis play window relative to the full scale of the measurement The offset is dynamically adjustable by the user providin
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17. 2 Use Linear Averaging for the measurement with an aver aging time sufficiently long that a stable value of transfer function is obtained Correction functions for 1 1 and 1 3 octave bandwidths are stored separately This means that once the proper correction function has been stored for each bandwidth the user can switch between bandwidths without re calculating the cor rection function However the user must be certain that the correction function being used has been generated using the same highpass and lowpass filters as the analyzer setup The octave bandwidth normalization functions created and stored while in the Cross Analysis Mode are used only when normalization is activated from the Cross Mode Creating Macros The operation of the Model 2900 can be simplified by the use of user defined key macros A key macro permits the user to define up to fifty sequential keypresses and upon executing the macro have the operation of the analyzer proceed as if each of these keypresses were being performed manually in the order programmed A simple example would be where the user is doing dual channel structural dynamics measure ments and wishes to store the excitation and response autospectra the transfer functions H1 and H2 in both rect angular and polar coordinates and the coherence Under manual operation each variable must be recalled in the desired format then stored By stringing together the key presses representing
18. 4 TACH 6 6 SPEED 6 6 dotted crsr z 2 INITIRL EDIT SETUPS NAME ASSIGN a JUDGE USE KEY m JUDGE In the Min mode they will be numbered sequentially in the downward vertical direction Assigning Class Lines to an Input Channel Repeatedly pressing one of the class line softkeys A B C or D will toggle the status of that line between ON and OFF ON status is indicated by an arrowhead symbol to the left of the softkey label Each may be set to ON or OFF indepen dently In the ON state class lines previously defined for each family will be displayed when not in the editing mode When more than one family is in the ON state the class lines for all the ON families will be displayed simultaneously A family of class lines cannot be assigned see below or used for com parison to a spectrum unless it is in the ON state 22 8 At any given time there could be as many as four families of class lines defined and in the ON state The assignment oper ation establishes which family or families of class lines are to be used for comparison with a spectrum measured for a particular channel Access the Assignment Menu by pressing ASSIGN L producing a display such as shown in Figure 22 8 Assignment Menu Classification Class Lines Optional Feature 2900 MANUAL Figure 22 8 Assignment Menu 29 DEC 17 00 02 MCURUS 1 CURUS 2 CURUS 3 CURUS 4 T Assign Data to Classes 8 0000 ONENTIAL 1764 LINEAR 26H
19. Arange XX on the lower right side of the screen indicating that the horizontal arrow keys are now programmed to adjust the off set of channel 2 with respect to channel 1 The numerical field XX in the message indicates the amount of offset in units of dB presently active Each press of the left arrow key will decrease the offset in 10 dB steps while pressing the right arrow key will increase the offset in 10 dB steps as indicated by the changing value of XX in the message on the lower right of the screen The offset is limited to 30 dB When the desired amount of offset has been selected press CURSOR to remove the horizontal arrow keys from continuing to adjust the offset Performing a Measurement A more convenient way to set the input gain is to use the autorange feature With the analyzer running press AUTO which will produce the message Auto Ranging is ENABLED on the upper right of the display This will automatically adjust the input gain until the amplitude of the peak detector for any input channel falls within the aperture of full scale without an overload While the autoranging process is in progress the screen message will switch between Auto Ranging is ENABLED and Ranging This switching will cease when the proper range has been achieved Pressing RANGE will return the range control to the horizontal arrow keys The 20 dB window below full scale into which the autoranging seeks to place the highest peak compo
20. Cross Spectrum Mag Phase Transfer Function H1 Mag Phase Transfer Function H2 Mag Phase Transfer Function H3 Mag Phase Coherence Mag Power Intensity All intensity display functions Selecting the Number of Analysis Channels The window entitled CH is used to select the number of channels for the Frequency Analyzer Mode Selecting the Number of Data Display Windows Setting the Range Input Gain Click on WIND to select the number of display windows Sin gle Dual or Quad Another choice is LCD which reproduces the LCD display of the 2900 on the color monitor In the present version of the 2900 software not all the display func tions available on the instrument display are available on the color monitor such as the vsTime display of autostored data In order to see this on the video display screen the LCD dis play mode can be used 24 8 To modify the amplitude range in 10 dB steps via a change of the input gain place the mouse pointer over the window GAIN and click on the left right mouse key to decrease increase the range key Use of External Color Monitor for Display and Instrument Control Selecting vsTime or vsTach Autostore 2900 MANUAL Running and Stopping the Analysis To select or turn off the autostore function click the mouse over the window labeled AUTOSTR and click to select from among the following Off by Time by Tach and Exit The name of the selection wil
21. In many measurement projects we typically take a single measured intensity spectrum as being the average value over some representative surface area and then calculate the actual power flowing across that surface by multiplying the measured intensity by the surface area The units of acoustic power are thus Watts The units of the acoustic power level are dB relative to 1 pW 1 0 x 10 12 W When an intensity spectrum is displayed both the intensity and the acoustic power levels corresponding to the position of the active cursor are displayed on the right side of the dis play The intensity level is shown as normal for the cursor readout with an s or a d to denote the solid or dotted cur sor The acoustic power level is displayed below the intensity level in the format POW XX Q xxxx m XX is the acoustic power level based upon the value used for the Surface Area xxxx The value of surface area is entered from the Setup Menu by pressing meter2 M which will bring to the upper 20 7 2900 MANUAL Job Part Area Labels right of the screen a field indicating the present value of Sur face Area If acceptable press EXIT otherwise type in the desired value using the keypad before pressing EXIT In the following section it will be shown how each individual measurement can have associated with it an AREA name as well as a value of surface area Upon entering the AREA name there will be a prompt to enter a value of surface are
22. 3 11 2900 MANUAL Overload Indication Autoranging An overload is indicated by an audible beep accompanied by the large inverse video message OVER on the screen The inverse video overload message will disappear when the over load condition no longer exists Since some of the measured parameters involve integration over time the existence of an overload at any time during the measurement would be a source of error To indicate that an overload had occurred during a measurement the letters OV will appear to the upper right of the digital display of the sound level This indi cation will not disappear until a reset of the data buffer is performed Measurement Range When measuring a stable sound level the user may wish to utilize the Autoranging function This is described in the sec tion Autorange of Input Gain in Chapter 7 In the worst case using flat weighting with the 1 Hz highpass filter selected a time interval of 45 seconds should be allowed for filter set tling after a range change In practice examination of the time history trace should indicate when the measured and displayed sound level has become stable 3 12 The range of sound pressure levels over which measurements in the SLM mode can be made to Type 1 accuracy are listed below for a range of Larson Davis microphones The lower limit is established as being 10 dB above the measured noise floor in order to maintain the error to less than
23. If only the amplitude and phase of the analyzer itself are to be normalized the broadband noise source is applied directly to the input connectors When using Larson Davis side vented 1 2 or 1 4 microphones such as supplied with the Model 2260 Sound Intensity Probe the user can utilize the Model CAL291 Residual Intensity Calibrator in conjunction with the noise source to amplitude and phase match the complete measurement system including the microphones and pream plifiers The CAL291 applies the same amplitude acoustic sig nal with zero phase difference between them to both microphones Connection of the Noise Generator The internal noise generator of the Model 2900 will be used for the normalization procedure If normalizing just the instrument use a BNC T connector and several cables to direct the output of the generator to both inputs using a ADPO12 BNC to 5 pin Switchcraft adaptor If normalizing through measurement microphones connect the output of the generator to the input of the CAL291 and press the microphones firmly into the microphone openings Control of Display Formats Cross Channel Normalization and Use of Key Macros 19 9 2900 MANUAL Normalization in Cross Mode Using FFT Filtering Selection of 100 Line Resolution Normalization using FFT filtering must be done using the same values of highpass and lowpass filters and choice of time weighting window as will be used for subsequent mea suremen
24. NWN urojs g Wouj nus Sjoso 02 92 snu W Aayyos 61 52 3 1 A61 S7 d NYONME I LOAVSIQ HHO NO nuo SunustoA KeldsiGq esq ss y uonesuadwoj Qprapueg o 850 a ff v f uoneIBonu EEN o qnoq 1o LAA 104 0 ST 814 ZP H Ui 5 aou A JAISALAS a WAS d HOVHAV fuo GNVLS PIP nus dnos uv pue Y HO pue uO end pue ASUS papa Sunusro jnopeo USIA opoJA Kejdsiqq apo N ejdsiqq 213301 Jos jssoooy pueqpeorig o ggO nn ds yssoL g T V 1 1 Spprapueq Qpriepueg kejdsiq 24810 jospeg 8 pue 9 Z enar snua SISATEUV ou Jo ouo WOU nuoJA e dsiq 12 92 snus 5 86L Sc TANDII Olwasn INIO v mM aasa Dio flv M LOM ON 4 t ft t SunusroA Ae dsiq II PAS g auam V IRAIJAZ t t ssoupno T 19391A7Z jo W0 PAPS 6 SZ m r nuo Kejdsiqq wouj nuon e dsr esi 22 92 snu W Aayyos 02 92 44n l4 HI 44A LAV I DIWINANOD HJ LNQOO A S INNOD lalN Oaxq OldXH a WNIT V SNI t t 4 1 euim dAL Sur8e1 AV VAS SUISPIOAY SISATEUV LHH nusyy 10199190q H AdA LAV 4 NITILH d dXH L8 D dX4 8 WNIT V SNIT out SUISBIDAY 199 9S dAL SUISPIOAY P S 8 pue 9 Z Sandy snuapy SISATEUV ou Jo ouo WOU SUIPIApUegq JABJIQJ NUAN 1032919 T
25. Selection of Averaging Parameters After the analyzer has been setup from the System Menu the user will exit to one of the three Analysis Menus to perform a measurement Before actually beginning the measurement the averaging parameters should be defined Since the same theoretical considerations apply to the averaging setup for each these analysis types this chapter is devoted to that sub ject and placed in sequence before the chapters describing the detailed operation of the analyzer Selecting Averaging Type Accessing Averaging Menu From any of the three Analysis Menus access the Averaging Menu by pressing DETECTR H The range of choices of averaging type will be represented by the softkeys along the top of the display The choices will be different depending upon whether Octave or FFT filtering has previously been selected Further information about these averaging methods is presented later in this chapter under Signal Averaging Considerations Averaging Type Octave Filters When Octave filtering has been selected pressing DETECTR H will cause the Menu illustrated in Figure 5 1 Octave Averaging Type Menu to be displayed Figure 5 1 Octave Averaging Type Menu Bl OER 12 29 49 LIN S LIN R EXP BT EXP BT LIN SPL Dual TRCH RU TIME 2 4800 LINEBR 20Hz 28kHz EXPONENTIAL 1 8 DI APR 927 KS 28 55 d 38 89 DIFF PHONS 98 2 8 8 SPEED 4 6 dotted crsr Selection of Averaging Par
26. The eight softkeys explained below are used to define the sep arate user defined text lines including location size and ori entation Each may be set ON or OFF individually To configure the custom graphic portion of the printout press GRAPHIC A In response to the message Print SCAL ABLE GRAPHIC on the upper right of the screen press YES A if a graphic is desired in the printout or NO C if it is not If NO the display will return to the Edit Menu If YES the configuration procedure will continue with the display of the message Enter Position X nn n Y nn n mm Enter numerical values defining the origin lower left corner of the graphic Following this the message Enter Size W m n H nn n will prompt you to enter values for the width and height of the portion to be used for the custom graphic in the same manner as the coordinates of the origin were input above Next the message Print FRAME AXES amp GRID prompts you to select either YES A or N C to turn ON or OFF the printing of these parameters of the custom graphic printout The following message Print DOTTED CURSOR permits you to select whether or not the dotted cursor with a digital printout of the frequency and amplitude corresponding to the cursor position is to appear in the custom graphic printout Select YES A or NO C If YES the message will prompt you for input of the origin of the Trace Legend bl
27. There are two way in which autostore records can be deleted From the Recall Menu the record which was last recalled indicated by the value of N in the message Recall By Time N on the upper right of the screen will be deleted upon pressing DELETE I The message Delete the current record on the upper right of the screen will appear for veri fication of the deletion Press YES A to continue with the deletion or NO C to abort the deletion Following the deletion the remaining records will be repacked Those records following the one deleted will be moved down one in sequence within the file reducing each of their record numbers by one As a result the message on the upper right of the screen will still indicate the same value of N as before the deletion but this record will now represent the record which had been stored just after the deleted record since its index has been reduced from N 1 to N Those records located before the deleted record in sequence within the file will maintain their positions and record numbers Individual autostore records can also be deleted from the Files Menu as explained in Chapter 13 under the section Record Operation From the Files Menu Averaging of Autostore byTime Records Autostore by Time Sequentially stored autostore records can be averaged together using the Block Averaging Function From the Recall Menu press B AVE B which will bring to the upper right of the screen the
28. 10 kHz and 1 Hz 20 kHz vveightings the error vvas less than 1 dB for frequencies above 10 Hz Selecting the Displayed Parameter 3 14 VVith the exception of the analog vveighting and highpass lowpass filters the Model 2900 is totally digital As such simultaneous measurements are made using the following detectors RMS Slow RMS Fast Impulse and Peak The Min and Max values of the RMS Slow Fast and Impulse detectors over the measurement period are maintained At the same time it calculates both LEQ and SEL integrated values In certain versions of the Model 2900 such as delivered to Ger man users the Min and Max values of the Impulse weighted sound level are replaced by the Taktmaximal Fast weighted 3 and 5 values Leq is a parameter used for the analysis of time varying acoustic signals It represents the steady level which inte grated over the measurement period would produce the same energy as the actual signal The time used for the cal culation is the elapsed time since the last data reset SEL Single Event Level is similar to Leq except that it repre sents the steady signal which integrated over a one second time period would produce the same energy as the actual signal integrated over the elapsed time since the last data reset Sound Level Meter Operating Modes 2900 MANUAL Sound Level Meter Operating Modes To select the desired display press one of the following SLOW I Produces a d
29. 15 16 Autostore by Time Autostore by Time 2900 MANUAL There are two formats available for the presentation of the waterfall plots In the two dimensional format produced by pressing DRAW 1 C the spectra are simply overlaid one at a time without any offsets in the vertical and horizontal directions This produces a graphic as shown in Figure 15 6 Waterfall Menu In the three dimensional format produced by pressing DRAW 2 D an offset in both the vertical and horizontal directions is added to each successive spectrum curve pro viding perspective to the view Figure 15 7 Waterfall Menu 3D Format 25 APR 16 18 23 DRRU 1 DRAW 2 START END DELTA Usually one begins by displaying all the spectra within the record using a large enough spectral increment number that the drawing does not take too long Then based on the obser vations of the display sequence the range of spectra is reduced to a sequence of particular interest with a smaller increment to produce more details of the spectral changes over that range of spectra 15 17 2900 MANUAL 15 18 Autostore by Time 16 Autostore by Tach Tachometer Input TACH On the top panel of the Model 2900 is a connector labeled TACH INPUT This is designed to be used with a tachometer which outputs an analog pulse train whose frequency is pro portional to the rotation rate of a rotating machine The 2900 detects the frequency of this pulse train and displays t
30. 8 dB appears on the upper right of the screen it means that a maximum unfavorable deviation greater than 8 dB has occurred in at least one frequency band when determining the values of the Indices Figure 21 7 Sound Reduction Index 11 MAR 17 19 09 D R DnT 60 SPL a 08008 EXPONENTIAL 1 8 Dual LINEAR 26Hz 26kHz RESET 11 MAR 97 16 12 51 FILTER 20 166 Hz L73 Sound Reduction Index R w 2 20 M a 32 def 28 TACH 68 8 SPEED 4 6 dotted crsr 21 17 2900 MANUAL Impact Sound Insulation Measurements 21 18 Parameter Index Level Difference D Weighted Level Difference Dw Apparent Sound Reduction Apparent Weighted Sound Index R Reduction Index R y and Air borne Sound Insulation Mar gin M Standardized Level Differ Weighted Apparent Standard ence Dy ized Sound Reduction Index Dor al The determination of Impact Sound Insulation whether in a laboratory or in the field requires the use of a standardized tapping machine to deliver impacts on the floor of the upper space which acts as a source of sound generation in the room below A space averaged 1 3 octave sound pressure spectrum of the sound in the test room below is measured while the tapping machine is in operation It is very impor tant to follow the standard carefully as it may be necessary to measure not only at different points within the test room but also with the tapping machine placed at several different position on the floor o
31. HPA q aaya V eM SUISPIOAY kejdsiaq AOS HEH YEAK wod PAS 92 snu W Aexyos 96 92 FTANIDIJ EP GZ Am IH GZ m r 6 Z m n LE SZ m r O AV Taa I dS Ind A HLIHM f NNId I HNIS spuooas IWILL ALPA 19g dAL eusig p f 10 nuoJA ss yi H LLV D LIV q NnM 44O 9 410 VINO tod uonenu ny 0 1 0 IPON euonveaod JO e1EUJN BUSTS 190S SZ ong n fy ur 3s4AS Wouj nud 1oje1ouor TEUS S Lv Sz snus fexyos 16 52 FTANDII 8 6c m rq d WALT o T oinv N auot z t t asuodsaz 1snfpy OAV OMY 19S nus 9uoj z ssoooy IN 1NnOO M OT JO JO NI HINIL TT NT PH dHHAS f INHO Il LYVLS t 1 t t 0 9uo d A alsa lag dl san D 9SN 40 JO fal s n Dis ol 121 si S 2A9 1 daams 19g S UILL dooASg 19g LE SZ zm n yy 10j amp 1ouor fEUS S WOU nus JOJEIOUSL 9UIS H LIV 9 LIV t t uonenu ny 0J1u07 q puo V 110184 t t surg daawe Aouonbod4 19g Zp GZ snu NW Aayyos 86 92 4MD L d WALA Ol Tomy N euo suods yi 1snfpy 9497 ONY 3 S NUJJA 9uoj SS V IN 1NnOO M OT JO JO IN AINLL TINIT Dl dHHAS f aNao Il LYVLSO H JV D 11 0 9uo d A sopnidury JOUJTIJJIA 39S 9An o 39S IO JO a aan DI9SN IO JO 3 Ek lal s a ast asr T l si g
32. a A r deeg Sua W id s S ara s 2 R Hz H kHz dotted crsr INITIRL ROOMS vsRPM STAT Mx Srec F TRIG SETUP FILES AUTOSTR Figure 1 8 Noise Floor in dB re 1 microvolt 200 line FFT SEL DISPLAY note DETECTR a ola w u w w w n W W w n a n w n n n w n w n n n n n a RE orma Note SHORTED INPUT x 66 6080 EE EE LINEAR SINGLE 68 0000 Input 1 LINERR 1Hz 2 kHz TOP 5 m 94 12 18 36 FRED 1660 H2AA v Channel 1 of 1 NORMAL v d 4 5 11 9 TRCH 8 0 SPEED 8 8 dotted crsr TRIG SETUP FILES AUTOSTR Figure 1 9 Noise Floor in dB re 1 microvolt 200 line FFT Energy Spectral Density 15 NOU 12 11 54 NORMRL Lea MIN MAX SEL DISPLAY note DETECTR Norma Note SHORTED INPUT B ou US 60 9000 LINEAR SINGLE 66 HAHA Input 1 LINEAR 1Hz 26kHz STOP 15 NOU 94 12 16 36 FREQ 1666 6606Hz H2AA v Channel 1 of 1 NORMAL d 24 5 8 1 TRCH 6 6 SPEED 4 6 U ofset 50 SETUP FILES AUTOSTR Introduction 2900 MANUAL Model 2800 and 2900 Specifications Input Measuring Range 10 to 200 dB SPL with appropriate transducer Impedance 10 GQ 2 0 pF with preamplifier Polarization Voltage 28 200 VDC Gain 30 to 90 dB in 10 dB steps Connector Multi pin for use with LarsoneDavis Models 900B 1 2 and 910B 1 4 microphone preamplifiers and ECXXX microphone extension cables Adapters Available for use with ICP accelerometers and direct voltage inputs Analog Input Filt
33. ments made at different spacial positions over a defined sur face enclosing the test specimen are used as indicators of the accuracy of the measurement procedure The formulas are as follows F L Ll eq 1 where L is the surface sound pressure level calculated from the equation 1 N 0 12 y 10 ir eq 2 i 10 Lin is the surface normal unsigned intensity level calculated from the equation Sound Intensity Measurements Negative Partial Power Indicator Field Non Uniformity Indicator Sound Intensity Measurements NOTE 2900 MANUAL N 1 Lim ii lm eq 3 i 1 where is the unsigned normal sound intensity at mea surement position i pum eq 4 where L is the surface sound pressure level calculated from equation 2 L is the surface normal signed intensity level calculated from the equation N E hod i l L 10log dB eq 5 1 is the signed magnitude of the normal sound intensity component measured at position i on the measurement sur face 1 is the reference sound intensity 1017 Wm Where the normal sound intensity component level L at position i is expressed as XX dB the value of shall be calculated from the equation x 100099710 Where the normal sound intensity component level shall be cal Ini Ini Ig L at position i is expressed as XX dB the value of L culated from the equation Ini Jux Go m If Y
34. note Hote dB P I 68 608088 55 XS LINEAR SINGLE 60 annan Dual H Wd Hz 4 0 dotted_crsr S gt JOB S gt PART S gt AREA S gt EDIT Ci F4 2 C2 F4 2 F3 F2 20 5 2900 MANUAL The Class 1 minimum pressure residual intensity require ments for a sound intensity measurement system specified by ANSI S1 9 1996 and TEC 1043 1993 are as follows Frequency Hz ANSI S1 9 1996 IEC 1043 1993 50 13 0 12 0 63 13 0 13 0 80 13 0 14 0 100 13 0 15 0 125 13 0 16 0 160 13 7 17 0 200 14 7 18 0 250 15 7 19 0 315 15 7 19 0 400 15 7 19 0 500 15 7 19 0 630 15 7 19 0 800 15 7 19 0 1 000 15 7 19 0 1 250 15 7 19 0 1 600 15 7 19 0 2 000 15 7 19 0 2 500 15 7 19 0 3 150 15 7 19 0 4 000 15 7 19 0 5 000 15 7 19 0 6 300 14 9 19 0 8 000 13 7 10 000 12 9 If the system is working properly and calibrated as specified the pressure residual intensity index should be significantly better than the minimum values specified by the standards Press EXIT to return to the Intensity Menu 20 6 Sound Intensity Measurements 2900 MANUAL Sound Intensity using Narrow Band FFT Analysis Although there are no standards governing the measurement of sound intensity using narrow band FFT analysis there are applications where such a measurement may be of great values particularly when it is important to know the fre quency content of the sound intens
35. From the System Menu access the Units Menu by pressing UNITS F which will produce the display shown in Figure 9 1 Units Menu Figure 9 1 Units Menu se NOU 17 56 24 SLOPE name SAME R UNITS Noise F mU cal U cal level Hote SPL 6 60068 ang nM E Iam ead EXPONENTIAL 178 Input 1 LINEAR 1Hz 28kHz 1 RESET 36 NOU 93 17 52 35 T eere IIS RR p LOCIS EE YE sro FILTER 25 Hz v Channel 1 of 1 NORMAL 1 d 23 8 3 GD EE D EIE PHONS 53 6 4 D T H 0 0 SPEED 4 6 dotted crsr z B z INITIRL dB vu SPL undef undef undef undef undef undef Selection of Units and Calibration The first step in calibration is to define the name of the mea surement unit which is to be used for each channel The row of softkey labels at the bottom of the display keys I P presents the choice of unit names When delivered the only keys representing actual unit names are dB QV I and SPL J the remaining keys names are labeled undef for UNDEFINED The user can create names to associate with the remainder of these keys such as g m sec ft sec2 psi mil etc as required Once created unless the user changes them or clears them these names will remain among the choices available To name attach a label to a softkey press name B and respond to the prompt Push units to name by pressing one of the softkeys K P The message Enter setup name fol 9 1 2900 MANUAL Assignment of
36. OFF ROOMSTST 1 0 SIG GEN INPUT clock COLOR SETUP FILES RESETS The user might choose to examine the instrument setup in detail as indicated on the right of the display and change item by item those parameters which are not as desired for his measurement but with some practice it is more efficient to simply create a totally new setup We will first concern ourselves with setting up those parame ters related to the measurement itself and address the I O Noise Clock Color Setup Files and Resets Menus later in this Chapter Selection of Analysis Type Standard Mode 4 2 The Analysis mode is selected by pressing one of the following softkeys Softkeys Softkey Functions STAND C for Standard Analysis CROSS D for Cross Analysis INTENSY E for Intensity Analysis The softkey SLM A B will place the 2900 in the Sound Level Meter with Analysis Mode permitting it to perform sound pressure level and frequency spectral measurements simultaneously as described in Chapter 3 In the Standard Analysis Modes six different forms of spec tra Normal Leq Min Max SEL and MaxSpec are calculated for each channel regardless of filter type The distinction between these is explained in Chapter 6 The softkey Chanls A toggles the Standard Mode between single and dual channel analysis as indicated by the message Channel 1 of 1 or Channel 1 or 2 on the right of the display 6th line down For single channel Standard An
37. OVER D Toggles On Off the beeper signal on overload condition ERROR E Toggles On Off the beeper signal on error condi tion The RS 232 interface is made active by pressing RS 232 I The Baud rate for the data transfer across the interface kilo byte second is selected by pressing one of the following soft keys Baud Softkeys 300 J 600 K 1200 L 2400 M 4800 N 9600 O 19200 P 4 30 The internal clock of the 2900 is set from the System Menu by pressing clock M A message on the upper right of the screen will prompt the user to enter the data and time in the format DD MM YY HH MM SS using the keypad and press EXIT 2900 Instrument Setup Via The System Menu The Resets Menu 2900 MANUAL 2900 Instrument Setup Via The System Menu Although there is often a reset softkey in individual softkey menus to reset certain user defined items or even the entire RAM memory the Model 2900 has combined these into a sin gle Reset Menu as well for efficient access The Reset Menu shown in Figure 4 21 Resets Menu is accessed from the System Menu by pressing RESETS P Figure 4 21 Resets Menu a2 ig 23 39 18 R MEMRY R UNITS R SETUP R RT6G R USER R MACRO R STRTS SPL a 000G EXPONENTIAL Input 1 LINEAR 28Hz 28kHz RESET 02 JAN 98 23 37 06 FILTER 1 88 Hz L 3 v Channel 1 of 1 NORMAL d Ze 19 7 PHONS 53 6 noise 88 8 Pressing each of the following keys will initiate the par
38. There will not necessarily be a label for every key some may be blank We refer to these as programmable keys or soft keys because the role of each hardkey is to enable an action or activity associated with the particular label which is dis played above or below it Thus the role of each key will change as the Menu being displayed changes In some cases pressing a softkey will result in a specific action such as opening a data entry field on the display so that a numerical or an alphanumeric value may be entered We have adapted the convention that the softkey label be written in lower case letters when the action of the softkey is to call for an alphanumeric entry In other cases pressing a softkey will cause the Menu displayed on the screen to be changed to another Menu with a different set of softkey labels In this manual when we refer to a particular softkey we shall use the format XXXX Y where XXXX is the softkey label and Y is the lower alphanumeric character imprinted on the Introduction 2900 MANUAL associated hardkey For example AUTOSTR P would refer to the key on the far right of the row below the display which has the character P imprinted on it and the label AUTOSTR displayed on the screen directly above it The Arrow Keys and associated Hardkeys Cursor Control The four keys on the lower right of the 2900 front panel with arrow symbols indicating upward vertical downward vertical left ho
39. These are selected by pressing PORTDEF G or LANDEF H respectively and responding to the message overwrite current setup on the upper right of the screen by pressing YES A Examples of these default custom printouts are shown in Figure 23 9 Portrait Default and Figure 23 10 Landscape Default 23 13 2900 MANUAL 23 14 Figure 23 9 Portrait Default Current Time 18 APR 94 13 13 25 Note EXAMPLE LARSON DAVIS 2900 RTA A4 22 Units SPL Run Time 6 1600 Detector EXPONENTIAL 1 64 Input LINEAR20Hz 20ktiz Spectrum Time 18 APR 94 12 44 27 Filter L 3 Channel Tof 2 SPL spectra F 74 753 Toch 0 0 Speed 0 0 Job Port Area Loc SEL DISPLAY note DETECTR EXPONENTIAL 1620 inb ir dus GE Es ac 81 4 TRCHe 8 0 SPEED 0 0 serue rit BP ROTER 1 80 Hz 0 33 2 00kHz 73 8 40 10 0kHz XA Figure 23 10 Landscape Default Le Eer S H eS 005 pik er De taa MO E mrt 20 osea ttes 00 eet 80Hz 40 10 0kHz Z A 2900 Printing Data Screen Displays and Tables Initiating Printing of a Custom Printout 2900 MANUAL 2900 Printing Data Screen Displays and Tables With the desired custom printout active and the desired data block displayed simply press user I to initiate the printout The message Print Error on the upper right of the screen indicates a problem with the communication between the analyze
40. ch 1 Impulse Response ch 2 vs ch 1 Inverse Transfer Function H1 ch2 vs ch 1 Cepstrum each channel Liftered Spectrum each channel In the Model 2900 cross channel measurements are between channels 1 and 2 The basic measurements performed by the Model 2900 in the FFT analysis mode are an autospectrum for each input channel G4 and Gog and a cross spectrum between Channel 1 and channel 2 12 The remaining parameters are calculated from these as indicated below e Coherence 2 Gi Yo 5 10822 e Transfer Function Estimates Gp Hs Gg Gy H 22 Gy Hu Displayed phase is from H In the following Ft is inverse Fourier Transform e Autocorrelation Rig FAG ji 1 2 Analysis Menus Selection Of Measurement And Display Parameters 6 7 2900 MANUAL Selection and Indication of Displayed Channel Display of Complex Data Records 6 8 NOTE Cross Correlation R t FIG Impulse Response A t F H Cepstrum C t F logG i 1 2 Liftered Spectrum Li f FILG COL 1 2 Where L 1 is the lifter defined below L wu Short pass lifter equals for quefrency greater than tr unity otherwise LL 4 Long pass lifter equals for quefrency less than Tr unity otherwise The value of t is selected with the horizontal cursor keys as indicated by the lifter message on the lower right of the dis play For all of the above frequency and t
41. from the Filter Menu press 1 1 oct A or 1 8 B to select the desired bandwidth Each of these standards employ a single measurement of sound intensity as the average intensity across a representa tive surface The ISO standard establishes a number of Field Indicators one which is a function of time and the others of spacial position and a detailed procedure which must be fol lowed to achieve a desired grade of accuracy Later in this chapter is a section describing how these indicators can be evaluated by the Model 2900 and displayed in a particularly Sound Intensity Measurements 2900 MANUAL useful format for field applications The ANSI standard pre sents an Appendix B which is not considered to be a part of the standard in which a number of indicators are described which may be used for evaluating data quality However these are included with the standard for guidance and infor mational purposed only The averaging time of the intensity measurement should be set according to the requirements of the particular standard being followed When using exponential averaging both the ISO and ANSI standards are satisfied by selecting Constant Bandwidth averaging using a BT product of at least 400 To setup the Model 2900 for this from the Main Menu press the softkey sequence DETECTR H BT EXP D AVE TIME H 512 J EXIT to set the instrument for BT 512 the 2900 does not include the value of 400 among the choices of averag
42. indicates the Nth record of type Ln Trace has been recalled from the active memory file If a dif ferent Ln Trace record number is desire use the horizontal arrow keys to access it Press another key such as CURSOR to remove the KNOB from the recall mode and keep the data on the screen The cursor can be used to readout the data values corre sponding the statistics parameter table and the displayed curves Hidden traces can also be unhidden However attempts to modify the values in the statistics parameter table by pressing N N will produce the message Illegal with recall data This is because the complete Statistics Table must be available to calculate statistics for values of n differ ent than those already present in the statistics parameter table Merging Statistics Tables To recall a Statistics Table press RCL TBL J The message on the upper right of the screen will prompt the user to enter the record number of the Statistics Table to be recalled using the numeric keypad and press EXIT This will produce the message ARE YOU SURE on the upper right of the screen warning the user that the recalled Statistics Table wil overwrite the Statistics Table presently active in the 2900 To proceed press YES A To abort the recall and maintain the present Statistics Table intact press NO C Once the Statistics Table has been recalled data and curves will be produced as described above The user may then mod ify the
43. o c n n c n BESSER EXPONENTIAL 1 6 i PREAMP LINEAR 18 20kHz i RESET 62 JAN 90 06 40 08 sa w a w w w W W w w cc w w w a W a W n W n w a w w n n n w m n n Basse FILTER 16 GkHz LAJ TRIG v Channel 1 of 2 NORMAL d Es 48 4 6B PUDE bee PHONS 61 8 102 i E 8 8 SPEED 0 0 TI IS Z6 33 46 dotted crsr TEST 1 byTACH TRCHSET F TRIG FILES In the Autostore byTime storage mode the 2900 will measure and store spectra at equally spaced time intervals in sec onds over a specified period of time also in seconds Any frequency or time domain data blocks may be autostored In the Analyzer mode of operation one or two data blocks are stored each time interval depending on whether single or dual channel analysis has been selected With the 2900 set for dual channel Cross analysis both time and frequency domain data may be stored When the SLM mode of operation has been selected in addi tion to a single channel frequency spectrum the following SLM data are stored at each time interval SLOW SLOW MIN SLOW MAX FAST FAST MIN FAST MAX IMPL MIN IMPL MAX Leq SEL Peak and Spectrum gt Autostore by Time 15 1 2900 MANUAL Defining Delta Time and End Time To prepare the 2900 for a byTime autostore operation first set the time interval desired between successive storages by pressing delta C which will produce the message DELTA TIME XXXXXX XXXX
44. obtained using a Post process order tracking A detailed description of the vsRPM Graphic capability is pre sented in Chapter 17 Autostore by Tach 17 vsRPM Graphics vsRPM Graphics As explained in Chapter 16 Autostore by Tach it is possible to read the RPM and Speed values of a vehicle or machine during a test and to autostore spectra at regular intervals of RPM or vehicle speed using the byTACH storage mode The VSRPM Graphics capability permits the 2900 to simulta neously display several different curves in an amplitude ver sus RPM Speed format Each curve would represent a particular channel and frequency band or order value user definable When octave bandwidth or standard FFT analysis is utilized the spectral data can be used directly to produce curves of frequency band versus RPM Speed However by using a pro cedure which we refer to as post process order tracking these curves can also be generated in the form of order ver sus RPM Speed This procedure is explained in detail later in the chapter under the section Post process Order Tracking There are two different modes of operation of the vsRPM Graphics 1 Real time vsRPM Graphics Without utilizing the autostore capability directly the sys tem can be set up to measure and plot the curves repre senting selected data as a function of RPM or Speed live on the display as the test takes place For example if a machine is run up from a low to a high v
45. of the frequency axis After positioning the cursors pressing Auto RE E will ini tiate the following sequence for each filter band between them 1 In the time domain the upper and lower threshold values relative to the maximum level during the measurement time are used to define the time interval over which the curvefit is to be performed In some cases where the back ground noise level is higher than the level corresponding to the initial noise level minus the decay of the lower threshold the decay curve will not cross the lower thresh old In such a case the curvefit for that frequency is aborted and a value of zero is assigned as the RT60 time Room Acoustics Measurements Room Acoustics Measurements 2900 MANUAL 2 Aleast squares best fit is performed on the portion of the decay curve within the time interval defined by the two thresholds to determine the slope of the decay 3 From the slope of the decay curve the data is extrapolated to produce the RT60 value in seconds to represent the time which would have been required for a decay of 60 seconds at the same rate of decay 4 The RT60 value for that frequency band is stored in the RT6O0 register replacing whatever value had been there previously The RE in the Auto RE E implies that the new value REPLACES the previous value At the conclusion of the automatic curvefit procedure the RT6O values for all the frequency bands between the cursors will be disp
46. polarized microphone is to be used the polarization voltage should be switched off Some users may wish to select a 28 volt bias voltage either to reduce the microphone sensitivity or to improve the microphone operation in extremely high humidity situations To change the bias voltage access the System Menu by pressing the hardkey SYSTEM and access the Input Menu shown in Figure 3 2 Input Menu by press ing INPUT K Figure 3 2 Input Menu 38 NOU 17 52 42 au 28U 200 U RUTO RR I TEST 118 n n n n n n n n n nn n n n n n nn PA sg teria dons ue ds 200 Volts Bias i Note 1 SPL 6 6008 ang nM A SEN EE EXPONENTIAL 178 Input 1 LINEAR 1Hz 28kHz RESET 36 NOU 93 17 52 35 T e ef w COCOS ria ius P lva sese FILTER 25 DA Hz L73 1 Channel 1 of 1 NORMAL i d 23 8 5 GE EET kr rr PHONS 53 6 LOC i TACH 8 8 SPEED 4 6 i WE DEE card LU dotted crsr z z INITIRL A WGT 1 20k 20 26k 1 18k 28 18k SAME aRRNGE Note that the value of the microphone bias voltage presently active will be displayed on the upper right of the screen for approximately 4 seconds To change the polarization voltage press one of the following Softkeys Softkey Functions 0 V A Bias voltage OFF for use with electret or prepolar ized microphones 28 V B 28 volt bias voltage active 200 V C 200 volt bias voltage active To return to the SLM Menu press EXIT twice So
47. see Intensity Sound Level Meter See SLM spectral density 19 7 SPL 6 10 20 11 STAND 2 4 2 Standard Analysis Mode 4 2 6 1 Statistics 18 1 18 3 calculation and display 18 4 A 5 2900 MANUAL merging tables 18 7 recalling Ln traces 18 6 storing and recalling tables 18 7 storing Ln Traces 18 6 Storage byTime autostore records 15 5 classification by record type 13 6 Ln Trace 18 6 Macros 19 14 non autostore records 13 6 setups 12 2 Statistics Table 18 7 Units 9 7 user weighting curves 10 6 10 7 Stored Records 13 14 block averaging 13 12 15 13 deleting 13 12 15 13 waterfall display 13 14 15 16 16 14 Summation Bands 19 2 T Taktmaximal 3 15 Test Signal 4 13 9 7 TIME 6 7 Time Display 6 7 Time Domain Trigger 11 1 Trace 18 6 recall Ln 18 6 storing Ln 18 6 Transfer Function 6 6 6 9 Trigger 11 1 arming and disabling 11 6 automatic re arming 11 7 Frequency Domain 11 4 15 4 selecting criterion 11 5 selecting frequency 11 5 selecting level 11 6 Time domain 11 1 15 5 U Units 9 1 names 9 1 storage and recall 9 7 user weighting 10 7 V vertical scale 19 5 vsRPM Post process Order Tracking 17 11 A 6 Real time Graphics 17 2 vsRPM Graphics 17 1 from vsRPM autostored data 17 9 W Weighting analog Analyzer 4 13 SLM 3 4 Weighting digital 19 2 active register 10 6 display 10 3 interpolation 10 5 user 10 5 White Noise see Noise Generator and Signal Gen erator X X FER 6
48. since there is not a power summation for intensity data taken in the vsTach autostore mode there is really no practical use for these names In order to display the TACH and SPEED data in the Intensity 16 1 2900 MANUAL byTach Autostore Mode from the Main Menu press SHIFT and G This will replace the display of PART and AREA with the field TACH X X SPEED Y Y Repeating this key sequence will return the right side of the screen to the usual Intensity Mode format Setting the Tacho Parameters Using the scaled values of RPM and Speed the 2900 can autostore spectra at regularly spaced increments of RPM and Speed beginning and ending at user specified values of both parameters The autostore may be done using either octave bandwidths or FFT frequency analysis A particular advan tage of using the octave bandwidths is that digital filter spec tra are produced much more rapidly from the processor than are FFT data blocks One can store 1 3 octave spectra as fast as 400 spectra second while successive FFT spectra will be at least 40 milliseconds apart The Autostore byTach function is controlled from the same Autostore Menu used for Autostore byTime This Menu shown in Figure 16 1 Autostore Menu is accessed from any of the Analysis Menus by pressing AUTOSTR P Figure 16 1 Autostore Menu 82 JAN 66 41 68 OFF byTIME delta endstor note Hote SPL 108 eer o n n n w n n n n n a o n
49. which plugs into a micro phone input has a six foot miniature cable terminating in a microdot connector This device provides a 2 mA current to drive accelerometers containing internal preamplifiers such as the ICPTM designs from PCB Piezotronics and the Isotron designs from Endevco Direct Voltage Inputs Charge coupled accelerometers should be connected to the analyzer inputs through the high impedance Model 900B microphone preamplifier by replacing the microphone car tridge with either the adaptor ADO10 BNC male cable con nection or the adaptor ADO15 microdot male cable connection AC Outputs The adaptor AD 045 is used to modify the 5 pin microphone input connector to a BNC input connector for use with direct voltage inputs Single Channel Standard Analysis Mode Introduction There are two connectors on the top panel producing AC out put signals AC 1 and AC 2 as indicated on the rear panel label The load impedance should be at least 2 kO When the 2900 is configured to the single channel Standard Analysis Mode the input signal may be applied to either Channel 1 or Channel 2 This is indicated by the message Input 1 or Input 2 on the right side of the screen third line down from the top The same AC output will be obtained from both AC 1 and AC 2 and this AC signal will be fre quency weighted by the user selectable analog input filter as indicated by the message on the right side of the scr
50. 1 DRAW 2 START END DELTA i Hote SPL 6 0050 EXPONENTIAL 1764 Dual LINEAR 28Hz 28kHz RESET 26 JAN 95 23 37 18 25 0 Hz L73 Channel 1 of 2 NORMAL 1 L OT 5 8 Hz 500 Hz 18 8 2 Z A OFF INITIAL On the right of the screen we see a table indicating the present values of START END and DELTA These represent the first and last spectra in sequence which are to be dis played and the incremental record number between dis played spectra respectively For example using the following combination START 0010 END 0020 DELTA 0002 Autostore by Tach vsRPM Graphics 2900 MANUAL The spectra displayed will be numbers 10 12 14 18 and 20 in sequence To edit any of these numbers press START E END F or DELTA G This will produce the message W FALL sXXXX eXXXX dXXXX with a flashing cursor to denote where inputs from the key pad will begin The only difference between initiating this input with the START E END F or DELTA G softkeys is that the flashing cursor will be positioned for immediate edit ing of the START END or DELTA values respectively Use the numeric keypad and the horizontal arrow keys to edit the values as required and press EXIT The display sequence will begin immediately upon pressing that key There are two formats available for the presentation of the waterfall plots In the two dimensional format produced by pressing DRAW 1 C the spectra are simply overlaid one a
51. 10 Noise Generator of the 2800 OPT 11 Signal Generator The LarsoneDavis Model CAL290 Sound Intensity Calibrator meets or exceeds the specifications of both these standards as a sound intensity calibrator It also meets the specifica tions of IEC 1043 1998 as a residual intensity testing device It does not however meet the more stringent residual inten sity testing device requirements of ANSI S1 9 1996 Sound Intensity Measurements Application Standards 2900 MANUAL ANSI S12 12 1992 Engineering Method for the Determination of Sound Power Levels of Noise Sources using Sound Inten sity This standard addresses both discrete point and scan ning measurement techniques ISO 9614 1 Acoustics Determination of sound power levels of noise sources using sound intensity Part 1 Measurement at discrete points ISO 9614 2 Acoustics Determination of sound power levels of noise sources using sound intensity Part 2 Measurement by scanning Setup and Calibration of the Measurement System Sound Pressure Level Calibration In the following we describe the calibration of a measurement system consisting of a Model 2900 analyzer and a Model 2260 Sound Intensity Probe Set the Model 2900 to the dual channel Standard Mode of analysis Set both channels to the frequency range 1 Hz 10 kHz Select SPL units for both channels Use a Type O 1 or 1L calibrator to calibrate each of the input channels as described in Chapter 9 Selection o
52. 12 Bandwidth Averaging Procedure nennen nennen nnns 17 13 Chapter 18 Statistics and Ln Calculations 18 1 Setup for Statistical Analysis EE 18 1 Setting the Update Interval nn 18 2 Setting Measurement 2 nennen inttr ense 18 2 Use of Autorangimg nennen nennen en i erret renes Qa aa asa a 18 2 Turning the Statistics Analysis On and On 18 3 Selecting the Ln Values for Calculation and Display 18 3 Running the Statistics Mode een 18 4 Calculation and Display of Data 18 4 Selecting the Display Channel Number 18 5 Modifying the Parameter Table Values A 18 5 RIdifig Mo m 18 5 Clearing the Statistics Table 18 6 otoring thie Bn Re 18 6 storing the Statistics Table ctr eere tege 18 6 Recalling kin Traces uie eie tenete 18 6 Recalling a Statistics Table 18 7 2900 MANUAL Merging Statistics Tables ii u ua u aa Q Le ee D e eed x oL p crea 18 7 Chapter 19 ControlofDisplayFormats Cross ChannelNormalizationandUseofKeyMacros 19 1 Accessing the Display Mem 19 1 Dual Channel Side by Side Display Mode eene 19 1 Displaying 1 3 Octave Spectra in 1 1 Octave Format 19 2 Digital Reading of A Weight and Summation Bande 19 2 Digital Display Weightlng rettet Ete ete e Pee Fee e Pon Dd 19 2 Display of Spectra Relative to a Reference Spectrum sse 19 3 Dual Channel Measuremen
53. 20 2 28 2 STOP B1 APR 9 12 37 07 TIME 66 6860mS H4AA vlmPulze Response Hi D 2 d 1 568 E 62 REAL Base Fresuencuz 00 000G TACH 6 6 SPEED 4 6 dotted crsr TRIG SETUP FILES AUTOSTR o 1 31 INT ALTERN BWNORM P lt gt R LIFT Select the parameter to be displayed by pressing one of the softkeys listed below The complex data types are indicated by an asterisk It is explained below how to change the dis play format of complex variables From first Menu form Softkeys Softkey Functions A SPECT A Autospectrum each channel C SPECT B Cross Spectrum ch 2 vs ch 1 X FER C Transfer Function ch 2 vs ch 1 Repeated presses display H1 H2 or H3 as defined below Analysis Menus Selection Of Measurement And Display Parameters Softkeys 2900 MANUAL Softkey Functions COHER D TIME E count ave only Coherence ch 2 vs ch 1 When the Coher ence is being displayed pressing ALTERN I will produce a display of Coherent Output Power Repeated presses will toggle the dis play between Coherent Output Power and Coherence Weighted and Unweighted Time Waveforms each channel Sequence of Displayed Data repeated presses of TIME E 1 Weighted Time Record 2 Time Record From second Menu form Softkeys A CORRE A C CORRE B IMPULSE C INVERSE D CEPSTRM E LIFTER L Softkey Functions Auto Correlation each channel Cross Correlation ch 2 vs
54. 21 20 Room Acoustics Measurements Noise Criteria Curves Room Acoustics Measurements 2900 MANUAL spectrum levels cannot be determined and the results should not be considered valid If a message Deviation 8 dB appears on the upper right of the screen it means that a maximum unfavorable deviation greater than 8 dB has occurred in at least one frequency band when determining the values of the Indices As an example Figure 21 10 shows an example of a Stan dardized Impact Sound Pressure Level display Figure 21 9 Standardized Impact Sound Pressure Level 11 HER 17 24 05 D R DnT 100 Hote TRPPING 6 9308 EXPONENTIAL 1 8 Dual LINEAR 20Hz 20kHz STOP 11 MAR 97 17 21 28 FILTER 20 166 Hz L 3 Standardized Impact SPL d 64 7 A 6 L nT uz 57 def 27 TACH G G SPEED 6 6 dotted crsr A single number technique for representing the character of steady indoor background noise is based on the 1957 Noise Criteria Curves These are a set of similar octave band refer ence curves which are overlaid graphically upon an octave frequency spectrum measured in the room to represent the background noise Each curve is designated by a number which represents the value of sound pressure level corre sponding to the 1 kHz band The user seeks that reference curve which is not exceeded by any of the background noise octave bandwidth levels but which is as close to touching one of them as possible In the 2900 this function
55. 2220 EXPONENT I AL 178 Dual LINEAR 20Hz 20kHz RESET 11 MAR 97 17 28 09 60 W W W W W w W a w n W w W w a n w w w n n n n a W n n n n a n n n n n a n n nn n a nn nen FILTER 14 25 8 Hz L v Channel 1 of 2 NORMAL d B 24 7 AD x 2 V V ee eee ee DIFF PHONS 36 4 REM g TACH 8 8 SPEED 4 6 25 5 Hz 500 Hz 10 0kHz H OFF ROOMSTST To select a new scaling format press one of the following Softkeys Softkey Functions LIN LIN A Linear gradations and cursor readouts on a linear scale LOG LOG B Log gradations and cursor readouts on a log scale LIN LIN C Linear gradations and cursor readouts on a log scale SQU LOG D Squared linear gradations and cursor readouts on a log scale useful for display of power spec tral density Control of Display Range Normally the screen will display an amplitude range of 80 dB using the logarithmic format In linear format this will be seen as 10096 to 096 from top to bottom expressed in units of percent of full scale This display range can be reduced from the Shift Menu accessed from the Analysis Menu by pressing SHIFT by pressing V SCALE C which will bring to the screen the Vertical Scale Menu shown in Figure 19 6 Verti cal Scaling Menu Figure 19 6 Vertical Scaling Menu as gan 63 56 49 J 4x 2 1 SELECT gt Vertical Scale Note SPL EXPONENTIAL 178 PREAMP LINEAR 20 20kHz STOP JAN 9 756 TRCH Op SPEED 4 6 range sa
56. 2800 2900 eene nennen nens 1 23 Standard Analysis Mode 2800 2900 Octave and 1 23 Intensity Analysis Mode 2900 only Octave and FFT 1 1 23 Cross Channel Analysis Mode 2900 only FFT a 1 23 Cross Channel Analysis Mode 2900 only Octave Bandwidths 1 24 Digital Averaging WEE 1 24 EE Ne Ve EE 1 24 EET Bandwidths emos ti E ate kk ep tags 1 24 Digital Display Weighting AA 1 24 For Standard 2800 2900 and Intensity Analysis 2900 only Modes 1 24 ln EE 1 25 MEMO E 1 25 GMOS Nomvolatiler erien R 1 25 Floppy DISK u a tee ate a isi S Oe S 1 25 Noise ee 1 25 Digital Output and Control 1 25 Analog Kell 1 26 Display GharacteristiS x et Ihre eem ieget eia fee rt Pe pa ra a Etre upas 1 26 internal LE LE 1 26 External Color Display Color Video Adapter required 1 26 Chapter 2 Chapter 3 2900 MANUAL Environmental u taia eee lied izole ae ka dwa kape EA m ki dya ba bend a 1 26 Physical d ess tan i etie oia oe i aaa bato 1 26 wo DUUM de 1 27 Battery Fower vue e caa dde ee ka al kw Pea aed 1 27 DLEA AONNE ER 1 27 2900 Blocle Diagram c tele erue Fre e ep e ENEAS 1 28 Menu Structure For Instrument Operation
57. 2900 only Octave Bandwidths Digital Averaging Autospectra Cross Spectra Transfer Functions H1 H2 Inverse Transfer Functions Coherence Coherent Output Power Octave Bandwidths FFT Bandwidths Linear Single 0 0025 sec s to 278 hours Linear Repeat 0 0025 sec s to 278 hours Exponential 1 64 sec to 512 sec s binary sequence BT Exponential 1 to 32 768 BT products binary sequency Exponential averaging BT Lin 1 to 32 768 BT products binary sequency Linear averaging Digital Display Weighting Linear single linear repeat exponential Exponential by N number of spectra Count single number of spectra Count repeat number of spectra Count manual number of spectra manual accept For Standard 2800 2900 and Intensity Analysis 2900 only Modes 1 24 Octave and FFT Bandwidths No weight A weight C weight user weight A weight C weight user weight Introduction 2900 MANUAL Units dB re 1 uV dB SPL dB re 1 pW m2 intensity dB re 1 pW sound power user definable and named units log or linear scale including single or double integration single or double differentiation scaling factor User selectable bandwidth compensation e g power spectral density Memory CMOS Non volatile 256 KB standard typical capacity of 992 1 3 octave or 142 800 line FFT spectra Additional 1 MB available Floppy Disk External 3 1 2 MS DOS c
58. 3 1978 E and R ISO 140 4 1978 E Level Difference L ISO 140 4 1978 E Standardized Level Difference Dy ISO 140 4 1978 E The standard ISO 717 1 1982 defines single number rating indices corresponding to each of these parameters which are determined by a curvefitting procedure described in the standard When each of the above parameters are displayed as a function of frequency the results of the curvefitting pro cedure are overlaid as well The calculated single number rating index or indices are displayed on the lower right of the screen The message def XX which appears to the right of the index value represents the sum of the deficiencies above the curvefit line as described in the standard To perform the calculation and display the result as a func tion of frequency on the analyzer screen simply press the softkey whose label corresponds to that parameter The parameters L and Lpr are discussed in a later section on Impact Sound Insulation As an example Figure 21 8 shows a display of Sound Reduc tion Index If a message WARNING High Background appears on the upper right of the screen this means that the difference between the Receiving Room spectrum and the Receiving Room background spectrum levels at one frequency or more is less than 3 dB In such a case precise values for the Receiving Room spectrum levels cannot be determined and the results should not be considered valid If a message Deviation
59. 6 6 9 Z Zw DIFF 6 5 Zw FREE 6 5
60. Averaging veod apaiia detii anaE EE RAR YR YY YY YR yaa nen nnns 5 6 Constant Confidence Time Averagimg eene nnns 5 6 Spectrum Averaging iui iere citer eb cite EE iet x dp SEENEN 5 6 leie exte e ACIE 5 7 Re NEE LE EE 5 7 Linear Repeat Time AV tag l 0 uu u enne ennt nnn nnns 5 7 Exponential Time Averagimg enne nennen nennen nnns 5 7 Analysis Menus Selection Of Measurement And Display Parameters 6 1 Standard AnalySlS u u 6 1 Selection of Display Format for Dual Channel Mode a 6 2 Average Spectrum Display ai a iaa i aia daadaa iaa aiaa iaat 6 2 2900 MANUAL Chapter 7 Chapter 8 Chapter 9 Selection of Display Parameter eee 6 3 Max Spectrum Display 55 ete etre Ie A ete Rr elektr c t 6 3 Dual Channel Display Mode eene nennen nenas 6 4 Loudness Measurement u L u nu isses YKLA niente nenne tren inten rennen nn 6 5 Gross Analysis lee tide redit p etre te EEN ke a Med mee Eee LS Ede auo 6 6 Cross Analysis of FFT Eiters nennen nnne hi aaa akay ens 6 6 Selection and Indication of Displayed Channel 6 8 Display of Complex Data Hecorde A 6 8 Display of Time Records incen ne AT ee eta EC eg odd aded dee 6 9 Cross Analysis with Octave Eiter 6 9 Intensity 515 ee fede e pala ky Deae tede ee Ua eene dex aan 6 10 Display ot Broadband M DEE i rs WAA 5 32 Eechen 6 10 Performing a Measurement
61. C The same sequence of messages prompt ing for user input will appear as they do for the Averaging operations described in the preceeding section The Autostore Block Maximum operation is limited to a maximum number of sequential records of twenty Upon pressing EXIT the operation will be performed and the resulting spectrum stored The word MAXIMA appears on the right of the screen 2nd line down in place of the elapsed time usually displayed with a measured spectrum to indicate that this spectrum is the result of the Block Maximum operation If the records con tained within the specified range are not all of the same type and bandwidth the Block Maximum operation will not be completed and the message NOT SIMILAR DATA will appear on the upper right of the screen Waterfall Display of Autostored Records 16 14 The waterfall display function permits the sequential display of a series of individual spectra within a By Tach type autostored record each one remaining on the screen after it has been displayed Thus we will see drawn upon the screen one spectrum then overlaid upon that another spectrum then another etc Access the Recall Menu by pressing RECALL and use the A Prev N and A Next O keys to recall the record number from which the spectra are to be displayed Then press W Fall A which will bring up the Waterfall Menu shown in Figure 16 8 Waterfall Menu Figure 16 8 Waterfall Menu 3a ZEN 93 42 13 DRAW
62. Channel 1 of 2 NORMAL d R 66 5 PHONS 71 4 TACH 1050 0 SPEED 4 6 recall data 16 11 2900 MANUAL 16 12 The RPM in the message on the upper right of the screen indicates that the records will be averaged in terms of the parameters associated with the vsRPM storage format In order to average the records in terms of the parameters asso ciated with the vsSpeed format press the softkey SPEED H which will change this RPM to SPEED To change back to RPM press the softkey TACH H The direction of the vertical arrow at the beginning of the message on the upper right of the screen must match the direction of the autostored data being averaged upwards if the RPM Speed values are increasing during the test down wards if they are decreasing otherwise the averaging will not be performed The softkeys TIF and J G are used to change the direction of the arrow in the message If the test values increase up to the upper limit then decrease back down to the lower limit the averaging is performed using data for either the upwards portion or the downwards portion corre sponding to the direction of the arrow at the beginning of the message In this manner a test which involved both direc tions can be divided into two data blocks one for each direc tion In this operation the averaging is performed over a user selected range of RPM or Speed utilizing a user specified increment or step size of RPM or
63. D Le i 1 1 TACH 08 8 5 8 8 z dotted crsr 125 Hz P INITIRL ADC 1 DC 2 ADC 3 BITE The connector pins 2 3 and 4 are connected to three sepa rate 8 bit A D converters for the purpose of reading the DC voltage applied by external devices These could for example be used to read the output of pressure and temperature transducers The input voltage can cover the range O to 5 volts To read the voltage applied to these inputs from the VO Menu press one of the following ADC 1 H ADC 2 J or ADC 3 K This will produce the message ADC Volts X XX on the upper right of the screen where X XX is the voltage level corresponding to the ADC which was selected by the keystroke These are associated vvith the connector pins 5 6 and 7 Each one has two TTL states either set and held Low or set High with the possibility of being set Low by an external device The CPU monitors the states of all three of these pins The state of each is set Low by pressing the following Softkeys Softkey Functions Low 1 A Sets I O Channel 1 Low Low 2 C Sets I O Channel 2 Low Low 3 E Sets I O Channel 3 Low The state of each is set High with the potential of having the state changed by an input signal by pressing the following Softkeys Softkey Functions Hi In 1 B Sets I O Channel 1 High Hi In 2 D Sets I O Channel 2 High Hi In 3 F Sets I O Channel 3 High To display the status of all three of these pins press BITS
64. Feature Classification Class Lines Optional Feature 2900 MANUAL points active If a class line has not already been created the display will be of the default setup as shown in Figure 22 5 The coordinates of a selected point are indicated graphically on the screen by the intersection of a horizontal and a vertical line and numerically on the upper right of the screen by the message point X of Y nn n ANSI filter number center frequency when using digital filters or the message point X of Y nn n center frequency when using FFT filtering X represents the number of the selected point Y represents the total number of points pres ently defined for the line nn n is the amplitude coordinate of point X and the center frequency is the frequency coordinate of point X The two default points will be located horizontally at the two lowest frequency band center frequencies with amplitudes of 80 0 and 90 0 dB for points 1 and 2 respectively The key point I and point J are used to move along the line from point to point Press these two keys and notice how the horizontal and vertical lines move to cross hair the selected point coordinates on the screen and how the ampli tude and frequency coordinates are displayed digitally on the upper right of the screen In this exercise we want to show how to create a class line from the default state To return the status of the class lines to the default st
65. Frequency Hz 1 1 500 2 2 500 3 1 lk 4 2 lk 5 1 2k VSRPM Graphics 2900 MANUAL Pen Number Channel Number Frequency Hz 6 2 2k 7 1 Ak 8 2 4k He may then select to display four curves or traces in each of the four windows by assigning these pens as follows Window 1 Trace Number Pen Number producing Channel Number Frequency Hz 1 1 1 500 2 2 2 500 Window 2 Trace Number Pen Number producing Channel Number Frequency Hz 1 3 1 lk 2 4 2 lk Window 3 Trace Number Pen Number producing Channel Number Frequency Hz 1 1 1 500 2 3 1 lk 3 5 1 2k 4 7 1 Ak Window 4 Trace Number Pen Number producing Channel Number Frequency Hz 1 2 2 500 2 4 2 lk 3 6 2 2k 4 8 2 4k The use of the color display is described in more detail in Chapter 24 In the remainder of this chapter it is assumed that the user is working with the LCD display of the analyzer LCD Display Pen Format LCD Display Pen Format When working with the LCD dis play of the 2900 the user can generate only a single set of up to six different traces at a time Because there is only one set of traces there is no reason to assign a particular pen to more than one trace As a result there really is no justifica tion for selecting pen numbers for each trace which are differ ent than the trace numbers themselves For this reason in the following we shall make it a standard procedure to keep the pen numbers the same as
66. Functions Selecting Trigger Frequency 2900 MANUAL Figure 11 2 Frequency Trigger Menu B3 JRH 00 05 14 38 yz 29 880 Hz 680 0 P 6 66068 a klere qoe eger aa nea reins mea EXPONENTIAL 1 64 Input 1 LINEAR 28Hz 28kHz RESET 05 JAN 90 00 05 00 TRIG w Channel 1 of 1 NORMAL d 6 8 2 20 t 5 53 6 Loc TO ZI Ki 43 Trigger TEST_1 A gt SLOPE SL FE lt MANUAL RE ARM OFF level When the Frequency Trigger Menu is first displayed the mes sage on the upper right of the screen will be of the following form Trigger Criterion Trigger Frequency Trigger Level The trigger Criterion will be gt T or 4 When the fre quency bandwidth is 1 1 or 1 3 octave the band number as well as the center frequency will appear For FFT only the fre quency will appear Selecting the Trigger Criterion The horizontal arrow keys are used to select the trigger fre quency as indicated by the message Trigger on the lower right of the screen The right and left horizontal arrow keys page forward and backward respectively through the range of available frequency values as indicated by the changing value of the trigger frequency displayed on the upper right of the screen When paging through the frequencies one step beyond the highest frequency is Spectrum X meaning that the autostore will trigger based on the level of the overall level Trigger
67. Generator Figure 4 10 Dual tone Generator se 02 17 03 Fstart Fend R se R es Lse Les L1 aF Note DUAL TONE TEST 24 448080 EXPONENTIAL 1 8 Input 1 LINEAR 26Hz 26kHz STOP 36 OCT 94 02 16 01 aa ngaadHz Hopp v Channel 1 of 1 NORMAL d 49 2 Ze 122 TACH 6 6 SPEED 4 6 dotted crsr i tone Auto L FILTER The frequency of the second tone will be greater than the first tone by a fixed number of cycles This is set by pressing AF H The message on the upper right will indicate the presently assigned value of the frequency difference Either 2900 Instrument Setup Via The System Menu Autolevel Control Sine Generator 2900 Instrument Setup Via The System Menu 2900 MANUAL press ENTER to keep the same value or modify the value using the numeric keypad and press ENTER The user selects the relative amplitude of the first tone L1 by pressing L1 G entering a value between O and 1 using the numeric keypad and pressing ENTER The sum of the rela tive amplitudes of the two tones are set equal to one so the relative amplitude of the second tone will be given by the rela tionship L2 1 L1 Setting L1 to 0 5 will result in both tones having equal amplitudes Once setup both tones can be swept in the same manner as a single tone This feature is used with the dual channel Model 2900 to per form calibration of accelerometers and microphones For accelerometer testing the output of the sine generator is use
68. L2 Frequency Value L3 Weighting of Time Buffer AA indicates that anti aliasing filters are active Rectangular Weighting Hanning Weighting Flat Top Weighting Zero Pad Weighting N m 2 Impact Weighting on Channel 1 Rectangu lar on others E Impact Weighting on Channel 1 Exponential Weighting on others The format of the message in this location is a function of the Active Analysis Type Channel X of Y Displayed Data Type where X is the Dis played Channel Number and Y is the Number of Active Chan nels Possible displayed data types are as follows NORMAL LEQ MIN MAX SEL Mx Spec Cross Analysis Displayed Data Type D Channel Indication When the data type is a single channel parameter such as autospectrum the number displayed after the D is the num ber of the displayed channel Possible single channel parameters are as follows Autospectrum Auto Correlation Impulse Response Mag nitude Cepstrum Time Weighted Time When the data type is a cross channel parameter the num ber displayed after the D is the number of the channel which has been crossed with channel 1 the reference channel Possible cross channel parameters are as follows Cross Spectrum Cross Correlation Coherence Transfer Function H1 H2 or H3 Inverse Transfer H1 H2 or H3 1417 2900 MANUAL Location N Amplitude Data corresponding to Cursor Position 1 18 Intensity Analysis Displayed Data Type Possible displ
69. LCD Display Pen Formats uii c ete dc t o ka f ie Det anba s ae mean tk ee e d 17 3 ACCESSING a e 17 4 miele rr 17 4 Ghannel Selection roce dre edge ge ka deco kip cx nece eL sas da 17 4 Frequency Band Gelechon nennen nennen trennen sistens 17 4 Order Selectionts daten nett bs MO Ert Ee A Ehe ken 17 5 RPM Speed Selection cas ean et e Ren tus 17 5 Horizontal Scale Selection eene eene enne ns 17 5 Slope Selection uite ou needed EE 17 5 Incremental Control of the Trace 17 6 Control of Trace SIatis e tie a ata Fe ente DE ua a eee se e TRE 17 7 Suspending Color Monitor Updates 17 7 Pertoriming a Test ene T eate temet ee EAE 17 7 Examination of the Traces ecscccccecesecccceeesseceeeeeeseceeeeesseceeeeeasaeceaeesseceeeeeseseeeeeeenseeeeenenties 17 8 Mano Le 17 8 Storage of Trace Displays aad ik ae ka ka pasan dada ap Ae Edda RENE 17 8 Recall of Trace 15 1 ENANA EAE tenni nennen en nnn nenne 17 8 vsRPM Graphics from byTach Autostored Records 17 9 Standard Mode CET 17 9 Modification of the Graphic Parameters a 17 9 Storage and Recall of Trace Records 17 10 Intensity Mode baa un uu D S SSS um R RAY Y YR aaa Yarar ayani 17 10 Post process Order Tracking pe Et n BAR baba 17 11 Peak Hunt Proced re i eere eed ne e Mr Ts rcu c ri Me e 17
70. Menu by pressing T TRIG M Figure 11 1 Time Trigger Menu 12 KE 16 44 41 A SPECT TIME note d SPL aa aa W W W W W W W W W W W W W w n n W w W n n n n w a nn n n a n n n n a n a n n n a n n nn n nn COUNT s I NGLE 8 Input 1 LINEAR 20 2 20 2 RESET 12 JAN 93 16 44 39 70 Mehr w w Ha a w a u w a W a W A U W A A W W A W W W 95 n FREQ abi VES vAuto Spectrum b 1 2 14 0 58 w w w w a n w W a n w n W a n a W n n n n n n n Wa n a w n n n n n n n n n n n n n na n n nn Base Freauenc y aa 7171515 00 t td 66 Ch2 68 LOC TACH 8 8 SPEED 4 6 SO eee b Popp KAES 220000 2000 Z A dotted crsr INITIAL RLTERN BUWNORM P lt oR SLOPE LEVEL DELAY 2 DELAY OFF The first two trigger criteria are the level and slope of the sig nal as indicated by the expression xx displayed on the right of the screen The trigger level is in percent of full scale and the slope is indicated by the positive or negative direction of the arrow Trigger Functions To increase or decrease the level press LEVEL M The mes sage trig level will appear at the lower right indicating that the horizontal arrow keys are to be used in setting the level As these keys are rotated the change in level can be seen on the display 11 1 2900 MANUAL Trigger Slope Trigger Delay The slope is toggled between positive and negative by press ing SLOPE L 11 2 When t
71. OI 16 92 snuey Aayyos a YONAA t SUOT IPUOD OLIO 10J a ATAO t PEOH AO qoy 1od oq 66 92 4un l4 D SATA t sosso1d Koy g TIV t suonipuoo L 10 oAnoy 11 92 enar NUN O I WOU nu yq Jadaag V INON t I d g ON 86 92 snu W Aayyos 92 FTANDII d I e991 I Ld taa JOSIND Sut onuoo Joye JOI e291 o pokejdsip Apuoesoud skoy pejuozuoy u3isseoy p1009Y oi19 od H dH lalwns q D XVW9 g HAV H Xoo qelep p ffe r ogeloAV Urnuirxe A SUISeIoAV 1921 m Se oues Wold old Wold ay dm s 0067 daas woad ULIOJ 10g NUON VOOY WOU WX 5591 nU VN IIe234I piepure1s V IIT t kejdsiaq rez1o3eM PAS 66 92 snu W Aayyos EU 96 92 3 1 W XX9N V N 91q V I arataa t t t 10s1no 8011021 02 197e e281 o SA Y MOJJE 9UOZIIOU uBisseoY 444 NOO1Q818p paea 1581 v SE oures n dm s 0067 doo DU TN 29 WO xq oouonbog oouonbog oSv101g UI jXou UI SnOIA2Jq PT05971 II p1009Y VIOY A HINLLSA lal was qa D XVW a t t t p y s uoneuuns UInurxepA JWI SNS IOA 2014 2019 ur eje JUISIIJ UIoj19q PIWAN a10 80 N8 MIM TIVITY 5524 NUSN I IE9 2 o10 SONV pokejdsip Apuosoid
72. PHONS 74 6 G G SPEED 4 6 solid crsr Lac RMS 1CH To select the use of a remote control described in the follow ing section press RS1 A To select the use of a sound intensity probe press one of the following based on the Model number of the probe being used INT2250 B INT2251 C or INT2260 D Remote Control using Model 3200RC Remote Control Module Figure 4 18 3200RC Remote Control B moner eier ae START CANCEL STOP PAUSE Setup The Model 3200RC Remote Control Module shown in Figure 4 18 3200RC Remote Control communicates with the Model 2900 through a cable to the RS 232 interface This module permits the user to perform the following activities 1 Run the analyzer 2 Stop the analyzer 3 Stop the analyzer and store the data block 4 Examine the names labels of the seven user defined ana lyzer setups 5 Reboot the analyzer to one of the seven user defined set ups The module is powered by an internal 9 volt battery However the RS 232 circuit board can be modified to power the remote control unit through the RS 232 cable If the remote control unit is ordered at the same time as the analyzer this modification will already have been made upon delivery Connect the 3200RC to the 2900 serial port RS 232 inter face From the I O Menu press 3200RC A to activate the communication link Press the 3200RC START key to turn on the module The 3200RC will display the
73. PHONS 78 1 TRCH 8 8 SPEED 4 6 dotted crsr 18 4925 70 50 530 LOC 18 56 Hz TEST 1 MINTEN Each of the fourteen labeled softkeys refers to a particular parameter associated with the measurement and stored as part of the data block whose status or value may be pre sented as a text string on the custom printout The specific parameters are as follows Softkeys Softkey Functions TIME A Current Time NOTE B Note stored with data block VERS C Version Number of Analyzer Firmware RECALL D If data has been recalled from memory identi fies the filename data type and record num ber UNITS E Units of displayed parameter R TIME F Run Time of the measurement DETCTR G Detector and Averaging Time INPUT H Input setting analog filters S TIME I Spectrum Time of measurement 2900 Printing Data Screen Displays and Tables User Text Strings 2900 MANUAL Softkeys Softkey Functions FILTER J Filter Type CHANNL K Channel Number TYPE L Data Type TACH M Tach and Speed values INTEN N Job Part and Area Names Upon pressing any of these keys and responding to the prompt by pressing YES A subsequent messages will prompt you to input the origin character height and orienta tion of the printout of that text string The text string can be oriented to print horizontally from left to right by selecting LEFT A or vertically from lower to upper by selecting UP C To turn OFF the
74. Print Menu The Model 2900 can print any displayed data directly to a Hewlett Packard compatible laser printer or an Epson Com patible printer equipped with Graphics capability via the Centronics parallel interface A tabular output of the data displayed on the screen can also be obtained Initializing the Printer The Print Menu shown in Figure 23 1 Print Menu is accessed by pressing the hardkey PRINT Figure 23 1 Print Menu Bl BER 12 53 41 screen table all List video LOGO TYPE SPL 2 5888 2022000000 00 EXPONENTIAL 1 8 ual LINEAR 268Hz 28kHz STOP 01 APR 97 12 53 26 eere 7000000211 FILTER 34 2 5 kHz 125 Channel 1 of 2 NORMAL d o _ 72 7 DIFF PHONS 83 3 TACH 8 8 SPEED 8 8 H d Hz a GER dotted crsr INT user SETUPS EDIT eject init Creating the Logo If the printer is connected and turned on when the 2900 is booted up the printer initialization is performed as part of the boot up procedure In cases where the initialization was not performed at that time such as when the printer has been connected after boot up press init O 2900 Printing Data Screen Displays and Tables A user defined logo or heading is printed at the top of each printout from the Model 2900 To create the logo press LOGO F and in response to the message Logo on the upper right of the screen type in the desired logo using the alphanumeric keypad in the same manner as used to create notes f
75. RPM nor the Speed values exceeds the HIGH limit of their Spans before the second phase deceleration coastdown is begun the sequence will not be stopped automatically and it will be nec essary to press the R S key to stop the autostore sequence Autostore by Tach Tach Speed Calibration Autostore by Tach 2900 MANUAL The following keys are used to set the Span and Interval val ues and the Slope setting Softkeys Softkey Functions t span B RPM Span for which data storage based on Tach value will occur format is LOW HIGH t Amin C Minimum Tach interval for which data storage will occur t Amax D Maximum Tach interval for which data storage will occur s span J Speed Span for which data storage based on Speed value will occur format is LOW HIGH s Amin K Minimum Speed interval for which data stor age will occur s Amax L Maximum Speed interval for which data stor age will occur SLOPE G Repeatedly pressing this key will change the sign associated with increments for the storage of data between and as indicated on the upper right of the screen There is another manner in which the scaling of the Tach and Speed signals can be performed dynamically based on the state of an operating vehicle or machine From the Tachset Menu access the Tach Speed Calibration Menu shown in Figure 16 3 Tach Speed Calibration Menu by pressing X cal F Figure 16 3 Tach Speed Calibration Menu SP
76. Tacho Speed Averaging Menus shown in Figure 16 4 Tach Speed Linear Averaging Menu and Figure 16 5 Tach Speed Exponential Averaging Menu from the Tachset Menu by pressing X AVE H Figure 16 4 Tach Speed Linear Averaging Menu Select Linear Dua Time SPL 6 6008 EXPONENTIAL 178 PRE Hz HP STOP 02 JAN 96 5 11 28 FILTER 829 800 Hz 125 v Channel 1 of 2 NORMAL A 56 4 PHONS 78 8 TRCH 5184 6 SPEED 8 8 dotted crsr INITIRL 6 G3sec 0 06sec G 12sec G 25sec 505 1 0 sec 2 085 Autostore by Tach Enabling Autostore byTach 2900 MANUAL Figure 16 5 Tach Speed Exponential Averaging Menu a2 ign 23 41 86 1 64 1 32 1716 1 8 1 4 1 2 1 2 SPL 6 6008 70 Mehr W W W hh W W W W n n n W hh hh w w w n n hh n n n n n n n n n n n n t ttn EXPONENTIAL 178 Input 1 LINEAR 20 2 20 RESET 62 JAN 98 23 41 06 Sa W ON W W W W W W W W W W W W W W W W W n W W W n W W W w n n w w n n n n w n n n n n n n n n n nn FREG 0888 2 Hopp v Channel 1 of 1 NORMAL d 35 1 E 7 9 66 0008 UU0H T1 20000 0000 Z A dotted crsr TEST 1 R 4 8 16 32 64 128 256 512 Figure 16 4 represents the Linear Averaging Mode and Figure 16 5 represents the Exponential Averaging Mode The mes sage at the upper right of the screen will indicate which of this is being displayed Pressing the key A which may be labeled Linear or EXPO will switch the display between the two The message on the upper right of the screen wil
77. Unit Names lowed by a flashing cursor prompts the user to type a setup name of up to 7 characters and press EXIT The newly cre ated label will now appear above the designated softkey Unless this label is changed or the set of user defined labels is reset it will remain active in the Units Menu The softkeys dB uV I and SPL J cannot be changed If the key R UNITS D is pressed the labels for all the user definable softkeys will be reset to UNDEFINED The unit names to be assigned to the individual channels are selected from among the choices of unit names represented by the softkeys along the bottom of the screen Select a par ticular channel by pressing the corresponding numerical key on the right of the front panel The displayed channel number will be indicated on the right side of the display sixth line down With only one channel active Channel 1 is automati cally selected Press the softkey having the desired units name as its label to assign that name to the selected channel Note that the name now assigned to that channel is displayed on the first line of the upper right of the display For dual channel applications if the channels are to have dif ferent units select the channels one at a time assigning a name to each as described above When finished use the numerical keys to page through the channels and verify that the proper name appears on the display for each channel If both channels are to have the same un
78. W W W W W W W W n W W W W W W W w w n w W w n n n w n n n nn non n n n nn FREG 0088 2 HSAA v Channel 1 of 1 NORMAL d 35 1 9 b u un ZUDM 1 19000 opp Z A dotted crsr TEST_1 A The message Select UPPER BAND EDGE will appear on the upper right of the display Make a selection by pressing one of the following softkeys 20kHz A 10kHz B BkHz C 2 5kHz D When performing a baseband analysis if the selected full scale frequency is 10 kHz using two channels the analysis will not be performed in real time When the FFT analysis is first selected the instrument is setup to perform a baseband analysis zoom 1 which means that the analysis range will extend from DC 0 Hz to the selected full scale frequency The frequency resolution of each filter will be the upper frequency divided by the number of lines used for the FFT analysis For example using 800 lines and a full scale of 20 kHz the frequency resolution will be 25 Hz 20 000 800 lines As the cursor is moved across the spectrum display from line to line the frequency will change in steps of 25 Hz If the full scale frequency is reduced to 5 kHz the frequency resolution will be increased that is the frequency increments from band to band will be decreased to 6 25 Hz 5000 800 Thus reducing the full scale frequency will increase the resolution However unless the spectral components of interest are at low frequencies the range of choices for
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80. a a u A A MA A W A MN A tt par i v Channel 1 of 1 NORMAL dz 55 4 63 8 anl 85 V ko PHONS 74 8 TACH 68 8 SPEED 4 6 dotted crsr SH Hz INITIAL DELETE At the same time one of the stored data records correspond ing to the 2900 display setup will be recalled Note Presentation The message RECALL XXXX N on the upper right of the screen indicates that the Nth record of the type XXX has been recalled from the active memory file and is being displayed In many cases the first record of that type will be recalled but if some recent operations have been made on one of the records for example if a record had recently been stored or recalled then that record number will be recalled The instrument setup corresponding to that recalled record will also be dis played Changing Displayed Record Number The note stored along with the record will also be displayed on the upper right of the display in the format Note XXXXXXXXX Only 19 characters can be displayed in this display format If the note field is larger than 19 charac ters press note G to display the entire note Press EXIT to return to the data display Cursor Utilization After a recall operation the message recall data on the lower right of the display indicates that the horizontal arrow keys now control the recall of records Pressing them will page sequentially through the records of the same type as
81. a spectrum the numerical classification of the spectrum will represent the maximum number of lines in that family which have been crossed at least three times As can be seen in the table the classifica tion in this example is 4 because four lines have been crossed 22 11 2900 MANUAL at a minimum of three frequencies and the fifth line has only been crossed at two frequencies Had the qualification value been zero this spectrum would have been classified as 6 because all six lines have been crossed at one frequency Storage of Class Lines to Setup Menu Softkeys Each set of four user defined and named class lines can be stored to non volatile memory from the Class Lines Setup Menu shown in Figure 22 11 Class Lines Setup Menu which is accessed from the Class Lines Menu by pressing SETUPS J Figure 22 11 Class Lines Setup Menu as JOM 19 16 32 NAME RESET STORE DEFRULT i SPL 8 8000 ang Oe EXPONENTIAL 178 y Ineut 1 LINEAR iHz 20kHz RESET ez JAN 94 17 29 16 T Se ss e F I LT TER 1 86 Hz S w Channel 1 of 1 NORMAL de 25 8 49 5 5a A 6 0 a a a a 6 a 6 a A G a a G N A A a A a a a a a a a a a a a a a a a a a e s ano nosen PHONS 53 6 LOC TACH 8 8 SPEED 8 8 50 Hz 125 Hz 20 GkHz dotted crsr OCTAVE SET 1 SET 2 SET 3 undef undef undef undef undef A different set of class lines can be stored under each of the eight softkeys at the bottom of the screen When first deliv ered each of thes
82. a transient sig nal select Linear Repeat Beginning with the trigger or the pressing of the R S key the analyzer will measure and dis play a series of linearly averaged spectra Since the detector is reset at the end of each averaging period each spectrum will represent the frequency analysis of time data occurring only during the time period when that average was being cal culated To store these spectra put the unit in the Autostore mode and use a data storage interval equal to the value of the linear averaging time Exponential averaging is based on the averaging characteris tics of analog RC detector circuits If a step input is applied to such a detector the output value rises in an exponential manner until the output level finally reaches that of the input level The time constant of such a detector is defined as the time required for the output level to reach 9996 of the input level 5 7 2900 MANUAL 5 8 With a digital analyzer a time constant is selected and a lin early averaged value is calculated for each time interval equal to the time constant The exponentially averaged value pro duced at any instant is calculated as a weighted sum of the previously measured linear values with the most recent val ues contributing the most weight to the sum As the analysis proceeds the result is a running average which is dominated by the most recent value but which is also smoothed out by the contributions of the preceding v
83. acceleration and continue the autostorage sequence In most tests where the byTach autostore is to be used there is a particular range of RPM or Speed over which the data is of interest In the Model 2900 this is defined as the span of interest and since there are two possible independent parameters RPM and Speed the user can define both an RPM Span and a Speed Span Each Span will be defined by a LOW and a HIGH value of RPM or Speed 16 5 2900 MANUAL Influence of Slope on Test Procedure 16 6 The positive slope condition SLOPE is appropriate for a vehicle acceleration or a machine runup In this case it is necessary that at the moment of initiation of the test sequence either the RPM or the Speed value or both be below the LOW value of the corresponding Span range As the test proceeds and the RPM and Speed values increase autostorage will be initiated when either of these variables increases sufficiently to exceed the LOW value thus falling within the Span Autostorage will then continue at positive incremental values RPM and Speed corresponding to t Amin and s Amin There will be no storage for negative incremental values of RPM or Speed When either RPM or Speed have increased enough to exceed the HIGH limit of the correspond ing Span the autostore sequence is stopped automatically The negative slope condition SLOPE is appropriate for a vehicle deceleration or a machine coast down In that case the s
84. accurate while others may be inac curate due to the overload While examining the individual spectra during the recall operation the same message OVERLOAD will appear along with each spectrum which corresponded to an overload condition during the data acqui sition Display of Amplitude vs Time To utilize the cursor for readout of the amplitude and fre quency values of the displayed spectrum press the hardkey CURSOR which will assign the horizontal arrow keys to con trol the cursor which was last active dotted or solid A sec ond press of that key will bring up the Cursor Menu for selection of cursor type Press recall P to reassign the horizontal arrow keys to the role of paging through the spectra within the autostore record Autostore by Time When a series of spectra have been autostored as a function of time it is possible to select any single frequency band and display the level in that band as a function of time exactly as if the original signal had been passed through a band pass filter and then displayed upon a level recorder To do this recall the desired autostore record move the active cursor to the desired frequency band and press vsTIME D The amplitude vs time curve will appear on the display as shown in Figure 15 4 By Time Display Figure 15 4 By Time Display si MAR 18 38 54 RT68 REPLACE AVERAGE Auto RE Duto DU note Note SPL W W W n W w a w n n W a w n w n n c c EXPONENTI
85. along the bottom of the display represent the eight possible instrument setups which can be defined at one time The one represented by the key DEFAULT I is a default setup delivered from the factory and it cannot be changed by the user The remaining ones will originally be labeled undef for undefined The user can create a particular instrument setup and store it under a particular softkey labeled with an appropriate name 12 1 2900 MANUAL Labeling and Assigning Softkeys Changing 2900 Setup from Softkeys When the 2900 has been configured as desired first assign a name or label to the softkey to be used for the setup by press ing name B then the choice of softkeys J to P In response to the prompt on the upper right of the display type in the desired name using the keypad and press EXIT If there is already a setup name displayed which is to be changed press SHIFT followed by CLEAR before typing in the new name The name will now appear as the softkey label To assign the present instrument setup to the softkey press STORE E The message PUSH SETUP TO STORE on the upper right of the screen will prompt the user to press the Setup softkey with the appropriate label for this setup Reset of User defined Setups Normally the 2900 will boot up to its default setup as defined at the factory during production To reconfigure the 2900 to one of the user defined setups created as described above access the Setup M
86. and Ln Calculations Turning the Statistics Analysis On and Off 3200 MANUAL OPT 42 The duration of the autoranging operation will depend upon both the averaging time and the highpass filter selection The fastest response results from the use of the lowest averaging time and the highest value of highpass filter When the application is such that significant noise events of short duration are of major interest and the general back ground levels are very low it is best that autoranging not be utilized The instrument range should be set to handle the events without overload In such a case much of the back ground noise may fall below the lower limit of the measure ment as indicated by significant values of the displayed parameter 00UNDER Repeated presses of the softkey ON OFF A will toggle the state of the statistics mode between on and off If the statis tics mode is off pressing this key will result in the message Statistics mode is ON on the upper right of the screen If the statistics mode is on at the time this key is pressed the mes sage on the upper right of the screen will be ARE YOU SURE to remind the user that the data presently in the Statistics Table will be lost if the statistics mode is turned off To proceed press YES A To abort the turn off procedure and leave the statistics mode on press NO C Selecting the Ln Values for Calculation and Display Statistics and Ln Calculations T
87. and rejection continue until the number of specified spectra to be averaged is reached When the signal is periodic such as a sinusoid square or triangular wave the amplitude as a function of frequency is well defined The detector will provide an accurate measure ment using an averaging time on the order of one period 1 frequency so lengthy averaging times are not required Near periodic signals are observed in rotating machinery at the first 3 to 5 harmonics of the shaft rotation speed and in gearboxes at the tooth mesh frequencies and their harmon ics Linear Repeat Time Averaging Exponential Time Averaging Selection of Averaging Parameters When the spectral characteristics of a signal are changing with time we face a more complex situation Typically one would wish to measure and observe a series of spectra taken at regular time intervals chosen sufficiently small that the time varying behavior of the spectra is clear This implies that the averaging time must be no larger than the time interval which represents a significant change in the spectral charac teristics Conflicting with this is the requirement that the averaging time be sufficiently long that a statistically accu rate result is obtained Because it is not always possible to satisfy both requirements a certain amount of experimenta tion with averaging times may be required to define the signal properly To utilize linear averaging for the analysis of
88. as indicated by the message Channel X of 2 on the right of the screen 6th line down X denotes the channel number whose spec trum is being displayed which is selected using the CH1 or CH2 hardkeys To calculate and display the average of these two spectra press AVERAGE D which will produce the mes sage Channel A of 2 on the right side of the screen 6th line down Repeated presses of AVERAGE D will toggle between the default and the average display modes When the instrument is in the Standard Analysis Mode per forming FFT frequency analysis the softkeys A and B invoke single and double integration respectively as shown in Figure 10 2 When either the single or double integration have been selected this will be indicated on the right side of the screen first line down Each integration is performed by dividing the level in each frequency band by 2zf This means that the levels for all bands at frequencies greater than 1 Hz will be reduced in value As a result many of the spectrum levels previously visible when the non integrated spectrum was being displayed may disappear below the minimum axis of the display following integration Use the Vertical Offset function in the Shift Menu to bring the displayed levels back up to within the range of levels being displayed Single and Double Integration of FFT spectra can also be invoked from the Units Menu as described in Chapter 9 However due to limitations related to
89. autostorage sequence will be automati cally stopped Once the autostorage has begun however the user can stop the sequence at any time by pressing R S And in cases where the sequence has begun but the parameters 16 9 2900 MANUAL do not satisfy the requirements for automatic termination of the autostorage sequence the manual stop will be required Recall of Data Autostored byTach Pressing the hardkey RECALL while the 2900 is in the autostore byTach mode will recall one of the By Tach type records from the active memory file whose name is listed on the lower left of the screen The message RECALL By Tach N on the upper right of the screen will indicate that the Nth record of the type By Tach has been recalled In most cases this will be the record number which was last stored or recalled To determine how many By Tach records have been stored in a particular record and to examine their note fields use the Files Menu If the desired record is in another memory file it will be nec essary to access the Files Menu change the active memory file and exit before performing the recall operation Upon pressing the RECALL key the Recall Menu shown in Figure 16 6 Autostore Recall Menu will be displayed Figure 16 6 Autostore Recall Menu 05 JAN 00 03 05 W Fall B RUE KEEP RECALL Normal 3 Note 8 CYLINDER SPL FACOMENTIAL w Channel 1 of 1 NORMAL d A E 78 4 5 76 7 recall data recall and
90. be defined as the reference spectrum for both channels This makes it very easy to display the difference between two spec tra measured simultaneously in the dual channel mode By pressing SetREF O the spectrum corresponding to channel 1 will be defined as the reference spectrum for chan nel 1 and the spectrum corresponding to channel 2 will be defined as the reference spectrum for channel 2 Control of Vertical Display All spectra are measured and stored in their absolute format the versus reference display mode is purely a display func tion Return to the normal spectral display format from the Shift Menu by pressing vsREF P a second time Repeated presses of vsREF P will toggle the vsREF display mode on and off 19 4 There are four different vertical display formats possible with the Model 2900 The default format active upon turning on the instrument unless the boot setup has been modified is log log meaning that the numbers along the vertical scale gradations and the cursor readout are in logarithmic dB units and the scaling format of the screen is logarithmic as well This is the format used most often for acoustic measure ments To modify the vertical scaling access the Y Axis Menu shown in Figure 19 4 by pressing the key sequence SHIFT Y AXIS X Control of Display Formats Cross Channel Normalization and Use of Key Macros 2900 MANUAL Figure 19 5 Y Axis Menu Hote TRPPING 0 8028 sa
91. cursor beneath the first character of the field prompts the user to type in a label name using the alphanumeric keypad and press EXIT 22 4 Press EDIT I and reply to the message Select Class to edit on the upper right of the screen by pressing one of the soft keys A B C or D The screen will look like Figure 22 5 Default Editing Menu unless a line or family of lines have been created previously Figure 22 5 Default Editing Menu 29 DEC 16 47 66 max REPEAT aUIDTH aualify Davee cee ri MS Deis Point 1 of 2 88 8 1 1 88 Hz 1 SPL a 000G ang TIPP i o PU I E e s EXPONENTIAL 1 64 Dual LINEAR 26Hz 16kHz 1 RESET 29 DEC 93 16 45 12 T I D c i west t n FILTER 32 1 680kHz LAS 1 v Channel 1 of 2 NORMAL 1 dz 25 A Sal OO OO OO OO OO OO OO bee PHONS 86 3 Le TACH 8 8 5 8 8 2 2 2 fresuencs INITIRL roint Point add rnt del rnt dotted frea Since we are describing the creation of a single class line if there are a family of curves displayed upon accessing the Edit Menu press REPEAT B use the numeric keypad to type 00 into the field on the upper right of the screen and press EXIT which will collapse the family of lines to a single base line The generation of a single class line is essentially the creation of a connect the dots sequence on the screen using up to a maximum of twenty points There are always at least two Classification Class Lines Optional
92. dB The statistics mode must be off to modify the mea surement range To observe the selected range or to modify it press dB SPAN C and note that the presently selected range is indicated on the lower right side of the screen in the form tbl XX YYY meaning that the statistics table is con figured to handle sampled level values ranging from XX up to YYY Note that XX may have negative values While this mes sage is displayed use the horizontal arrow keys to move this 120 dB range to encompass the desired range of input values for the measurement to be made 18 2 The autoranging function is meant to deal with situations where the general sound level increases or decreases signifi cantly yet slowly over time such as may occur during 24 hour measurements where the night time levels are substan tially lower than the day time levels During the short time period typically several seconds when the autoranging pro cess is taking place data will not be available for updating of the statistical table so there will be a loss of information As a result the autoranging function may not be able to deal effectively with short term events which initiate an autorang ing operation For example should the instrument gain be set such that a vehicle passby produces an overload there fore initiating an autorange operation data corresponding to the passby would be lost during the overload and the autor anging operation Statistics
93. data reset as shown in Figure 3 10 Impulse Display The averaging time of the Impulse detector is 35 milliseconds but it is also characterized by a very slow 3 dB second decay rate For the ver sions producing the Taktmaximal 3 and 5 val ues the weighting is Fast even though the display of these is accessed by pressing the IMPULSE K softkey Figure 3 10 Impulse Display 25 RPR 15 55 56 NORMAL Lea DISPLAY note DETECTR SEL SPL 25 8125 EXPONENTIAL 1 8 Input 1 LINEAR A zs IMPULSE e w L WON KI Min 65 5 Max 79 7 SLM DATA dotted crsr FRST IMPULSE LEQ Weight SETUP FILES AUTOSTR 3 15 2900 MANUAL Frequency Analysis Display 3 16 LEG L Produces a display of the Leq integrated level along with the SEL integrated level and the maximum Peak level which has occurred since the last data reset as shown in Figure 3 11 Leq Display The Peak detector has a rise time of 50 microseconds Figure 3 11 Leq Display a2 ign 23 29 31 NORMRL Lea MIN MAX SEL DISPLAY note DETECTR SPL 12 8575 T af a n a W W W W n W W W W w n W W W W w n n n W a n n n n w n n n n n n a n n n n mtn EXPONENTIAL 178 Input 1 LINEAR 28Hz 28kHz i STOP 02 JAN 90 23 29 25 58 E MAue 0000000000 0010 FILTER 8 6 30 Hz 125 Channel 1 of 1 NORMAL d 6 4 Ze 45 8 A WEIGHT Loc 5 2 18 d BE Sel 64 0 Peak 89 2 2 SLM DRTR dotted crsr TEST_1 R SLOW FAST IMPULSE
94. e poke atiende dece ud Ree pee ere 21 21 N lse Rating Kee 21 22 The RC Noise Rating Procedure sse nennen 21 22 Chapter 22 Classification Class Lines Optional Feature 22 1 General Explanation of the Concept 22 1 Accessing the Class llnes nennen enne sn nnne nnn senes 22 3 Labeling the Class Lines nennen nnne nint rennes nnns enn 22 4 Greating a Single Class Lie uuu iie teer o rite an w ok ki ra a ek P boc i eebe 22 4 Assigning Max or Min Mode nennen nene eee r reak nn en nnns nennen 22 7 Creating Multiple Class Lines eee nennen nnne nennen 22 8 Turning On a Class Line n e nia C seen enne nnne nnne nnne nent 22 8 Assigning Class Lines to an Input Channel nn 22 8 Automatic Judgement of Spectra all channels Using a Softkey 22 9 Manual Judgement of a Displayed Spectrum using a Softkey 22 10 Automatic Judgement Based on Stop State of Analvzer e l ii Lll 22 11 Classifications Requiring Line Crossings at Multiple Frequencies 22 11 Storage of Class Lines to Setup Menu 5 5 22 12 Recalling a Set of Class Lines from Setup Menu Goftkeys 22 12 Storing Class Lines Stored under Setup Menu Softkeys to Non volatile Memory 22 13 Recalling Class Lines from Non volatile Memory to the Class Lines Se
95. either the channel 1 spectrum on the left half of the display or the channel 2 spectrum on the right half of the display This will also be indicated by the message Channel 1 of 2 or Channel 2 of 2 on the right of the display 6th line down 6 2 In the dual channel mode the user can also select to view the average of the spectra of the two channels The average is activated from the Display Menu accessed from the Main Menu by pressing DISPLAY F From the Display Menu repeated presses of the softkey AVERAGE D will toggle the average mode between ON and OFF When the averge mode is ON the message on the right of the screen 6th line down will be Channel A of 2 If the dual display mode is active at the time the average spectrum will appear only on the left half of the display Thus repeated presses of the AVERAGE D key will shift the left half of the display between a representation of the vector sum and the spectrum for channel 1 The right half will continue to display the spec trum for channel 2 Analysis Menus Selection Of Measurement And Display Parameters Selection of Display Parameter 2900 MANUAL Max Spectrum Display Select the particular spectrum type to be displayed by press ing one of the following Softkeys Softkey Functions NORMAL A Normal displays the averaged spectrum as selected from the Averaging Menu Leq B Leq is a parameter generally used for the anal ysis of time varying acoustic
96. executing 19 13 recalling 19 14 resetting 19 13 Macros storing 19 14 Manual control 7 1 MAX 6 3 Max Spectrum 6 3 Menus Analyzer 2 1 ASTM Rooms 21 15 25 24 Autostore 15 1 16 2 25 29 Autostore Recall 16 10 Autostore recall 15 8 25 39 Beeper 25 37 Block print 23 3 byTach Block Averaging 16 11 byTime display 15 9 Class Lines 22 4 25 48 Assigning 22 8 Editing 22 4 25 49 Setups 22 12 25 50 A 3 2900 MANUAL Color monitor 24 3 25 15 Cross analysis with FFT Filtering 25 8 Cursor 8 1 Decay curve 21 4 Detector 25 22 Digital Display 10 3 Display 19 3 25 20 25 21 Dual Tone 25 42 External monitor 24 4 FFT 4 4 FFT averaging 5 2 FFT baseband 4 9 25 33 FFT Window 4 7 25 32 FFT zoom 4 10 25 31 Files 13 1 25 17 Files Records 25 18 Filter 4 4 25 11 Frequency trigger 11 5 15 4 25 28 Horizontal scaling 19 8 VO 4 23 25 12 Input 3 2 4 12 25 14 Intensity analysis 6 10 20 3 25 9 IO port 4 27 25 36 ISO Rooms 21 16 25 25 Leq in vsTime display 15 10 Loudness 6 5 Multi Display 19 1 Noise 4 14 25 13 Noise Criteria 21 22 Normalization 19 11 Note 14 1 Octave averaging type 5 1 Peak Hunt 17 12 Pink Noise Bandlimited 4 20 25 44 Pink Noise Wideband 4 20 25 43 Power summation 20 15 Pressure residual intensity display 20 5 Print 23 1 Pulse Generator 4 22 Pulse Noise 25 47 Recall 13 11 15 8 Records 13 5 Resets 4 31 25 19 Rooms 25 23 RSI INT 4 24 RT60 21 5 Setup 12 1 25 1
97. in a room containing no sources of noise due to the presence of impact excitation on the upper side of the floor ceiling assembly such as footsteps on the floor of the space above the room Room Acoustics Measurements 2900 MANUAL There exist clearly established standards for the measure ment and calculation of the parameters associated with both airborne sound transmission loss and impact sound insula tion It is essential that the user be familiar with these stan dards before undertaking such tests since there are many fine details which must be addressed precisely during the measurement phase of the project These details are beyond the scope of this manual The firmware within the Model 2900 is designed to perform the calculations as specified in these standards but the accuracy of the final results is highly dependent upon the proper attention to measurement details There are two different standards organizations whose stan dards are followed by the majority of the acoustic profession als In the United States the standards from the American Society of Testing Materials ASTM are usually appropriate while in the remainder of the world the standards from the International Standards Organization ISO are most com monly followed Many countries have also instituted their own national standards but in most cases these are identical in procedure to the ISO standards As you will see in the fol lowing sections the calculati
98. information needed to assess what actions may be required in order to satisfy the requirements of the standard The parameter F is used to determine the adequacy of mea surement positions referred to in the standard as criterion 2 as follows The number N of probe positions uniformly dis tributed over a chosen measurement surface is regarded as sufficient if N gt The value of N is a function of frequency as well as the degree of precision desired Precision Grade 1 or Engineering Grade 2 To evaluate the adequacy of measurement positions used over a particular Part perform a two level search To determine and display N as a function of frequency corre sponding to the Precision Grade 1 requirement press C1 F4 2 N The result will resemble Figure 20 8 C1 F42 Display Figure 20 8 C1 F4 Display Z her 15 49 39 Power F2 P I F3 HPP F4 FNU note Hote SPERKER TEST oints 4 880808 750 e o o n n n n B ng Sg Mg Sg Sg n ennan LINEAR SINGLE 4 annan Dual LINEAR 20Hz 28kHz RESET 24 FEB 94 16 53 57 san LL NEN eee tn B ng Bg ng ng n ene nen FILTER 20 166 Hz L vvCi F4 2 Grade 1 H d 851 300 9000m JOB _ SPEAKER PART PRONT dotted_crsr Ci F4 2 2 422 F3 F2 SPERKER 52 SSPBRT S gt AREA S gt EDIT To obtain the same information corresponding to the Engi neering Grade 2 requirement press C2 F442 O In either case if the largest value of N obtained across the frequency range used for
99. interval Delta Time and time period End Time are used and if the time delay between the beginning of the analysis and the shutoff of the time gen erator is consistent between tests then the time indices for all M of the Nth spectra will be nearly the same and the aver aged value of the time index assigned to the Nth spectrum in the average record will be meaningful One could imagine however an instance where the interval Delta Time used for spectral storage of the different autostore records were vastly different due to the measurement setups being different yet the number of spectra per record happen to be the same The averaging process would calculate values of the Time Index for each spectrum in the average record as described above but the result would be meaningless Block Maximum of Autostored byTime Records 15 14 The Block Maximum operation can be applied to Autostored byTime records of the same type and bandwidth which have been stored sequentially record numbers in a sequence As explained above the result of the Block Averaging operation is a similar autostore record where the Nth spectrum is the average of all the Nth spectra contained in the separate autostore records being averaged The Block Maximum oper ation is similar except that for each frequency band in the Nth spectrum the amplitude is that of the highest level occurring at the same frequency across all the Nth spectra in the separate autostore recor
100. is being displayed the data records for that type will be recalled instead Press RECALL to recall a Trace Record which will produce the message RECALL vsRPM Trace N on the upper right of the screen to indicate that the Nth record of type vsRPM Trace has been recalled from the active memory file Use the vsRPM Graphics 2900 MANUAL horizontal arrow keys to recall other vsRPM Trace records from the active memory file vsRPM Graphics from byTach Autostored Records Standard Mode Data Modification of the Graphic Parameters The procedure for generating vsRPM Graphics from byTach autostored records is not greatly different from that used for the Real time vsRPM Graphics The first step is to activate the byTach autostore mode press RCL and use the A Prev N and A Next O keys to recall the desired autostore records Then press vsRPM C to access the vsRPM Graphics Menu as shown in Figure 17 1 Upon accessing the vsRPM Graphics Menu the RPM axis will be scaled to the X Span used for the autostored data and a graphic will be generated corresponding to the frequency order values and channel numbers already programmed into the table Use the keys to modify the parameters in the table as desired and press REDRAW M to obtain a new graphic display The user can press the key and use the cursor to read out the levels of the different traces and to hide them as desired The user can now use the cursor to readout the val
101. is set to Leq the Slow response will be used for this When the 2900 is in the Standard Analysis mode it is the broadband sum level calculated by summing the energy in all the frequency bands indicated by the height of the vertical bar on the right of the frequency spectrum display which has the summation symbol beneath it In this case both the broadband level and all measured spectra will have the same analog weighting as selected by the user However if the mea surement had been made using A or C weighting the user could still use the A or C digital display weighting func tions to examine the measured spectra in an unweighted form To display the Max Spectrum when in the frequency analysis mode from the Analysis Menu press Mx Spec L When in the SLM mode this is done by pressing the key sequence DISPLAY F Mx Spec C The message Mx Spec on the right of the screen alongside the displayed channel number indicates that the spectrum being displayed represents the spectrum associated with the highest broadband level since the last data reset Note that this spectrum is not automati cally stored to memory The user must press STORE to store the Mx Spectrum or Spectra The storage and recall of data records is discussed in Chapter 13 For each vehicle passby measurement the user would reset the data buffer by pressing SHIFT RESET begin the mea surement by pressing R S as the vehicle approaches end the measuremen
102. labels on these keys vvill depend upon the selected svveep mode as described in the following four paragraphs When the sweep mode is LOG these keys will be labeled R se C and R es D R for rate Pressing either of these keys will produce a message on the upper right of the screen indicating the present value and prompting the user to make a modification via the numeric keypad if desired and press ENTER The units in the logarithmic sweep mode are decade second When the sweep mode is linear and based on time these keys will be labeled T se C and T es D and the units are sec onds per sweep Press either key to display the present value and to modify the value as described in the preceding para graph 4 17 2900 MANUAL Sine Generator Dual Tone 4 18 When the sweep mode is linear and based on cycle count these keys will be labeled N se C and N es D and the units will be the number of cycles per sweep Press either key to display the present value and to modify the value as described previously When in the linear sweep mode repeatedly pressing the soft key M will toggle between time and count as can be seen by the changing of the label between TIME and COUNT The output level corresponding to the Fstart to Fena portion of the sweep is set using the softkey Lse E and that for the Fend to Fstart portion of the sweep using the softkey Les F Upon first pressing either key the presently as
103. labels to undef press RESET B The message ARE YOU SURE prompt for confirmation of the reset operation Press YES A or NO C as appropriate Recalling a Custom Print Setup from a Softkey Storing Print Setups to Memory To recall or make active a custom print setup which has been stored to a softkey simply press the labeled softkey to which the desired setup has been previously stored The mes sage Overwrite current setup warns that the presently active setup will be lost when the one being recalled is made active Press YES A to proceed with the recall or press NO C to abort the recall operation 23 12 The storage operation described above is to store a single custom print setup to one of the eight softkeys in the Custom Print Setup Menu These setups will remain active in non vol atile memory when the instrument is shut off However it is possible to store the entire set of eight setups with their soft key labels to non volatile memory as well Thus while you can have access of up to eight different setups from the Cus tom Print Setup Menu any number of these sets of eight set ups can be recalled from memory as well replacing the eight which were previously available Press STORE to store the present set of Custom Print Setups to memory The Message STORE Print Setup N on the upper right of the screen indi 2900 Printing Data Screen Displays and Tables Recalling Print Setups from Memo
104. line is now completed Use the point H and gt point J keys to move back and forth through the sequence of points If you press EXIT the class line will disappear because we are out of the editing mode and have not turned them ON If you do exit you can return to editing this line by pressing EDIT I TEST A As points are added deleted and moved they are always numbered sequentially across the screen from left to right In the editing mode when an existing point is accessed it can still be moved vertically and horizontally For small move Classification Class Lines Optional Feature Assigning Max or Min Mode 2900 MANUAL ments you will see that is simply deforms the shape of the line as would be expected However if it is moved horizon tally sufficiently far that it passes one of the other existing points either to the left or the right its point number is shifted accordingly and the point which had been passed now assumes the point number previously associated with the point being moved and the point which was moved will have a point number one lower or higher depending upon whether it has moved to the left or right of the existing point When an existing point is deleted all the numbers of the points in sequence to the right of that point are decreased by one and when a point is added within a sequence of existing points all the numbers of the points in sequence to the right will be increased by one The be
105. lines the time weighting window and the full scale frequency 2900 Instrument Setup Via The System Menu Selection of Number of Lines Selection of Time Weighting Window 2900 Instrument Setup Via The System Menu 2900 MANUAL Select the FFT analysis mode and the number of lines by pressing one of the following softkeys Lines Softkeys 100 line I 200 line J 400 line K 800 line L The last four characters in the fifth row down on the right side of the display will indicate the state of the FFT filter setup H8AA for example The first character indicates the type of time weighting window which is active R H F Z I or E as explained in the following section The second character indicates the multiple of 100 lines which has been selected 1 2 4 or 8 The characters AA appearing at the end of the field indicate that analog anti aliasing filters are present before the A D converter in the analog portion of the instru ment Because of the large number of parameters calculated in the Standard Analysis configurations Normal Max Min Leq etc the 800 line resolution cannot be used in the dual channel Standard Analysis STAND 2 mode There is no restriction for the single Standard Cross or Intensity modes If the analyzer had been set to FFT analysis earlier in the same measurement session the time weighting window will be the same as set at that time Otherwise it will be as set by the internal software when
106. may be connected directly to mains The advantage of using this connector is that the power to the monitor will be switched on when the 2900 is booted up 24 2 Use of External Color Monitor for Display and Instrument Control 2900 MANUAL Activating the External Monitor The hardware module and the external monitor should be switched on when the 2900 is turned on and booted up If the monitor is connected later a reboot will be necessary After the bootup procedure is completed press SYSTEM and then COLOR M to access the Color Monitor Menu shown in Fig ure 24 3 Color Monitor Menu Figure 24 3 Color Monitor Menu 92 JON 86 25 25 OFF 6480x358 640x480 800x600 SPL 6 6008 166 d seas Ses aie a CODEC EXPONENTIAL 1 64 H PREAMP LINEAR 16 26kHz RESET 02 JAN 90 66 22 41 sa kk EE FREQ 456 aaaaHz HSAA v Channel 1 of 2 NORMAL H d 4 6 E 27 3 TERR LOC e TRCH 8 8 SPEED 6 8 00 2000 ZUDM 1 585 5008 Z A noise 8 2 TEST 1 SINGLE DUAL QUAD LCD Select the proper screen resolution by pressing one the fol lowing e 640 X 350 B For EGA Monitors 640 X 480 C For VGA and Super VGA Monitors 800 X 600 D For Super VGA Monitors When using a Super VGA monitor the 800 X 600 mode will give the finest reproduction of the alphanumeric characters on the screen However the time response of the display will be slightly slower which may be noticeable when using FFT analysis with a high number of lines The vertical scan
107. message L D RC Terminal System Ready If the cable is connected and work ing properly the 2900 will display the message 3200RC is on on the upper right of the screen and then the 3200RC will display the message Communications with 2900 OK If instead the message L D RC Terminal System Ready 4 24 2900 Instrument Setup Via The System Menu Operation Communication with User defined Setups 2900 Instrument Setup Via The System Menu 2900 MANUAL remains on the module there is either a problem with the cable or the user has not set the 2900 for the 3200RC func tion The following keys on the 3200RC module are used for remote operation of the 2900 3200RC Key START STOP CANCEL PAUSE Function Places the 2900 in the RUN mode and dis plays the message START on the 3200RC If the last command from the 3200RC had been STOP or CANCEL the data buffer will be reset before the analysis begins If the last command from the 3200RC had been PAUSE the data buffer is not reset before the analysis begins Places the 2900 in the STOP mode and stores the data block The 3200RC will display the message STOP STORED n where n is the record number into which the data block has been stored The next press of START will reset the data buffer before starting the analy sis Places the 2900 in the STOP mode without storing a data block The 3200RC will display the message CANCEL The next press
108. message AVERAGE 0001 0002 Use the 15 13 2900 MANUAL numeric keys and the horizontal arrow keys to edit the two numeric fields until they represent the range of record num bers of the autostore records which are to be averaged together The number of blocks which can be averaged in a single operation is limited to twenty Upon pressing EXIT a single averaged autostore record will be created and stored into the next available autostore record number As with non autostored spectra it is necessary that the filter type and bandwidth and highpass and lowpass filters used for the autostored measurements be the same In addition it is necessary that the number of spectra in each record be the same The average is a spectrum by spectrum average meaning that if there are M autostore records being averaged the Nth frequency spectrum in the averaged record repre sents the energy average of the M different Nth spectra one per record Each spectrum in an autostore byTime record has associated with it a time index When averaging is performed the M val ues of time associated with the Nth spectrum in each record are averaged together to produce an averaged value to assign to the Nth spectrum in the averaged record The user is cau tioned to think carefully when performing averaging of autostored blocks in order to understand just what the result may mean physically In the case of sound decay measure ments where the same values of time
109. n n F I LTER 1 4 2 LAJ Channel 1 of 2 NORMAL d a 34 7 5a d Ee DIFF PHONS 52 5 REM TACH 6 6 SPEED 4 68 25 0 Hz 500 Hz IG BkHz dotted crsr ROOMSTST ASTM 150 SET SOURCE RECEIVE BRCK GD CLR BG Input values of the Test Partition Surface Area m and the Receiving Room Volume m by pressing surface D and volume E respectively typing in the value via the numeric keypad and pressing EXIT Recall the space averaged Source Room spectrum and press the key sequence SET I SOURCE M to define it as such for the calculation Similarly recall the space averaged Receiving Room spectrum press SET gt I RECEIVE N and recall the Receiving Room background spectrum and press SET gt I BACK GD O to define them for the calcula tion Once they have been defined these data blocks can be displayed by Dressing SOURCE M RECEIVE N or BACK GD O to examine the Source Room Receiving Room or Receiving Room background spectra respectively Only the data in the frequency range 100 Hz 4 kHz are saved in these files since the analysis is limited to that frequency range In some cases a user may be confident that the Receiving Room spectrum is sufficiently above the background spec trum that no correction will be necessary and not wish to Room Acoustics Measurements 2900 MANUAL measure the background spectrum In this case simply press CLR BG to reset the levels of the backgro
110. normalize the RPM or Speed increment of a single record as described above set both fields to the same record number The resulting record will be stored in the next available record of the type By Tach and then recalled as indicated by the message RECALL byTach N on the upper right of the screen where N is the record num ber into which it was stored Note that when displaying the first spectrum in sequence within the block the note AVER AGED is displayed on the first line on the right of the screen to indicate that this data block was the result of an averaging process and not the result of an actual measurement Block Maximum of Autostored byTach Records Autostore by Tach The Block Maximum operation can be applied to Autostored byTach records of the same type and bandwidth which have been stored sequentially record numbers in a sequence As explained above the result of the Block Averaging operation is a similar autostore record where the Nth spectrum is the average of all the Nth spectra contained in the separate autostore records being averaged The Block Maximum oper ation is similar except that for each frequency band in the Nth spectrum the amplitude is that of the highest level occurring at the same frequency across all the Nth spectra in the separate autostore records rather than their average To perform the Block Maximum operation from the Recall Menu 16 13 2900 MANUAL NOTE press B MAX
111. number of spectra that a very stable accurate measure ment of transfer function is made Observe the display of the transfer function during the measurement to verify that is has converged to a stable value If there is any doubt average over a larger number of spectra Control of Display Formats Cross Channel Normalization and Use of Key Macros Normalization 2900 MANUAL Toggling Normalization ON and OFF Access the Shift Menu shown in Figure 19 8 Normalization Menu by pressing SHIFT and quickly press NORMSET M Figure 19 8 Normalization Menu 23 APR 89 37 16 YES NO N Are you sure SEL 36 1200 lt LINEAR SINGLE 60 0000 Dual LINEAR 1 2 20 2 EL TE 23 RPR 33 69 37 08 FILTER 1 B0 Hz L73 vinyerse Transfer Hi D 2 d 6 9962 REAL TACH 8 8 SPEED 4 6 dotted crsr 88 Hz 80 0 Hz 19 GkHz The real part of the inverse transfer function will be displayed on the screen at this time To display the imaginary part press ALTERN I The message are you sure on the upper right of the screen will prompt the user to verify that he wishes to replace whatever correction function may have pre viously been stored for that baseband frequency value with the newly calculated correction function To store the correction function press YES A The display will return to the Menu which had been active prior to accessing the Shift Menu and the Normalization Mode of the 2900 will be active as shown by th
112. octave filtering no autostorage exponential averaging of 1 8 s 2 Access the Noise Menu from the System Menu by pressing NOISE J 3 Select pink noise by pressing PINK M and turn the gen erator on by pressing ON A The noise generator will now deliver a pink noise signal to the amplification system 4 The horizontal arrow keys will control the output level of the noise generator indicated by the message noise X X where X X is the output level with respect to the max imum output 5 Begin measuring by pressing the RS key 6 Set the gain appropriately and then adjust the noise gen erator and the sound reproduction system until the room is well excited by a spectrum which is fairly flat in the fre quency range of interest If the level is not high enough there may not be sufficient range between the exited levels and the background noise to make a meaningful measure ment 7 Change the averaging to Linear Repeat 8 With respect to the anticipated decay time set a very short averaging time say 0 05 s 9 Put the analyzer into the autostore mode using an inter val equal to the averaging time and an Endstore longer than the anticipated decay time possibly 2 s Room Acoustics Measurements Use with Impulsive Excitation 2900 MANUAL 10 Access the Noise Menu again and press OFF RUN D to put the noise generator into the Off with Run mode Set a delay time long enough for the lowest frequency
113. of START will reset the data buffer before start ing the analysis Places the 2900 in the STOP mode without storing a data block The 3200RC will display the message PAUSE The next press of START will continue the analysis without resetting the data buffers The ability of the 2900 to name label store and recall up to seven user defined instrument setups is described in Chap ter 12 The user should read this chapter before proceeding with this section The following keys on the 3200RC are used to communicate with the remote setups of the Model 2900 3200RC Key Numeric keys 1 7 Function The numbers 1 7 refer to the seven softkeys aligned below the 2900 display which can be labeled by the user and to which user defined setups can be stored The numbers 1 7 are assigned from left to right across the row of softkeys Upon pressing one of these numeric keys the user defined label for that softkey will be displayed on the 3200RC in the format Setup n is SSSSSSS 4 25 2900 MANUAL DC Output 3200RC Key Function This key represents a shift function Press ing it will produce an s on the lower right of the 3200RC display The subsequent keypress will be treated as a different func tion than the keypress without the preced ing shift operator After the keypress following the shift has been made the shift state is reset to normal After the shift has been initiated by the key and before another key h
114. of spectra will begin Actual aver aging and autostorage of spectra will not begin until the sequence is initiated by the satisfaction of the Frequency Trigger criteria When this occurs the state of the 2900 will change to RUN as indicated on the right of the display If no event occurs to produce a frequency trigger a subse quent press of the R S key will disarm the frequency trigger and the message NO TIME HISTORY STORED will appear on the upper right of the display Continued presses of the R S key will simply toggle the 2900 between the armed and disarmed states To disable the Frequency Trigger altogether access the Frequency Trigger Menu from the Autostore Menu by pressing F TRIG M and then press OFF For cases where the analyzer is to be used unattended it is convenient to have the 2900 rearm itself automatically after Autostore by Time 2900 MANUAL an autostore initiated by the frequency trigger so that data associated with a series of events can be captured This is done from the Frequency Trigger Menu by pressing RE ARM N after selecting the frequency trigger criteria This will produce the message Autostore rearm mode set on the right of the display As usual pressing R S will arm the fre quency trigger function However after the completion of an autostore sequence initiated by the frequency trigger the 2900 will return to the ARMED state so that a subsequent trigger will initiate another autostore s
115. of the screen should be Sine If instead it is 2tone indicating that the dual tone mode is active press 2 tone N to put it back into the single tone mode The sine generator can be used with either 1 1 1 3 octave digital filters or FFT analysis When learning to use the sine generator function it is particularly useful to use the sine generator as an input to the analyzer with the FFT analysis mode selected The user can define two frequency limits Fstart and Feng by pressing the softkeys Fstart A and Fend B respectively using the numeric keypad to enter a value of frequency in Hz and pressing EXIT Upon pressing either key the frequency 2900 Instrument Setup Via The System Menu 2900 Instrument Setup Via The System Menu 2900 MANUAL value presently assigned is indicated on the upper right of the screen The displayed value will change in response to modifi cations made using the numeric keys The output frequency from the signal generator can be manu ally set to the value of Fstart by pressing START I and to Fena by pressing END J A frequency sweep is begun by pressing SWEEP K The frequency of the output signal will then sweep from Paan to Feng producing a constant user defined voltage output L and then from Feng back to Fstart producing another constant user defined voltage output Les The frequency will continue to sweep back and forth between Fstart and Fena producing the programmed levels
116. on a single 3 1 2 inch disk Following the upgrade access the Reset Menu and manually reset all of the functions represented by softkeys in this menu before using the instrument Setting Backlight and Viewing Angle Introduction To adjust the screen display parameters press SCREEN and note the message ADJUST CONTRAST AND EXIT on the upper right of the screen Also the message contrast on the lower right of the screen will indicate that the horizontal arrow keys are now controlling the view angle of the LCD screen Press these keys until the optimum viewing angle for the present user position is obtained Figure 1 4 Screen Menu 19 OER 11 82 14 BKLT N BKLTOFF i ADJUST CONTRAST amp EXIT 8 0008 ang m akt EN EXPONENTIAL 178 i Dual LINEAR 20 2 20 2 i RESET 19 APR 93 11 01 26 T l A 1 FILTER 1 GD Hz 125 i Channel 1 of 2 NORMRL d 23 A 34 7 5a 200 221 PHONS 53 6 1 TACH 6 6 SPEED 6 a 88 8 Hz 10 0kHz H contrast INITIAL 1 7 2900 MANUAL Pressing the softkey BKLT ON C will turn the display back lighting ON and pressing BKLT OFF E will turn it OFF The backlight does increase the current draw on the battery so it is recommended that the backlight be used only when neces sary when operating the 2900 from internal batteries In order to conserve power for battery powered units the back light automatically turns off when no keys have been pre
117. or more particular instrument setups are used frequently the user may save each of these setups or even replace the bootup setup with one of them 2900 Instrument Setup Via The System Menu These Menus are accessed directly from the System Menu SYSTEM Units Filter VO Noise Input Setu Menu Name Menu Function System Selection of number of input channels and path betvveen the System submenus and the Analysis Menus Units Select units define and store user defined units perform calibration Filter Selection of Filter type and parameters I O Setup of computer 1 O interface Noise Setup of Noise generator mput Setup of mput modules Color Setup Menu for external Color monitor Setup Storage and recall of user created instru ment Setups Files Creation selection and directory of stored data Files Resets Menu for Resets 4 1 2900 MANUAL Accessing the System Menu The System Menu Figure 4 1 System Menu is accessed from any Softkey Menu by pressing SYSTEM Figure 4 1 System Menu E 17 28 37 Chanls SLM A STANDRD CROSS INTENSY UNITS FILTER CLASS Note TAPPING 6 9008 sa 5602000 seseo EXPONENTIAL Dual LINEAR 2 Hz 28kHz RESET 11 MAR 97 17 28 09 en W W w W W w W n n a w w W w a n W w w n n n n W W n n n n W n n n n n n a n nn nan n nan FILTER 14 25 a Hz L 3 v Channel 1 of 2 NORMAL de 13 8 R _ 24 7 40 REEL DIFF PHONS 36 4 REM TRCH 8 8 SPEED 4 6 25 0 Hz 500 Hz TO BkHz
118. oureu I r p 4 t UMoq JuSrIu rH 9rd A Arour yy YSI 1euro OPIS JOT MOWN Dau oureuosg PAYSIYSTH LI SZ 9Jn814 lal q q ISP ol 4 sTHOOd V dN 1U5U51H ASIC 01 f ATOWAN dN 48511431H ri ATOWAN A1ouro q e pIS ETA AOW PAYSTTYSTH 2101S OPIS YOT au0ta PANYSHYSIH ur spiooesp AST 9ureN pue avery 8 pue L 9 Z sonar snus srsA euy ou Jo ouo JO Gc ANJI n yl urojs S wouj AIOWAJA NUAN S H 81 92 snu W Aexyos 11 82 JANDIJ N IN 4 OPIS YOD MA PASIIYSIH Wouj UAOQI 14311431H OPIS US P1009Y Dous pIS ETA AON x1 4 f oureuor f H dH UAOQI 14311431H ATOUIIN p1ooes PaYSIYSTH 17971 MOWN D3IUSIIUSZIH oureuosq PAYBIIYSTY IAMA se UIES aq JoZ eue dm s pu nuon 9 H xq D aou lal y 121 V Dout dn p usrusrH dn p r rusi f KOWON e JO PIPIA AON VPA PIS ISTA MOW OPIS ST MOWN ureN pue IWAN 91 Z on314 AIOWAJN NUAN SOTL WOU Sp1009Y nuo N 5914 61 92 snu W Aayyos 81 52 JANDIJI D SIVLSA 3 fal AASA A e qe1 soroeu o SUNYSIOM enisip SonsneIs p un p r sn p un p r sn oui 1989 SIN HE SoN q 091 4 0141 25 4 8 SLINA A V 4 sdm s sun Josox IOUIOUI 0914 canoe p un p r sn T ZATEUE PSIA Ian soy 1 6Z m3r
119. phase normalization press SHIFT NORMSET M YES A This creates the correction function and activates its use in subsequent measurements as indicated by the message NORM on the left of the screen The use of this correction function may be toggled on and off by subsequent presses of the key sequence SHIFT NOR MALZ N The correction function will remain as last mea sured until changed by a new normalization procedure To verify that the system has been properly normalized per form a second one minute measurement using the residual intensity testing device with pink noise as the source To uniquely define this measurement as one associated with the verification of the normalization procedure assign it the JOB name NORM by pressing job I using the keypad to enter the name NORM into the field on the upper right of the dis play and pressing EXIT Store the measurement as JOB NORM by pressing STORE Of course some other name may be used for this purpose as long as the user is careful not to use a similar JOB name during subsequent measure ments Having completed this naming storing sequence the pressure residual intensity index associated with this mea surement can be displayed by pressing the key sequence POWER A S gt JOB I F2 P I B The results should resemble those in Figure 20 2 measured with the instrumen tation system set for a 25 mm spacer distance Figure 20 2 Pressure residual intensity display
120. pressing ARANGE P which will assign the horizontal arrow keys the role of adjusting the gain offset as indicated by the message Arange XX on the lower right of the screen The XX denotes the offset between chan nel 2 and channel 1 and this will change as the horizontal arrow keys are pressed Both positive and negative values of offset are permitted After the offset has been set assign the horizontal keys to another function such as controlling the cursor The normal range control will continue to adjust the gain of both channels together in 10 dB steps but the offset will remain between them as seen by comparing the full scale val ues of the two channels To remove the offset repeat the same procedure used to set the offset but adjust for a zero value of offset Setting the Autorange Aperture The 2900 input range settings may be set automatically by the Autorange Function which is described in detail in Chap ter 6 Under autorange control the system seeks to set the input attenuators such that the maximum displayed signal amplitude falls within an amplitude window extending from full scale down to a level equal to the Autorange Aperture without an overload The default value of the Autorange Aper ture is 20 dB This may be changed by the user from the Input Menu by pressing AUTO RA E and in response to the prompt on the upper right of the display typing in a value using the keypad and pressing EXIT This concludes the p
121. rate areas we could label them as UP LEFT UP RIGHT LOW LEFT and LOW RIGHT The complete test would involve the measurement of four spectra for each of the five surfaces making up the total enve lope a total of 20 measurements As each measurement is made the proper value of Surface Area is entered Then the position of that measurement in the hierarchy of labels is defined by assigning AREA PART and JOB labels to each Following our example the JOB PART AREA labels for the measurements would be as follows SOURCE TOP UP LEFT SOURCE TOP UP RIGHT Sound Intensity Measurements 2900 MANUAL SOURCE TOP LOW LEFT SOURCE TOP LOW RIGHT SOURCE FRONT UP LEFT SOURCE FRONT UP RIGHT SOURCE FRONT LOW LEFT SOURCE FRONT LOW RIGHT SOURCE REAR UP LEFT SOURCE REAR UP RIGHT SOURCE REAR LOW LEFT SOURCE REAR LOW RIGHT SOURCE LEFT UP LEFT SOURCE LEFT UP RIGHT SOURCE LEFT LOW LEFT SOURCE LEFT LOW RIGHT SOURCE RIGHT UP LEFT SOURCE RIGHT UP RIGHT SOURCE RIGHT LOW LEFT SOURCE RIGHT LOW RIGHT There is no obligation that the numerical values of surface areas used for the individual measurements be equal Once the measurement has been made the Surface Area defined and the JOB PART AREA labels assigned the measurement is stored In the Power Summation section of this chapter we will see how we can use the internal programming of the 2900 to sum the rese fenm aranma af ADDAg ta aktain eee far anak 1 1 Octave Ba
122. records higher in number than the one being displayed When performing a recall from the Intensity Menu the Inten sity spectrum will always be displayed even though the dis play parameter may have been different SPL Quality or Particle Velocity at the time the recall was initiated However following the use of the KEEP H key to maintain the selected record on the screen any of those alternative param eters can be displayed by pressing QUALITY C SPL D or P VELOC E Note that Intensity SPL Quality and Particle Velocity spectra can also be stored automatically as a function of time or RPM Speed using the byTime and byTach autostore func tions as described in Chapters 15 and 16 Upon recall these data can be displayed in the formats level versus time or level versus RPM Speed Editing the JOB PART and AREA Names the surface Area value and the Note Field of a Stored Intensity Spectrum 20 14 First recall the spectrum whose parameters are to be edited by pressing RECALL and using the horizontal arrow keys to bring to the screen the desired record Then press edit K and respond to the message ARE YOU SURE on the upper right of the screen by pressing YES A To abort the edit operation instead press NO C Each of these parameters can now be edited by pressing the associated softkey Note G job I part J area K or meter2 IM typing in the new entry using the alphanumeric Sound ntensity Measurement
123. right of the 2900 will change as the selected type is changed Averaging Time with Linear Types After an averaging type has been selected press AV TIME I to select an averaging time Averaging Time with Exponential Types When the selected averaging type is Linear Single or Linear Repeat a message on the upper right of the display will prompt the user to enter a value in seconds using the key pad then press EXIT Selection of Averaging Parameters When the selected averaging type is Exponential the Menu shown in Figure 5 3 Exponential Averaging Time Menu will present the user with 16 different values of averaging time from 1 64s to 512s in a binary sequence Press the key above or below the desired value then press EXIT 5 3 2900 MANUAL Figure 5 3 Exponential Averaging Time Menu mu 12 33 15 1764 1732 1716 178 174 172 1 2 SPL 1 86808 EXPONENTIAL 1 8 Dual LINEAR 26Hz 26khHz STOP _ 01 APR 97 12 32 54 FILTER 14 25 8 ke LAS Channel 1 of 2 NORMAL d DIFF PONS 85 3 TACH 6 6 SPEED 6 6 dotted cran 128 256 512 Averaging Time with Constant Confidence Type Octave Bandwidths Only When the selected averaging type is Constant Confidence the Menu shown in Figure 5 4 Constant Confidence Averaging Time Menu will present the user with 16 different values of BT product from 1 to 32 786 in a binary sequence Press the key above or below the desired value then press EXIT F
124. right of the screen Presses of the left arrow key will produce a paging backwards in sequence toward the first spectrum stored Cursor Control When the autostore operation was performed with two chan nels active there will be a complete set of spectral data for each channel To select the input channel whose data are to be displayed use the hardkeys CH1 and CH2 and note on the right of the display sixth line down the change in the indicated channel number To utilize the cursor for readout of the amplitude and fre quency values of the displayed spectrum press CURSOR which will assign the horizontal arrow keys to control the cursor which was last active dotted or solid A second press of that key will bring up the Cursor Menu for selection of cur sor type Press recall P to reassign the horizontal arrow keys the role of paging through a spectra within the autostore record Averaging of Autostore byTach Records Autostore by Tach It is possible to average together a series of byTach autostore records when they have been stored in sequential records To initiate this operation recall one of these records and from the Recall Menu press B AVE B producing the byTach Block Averaging Menu as shown in Figure 16 7 byTach Block Averaging Menu Figure 16 7 byTach Block Averaging Menu tor SPEED RPM s6 060 285000 s0050 AVERAGED EXPONENTIAL 1 64 Dual LINEAR 28Hz 28kHz 95 23 37 18 FILTER 14 25 0 Hz 125 v
125. same type and bandwidth can be averaged together using the Block Summation func tion This is a Root Mean Square summation which is appro priate for the addition of decibel levels From the Recall Menu press B SUM D which will bring to the screen the following message Last N RMS SUM 0001 0002 Use the numeric keypad and the horizontal arrow keys to enter values representing the record numbers of the first and the last records to be summed Upon pressing EXIT the summation will be performed and the resulting spectrum dis played Note that the word SUMMATION appears on the right side of the screen 2nd line down in place of the elapsed time displayed for measured spectrum to indicate that this spec trum is the result of a block summation rather than a mea surement This spectrum is not automatically stored Press STORE to store the spectrum following which the record into which the spectrum has been stored will appear on the upper right of the screen If the records contained within the specified range are not all of the same type and bandwidth the Block Summation oper ation will not be completed and the message NOT SIMILAR DATA will appear on the upper right of the screen 18 18 2900 MANUAL Waterfall Display of Stored Records 13 14 The waterfall display function permits the sequential display of a series of individual spectra of the same type which have been stored in sequence each one remaining on the scre
126. screen simply press the softkey whose label corresponds to that parameter The parameter Ln is discussed in a later section on Impact Noise Isolation If a message WARNING High Background appears on the upper right of the screen this means that the difference between the Receiving Room spectrum and the Receiving Room background spectrum levels at one frequency or more is less than 5 dB In such a case the corrected spectrum can only be used as an estimate of the upper limit of the impact noise level and this should be noted in the report 21 15 2900 MANUAL As an example Figure 21 6 shows a display of Field Trans mission Loss Figure 21 5 Field Transmission Loss Display 11 e 17 17 22 NR HHF TL FTL SPL 6 6008 ER EXPONENTIAL 178 Dual LINEAR 2 2501 RI DP M 7 FILTER 21 125 is LAS Field Transmission Loss TIC Sc z is def 88 REM TACH 8 8 SPEED 6 8 l Hz Z A dotted crsr ROOMSTST ASTM Standard E413 87 defines single number rating indi ces corresponding to each of the above parameters which are determined by a curvefitting procedure described in the standard When each of the above parameters are displayed as a function of frequency the results of the curvefitting pro cedure are overlaid on the screen as well The calculated sin gle number rating index or indices are displayed on the lower right of the screen The message def XX which appears to the right of the index value represents
127. signals It repre sents the steady level which integrated over a time period would produce the same energy as the actual signal The time period used for the calculation is the elapsed time since the last data reset MIN C A Minimum spectrum displays the minimum signal level measured in each filter band since the last data reset MAX D A Maximum spectrum displays the maximum signal level measured in each filter band since the last data reset SEL E SEL Single Event Level is similar to Leq except that it represents the steady signal which integrated over a one second time period would produce the same energy as the actual signal over the time since the last data reset While making a measurement one generally selects Normal in order to view the spectrum of one or both of the input channels live on the display However for any measurement made in the Standard Analysis Mode the four other spectra Leq Min Max and SEL are also calculated for channel 1 STAND 1 or both channels STAND 2 These can be viewed during or after the measurement by simply selecting the desired spectrum type as explained above To change the dis played channel for dual channel analysis simply press CH1 or CH2 The displayed spectrum type is indicated on the right of the screen sixth line down If the measurement is stopped and started repeatedly without a reset the calculation of the Leq Min Max and SEL spectra continue without reset
128. statistics parameter table and the displayed curves as desired Statistics and Ln Calculations A stored Statistics Table can be merged with the active statis tics table by pressing MRG TBL K This will produce the message Enter RECORD number XX prompting the user to enter the record number of the stored Statistics Table which is to be merged with the active Statistics Table using the numeric keypad and press EXIT This will be followed by the message ARE YOUR SURE warning that the newly merged Statistics Table will overwrite the presently active Statistics Table To continue press YES A To abort the merge and preserve the present Statistics Table press NO C An example of the use of the merge function would be where one wishes to know the noise statistics for the morning rush hour each day during the workweek and also the statistics for the entire weeks morning rush hour periods The Statis tics Table measured each morning will give the daily informa tion If the Statistics Table is stored daily then at the conclusion of the week all five of these tables could be merged 18 7 3200 MANUAL OPT 42 together to produce a single table representing the week long morning statistical data for use in producing statistics for that entire sample period 18 8 Statistics and Ln Calculations 19 Control of Display Formats Cross Channel Normalization and Use of Key Macros Accessing the Display Menu Many o
129. the Root Mean Square RMS sum of all the Nth spectra con tained in the separate autostore records being summed This is the proper sum to utilize when adding decibels To perform the Block Summation operation from the Recall Menu press B SUM D which brings to the upper right of the screen the following message Last N RMS SUM 0001 0002 Use the numeric keypad and the horizontal arrow keys to enter values representing the first and last sequence of record numbers over which the summation is to be per formed The autostore block summation operation is limited to a maximum number of sequential records of twenty Upon pressing EXIT the operation will be performed and the resulting spectrum stored The word SUMMED appears on the right of the screen 2nd line down in place of the elapsed time usually displayed with a spectrum to indicate that this spectrum is the result of a block summation operation If the records contained within the specified range are not all of the same type and band width the block summation operation will not be completed 15 15 2900 MANUAL and the message NOT SIMILAR DATA will appear on the upper right of the screen Waterfall Display of Autostored Records The waterfall display function permits the sequential display of a series of individual spectra within a By Time type autostored record each one remaining on the screen after it has been displayed Thus we will see drawn upon the screen o
130. the cursors to determine the RT60 value but in this case he would press AVERAGE D which would average the new RT60 value with the previously stored value and store the average value in the register In the RT60 Menu the value of AVE which would now be displayed for that band will be two Continuing in this manner the user could manually average RT60 values for each frequency band over the entire set of decay measure ments The number of averages used for each frequency band need not be the same Although this manual method is slower than the automatic method described below there is an advantage in that each decay curve can be examined by the user and the best time segment of each used for evaluating the RT60 value With the automatic method there can be particular problems obtain ing satisfactory decay curves at the low and high frequency limits The manual method permits the careful selection of data to be used Automatic Determination of RT60 Using Max based Thresholds Room Acoustics Measurements A common practice in the determination of RT60 values from sound decay curves is to apply the curvefit to the portion of the decay curve beginning when the sound level has decayed to 5 dB below the initial noise level and ending when the level has decayed even further below the initial noise level 25 dB for example This is achieved automatically in the Model 2900 using Max based threshold levels From the vsTime Menu if the te
131. the measurement is less than the number of separate measurements Areas used within that Part then this aspect of the standard is satisfied If that is not the case repeat the test using a number of measurements Areas equal to or greater than N and examine this criterion again Another parameter of importance is F4 F5 which is used in conjunction with criterion 2 to suggest actions to be taken to improve the accuracy of the measurement Using the same the value of N press F3 F2 P to obtain the display shown in Figure 20 8 20 23 2900 MANUAL Figure 20 9 F3 F2 Display 23 MAR 15 50 11 2 P I FS NPP F4 FNU note Note SPEAKER TEST dB F3 9008 3 0 VEER LINEAR SINGLE 4 at Dual _ LINEAR 280Hz 20kHz ua RESET 24 FEB 94 16 53 57 2 8 17 FILTER 421 125 Hz LAJ R vvF3 F2 Hea Pos Flow d 1 8 dB aaa 900002 1 4 G DB n n n n o ng ng Ri JOB_ SPEAKER Loc PART FRONT PESCE RE AREAS s Wd Hz A GkH dotted crsr SPERKER S gt JOB S gt PART S gt AREA S gt EDIT Ci F4 2 2 422 F3 F2 The manner in which the standard is written places empha sis on which of the following is obtained F3 F2 1 dB 1 dB lt F3 F2 lt 3 dB F3 F2 gt 3 dB It is a simple matter using the display format of Figure 20 9 F3 F2 Display to determine which of these situations corre sponds to the measured data over
132. the message recall data on the lower right of the screen will indicate that the horizontal arrow keys are assigned to recall the individual spectra from the recalled record To recall an autostored record stored earlier previous to the one which has been recalled press A Prev N and note that the index N in the message on the upper right has been decreased by one indicating that the previous record has now been recalled Repeated presses of A Prev N will page the recall procedure continually towards the first record stored in that file Similarly pressing A Next O will result in the recall of the autostored record which was stored later after the one which had originally been recalled as indicated by a unity increase in the value of N in the message on the upper right Repeated presses of A Next O will page the recall procedure continually towards the last record stored in that file 16 10 Autostore by Tach Displaying Individual Spectra 2900 MANUAL Channel Selection Once the desired record has been recalled presses of the right arrow key will page through the individual spectra con tained in the autostore record bringing them sequentially to the screen Each spectrum is tagged with the time relative to the initiation of the autostore sequence This is displayed on the right screen first line down The values of Tach and Speed corresponding to the instant of spectrum storage are also displayed at the lower
133. the microphone at different positions in the room often performing a number of tests at each position In any case the data for each individual decay measurement will be stored in a unique autostore record Several autostore decays may be averaged together with the block averaging function See Chapter 15 Averaging of Autostore Records This will give a smoother decay plot to use for RT60 measure ments 21 1 2900 MANUAL Use of the Noise Generator Procedure 21 2 When using electronic amplifiers and speakers to excite the room for a reverberation test the noise generator built into the Model 2900 is ideal Typically one would select Pink Noise in order to provide approximately equal acoustic power per 1 3 octave band width One would like to achieve a fairly flat sound spectrum over the frequency range of interest in the room previous to beginning the decay measurement because that provides a good dynamic range at each frequency for the decay mea surement In some cases it is desirable to use a spectrum shaper between the noise generator and the amplification system to optimize the initial sound spectrum In this description we refer to the Noise Generator Instruments equipped with the Signal Generator could use either Wide band Pink Noise or 1 3 Octave Bandlimited Noise which would permit the utilization of the autolevel function 1 Using a microphone input configure the 2900 as follows Standard analysis 1 3
134. the previously measured and stored value of noise floor for the selected weighting Press YES A to replace the old value with the one just mea sured Otherwise press NO C to keep the previous value of noise floor 3 19 2900 MANUAL Now when performing a sound level measurement whenever the measured sound pressure level falls to within 5 dB of the noise floor the message N will appear to the lower right of the digital display of the sound pressure level on the lower right of the screen Since there are six different weightings possible A C and four different combinations of highpass lowpass filters it is recommended that the user measure and store a noisefloor for each of these such that the proper noisefloor proximity indication will occur no matter which has been selected at the time of the measurement When the units are reset from the Resets Menu by pressing R UNITS B as described in Chapter 4 the noise floor val ues for all the weightings will be reset to zero Environmental Effects on SLM Measurements Magnetic Field Temperature The maximum noise floor of the Model 2900 equipped with a Model 2541 high sensitivity microphone when exposed to a 60 Hz magnetic field of strength 10 A m2 1 Oersted is as follovvs A vveighting 15 dB C weighting 24 dB Flat weighting 25 dB 20 Hz 20 kHz Humidity The maximum variation of sound pressure level due to tem perature variation over the ran
135. the selection of display parameter the coordinate system where applicable and the store com mand within a macro simple execution of the macro would perform the complete sequence and it would be available for user execution whenever required Up to eight different mac ros can be available at one time Macros can also be stored to memory and recalled for keyboard use 19 12 To create a macro press the key sequence MACRO CREATE A which will display the Macro Menu As directed by the message on the upper right of the screen press one of the keys I P to select which key is to be used later to exe cute the macro type in a label to identify it and press EXIT Control of Display Formats Cross Channel Normalization and Use of Key Macros 2900 MANUAL Following this sequence it will record sequential keypresses performed by the user until either the hardkey is pressed again or fifty keypresses have been performed While making key presses during the creation of a macro if the SPACE key is pressed previous to pressing a key that key press will be included in the macro but it will not be exe cuted during the programming of the macro This is very use ful when utilizing the keys STORE and RS during the definition of a macro McSTOP and McWAIT and McREPT Softkeys Resetting Macros The are three softkeys in the Shift Menu which can be used in the creation of macros McSTOP I will cause the macro processor to pa
136. the trace numbers The preced ing section was presented simply because it is possible to define them differently and if the user chooses to do so he may Parameter Selection From the Standard Analysis Menu access the vsRPM Graphics Menu shown in by pressing vsRPM J vsRPM Graphics 17 3 2900 MANUAL Accessing a Trace Figure 17 1 vsRPM Graphics Menu A4 UN 23 28 16 SLOPE alevel TRGBHRS X SPAN VIDEO RPM SPD note PKWIDTH SOURCE IS TACH INPUT 8 5225 EXPONENTIAL 1 84 iz HP RESET 84 JAN 96 04 10 54 PEN LEVEL 75057 2 01 83 3 122 508 2 02 75 7 1 38 1 60k 3 83 99 7 1 33 2 66k 4 04 62 2 1 36 4 66k 5 05 55 2 1 59 8 00k 40 6 06 92 5 1 28 166 1000 6000 RPM 5188 crsr 49 INITIRL STATUS HIDE B ORDER CAL PEN CHANNEL FREQ The parameters which define the individual traces are con tained in the table on the lower right of the screen Each row represents a specific trace numbered 1 6 along with the presently assigned values of PEN channel C and frequency FREQUENCY or order ORDER arranged in rows Pen Selection To modify the parameters associated with a particular trace use the numeric keypad and press the key corresponding to the number of the trace to be modified The symbol gt will appear to the left of that trace number to indicate that it is now the trace to which modifications will be assigned Channel Selection As mentioned above we will adopt the convention that the pen n
137. the unit is booted up The default setup for the 2900 as delivered from the factory selects the Hanning window Because many users utilize the same time weighting window for most of their FFT analysis particularly the Hanning window it may not be necessary to modify the window selection when creating an FFT setup The Time Weighting Window Menu shown in Figure 4 3 FFT Window Menu is accessed from the Filter Menu by pressing WINDOW N Figure 4 3 FFT Window Menu 82 JAN 66 26 89 RECT HANNING FLAT ZEROPAD IMPACT 2 EXP 4 EXP 6 SPL 6 60068 100 25 EXPONENTIAL 1 64 PREAMP LINEAR 18 280kHz RESET 02 JAN 96 6 19 52 FREQ 900 0000 2 Channel 1 of 2 NORMAL d 8 0 Ze 27 3 Lac i TACH 6 6 SPEED 4 6 48 aa 8588 ZUDM 1 10000 0000 Z A dotted crsr 4 7 2900 MANUAL 4 8 Select the desired time weighting window by pressing one of the following Softkeys Softkey Functions RECT A for Rectangular Weighting on all channels HANNING B for Hanning Weighting on all channels FLAT C for Flat Top Weighting on all channels ZEROPAD D for Zero Pad with without Bow Tie Correction on all channels IMPACT E for Impact Weighting on channel 1 Rectangular Weighting on channel 2 EXP 2 F Impact Weighting on channel 1 Exp 2 Weighting on channel 2 EXP 4 G Impact Weighting on channel 1 Exp 4 Weighting on channel 2 EXP 6 H Impact Weighting on channel 1 Exp 6 Weighting on channel 2 The active time we
138. this chapter A simple example of the use of class lines applied to fre quency spectra is a quality control application where a sound or vibration spectrum measured for a machine under test is compared to a curve in the frequency domain to determine whether or not the machine is acceptable or not e g Pass Fail decision In Figure 22 1 Pass Example below the spectrum is below the curve at all frequencies indicating an acceptable unit Pass while in Figure 22 2 Fail Example the spectrum level at 1 6 kHz exceeds the curve indicating an unacceptable unit Fail based on that criterion even though the spectrum lev els are below those of the spectrum shown in Figure 22 1 at most frequencies Figure 22 1 Pass Example 29 DEC 16 31 86 T 166 ass Judgment 1 CURUS 1 CURUS 3 CURUS 2 CURUS 4 22 1 2900 MANUAL 22 2 Figure 22 2 Fail Example 29 DEC 16 31 58 t 100 See SE WA ache Mowe We alate TCR RENE NW CURUS 1 CURUS S CURUS 2 CURUS 4 Ch 1 1 data A more advanced approach is indicated in Figure 22 3 Clas sification Example where a family of parallel curves are used for the comparison with the test spectrum Figure 22 3 Classification Example 29 DEC 16 44 29 N The classification of the spectrum in this case could be based on the frequency for which the level has exceeded the maxi mum number of curves of this family In this case there are six curves labele
139. toggle the system between the states Video updates suspended and Video updates restored as indicated by the message on the upper right of the screen vsRPM Graphics When the parameters have been input as required simply press the R S hardkey to begin a test The scaled values of RPM and Speed can be read on the lower right of the display as the test proceeds Whenever the RPM Speed values fall between the lower and upper limits of the screen the points for each of the curves will be drawn across the screen corre sponding to the incremental RPM Speed and amplitude lev els and the slope parameter In a typical machine runup or automobile acceleration test the RPM will begin at a value less than the lower limit of the screen As soon as the RPM reaches the lower limit value the curves will begin to appear and will be drawn from left to right across the screen If the limit of the memory is exceeded during a test the oldest data points will be replaced with newer ones although the 17 7 2900 MANUAL Examination of the Traces portions of the curves corresponding to the older points already drawn of the screen will remain At the conclusion of the test press R S to stop the data acquisition and graphics generation Hiding Traces At the conclusion of the test the cursor can be used to exam ine the data point by point Level values for each trace corre sponding to the cursor position are presented in the paramet
140. top of the screen and 31 possible display types for each display window from which to choose In many cases there will be among the choices for the dis play type those which are the same as the choices for MAS TER Others will be different For example in the Standard Analysis Mode the choices for MASTER will be Normal Leq Lmin Lmax SEL and vsTach The choices for display type will be Normal Leq Lmin Lmax SEL vsTach and Max Spectra The processor of the Model 2900 cannot update all the available display types and transfer them to the color monitor fast enough to present a satisfactory display There fore only in a display window whose display type matches Use of External Color Monitor for Display and Instrument Control 24 9 2900 MANUAL Channel Number that selected in MASTER will the display be updated rapidly during a measurement Those windows whose display types do not match will show a static grey outline during the mea surement However after the analyzer is stopped the data in all these windows will be updated and displayed Consider an example where the user selects a four window data display Most often the user would like to observe the dynamically changing spectra during the measurement so he would select both the MASTER Global Configuration Win dow and one of the four display windows to be Normal The display types for the remaining three windows might be Leq Lmax and Max Spectrum During the measureme
141. type the desired characters into the field and press EXIT Note that the names must be literally identical to those used as JOB PART and AREA names including blank spaces For exam name to be entered is CAR then the three letters must be fol lowed by four spaces Performing a Power Summation There is a much easier way to enter names into the search field without the necessity of typing them Before accessing the Power Summation Menu recall one of the stored spectra which already has the desired labels stored with it Don t for get to press KEEP H These labels will appear in the fields at the lower right of the display as each spectrum is recalled When the Power Summation Menu is accessed they will remain there requiring only the use of the S JOB I S gt PART J and S gt AREA K softkeys to transfer them into the upper right search field 20 16 NOTE When the desired names have been entered into the power summation search field press Power A to perform the sum mation The spectrum representing the power sum will then be displayed When the summation has been completed the search field will no longer be displayed on the upper right of the screen but the JOB PART and AREA names associated with the search and whose spectra have been summed to produce the displayed power spectrum are indicated on the lower right side of the screen When in the Power Summation Menu the units indicated on the right of the sc
142. until either the sweep is paused by pressing SWEEP K or the fre quency is set manually to either Paan or Feng by pressing START I or END J When the sweep has been paused pressing SWEEP K again will result in the contin uation of the sweep from the state it was in when the pause occurred The rate of the sweep can be either logarithmic or linear in the frequency domain Whenever one of the parameters of the sine generator is changed the frequency state of the output signal is indicated on the upper right of the screen for approximately ten seconds This message will indicate whether the frequency is fixed at the Start frequency fixed at the End frequency or in a Sweep mode It will also indi cate whether the generator output is ON or OFF and whether the selected sweep rate is LOG or linear in which case the sweep rate may be defined either by the time of the sweep or by the count of the number of cycles per sweep The sweep mode is toggled between logarithmic and linear modes by repeated presses of the softkey L The label of that softkey at anytime will be either LOG or LIN indicating that pressing the softkey will change it to the mode corresponding to the label The active mode is briefly indicated on the upper right of the screen when most of the softkeys are pressed The Fstart to Fena sweep rate is set using the softkey C and the Fena to Fstart sweep rate is set using the softkey D The
143. weighting window where the attenuation at the end of the time window is N 10 dB with respect to the unity attenuation at the begin ning of the time window By forcing the response amplitude to near zero at the end of the response time window the effect of leakage on the measurement of the frequency response function is minimized However this also has the effect of adding artificial damping to the measured results 2900 Instrument Setup Via The System Menu Selection of Baseband Full Scale Frequency Base Bd FFT Zoom Analysis to Increase Frequency Resolution 2900 Instrument Setup Via The System Menu NOTE 2900 MANUAL which must be taken into account when the analytical results of the modal analysis are used to estimate structural damping After selecting a time weighting window the instrument will return to the Filter Menu The FFT analysis is begun with a baseband analysis which means that the frequency range of the analysis will extend from DC 0 Hz to a selected full scale frequency value The Full Scale Frequency Menu shown in Figure 4 4 Base Band Menu is accessed from the Filter Menu by pressing BASE Bd O Figure 4 4 Base Band Menu 82 JAN 23 33 17 20 2 18kHz SkHz 2 5kHz EI eR I RR I RII RI I Select UPPER BAND EDGE SPL 6 6008 70 V6 dl rae AR EE HR ENEE sd TR PA O70 m s 0 8 Mn e 579 MN EE EXPONENTIAL 178 Ineut 1 LINEAR 28Hz 28kHz RESET 62 JAN 96 23 33 11 Sa ON W W W W W W W W W
144. 0 4 dB The upper limit is established as the level at which overload occurs when excited by a sinusoidal signal For signals hav ing a crest factor of 10 the overload will occur at a level 20 dB below the stated limit 1 Using Larson Davis Model 2570 or 2575 1 microphones having a nominal sensitivity of 45 mV Pa with a Model 900B preamplifier Weighting Measurement Range A weighting 13 135 dB C weighting 15 135 dB 20 Hz 20 kHz 17 135 dB 1 Hz 20 kHz 25 135 dB Sound Level Meter Operating Modes 2900 MANUAL 2 Using Larson Davis Model 2541 or 2560 1 2 micro phones having a nominal sensitivity of 44 mV Pa with a Model 900B preamplifier Sound Level Meter Operating Modes Weighting Measurement Range A weighting 18 135 dB C weighting 23 135 dB 20 Hz 20 kHz 25 135 dB 1 Hz 20 kHz 35 135 dB 3 Using LarsoneDavis Model 2540 or 2559 1 2 micro phones having a nominal sensitivity of 12 5 mV Pa with a Model 900B preamplifier Weighting Measurement Range A weighting 36 148 dB C vveighting 36 148 dB 20 Hz 20 kHz 37 148 dB 1 Hz 20 kHz 48 148 dB 4 Using LarsoneDavis Model 2520 1 4 microphone having a nominal sensitivity of 4 mV Pa with a Model 910B pream plifier Weighting Measurement Range A weighting 47 157 dB C vveighting 54 157 dB 20 Hz 20 kHz 55 157 dB 1 Hz 20 kHz 65 157 dB 5 Using Larson
145. 1 Field Non Uniformity Indicator AAA 20 21 Alternate Presentation Format for F2 E3andEA 20 23 Room Acoustics Measurements 21 1 Sound Decay MeasUrements ED Pp eg emetris e Po boys ton More ee 21 1 Use of the Noise Generator 21 2 i e cf E 21 2 Use with Impulsive Excitation inaen iaae aai n EAEE T ay nennen 21 3 Evaluation of Reverberation Te 21 4 AGO Ke EE 21 4 Reading Current HIT 21 5 Manual Entry of RT60 Values nne nennen nn nennen nn nnns nennen ens 21 5 Manual Determination of RT60 Using the Cursors ss el si asi iiai iii ii l 21 6 Automatic Determination of RT60 Using Max based Thresholds 21 7 Automatic Determination of RT60 Using Fixed ThresholdS AAA 21 10 Averaging of Autostored Time Decay 05 sse 21 11 Storage and Recall of RT60 Data 21 12 2900 MANUAL Recall of RT00 ER 21 12 Room Acoustics Measurements nennen nennen nene 21 12 Airborne Sound Transmission Loss Measurements sse 21 13 ASTM Airborne Sound Transmission 5 21 15 ISO Airborne Sound Transmission Parameter sse 21 16 Impact Sound Insulation Measurements eene 21 18 ASTM Impact Sound Transmiesion sse enne 21 19 ISO Impact lsolation EE 21 20 Noise Criteria CUErVOs u
146. 2 BOOT ROM VERSION X XX C 1993 Larson Davis Inc The message is to inform the user which keys to press during the pause to reboot the RAM or to reload the internal soft ware via the floppy disk or the RS 232 interface If no action is taken the message will disappear after about seven sec onds and the bootup will continue To terminate the pause and continue immediately with the bootup press the hardkey as indicated in the message When the 2900 is first booted up from the ROM the software is transferred into the RAM From then on unless the ROM is reset the 2900 will boot up using the software stored in the RAM Just before the bootup procedure is complete on the upper right of the display will briefly appear a message of the form Version 5 XX 1991 96 followed by another message of the form Vers SLM A 4 43 SLM 1 0 For the purpose of cer tification the code versions associated with the sound level meter functions have been separated from the general operat ing and analyzer code Once a sound level meter code version has been released no modifications are made without chang ing the code version Most certifications are made for a spe cific code number Thus while the general operational and analyzer code may be modified frequently to make improve ments and add new features the sound level meter versions are rarely changed once they have been shown by a certifying agency to be acceptable The first message Vers
147. 2 NORMAL on the right side of the screen Although the frequency weighting can be selected indepen dently for each channel the same weighting will apply to both the SLM and the frequency analysis function The fre quency weighting is selected using the lower set of softkeys in Sound Level Meter Operating Modes 2900 MANUAL the Weighting Menu The lower limit of the frequency display will be set to 6 3 Hz when the selection has a 1 Hz lower lim iting frequency and 25 Hz when it has a 20 Hz lower limiting frequencyor when the A or C weighting have been selected The lower limit of the frequency display can be changed to 0 8 Hz by pressing WIDE H Pressing this softkey again will return the lower limit of the frequency display to the previous setting Each channel should be individually calibrated pressing CH1 or CH2 to access that channel prior to calibrating Also the noise floor measurement and proximity message should be set up individually for each channel Sound Pressure Level Measurement Dual Channel Sound Level Meter with Frequency Analysis SLM A Single Microphone In this model the signal from a single microphone is branched to both SLM A measurement channels permitting measurements of the same signal to be performed using dif ferent frequency weightings The two channels are setup as described in the section above Then before initiating the analysis from the Input Menu press Inputs G which will change the pa
148. 21 21 Rooms ISO 21 17 RT60 21 5 SLM 3 2 SLM Fast 3 15 SLM Impulse 3 15 SLM Leq 3 16 SLM Slow 3 15 SLM WDR 3 24 Sound Reduction 21 17 Standard Analysis 6 1 Statistics 18 2 Vertical scaling 19 5 vsRPM Graphics 17 4 vsRPM Intensity 17 10 Waterfall 13 14 15 16 16 14 Y axis 19 5 E elapsed time 3 11 end time 15 2 external monitor 24 1 F FFT 4 9 FFT analysis 4 3 4 6 Files accessing 13 1 creating 13 2 deleting 13 3 description 13 1 renaming 13 2 selecting active 13 4 transfering to from disk 13 3 Filters 4 3 analog 4 13 fractional octave 4 4 floppy disk 13 3 G Gain Control 3 11 7 2 Offsetting between channels 7 3 H horizontal scale 19 8 I I O Channels 4 27 I O Port Control 4 27 IMPULSE 6 7 Impulse Response 6 7 Input 3 2 Input gain control 3 11 7 2 Integration 9 2 Intensity 20 1 Definition of Areas 20 7 Entering Labels 20 10 Job Part Area 20 8 Power Summation 20 15 Selection of Display 20 11 Intensity Analysis Mode 4 3 Interface operations 4 24 RS 232 4 30 INTNSTY 6 10 20 11 INVERSE 6 7 6 9 2900 MANUAL Inverse Transfer Function 6 7 6 9 K key macros 19 12 Keys arrow hardkeys 3 11 Arrow Keys cursor 1 5 Range 1 5 cursor hardkey 1 5 dedicated hardkeys 1 2 1 5 horizontal arrow 3 11 macros 19 12 R S hardkey 7 1 Range hardkey 1 5 softkeys 1 4 vertical arrow 3 11 L Leq 6 3 LIFTER 6 7 Liftered Spectrum 6 7 Ln Calculations 18 1 Loudness 6 5 M Macros 19 12 creating 19 12
149. 6 Setuser 10 4 25 34 Shift 2 4 19 3 25 51 A 4 Signal Generator 4 16 25 40 Bandlimited Pink 4 20 25 44 Dual Tone 4 18 25 42 Psuedo VVhite 4 22 25 46 Pulse 25 22 25 47 Sine 4 16 25 41 VVideband Pink 4 21 25 43 VVideband VVhite 4 22 25 45 Sine Generator 25 41 Sine Generator Dual Tone 4 18 Sine Generator Single Tone 4 16 SLM 3 2 25 3 SLM display 25 5 SLM weight 3 4 25 4 Slope 9 2 Standard Analysis 6 1 Standard Analysis 1 and 2 channels 25 6 Standard recall 25 38 Statistics 18 2 25 27 System 2 1 4 1 4 2 25 2 Tach Speed Averaging 16 8 16 9 Tach Speed Calibration 16 7 Tachset 25 35 Time trigger 11 1 25 30 time weighting 4 4 Units 9 1 25 10 Vertical scaling 19 5 vsRPM 25 26 vsRPM graphics 17 4 17 10 Waterfall 13 14 15 16 16 14 White Noise Psuedo 4 22 25 46 White Noise Wideband 4 22 25 45 Y Axis 19 5 25 52 Microphone Connection 1 10 electret 3 3 polarization voltage 3 3 preamplifier 3 7 prepolarized 3 2 MIN 6 3 Multi 6 2 6 5 19 1 NC 21 21 Noise Criteria Curves 21 21 noise floor 1 20 3 19 Noise Generator 4 14 Noise Generator see Signal Generator also 4 14 2 2 Noise Rating Curves 21 22 NORMAL 6 3 Normalization Amplitude Phase 19 9 Cross Mode FFT 19 10 Cross Mode Octaves 19 12 note 14 1 NR 21 22 O Outputs AC 1 11 DC 4 26 overload indication 3 11 P P VELOC 6 10 20 11 Particle Velocity 6 10 20 11 Pink Noise see Noise Generato
150. 6 4 1 C C SPECT 6 9 C CORRE 6 7 C SPECT 6 6 Calibration 3 17 analyzer 9 6 SLM 3 17 using internal test signal 9 7 using transducer sensitivity 9 4 CEPSTRM 6 7 Cepstrum 6 7 Channel Dual 6 1 Single 6 1 Channel Selection 6 2 Class Classification Lines 22 1 25 48 Accessing 22 3 Assigning 22 7 22 8 Creating 22 4 22 8 Judgement 22 9 22 10 22 11 Labeling 22 4 Recall 22 12 22 13 Storage 22 12 22 13 Turning On 22 8 Clock 4 30 COHER 6 7 6 9 Coherence 6 7 6 9 Color Monitor 24 1 Complex 6 8 CROSS 6 6 Cross Analysis Mode 4 3 6 6 Cross Correlation 6 7 Cross Spectrum 6 6 6 9 Cursor control 1 5 dotted 1 18 8 1 fixing positions 8 3 harmonic 8 2 moving 8 1 solid 1 18 8 1 C Weight 3 4 D DC Output 4 26 Deleting autostore records 15 13 A 2 non autostored records 13 12 delta time 15 2 Differentiation 9 3 Disk operations 13 3 Display 1 7 backlight 1 8 channel selection 6 8 color monitor 24 1 complex functions 6 8 control horizontal range 19 8 control of 1 9 control vertical range 19 4 polar coordinates 6 8 printing 23 2 rectangular coordinates 6 8 Sine Generator 4 16 spectra relative to a reference spectrum 19 3 viewing angle 1 7 displayed 10 8 Displays byTime 15 9 Display 19 3 FFT 10 1 Field indicators 20 20 20 22 Intensity 6 10 20 1 Leq byTime 15 10 Loudness 6 5 Multi spectra 19 1 NC 21 22 Octave Cross 6 9 octaves 10 1 Pressure residual intensity 20 2 Rooms ASTM 21 15 Rooms Impact 21 20
151. 6 57 26 max REPEAT WIDTH aualify 118 eee eee ee P oint 1 of ia fa a 10 18 8 Hz 6 6006 ang een w w w W w w af W W W n W W W n n n W W a n n n n w a nn n n n n n n n n n n nn n nn EXPONENTIAL 1 64 Dual LINEAR 28Hz 18kHz RESET 29 DEC 93 16 45 12 66 FILTER 7 5 66 Hz L73 v Channel 1 of 2 NORMAL d 23 8 A 34 7 Bg vov ori OE hv yaq wees v y mme i445 4 PHONS 53 6 TRCH 6 6 SPEED 4 6 R 2 B z fresuency INITIRL roint Point add rnt del rnt dotted frea Begin by accessing point 1 and using the vertical and hori zontal arrow keys to move it to the coordinates 70 dB 10 Hz Note that as this point is moved horizontally to the right its designation is changed to point 2 because it is now to the right of the other point now designated as point 1 Next access the other point now point 1 and move it to the coordinates 70 dB 63 Hz Fix the location of this point by pressing add pnt K and notice that the coordinates listed on the upper right are for point 3 Use the cursors to move point 3 to the coordinates 80 dB 63 Hz and press add pnt K Continue the sequence as follows move point 4 to 80 dB 630 Hz add pnt IK move point 5 to 60 dB 630 Hz add pnt K move point 6 to 60 dB 2 kHz add pnt K move point 7 to 50 dB 2 kHz add pnt K move point 8 to 50 dB 4 kHz add pnt K move point 9 to 40 dB 4 kHz add pnt K move point 10 to 40 dB 10 kHz add pnt K The class
152. 6 7 Auto Spectrum 6 9 Autorange 7 3 Autospectrum 6 6 Autostore byTach 16 1 Enabling autostore byTach 16 9 Influence of slope 16 6 Interval Span settings 16 4 Recall and display of data 16 10 Setting Tach parameters 16 2 Speed Input 16 1 Tach Speed calibration 16 7 Tach Speed scaling 16 4 Tacho Input 16 1 Autostore byTime 15 1 amplitude vs time display 15 9 averaging 15 7 block maximum 13 12 broadband vs time 15 11 concluding sequence 15 5 displaying spectra 15 8 initiating a sequence 15 3 recall and display 15 7 SLM data vs time 15 11 waterfall display 15 16 16 14 Average 6 2 Average spectrum display 6 2 Averaging 5 1 autostore byTime 15 6 15 13 constant confidence time 5 6 continuously running time 7 1 count 15 3 exponential time 5 7 FFT filters 5 2 finite length time 7 2 linear repeat time 5 7 linear time 5 6 methods 5 2 octave filters 5 1 periodic signals 5 7 signal 5 5 spectrum 5 6 5 7 time 5 5 time decay records 21 11 Averaging Consideration 5 5 Averaging time 5 3 Averaging Type FFT filter 5 2 Octave Filters 5 1 Averaging Spectra Constant Confidence 5 4 Exponential 5 4 FFT 5 2 Octaves 5 1 A Weight 3 4 19 2 B Bandwidth Compensation 19 7 Battery 1 9 Beeper control 1 9 4 30 Block Averaging 16 13 byTach Autostore 16 11 byTime Autostore 15 13 Standard 13 12 Block Maximum byTach Autostore 16 13 byTime Autostore 15 14 A 1 2900 MANUAL Standard 13 12 boot up 1
153. 66 5 Use of External Color Monitor for Display and Instrument Control Selecting vsRPM or vsSpeed 2900 MANUAL Assigning Pens to Frequencies or Orders When the vs Tach display mode is active the layout of the available parameter windows above and below that data dis play window will change To the right above each display win dow will be two windows referring to RPM and SPEED respectively When operating in the vsRPM mode these two will display the value of the RPM and Speed signals in the same manner as they are displayed on the lower right of the 3200 screen The label RPM or SPEED of one of these will be brighter than the other to indicate that the display format selected corresponds to that mode Clicking the mouse on either of these two parameter windows will offer the user the choice of RPM or SPEED As explained in Chapter 17 the user can define up to 32 dif ferent pens each of which will be assigned to represent a par ticular frequency or order value and a particular channel when multiple channels are being used To make such an assignment click the mouse on the window entitled PEN Use the mouse to select one of the 32 The selected pen number will appear in the PEN window If the number is displayed brightly that pen is already enabled and the window to the right will display the bright message On If that pen has not been enabled it is dis abled In that case the number will not be displayed brightly an
154. A J C K USER L A IMI No Weighting A VVeighting C Vveighting User Defined VVeighting A Weighting negative C N USER O C Weighting negative User Defined Weighting negative Exiting From Display Weighting Press EXIT to exit from the Display Weighting Menu back to the active Analysis Menu User Weighting Creation storing recalling and manipulation of user weight ing curves are performed in the Setuser Menu Figure 10 4 Setuser Menu accessed from the Display Weighting Menu by pressing SETUSER F Figure 10 4 Setuser Menu 2 JAN 96 33 21 w n n n n n n n n n n cc e LEAR cc afe USER SPL U 6 9606 07 EXPONENT IAL 1 64 PREAMP LINEAR 18 20kHz RESET 02 JAN 90 06 31 20 sa DDD WEINE FILTER 8436 19 6kHz L712 USER DATA USER ea xn LOC e 1 0000000000 TRCH a 0 SPEED 9 8 Fe solid crsr TEST 1 MAKE INTERP edit 10 4 Digital Display including Broadband Acoustic Frequency Weighting User defined Frequency Weighting and Integration of FFT Spectra Creating a User Weighting Curve 2900 MANUAL Interpolation Function To create a user weighting curve first press CLEAR C to ensure that the working buffer is zeroed For each bandwidth which is to have a non zero value move the cursor to that band press edit P and in response to the prompt on the upper right of the display use the keypad to type in the desired value then
155. AL The above illustration highlights a number of hardkeys on the front panel of the Model 2900 whose functions are as fol Turn ON analyzer When pressed simultaneously with the SHIFT key produces a hard reset and re Adjust SCREEN angle and control backlight Put analyzer into LOCAL control mode SHIFT key to activate upper letter symbol word on hardkeys Press SHIFT release then press EXIT from a softkey menu to a higher level menu Also used to enter alphanumeric data after it has been input into the open data field on the upper right of the screen e g when writing a note or entering a value of linear averaging time RECALL and display a stored data record CLEAR the alphanumeric string in the open data field on the upper right of the screen e g when Select input connector 1 nearest the right side of the top panel of the 2900 for the input signal to the sound level meter and frequency analyzer functions indicated by the message Input 1 on the right side of the screen third line down Select input connector 2 nearer the center of top panel of the 2900 for the input signal to the sound level meter and frequency analyzer func tions indicated by the message Input 2 on the right side of the screen third line down lows HardKeys Hardkey Functions OFF Turn OFF analyzer ON boot SCREEN SYSTEM Display SYSTEM Menu LOCAL RESET RESET data buffers R S Run Stop of analyzer PRINT PRINT a hardcopy of data
156. AL 178 Dual A WEIGHT RESET 24 MAR 97 18 11 15 DATA 32 1 68kHz L 3 Channel 1 of 2 vsTIME v Ld Td 6 2468 58 annuere RT a 24 ct a 1666 VM RutoTH Max 25 5 8 k b k 30 5 Cu e Lea 79 3 v9 4 29 5 2 18 new data INT lthresh hthresh R Prev R Next DATA SOLID DOTTED BOTH 0 0800 15 9 2900 MANUAL The cursors can now be used to read the amplitude and time values of the displayed data To display the broadband level versus time see the section Broadband Level versus Time The amplitude versus time display mode is available for use with the following 1 Normal Leq Max Min and SEL data records autostored By Time using the Standard Analysis mode 2 Intensity and SPL data records autostored By Time using the Intensity Analysis mode In this case the softkeys INTENSITY B and SPL D are used to select which parameter is to be displayed Although data records can be autostored By Time using the Cross Analysis mode the amplitude versus time display mode cannot be used with these records If any of the individual spectra within the autostored record correspond to overloads upon pressing the vsTIME C soft key to obtain a vsTime display the inverse video message OVERLOAD will also appear Also both cursors will con verge together at the position along the horizontal axis corre sponding to the time when the overload condition first occurred during the autostore acquisition sequence O
157. ART S gt AREA S gt EDIT Ci F4 2 C2 F4 2 F3 F2 Figure 20 6 F3 Display 25 MER 15 48 13 Note SPEAKER TEST 9608 MW lt SR LINEAR SINGLE 4 9008 Dual NEAR oe 2 kHz 6 53 57 d 3 6 dB Sie B JOB SPEAKER LOC PART FRONT BB 4 AAA AAA uu AREA 7777777 P dotted crsr SPERKEF BOTH SOLID DOTTED Figure 20 7 F4 Display Ki yon 15 48 46 Power F2 P I F3 NPP F4 FNU note 1 Note SFEHKER TEST 000G R LINEAR ETNGLE 4 a Dual LINEAR oe 28kHz RESET 24 FEB 94 16 53 57 QNNM Gu F IL TER 21 1 25 is LAS vvF4 Non Uniformits Ind d 1 83 206 9000n2 JOB SPEAKER BRE FRONT dotted Ci F4 2 2 422 F3 F2 S JOB SSPBRT S gt AREA S gt EDIT In order to calculate these parameters over the complete set of intensity measurements which represent all the separate area elements contained with all the Parts use the single these parameters should only be used when equal surface area values have been utilized for every intensity measure ment Sound Intensity Measurements 2900 MANUAL Alternate Presentation Format for F F4 and F Sound Intensity Measurements The manner in which these Field Indicators are applied to a sound intensity project requires that further calculations be performed In the following section we present several other parameters which can more directly provide the user with the
158. Aq t nuoJA t 1olsoj nv jesuoe SS V qoer Aq O ep 1 1o so nv eurr q PS nuoJA 9101soan y PAS g HINLL q t 1o so nv eur Aq PAAS nuoJA ejdsiq TVTS wouj V 44 t uonouny 1olsojnv HO UNL 06 92 snu W Aayyos 92 42 FTANDII d 4140 O AV TAA T N AV Tad IN THAT 1 HdO IS JOSS oui I YO 01 T A 10 Aepoq Daa 1 JO La Ho umn Kejap c uo 1snfpy Jossuy 1snfpy Jossip 1snfpy edo S 8301 X 44 f NAONAM 9 I NYALTV Sojeurp1oo MJU Py HHO NO Uonesuodwo j oseqg Sv A Jo Seurl e 2 Io TeToq PAS Qprepueg 33301 Jejourereq xo duio PAS 5 30u A INIL V LOHdS V Pld JON Ke dsiq Ke dsiq JPA IALAID urewoq 2011 129 og wnnoads PS L ST m u NUN Surio LAJ YIM S SATEUV SSO1J WOU nuoJA ASSLT oun LE 8Z snus Aayyos 12 42 FTANDII Ol zH asvq bil zis 1962 M szi o vo alze 4191 las lol laz TV T SISATEUV utooz JO Iendnn A 1007 3 y Aouanbanj 1ejuo3 3 y s skaj pejuozuouy ST 01 21031 nuo old Woy nu yv urooZ LAJ 26 92 snu W Aayyos 82 42 FTANIDIJ ST ST mr Hl9 dXH 1 4 2 lal zaxa a LOVdWI qa avaovaz D IVA 8 ONINNVH V Lg tet t O f 10 t uonouny Sunu8SI AA oun 199 9S 01 Sc 210814 MWIN s yi WO nuoJA SunuSroA JWIL LAJ GZ snu W Aayyos DIZAN S7T t 01 42 91n314 n yq s yi
159. CURSOR will assign the horizontal arrow keys to control the movement of which ever cursor dotted or solid was last active A second press of CURSOR will produce the display of the Cursor Menu shown in Figure 8 1 Cursor Menu If the cursor had already been under control of the horizontal arrow keys then a single press of CURSOR will produce the Cursor Menu Figure 8 1 Cursor Menu 81 APR 12 44 51 100 SPL 3 2000 EXPONENTIAL 178 Dual LINEAR 20 2 20 STOP 81 APR 97 12 44 26 FILTER 852 1 68kHz 125 v Channel 1 of 2 NORMAL d 88 DIFF PHONS 88 7 TACH 6 6 5 4 6 dotted crsr BOTH SOLID Solid and Dotted Cursors Moving Independently Cursor Control There are two cursors available a solid cursor and a dotted cursor To have the horizontal arrow keys control the position of either of these press one of the following keys Softkeys Softkey Functions SOLID O Solid Cursor Control by horizontal arrow keys DOTTED P Dotted Cursor Control by horizontal arrow keys When one of these is selected the message solid crsr or dotted crsr will appear on the lower right of the display to indicate which is active The frequency corresponding to the active cursor position will be displayed on the right of the screen fifth line down just above the line of triangles The amplitude value corresponding to the frequency time posi tion of the active cursor will be displayed on
160. DELAY O Note the message delay X X s on the lower right of the screen indicating that by pressing the horizontal arrow keys the user can set the delay time in seconds as desired To release the horizontal arrow keys from controlling the delay time press CURSOR The use of the 2900 for the measurement of reverberation time is described in detail in Chapter 21 The 2900 also provides a noise burst mode which generates repetitive noise bursts having a 1 millisecond duration The initial burst is resequenced for the subsequent bursts so that the spectral content of each burst is identical The soft keys PINK M and WHITE N are used to select the general spectral shape of the noise burst The bursts are initiated by pressing BURST E which produces the message PINK NOISE IS BURST or WHITE NOISE IS BURST on the upper right of the screen The repetition rate of the burst is set by pressing DELAY O and using the horizontal arrow keys to adjust the rate in seconds as indicated by the message delay XX Xs on the lower right of the screen 4 15 2900 MANUAL Operation of the Signal Generator OPT 11 Required Operational Mode Sine Generator Single Tone 4 16 The OPT 11 Signal Generator provides swept sine with track ing filter and feedback level control dual frequency swept sine and a pulse generator in addition to the pink and white noise provided by the OPT 10 Noise Generator Also there is an autolevel
161. Functions The trigger criterion and amplitude level are selected as follows Signal Level gt Specified Level Press gt I and note the message gt on the upper right of the display Triggering will occur whenever the level in that band equals or exceeds the programmed value Signal Level lt Specified Level Press lt L and note the message lt on the upper right of the display Triggering will occur whenever the level in that band is less than or equal to the trigger level Signal Level Specified Level positive slope Press SLOPE J and note the message T on the upper side of the display Triggering will occur whenever the signal 11 5 2900 MANUAL Selecting the Trigger Level in the specified band has both the trigger level and a positive slope Signal Level Specified Level negative slope Press SLOPE K and note the message J on the right side of the display Triggering will occur whenever the signal in the specified band has both the trigger level and a negative slope From the Frequency Trigger Menu the trigger level set by the user wil always be displayed in decibel format at the top right of the screen as shown in the figure depicting the Fre quency Trigger Menu However when the vertical scale has been set to linear upon pressing level P to input the trigger level it will be seen from the format of the entry field that the trigger level should be input in
162. In cases where the YoUNDER is high and the Lmax levels are much lower than the upper limit of the measurement range the input gain should be increased thus shifting the measurement range downward to include more lower level values Modifying the Parameter Table Values With the Model 2900 set to dual channels mode STAND 2 independent Statistics Tables are generated for each channel Ln statistics and curves can be displayed for only one chan nel at a time The number of the channel whose statistics are being displayed 1 or 2 is displayed on the right of the screen 5th line down to the right of the frequency corre sponding to the cursor position The default selection is channel 1 Pressing the softkey CHANNNEL Ol will toggle this between the two channels as indicated by changes in the 5th line on the right of the screen Hiding a Trace The parameter value n for any trace may be changed in the statistics parameter table by simply addressing the desired trace using the numeric keypad pressing N N and using the horizontal arrow keys in the same manner as originally used to set the statistics parameter table values The entire set of curves will be regenerated and drawn immediately upon changing any parameter value Even though a redraw is in progress the user can continue to use the horizontal arrow keys to modify a parameter Eventually after a series of redraws the display will correspond to the final value ente
163. KER S gt JOB S gt PART S gt AREA S gt EDIT Ci F4 2 2 422 F3 F2 Sound Intensity Measurements At the upper right of the screen will be the power summation the stored intensity spectra are to be summed The format of the search field is as follows JOB_name PART_name AREA_name If names are inserted into the JOB PART and AREA fields in the search field then all stored spectra which have these same three labels can be summed together to produce a sin gle power spectrum Since each measurement is unique there should not be more than one stored spectrum with the same JOB PART and AREA labels In that case the dis played power spectrum will be for a single measurement 20 15 2900 MANUAL However if the user specifies names for JOB and PART only leaving in the AREA field for example and PART labels in this example FAN and FRONT regard less of the AREA labels will be summed and the resulting power spectrum displayed If only a name for JOB is specified for example based upon all the spectra having that specified JOB label in this example FAN regardless of their PART and AREA labels Manually Entering Labels into the Search Field Entering Labels by Recalling Spectra Names can be typed directly into the search field by pressing the key S gt EDIT L This will result in a flashing cursor below the first character of the JOB field Use the alphanu meric keypad and the horizontal arrow keys to
164. L The I O Channel 1 has an alternative function as a 4 27 2900 MANUAL counter such that is can measure the frequency of an input pulse train A typical application is with a wind speed moni tor which produces pulses as it rotates Frequency Domain Interface Trigger of UO Channel 3 It is possible to trigger the analyzer into the Run state based on the level of the input signal in a specified frequency band or the sum band or one of the sound level meter parame ters as described in Chapter 11 This is referred to as the Frequency Domain Trigger Function This same criteria can be used to change the state of the I O Channel 3 from High to Low independent of whether the Fre quency Domain Trigger Function controlling the Run state is active or not We shall refer to this as the Frequency Domain Interface Trigger By monitoring the state of I O Channel 3 the user can detect the satisfaction of the trigger criteria by the change of state from High to Low It is the responsibility of the user however to provide the hardware necessary to invoke the desired action based upon the detection of this change of state The desired frequency domain trigger criteria is established from the Frequency Trigger Menu exactly as described in Chapter 11 After the trigger criteria has been set if this is not to be used to trigger the Run state i e the frequency domain trigger function is to be inactive be sure to press OFF O before exit
165. L 6 6068 EXPONENTIAL 178 PREAMP 188 Hz HP STOP 02 JAN 90 5 11 28 FILTER 829 800 Hz 125 v Channel 1 of 2 NORMAL dz 48 6 A 56 4 PHONS 70 8 TRCH 5184 6 SPEED 4 6 dotted crsr As described in the preceding section the fundamental read out of the Tach and Speed is in units of frequency represent ing on the number of pulses per second seen at the two inputs The scaling is done to convert these frequencies to alternative units such as RPM Tach or Miles Hour Speed In the calibration method the user specifies a value of Tach or Speed or both which he wishes the 2900 to display at the instant he manually initiates the calibration procedure The scaling is then automatically performed such that the fre quency measured at the input s will produce the specified value s on the screen For example suppose the user wishes to drive a vehicle at a speed of 50 miles hour as indicated by the speedometer and 16 7 2900 MANUAL Trigger Smoothing perform the Speed calibration at that moment He would press C speed B and in response to the message ENTER SPEED on the upper right of the screen type 50 0 using the keypad and press EXIT Now whenever the 2900 sees a sequence of two presses of the R S key the Speed scaling will be set such that the display readout of Speed is 50 He will now press R S once to begin the analysis and drive the vehi cle until a speedometer reading of 50 miles hour is obtained At this point th
166. LEQ Weight SETUP FILES AUTOSTR Since the Model 2900 performs a single channel frequency analysis function simultaneous with sound level meter mea surements a frequency spectrum of the acoustic signal is presented on the left side of the screen at the same time the sound level is being displayed Although different values of analog highpass and lowpass filters may be inserted in the signal path of the frequency analysis function the frequency spectrum display presented in the SLM Mode will always rep resent the frequency range 6 3 Hz 20 kHz As explained earlier in this chapter the weighting functions for the sound level meter and the frequency analysis func tions can be independently selected from the Weight Menu In most cases the user will select the frequency analysis weighting from among the four linear weightings with differ ent combinations of highpass and lowpass filters 1 Hz 20 kHz 1 Hz 10 kHz 20 Hz 20 kHz and 20 Hz 10 kHz There is tremendous power and flexibility built into the fre quency analysis capability of the Model 2900 The remaining chapters of this manual are largely devoted to describing its use as a frequency analyzer It is recommended that the user read these chapters carefully to fully appreciate the features provided In the remainder of this chapter we seek only to provide suf ficient explanation of the frequency analysis function to per mit the user to properly calibrate the instrument for so
167. Larson Davis Laboratories LD LARSON DAVIS LABORATORIES 2900 User Manual 5 xx Code 1681 W 820 N Provo UT 84601 November 26 1997 2900 Manual LarsonsDavis Laboratories Larson Davis Incorporated 1681 VVest 820 North Provo Utah 84601 801 375 0177 Copyright Copyright 1993 by Larson Davis Incorporated This man ual and the hardware described in it are copyrighted with all rights reserved The manual may not be copied in whole or in part for any use without prior written consent of Lar soneDavis Inc Trademarks MS DOS is a registered trademark of Microsoft Corp Warranty Larson Davis warrants this product to be free from defects in material and workmanship for two years from the date of orig inal purchase During the first year of the warranty period LarsoneDavis will repair or at its option replace any defective component s without charge for parts or labor During the second year of the warranty period there will be no charge for replacement parts For customers within the continental United States service is provided for instruments returned freight prepaid to an autho rized service center The product will be returned freight pre paid For international customers please contact your exclusive Lar son Davis representative for details on local service and ship ping arrangements The Larson Davis warranty applies only to products manufac tured by LarsoneDavis Inc and does not includ
168. OdNI f NHD os t ISION 1 Of H sse eun pue simp SSEdALO T SSEdUSTH So euy Joje1ouor euSIg S110q 01dQ ure1504q Teuondo sour aegis Suruonrpuo reusis syndur dmesg JO SION ONUOZ PAS SSe 199 9S L S m31 01 42 amgu cc INST cc m r 9 Z 1 G GZ m n Z SZ m n D WALT 3 SLINA H ALISNALNI dl SSOM DI AAVANVIS 8 V INTS V st 4 t t t t SUL NH js SHUN PAPS uonouny sisAfeuy VPS c 101 s ouueyo Jo JoqunN VAS WALSAS 552 4 nuoJA ur9 s GZ SNUSW Aoyyos 2 92 34 914 ST ST am 11 92 91 42 omsrT d ALSOLAV Lo SAT qoe q eurr q o101s01ny dm nu9JA s li ss222y 11 92 or SZ andi 0T ST ONT N anLas IN 102194 oat Mastan MIS 1 Mots H MLOHLAQ sdm Sion b Ke dsiq o Jojoure1eq IozKTeu noun T ZATEUV uv odk AUS pue 19 9 A 9 9 punog Tojoure req A PUNOS PAPS 10 SILA Sopeuy PS Dame FC ONS D sou 141 AV IdSId H as a xvW DININ 161 b v TVINAON PIPL 90N Keyds q ds xyy pue Jejourereq Ae dsiq AS npa ye r nuo JA Sonsnejg ssoooe pue SunusroA TENSIA PAS 1 67 NUN WALSAS WOI nuo V WN IS t 95Z SNUSW Aoyyos CG 34 91 N 01 02 IN XOT T T 107 02 al 407 1 t t t t uon unH WIS 10 Sunusr AA 199 9S 4 401 02 A 01 1 q 407 02 O 407 1 uonouny sisApeuy SunusroA 129 og T SZ OMF n yy JTS t
169. Or one may wish to generate curves dur ing an automobile acceleration and be certain that the curves will not reverse back toward the left when the automobile decelerates after the test is completed Setting the slope parameter to would provide the desired results 17 6 New data points which could be used by the graphics routine are generated every time a new spectrum is produced by the processor To limit the density of these points on the screen new points for each curve are only generated whenever the data satisfies user selected criteria for display Graphically in order to avoid having a large number of points for each curve plotted very close together when either the level values or the RPM Speed values or both are not chang ing rapidly the user establishes a minimum variation of each one of which must be exceeded if a new point is to be drawn For example if the minimum level variation is 2 0 dB and the minimum RPM variation is 10 RPM then a new point will not be plotted until the new data point has either a level 2 0 dB or more above or below the point plotted previously for that curve or an RPM value 10 or more above or below the previously plotted point The incremental RPM Speed value required for the genera tion of a new point is determined by the value of t Amin and s Amin as set from the Tachset Menu In addition to mini mize the possibility that a sudden spike in the value of RPM Speed might create disconti
170. RT60 data indicating that if the RT60 recall operation is continued this newly recalled data will take the place of the data previously in the RT60 register To continue press YES A To abort the recall and save the data which is presently in the RT60 register press NO C Upon continuing the recall the message RECALL RT60 N on the upper right of the screen will indicate that the Nth RT60 record has been recalled from the active memory and placed in the RT60 register which is now being displayed The message recall data on the lower right of the screen indicates that the horizontal arrow keys are assigned to recall RT60 records Press the horizontal arrow keys to recall and display the particular RT60 record which is desired Press CURSOR to reassign the horizontal arrow keys so they will no longer control the record recall function Room Acoustics Measurements 21 12 Airborne sound transmission loss is a measure of the acous tical isolation provided between adjacent rooms or spaces by walls or partition elements such as floor ceiling assemblies doors windows or roofs It is used to estimate the level of noise which will exist in a room containing no sources of noise due to the presence of a noise source within an adja cent room Impact isolation is a measure of the impact sound insulation of a floor ceiling assembly and associated supporting struc tures It is used to estimate the level of noise which will exist
171. S7 8 ATA OFF IMP INITIRL SLOW FAST ULSE LEQ STAT SETUP FILES AUTOSTR In this mode the following parameters are measured simul taneously Sound Pressure Level Ly using Slow Weighting Maximum and Minimum values of Slow Lp since last reset Sound Pressure Level Ly using Fast Weighting Maximum and Minimum values of Fast L since last reset Sound Pressure Level Lp using Impulse Weighting Maximum and Minimum values of Impulse Lp since last reset Equivalent continuous Sound Pressure Level Leg Single Event Level SEL Peak Sound Pressure Level Lyeax Slow Fast and Impulse sound pressure levels are indicated by the bar graphs on the left of the display Digital values of the measured parameters are displayed on the lower right of the display Select the parameters to be displayed using the following keys Softkeys Softkey Functions SLOW I Lp Slow with Max and Min values FAST J Lp FAST with Max and Min values IMPULSE K Impulse with Max and Min values LEQ L Leg SEL Lpeak eq Note that the cursor is inactive in the VVDR SLM function as indicated by the message OFF on the lovver right side of the screen Selecting the Microphone Input and the Bias Voltage 3 24 The active microphone input is shown on the right of the dis play as Input 1 or Input 2 The default setting of the instrument when delivered from the factory is Input 1 cor responding t
172. SHIFT hardkey EXIT STORE STORE displayed data block RECALL CLEAR editing a note AUTO Activate input AUTOranging CH 1 CH 2 SLM Brings the Wide Dynamic Range Sound Level Meter WDRSLM Menu to the display of the 2900 for setup and data display With the exception of the hardkeys listed above the remain ing hardkeys on the front panel of the Model 2900 are imprinted with two different ASCII characters number letter character or space One role of these keys is to input alpha numeric data when naming data files and when writing mes sages into the data block note fields previous to storage Whenever such a data field is open at the upper right of the 1 3 2900 MANUAL Softkeys display indicating that alphanumeric characters are to be entered these keys will perform that function When the upper character on the key is desired the SHIFT hardkey must be pressed prior to pressing the key itself Figure 1 3 Softkeys OFF Q s l Uu V w x ON A E F G H M l SCREEN LARSON DAVIS MODEL SYSTEM 2900 PRINT RESET SHIFT The hardkeys aligned horizontally above and below the dis play as illustrated above play a major role in the operation of the 2900 When the instrument is in operation one of a variety of different softkey Menus will be displayed on the screen which will place a series of alphanumeric labels directly below upper row and above lower row these keys
173. Speed The message dis played on the screen indicates the start value of RPM or Speed over which the averaging is to be done indicated by the s the end value indicated by the el and the incre mental value The default values of s e and delta which appear on the screen will correspond to the RPM or Speed range and incremental value utilized at the time of data acquisition The user is not constrained to use these default values for the averaging the values in the three display fields can be edited by using the numeric keypad and the horizon tal arrow keys and pressing EXIT In each autostored record there is a range of RPM or Speed values over which there is one spectrum per channel stored at approximately equal intervals In general neither the lower or upper limits of the range nor the interval sizes themselves will be exactly the same for different records even though they may have been captured using the same instrument setup When specifying the range for the averaging it is rec ommended that the start and end values of RPM or Speed be chosen such that they will fall within the range of values cov ered by each of the autostored records If not the actual range of RPM or Speed values for which data will be produced in the averaged record will be reduced such that all of the individual records have data points within that range When the averaging is performed extrapolation between the actual RPM or speed values in th
174. T Averaging Time sec From this the statistical accuracy of the measurement can be estimated as follows There is a 68 396 probability that the measured value is within te of the statistically correct value a 95 596 probability that it is within 2e of the correct value and a 99 796 proba bility that it is within 3e of the correct value 5 5 2900 MANUAL Linear Time Averaging Constant Confidence Time Averaging Spectrum Averaging 5 6 Example We are performing an 800 line FFT measurement on a random signal using a frequency range of O to 10 kHz and wish to have 68 396 confidence that the result is within 0 5 dB of the statistically correct value What value of averag ing time should we select B 10 000 Hz 800 12 5 Hz 1 434 1 434Y ra nalts If the frequency range were 0 500 Hz an equally accurate measurement would require an averaging time of 120s When using the FFT measurement mode of the instrument the bandwidths are all equal and therefore the averaging time required for equal accuracy in each bandwidth will be the same Therefore a linear average is generally selected when measuring stationary signals with constant bandwidth filters The linear average for each filter is calculated by divid ing the sum of the individually sampled values in linear units by the number of samples When using constant percentage bandwidth filters such as 1 1 and 1 3 octave bands the bandwidths become narrow
175. TNSTY SPL and P VELOC displays only represent the total energy between the high pass and low pass filters denoted by the summation symbol X beneath and the total A weighted energy between the high pass and low pass filters denoted by the symbol A beneath Either of these values may be displayed digitally At any par ticular time the digital indication on the right of the screen alongside the indication of the cursor amplitude will be assigned to represent one of these two as indicated by the symbol A or x alongside the corresponding digital value Pressing the softkey SUM E in the Display Menu will toggle this display between these two Sound Intensity Measurements In the intensity mode the default frequency display range is 25 Hz 10 kHz Depending upon the nature of the sound source being measured there may be very little sound power emitted above 5 kHz And unless the 50 mm spacer is being used the sound intensity data measured at the lower fre quencies will be invalid In these instances the horizontal 20 11 2900 MANUAL Reducing the Amplitude Display Range display scaling can be changed to decrease the display range and increase the resolution as described in Chapter 19 sec tion Control of Horizontal Display For example if the cur sor is placed at 1 25 kHz and the horizontal scaling changed to 2 the frequency display range will be 315 Hz 5 kHz Due to the relatively small valid dynamic
176. TZ 9 cc omsrT SI SZ omar d ALSOLAV O SAT N dn Las yoeLAqs owiILAq nuoJA 591 sdnjos Joz euv a10 0 NY dm SS OV 829 9 1 02 52 90314 f NYONMA I NHAELTV H MLOHLAQ JJO UO oseug opniruse q Jojoure1eq pue dAL uonesuadwoj JojoureJeqd SUTSEH AV VAS Qprepueg 33301 xo duio 129 og 5 91ou a HSWHANI l dlwHHOO DIAAAIX laldaasd V OHasv PIOI 910N Jrojourereq Ae dstq 3 y s UA TI el SINI pue SSO 80 9 5 INFL I GZ ANFIA n yy WI SAS WOUJ JIXA 90112111 YUM NUON S SATEUV SSOID 8 Gc snue N Aoyyos 1 86 34 91 ST ST AMSHA 11 42 OI GZAMBY I ANBA 9T ST ANSI T NH LJTT d ALSOLAV O ST TIJ N anLas W ORIL L T SVITV yoeLAqsoun LAq nud STL sdm 1ozA puy umjoedg porary Aejdsiq aroysoiny dm SS V eLoY 21018 T SSLHL oun dm Ho uo SI LI 3uiserfe nuy 3 3301 OZ S7 bil gt d r 1 us H K Zb 5 t Te n3uvjoos Ie od Jo uo oseuq opniruSv A lojoureIeq PRIH 930N 5 uonesuodwo JO 8801 189 pue od T UPAMA a3eup100J 159 9S Qprepueg o 830 Iojoure1eq Xo dwoj 1S SUTSET AV IS HIWX LSdHO q ASATANI 9 ASTAJINI g TAAOD D V RRIOD V 4 AV IdSIG A HINLL d MAHO D WHd X g LOHdS O V LOHdS V 1 t t t I y Aeydsiq seo 1emoT pue reddn 19J ouupIoq Ae dsiq 129 og SUNIY LAA pu SSOM Sunoojes Jaye T Z m r n fy u
177. Tach fre quency units as described in the preceding examples The format is exponential X XXX E XX s scale I This is the user defined scale factor which con verts the pulse rate to the desired Speed fre quency units as described in the preceding examples The format is exponential X XXX E XX Whenever the analyzer is running the scaled values of TACH and SPEED are displayed in real time on the lower right of the screen 16 4 The purpose of the Autostore byTach function is so that a series of spectra can be stored automatically at user defined intervals of RPM and or Speed as a vehicle or machine is accelerating or decelerating The intervals for RPM and Speed are set independently by the user who can also select a slope or for the interval sequence The autostorage function is independent of the data acquisi tion As an analyzer the 2900 will be operating in a normal manner during an autostore sequence producing new spec tra at regular intervals of time based on the selection of the analysis type and the averaging method and time See the preceding chapter for more information on averaging time considerations As each spectrum is produced from the pro cessor the values of TACH and SPEED are looked at to deter mine if a spectrum storage is called for by either of these parameters If so the data block in the buffer is stored along with the current values of TACH and SPEED if not the sys tem waits for
178. The user would use the Units Menu to name the units IN S invoke a single integration to obtain velocity from acceleration and then use the calibration to obtain the proper scaling The result would be a display of a velocity spectrum in inch second units as a function of frequency Let us further suppose that this measurement is stored and in the meantime the units are changed such that there is no integration or differentiation and the scaling is changed Upon recall the spectrum which will be seen will be in the form of acceleration versus frequency and the magnitude will be whatever corresponds to the presently active units calibra 9 7 2900 MANUAL Storage of Units Data tion To obtain the results which had previously been dis played at the time of the measurement the same Units setup must be employed Thus it is recommended that the Units be stored in addition to the measured data so they can be recalled and used when the data are recalled and displayed Recall of Units Data To store the complete set of Units softkeys which have been created press STORE The message STORE Units Data N on the upper right of the screen indicates that this set of Units softkeys have been stored to the active memory files as the Nth record of Type Units Data 9 8 To recall a set of Units Data from the active memory file press RECALL The message Over Write ALL UNIT data on the upper right of the screen indicates that t
179. Then while still in the Recall Menu press PRINT which will display the complete Print Menu as shown in Figure 23 1 Print Menu including the softkey BLOCK D Pressing BLOCK D will then display the Block Print Menu shown in Figure 23 2 Block Print Menu and the message Pick data to block print on the upper right of the screen Figure 23 2 Block Print Menu 17 DV 15 41 33 screen table all PICK DRTR TO BLOCK PRINT Hote 16 4925 EXPONENTIAL z Input 1 LINEAR 280Hz 28kHz STOP 17 NOU 93 15 33 54 FILTER 854 2 580kHz 125 v Channel 1 of 1 NORMAL A 63 7 d PHONS 78 1 TRCH 8 80 SPEED 4 8 dotted crsr TEST 1 user Select among the options by pressing one of the following screen A table B or all C The message RECORD A XXXX YYYY on the upper right of the screen will indicate the range of record numbers of that type which are presently stored in the active file Use the key pad to edit these numbers such that they represent the range of sequential records which are to be printed and press EXIT To abort a printout in progress press abort P 2900 Printing Data Screen Displays and Tables 23 3 2900 MANUAL Custom Printouts Accessing the Custom Printout Module When using either laser or Epson compatible printers you can generate and store up to eight custom printout formats capable of presenting the displayed data block using a scal able graph size in either portrait or l
180. Weighting has been selected to be other than No Weighting NO WGT the displayed values will be different from the measured values by the amount of the selected weighting function The display weighted values are printed under the column labeled DISP dB Printing LCD Screen Display and Data Table Print to Screen List Function To obtain a printout of both the display presently on the LCD screen and a data table representing the data being dis played press all C To print a Data Table to the screen instead of a printer press List D which will provide the user with softkeys to select the desired format of the listing Left Right and Wrapped 2900 Printing Data Screen Displays and Tables 2900 MANUAL Aborting a Printout To abort a printout in progress of LCD screen data press abort P Ejecting a Sheet of Paper or Making a Form Feed To eject a single sheet of paper from the printer or to create a form feed press eject N Printing the Color Monitor Display To obtain a black and white printout of the display shown on the optional Model 2500 Color Video Adaptor press video E Block Printing of Stored Data Records The block print function permits the Model 2900 to recall and print a sequence of stored data records of the same data type To do this first recall a record of the type which is to be printed The softkey BLOCK D will not appear until after a stored record has been recalled
181. Zwicker Loudness on the upper left only appear when 1 3 octave filters are active The use of Zwicker Loudness function is discussed in Chap ter 6 Analysis Menus Selection of Measurement and Display Parameters The A and C weighting curves are defined by the sound level meter standards IEC 651 1979 and ANSI S1 4 1983 The user can select to weight the displayed spectrum by positive or negative versions of either the A or the C curve When recording environmental noise using a sound level meter with the AC output connected to a recorder some users like to A or C weight the AC output This tends to increase the mea surement range of the recording because environmental noise tends to have large levels at frequencies below the human hearing range which are not of interest When playing back such a recording for analysis the use of the negative weightings will produce an unweighted spectrum display In other applications such as the analysis of hand arm or whole body vibration users wish to weight the spectrum by a user defined weighting spectrum The procedure for setting up and storing user defined weightings is described in the following section The default state is No Weighting Digital Display including Broadband Acoustic Frequency Weighting User defined Frequency Weighting and Integration of FFT Spectra 10 3 2900 MANUAL The desired digital display weighting is selected as follows Softkeys Softkey Functions NO WGT I
182. a 1 1 octave bandwidth format from the Rooms Menu press NR B 21 22 The RC Noise Rating Procedure is presented in the ANSI Standard ANSI S12 2 1995 Criteria for Evaluating Room Noise In addition to producing a single number rating of the background steady background noise the quality of the spec tra is described in terms of one or more of the following Neutral Spectrum N Rumbly Spectrum R Hissy Spectrum H Acoustically Induced Perceptible Vibration Va and or Vb The spectrum measurement must use either the 1 Hz 10 kHz or the 1 Hz 20 kHz frequency range to have the required low frequency bands As with the NC and NR rating procedures the steady background noise spectrum is displayed in the 1 1 octave bandwidths format Then from the Rooms Menu press RC C Room Acoustics Measurements p Classification Class Lines Optional Feature General Explanation of the Concept Classification Class Lines Optional Feature The class lines function of the analyzer is a graphical tech nique for classifying a spectrum or spectra in terms of its interaction with a family or families of user defined curves In this section we describe the use of class lines as applied to spectral data displayed on the analyzer in the amplitude ver sus frequency format The class lines function can also be employed with spectra order data displayed in the multi line vsRPM Speed format This is described in a later section of
183. a as well in which case it is not necessary to use the meter2 M key to input a value of surface area 20 8 As explained in the preceding paragraph one generally asso ciates a value of surface area with the measurement of an acoustic intensity spectrum in order that the acoustic power flowing through that surface may be calculated and dis played Furthermore as described in the introduction to this chap ter it is especially convenient to build upon these measure ments and areas a structure which permits the summation of the acoustic power over logical groups of areas which are meaningful in terms of the test object itself In the 2900 we do this by permitting the user to define an area label for each measurement in addition to a numerical value of surface area We call this the AREA label We may then decide that a designated number of AREAs are to make up a larger group ing which we label as a PART Finally we may decide that a designated number of these PARTs are to make up an even larger grouping which we label as a JOB It is quite common in acoustic power measurements to imag ine a rectangular envelope in space enclosing a test object which is placed on the ground We might choose to call the entire surface by the JOB label SOURCE The well defined surfaces making up the totality of this envelope could be assigned PART labels TOP FRONT REAR LEFT and RIGHT If we choose to subdivide each of these PARTS into four sepa
184. a corresponding change in the SLM weighting displayed at the lower right of the screen The weightings represented by the softkeys above the screen are for the frequency analysis function as seen by the fact that a change of this selection is reflected by a corresponding change in the frequency analysis weighting displayed on the right side of the screen third line down For the linear weightings the upper frequency of the spec trum display will always be the same as the upper frequency selected for the analysis For A and C weighting the upper frequency will be 20 kHz However the value of the lower fre quency used for the spectrum display can be selected between two different values as follows Weighting Lower Frequency Options Hz A Weight 0 8 25 C Weight 0 8 25 Linear 1 10 kHz 0 8 6 3 Linear 1 20 kHz 0 8 6 3 Linear 20 10 kHz 0 8 25 Linear 20 20 kHz 0 8 25 Upon selecting the frequency range the higher of the two optional values of lower frequency will be used in the display Repeated presses of the softkey WIDE H will toggle the lower frequency value between the two optional values A two minute warm up time should be allowed before valid readings of Sound Level can be made Alignment of the Microphone Boom and Microphone Preamplifier Microphone Boom Alignment Sound Level Meter Operating Modes The microphone boom fixation is designed such that the main boom element extends outward fr
185. ach multiple of the reference frequency to determine the amplitude of the higher orders As far as setting up the 2900 to perform Post process order tracking the user proceeds as explained above in the sec tions describing Real time vsRPM Graphics and vsRPM Graphics from byTach autostored data The main difference is that the parameter to be setup in the last column for each trace will be ORDER instead of FREQUENCY If the vsRPM Graphics Menu is indicating a softkey FREQ P press B FREQ L to change FREQ to ORDER When setting this parameter pressing the horizontal arrow keys will page through a sequence of order numbers instead of frequency 17 11 2900 MANUAL Peak Hunt Procedure 17 12 In cases where the rate of change of the reference signal is high the time delay inherent in the digital filters may cause the peaks associated with the different orders to fall into one of the frequency bands adjacent to the one where the calcula tion predicts it ought to be found Fortunately in many cases where order analysis is used most of the dominant compo nents are order related In such instances the use of a peak hunting routine can correct this problem From the vsRPM Graphics Menu press WIDTH H which will produce the Peak Hunt Menu shown in Figure 17 3 Peak Hunt and Bandwidth Averaging Menu Figure 17 3 Peak Hunt and Bandwidth Averaging Menu 27 JAN 23 59 42 Pick 1 Pick 3 Pick Pick 7 118 ess m m sm sm
186. ade while in the Class Lines Menu exit to either the System Menu or the Main Menu using the EXIT hardkey From there either perform a new measurement or recall and keep a previously stored mea surement and access the Class Lines Menu by pressing CLASS H if in the System Menu or the sequence SYSTEM CLASS H if in the Main Menu Perform the judgement by pressing a JUDGE N which will produce a display similar to that shown in Figure 22 9 Automatic Judgement Exam ple Figure 22 9 Automatic Judgement Example 29 DEC 17 84 19 t 118 d C s Judgment Las CURUS 1 CURUS 3 CURUS 2 CURUS 4 22 9 2900 MANUAL In the table displayed on the right of the screen for each channel there will be a number corresponding to each of the assigned class line families indicating the classification of that spectrum with respect to that particular family of class lines In this example note that the family CURVS 1 is in the Max mode while the family CURVS 2 is in the Min mode An example of this combination of modes might be where the most desireable result is that the spectrum lie completely between the two families and the larger the variation in either the upward or downward direction the less acceptable the result Even though only one spectrum can be displayed at a time channel 1 or channel 2 the judgement is made for both channels at the same time If just previous to the judgement the highlighted line in the Assig
187. ady contains val ues pressing the key Auto AV F instead of Auto RE E will cause the RT60 values automatically measured at each frequency to be averaged with the value or values already contained in the RT60 register rather than to replace them Using the vsTime autostore synchronized with the noise gen erator it is easy to rapidly measure multiple decays each of which will be stored in a separate vsTime record Note that the softkeys Auto RE E and Auto A F are available in the vsTime Menu as well as the RT60 Menu When the data are well behaved it is more convenient and rapid to do the curve fitting from the RT60 Menu because the A Prev K and A Next L keys used for moving between different vsTime autostored blocks are in that Menu Using the automatic 21 9 2900 MANUAL curve fit technique the user would recall the first vsTime record and determine a set of RT60 values using the key Auto RE E Then upon pressing A Next L the next vsTime record will be recalled Pressing Auto Av F will then produce a second set of RT60 values based on the second vsTime decay record and these would be averaged with the first set of RT60 values already in the RT60 register Continu ing in this manner each of the vsTime records would be sequentially recalled and automatic curve fit performed to produce RT60 values based on the average of a number of separate decay measurements At any time during the recall and curvefitting process
188. all other record numbers of the same data type click on the center mouse button to open the Global Configuration Window and click on the left or right arrow keys to page backwards or forwards through the stored data records just as is done when operating the instrument from the front panel The message on the upper right of the display will reflect the change in record number and note field if any as different record numbers are recalled When a recall has been performed the labels of two of these windows will change to EXIT and KEEP Clicking on EXIT will return the analyzer to the state which was active previ ous to the recall operation causing the recalled data to dis appear from the display Clicking on KEEP will change the setup of the 2900 to that used to make the displayed mea surement and the recalled data will remain on the display Recalling Setups Key macros can be run from the color display by clicking upon the window MACROS on the upper right of the screen A window will open permitting the user to select from one of ten previously defined and stored macros The definition and storage of the macros from the color monitor requires the use of the Control Window To recall a previously defined and stored instrument setup click the mouse on the window SETUPS on the upper right of the display A window will open permitting the user to select one of eight previously defined named and stored setups Use of External Co
189. along with the flashing window cur sor indicated that a numerical input is required Type in the number and press EXIT Note that the value last entered for Delta Time is already displayed so if the same value is desired simply press EXIT immediately Next set the total time period over which the automatic stor age is to continue by pressing endstor D which will produce the message END TIME XXXXXX XXXX Type a value using the numerical keypad and press EXIT As for the Delta Time the data field for the entry of the END TIME value will already contain the value last entered so if that same value is desired simply press EXIT Delta Time Limitations The time required to transfer the data to memory during the autostore sequence places some limitations on the minimum value which can be set for the DELTA TIME This is a func tion of the bandwidth and the number of channels as indi cated below If the user selects a value less than the minimum permitted value the DELTA TIME will default to the minimum value This is easily demonstrated by inputting a zero value for this parameter then pressing the delta C softkey and noting the value which is displayed in the para meter input field on the upper right of the display Table 15 1 Minimum DELTA Time milliseconds using Octave and Fractional Octave Bandwidths Filter Bandwidth octaves 1 1 1 3 if Channels 1 2 5 2 5 2 5 0 5 0 Table 15 2 Min
190. alue of RPM the curves would be drawn on the display from left to right as the test proceeds Only spectra measured in the Standard Analysis Mode can be handled in this manner The data corresponding to these curves can be stored to memory for subsequent recall viewing and printing The spectra may be autostored in the byTach mode at the same time but this is not required 2 vsRPM Graphics from byTach Autostored Records When the byTACH autostore capability have previously been utilized to measure and store Standard and Intensity spectra as a function of RPM Speed the vsRPM Graphics can be used in conjunction with the stored data to gener ate sets of curves as a function of RPM or Speed Each set of curves generated by this procedure can be stored to memory for subsequent recall viewing and printing Note that the Real time vsRPM display mode can be active dur ing a test in which the byTACH autostorage procedure is 1741 2900 MANUAL Real time vsRPM Graphics used to store data as a function of RPM Speed During the test the data can be observed in real time on the screen as the test proceeds permitting the test engineer to verify that the test has proceeded as desired Color Monitor Pen Format The first step in performing Real time vsRPM Graphics is to setup the 2900 to the desired measurement configuration including number of channels analysis type filter type aver aging type and time etc The 2900 must be in the St
191. alues An example is the analog meter The position of the needle follows the output of the RC averaging circuit When the averaging time is small the needle may oscillate very rapidly in response to a varying signal The observer can see the short term variation of the signal but the averaging time may be too short to provide a readable value With a longer aver aging time a smaller less rapid needle variation occurs pro viding a more readable number Exponential averaging is frequently used when one wishes to visually observe on the display screen the time dependent behavior of the spectrum of a signal The averaging time is adjusted until the short term variations are minimized yet 2900 the response is still sufficiently rapid to follow the long term time variation of the spectrum Even with steady sig nals the user will frequently use exponential averaging to ini tially observe the signal and set the input attenuators for a near full scale signal level without overloads Then he will switch to linear averaging to perform the analysis more accu rately Selection of Averaging Parameters 6 Analysis Menus Selection Of Measurement And Display Parameters The parameters which can be measured and displayed by the Model 2900 depend upon which Analysis mode has been selected by the user from the system menu Standard Analysis Spectral data are measured for each of the input channels but no cross channel parameters are meas
192. alysis the user may select to use either of the two input connectors by using the hardkeys CHL and CH2 The connector closest to the right side of the instrument represents channel 1 2900 Instrument Setup Via The System Menu Cross Mode Intensity Mode Frequency Range Considerations 2900 MANUAL For dual channel Standard Analysis the two input connec tors are used simultaneously to represent channels 1 and 2 with the one closest to the right side of the instrument being channel 1 The results of this measurement are comparable to having a single channel analyzer connected to each of the inputs since no cross channel parameters are measured In the Cross Mode of operation with FFT filtering the follow ing data are measured and displayed Autospectra Cross Spectra Auto Correlation Cross Correlation Transfer Func tions 3 forms Impulse Response Coherence Coherent Out put Power Time Waveforms and Weighted Time Waveforms In the Cross Mode of operation with Octave filtering the fol lowing data are measured and displayed Autospectra Cross Spectra Transfer Functions three forms Coherence and Coherent Output Power Used in the Intensity Analysis mode with a LarsoneDavis Acoustic Intensity Probe the Model 2900 will measure and display Acoustic Intensity Particle Velocity Sound Pressure Level and Quality Intensity Pressure The format of the data presentation in the frequency domain will be the same as the fi
193. ameters 5 1 2900 MANUAL Select the desired averaging method by pressing one of the following Softkeys LIN S A LIN R B EXP C BT EXP D BT LIN E Averaging Type FFT Filters Softkey Functions Linear Single seconds Linear Repeat seconds Exponential seconds Constant Confidence with Exponential Averag ing Constant Confidence with Linear Averaging When FFT filtering has been selected pressing DETECTR H will cause the Menu illustrated in Figure 5 2 FFT Averaging Type Menu to Figure 5 2 FFT 81 APR 12 38 55 1168 be displayed Averaging Type Menu LIN S LIN R EXP EXPO N COUNT S COUNT R RU TIME SPL 2 72080 EXPONENTIAL Dual LINEAR 28Hz 28kHz STOP l APR 97 12 36 31 FREQ B bBOBOKHZ Happ v Channel 1 of 2 NORMAL d 39 8 2 86 7 TACH 6 6 SPEED 4 6 dotted crsr Select the desired averaging method by pressing one of the following Softkeys Softkey Functions LIN S A LIN R B EXP C EXPO N D COUNTS E COUNT R F COUNT M G Linear Single seconds Linear Repeat seconds Exponential seconds Exponential Averaging based on number of spectra spectra Spectral Single spectra Spectral Repeat spectra Spectral Manual Accept With Linear Single averaging continues until the specified averaging time is reached then averaging is stopped With Linear Repeat after the averaging time is reached the detector is reset and the a
194. an kuki nen a ha entres enn sinet 3 23 Selecting the Microphone Input and the Bias 3 24 Selecting the Frequency Weighting sess 3 25 Chapter 4 2900 Instrument Setup Via The System Menu 4 1 SYSTEM EEN 4 1 Accessing the System Menu n innen nnn entrent ense en 4 2 Selection of Analysis Tvpe entente nnns tnnt enisi nnns 4 2 Standard ioo RE 4 2 Gross Mode EET 4 3 Intensity MOGO teet ereptus IM dete ES 4 3 Frequency Range Considerations sss 4 3 Octave Frequency Analyse 4 3 FFT Frequency 555 u Su u aqu esee e iai e A AN akawa nnns 4 3 Selection of Filter Jupe u tiyo Rr nte itd nb e ae tete eeu 4 4 Accessing the Filter Men 4 4 Selection of Octave and Fractional Octave 4 5 Selection of FFT Filtering a nnne nnns ertet nnns 4 6 Selection of Number of Lines see aran 4 7 Selection of Time Weighting Window sse nnne nnne 4 7 Selection of Baseband Full Scale Frequency Base Bd 4 9 FFT Zoom Analysis to Increase Frequency Hesoluton esee 4 9 Limitation on Zoom a a a E eene 4 11 Printing FFT Data in Tabular Format 4 12 Accessirig Input Menu niis e ete gei e Pe tena exte Ee edu 4 12 Setting the Microphone Bias Voltage nennen nnn
195. and store them along with the data block The softkey note G which is used for the annotation feature is found in nearly all the Menus of the 2900 To access the Note Menu shown in Figure 14 1 Note Menu press note G If there was already a note attached to the data block displayed when the key was pressed it will now be displayed on the screen along with the number of characters of the note on the upper right of the display Otherwise the note field will be blank Figure 14 1 Note Menu 82 JAN 86 38 22 R B F G H CURRENT NOTE SIZE 23 KEYS CEXITJ done lt gt J delete RANGE newl ine SPL 6 9608 EXAMPLE OF A NOTE INPUT EXPONENTIAL 176 PREAMP LINERR 18 20kHz ET 02 JAN 96 66 28 48 v Channel 1 of 2 NORMAL de 33 7 E 48 4 PHONS 61 8 LOC TACH G G SPEED 4 6 Cursor TEST 1 I J K L M H If creating a note from a blank field simply type in the note via the keypad and press EXIT when finished There are a number of editing features associated with the creation of the note field to provide flexibility and format control When typing into the note field with the alphanumeric keys after 40 characters appear on a line a symbol will appear at the end of the line and the blinking cursor will move to the next line down at the left margin for the beginning of a new line While entering characters pressing the RANGE hardkey on the lower right of the front panel will terminate the present line and mo
196. and the number of averages which have been used to determine that RT60 value FAVG When evaluating a new set of RT60 values begin by setting all RT60 values to zero by pressing R RT60 D Suppose the value of RT60 is known from previous measure ments for one or more frequency bands and the user wishes to simply enter these values into the register Move the cursor to the desired band press edit P and respond to the prompt on the upper right of the display by typing in the value using the keypad and pressing EXIT Note that the entered level will appear as a vertical bar on the screen and that the number of averages will be unity One reason the user may wish to enter values manually is to make use of the Transmission Loss calculation software which requires RT60 values which the user may have previ ously determined Room Acoustics Measurements 21 5 2900 MANUAL Manual Determination of RT60 Using the Cursors 21 6 The evaluation of RT60 values from autostored decay time records is done from the Autostore Menu From the Autostore Menu with the vsTime autostore mode active recall an autostored decay measurement by pressing RECALL Move the cursor to a frequency band of interest and press vsTIME C to obtain a decay curve for that frequency band Use the softkeys SOLID N DOTTED O and BOTH P the and the horizontal arrow keys to move the solid and dot ted cursors such that they define the portion of the cu
197. and the display proce dure are presented later in this Chapter When the manual start method is being used to initiate autostore sequences using the R S key at the conclusion of each sequence another sequence can be initiated immedi ately by another press of the R S key The user may continue to perform autostore operations in this manner until the memory is full indicated by the message OUT OF MEMORY on the upper right of the display Autostore by Time When the 2900 is in the Autostore byTime mode of operation as indicated by the message bTime on the left of the display pressing the softkey OFF A will return the operating mode 15 5 2900 MANUAL Data Storage Format to the standard non autostore storage mode The message bTime will then no longer be displayed Autostorage can be used with 1 or 2 channels in all three Analysis Modes with either Octave or FFT filtering There are a variety of data display formats available with each Analysis mode Normal Leg Max Min and SEL for Standard Autospectra Cross Spectra Transfer Function etc for Cross and Intensity Quality Average SPL and Particle Veloc ity for Intensity The display format of the sequentially acquired and stored spectra will be the same as the display format active at the time of storage Averaging Time Considerations FFT Analysis 15 6 Example Example Example When using the Linear Repeat averaging type the tim
198. and will include the contributions of all signals since the last reset There are some applications such as vehicle passby measure ments where the user wishes to display the frequency spec trum associated with the highest broadband level which has occurred during a testing interval In addition to calculating the Leq Minimum Maximum and SEL spectra during a mea surement sequence since last data reset as described above the 2900 also saves a spectrum Max Spectrum correspond Analysis Menus Selection Of Measurement And Display Parameters 6 3 2900 MANUAL Dual Channel Display Mode ing to the highest broadband level which has occurred The specific broadband level which is used to determine the Max Spectrum depends upon the operational mode of the 2900 When the 2900 is in the SLM mode it is the sound pressure level measured by the sound level meter function which is used This permits different weightings to be applied to the SLM and analysis functions For example if the user wishes to see the unweighted spectrum associated with the maxi mum weighted sound pressure level he should measure the Max Spectrum with the 2900 in the SLM mode with SLM function weighted appropriately A or C and the analysis function set to one of the four linear weightings When the sound level meter response is set to Slow Fast or Impulse the sound pressure level measured for that response is used in determining the Max Spectrum If the response
199. andard Analysis mode It is not necessary to activate the byTach autostore mode to perform real time vsRPM Graphics How ever the user may select to perform a vsRPM autostore at the same time as generating a real time vsRPM display The two procedures are totally independent 17 2 Although we have not yet discussed the use of the color mon itor in this manual it is necessary to first explain the manner in which this display is constructed on the color monitor in order to describe the similar display operation on the LCD screen The color display permits the user to have as many as four different display windows active at one time Since each win dow may contain a different combination of curves arranged in such a fashion that some curves appear in more than one window we permit the user to define as many as 32 different pens Each pen is user defined to represent a particular channel and either a particular frequency or a particular order number depending on the nature of the data The user then decides which pens he wishes to see in each window Up to six curves or traces can be presented in each window so the user assigns a pen number to each trace as part of the vsRPM display setup Consider an example where the user is dealing with two channels of 1 3 octave spectra as a function of RPM Speed For the purpose of the vsRPM Graphics display he may define the pens as follows Pen Number Channel Number
200. andscape orientation Along with the measured data the custom printout can include most of the measurement setup parameters as text strings and eight user defined text strings whose characters location size and location vertical horizontal are under your control Scaling of the Custom Printout From the Print Menu press EDIT IK to access the Edit Menu shown in Figure 23 3 Edit Menu custom printouts Figure 23 3 Edit Menu custom printouts 17 DV 15 42 18 PSCREEN TEXT DORIENT Hote SPL 18 4925 Se o o cl o o c EXPONENTIAL 178 Input 1 LINEAR 26Hz 20kHz x STOP 17 NOU 93 15 33 54 w w a anne n a cc HA s W A d FILTER NA 2 nz 125 d 1 r m na um ef PHONS 78 1 TRCH 8 80 SPEED 4 6 S0 H Hz d ak Hz dotted crsr TEST 1 UsrTx1 UsrTx2 UsrTx3 UsrTx4 UsrTxS UsrTx UsrTx UsrTx8 23 4 The workspace available for the custom printout depends upon the orientation selected for the graphic In the portrait orientation the available height is 260 mm and the available width is 200 mm In the landscape orientation the available height is 200 mm and the available width is 260 mm Figure 23 4 Portrait Worksheet and Figure 23 5 Landscape Work sheet present worksheets to assist you in the layout of the custom printouts for portrait and landscape orientations respectively As part of the definiti
201. apter it is strongly recommended that you read the pre ceding sections as well since they contain many operational details specifications and information such as microphone alignment calibration and noise floor measurement which are not repeated in the sections which follow 3 1 2900 MANUAL Sound Pressure Level Measurements Single Channel Sound Level Meter with Frequency Analysis SLM A Mode Setup From the Main Menu access the System Menu by pressing SYSTEM Select the SLM A mode by pressing SLM A B Since this section is concerned with the single channel ver sion of the SLM A Mode press the key Chanls A until the message Channel 1 of 1 NORMAL appears on the right of the screen 6th line down The dual channel mode corre sponding to the message Channel 1 of 2 NORMAL is described later in this chapter Press EXIT to return to the SLM Menu shown in Figure 3 1 SLM Menu Figure 3 1 SLM Menu a2 JOU 23 21 83 NORMAL Lea MIN MAX SEL DISPLAY note DETECTR i SPL 6 3168 5a nn EXPONENTIAL Input 1 LINEAR 20 2 20 2 i STOP 02 JAN 96 23 26 56 3a el Ea FILTER 8 6 380 Hz 125 Channel 1 of 1 NORMAL T d 16 8 2 48 5 A WEIGHT m LOC SLOU NEN 14 2 Min 28 2 30 6 2 SLM DATA dotted crsr TEST_1 A SLOW FAST IMPULSE LEQ Weight SETUP FILES AUTOSTR When the 2900 is in the SLM A mode there are three lines of display on the lower right of the scr
202. ar operation by pressing NO C Exit back to the vsTime display by pressing EXIT To enter the value of RT60 for that frequency into the RT60 register press REPLACE C The name implies that this value will replace whatever value was previously in the regis ter at that frequency One could then access the RT60 Menu press RT60 B to verify that the value has been accepted into the register Place the active cursor on the band of inter est and note the expression RT60 X XX FAVEz 01 indi cating that the value of RT60 at the cursor position is X XX and that only a single curvefit has been used to determine this value To continue with the manual method of determining RT60 values press DATA M and use the horizontal arrow keys to Room Acoustics Measurements 2900 MANUAL change the frequency of the displayed decay curve and repeat the procedure for curvefitting and storing the result for this frequency into the corresponding RT60 register With one autostore set of data the user could thus calculate and store an RT60 value for each frequency of interest without leaving the vsTime Display Menu If the user has made several decay measurements after cal culating and storing the RT60 value from one of the autostore records he could press A Prev K or A Next L while still in the vsTime Display to bring to the screen the decay curve for the preceding or subsequent measurement without changing the frequency Again he could use
203. ared trace is addressed the parameter value which had been displayed at the time the trace was cleared will reap pear Calculation and Display of Data When the statistics mode has been turned on and the statis tics parameter table set as desired press R S to begin the analysis The state of the analyzer as indicated on the fourth line down on the right side of the screen will change to RUN to indicate that the analysis has begun and that the Statistics Table is receiving input and being updated at the regular time intervals set by the user However no curves will be drawn until either the analysis is stopped by pressing R S or until the softkey REDRAW H is pressed When either of these keys is pressed the Ln data and curves representing them are generated from the data in the Statistics Table at that instant There is no mode whereby the Ln values and curves are generated and displayed in real time It is not necessary to keep the Statistics Menu on the screen during the analysis Most users would probably prefer to return to the Standard Analysis Menu in order to observe the spectral display during the analysis period 18 4 After the analysis has been running from the Statistics Menu press either R S or REDRAW H to generate and display the curves corresponding to the parameters in the statistics parameter table When the statistics are being calculated from the analyzer mode of operation the complete horizontal scale
204. as been pressed a second press of the key will reset the shift state to normal followed by a The 2900 will reboot the setup represented digit 1 7 e g Dy the digit The 3200RCwill display the shifted digit message Boot setup n ssssss where n is the setup number and sssssss is the setup name label START e g The 3200RC will turn off The 2900 will dis shift START play the message 3200RC is off The 3200RC will turn itself off after a period of 15 minutes without a keypress in order to preserve the battery power 4 26 There is a connector on the rear panel of the 2900 as indi cated on the label which produces a DC voltage proportional to a user selected frequency or sound level meter parameter The load impedance should be at least 2 kO Full scale is rep resented by 4 5 volts decreasing 1 volt 20 dB This is selected from the I O Menu by pressing DC out B which wil produce the message DC output XXXXXX where XXXXXX indicates which frequency band or sound level meter parameter is to be represented by the DC output volt age If the 2900 is set for 1 1 or 1 3 octave bandwidths the message will indicate both the ANSI filter number and the center frequency If it is set for FFT analysis only the center frequency will appear The horizontal arrow keys are now used to select a frequency or sound level meter parameter The sound level meter parameters are higher in sequence than the frequency bands mean
205. at the input 1 Hz will be a DC offset as well as some distortion of the rectangular shape of the pulses This is purely a measurement phenome non not a true representation of the actual signal being gen erated The I O Menu shown in Figure 4 16 I O Menu is accessed from the System Menu by pressing I O I Figure 4 16 UO Menu 25 APR 15 57 20 5280 out 10 Fort KEV A KEY B Beerer RS1 80 RS232 19200 Baud Selected SPL 6 9606 EXPONENTIAL Input 1 LINEAR 20Hz 20kHz RESET 25 APR 34 15 56 51 ea 48 FILTER 24 250 z LAS v Channel 1 of 1 NORMAL d Ze 11 1 20 PHONS 94 8 TACH 6 6 SPEED 4 6 R 2 2 R z dotted crsr INITIAL RS 232 580 608 1200 2400 4800 9600 19200 Selection of Intensity Probe or Remote Control 2900 Instrument Setup Via The System Menu The opto isolated inputs see page 4 26 can be used among other things to communicate with a sound intensity probe or a remote control To make a selection press RSIANT H 4 23 2900 MANUAL from the I O Menu which will bring up the RSIANT Menu shown in Figure 4 17 RS1 INT Menu Figure 4 17 RS1 INT Menu 16 MRY 16 25 18 RS1 INT2258 INT2251 INT2268 sa DCH CENTRE W w w n w w a w a n a w n n n n n n n n n n n nn n nn Rat Kes R Kes B3 ote SPL 6 3158 B LINEAR SINGLE 18 annan Input 2 LINEAR 28Hz 28kHz RESET 16 MAY 94 15 41 06 Q ooo T TT hU FILTER 16 46 6 Hz 125 Channel 1 of 1 NORMAL s 44 0
206. ate press the follow ing key sequence from the Class Lines Menu SETUP J DEFAULT H YES A EXIT which will reset all the labels for A B C and D to default and replace all the pre existing curves to two point curves having the coordinates described above For the purpose of this exercise we will create a class line named TEST Begin by naming this class line by pressing the key sequence NAME K A SHIFT CLEAR T E S T EXIT To create the class line press the key sequence EDIT I TEST A Use the keys point l and gt point J to move the horizontal and vertical cross hair lines between points one and two noting their coordinates as displayed on the upper right of the screen We will begin the creation by accessing point 1 Press the up and down vertical arrow hardkeys on the lower right of the front panel and notice that point 1 will be moved up or down in steps of 0 1 dB If the SHIFT hard 22 5 2900 MANUAL 22 6 key is pressed at the same time point 1 will move up or down in steps of 1 0 dB Pressing the left or right horizontal arrow keys will shift the location of point 1 left or right along the fre quency axis in steps of one filter bandwidth Pressing the SHIFT hardkey at the same time will result in a much larger step size In this exercise we are going to create the line shown in Fig ure 22 6 Single Class LIne Example Figure 22 6 Single Class Line Example 29 DEC 1
207. ate t t note KEEP Memory Used 3072 Disk Used 1024 1 Memory Free 126266 Disk Free 1456640 RECORDS NOTE POINT 1 FAN TEST 61 62 96 Ge a POINT 3 MOTOR 01 02 90 Ho POINI 4 PUMPTEST 61702790 G7 POINT S BLADES 1 62 96 c POINT 6 COUPLING 61 62 96 G7 delete rename RECORDS delete The softkeys T E and J M can be used to shift the record listing vertically upwards and downwards while the highlight on the left of the screen remains on the name of the file whose records are being displayed The listing of the records includes the Record Type and Record Number of each along with a Note The note field displays the first 17 characters of the note which was attached to the record at the time of stor age In order to see a note which is more than 17 characters in length press note G Deleting Records When the records are listed as described above the user may create or edit the note field of the highlighted record by press ing note G The creation and editing of notes is described in detail in Chapter 14 Recalling a Record from the Files Menu The highlighted record on the right side of the screen can be deleted from the memory file highlighted on the left side of the screen by pressing delete N The message Delete record on the right of the screen prompts the user to verify the deletion operation Press YES A to proceed with the deletion or NO C to abort the deletion operation
208. ated from the 2900 are stored to non volatile RAM memory or optionally to volatile DRAM memory as data records within user created and named data files When the optional floppy disk drive Model 2510 is con nected these files can be subsequently transferred from internal memory to a floppy disk and also from a floppy disk back into the internal memory Files Information The Files Menu shown in Figure 13 1 Files Menu is accessed from any of the Analysis Menus by pressing FILES O Figure 13 1 Files Menu 02 JAN 07 03 27 Create RECORDS disk Memory Used 3072 Disk Used 1024 1 Memory Free 12624 Disk Free 1456648 X on DATE TIME SIZE LOC MEMORY delete rename mem delete rename Storing and Recalling Non Autostore Data The left half of the screen displays information concerning the files stored in the memory of the 2900 This consists of the name date and time of file creation and the size of the file in bytes The right half of the screen displays similar infor mation concerning the files stored on the floppy disk 13 1 2900 MANUAL Creation of Files Near the top of the display the amount of memory already used for stored data records and the amount of free memory available for further data storage are indicated for both the internal memory and the disk memory on the left and right halves respectively of the screen The capacity and volume name user assigned of the disk in
209. ation and differentiation operations are purely display functions This means that when single or double integration has been selected the displayed spectrum will include the effect of this operation but the spectrum which is stored is neither inte grated nor differentiated Should that stored spectrum be recalled without integration or differentiation selected there will be no integration or differentiation of the displayed spec trum However if the user selects an integration or differenti ation operation previous to the recall operation that function will be represented in the displayed spectrum Note that the effect of an integration division by 2 x f is to decrease the levels at all frequencies above 1 radian sec For example the level at 1 kHz will be reduced by 76 dB which could cause the resulting spectrum to drop below the bottom of the screen It is often necessary to utilize the vertical offset func tion described in the Section Control of the Vertical Display in Chapter 19 to bring the integrated spectrum back up onto the screen FFT Integration and Differentiation Operations Selection of Units and Calibration Due to the large number of spectral lines used with FFT anal ysis the integration and differentiation operations are per formed in the DSP processor and are therefore not a display function This means that the integration and differentiation operations are performed as part of the measurement and are r
210. ation or differentiation symbols are shown on the screen Simply stated when working with FFT spectra the integration and differentiation operations are performed on the measurement but not upon data recalled from memory Because of this it is important that the user store the units used for the measurement along with the data This way by recalling the stored units at the time of recalling the data block any integration or differentiation operations which had been performed at the time of the measurement will be indi cated on the right of the screen Calibration is done one input at a time Select the input to be calibrated using the numeric keypad then follow the appro priate calibration procedure described in the following sec tions Calibration Based on a Transducer Sensitivity Value Logarithmic Units Calibration dB Volt 9 4 When a calibrator is not available the analyzer can be cali brated by using a known value of the sensitivity of the trans ducer and signal conditioning system There are two alternative procedures which may be used with the Model 2900 depending upon whether the user wishes to express the data in logarithmic units dB or linear units After a unit name has been assigned to the channel to be cal ibrated the desired integration or differentiation defined and that channel has been selected using the numerical keypad press V cal IG The message Enter dB Volt XXX on the right of the d
211. ator there is a low pass filter after the detector whose response can be adjusted by the user using the softkey FILTER P The selected value can be between O and 16 with 16 representing the slowest loop response In general the user would begin using a zero value and should instabil ity be observed which could be due to a time delay this value could be increased to improve the stability For microphone testing in a relatively anechoic acoustically non reflective environment the reference and test acceler ometer are replaced by reference and test microphones placed near one another yet not so close as to interfere with the respective responses in the radiated field of a loud speaker The output of the sine generator is used to drive the amplifier speaker system and the reference microphone is used as the feedback signal for the generator The Wideband Pink Noise Menu shown in Figure 4 11 Wideband Pink Noise is accessed from the Signal Generator Menu by pressing PINK J Figure 4 11 Wideband Pink Noise 3e 981 82 24 38 173 LEUEL ATT gt ATT Note PINK NOISE i I 26 4225 188 Ga w n n n n n n n n n n n an n a n n n a a na ci ee n n a o t EXPONENTIAL 1 i Input 1 LINEBR 20Hz 20kHz STOP 36 OCT 94 02 24 36 880 QZ nd n LA ve y FILTER 34 2 5OkHz 125 Channel 1 of 1 NORMAL d 2 188 9 PHONS 121 6 TRCH 8 80 SPEED 6 6 dotted crsr BIL 0000060755 ie LOC B81
212. available Although these other types of spectra can be displayed they cannot be stored while the instrument is in the Autostore mode So following the conclusion of the autostore sequence turn off the autostore mode from the Autostore Menu access the Main Menu and use the Leq B MIN C MAX D SEL E and Mx Spec L hardkeys to dis Autostore by Time Deleting Autostore Records 2900 MANUAL play each of these other types of spectra and use the STORE hardkey to store the displayed spectrum type Because the autostored spectra themselves can be of the type Normal Leq MIN MAX SEL or Mx Spec depending upon which display type is active at the initiation of the autostore sequence be careful when switching between these display types while doing multiple autostore measurements Most applications call for the autostorage of Normal spectra but if the display type is switched to Leq for example to display and store the Leq spectra following the autostore sequence and the display type is not changed back to Normal before the next autostore sequence the next sequence will store Leq spectra instead of Normal spectra It is possible to create a key macro function which will in one operation perform the autostore sequence and then sequen tially display and store each of the other spectra and reset the display type to Normal in preparation for the next autostore sequence Key macros are described in Chapter 17 of this manual
213. ayed data types are as follows INTENSITY QUALITY SPL PARTICLE V POWER N1 Dotted Cursor Active With the dotted cursor active denoted by the message dot ted cursor on the lower right of the screen the value dis played in location N1 will be the amplitude corresponding to the dotted cursor position in the format d XX X to indi cate that the level is for the dotted cursor N1 Solid Cursor Active With the solid cursor active denoted by the message solid cursor on the lower right of the screen the value displayed in location N1 will be the amplitude corresponding to the solid cursor position in the format s XX X to indicate that the level is for the solid cursor N1 Both Cursors Active With both cursors active denoted by the message both crsrs on the lower right of the screen the value displayed in location N1 will be the level associated with the dotted cursor minus the level associated with the solid cursor The format used is A XX X to indicated that the number represents a difference in levels N2 Dotted or Solid Cursors Active With either the dotted or solid cursor active the value in N2 corresponds to the total energy between the analog highpass and lowpass filters selected for the inputs modules the fre quency range of which is displayed in location I The value of the linear or non weighted total energy is indi cated in the format S XX X The value
214. be reset and begin calculating another average Autostore by Time Octave Filters 2900 MANUAL For true by time operation of Autostore function the user will generally select Linear Repeat Exponential BT Exp or BT Lin averaging The storage operations are governed by the internal clock and whenever an integer multiple of the selected value of Delta Time is reached whatever data is in the averaging buffer s is stored Using Linear Repeat it is logical to set the Delta Time value to equal the averaging time Since the averager is reset at the end of each interval each spectrum stored would represent an average calculated over the preceding Delta Time interval Should the Delta Time be set to three times the averaging time the detector would be reset twice before storage of a spectrum meaning that the spectrum stored would represent only data measured over the last third of the interval time Similarly with Exponential Averaging it is logical to set the Delta Time to be close in value to the averaging time If the Delta Time were much less than the averaging time there would be very little difference between the stored spectra due to the time constant of the averaging process If it were much larger there could be great changes in the spectra between intervals which would not be seen One could use Linear Sin gle with a Delta Time less than the averaging time but this would only display the build up of the averaging proce
215. be applied to measured spectral data before it is displayed This will be in addition to analog weighting which may have been applied at the input Digital display weighting is described in detail in Chapter 10 The key SETUSER F is used to create the User Weightings Dis play weighting is not possible when using Cross Analysis Display of Spectra Relative to a Reference Spectrum In some application it is desirable to compare two spectra or to display spectra relative to some user defined spectrum Although the 2900 can only display a single spectrum on the LCD screen at one time it is possible to display relative to a reference spectrum This is quite useful when using logarith mic amplitude scales dB because this format produces a spectrum which represents the difference between the selected and the reference spectrum The spectrum which is to be defined as the reference spec trum must first be displayed In most cases it will be a spec trum already measured and stored so simply recall it If it has not already been stored it is best to store it at this time since one will probably need to recall it at a later time to show just what the reference spectrum looked like Access the Shift Menu shown in Figure 19 4 Shift Menu by pressing SHIFT and then press SetREF O The message vsREF on the left of the screen along the vertical axis indicates that the amplitudes correspond to a spectrum being displayed relative to the refere
216. bel letter lt 13 AA lt 25 A lt 50 B lt 100 C gt 100 D Criteria for selecting Sub Type letter In terms of the IEC International Electrotechnical Commis sion the most recent standard governing octave filters is IEC Publication 225 1966 The Technical Committee No 29 is presently working on a revision to the document 4 5 2900 MANUAL Selection of FFT Filtering 4 6 There are three different octave type digital filter algorithms available in the Model 2900 represented by the softkeys LONG F SHORT G and REVERSE H on the right of the upper row With regard to the ANSI standard the Long filter satisfies the ANSI S1 11 1986 requirements for Type 0 AA the highest classification possible under that standard The Short filter satisfies the requirements for Type 1 D For measurements which require a particularly fast filter time response such as measuring gunshots the Short filler may be preferable although the slope of the filter skirts is less than that of the Long filter so the filter resolution is not as fine In the previ ous standard ANSI S1 11 1986 R 1976 which was super ceded by the 1986 version the highest classification of 1 3 octave filters was Class III For those whose measurement require mentsmight still be governed by the old standard note that all these 1 3 octave filters of the Model 2900 exceed the requirements of Type III Before the advent of digital filters many of the co
217. cal axis to an appropriate scale as described in the previous section When the sensitivity of the transducer is known the 1 kHz square wave test signal can be used to calibrate the 2900 This procedure is simpler than that described above Simply calculate the excitation amplitude to the transducer which would be required to produce an output of 1 Volt Perform a measurement with the test signal ON stop the measurement and move the cursor to the 1 kHz frequency band represent ing the fundamental frequency Press level H enter the cal culated amplitude value using the keypad and press EXIT Storage and Recall of Units Information Selection of Units and Calibration It is important to realize that the units names integration or differentiation and calibration are display functions As men tioned previously the actual input to each channel is a volt age signal which is then integrated or differentiated and scaled to produce the measurement units as defined by the user in the Units Menu Because these are purely display functions when the data are stored they are stored in the same pure voltage form as measured without the integra tion differentiation and scaling operations which were per formed as part of the display function For example suppose the transducer were an accelerometer and the user wished to see the data in units of inch sec The actual measurement would produce a voltage proportional to the acceleration
218. can be performed automatically using a displayed 1 1 octave spectrum which has either just been measured or has been recalled from memory If the spectrum has been measured using 1 3 or octaves it must first be converted to the 1 1 octave bandwidth format from the Display Menu by pressing 1 1 A Access the Rooms Menu from the Analysis Menu by pressing ROOMS I and then press NC A to obtain the display shown in Figure 21 10 NC Menu The best fit NC curve is displayed as an overlay with the spectrum and the NC value corresponding to that curve is displayed digitally on the right side of the screen in the format NOISE CRITERION XX X The NC display cannot be stored to internal memory but it can be printed out in the usual manner 21 21 2900 MANUAL Noise Rating Curves Figure 21 10 NC Menu 18 MAY 10 25 21 NC NR RC RT6G STC Ia Ii Note OFFICE BACKGROUND 4 8525 EXPONENTIAL Input 1 LINEAR 28Hz 28kHz STOP 18 MAY 94 10 23 15 FILTER 15 31 5 Hz L 5 Channel 1 of 1 HOFMRL NOISE CRITERION 52 2 TRCH 0 0 SPEED 8 8 dotted crsr 6 Hk HZ surface volume The RC Noise Rating Procedure The Noise Rating NR Curves are used in the same manner as the Noise Criteria NC Curves to produce a single number rating of steady background noise according to the ISO Rec ommendation ISO R 1996 1971 Acoustics Assessment of Noise with Respect to Community Response With the spec trum of the background noise displayed in
219. cord of type Power Power Summation Example Power spectra are recalled from the Power Summation Menu by pressing RECALL which will produce the message RECALL Power N on the upper right of the screen to indi cate that the Nth record of type Power has been recalled from the active files and is being displayed The message recall data on the lower right of the screen indicates that the hori zontal arrow keys are programmed to control which record is being recalled and displayed Presses of the left arrow key will sequentially recall records lower in number than the one presently recalled while the right arrow key will sequentially recall records higher in number than the one presently recalled Once the desired record has been recalled press KEEP H to stop the recall operation and return the system to the Power Summation Menu with the recalled spectrum on the display Pressing EXIT instead of KEEP H will abort the recall process clear the display and return control to the Power Summation Menu without a recalled spectrum being displayed Sound Intensity Measurements Consider a sound intensity measurement project consisting of a JOB named MACHINE that radiates noise from PARTs named FRONT and REAR To accurately define the noise 20 17 2900 MANUAL Three Level Search Two Level Search Single Level Search 20 18 radiation characteristics of the MACHINE FRONT and REAR are each divided into four AREAs na
220. cords 1 2 3 and 4 because they all satisfy the search field criteria To calculate and display the power spectrum corresponding to the entire JOB labeled MACHINE from the Intensity Anal ysis Menu recall any one of the records 1 8 since all of them have the desired JOB label Access the Power Summation Menu and press S gt JOB I which will make the Power Search Field read MACHINE Pressing Sound Intensity Measurements 2900 MANUAL Power A will calculate the summation of the intensity spectra stored in records 1 through 8 because all of them sat isfy the search filed criteria Field Indicators Specified in the Standard ISO 9614 1 1993 E Temporal Variability Indicator F4 Sound Intensity Measurements The temporal variability indicator is calculated from a series of short time average measurements of intensity at a single position as follows M 1 1 2 pum Ink In where In is the mean value of In for M short time average samples Ink calculated by the formula M 1 In AS K 1 With the Model 2900 we utilize the vsTime autostore capabil ity to evaluate F With the analyzer setup to measure inten sity using the desired selection of filter type and bandwidth pressure temperature spacer length and a representative value of surface area select Linear Repeat Averaging by pressing the following key sequence DETECTR H LIN R B Select the desired short time average valu
221. ctly below After completing an averaging cycle a subsequent press of the R S key will auto matically reset the data buffer and begin another average It is not necessary to manually reset the data buffer before beginning another averaging cycle If the R S key is pressed before the averaging cycle is completed the averaging process wil be paused Pressing R S again will recommence the same averaging cycle without loss of data measured during the previous time interval and the run time will continue from the value displayed at the time of the pause Manual Control of Input Gain When making a measurement the input gain should be set such that none of the input channels are overloaded yet the signals produce significant amplitude levels on the frequency display When there is an overload in any of the input chan nels while the analyzer is running the message OVER will appear in an inverse video form near the center of the screen When making a measurement with fairly steady signals it is common practice to set the Averaging Type to one of the con tinuously running forms of averaging such as Exponential BT Exp or BT Lin using a small value of averaging time such that time variations of the signal amplitude will be clearly visible on the screen The input gain control is then adjusted to obtain an optimum setting for the given input sig nals Once a satisfactory setting has been made the averag ing time is then increased for superi
222. ctly radiated sound energy This is referred to as a free field incidence measurement situation In terms of this standard the choice and orientation of the microphone should be such that the measurement will be most accurate in cases where the sound field is indeed radiated from that source For this reason most European users will select a free field microphone for use with their Model 2900 Microphone Preamplifier Alignment The approach of the ANSI standard is that in many acoustic measurement situations the exact location of the noise source is not clear such as observed in room acoustics situa tions where the sound field is often diffuse due to reflections of the sound waves from various solid surface and the exist ence of multiple sound sources This is referred to as a ran dom incidence measurement situation Another instance is where the sound source is moving such as in passby mea surements of vehicle noise or aircraft operations In terms of measuring a single noise source the ANSI standard seeks to obtain the greatest accuracy for any possible position of the source with respect to the microphone For this reason most American users will select a random incidence microphone for use with their Model 2900 3 6 When using the Model 2900 for a sound level measurement it is important to establish whether or not the measurement to be made is free field or random incidence Sound Level Meter Operating Modes Free Fiel
223. ctret or prepolar ized microphones 28 V B 28 volt bias voltage active 200 V C 200 volt bias voltage active 2900 Instrument Setup Via The System Menu 2900 MANUAL Branching a Signal from One Input Connector to both Analysis Channels Dual Channel Analysis Only Standard or Sound Level Meter Setting the Analog Filters for the Frequency Analysis Function Internal Calibration Signal When performing a dual channel analysis there may be applications where the user wishes to direct the signal from a single microphone accelerometer or other input to both anal ysis channels since these can be setup with different fre quency weightings Once the measurement parameters have been established for the two anayses press Inputs G and then either CH1 or CH2 to select the input connector to which the transducer whose signal is to be measured is con nected The selection will be confirmed by the message Input 1 or Inputs 2 on the right of the screen 3rd line down From the Input Menu the user can select to utilize either a broadband weighting filter A weight or C weight in the sig nal path or a pair of highpass lowpass filters by pressing one of the following Softkeys Softkey Functions A WGT I Inserts an A Weighting filter in the signal path C WGT J Inserts a C Weighting filter in the signal path 1 20k K Inserts a 1 Hz highpass filter and a 20 kHz lowpass filter in the signal path 20 20k L Inserts a 20 Hz h
224. cture For Instrument Operation 3 Sound Level Meter Operating Modes Sound Level Meter Operating Modes A sound level meter is an instrument designed to measure and display the broadband sound pressure level of an acous tic signal Very stringent performance specifications for sound level meters have been established internationally The Model 2900 is designed to satisfy or exceed the requirements of the following standards ANSI S1 4 1983 TYPE 1 IEC 651 TYPE 1 IEC 804 TYPE 1 Although sound level meters can be equipped with filters to permit the user to measure the energy content of a signal as a function of frequency this capability is outside the defini tion of a sound level meter and no reference to a frequency analysis measurement capability is contained in the interna tional sound level meter standards In this chapter we discuss the setup and operation of the sound level meter functions available on the Model 2900 in the following order Single Channel Sound Level Meter with Frequency Analy sis Mode 1 1 and 1 3 octave digital filters or FFT analysis to 20 kHz Dual Channel Sound Level Meter with Frequency Analysis Mode 1 1 or 1 3 octave digital filters to 10 kHz Wide Dynamic Range Sound Level Meter Mode no fre quency analysis provided Although the sections describing the Dual Channel Sound Level Meter with Frequency Analysis Mode and the Wide Dynamic Range Sound Level Meter Mode appear later in this ch
225. cursor to the frequency about which the zoom analysis is to be performed then press the softkey corresponding to the desired zoom factor The message ZOOM XX displayed below the frequency axis indicates that the active zoom factor is XX Once in the zoom mode one can dynamically pan the fre quency range of the analysis to lower or higher frequencies This is done by pressing BASE Hz O and using the horizon tal arrow keys to shift the location of the center frequency about which the analysis is being performed To exit from the Zoom Menu press EXIT When the FFT parameters are set as desired return to the System Menu by pressing EXIT Once selected FFT analysis can be operated from any of the Analysis Menus Standard Cross or Intensity but to invoke or modify zoom analysis it is necessary to return to the Zoom Menu When the Model 2900 is operating in a dual channel mode Stand 2 Cross or Intensity using FFT analysis and the full scale frequency has been selected to be 20 kHz the analysis will not be performed in real time In this case the zoom 4 11 2900 MANUAL Printing FFT Data in Tabular Format Accessing Input Menu function is buffered rather than real time which will limit the maximum permissible value of zoom multiplier to 32 The use of the printing capabilities of the Model 2900 is described in Chapter 23 When dealing with FFT spectra measured using many lines of resolution it may happen tha
226. d from the sum of the energy measured 1 Hz and 20 kHz These are identified below the bars by the letter A and the summation symbol S respectively Repeatedly pressing SUM E will cause the digital value displayed on the lower right of the screen to toggle between these two as indicated by the A or summation symbol on the line below the Chan nel Indication When the both cursor mode is active these bands repre sent the A Weighted and Linear broadband levels calculated from the sum of the energy between the two cursors rather than between the highpass and lowpass filters Digital Display Weighting is controlled from the Display Menu shown in Figure 19 3 Display Menu which is accessed from either the Standard or Intensity Analysis Menu by pressing DISPLAY F Control of Display Formats Cross Channel Normalization and Use of Key Macros 2900 MANUAL Figure 19 3 Display Menu 25 gen 15 58 44 171 143 Y SUM SUM SETUSER note Multi PL 6 6008 T M EXPONENTIAL 178 Input 1 LINEAR 20 2 20 ES T 25 APR 34 15 Set n RI w wooo un Ho H eu w un n a u oun n a ttn UN AU ttc s A MM UK KA us FILTER 24 250 Channel 1 of 1 NORMAL dz 5 4 Ze 11 1 E 2 94 0 1 I TRCH 6 6 SPEED 6 6 R 2 dotted crsr INITIAL NO WGT A USER R C USER BWNORM This Menu permits the user to select an A C User A C or User Weighting Function to
227. d 0 5 Although the level has exceeded one curve at 10 Hz and at 80 Hz and two curves at 125 160 and 400 Hz the maximum incursion of the spectrum into the family of curves is at 1 6 kHz where the spectrum level crosses four curves The classification table on the right of the screen indicates that for the spectrum measured in chan nel 1 of the analyzer the classification is based on a family of classification curves named CURV 1 The classification value of 4 reported in the table indicates that this spectrum has at one frequency crossed four of the lines of that family of classification curves and that at no other frequency did the spectrum cross a larger number of curves five or more Looking back at Figure 22 1 and Figure 22 2 we see that the classification table also indicates Pass or Fail as O Pass no crossing of curve or 1 Fail curve has been crossed Further examination of the classification table indicates the possibility of comparing the test spectrum with four different families of curves denoted in this example as CURV 1 CURV 2 CURV 3 AND CURV 4 since there are four col umns available In addition the existence of two rows corre sponding to Ch1 and Ch 2 implies that the spectra measured for channels 1 and 2 can be compared independently against these four families of curves Of course one can only display one of the two spectra at one time along with the appropriate family of classification curves Whe
228. d Measurements 2900 MANUAL Sound Level Meter Operating Modes When the measurement is of the free field type the best results will be obtained using a free field microphone Lar soneDavis Models 2520 2540 2541 or 2570 In this case the microphone should be aligned such that the sound waves radiated from the source impinge the microphone in a direc tion normal to the diaphragm Thus the axis of the micro phone is aimed at the source With the microphone boom aligned with the source as described in the section Micro phone Boom Alignment turn the microphone preamplifier holder such that the axis of the microphone and preamplifier are also aimed toward the source The best free field response of a random incidence micro phone is obtained when the sound waves radiated from the source pass over the microphone in a direction nearly parallel to the diaphragm which is referred to as grazing incidence Thus in cases where it is necessary to make a free field mea surement with a random incidence microphone the micro phone should be aligned such that the angle between the microphone axis and the line between the microphone and the sound source is approximately 85 As above the micro phone boom should be aligned with the source but the microphone preamplifier holder turned to produce the desired angle The angular response of the random incidence microphone is not so sensitive that the angle of incidence be exactly 85 but
229. d on the upper right of the screen In order to accurately read the battery voltage level just after unplugging the AC DC converter see below let the instrument run for an instant and stop it prior to performing that measurement While operating should the battery voltage drop to below 6 9 volts the flashing message Recharge BATTERY soon will be displayed on the upper right of the screen Should the battery voltage level be further reduced to below 6 5 volts the instru ment will be shutdown automatically since the processor might not function properly at that reduced voltage level Just prior to the shutdown the message DEAD BATTERY Shut Down will appear on the upper right of the screen accompanied by an audible beep 1 9 2900 MANUAL DC Power Charging Batteries The Model 2900 can be powered from an external 11 16 Vdc power supply plugged into the miniature phono plug located on the extreme left of the top panel An AC DC converter is delivered with the 2900 to permit operation from mains power When a DC voltage source is supplied the supply volt age can be read in the same manner as described above for reading the battery voltage Microphone Connection When an external DC voltage is supplied typically using the mains powered AC DC converter supplied with the instru ment a charging voltage is applied to the rechargeable bat tery pack within the instrument A totally discharged pack will require approxima
230. d scale factor default value of unity to per mit the use of a variety of units To detect the shaft rotational rate a probe is used near a gear on the shaft The gear has 32 teeth thereby producing a pulse train at the rate of 32 times the shaft speed The desire is to calibrate the 2900 so that the TACH value is measured in units of Hz rev sec Set the Scale factor 1 N 1 32 0 03125 rev pulse Signal into the TACH module X Pulse sec Scaled value X pulse sec x 0 031295 rev pulse 0 03125 x X rev sec The axle rotation is monitored Every rotation the axle moves 2 x mx r which equals 6 28r ft The desire is to calibrate the 2900 so that the Speed value is measured in units of ft sec Set the Scale factor 6 28r which has units of ft rev Signal into the module X pulse sec Scaled value X pulse sec x1 rev pulse x 6 28r ft rev 6 28r x X ft sec The gear in Example 1 is on the axle in Example 2 The desire is to calibrate the 2900 so that the Speed value is measured in units of ft sec Set the Scale factor 0 03125 rev pulse x 6 28r ft rev 0 196 ft pulse Signal into the module X pulse sec Scaled value 0 196 ft pulse x X pulse sec 0 19625 x X ft sec 16 3 2900 MANUAL Interval and Span Settings The following keys are used to set the Tacho and Speed Scaling Softkeys Softkey Functions t scale A This is the user defined scale factor which con verts the pulse rate to the desired
231. d the micro phone preamplifier will not require a correction to the cali bration Noise Floor Measurement and Proximity Message Sound Level Meter Operating Modes When measuring low level sound pressure levels we wish to be certain that the indicated value is not affected by the noise floor of the instrument More specifically we would like to know when the measured sound pressure level is within 5 dB of the noise floor of the instrument To do this we first measure the noise floor of the instrument This should be done by replacing the microphone to be used by a dummy microphone having the following electrical impedance I 1 5 KQ 18 pF Signal e e Preamplifier Input ms T 1 000 pF Dummy microphones are available from Larson Davis Labor atories If a dummy microphone is not at hand it is possible to simulate the same condition by turning off the microphone bias voltage A short circuit is made at the input before mak ing the measurement Set the 2900 to the weighting which is to be used for the measurement A C or one of the linear weightings select the Slow detector and make a measure ment Adjust the gain until the measured value is within 20 dB of the full scale When the indicated value of SPL is stable press R to stop the measurement To modify the noise floor press the following sequence of keys SYSTEM UNITS F Noise F E This will produce the message New NOISE FLOOR was X XX where X XX is
232. d the window to the right will display the message Off in a non brightly displayed state To enable or disable that pen click the mouse on the STAT window and click either On or Off Next for that pen number click on the CH window to select the channel which it is to represent To select the frequency or order number which the pen is to represent place the mouse pointer in the ORDER window depress the left mouse button and slide the mouse left or right to scan through the range of permitted values of this variable Single presses of the left right mouse button will increment the selection downward upward When one is selecting the frequency or order value it is best that the 2900 be in the vsRPM Menu which is accessed from the Main Menu If the 2900 happens to be in the vsRPM mode associ ated with the recall of stored data the data will be redrawn each time the frequency order variable is changed which takes too much time to be practical Use of External Color Monitor for Display and Instrument Control 24 15 2900 MANUAL Assigning Traces to Pens Hiding or Unhiding Traces There are six traces numbered 1 6 that may be displayed for each data display window which has been set to the vsTach display format The trace parameters are presented below each data display window To the right of each trace number are two windows indicating the pen number assigned to that trace and the amplitude value of that trace correspond
233. d to drive a shaker upon which are mounted both a refer ence accelerometer and a test accelerometer The signal from the reference accelerometer is connected to the Channel 1 input and the signal from the accelerometer under test is connected to the Channel 2 input The instrument is set to the STAND 2 Mode with FFT filtering active and the Max level selected for display Before beginning the test the output frequency is set to Fstart by pressing START I at which time the level will corre spond to that set for Lse The autolevel mode is actuated by pressing Auto L O which will produce a message on the upper right of the screen whose first word is either Auto if in the single tone mode or Auto2 if in the dual tone mode The test is begun by pressing SWEEP K With the autolevel mode active Channel 1 is used as a feedback channel with the output of the sine generator being modified as necessary to maintain the level measured in Channel 1 constant Thus should the frequency of the signal approach a resonant fre quency of the amplifier shaker system the detection of an increase in the measured level would result in a decrease of the output level in order to maintain a constant acceleration level of the shaker A digital tracking filter in the feedback loop assures that only the feedback level at the signal genera tor frequency is being compared to the programmed output level for shaker control Unless the system under test is extre
234. d vertical arrow keys to adjust the range until the sound level trace on the screen falls within 20 dB of the full scale The spectrum displayed on the left of the screen should indicate a dominant peak at the frequency of the sound produced by the calibrator Press R a second time to stop the measurement Using the left and right horizontal arrow keys move the dot ted cursor until it is located over the frequency band corre sponding to the predominant frequency peak in the spectrum On the right side of the screen fifth line down from the top is displayed the frequency of this cursor position This value should agree with the frequency specification of the calibrator On the seventh line down from the top is displayed the level corresponding to the cursor position of the spectrum display in the format d XXX X The letter d indicates that this value is for the dotted cursor position If the displayed level value is equal to the sound pressure level specification of the calibrator at that frequency then the 2900 is properly cali brated and no further adjustments are required In the default setup of the SLM function the displayed sound pressure level is A weighted while the 1 3 octave spectrum is unweighted Thus the measured sound pressure level dis played on the lower right of the screen will not equal the level corresponding to the calibrator frequency of spectrum display unless the frequency of the calibrator is 1 kHz in wh
235. defined by the standard ISO 140 7 1978 Field measurements of impact sound insulation of floors Another standard ISO 140 6 1978 Laboratory measurement of insulation of floors is appropriate for labora tory testing but the calculation procedure is the same as used for the field measurements Thus we use the parame ter symbols with a prime denoting field measurements in the analyzer firmware Parameter Standard Normalized Impact Sound ISO 140 7 1978 E and ISO Pressure Level L 140 8 1978 E Standardized Impact Sound ISO 140 8 1978 E Pressure Level L y7 The standard ISO 717 2 1982 defines single number rating indices corresponding to each of these parameters which are determined by a curvefitting procedure described in the stan dard Parameter Index Normalized Impact Sound Pres Weighted Normalized sure Level L Impact Sound Pressure Level o w and Impact Sound Protection Margin Mj Standardized Impact Sound Weighted Standardized Pressure Level L y7 Impact Sound Pressure Level Lar w To determine and display these ISO parameters simply press the softkey whose label corresponds to the desired parameter If a message WARNING High Background appears on the upper right of the screen this means that the difference between the Test Room spectrum and the Test Room back ground spectrum levels at one frequency or more is less than 3 dB In such a case precise values for the Receiving Room
236. di tion to those for the 1 1 or 1 3 octave bandwidths Because the weighting of the SLM function is selected independently from the weighting of the Analyzer function the user can select A or C weighting for the SLM statistics and linear weighting for the frequency band statistics If using the 2900 in the Analyzer Mode access the Statistics Menu shown in Figure 18 1 Statistics Menu from the Ana lyzer Menu by pressing STAT K If using the 2900 in the SLM Mode access the Statistics Menu from the SLM Menu by pressing the sequence DISPLAY F STAT B 18 1 3200 MANUAL OPT 42 Setting the Update Interval Setting Measurement Range Figure 18 1 Statistics Menu 17 yoy 49 06 12 S Time dB SPAN R STRT HIDE CLEAR REDRAW 18 25 0 Hz 638 Hz RMS 1CH STO TBL RCL TBL MRG TBL 28 8kHz Z A Data are taken from the measurement buffer to the Statistics Table at regular time intervals specified by the user Before turning on the statistics mode set this interval by pressing S Time B which will bring to the upper right of the screen the message UPDATE DELTA XXXXXX XXXX Use the numeric keypad to type in the desired value in seconds and press EXIT The statistics mode must be off when moditying the update interval If it is on the message Turn statistics off first will appear briefly on the upper right of the screen Use of Autoranging The measurement can be made over a measurement range of 120
237. dicated by two vertical bars on the right of the win dow and digital values are displayed just above the upper right corner of the window The data presented in green represents the linearly weighted overall value calculated over the range 1 Hz 20 kHz The data presented in orange represents the A Weighted over all value over the range 1 Hz 20 kHz Use of External Color Monitor for Display and Instrument Control Recall and Display of Data 2900 MANUAL Running Macros Clicking on either of the two windows entitled STORE and RECALL on the upper right of the color display replicates the action of pressing the similarly named hardkeys on the front panel of the instrument When performing a recall operation the data type recalled will correspond to the selection in the MASTER window just as when using the instrument in a stand along configuration the setup of the analyzer will determine what type of data are recalled For example if the MASTER window shows Leq then only data of type Leq will be recalled Also if it is desired to recall data of the type byTime the analyzer must be config ured to the byTime autostore mode before performing the recall It is necessary to utilize the Control window in order to change the 2900 between byTime autostore and Standard storage After clicking on RECALL the data type record number and note if any will be displayed in the blue field on the upper right of the display In order to rec
238. dicated on the right side of the screen second line down will be dB SPL When the dis play represents intensity the units will be dBpW m2 If some of the traces have been defined to represent intensity and others pressure then graphic data will appear for either the Intensity or the Sound Pressure display choice Note that the table will present both intensity and sound pressure level amplitudes corresponding to the cursor position regardless of which graphics mode has been selected vsRPM Graphics Post process Order Tracking 2900 MANUAL vsRPM Graphics Post process Order Tracking permits the user to generate curves of order versus RPM Speed when octave bandwidths or standard FFT filtering are utilized The key to this is the availability of the Tach and Speed data for each spectrum In the real time mode values of Tach and Speed are being read with each spectrum When byTach autostored data are being used values of Tach and Speed have already been stored along with each spectrum When performing Post process Order Tracking either Tach or Speed will be selected by the user to serve as the reference frequency The methodology for Post process order tracking is to note the value of the reference frequency associated with the spec trum determine into which filter band that frequency would fall and take the amplitude of that bandwidth as the ampli tude of the first harmonic A similar procedure is followed for e
239. ds rather than their average To Autostore by Time NOTE 2900 MANUAL perform the Block Maximum operation from the Recall Menu press B MAX C which will bring to the upper right of the screen the following message Last N MAXIMUM 0001 0002 Use the numeric keypad and the horizontal arrow keys to enter values representing the first and the last of the sequence of record numbers over which the block maximum operation is to be performed The Autostore Block Maximum operation is limited to a maximum number of sequential records of twenty Upon pressing EXIT the operation will be performed and the resulting spectrum stored The word MAXIMUM appears on the right of the screen 2nd line down in place of the elapsed time usually displayed with a measured spectrum to indicate that this spectrum is the result of the Block Maximum operation If the records con tained within the specified range are not all of the same type and bandwidth the Block Maximum operation will not be completed and the message NOT SIMILAR DATA will appear on the upper right of the screen Block Summation of Autostored byTime Records Autostore by Time NOTE Like the Block Average and the Block Maximum operations the Block Summation operation can be applied to Autostored byTime records of the same type and bandwidth which have been stored sequentially record numbers in sequency The result is a similar autostore record where the Nth spectrum is
240. dure is to begin with a baseband full scale fre quency no higher than is sufficient to analyze the frequencies of interest Then to examine in more detail specific frequency components or sub sections of the original frequency range use the zoom analysis capability The analysis performed by the zoom FFT depends uniquely upon the upper frequency time weighting and number of lines used for the baseband analysis and the selected zoom factor If one performed a baseband analysis followed by a zoom analysis using a multiplier of 4 then another zoom analysis using a zoom factor of 32 the result would be the same as if the zoom factor of 32 had been used initially after the baseband analysis assuming the same center frequency were used for both analyses The zoom analyses do not build upon one another The time required for the zoom analysis to be performed will always be longer than that required for the original baseband analysis In fact there is an inverse relationship between the time required and the bandwidth zoom multiplier A zoom analysis using a zoom multiplier of 64 will require a time interval 64 times longer than the baseband analysis upon which it is based The user must bear this in mind when using very large zoom factors since the time required until the first spectrum appears on the screen could be a number of minutes even with the very high speed processor used by the Model 2900 Once in the Zoom Menu move the
241. e click for selection of the number of lines one for selection of the time domain window one for selection of baseband full scale frequency and finally another to select a zoom value However since these parameters are independently selected in many cases the parameters such as weighting function baseband full scale frequency and zoom value may already be as desired Selection of Averaging Time The detector type is selected by clicking on DETECTOR and clicking on the desired type from among those presented in the window 24 6 The averaging time is selected by clicking on AVG TIME When the detector type has been set to Exponential BT Exponential or BT Linear the window which opens will present a list of averaging types available for the active detec tor type Simply click on the desired choice Use of External Color Monitor for Display and Instrument Control Selection of Master Display Type 2900 MANUAL When the averaging type has been set to Linear Single or Lin ear Repeat the message Click for AVG Time will appear within the window When the selected averaging type is Linear Single or Linear Repeat it is necessary to enter the averaging time character by character rather than select from a list of available values In such a case upon clicking the AVE TIME window it is necessary to click upon the message Click for AVG TIME which will bring the message and data field DETECTOR TIME 0000000 0000 to the u
242. e example if the cursor had been placed at 1 kHz before the zoom 1 kHz will be the center of the new 1250 Hz wide fre quency range Therefore the frequency scale seen on the dis play will be from 375 Hz to 1 625 Hz 1250 Hz 2 625 Hz 1 kHz 625 Hz 375 Hz 1 kHz 625 Hz 1 625 Hz Had the cursor been located at 5 kHz the zoom analysis would cover the range from 4 375 Hz to 5 625 Hz During the zoom analy sis the cursor will move to the center of the screen still rep resenting the same frequency value and the display will show the total frequency range of the zoom analysis If the cursor position before the zoom analysis is less than 1 2 of the zoom total frequency range say 500 Hz in our example the above calculation indicates that a negative value for the low frequency limit would result 500 625 125Hz In such a case the zoom center fre quency is made equal to 1 2 of the zoom total frequency range in the example to 625 Hz producing a zoom fre quency range beginning at O Hz Similarly should the cursor be located very near the upper frequency limit of the base band range the zoom center frequency would be adjusted to a lower frequency value if necessary so that the zoom fre 2900 Instrument Setup Via The System Menu Limitation on Zoom Multiplier 2900 Instrument Setup Via The System Menu 2900 MANUAL quency upper limit would never be greater than the baseband upper frequency limit The best proce
243. e the standard recommends 8 12 seconds or an integral number of cycles for periodic signals by pressing AV TIME H enter ing the desired number using the numeric keypad and pressing EXIT Return to the Intensity Main Menu and access the Autostore Menu by pressing AUTOSTR P Set the time interval between autostored spectra to equal the value of the short time average value by pressing delta C entering the value using the numeric keypad and pressing EXIT The number of short time averaged values to be stored during a measure ment sequence M is established by setting the total time period for the autostore equal to the short time average mul tiplied by M The standard recommends a value of M 10 For example if the short time average value is 10 set the value of endstore to M 10 100 This is done by pressing endstor D entering the value using the numeric keypad and pressing EXIT Activate the byTime autostore mode by pressing bytime B which will produce the message bTIME along the vertical axis on the left of the screen Place the intensity probe in position relative to the test speci men where the temporal variation is to be determined and 20 19 2900 MANUAL press R to begin the measurement A sequence of M spec tra each measured over the short time average period will be stored automatically in a single block at the conclusion of the sequence Note the record number under which this mea surement
244. e 4 12 Branching a Signal from One Input Connector to both Analysis Channels Dual Channel Analysis Only Standard or Sound Level Meier 4 13 Setting the Analog Filters for the Frequency Analysis Function 4 13 Internal Calibration Gong 4 13 Offsetting Gain Between Channels nennen nennen nnne 4 14 Setting the Autorange Aperture 4 14 Operation of the Noise Generator OPT 10 Required 4 14 GONDEGUON i ts ee be ete PENNE PET 4 15 Selecting Spectral Content 4 15 Selecting Operational Mode A 4 15 Operation of the Signal Generator OPT 11 Required 4 16 Operational Mode or ci er rte e pepe c e ttti egt ua Bb St dard 4 16 Chapter 5 Chapter 6 2900 MANUAL Sine Generator Single LONG a a Lg ee eege ey Ya da 4 16 Sine Generator Dual FoORBez Tu etin nci innt ra Ga a n rna a ndo a degen 4 18 Autolevel Control Sine Generator 4 19 Pink Noise Generator Wideband or Bandlimited 4 20 Autolevel Control Bandlimited Pink NoiSe nnne 4 21 White Noise Generator Wideband or Pseudo nnne 4 22 e IEN te EE 4 22 lun Gel e EE 4 23 Selection of Intensity Probe or Remote Control 4 23 Remote Control using Model 3200RC Remote Control Module 4 24 SOU Ie IM 4 24 Operation edel an o dede ete ae St d vue e aaa i die cae 4 25 Communication with User defined Setups
245. e analog waveforms sampled before the trigger event occurred 2 One could elect to save none of the data points within the buffers at the instant of triggering and begin filling the buffers anew from that instant 3 One could elect to save none of the data points in the buff ers at the instant of triggering and also to wait a selected number of samples before beginning to fill the buffers again The manner in which the system deals with these possibili ties is determined by the Trigger Delay Trigger Functions Trigger Functions Example 2900 MANUAL Zero Trigger Delay represents saving none of the previously measured data points as in item 2 above A Trigger Delay of N samples implies item 3 above where N is the number of samples which are allowed to pass before storage into the buffers begins A Trigger Delay of N samples corresponds to item 1 above where N is the number of most recent values in the buffers which are saved at the instant of triggering The Trigger Delay is set by pressing DELAY N using the horizontal arrow keys the right arrow to increase the value of the delay and the left arrow to decrease it The message trig delay on the lower right of the display indicates the role of the horizontal arrow keys As they are pressed the value of the Trigger Delay is displayed on the right of the screen by the message td xx where xx is the delay in number of samples With FFT filtering
246. e batteries Accessories and items not manufactured by LarsoneDavis Inc are covered by the warranty of the original equipment manufac turer Product defects caused by misuse accidents or user modifica tion are not covered by this warranty No other warranties are expressed or implied Larson Davis is not responsible for consequential damages Chapter 1 TABLE OF CONTENTS le OUE LO Mere ev rt 1 1 Front Panel Controls x t ordi dE ed dut eate a dc sitae bata Reni 1 2 Dedicated Hardkeys is u eben tie e Dea are ebat D te xta E eR AR ak kk a RR Axa 1 2 ASGIEEardkeys tete tet Ree it dite E Go eto det etii tuit 1 3 Me r ac USD 1 4 The Arrow Keys and associated HardkeyS eene 1 5 e eeraennicm 1 5 Flange GOmtrol te ETUR EE 1 5 Instrument Boot up Procedure eee nn nnn nnn nnne nis 1 6 Resetting RAN iiti ier Ua ERR eie 1 7 Upgrading Re 1 7 Bee ul te DEE 1 7 Setting Backlight and Viewing Angle U r 1 7 Beeper Controls EDD 1 9 Color MOnitor Ate iie tat A tet ie ee li eet 1 9 Power Supply Sima uertit eei trente UND I asas 1 9 Battery le 1 9 Biel UE 1 10 Charging Batteries ee Ente enean uA Yuya 1 10 Microphornie Gonrnection 2523 etre e EE 1 10 Alternatve Inp ts m eer IR itii 1 11 Accelerometers with Internal Elechonics emnes 1 11 Charge coupled Accelerometers ent
247. e down Either the summation symbol or the letter A will appear to indicate which of the two broadband levels is being displayed To switch between these two presentations access the Display Menu and press SUM E which toggles this digital display between them Analysis Menus Selection Of Measurement And Display Parameters 6 11 2900 MANUAL 6 12 Analysis Menus Selection Of Measurement And Display Parameters 7 Performing a Measurement Manual Control of Run Stop In this section we discuss the use of the R S key to manually initiate and stop a measurement how to reset the data buffer manual control of input gain and use of the autorang ing function for automatic input gain adjustment A mea surement can also be initiated by the input signal amplitude itself and from an external pulse as explained in Chapter 11 Trigger Functions Continuously Running Time Averaging Manual control of the 2900 to initiate and stop a measure ment is via the R S hardkey at the lower left of the front panel The initial press will begin the averaging process On the right of the display fourth line down the operational sta tus will be indicated as RUN The run time display on the right end of the first line will indicate the number of seconds which have elapsed since the averaging was initiated Performing a Measurement If the averaging type has been selected to be Linear Repeat Exponential BT Exp BT Lin or Count Repea
248. e individual autostored records is performed which permits the user to select a value of increment A different than that which may have been pro grammed during the data acquisition process The result is that the spectra in the averaged block will appear at precisely Autostore by Tach 2900 MANUAL the requested RPM or speed increments For example if the data storage had been programmed to nominally store data every 100 RPM the user can select the perform the average using an increment of 10 RPM providing better resolution over the range of the test data This also means that the aver aging process can be utilized on a single record to normalize the RPM or Speed increments in the data block As was explained earlier in practice the data will not be stored at exactly the specified increments of RPM or Speed By per forming an average of this record using the same value of RPM or Speed increment originally specified for the autostore the resulting spectra will appear at precisely the desired increments Once the values of s e and delta have been set as desired and entered by pressing EXIT the following message will appear on the screen to prompt the user to specify the sequence of record numbers over which the average is to be performed Last N AVERAGE 0001 0002 Use the numeric keypad and horizontal arrow keys to edit this field as desired and press EXIT to perform the average In the case where one wishes to simply
249. e intensity probe and note the length Pressing prtsp l wil open the appropriate data entry field on the upper right of the screen Enter these parameters using the numeric keypad and press EXIT Amplitude and Phase Normalization 1 1 1 3 Octave Measurements For sound intensity measurements it is essential to have the best possible amplitude and phase match between channels in order to meet the pressure residual intensity specifica tions of the standard It is recommended that the Lar soneDavis Model CAL291 Residual Intensity Calibrator be used for this procedure In order to use the CAL291 the Model 2900 must be equipped with either the 2800 OPT 10 Noise Generator or the 2800 OPT 11 Signal Generator The LarsoneDavis Model CAL290 can be used in the Residual Intensity Mode if following the ISO standards but better phase accuracy will be obtained using the CAL291 Loosen the connection of the adjustable arm of the intensity probe remove the spacer lay the probe on the surface sup porting the calibrator with the handle positioned above the calibrator and press the microphones firmly into the two microphone openings Set the detector of the 2900 to expo nential averaging with a 1 second averaging time If using the CAL291 set the Noise Generator or the Signal Generator to provide a pink noise signal If using the CAL290 select the Residual Intensity Mode and 1 3 octave band sig nal Press R S to begin an intensity measurement U
250. e inter val between storage of spectra should be set equal to or greater than the averaging time to avoid trying to store data before it is available A spectrum or pair of spectra for dual channel is read from the averaging buffer for storage at the time interval set by Delta Time At this time the averaging buffer is reset to zero If the time interval is less than the averaging time zero data is stored prior to good data being available Suppose the analyzer is configured for single channel and 800 line FFT At this configuration the smallest autostore time interval which can be input is 0 04 s because that is the rate at which new FFT spectra are produced If the autostore time interval is smaller than that say 0 01 s an empty aver aging buffer will be read three times before a full one is avail able If the time interval had been selected to be 0 12 s the average value would change every 0 04 s as a new spectrum is added to the linear average After 0 12 s the average of three spectra would be stored and the averaging buffer would reset and begin calculating a new average If the time interval was not used but rather the averaging had been selected to be Count 4 storing of data would be after four spectra are averaged The value in the averager would be updated every 0 04 s as a new spectrum is added to the spec trum average But after four spectra had been averaged 0 16 s the data would be stored and the averager would
251. e message NORM on the left of the screen To abort the storage procedure press NO B The screen will revert to the Menu active prior to accessing the Shift Menu but the Normalization Mode of the 2900 will not be active If it happens that the 2900 already had the Normalization Mode active at the time of attempting to set the normalization correction function the message Normalization must be OFF will appear on the upper right of the screen It will be necessary to turn off the normalization mode and repeat the transfer function measurement before completing the nor malization procedure From the Shift Menu shown above the normalization mode is turned on and off by repeated presses of the softkey NORMALZ N The corresponding messages on the screen will be Normalization is ON or Normalization is OFF Thus whenever the Normalization is OFF the measurement is a simple cross channel measurement and when it is ON the stored correction function corresponding to the selected baseband full scale frequency will be used to correct the mea sured results Control of Display Formats Cross Channel Normalization and Use of Key Macros 19 11 2900 MANUAL Normalization in the Cross Mode using Octave Bandwidths Key Macros The normalization procedure used with Octave Bandwidths is nearly identical to that used with FFT bandwidth The main differences are as follows 1 Pink noise is recommended rather than white noise
252. e n te fen t it ee P ed Esc Ferte ne re 24 9 Channel N mb er eerie fie e ot edente aede u Fade 24 10 Selection of Broadband and Highpass lowpass Filters sss 24 10 Selection of Units ep rira been ioo Et ntes 24 10 Cursor Control and Selection of Graphic Display Parameters 24 11 Cursor Gontrol oo iad aed on tnd ae a EI nwa in a Gai 24 11 Vertical Display Range Control 24 11 Horizontal Display Range Control 24 11 EE E 24 12 Linear and A Weighted Data 24 12 Recall and Display of Data 24 13 Running Mars e eite t Ro He e dons ren fet eee v cer eco ren Ee lu rdiet lee i ult 24 13 Recalling Setups theta ato ott exaudi e 24 13 Displaying in the vsRPM Speed Format 24 14 2900 MANUAL Selecting the vsRPM Speed Format 24 14 Selecting vsRPM or vsSpeed enne entere nnne nennen nennen 24 15 Assigning Pens to Frequencies or Orders eene 24 15 Assigning Traces BEEN 24 16 Hiding or Unhiding Traces AA 24 16 Cursor GON MO ke ake a ki on oak pe Sele A E Eh Uu Rs Een 24 16 Modifying the Left and Right RPM Speed Axis Limit Ae s ei eeeiiai s iii ii l 24 16 Selecting Band Tracking eene nennen entere ay sinet 24 17 Chapter 25 Softkey Men s 25 1 Appendix A RAR RA ARAR AA Rad
253. e of the time records for each channel This is so that an integral number of time records are dealt with in the averaging process Sequential presses of TIME E will produce displays of the Weighted Time Record and the Time Record unweighted The Time Record is the time waveform for each input channel as sampled and stored into the time buffer The Weighted Time Record is the same data after having been multiplied by the time weighting function Hanning Flat Top etc previous to the FFT calculation Cross Analysis with Octave Filters Compared to the many parameters produced by Cross Analy sis using FFT filtering with Octave filtering only the fre quency domain parameters are calculated and displayed After setting up the analyzer and exiting from the System Menu the Cross Menu with Octave Filters shown in Figure 6 5 Octave Cross Analysis Menu is displayed Figure 6 5 Octave Cross Analysis Menu BER 12 48 32 A SPECT C SPECT X FER COHER INVERSE note DETECTR i SPL 1 6258 7 eoo EXPONENTIAL Dual LINEAR 2 Hz 28kHz STOP 81 APR 97 12 39 45 eet w nn n nn e n o nenm m FILTER 14 25 0 Hz L73 Coherence D 2 d 8 8722 mom s s s s s o s s c ss da Base Fresauency B 000A TACH 6 6 SPEED 4 6 6 Hz Wd Hz kHz Z A dotted crsr INT ALTERN BWNORM SETUP FILES AUTOSTR Select the parameter to be displayed by pressing one of the softkeys listed below Softkeys Softkey Functi
254. e readout of Speed will be in units of fre quency He then presses R S a second time to perform the calibration and to stop the analysis The 2900 will now be calibrated to display Speed in units of miles hour for that particular vehicle Suppose upon accessing the Tach Speed Calibration Menu only the key C tach A is used to preset a value of the Tach readout to be calibrated for a particular machine condition Then following two successive presses of the R S key the Tach scaling will be set such that the readout will indicate that preset calibration value for whatever frequency was being read at the Tach input at that instant If both the C tach A and C speed B keys are used to input calibration values after accessing the Tach Speed Calibration Menu then both will be scaled to these calibration values fol lowing two successive presses of the R S key 16 8 In some instances the signal from the tachometer pickup may develop some FM jitter due to vibration of the rotating structural element of the machine under test which is being used for detection of the tacho signal An example of this would be a tire upon which a white target line has been drawn to trigger a signal from a photo electric sensing probe At high speeds tire vibrations would produce such an effect on the signal To improve the performance under these circumstances the digital treatment of the Tach Speed signals includes averag ing algorithms Access the
255. e same manner by pressing Ithresh T which will produce the message ENTER THRESHOLD Max nnn n Use the numeric keypad to enter a value which will define the end of the curvefit time interval as the instant the sound level has decayed to nnn n dB In the example above this would be 070 0 dB Press EXIT to accept the value which will then appear as XX X in the text field THRESHOLDS XX X YY Y on the right of the screen The curve fit are performed as described for the Max based thresholds The key Auto RE E will initiate an automatic curvefit based on the fixed thresholds and the RT60 values will replace the values previously stored in the RT60 register The key Auto AV F will initiate an automatic curvefit based Room Acoustics Measurements 2900 MANUAL on the fixed thresholds and the RT60 values will be averaged with those already stored in the RT60 register There is one aspect of using the fixed thresholds to bear in mind however When using fixed thresholds it is a required condition that the decay curve at each frequency begin above the upper threshold and decay to a level below the lower threshold For any frequency band for which both conditions are not satis fied the curvefit procedure is aborted and the value RT60 is assigned to be zero This produces the message THRESH OLD NOT MET NO RT60 to warn that for at least one fre quency band a zero value of RT60 will appear in the RT60 register When using Max based
256. e softkeys will have the label undef to indi cate that no user defined label has yet been defined for them Prior to storing a set of class lines to a particular softkey it is best to assign a meaningful name to its label in order to be able to remember in the future which set of class lines has been stored there This is done by pressing NAME A responding to the message Push Setup to Name on the upper right of the screen by pressing the softkey whose label is to be defined responding to the subsequent message Enter setup name by typing in a name using the alphanu meric keypad and pressing EXIT This name will now appear as the softkey label above the hardkey it represents This pro cedure simply labels a softkey so the user may label as many of these eight softkeys as desired either all at once or as con venient To store the presently active set of class lines to any of the eight softkeys along the bottom of the screen press STORE C and in response to the message Store in this setup on the upper right of the screen simply press the soft key to which that set of class lines is to be stored Recalling a Set of Class Lines from Setup Menu Softkeys 22 12 To recall a set of class lines stored under a softkey in the Class Lines Setup Menu simply press that key The message Overwrite current setup on the upper right of the screen warns that this procedure will cause the four class lines pres ently active to be replac
257. eDavis Model 2530 1 4 microphone having a nominal sensitivity of 1 5 mV Pa with a Model 910B preamplifier Weighting Measurement Range A weighting 54 166 dB C vveighting 60 166 dB 20 Hz 20 kHz 61 166 dB 1 Hz 20 kHz 69 166 dB 3 13 2900 MANUAL Primary Indicator Range Non linear Distortion The primary indicator range is defined by IEC 651 and ANSI S1 4 1983 as a specified range of the indicator for which the sound level meter readings are within particularly close toler ances on level linearity Linearity is measured using sinusoi dal test signals The primary indicator range of the Model 2800 2900 SLM A mode is 65 dB This means that although the dynamic range of the instrument as an analyzer is greater than 80 dB mea surements of sound level made using the instrument in the SLM mode will be within the Type 1 primary indicator range linearity specifications when the level is within 65 dB of the full scale value During a measurement whenever the mea sured sound pressure level drops to more than 65 dB below the full scale value two question marks will be displayed to the right of the sound level digital readout on the lower right side of the screen Measurements were made to determine non linear distortion between the sound input and the signal output according to TEC 651 subclause 6 9 and ANSI S1 4 1983 sub clause 5 9 Using A C and Flat 20 Hz 10 kHz 20 Hz 20 kHz 1 Hz
258. eated instrument Set ups Creation selection and directory of stored data Files Menu for Resets The Main Menu has a number of submenus as shown in the following diagram 2 2 Menu Structure For Instrument Operation 2900 MANUAL Analyzer Menu Display Note Detector Sound Level Meter Modes 1 1 vsRPM Stat FTrig Setup Files Autostore octave bandwidth bandwidth C only The general functions performed within each of these Menus and Submenus are as follows Menu Name Menu Function Display Selection of digital or user weighting for data Dis play Notes Annotate add Notes to data blocks before storage Stat Menu for measuring and displaying Statistics and Ln data F Trig Setup of Frequency Trigger Setup Storage and recall of instrument Setups Files Creation selection and directory of stored data Files Autostore Setup and selection of parameters for Autostore of data byTime Rooms Room acoustics post processing routines vsRPM Access vsTach Autostore Display Menu Menu Structure For Instrument Operation There are two sound level meter modes of operation available The Wide Dynamic Range Sound Level Meter WDRSLM Mode serves solely as a precision sound level meter This function is fully described in Chapter 3 Sound Level Meter Operating Modes Also available are the SLM A Modes single and dual chan nel for which frequency analysis is performed in parallel with the sound level mete
259. eating the note field for the data block store the block and the note by pressing STORE I Now recall the data block by pressing RECALL J and observe that the first 19 characters of the note field are displayed on the upper right of the display If the stored note field is larger than 19 charac ters simply press note G to display the complete note in the center of the display To edit the note field of a particular data block after it has been stored it is necessary to work from the Files Menu This is explained in detail in Chapter 13 under the section Record Operations from the Files Menu Annotation of Data Blocks T5 Autostore by Time This chapter describes the byTime autostore capability of the 2900 Before beginning this chapter read Chapter 13 Stor ing and Recalling Data to understand the general file struc ture used for data storage and how to perform file operations Setup for an Autostore Sequence Accessing the Autostore Menu Before beginning an autostore operation the data file into which the autostore data records are to be stored must be opened as explained in the preceding chapter Following this return to one of the Analysis Menus Access the Autostore Menu shown in Figure 15 1 Autostore Menu by pressing AUTOSTR P Figure 15 1 Autostore Menu 82 JAN 66 41 68 OFF byTIME delta endstor note Hote i SPL n 188 9 W a n n n w n w n a n w n n n n n n n n n cc n a n n
260. ecision condenser microphones and is becoming increas ingly common with accelerometers as well Many acoustics professionals will first calibrate the system using the K factor of the microphone They will then use a sound level calibrator as described below to verify the K factor calibration An error greater than a few tenths of a decibel could be an indication of a faulty microphone preamplifier or cable When using a sound level calibrator the known excitation level will be in decibels so the vertical scale should be loga rithmic While applying the known excitation to the trans ducer perform a measurement and stop the analysis with the measured spectrum displayed on the screen when using an acoustic calibrator select the Long 1 3 Octave filters Move Selection of Units and Calibration Calibration Using the Test Signal 2900 MANUAL the cursor to the frequency of the excitation then press level G The message Enter Level XXX on the right of the display will prompt the user for a numerical entry Type the known amplitude of the excitation via the keypad and press EXIT If using a LARSON DAVIS Model CA 250 Sound Level Calibrator the excitation frequency will be 250 Hz the Cali bration Level will be 114 dB and no differentiation or inte gration is necessary When using an accelerometer calibrator the known excita tion will typically be in units of g or m s so before per forming the calibration set the verti
261. ected bandwidths as a function of time Additional on board software permits the calculation and dis play of reverberation time sound transmission loss NC and STC Along with these analysis capabilities the 2900 pro vides a high degree of versatility in data presentation on the screen The user may control the vertical and horizontal screen formats log linear as well as the display ranges In conjunction with horizontal and vertical display expansion capabilities to provide the highest visual resolution of data vertical window and horizontal pan functions may be used to move the expanded data blocks for easy examination 2900 MANUAL Front Panel Controls Figure 1 1 Front Panel OFF Q s T U V w x ON A F G H EXIT CURSOR CH2 AUTO CH1 RANGE CLEAR RECALL RESET lt gt SPACE iii STORE A A IE ETE Some of these hardkeys have a label imprinted on the upper and lower levels of the key face When simply pressing the key the action associated with the lower level label is invoked The action associated with the upper label is invoked by pressing the SHIFT key prior to pressing the key itself Dedicated Hardkeys Figure 1 2 Dedicated Hardkeys OFF Q s T U V W x ON A F G H CURSOR EXIT CH2 gt AUTO 6 CH1 RANGE STORE CLEAR RECALL SHIFT HHEH AHB 1 2 Introduction ASCII Hardkeys Introduction 2900 MANU
262. ectra in the bandwidth compensated format access the Display Menu from the Analysis Menu press DISPLAY F and press BWNORM P The fact that band width compensation is active is indicated on the right of the screen first line after the units name by the symbol x 1 Repeated presses of BWNORM P will turn bandwidth com pensation on and off When using the LIN LIN or LIN LOG vertical display format with the bandwidth compensation active the units will be linear unit Hz When using the SQU LOG vertical display format with the bandwidth compensation active the units will be linear unit 2 Hz Thus with the system calibrated to units of g the LIN LIN and LIN LOG vertical displays will gi JHz while the SQU LOG vertical display will provide g Hz Control of Display Formats Cross Channel Normalization and Use of Key Macros 19 7 2900 MANUAL Control of Horizontal Display Selection of Logarithmic Linear Format When displaying spectra measured using fractional octave fil ters the horizontal axis representing frequency will be loga rithmic When displaying time domain functions the horizontal axis representing time will be linear Neither of these can be changed When displaying spectra measured using FFT filtering the default setting of the horizontal axis representing frequency will be linear However from the Shift Menu shown in Figure 19 2 repeated presses of X AXIS B will toggle the format of this
263. ed then change to a long linear average to obtain a very accurate result Prepare by selecting exponential averaging select an averaging time of 1 64s then select linear single and an averaging time of 16s Now whenever exponential is selected the 1 64s time will appear but when the averaging method is changed to linear single the 16s time will be recalled Signal Averaging Considerations Stationary Signals The spectra measured with most acoustic and vibration transducers contain a certain amount of random variability partly because the exciting force and mechanical response characteristics are frequently random in nature such as aerodynamically generated sound and structural vibration and partly because there is often random noise associated with the measurement system itself Time Averaging Selection of Averaging Parameters A signal which is steady except for the effect of random vari ations which have well defined statistical characteristics is referred to as stationary The statistical accuracy of measuring stationary signals can be increased by Time Averaging In principle the accuracy of the measurement increases as the averaging time is increased the trade off is between accuracy and measure ment time For Gaussian white noise passing through an ideal bandpass filter the standard deviation can be approximated as follows amp Standard deviation of the rms level dB B Bandwidth of Bandpass Hz
264. ed by the set which is being recalled and unless the presently active set has already been stored Classification Class Lines Optional Feature 2900 MANUAL it will be lost Press YES A to continue with the recall or NO C to abort the recall operation After completing the recall operation and exiting from the Class Line Setup Menu to the Class Lines Menu the names of the four class line fam ilies which have been recalled will appear as softkey labels at the top of the screen Storing Class Lines Stored under Setup Menu Softkeys to Non volatile Memory As explained above a set of four class line families can be stored to each of the eight softkeys in the Class Lines Setup Menu which represents a total of thirty two class line fami lies All of these can in turn be stored to the non volatile memory as a Class setup record and if desired stored to floppy disk as well Thus the user can develop a library of dif ferent class lines each stored in either non volatile memory or on disk Upon recalling a single Class setup record all thirty two families are recalled in groups of four one per soft key From the Class Lines Setup Menu press STORE and note the message on the upper right of the screen STORE Class setup n indicating that all class lines stored under all eight of the softkeys have been stored to the nth record of type Class setup Recalling Class Lines from Non Volatile Memory to the Class Lines Setup Softke
265. een third line down from the top far right side This could be A weight ing C weighting or linear weighting with one of the various available combinations of highpass and lowpass filters 1 11 2900 MANUAL Dual Channel Standard Cross or Intensity Analysis Mode SLM Mode When the 2900 is configured to the dual channel Standard Cross or Intensity Analysis Mode the signal produced from AC 1 will correspond to the Channel 1 input signal and the signal produced from AC 2 will correspond to the Channel 2 input signal Both signals will be frequency weighted by the same choice of user selectable analog input filter as indi cated by the message on the right side of the screen third line down from the top far right side This could be A weight ing C weighting or linear weighting with one of the various available combinations of highpass and lowpass filters Front Panel Display Format When the 2900 is configured to one of the SLM Modes of operation different weightings can be selected for the SLM and the Frequency Analysis functions In this case the out put from AC 1 is weighted the same as the Frequency Analy sis Function and the output from AC 2 is weighted the same as the SLM The setup of the 2900 is completely described by the parame ters shown on the screen In addition descriptive information concerning the data block is being displayed One way to assist you the operator to appreciate the control whic
266. een which indicate the setup of the sound level meter function as well as displaying the measured sound pressure level In the default setup as delivered from the factory the Chan nel 1 microphone input will be active with a 200 volt DC bias voltage applied This is the recommended bias voltage for use with Larson eDavis air condenser microphones and the Model 900B 1 2 or 910B 1 4 microphone preamplifiers It is pos sible to change the bias voltage to 28 volts or to turn off the polarization voltage for use with electret or prepolarized microphones as described below In the default setup an analog A weighting filter is inserted into the input signal path and the 2900 is thus set to display the A weighted RMS Slow sound pressure level along with the Min and Max values of the RMS Slow level during the mea surement interval The A weighted sound pressure level mea sured with the RMS Slow detector is the measurement most commonly called for in application standards 3 2 Sound Level Meter Operating Modes Changing the Microphone Bias Voltage 2900 MANUAL Changing the Microphone Input Normally the Model 2900 will be used with one of the Larson Davis air condenser microphones and either the Model 900B 1 2 or Model 910B 1 4 microphone preamplifier which requires a highly stable DC polarization voltage In the default setup the 2900 is set to use the Channel 1 micro phone input with a 200 volt bias voltage If an electret or pre
267. efined note which can be stored with specific data blocks However because this line may not always appear unless some note operations have been performed we have not included it as one of these locations For the same reason when in the following chapters we describe a particular parameter as being displayed on the right side of the screen Nth line down we do not include the Note line in the count The units name presently defined for the channel being dis played will appear in this location This will be dBuV SPL or a user defined name created from the Units Menu d Double Differentiation multiply by o dl Single Differentiation multiply by jo 1 Single Integration division by jo 2 Double Integration division by 0 ntroduction Location C Digital Display Weighting and Status of Time Trigger Location D Run Time Location E Averaging Type Location F Averaging Time Introduction blank USER blank ARM 2900 MANUAL Indicates that bandwidth compensation is ac tive producing amplitude as power spectral density This symbol appears alongside those described above Indicates that neither digital differentiation nor digital integration are active and that the spec tra are in RMS units bandwidth compensation is inactive A Weighting Active C Weighting Active User Weighting Active Negative A Weighting Active Negative C Weighting Active Negative User Weighting Active No Digital Wei
268. eighting Selected 1 16 Location J Operational Status n 1 16 Location K Date and Tite sio ce oe E Lee t ad Ave do ay eh dre e d ex d 1 16 Location L Filter Status and Frequency at the Cursor Position 1 16 Location M Channel and Parameter Information 1 17 Location N Amplitude Data corresponding to Cursor Position 1 18 Location Q Eoudriess Eevel n er ter e d vea UA Pa e dex ve daj 1 19 Location P Data from Tacho or Order Tracking BoardS sss 1 19 Location Q Status of the Horizontal Arrow keys ss i s l 1 19 NOISE elelo ee ei ert b er s da Bra se kad ke s b bi 1 20 Model 2800 and 2900 Specifications a 1 21 Der 1 21 Analog Input e UC EC 1 21 Digital Characteristics nsa sas eee need Ure i ee din ena dE lends o dde o D 1 21 Digitization iion te tated ete tied a I ate e a d E bt a t uy Ente 1 21 AnmEdligSI fg EE 1 21 DETECHON T ENEE A ENEE ee ee ee 1 21 Dynamic Range Mb 1 22 Amplitude Stabllity z EE 1 22 Amplitude Linearity TEE 1 22 diste Pc 1 22 Octave and Fractional Octave nennen nnns sn trennt nnns nenas 1 22 PET RE 1 22 Zoom Beete IN 1 22 Time Domain Windows FFT analysis 1 23 Measured And Displayed Parameters AA 1 23 Sound Level Meter Mode
269. elated moving the cursor until there is good alignment between the harmonic cursors and these spectral peaks is a good way to accurately determine the fundamental frequency of the harmonic series The higher harmonics are very sensitive to slight changes in the value of the fundamental frequency so small cursor movements which seem to have a negligible effect upon the position of the cursor with respect to the fundamental fre quency will produce large displacements of these higher har monic cursors Pressing OFF K will fix the cursor positions on the screen essentially disengaging the horizontal arrow keys from con trolling the cursors without assigning it to another role This will be accompanied by the message OFF on the lower right of the screen Pressing BOTH N SOLID O or DOTTED P will reassign the cursor to horizontal arrow key control Pressing EXIT exits from the Cursor Menu to whichever menu had been previously displayed Cursor Control 8 3 2900 MANUAL 8 4 Cursor Control 9 Units Selection of Units and Calibration The input to each channel of the 2900 will in all cases be a voltage signal from a transducer The role of calibration is to relate this signal to the sensitivity of the transducer and if required to perform integration or differentiation of the sig nal and modify the units of the data output to those desired by the user Accessing Units Menu Creation of Unit Names
270. els to measurements but without them the power summation capability of the 2900 cannot be utilized It is possible to assign labels or to modify them after they have been stored but it may be more conve nient to do this at the time of data acquisition and storage Sound Intensity Measurements 2900 MANUAL Selection of Display Parameters Selecting Displayed Parameters In the Intensity Analysis Mode the user can choose to dis play the intensity level spectrum the SPL level of Channel 1 the particle velocity spectrum or the quality spectrum Qual ity is calculated as the ratio of the intensity to the average sound pressure level or in logarithmic format the difference between the intensity level and the average sound pressure level Quality is used as an indication of the degree to which the intensity data can be taken as an accurate representation of the true intensity Readout of Broadband Levels To select the spectrum to be displayed press one of the fol lowing Softkeys Softkey Functions INTNSTY B Displays the Acoustic Intensity Spectrum QUALITY C Displays the Quality Spectrum SPL D Sound Pressure Level Spectrum of Channel 1 P VELOC E Displays the Particle Velocity Spectrum in units of dB re 1 nm s These parameters will be associated with a single microphone pair connected to channels 1 and 2 Reducing the Frequency Display Range The two vertical bars displayed to the right of the spectrum IN
271. ement And Display Parameters 6 1 2900 MANUAL When single channel Standard Analysis has been selected the active input channel is indicated on the right side of the screen by the message Input 1 or Input 2 Use the hard keys CH1 and CH2 to select which is to be used When dual channel Standard Analysis has been selected this message will read Dual to indicate that both channels are being measured simultaneously Selection of Display Format for Dual Channel Mode Average Spectrum Display When dual channel Standard Analysis has been selected the user can choose to view the spectrum for channel 1 the spec trum for channel 2 or the spectra for both channels in a side by side format For a single channel spectral display press CH1 or CH2 depending upon which channel is to be displayed This selection is also indicated on the right of the display 6th line down by the message Channel 1 of 2 or Channel 2 of 2 The dual channel display mode is activated from the Display Menu accessed from the Main Menu by pressing DISPLAY F From the Display Menu repeated presses of the softkey Multi H will toggle the dual display mode between ON and OFF When the dual channel display mode is active the message Multichannel Display will appear below the horizontal axis toward the left side When the dual channel display mode is active the CH1 and CH2 keys are used to position the cursor to readout the levels corresponding to
272. en after it has been displayed Thus we will see drawn upon the screen one spectrum then overlaid upon that another spec trum then another etc Once in the Recall Menu press W Fall A which will bring up the Waterfall Menu shown in Figure 13 4 Waterfall Menu 2D Format Figure 13 4 Waterfall Menu 2D Format 25 9ER 16 64 16 DRAW 1 DRRU 2 START END DELTA TC nr EUM RECALL Normal 9 SPL 7 7425 EXPONENTIAL 178 Input 1 LINERR 1Hz 28kHz RESET 25 APR 94 16 03 31 On the right of the screen we see a table indicating the present values of START END and DELTA These represent the first and last records in sequence which are to be dis played and the incremental record number between dis played spectra respectively For example using the following combination START 0010 END 0020 DELTA 0002 the records displayed will be numbers 10 12 14 18 and 20 in sequence To edit any of these numbers press START E END F or DELTA G This will produce the message VV FALL sXXXX eXXXX dXXXX with a flashing cursor to denote where inputs from the keypad will begin The only difference between initiating this input with the START E END F or DELTA G softkeys is that the flashing cursor will be posi tioned for immediate editing of the START END or DELTA values respectively Use the numeric keypad and the hori zontal arrow keys to edit the values as required and press EXIT The display sequence will begi
273. encies 1 20k 20k 10k 5k 2 5k 2 10k 10k 5k 2 5k Selection of Filter Type The following diagram shows the Menus accessed directly from the Filter Menu SYSTEM Filter t t t FET zoom VVindovv Base Hz The functions performed vvithin each of these Menus are as follovvs Menu Name Menu Function Filter 1 Select and configure octave type Filters 2 Select FFT Filtering and number of lines FFTzoom Select FFT zoom factor Window Select FFT time weighting Window Base Hz Select FFT Baseband full scale frequency Note that all the submenus refer to FFT analysis All actions required to select and configure octave type filters are done from the Filter Menu itself Accessing the Filter Menu The Filter Menu shown in Figure 4 2 Filter Menu is accessed from the System Menu by pressing FILTER G Figure 4 2 Filter Menu 19 967 14 38 82 1 1oct 1 3oct long short reverse SPL 0 000G IL PP vVyYV spvsv EXPONENTIAL Dual LINEAR 20Hz 20kHz RESET 16 OCT 97 sa ON W W W W W W W W W W W W W W W W W W W W n W W W n n n w n w n n on n n n n n n n n n n n nn FILTER 14 25 8 Hz v Channel 1 of 2 NORMAL dz 38 7 A 6 ea R pct ka wae ss ky pa wave DIFF Ph 71 8 Sn 8 58 REM TACH 08 8 SPEED 4 6 Ken nz cwm m dotted crsr TL TRRD iGaline 28801ine 406line 8001ine FFTZOOM WINDOW BASE Bd The softkeys along the top of the display apply to octave and f
274. ency of 20 kHz Introduction Time Domain Windows FFT analysis 2900 MANUAL Rectangular Hanning Flat Top ZeroPad w or w o Bowtie correction Impact Exponential 2900 Only Triggering Continuous free run Digital remote via interface Frequency domain level in selected frequency band Time Domain Level in channel 1 99 to 99 full scale adjustable ch 1 delay 4 adjustable ch 2 delay w r to ch 1 only Measured And Displayed Parameters Sound Level Meter Mode 2800 2900 Simultaneous measurement of sound pressure level A C or Linear weighted corresponding to the following detectors RMS Slow RMS Fast Min and Max RMS Slow and RMS Fast Impulse Leq Peak Taktmaximal 3 and Taktmaximal 5 A time history trace of RMS Slow RMS Fast Leq or Impulse is displayed in real time simultaneously with a frequency spectrum display Standard Analysis Mode 2800 2900 Octave and FFT Normal Leq Max Min and SEL Spectra plus MaxSpec Intensity Analysis Mode 2900 only Octave and FFT Intensity SPL Particle Velocity Quality Int SPL Cross Channel Analysis Mode 2900 only FFT Introduction Autospectra Cross Spectra Transfer Functions H1 H2 Inverse Transfer Functions Coherence Coherent Output Power Waveforms Weighted Waveforms Auto correlation Cross correlation Impulse Response Cepstra Liftered Spec tra 1 23 2900 MANUAL Cross Channel Analysis Mode
275. ent choices of the peak hunt parameter When using octave bandwidths for Post process order track ing selecting the SHORT filter algorithm rather than the LONG one will reduce the filter delay Since in most cases the signal components of concern will be harmonically related the loss in bandwidth selectivity will not affect the accuracy significantly vsRPM Graphics Bandwidth Averaging Procedure 2900 MANUAL vsRPM Graphics When working with fractional octave filters the amplitude at the crossover point between adjacent filters is 3 dB relative to the passband Therefore when tracking a constant ampli tude signal which is changing in frequency the order vsRPM Speed curve will dip by 3 dB each time the signal falls between two filter bands This effect can be reduced by aver aging the levels in more than one bandwidth The number of bandwidths over which the averaging is to be performed is selected from the Peak Hunt and Bandwidth Averaging Menu shown in Figure 17 3 The choices are repre sented by the softkeys below the screen Another reason for utilizing the Bandwidth Averaging is to increase the effective bandwidth of the analysis for the pur pose of comparing the data with that measured using a dif ferent bandwidth such as that measured using a different analysis system 17 13 2900 MANUAL 16 Setup for Statistical Analysis Statistics and L Calculations Statistics and Ln values n 1 99 in i
276. ente enne en 1 11 Direct Voltage Inputs ee i hee tee e ee eet Der ete p ce E DURER Md 1 11 AG Outputs EE 1 11 Single Channel Standard Analysis Mode sse enne 1 11 Dual Channel Standard Cross or Intensity Analysis Mode 1 12 SEM Model n 1 12 Front Panel Display Format en eene eene AEO aa nnne 1 12 Messages Displayed on the Left of the Green 1 12 Location A Displayed Data Type 1 13 Location B vsREF Display Status and Statistics sss 1 13 Location C Autostore Giatus nnne nen 1 13 Location D Frequency Trigger Gtatus enne 1 13 L cation E eut re BC UE 1 14 Eocation Ez Active EE 1 14 Messages Displayed on the Right of the Green 1 14 Note Display Linie eri eer Re PCR ERE REI Xe Eee PRI OE Reo eR 1 14 Location A Units Name ae e ea ee Pet ae be e data d s 1 14 Location B Digital Differentiation or Integration and Bandwidth Compensation Status 1 14 Location C Digital Display Weighting and Status of Time Trigger 1 15 Location D Bb TIImes EE 1 15 Location E Averaging Type iid eee e ede eet Atti dees 1 15 Location F Averaging TIMO eene 1 15 Location G INpUt TY Pe y nu ada Mr eripe Hb ede A ecc eins 1 16 2900 MANUAL Location H Analog Input Weighting u 1 16 Locationl Frequency Range betweenHighpass LowpassFilters with Linear W
277. entially in the downward vertical direction start ing with O The classification of a spectrum indicates the degree to which the spectrum levels have penetrated down wards across the family of lines and how many lines have been crossed in that direction In the editing mode repeated presses of the softkey A will toggle the mode between Max and Min as indicated by the label displayed above that key 22 7 2900 MANUAL Creating Multiple Class Lines Turning On a Class Line Family A family of parallel class lines can be generated from a single class line by pressing REPEAT B and in response to the message Number of repeats nn on the upper right of the screen use the numeric keypad to type in a value and press EXIT To set the spacing between the lines press AWIDTH C and in response to the message Repeat Delta nn dB use the numeric keypad to type in the number of dB spacing to used between lines and press EXIT When in the Max mode the class lines will be numbered sequentially in the upward vertical direction as shown in Fig ure 22 7 Multiple Class Lines Example Figure 22 7 Multiple Class Lines Example 29 DEC 16 58 49 TEST default default default C OFF D SPL Bann 90 TEE eebe EXPONENTIAL 64 1 Dual LINEAR 28Hz 18kHz 1 RESET 29 DEC 93 16 T 22 FILTER 7 5 66 Hz Lvs i v Channel 1 of 2 NORMAL dz 23 0 A 34 7 S oec E 00200 s PHONS 53 6
278. enu by pressing SETUP N and press the user defined and labeled softkey J P which represents the desired analyzer setup The 2900 will immediately be reconfigured as specified by the user defined setup which that softkey represents If it is desired that the 2900 boot up directly to one of the user defined setups instead of to the default setup press 5BOOT F and in response to the message PUSH SETUP FOR ATTN BOOT press the softkey which represents the analyzer setup which is to be active after the analyzer boots up when turned on Storage of User defined Setups Pressing the softkey R SETUP D will produce the message ARE YOU SURE on the upper right of the screen To con tinue with the reset press YES A To abort the reset press NO C After a reset the labels on all the user defined soft keys will return to undef 12 2 The entire set of user defined setups including the softkey labels will be stored as a record to the active memory file whose name is displayed on the lower left of the screen by pressing STORE The message STORE Setups N on the upper right of the screen indicates that they have been stored into the Nth record of type Setups in the active memory file Storage and Recall of Instrument Setups Recall of User defined Setups 2900 MANUAL Exiting from the Setup Menu Pressing RECALL from the Setup Menu will result in the recall of a set of User defined setups and soft
279. epends upon the rate at which they are pro duced by the processor which in turn depends upon the number of lines and number of channels used Therefore the autostorage is not strictly speaking a byTime operation and one loses the reference to absolute time because only the spectrum number is identified with each spectrum Neverthe less the mechanics of the process are similar enough in pro cedure that the same general description should suffice Initiation of an Autostore byTime Sequence Manual Start An autostore sequence may be initiated manually or auto matically using a Frequency Trigger Autostore by Time Once the Autostore parameters Delta Time and End Time have been set and the 2900 has been put into the Autostore Mode by pressing byTIME B an autostore sequence will begin as soon as the R S key is pressed Both the measure ment of the spectra and their automatic storage will be initi ated in this manner In some instances the user would like to be able to observe spectra being measured and displayed before manually beginning the autostorage sequence This is done from the Frequency Trigger Menu accessed from the Autostore Menu 15 3 2900 MANUAL Frequency Trigger Start by pressing F TRIG M and then pressing MANUAL M This will produce the message Manual use R S on the upper right of the display Following this pressing the R S hardkey will begin the measurement and display of spectra al
280. epresented in the spectrum previous to display The integration operations described here can be applied to FFT spectra measured using either the Standard or the Cross Analysis Modes since the effect of the integration on phase between channels has been taken into consideration How 9 3 2900 MANUAL Calibration ever due to limitations associated with the number of avail able bits of resolution the integrated levels of FFT spectra are only valid for frequencies above 196 of the full scale fre quency For frequency bands at frequencies below 196 of full scale the integration operation is not performed and the lev els will not be altered For applications where phase is not of concern and the spectra are measured using the Standard Analysis Mode single and double integration can be per formed as a display weighting function from the Digital Dis play Weighting Menu discussed in Chapter 10 These integrations are valid over the complete frequency range Upon storage the integrated or differentiated spectrum is stored and upon recall without selecting integration or dif ferentiation the displayed spectrum will already include the integration or differentiation operation which was performed at the time of measurement and storage Furthermore if integration or differentiation had been selected previous to the recall the displayed spectrum would be the same one which was stored regardless of the fact that single or double integr
281. equence In this mode there is no message on the display indicating the storage of a record Pressing the R S key will disarm the frequency trig ger and return the system to the manual trigger mode The message NO TIME HISTORY STORED simply means that this last press of the R S key did not produce an autostore and does not indicate that the preceding frequency triggered records were not stored Conclusion of an Autostore byTime Sequence Disabling Autostore byTime Whether the autostore sequence is initiated by a manual trig ger or by a frequency trigger the 2900 will then begin pro ducing spectra which will be stored automatically at the time intervals selected by Delta Time until the time period corre sponding to End Time is reached A value of elapsed time is stored with each spectrum or set of spectra if multichannels were used In the special case of FFT filtering with Count Averaging the spectrum number rather than the elapsed time is stored and the sequence ends when the total number of stored spectra specified under End Time is reached At the conclusion an autostore sequence except when the RE ARM Mode is active the data will be automatically stored and then recalled for display to the screen to indicate into which record number the data have been stored The mes sage will be STORE By Time N where N is the record num ber into which the data have been stored Detailed descriptions of the data storage format
282. equency analysis as indicated by the spectra appearing on the screen However spectrum Trigger Functions Automatic Re Arming 2900 MANUAL averaging will not begin until the trigger criterion is satisfied This can be verified by watching the elapsed time indication on the first line down on the right side of the screen and not ing that nothing appears until after the trigger criterion is satisfied With the instrument in the byTime autostore mode pressing the R S key will initiate spectrum analysis as indicated by the display of spectra along with the message AUTO STORE IN PROGRESS on the upper right of the screen However spectrum averaging and autostorage will not begin until the trigger criterion is satisfied The use of the Frequency Domain Trigger with the byTime autostore operation is useful for the capture of data automatically based upon an even which may occur when the instrument is left unattended Multiple events can be stored using the Automatic Re Arming function described below When the 2900 has been set in the autostore mode with a fre quency trigger established and armed by pressing the R S key and no trigger has occurred a subsequent press R S will disarm the frequency trigger and the message No Data Stored will appear on the upper right of the display Contin ued presses of the R S key will simply toggle the 2900 between the armed and disarmed states Trigger Functions If one wishes the 2900 to r
283. er as the center frequencies become lower The statistical accu racy will be progressively less at lower frequencies when using a linear average with these filters In order to have equal statistical accuracy for all bandwidths each filter must have a different averaging time For this reason the constant confidence averaging BT constant is generally used The following table shows the standard deviation associated with some of the BT product values provided with the digital filter version of the 2900 BT e dB 1 4 3 4 2 2 16 1 0 32 0 8 64 0 5 256 0 3 512 0 2 2048 0 1 8192 0 05 When using the Model 2900 in the constant confidence mode either linear or exponential averaging may be selected Expo nential averaging is discussed below under Transient Sig nals When the amplitude of the signal is too high during Time Averaging the instrument will indicate with the message OVER that an overload has occurred The only way to correct Selection of Averaging Parameters Periodic Signals Transient Signals 2900 MANUAL this situation is to keep increasing the range and taking mea surements until no overloads occur In the FFT mode spectrum averaging is permitted The spec trum of each measurement is included in a single averaged spectrum The number of spectra to be averaged is specified but before a spectrum is included in the average it is exam ined for overloads Overloaded spectra are rejected Measure ment
284. er table The value of RPM Speed and the point number for the cursor position are displayed on the lower right of the screen Numbers travel with the cursor on the screen to identify the individual traces Pressing RPM SPD F will switch the format between vsRPM and vsSpeed Storage of Trace Displays In many cases it may be desirable to improve the readability of the Trace Display by removing or hiding one or more traces from the screen A trace is hidden by accessing it with the numeric keypad and pressing HIDE J The fact that a pen is hidden is indicated by a letter H to the right of the trace number in the parameter table A second press of HIDE J will unhide the trace or cause it to reappear on the screen Recall of Trace Displays At the conclusion of a test pressing STORE will result in the storage of the Trace Display presently on the screen To store both vsRPM and vsSpeed Trace Displays they must each be displayed and stored The message STORE vsRPM Trace N on the upper right of the screen will indicate the Trace Display has been stored to the active memory file as the Nth record of the type vsRPM Trace The data representing all traces hidden or not are stored along with the parameter table 17 8 To recall a Trace Display the autostore function must be off and the 2900 in the vsRPM Menu If either byTime or byTach autostore is active at this time these will override the fact that the vsRPM Menu
285. ers Highpass Lowpass Filters 3 pole Chebyshev Highpass 1 Hz 20 Hz Lowpass 10 kHz 20 kHz A weight and C weight Filters in accordance with the follow ing ANSI S1 4 1983 Type 0 TEC 651 Type O and TEC 804 Type 0 Digital Characteristics Digitization 16 bit A D per channel Anti aliasing Oversampling delta sigma converter providing anti aliasing stop band rejection 596 dB Detector Digital true RMS with 0 1 dB resolution Introduction 121 2900 MANUAL Dynamic Range Amplitude Stability 80 dB Amplitude Linearity 0 1 dB Filters The greater of 0 05 dB or 0 00596 of the maximum input signal Linearity is measured using a sine wave test signal in the upper 40 dB of the dynamic range For signals more than 40 dB below maximum input the linearity is measured using a two tone test procedure Octave and Fractional Octave FFT 1 1 and 1 3 octave real time digital filters Satisfying or exceeding requirements for ANSI S1 11 1986 Type 0 AA and Type 1 D user selectable and TEC 225 Lower Frequency Limit 1 Hz Upper Frequency Limit 20 kHz 1 channel 10 kHz 2 channels Zoom Capability 100 200 400 800 line FFT analysis Upper frequency limit 20 kHz in 4 ranges 1 or 2 channels Maximum real time frequency 20 kHz 1 channel 10 kHz 2 channel 1 22 Real time zoom X512 Buffered non real time Zoom X32 applies to dual channel FFT with full scale frequ
286. es these keys are programmed for rapid acquisi tion and storage of data when using the acoustic intensity probe by programming KEY A to simulate the R S key and KEY B to simulate the hardkey STORE When exponential averaging has been selected the user will press KEY A once to initiate averaging another time to stop averaging then KEY B to store the measured data In many instances however linear averaging will be selected and the user will scan the probe across a particular surface during the linear averaging process In this case one press of Key A will initiate averaging and the averaging will automati cally stop at the end of the averaging time which will be indi cated on the LED on the upper end of the probe handle Then simply press KEY B to store the data 4 29 2900 MANUAL Beeper Control Selecting the RS 232 Interface Setting the Clock The function of the audio beeper signal is controlled from the Beeper Menu accessed from the I O Menu by pressing Beeper F The beeper can be programmed to output an audio signal corresponding to the following 1 The press of a hardkey or softkey 2 An overload condition at one of the inputs 3 An error condition 4 Any combination of the above three The following softkeys program the beeper function as fol lows Softkeys Softkey Functions NONE A No beeper signal at all ALL B Beeper signal for 1 2 and 3 KEYS C Toggles On Off the beeper signal for a key press
287. escribed in Chapter 13 Record Operations from the Files Menu And like any other record User Curves can be transferred from memory to the floppy disk and recalled back into memory from the floppy disk Exiting from the Setuser Menu To recall a User Curve record from the active memory file press RECALL The message RECALI User Curves N on the upper right of the screen indicates that the Nth record of the type User Curves has been recalled The contents of the active user weighting register and the four storage registers will now contain the user weighting curves which had been recalled from Nth User Curve record The curve from the active register corresponding to the analyzer bandwidth will be displayed The message recall data on the lower right of the screen indicates that the horizontal arrow keys are assigned to con trol the recall of records from within the file Presses of these keys permits the user to page backwards and forwards through the sequential User Weighting records to find the one which is desired As this paging takes place the displayed user curve will change to reflect the user curve of that band width stored in the newly recalled User Record The user may now recall a set of user weighting curves from any one of the four storage registers into the active register as described earlier in this section Pressing the EXIT key will exit from the Setuser Menu back to the Display Weighting Menu The dis
288. eset itself following a triggered autostore sequence and rearm the Frequency Trigger to be ready to autostore following a subsequent event from the Frequency Trigger Menu before selecting the trigger criteria press RE ARM N This key toggles the Rearm function on and off as indicated by the message Autostore rearm mode set or Autostore rearm mode off on the upper right of the display 11 7 2900 MANUAL 12 Storage and Recall of Instrument Setups Storage and Recall of Instrument Setups When the 2900 is first delivered there will be one default instrument setup to which the unit will configure whenever it is turned on and the software is booted up The Instrument Setup Menu shown in Figure 12 1 Setup Menu is accessed from the System Menu by pressing SETUP N permitting the user to define a number of different Setups The Menu can be used to change the existing instrument Setup to one of the stored Setups and also to define to which of the stored Set ups the unit will be configured when it is next booted up Figure 12 1 Setup Menu 82 JAN 96 26 18 name R SETUP STORE BOUT note SPL 6 9008 168 255 6 EXPONENTIAL 1 64 PREAMP LINEAR 18 20kHz RESET 62 JAN 90 06 22 41 80 2525 FREQ 450 20 2 Hopp v Channel 1 of 2 NORMAL d 4 6 Ze 27 3 ea LOC TACH G G SPEED 4 6 a ZUDM 1 58 0008 Z A dotted crsr TEST 1 DEFAULT undef undef undef undef undef undef undef The softkeys
289. esses of SLOPE A will toggle the slope parame ter between and as indicated by the message on the upper right of the screen DISPLAY SLOPE IS SET TO XX where XX is either or 17 5 2900 MANUAL Incremental Control of the Trace When the slope parameter is the curves will be drawn from left to right across the screen in a continuous manner only for positive increments of RPM Speed Should the RPM Speed decrease temporarily during a test and then begin increasing the curve generation will be seen to pause during the period the RPM Speed is less than the maximum value previously achieved and then will be renewed when the RPM Speed values exceed that previous maximum value When the slope parameter is the inverse applies and the curves will be generated from right to left corresponding to decreasing values of RPM Speed When the slope parameter is the generated curves may move to the left or right across the screen and in instance where the RPM Speed value changes both positively and neg atively during a test a loop pattern may be generated In some tests it is desired to observe data produced only by increases or decreases in the RPM or Speed values For example during a machine run up there may be a temporary reduction in RPM which would cause the drawn curves to loop back to the left on the screen before continuing to be drawn toward the right One may wish not to show that por tion of the curves
290. ey is pressed again there will be no additional response time and the data display and calcula tion of parameters such as Leq will be resumed immediately Possible Overload Indication upon Resuming Analysis 74 Suppose that during the period when the measurement is paused between presses of the R S key as explained above an input signal capable of overloading the analyzer occurs Since the display is not running the overload indication can not appear at that instant But because the overload indica tion is a latching one the overload indication will appear when the R S key is pressed to resume the analysis In such an instance it could be puzzling to the user to see an over load indication upon resuming the measurement when it is known that the input signal at that instant was not sufficient to produce an overload it is rather an indication that an overload did occur sometime during the time interval when the measurement was paused but the analysis function was still running Performing a Measurement 8 Cursor Control The cursors are controlled by the horizontal arrow softkeys at the lower right of the front panel The hardkey CURSOR is used to place the cursors under control of these keys The manner of which this is done depends on the state of the hor izontal arrow keys at the time If these keys have been assigned to perform some function other than cursor move ment such as controlling the gain then pressing
291. f Units and Calibration The Model CAL290 can also be used to perform the sound pressure level calibration using the Sound Pressure Level Mode Setup for 1 3 octave Intensity Measurement Sound Intensity Measurements From the Main Menu set the Model 2900 to the Intensity Mode by pressing SYSTEM INTENSY E and press EXIT to display the Intensity Analysis Menu shown in Figure 20 1 Figure 20 1 Intensity Analysis Menu d r mn 2 98058 si BRPOMENTIOL 1 8 Dual i aa 2 kHz a BER 12 43 46 POWER INTNSTV SPL P UELOC DISPLAY note DETECTR STI or E 12 43 19 FILTER m v Zkz 4 vr INTE YA de 13 6mm e efe s s s ee ee Zou KM 4tdB ai 060002 JOB PART CRIT lesse enn RRER 25 8 Hz A 500 Hz 18 0 2 E A dotted crsr INT job Part area prob meter2 SETUP FILES AUTOSTR Select the 1 Hz 10 kHz frequency range by pressing SYS TEM INPUT K 1 10K M EXIT Select the long 1 3 octave filters by pressing SYSTEM FILTER G 1 3oct B long F EXIT The 1 1 octave filters could be selected but 20 3 2900 MANUAL data measured using 1 3 octave filters can also be displayed in 1 1 octave format Pressure Temperature and Spacer Length Input Determine the atmospheric pressure in millibars and the temperature in C at the location where the measurement is to be made This data is provided by the Model CAL290 Select the microphone spacer to be used based on data pro vided with th
292. f a complex spectrum PHASE Phase of a complex spectrum REAL Real part of a complex spectrum IMAG Imaginary part of a complex spectrum dBPP Magnitude of the Cepstrum vsREF Indicates display is relative to a user designat ed reference spectrum STAT Indicates the Statistics Mode Ln is active blank Indicates the display is not relative to a refer ence spectrum bTIME Indicates autostore byTime is active bTACH Indicates autostore byTach is active blank Indicates autostore is not active TRIG Indicates frequency trigger is enabled 1 13 2900 MANUAL Location E Control Status Location F Active File blank Indicates frequency trigger is inactive REM Instrument is under remote control LOC Instrument is under local control This location displays the name of the active memory file into which data will be stored and from which data will be recalled Defined by the user from the Files Menu Messages Displayed on the Right of the Screen Note Display Line Location A Units Name Location B Digital Differentiation or Integration and Bandwidth Compensation Status 1 14 There are 17 different locations on the right side of the screen as shown in Locations at the Right of the screen on page 14 within which messages may be displayed Figure 1 6 Locations at the Right of the screen There may be another line displayed above these locations which begins with the expression Note This is a user d
293. f a new measurement is initiated it may appear that there is a malfunction in the measurement sys tem when no data appears on the screen It may simply be that the highest component in the spectrum is more than 10 dB below the full scale and therefore not visible without mov ing the viewing window Bandwidth Compensation Power Spectral Density When displaying spectra whether in octave or FFT band widths the amplitude of each filter band represents the RMS values of the energy measured contained within that band This is not typically a problem when using octave bandwidths because their bandwidths and center frequencies are estab lished by international standards However when performing FFT analysis the bandwidth of each filter depends upon the following factors number of lines baseband full scale frequency and zoom factor Since a variety of each of these are available with most analyzers it could be very difficult to compare measurements made with different combinations of these parameters One way of deal ing with this is to compensate for the bandwidth by dividing the energy within each band by the bandwidth of the filter and use this as the amplitude value for the display The units would then be in the form of energy Hz This form of data presentation is often referred to as power spectral density A very common application is in the measurement of random vibration where the desired amplitude units are g2 Hz To display sp
294. f the functions discussed in this Chapter are initiated from the Display Menu shown in Figure 19 1 which is accessed from the Main Menu by pressing DISPLAY F Figure 19 1 Display Menu 14 BER 14 25 19 171 143 AVERAGE SUM SETUSER note Multi SPL 2 628080 EXPONENTIAL Dual LINEAR 26Hz Z6kHz STOP 14 APR 97 14 23 54 FILTER 14 25 0 Hz 125 v Channel 1 of 2 NORMAL d 39 2 A DIFF PHONS 86 6 TACH 6 6 SPEED 4 6 l H GO H A Lk H dotted crsr TEST Dig WGT BIJNORM Dual Channel Side by Side Display Mode When the Model 2900 is configured for dual channel mea surements in the Standard Analysis Mode it is possible to display the spectra for both channels simultaneously in a side by side configuration as shown in Figure 19 2 Multi Display Format The spectrum for channel 1 is displayed on the left side of the screen and the spectrum for channel 2 is displayed on the right side of the screen Figure 19 2 Multi Display Format 29 BER 02 08 30 NORMAL Lea MIN MAX SEL DISPLAY note DETECTR Note MULTI CHANNEL DISPL 15 3600 Ium EXPONENTIAL 1 64 PREAMP LINEAR 16 1 kHz RESET 29 APR 98 61 46 41 DII 2 KEE ar ZO EO FILTER 24 258 Hz L712 v Channel 2 of 2 NORMAL d 45 8 66 6 TACH 6 6 SPEED 4 6 D kHz and dotted crsr Mx Srec F TRIG SETUP FILES AUTOSTR This function is enable from the Display Menu by pressing Multi H Repeated presses of this softkey will toggle between the single and the dual channel d
295. f the upper room The use of the block averaging function will serve to combine the spectra from these different measurements into a single space averaged spectrum as required A background spectrum is also measured in the test room while the tapping machine is not being operated As is done for the measurement of airborne sound transmis sion it is necessary to measure the sound decay time RT60 in the test room as described earlier in this Chapter Actually the procedure for the determination of Impact Sound Insula tion is similar to that for airborne sound transmission loss with the exception being that the tapping machine produces the acoustic excitation in the test room so there is no Source Room as such just a Receiving Room At the conclusion of the measurement phase of the project the following data will have been measured and stored in the analyzer 1 Test Room Receiving Room spectrum space averaged possibly source position averaged as well 2 Test Room background spectrum 3 Sound decay time RT60 To determine the impact sound insulation parameters access the Rooms Menu as shown in Figure 21 4 from the Main Menu by pressing ROOMS I Room Acoustics Measurements ASTM Impact Sound Transmission 2900 MANUAL Input the value of the Test Room volume m by pressing volume L typing the value via the numeric keypad and press EXIT Recall the space averaged Test Room spectrum and press RECEIVE N t
296. feature for use with the pink noise to assist in equalizing the noise level in a test room The Signal Generator Menu shown in Figure 4 8 Signal Generator is accessed from the System Menu by pressing SIG GEN J Figure 4 8 Signal Generator 28 118 23 57 88 N OFF ONZRUN OFFZRUN amp RTT gt ATT W a n w w w n n w w a n n n a w a w n a w a n n n a w a w a n n n a n n n n n n a n n nn nn PI HK ON 00 i SPL 6 00668 ang DLE EXPONENT I AL Dual LINEAR 20Hz 28kHz RESET 24 JAN 96 23 52 57 T 5 F I LTER 25 0 Aa Hz LAJ UEM 1of 2 Dec e d 23 8 A 34 7 5a SEET EE EE PHONS 53 6 LOC TACH 8 8 SPEED 0 6 ko DU a n s b ooo bas XA S k Ries Nea SS W s CLIE f 25 0 Hz 500 Hz IB8 BkHz dotted crsr INITIAL SINE PINK WHITE PULSE DELAY The operational mode of the signal generator On Off OnRun and OffRun is set from this Menu in exactly the same manner as described for the Noise Generator in the pre ceding section The Sine Generator Menu shown in Figure 4 9 Sine Gener ator is accessed from the Signal Generator Menu by press ing SINE I Figure 4 9 Sine Generator 50 OCT 82 14 32 Fstart Fend R se R es Lse Les lt RTT RTT 138 Sine End ON LOG 00 Note SINE WAVE TEST 5 7688 EXPONENTIAL TACH 6 6 SPEED 4 6 aa dotted crsr INITIRL START END SWEEP LIN 2 tone Auto L FILTER Upon accessing this menu the first word in the message appearing briefly on the upper right
297. file reducing each of their record numbers by one As a result the message on the upper right of the screen will still indicate the same value of N as before the deletion but this record will now represent the record which had been stored just after the deleted record since its index has been reduced from N 1 to N Those records located before the deleted record in sequence within the file will maintain their positions and record numbers Individual stored records can also be deleted from the Files Menu as explained in this chapter under the section Record Operations From the Files Menu Block Averaging of Stored Records Sequentially stored records of the same type can be averaged together using the Block Averaging Function From the Recall Menu press B AVE B which will bring to the upper right of the screen the message AVERAGE 0001 0002 Use the numeric fields until they represent the range of record num bers which are to be averaged together Upon pressing EXIT a single averaged spectrum will be created and displayed Note that it will have the word AVERAGE on the right side of the screen first line down instead of the elapsed time which is usually displayed with measured spectra In order to store this averaged spectrum press STORE The message on the upper right of the screen will indicate into which record it has been stored Block Maximum of Stored Records The Block Maximum operation can be applied to sequen
298. filter to respond before the noise shuts off 11 Return to the Standard Analysis Menu and press the R S key to begin analysis and the autostorage of data 12 At the completion of the autostore sequence the autostored record will be recalled and displayed Move the cursor to a frequency band of interest and press vsTIME C to examine the decay curve Press DATA M and use the horizontal arrow keys to examine the decay curves for the other frequency bands See Chapter 15 for a more detailed description of the use of the autostore mode and the control of the display Based upon the results of this test the user may decide to modify the values of averaging time Endstore and initial exci tation sound level to improve the measurement Autostore records whose data are not satisfactory for later analysis may be deleted Room Acoustics Measurements When an external source of impulsive noise is to be used for the tests the Frequency Domain Trigger capability can be utilized Move the active cursor to a frequency band which will be strongly excited by the source Set the trigger criteria to be SLOPE It may be necessary to experiment with the value of the trigger amplitude until a value is found which triggers reliably but not too long before the decay begins The 2900 will be configured for Standard Analysis 1 3 Octave and autostore mode as described in the preceding section In some situations such as music hall acoustics s
299. from the same bandwidths are added together so each of the four bandwidth user curves in the active register reflect the result of the addition process Storage of User Curve Records The user can subtract the set of user curves in any of the four storage registers from the set in the active register by press ing SUBTRCT L The message USER 1 4 TO SUBTRCT N prompts the user to input a storage register number using the numeric keypad and press EXIT The user weighting curve resulting from the subtraction is displayed User curves from the same bandwidths are subtracted so each of the four bandwidth user curves in the active register reflect the result of the subtraction operation Pressing the hardkey STORE will result in all the user weighting curves 15 contained in the active register and the four storage registers being stored into a single record in the active memory file whose name is displayed on the lower left of the screen The message STORE User Curves N on the right of the screen indicates that these curves have been Digital Display including Broadband Acoustic Frequency Weighting User defined Frequency Weighting and Integration of FFT Spectra 10 7 2900 MANUAL Recall of User Curves stored as the Nth record of the type User Curves into the active file Like any other record a note field may be added to the record previous to storage and the note field can be edited from the Files Menu as d
300. g a moveable display window of high resolution which can be shifted up or down through the range of the measured data This is done from the Shift Menu by pressing V OFSET D which will produce the message V Offset xx indicating that the horizontal arrow keys have been assigned to control the position of the vertical display window Use the horizontal arrow keys to shift the window in step of 10 dB As the win dow is shifted the value of xx in the message will change to indicate the position of the window in multiples of 10 dB rel ative to the full scale of the original display For example the message V Offset 03 indicates that the displayed full scale value is 30 dB below the full scale of the actual measured data To reset the window to the zero position simply press V OFSET D a second time or move it back with the hori zontal arrow keys and then assign the horizontal arrow keys to another role such as controlling the cursor Control of Display Formats Cross Channel Normalization and Use of Key Macros 2900 MANUAL Note that the vertical display range and offset are set uniquely for each display function This means for example that in the Cross Analysis Mode different ranges and offsets can be set for the display of Autospectum Transfer Function and Coherence data The use of very small display ranges such as 10 dB can lead to confusion if the user forgets that it has been selected as such For example i
301. ge 10 to 50 C referred to the indication at 20 C is less than 40 5 dB At low tempera tures approaching O C or below the response of the LCD display may become very slow However the accuracy of the data measured and stored will remain within specifications 3 20 The range of humidity over which the complete instrument including the microphone is intended to operate continu ously is O to 9996 relative humidity non condensing The maximum variation of sound pressure level due to humidity variation over the range 3096 to 9596 relative humidity non condensing referenced to the indication at 65 is less than 0 5 dB Sound Level Meter Operating Modes 2900 MANUAL Temperature and Humidity Permanent Damage Effect of Vibration The range of temperature and humidity conditions beyond which permanent damage to the instrument may result 20 to 60 C O to 9996 relative humidity non condensing Temperature Humidity Figure 3 12 below presents the broadband sound pressure level measured over the frequency range 20 Hz 20 kHz when the instrument is excited by a sinusoidal vibration of ampli tude 1 m s compared to that measured by a non vibrating microphone placed near the vibrating microphone The instrument is mounted on the exciter with the front panel horizontal and the vibration excitation applied in the vertical direction Two cases are studied with the microphone aligned horizontally such as would t
302. ger parameters will remain on the lower right of the display to indicate that the Time Trigger is active Pressing R S will arm the trigger indicated by the message ARM at the upper right of the display The sampling of input data and transfer to the time buffer will begin at this point As soon as the input signal in Channel 1 satisfies the trigger criteria data analysis will begin At the same time the message on the upper right of the display will change from ARM to GET to indicate the occurrence of triggering The time trigger function is turned off from the Time Trigger Menu by pressing OFF P The time trigger parameters will then disappear from the display When Frequency Domain Triggering is active the criteria used to determine when the analyzer is to be triggered into operation are the amplitude of the signal in a specified fre quency band and the slope if desired This method of trig gering can be used with either Octave or FFT filtering except with Count Averaging The Frequency Trigger Menu shown in Figure 11 2 Frequency Trigger Menu is accessed from either the Standard Analysis Menu or the Autostore Menu by pressing F TRIG M When doing Standard Analysis it is eas iest to access this from the Standard Menu for the other forms of analysis the Autostore Menu must be used Since in the majority of cases the Frequency Trigger is used with Autostore however this is not a major inconvenience Trigger
303. ghting Active Indicates that the Time Trigger is Active and Armed Elapsed runtime of analyzer in seconds since the last data buffer reset LINEAR SINGLE Linear Single seconds LINEAR REPEAT Linear Repeat seconds EXPONENTIAL Exponential seconds BT EXPONENTIAL Constant Confidence with Exponen tial Averaging Octave Bandwidths only BT LINEAR Constant Confidence with Linear Averaging Octave Bandwidths only EXPONENTIAL by N Exponential Averaging based on number of spectra FFT only COUNT SINGLE Linear Spectrum Averaging based on Number of Spectra FFT only COUNT REPEAT Linear Repeat Spectrum Averaging based on Number of Spectra FFT only COUNT MANUAL Linear Spectrum Averaging based on ACCEPT Number of Spectra manual Accept FFT only For Linear Single Linear Repeat and Exponential Averaging a value in seconds will be displayed For BT Exponential and BT Linear Averaging a value in units of Bandwidth Time Product will be displayed 1 15 2900 MANUAL Location G Input Type Location H Analog Input Weighting Location l Frequency Range between Highpass Lowpass Filters with Linear Weighting Selected Location J Operational Status Location K Date and Time Location L Filter Status and Frequency at the Cursor Position 1 16 For Exponential by N Count Single Count Repeat and Count Manual Accept Averaging a values representing Number of Spectra will be displayed Input 1 Indicates the 2900
304. gure 4 13 Wideband White Noise sa gT 82 26 16 PSEUDO I LEUEL amp RTT ETT Note WHITE NOISE 6 328080 EXPONENTIAL Input 1 LINEAR ri 2 kHz STOP 38 Har 62 26 02 FREQ 5262 Siet HSAA v Channel 1 of 1 NORMAL v d 86 1 107 8 TACH 8 8 SPEED 4 6 dotted crsr When FFT analysis has been selected a pseudo white noise output is possible The Pseudo White Noise Menu shown in Figure 4 14 Pseudo White Noise is accessed from the White Noise Menu by pressing the key PSEUDO A Figure 4 14 Pseudo White Noise sa ET 82 27 46 WIDE x ATT gt RTT Note PSEUDO WHITE NOISE 118 EXPONENTIAL 1 Input 1 LINEBR 28Hz 28kHz STOP 538 OCT 94 02 27 33 a i FREQ 5262 5080 Honn Channel 1 of 1 NORMAL 9 7 116 9 G G SPEED 0 0 dotted crsr When FFT analysis is taking place the analysis represents a finite number of frequency bands based on the number of lines selected for the measurement 100 200 400 or 800 It is not really necessary therefore for the generator to produce a truly wideband signal In the pseudo white noise mode the signals are generated at the center frequency of each of the bands represented by the lines of the frequency analysis This permits the generator output power to be concentrated on the same frequencies which are being measured by the FFT analysis even when zoom analysis is being performed The Pulse Generator Menu shown in Figure 4 15 Pulse Generator is accessed fro
305. h you have over the manner in which the 2900 measures and displays data is to list the many different messages which may appear on the screen and to provide a brief expla nation of each Use this section as a quick reference as well when the mean ing of a particular message is not clear We have used bold type to indicate messages which would appear literally as shown here and regular type when the message will be an alphanumeric string which is not predefined by the system Messages Displayed on the Left of the Screen 1 12 The messages which may appear on the left of the screen will appear in six distinct positions or locations as shown in the Locations at the Left of the Screen on page 13 Listed below are the different messages which may appear within each of these locations Introduction Location A Displayed Data Type Location B vsREF Display Status and Statistics Location C Autostore Status Location D Frequency Trigger Status Introduction 2900 MANUAL Figure 1 5 Locations at the Left of the Screen The following messages may appear when Standard Analysis has been selected Leq Equivalent Level Spectrum an acoustic parameter MAX Maximum Spectrum MIN Minimum Spectrum SEL Single Event Level an acoustic parameter Max S Spectrum measured for highest broadband level blank Normal Spectrum The following messages may appear when Cross Analysis has been selected MAG Magnitude o
306. he value digitally on the lower right of the screen in the format TACH XXX X The frequency can be scaled using internal software permitting the display of frequency in units other than Hz such as RPM This is also useful for cases where there are more than one pulse per revolution of the machine We recommend the LarsoneDavis Model T100 Tachometer which is battery operated and works with inductive optical and piezoelectric pickups Second Tachometer Input SPEED There is a second tachometer input available on the I O Port pin 5 which works totally independent from the signal on the TACH INPUT connector The software scaled value of the fre quency of this pulse train is also displayed on the lower right of the 2900 in the format SPEED XXX X The name derives from the most common application a vehicle test in which the TACH INPUT is a tachometer signal from the engine and the other input is from a tachometer using an optical pickup aimed at a reflective line on a tire thereby pro ducing a frequency proportional to vehicle speed However this is really just another tachometer channel so it need not be measuring speed in spite of the label used in the display TACH SPEED Display in Intensity Mode Autostore by Tach When in the Intensity mode there is normally insufficient space on the right side of the screen for the display of the TACH and SPEED values due to the space taken up by the JOB PART AREA names However
307. he Statistics Table which is generated during a measure ment when the statistics mode is on is capable of producing Ln values between 1 and 99 in integer steps for each fre quency and for the broadband level Up to six statistics curves each corresponding to a particular value of n can be calculated and displayed at one time The statistics parame ter table on the right of the screen is used to assign a value of n to each of the six curves which may be drawn Select the trace number 1 6 whose parameter value is to be changed by pressing that numerical value on the keypad The symbol 55 will appear to the left of the trace number indi cating that it has been addressed and may be modified To change the value of n corresponding to the desired Ln press N N and press the horizontal arrow keys until the desired value appears Note that one increment below the value n 1 the word Max will appear indicating that the parameter is set for the maximum value Similarly one increment above the n 99 the word Min will appear indicating that the parameter is set for the minimum value If it is desired that less than six traces are to be used addressing any trace and pressing CLEAR G will disable that trace indicated by a space where the parameter value would normally appear No data is calculated or displayed for a trace which has been cleared Note that when a previously 18 3 3200 MANUAL OPT 42 Running the Statistics Mode cle
308. he order number for each trace as described in the preceding paragraph When creating order plots from standard frequency analysis measurements it may also be desirable to set the peak search parameters It is suggested that the user read the section Post process Order Tracking before selecting orders when working with octave bandwidth or standard FFT filters Horizontal Scale Selection A message on the upper right of the screen will state either SOURCE IS TACH INPUT meaning that the format of the plot will be amplitude versus RPM or SOURCE IS SPEED INPUT meaning that the format will be amplitude versus Speed Pressing RPM SPD F will toggle between these two as indicated by the change in the message Slope Selection Select the lower and upper horizontal scale limits by pressing X SPAN D which will produce the message LOW HIGH XXXXX YYYYY on the upper right of the screen where XXXXX represents the left end of the screen and YYYYY the right end of the screen in either RPM or Speed scaled units whichever is active at the time Use the numeric keypad to enter the desired values and press EXIT These lower and upper values will be displayed on the screen just below the axis Note that data for both RPM and Speed are saved during each test which means that both a vsRPM and a vsSpeed plot may be displayed following a test although only one of them may be active during the test vsRPM Graphics Repeated pr
309. he present set of Units will be lost if the recall is continued Press YES A to continue the recall and press NO C to abort the recall oper ation If the recall is continued the message RECALL Units Data N on the upper right of the screen indicates that the Nth record of the Type Units Data has been recalled and the soft key labels will change to reflect those in the stored record The message recall data on the lower right of the screen indicates that the horizontal arrow keys are assigned to con trol the recall of Units Data records from the active memory file Pressing these keys permit the user to select the particu lar record number which contains the desired set of Units Data Reassign the horizontal arrow keys to control the cur sor in order to prevent the recall of other records Selection of Units and Calibration 10 Digital Display including Broadband Acoustic Frequency Weighting User defined Frequency Weighting and Integration of FFT Spectra Accessing the Display Menu The Display Menu is accessed from either the Standard Anal ysis Menu or the Intensity Analysis Menu by pressing DISPLAY F The display functions are not available for use with the Cross Analysis Mode The resulting Menu will resemble either Figure 10 1 or Figure 10 2 depending upon whether the octave filters or the FFT analysis is active Figure 10 1 Display Menu octave bandwidths 24 MAR 16 20 57 1 4 1 3 AVERAGE SUM SETUSER
310. he trigger function is Armed by pressing R S the sampling and storage of waveform data into the time buffers of both input channel begins The size of the time buffer in number of samples depends upon the number of lines selected for the FFT analysis as follows Lines Samples 100 256 200 512 400 1 024 800 2 048 However once the buffers are full instead of transferring the contents to the FFT processor as is usually done in FFT anal ysis the data is shifted through the buffer sample by sample the oldest data being lost as new data points enter Once full each buffer will at any instant hold a full set of samples rep resenting the time waveform over the preceding time interval required to fill the buffer e g using 400 line and a full scale of 10 kHz 1024 samples spaced 39 microseconds apart rep resenting a time interval of 40 milliseconds At the instant the trigger criteria are satisfied by the data being sampled at the input of channel 1 there are a number of different ways the analysis can proceed 1 One could elect to save all or a selected number of the most recent samples in the time buffers then fill the remainder of the buffers with data points sampled after the trigger When the buffers are full they are transferred to the FFT processor and the system then continues as in a normal FFT analysis With this option by saving data points already in the buffers the system has pre trigger information describing th
311. ibility inherent in the 2900 offering the choice of octave and FFT bandwidths and such features as byTime autostorage frequency domain triggering noise generator control room acoustics etc we draw a distinction between the setup and the operation of the analysis function by creat ing a hierarchy of Menus which differentiate between setup operations and general measurement and analysis opera tions The following diagram indicates the structural interac tion between the Analyzer Menu the System Menu and the System submenus 2 1 2900 MANUAL Analyzer Menu System Menu accessed by hardkey SYSTEM Sig Gen Or Units Filter Class tou I O 1 Noise 1 Input 1 Color Files Resets Setup 1 System Submenus The functions which are performed within each of these Menus are as follows Menu Name Menu Function Analyzer System Units Filter Class I O Sig Gen Noise mput Color Setup Files Resets Submenus Operational menu for Analysis Selection of number of input channels and path betvveen the System submenus and the Main Menu Select units define and store user defined units perform calibration Selection of Filter type and parameters Setup of Class Lines Setup of 1 O operations Setup of digital signal generator Setup of Noise generator Setup of Input modules Setup Menu for external Color monitor Storage and recall of user cr
312. ice Selecting SLM and Frequency Analysis Weighting 3 4 The weighting can also be modified from the Weight Menu shown in Figure 3 3 SLM Weight Menu which is accessed directly from the SLM Menu by pressing Weight M Figure 3 3 SLM Weight Menu a2 FEP 84 41 45 A WGT C WGT 1 280k 20 20 1l 18k 28 18k WIDE SPL 3 8358 c c cc ed M I RR n n n n ff EXPONENTIAL 178 Input 1 LINEAR 20 2 20 2 STOP 02 FEB 95 04 41 13 ecc nn ne nen SERE de I IRI III FILTER 28 630 Hz 125 Channel 1 of 1 NORMAL 32 2 E 71 8 R WEIGHT SL OM 3 Min 49 8 75 7 SLM DRTR dotted crsr C WGT i 28k 28 20 1 16k 28 168k INITIAL UBT This Menu permits the user to select the weightings for both the sound level meter function and the frequency analysis function from the same menu These weightings are indepen dent from one another Unless one is changing the micro phone bias voltage at the same time most users will utilize the Weight Menu for changing the weighting function when in the sound level meter mode because it is more convenient to access one keystroke from the SLM Menu and because it Sound Level Meter Operating Modes Warm up Time 2900 MANUAL permits modification of the frequency analysis weighting at the same time The weightings represented by the softkeys below the screen are for the sound level meter function as seen by the fact that a change of this selection is reflected by
313. ich case they may be equal This is why the calibration is performed using the spectrum level measured at the fundamental fre quency of the calibrator If the displayed level is different than that specified for the calibrator press the following key sequence SYSTEM UNITS F and level H which will produce the message Enter Level XXX X on the upper right of the screen The XXX X represents the level presently being displayed for the frequency band covered by the dotted cursor The flashing cursor beneath the first digit prompts the user to enter the numerical value of the sound pressure level produced by the calibrator using the numeric keypad on the front of the 2900 and press EXIT Press EXIT twice more to return to the SLM Menu Sound Level Meter Operating Modes Effect of Microphone Extension Cable 2900 MANUAL Check the calibration by switching the calibrator ON once more setting the instrument to the recommended reference range setting of 120 dB full scale making another measure ment and verifying that the sound pressure level read for the cursor position is the same as the level produced by the cali brator When the original calibration was far from the proper setting a second calibration may be required to get complete agreement within 0 1 dB Following calibration insertion of a LarsoneDavis Model ECXXX microphone extension cable having a length of less than 500 feet 150 m between the instrument an
314. idity non condensing 9096 max at 104 F 40 C Physical Size 11 wide x 7 75 high x 2 4 thick 28 cm x 19 7 cm x 6 1 em Weight 7 5 Ib 3 4 kg 1 26 Introduction Power Battery Power 2900 MANUAL Typical operating time in Run mode is 4 hours using remov able NiCd pack supplied with the instrument reduced by operation of the noise generator and the floppy disk drive When On but not Running power consumption is reduced by approximately 4096 When using the AC DC converter supplied with the instrument the NiCd battery pack is charged while within the instrument Typical charge time after total discharge is 15 hours DC Power 11 16 VDC Typical current requirements 1 5 Amp 11Volt 0 5 Amp 16 Volt AC DC converter is supplied with the 2800 2900 Introduction 1 27 2900 MANUAL 2900 Block Diagram 2900 Block Diagram Pr ampbin Filters AC T HP LP Out 1 Switching 1HZ 10kHz Matrix 20Hz 20kHz AC Out 2 Ch 2 Awt Cwt Source Output v 1KHz or NOISE if option is installed 5v logic pos edge trigger Preamp 1V Q 1KHz Bias Test 0 28 200 V Oscillator tevondo 10 Microprocessor 8 Digital Signal Processor X 2 Printer A D amp RS232 History Optional VO Control Interface Data 1M or 4M 25 Pin 15 Pin 9 Pin Storage Expansion 256KB Memory 26 Pin External Interface Keyboard Power amp External Disk Dri
315. ighpass filter and a 20 kHz lowpass filter in the signal path 1 10k M Inserts a 1 Hz highpass filter and a 10 kHz lowpass filter in the signal path 20 10k N Inserts a 20 Hz highpass filter and a 10 kHz lowpass filter in the signal path When the Model 2900 is in a dual channel mode STAND 2 the analog filters can be selected independently for each input channel The filters for channel 1 are set by pressing CHL prior to making the selection resulting in the message Channel 1 of 2 on the right of the screen and the filters for channel 2 are set by pressing CH2 prior to making the selection resulting in the message Channel 2 of 2 on the right of the screen To have the same choice of filters for both channels press SAME 0 which will set the filters for the channel not being displayed to be the same as those of the channel being displayed 2900 Instrument Setup Via The System Menu From the Input Menu the user can select to insert a 1 kHz square wave signal whose fundamental frequency amplitude is 1 volt through the input for purposes of verification and instrument calibration Press TEST O to turn on this sig nal which will also produce the message Internal Calibra tion On on the upper right of the screen Press TEST O a second time to turn off the calibration signal 4 13 2900 MANUAL Offsetting Gain Between Channels The gain of channel 2 with respect to channel 1 is adjusted from the Input Menu by
316. ighting window is indicated on the right of the display fifth line down fourth character from the right R H E Z or I corresponding to the first letter of one of the above choices For the analysis of steady signals most users will select either the Hanning or the Flat Top window The Hanning gives better frequency resolution while the Flat Top gives bet ter amplitude accuracy in the passband Rectangular weight ing provides the finest frequency resolution but it is often accompanied by excessive leakage of energy to the neighbor ing sidebands The Impact and Exponential Weighting windows are generally used for modal analysis applications The Impact Weighting is used on the channel where an impact excitation is applied to a structure typically using an instrumented hammer pro viding an analog signal of force versus time The Impact Weighting window consists of a 1 2 cosine curve rising from zero to unity over eight samples followed by a horizontal sec tion of length thirty two samples at unity height followed by another 1 2 cosine dropping from unity to zero over eight samples The user selects the trigger delay of the FFT analy sis such that the actual force waveform occurs totally within the window and signals outside the window are reduced to zero digital values Exponential Weighting is used on the channel where the response of the structure to the impact excitation is being measured The term Exp N refers to an exponential
317. igure 5 4 Constant Confidence Averaging Time Menu mu 12 35 20 1 2 4 8 16 32 64 128 2 808808 RR Dual LINEAR 28Hz 28kHz TOI or APR 9 12 33 36 2 z LAS w Channel 1 of 2 NORMAL de 5 2 58 8 DIFF PHONS 83 2 8 8 SPEED 4 6 H 00 Hz Hu Hi dotted crsr INT 256 512 1024 2048 7 496 8192 16384 32768 Averaging Time with Spectral Type Averaging FFT Bandwidths Only 5 4 When the selected averaging type is EXP N or Count Single Count Repeat or Count Manual the Menu shown in Figure 5 5 Count Averaging Menu will present the user with 16 dif ferent values from 1 spectrum to 32 786 spectra in a binary sequence Press the key above or below the desired value then press EXIT Figure 5 5 Count Averaging Menu 12 52 21 1 2 4 8 16 32 64 128 i SPL as aa COUNT SINGLE 8 Dual LINEAR 28Hz 20kHz STOP l APR 97 12 31 52 T FREQ aa Sieg HAB v Channel 1 of 2 NORMAL H d 43 9 Ze 84 6 50 REM TACH 8 8 SPEED 8 8 aa dotted crsr INT 256 512 1824 2048 4096 8192 16364 52768 The averaging times for Linear Exponential Constant Confi dence and Spectral averaging are stored independently Once a value has been selected for each of these that value of aver aging time will reappear with the selection of that averaging type Selection of Averaging Parameters 2900 MANUAL A common procedure is to begin an analysis using a fast exponential averaging while the range setting is adjust
318. igured to one of these Both digital fil ters and FFT analysis may be used Access the Class Lines Menu from the System Menu by pressing CLASS H If the Class Lines function is already ON the Class Lines Menu shown in Figure 22 4 Class Lines Menu will be displayed If the Class Lines function is switched OFF press C ON F to 22 3 2900 MANUAL Labeling the Class Lines turn it ON The default bootup has the Class Lines function switched OFF Figure 22 4 Class Lines Menu 29 DEC 16 46 86 default default default default C OFF SPL 6 0000 ang e w w n w n w w n n n n n w nn n n n n n n n n a n nn n nn ttt i ehh m m m n n nn EXPONENTIAL 1 64 1 Dual LINEAR 20Hz 18kHz 1 RESET 29 DEC 93 16 45 12 T I c H onn en t nen FILTER 32 1 680kHz L73 1 v Channel 1 of 2 NORMRL 1 d 23 A 34 7 50 bee PHONS 86 3 LOC i G G SPEED 4 6 BEE EE f R B E dotted crsr INITIRL EDIT SETUPS HRME RSSIGN a JUDGE USE KEY m JUDGE Creating a Single Class Line To identify a set or family of class lines the user can assign a label having up to seven characters to each of the softkeys A B C and D When delivered each of these softkeys will be labeled default Create a label by pressing NAME K which will produce the message Push Class to Name on the upper right of the screen Press the softkey for which label is to be defined The message Enter class name with a flash ing
319. ime domain parameters the displayed channel is changed by pressing CH1 or CH2 In the case of autospectrum and autocorrelation the dis played channel number refers to the input channel The cross channel functions are always calculated between chan nel 1 the reference channel and channel 2 A complex variable requires two functions to express it One can represent such a function by a pair consisting of a mag nitude function and a phase function polar coordinates or by a pair consisting of a real function and an imaginary func tion rectangular coordinates When the user presses the key to display one of these functions he will obtain either a real or a magnitude function as indicated at the upper left of the screen To observe the other function within the coordinate system real imaginary or magnitude phase simply press ALTERN I To change from one coordinate system to the other polar rectangular press P lt gt R K The cursor does not change position when these keys are used This permits the user to move the cursor to a frequeney of interest and read the values of magnitude phase real and imaginary for that frequency by simply changing the display format even though he cannot display more that a single function at one time Analysis Menus Selection Of Measurement And Display Parameters 2900 MANUAL Display of Time Records It is necessary to select Count Averaging L R or M in order to be able to view on
320. imum DELTA TIME milliseconds using FFT bandvvidths FFT Analysis Number of lines if Channels 100 200 400 800 15 2 5 10 20 40 10 20 40 80 Autostore by Time 2900 MANUAL Although we have entered the autostorage parameters the autostore function is not yet enabled The 2900 can still be run in a standard manner by pressing R S The autostore byTime mode is enabled by pressing byTIME B The mes sage bTIME will appear to the left of the display to indicate that the Autostore byTime mode is active Selection of Spectral Type to be Autostored Count Averaging Special Considerations It is the displayed spectrum type which are sequentially stored into the autostore record Thus it is possible to autostore Normal Leq MIN MAX SEL or Mx Spec spectra In most applications it will be the Normal spectra which will be desired for the autostore operation If the active display type is not that which is desired for the autostore exit from the Autostore Menu to the Main Menu and change to the desired display type before initiating the autostore sequence When FFT filtering is used in conjunction with Count Averag ing the DELTA and ENDSTORE numbers refer to number of spectra rather than time In that case the prompts for data entry on the right of the screen will refer to DELTA COUNT and END COUNT respectively The actual rate at which spec tra are stored d
321. indicated by the changing value of N in the message on the upper right of the screen The right horizontal arrow recalls records placed later in the sequence higher record numbers and the left horizontal arrow recalls records placed earlier lower record numbers in the sequence To jump faster through the record numbers use the SHIFT key in conjunc tion with the horizontal arrow keys Storing and Recalling Non Autostore Data In order to utilize the cursor to readout the data being dis played press CURSOR This will activate one of the cursors and place it under the control of the horizontal arrow keys 13 11 2900 MANUAL The use of cursors is explained in more detail in Chapter 8 Press recall P to reassign the horizontal arrow keys to the role of paging through the stored records of that type Deleting Stored Records There are two ways in which stored records can be deleted From the Recall Menu the record which was last recalled indicated by the value of N in the message Recall Type N on the upper right of the screen vvill be deleted upon press ing DELETE I The message Delete the current record on the upper right of the screen will appear for verification of the deletion Press YES A to continue with the deletion or NO C to abort the deletion Following the deletion the remaining records will be repacked Those records following the one deleted will be moved down one in sequence within the
322. ing Modes Random Incidence Measurements 2900 MANUAL Sound Level Meter Operating Modes When the measurement is of the random incidence type the best results will be obtained using a random incidence microphone LarsoneDavis Models 2530 2559 or 2560 In such a case alignment is of no concern since the position of the radiating source cannot be clearly identified In most cases one would align the microphone preamplifier holder such that the axis is vertical since this would minimize the effect of the body of the operator on the resulting sound field Due to the relatively strong directionality characteristics of a free field microphone it is not recommended that they be used for precision measurements in a random incidence measurement situation Figure 3 7 2900 random incidence response using Model 2560 random incidence microphone 0 8 0 6 0 4 0 2 0 2 0 4 0 6 0 8 Relative SPL dB 400 800 1200 1600 2000 3600 4000 S O CH CH omcooco I cO O TO LO LO 2400 2800 3200 4400 4800 Frequency Hz 3 9 2900 MANUAL Effect of Windscreen The corrections which should be added to the measured data when using the LarsoneDavis Model WS001 3 1 2 diameter windscreen with a 1 2 Larson eDavis microphone are as indicated in the following graphs 0 Degree Incidence 2 dB Co
323. ing from the Frequency Trigger Menu In preparation for the use of the frequency domain interface trigger access the I O Port Menu and press HiAn 3 F to set the Channel 3 state to High To assign the frequency trig ger criteria already established to change the state to Low upon satisfaction of the trigger criteria press TRIG G Subsequent presses of this key will toggle the Frequency Domain Interface Trigger between On and Off When this is On or active a T will appear as part of the status of I O Channel 3 For example suppose the model 2900 is monitoring the sound pressure level produced by an external electronic noise source and that the noise source is to be shut down if the peak sound pressure level exceeds a user specified level The user could develop a hardware module capable of switch ing off the signal to the speaker upon detection of the High to Low state change of I O Channel 3 Since the Peak SPL is the parameter of interest the SLM Mode should be selected From the SLM Mode it is necessary to access the Autostore Menu in order to access the Frequency Trigger Menu From there select to monitor the Peak Level and select the 2 cri teria and use the level P to set the maximum permitted Peak level Since the Frequency Domain Trigger function is not to be used press OFF O before exiting the menu by pressing EXIT Following this return to the I O Port Menu and press the key sequence HiAn 3 F TRIG G and exit t
324. ing that when a frequency band is indicated continual presses of the right arrow key will access higher and higher frequencies and following that the sound level meter parameters SLOW SLOW MIN SLOW MAX FAST FAST MIN FAST MAX IMPULSE IMPL MIN IMPL MAX LEQ SEL PEAK and finally Spectrum X Spec trum X is not a sound level meter parameter but the summa tion of the energy contained in all the bands of the frequency spectrum Presses of the left arrow will move downward in sequence through these sound level meter parameters and then the frequency bands 2900 Instrument Setup Via The System Menu O Port Control 2900 MANUAL A D Inputs 1 2 and 3 Channels 1 2 and 3 2900 Instrument Setup Via The System Menu As indicated by the label on the rear panel of the 2900 there is a separate I O Port connector for communication with external devices Operations with this port are performed from the I O Port Menu shown in Figure 4 19 I O Port Menu which is accessed from the I O Menu by pressing IO Port C Figure 4 19 I O Port Menu 25 APR 15 57 42 Low 1 Hi In 1 Low 2 Hi In 2 Low 3 HizIn 3 Ne eegener 1 H 2 H 3 H SPL 6 6008 en I II PP Wi UESTRE SES Va oS ke EXPONENT I AL Y Input 1 LIHERR 20 2 20 i RESET 25 APR 94 15 56 51 40 wan K wa a SIE AS FILTER 24 250 Hz L73 i v Channel 1 of 1 NORMAL dz Ze 11 1 26 e w w ao n n a na nn na nn g a ee a I esi x Neg PHONS 94
325. ing the active memory file involves accessing the Files Menu highlighting the desired memory file name creating and naming a new one if necessary and exiting back to the Analysis Menu Record Operations from the Files Menu Classification of Record Types 13 4 When data is stored from the analyzer data buffers to the active file record the data blocks are classified into 45 differ ent record types based on the type of data being stored These are the record types which are permitted Normal Leg Minimum Maximum SEL RT60 vsRPM Trace Ln Trace Ln Table Intensity Power Autospec trum AutoCorrel Normalizatn CrossSpectr CrossCorrel Transfer Fn Impulse Coherence Time Wavefm Cep strum Lifter By Tach By Time User Curves Setups Units Data SLM Normal SLM Leq SLM Minimum SLM Maximum SLM SEL SLM MaxSpec SLM ByTime SLM ByTach SLM MaxSpectrum Macros Data By Tach Int By Time Int By Tach Crs By Time Crs Print Setup Class Setup and FieldInd See the section Record Classification later in this chapter for a more detailed explanation Storing and Recalling Non Autostore Data Records Listing 2900 MANUAL Note Editing From the Files Menu a listing of the data records stored in the highlighted memory file is displayed on the right half of the screen as shown in Figure 13 2 Records Menu by press ing RECORDS B Figure 13 2 Records Menu 02 JAN 07 04 34 cre
326. ing the sensitivity of the transducer as in the example above this is straight forward However when the named units are to be different from those used to express the transducer sensitivity the entered sensitivity must be properly scaled to represent the named units Continuing with the above example suppose one wishes to read the data in units of ft sec 2 First create the units name FT SEC2 and 57 it to the channel to be calibrated Since 1 0 g 2 Jus s we can always multiply the given sensiti vity by 1732 28 because it has a value of unity Thus we cal culate the G nsitivity unit as follows 50 mV 9 x 123228 1 553405 sensitivity value If we wished to express the data as a velocity in units of ft s we would assign the units name of FT SEC to that channel We would select to single integrate the signal to obtain veloc ity and would still use 1 553 as the value of mV unit because the single integration would transform the ft s to ft s If we wanted the velocity expressed in in s the proper sensitivity in mV unit would be calculated as follows 1 553mV x LE my ft s d 5 sensitivity value 9 6 The preferred method of calibration is to apply a known exci tation level to the transducer and calibrate the analyzer to that value The advantage in using this method is that it veri fies the integrity of the transducer and the cable connecting it to the input module This is common practice when using pr
327. ing times in this mode This is a continu ously running average It is up to the user to determine when to stop the measurement If the user is watching the instru ment display it would be sufficient to run until the displayed spectrum is seen to be stable over the frequency range of interest Alternatively the averaging should continue until the run time is equal to or greater than the value of T corre sponding to the lowest frequency of interest T 512 B where B is the bandwidth of the lowest frequency filter The bandwidth is calculated from the center frequency of the filter band as follows The ANSI standard also permits the use of fixed time period averaging In such a case one could set the instrument to uti lize linear averaging with an averaging time equal to or greater than the value of T calculated in the preceding para graph This is done from the Intensity Main Menu by pressing the softkey sequence DETECTR H LIN S A AVE TIME H using the numeric keypad to enter the value of T then pressing EXIT When using this linear averaging method the averaging will stop automatically when the pro grammed averaging time has passed When using a Lar son Davis intensity probe a change in the status of the LEDs will inform the user when the measurement has been com pleted The ANSI standard also permits the use of scanning during the measurement meaning that the intensity probe is moved uniformly over each area segment duri
328. ing to the position of the cursor across the RPM Speed axis To assign a pen to a trace number click the mouse on the first window to the right of the trace number and select from among the 32 available pen numbers Cursor Control If the simultaneous display of all six traces is confusing any number of traces may be hidden to prevent their display on the screen although the data remains accessible To hide or unhide a trace click the mouse on the window presenting the trace number and select either HIDE or UNHIDE When a trace is hidden the letter H will appear in place of the trace number There is not a cursor as such in terms of a moveable vertical line but a set of numbers 1 6 for each trace which move together across the RPM Speed axis This is done by placing the mouse pointer within the second window to the right of any of the active traces depressing the left cursor button and sliding the mouse left or right Single presses of the left and right mouse buttons will result in single interval movements to the left or right respectively The value of RPM or Speed corresponding to the cursor position will be displayed in the RPM or SPEED window directly above the data display win dow Modifying the Left and Right RPM Speed Axis Limit 24 16 The value of RPM Speed corresponding to the left and right limits of the horizontal axis are indicated in windows just below the axis at both ends To shift either of the
329. ion 5 XX shown refers to the general operating and analyzer code In the second message SLM A refers to the code version for the SLM with parallel frequency analysis function and SLM refers to the wide dynamic range sound level meter WDRSLM function Introduction Resetting RAM 2900 MANUAL Upgrading Software Should the software in the RAM somehow become corrupted operational difficulties could be experienced In that case during the interval the above message is displayed the user could press the key which requires a press of the SHIFT key first to invoke the upper character on the key to reset the RAM as indicated by the message This will generate a reset of the RAM followed by a re boot of the 2900 from the ROM Since all data stored in the 2900 will be lost when the RAM is reset it is recommended that the user contact the Larson Davis customer service department before initiating this procedure Display Control It is possible to upgrade the internal software of the 2900 via the floppy disk drive or the RS232 interface To upgrade via the floppy disk drive place the disk containing the updated software file into the drive and while the above message is being displayed press the key which requires a press of the SHIFT key first to invoke the upper character of the key This will load the ROM memory with the new software code and initiate a re boot using this software A software upgrade is delivered
330. is in the SLM mode or the sin gle channel Standard Analysis mode and that channel 1 is the active input Input 2 Indicates the 2900 is in the SLM mode or the sin gle channel Standard Analysis mode and that channel 2 is the active input Dual Indicates that the 2900 is in one of the dual chan nel modes such as dual channel Standard Cross or Intensity and that both channels 1 and 2 are active A WEIGHT Analog A Weighting Active C WEIGHT Analog C Weighting Active LINEAR No Analog Weighting Active 1 Hz 20 kHz 20 Hz 20 kHz 1 Hz 10 kHz 20 Hz 10 kHz In Dual channel mode STAND 2 these may be different for each channel The frequency range indicated on the screen is for the channel being displayed as indicated in Location M STOP No Sampling in Progress RESET No Sampling Data Buffer has been Reset RUN Sampling in Progress These correspond to the beginning of a measurement Add to this the run time to obtain the date and time of the comple tion of the measurement The date format ddmmmyy The time is in the 24 hour format hh mm ss The message format for this location is a function of the active filter type Octave Filters L1 FILTER 4 ANSI Filter Number L2 Frequency Value L3 1 1 Long Filter 1 1 Octave L 3 Long Filter 1 3 Octave Introduction Location M Channel and Parameter Information Introduction 2900 MANUAL S 1 Short Filter 1 1 Octave S 3 Short Filter 1 3 Octave FFT Filtering L1 FREQ
331. is stored This is displayed on the upper right of the screen in the format STORE By Time Int N where N is the record number If is to be evaluated at a number of different positions it is recommended that the Note Field or the JOB PART AREA fields be defined prior to each measurement to facilitate dif ferentiation between records upon recall To display F make sure the instrument is set to the Inten sity Mode and that the autostore mode is active which it will be if the display is performed immediately following the mea surement Press RECALL to initiate a recall operation and use the A Prev N and A Next O softkeys to access the desired record number When the desired autostore record has been recalled press F1 FTV G to display F as a func tion of frequency as shown in Figure 20 4 F1 Display The standard recommends that the values of F not exceed 0 8 over the frequency range of the intensity measurement Figure 20 4 F1 Display 23 MAR 15 46 05 4 00 Note SPERKER ETU Index 6 95668 LINEAR REPEAT 6 656 ual LINEAR 20 2 MM RESET 24 FEB ER Her 34 FILTER 20 Hz E vvFi Tenporal IER d 3 22 301 odam JOB SPERKER PART FRONT AREA 1 dotted crsr R Preu R Mext Surface Pressure intensity Indicator F Negative Partial Power Indicator F4 and Field Non uniformity Indicator EA Surface Pressure intensity Indicator 20 20 These parameters calculated from a sequence of measure
332. is used to represent the frequency range of the analysis The horizontal arrow keys are used to move the cursor across the frequency range The cursor position is indicated on the right of the screen fifth line down The Ln values for each pen corre sponding to the cursor position are presented in the table When the statistics are being calculated from the SLM mode of operation the left three quarters of the horizontal scale represent the frequency range and the remaining portion rep resents the sound pressure level statistics As the cursor is moved upwards through the frequency range after passing through the highest frequency band continued movement to the right will produce in sequence the statistics associated with the Slow detector of the SLM those for the Fast detector and the spectral sum The last parameter is not produced from the sound level meter function but calculated from the frequency analysis as the sum of the energy of all the fre quency bands Statistics and Ln Calculations Selecting the Display Channel Number 3200 MANUAL OPT 42 The median and standard deviation are calculated as follows n DEE mean x Xi n izl a NN xy STDDEV an i l The instrument cannot of course measure levels which are below the lower limit of the selected measurement range In order to provide an indication that levels are frequently falling below this lower limit the parameter YoUNDER is displayed
333. isk All data transfers to the disk are from internal memory data cannot be stored directly to disk from the analyzer data buffers To transfer the highlighted memory file to the disk press disk D Following the transfer the file will appear high lighted with the same name at the bottom of the floppy file listing If there is already a file on the floppy disk having the 13 8 2900 MANUAL Selection of the Active File same name the message Overwrite this file will appear on the right of the screen To approve this overwriting operation which will cause the original file of this name on the floppy disk to be lost press YES A To abort the file transfer and save the original file on the disk press NO C The highlighted disk file can be transferred to the internal memory in a similar manner by pressing mem L When measuring with the 2900 only one of the internal memory files can be active All storage of data from the ana lyzer to internal memory will be to the active file and all data which is recalled from internal memory will be from the active file The active file is determined by the internal memory file which is highlighted when the EXIT key is pressed which returns the 2900 to the Analysis Menu which had been active when the Files Menu was originally accessed Whenever the 2900 is being used for measurements and analysis the name of the active file appears on the lower left of the display Chang
334. isplay formats The cursor and the data readouts on the right side of the screen will correspond to one of the two displays channels as indi cated by the message Channel 1 of 2 NORMAL or Channel Control of Display Formats Cross Channel Normalization and Use of Key Macros 19 1 2900 MANUAL 2 of 2 NORMAL on the right side of the screen sixth line down Use the hardkeys CH1 and CH2 to select which of the two channels are to be accessed by the cursor and readout on the right side of the screen Displaying 1 3 Octave Spectra in 1 1 Octave Format When a spectrum has been measured using 1 3 octave band widths it is possible to sum these in groups of three in order to produce a spectrum having 1 1 octave bandwidths This is displayed from the Display Menu Figure 19 1 by pressing 1 1 A To return to the 1 3 octave bandwidths representa tion press 1 8 B When 1 1 octave bandwidths have been used for the mea surement only the 1 1 octave format is possible so neither of the softkeys 1 1 A or 1 8 B will appear in the Display Menu Digital Reading of A Weight and Summation Bands Digital Display Weighting 19 2 Also located in the Display Menu is the key SUM E which controls the digital readout of the broadband levels repre sented by the two vertical bars on the right of the spectrum display When solid or dotted cursors are active these repre sent the A Weighted and Linear broadband levels calculate
335. isplay of the RMS Slow level along with the Min and Max values of the RMS Slow level since the last data reset as shown in Fig ure 3 8 Slow Display The averaging time of the Slow detector is 1 second Figure 3 8 Slow Display a2 Jgn 23 25 83 NORMRL Lea MIN MAX SEL DISPLAY note DETECTR FAST J SPL TEE ch en EXPONENT 19 8600 IAL 178 Input 1 LINEAR 2 Hz 2 kHz STOP 822 JAN 98 23 24 56 5 Hz L73 Channel 1 of 1 NORMAL d 6 9 E 45 3 WEE pae poc MN RC FILTER B WEIGHT SLO B 53 z SLM DRTR dotted crsi SLOW FAST IMPULSE LEQ Weight SETUP FILES AUTOSTI ze R Produces a display of the RMS Fast level along with the Min and Max values of the RMS Fast level since the last data reset as shown in Fig ure 3 10 Impulse Display The averaging time of the Fast detector is 1 8 second Figure 3 9 Fast Display a2 gen 23 26 52 NORMAL Lea MIN MAX SEL DISPLAY note DETECTR TEST 1 A SPL einem d did KO EIEE dE Ne EXPONENTIRL 12 15 9250 Input 1 LINEAR 2 Hz 2 kHz STOP 02 JAN 90 23 26 33 Kg Sa avan dTi AYL LEE A FILTER 8 N 38 As L v Channel 1 of 1 NORMAL d 8 3 Ze 55 1 A WEIGHT a FAST Xi KOW YO v NE KO lan d n L Min 31 9 Max 59 0 z SLM DRTR dotted cran SLOW FAST IMPULSE LEQ Weight SETUP FILES AUTOSTR IMPULSE K Produces a display of the Impulse weighted lev el along with the Min and Max values of the Impulse weighted level since the last
336. isplay wil prompt the user for a numerical Selection of Units and Calibration Logarithmic Units Calibration Microphone K factor Linear Units Calibration Selection of Units and Calibration Example Example 2900 MANUAL entry Use the keypad to type the sensitivity in dB Volt and press EXIT The microphone being used has a sensitivity of 50 mV Pa No differentiation or integration is required for a sound pressure level measurement To have an output of 1 V from this micro phone it would have to be exposed to a sound pressure of 20 Pa e g 50 mv Pa X 20 Pa 1V The sound pressure level Lp corresponding to this is calculated as follows L 20 log o P P eyl 20 1og 9 20 20x10 Lp 120 dB Enter this value as the calibration level A microphone which has a sensitivity of exactly 50 mV Pa will have a logarithmic sensitivity of 120 dB Volt The open circuit K factor Ko is an indication of the degree to which the sensitivity of a microphone varies from this 50 mV PA refer ence value Thus when performing a calibration using decibel units the sensitivity can be calculated from the K factor pro vided on the microphone calibration chart as follows dB Volt 120 Ko When using LarsoneDavis analyzers with Larson Davis microphone preamplifiers the system sensitivity is relatively independent of the length of the microphone extension cable up to lengths exceeding 50 feet However when using exten sion cables
337. it names after assigning a name to one of the channels press SAME C and that same name will be assigned to the other channels Assignment of Integration or Differentiation 9 2 Use the numerical keypad to select the channel which is to have digital integration single or double or differentiation single or double applied to its signal Press SLOPE A to access the Slope Menu shown in Figure 9 2 Slope Menu Figure 9 2 Slope Menu 02 JAN 86 18 53 d2 dt2 d dt si9nal inteorl dbl int 1900320003 LEE e e E x R e M SR 6 8 nis m UNIT signal 1 8 80 SPEED 6 6 IS Z6 33 an dotted crsr Selection of Units and Calibration 2900 MANUAL Press one of the following keys to define the integration or differentiation which is desired Softkeys Softkey Functions d2 dt2 A Double Differentiation d dt B Single Differentiation signal C No Differentiation or Integration integrl D Single Integration dbl int E Double Integration When the selection is made the choice is indicated by a sym bol in the first line on the right of the display Each digital integration is performed by dividing the level at each frequency band by 2 x f where f is the center fre quency of the filter and each digital differentiation is per formed by multiplying the level at each frequency by this same factor 1 1 and 1 3 Octave Integration and Differentiation Operations When using the 1 1 and 1 3 octave filters the integr
338. itation of the Source Room In cases where the spectrum levels measured in the Receiving Room during excitation from the Source Room are close in magnitude to those of the background spectrum levels the 21 13 2900 MANUAL 21 14 standards call for a correction factor to be applied to the mea sured Receiving Room levels to account for the effect of the background noise on the measurement The fourth parameter which must be measured is the sound decay time RT60 within the Receiving Room This is typi cally done by moving the speaker from the Source Room to the Receiving Room and following the procedures described earlier in this Chapter of the manual At the conclusion of the measurement phase of the project the following data will have been measured and stored in the analyzer 1 Source Room spectrum space averaged 2 Receiving Room spectrum space averaged 3 Receiving Room background spectrum 4 Sound decay time RT60 To calculate and display the airborne sound transmission parameters access the Rooms Menu as shown in Figure 21 4 from the Main Menu by pressing ROOMS I Figure 21 3 Rooms Menu 11 MAR 17 15 35 NC NR RC surface volume RT6B I SPL 8 0000 ang pos Re e R l RR l BESTE IE i ila e EH RORUR 6 SR R29 a EXPONENTIAL 178 Dual LINEAR 20 2 20 ESET 11 MAR 97 16 12 51 T W w w w u n a o W W W W W co o W W W W W W W W W W n W n n n a
339. ituation is the reverse of that for the positive slope Either RPM Speed or both must be above the HIGH value of the corresponding Span at the initiation of the sequence and autostorage will begin when one of these falls within the appropriate Span range Autostorage will then occur at nega tive incremental values of RPM and Speed until one of them falls below the LOW value of the corresponding Span at which time the autostorage sequence will be stopped The positive negative slope condition SLOPE is appro priate for a vehicle acceleration followed by a deceleration or a machine runup followed by a coastdown In the first phase the procedure is the same as that for a positive slope condi tion in that either or both RPM and Speed must be below their LOW Span values at the time of initiation of the test and once one of these values moves into its Span range autostor age will occur at positive incremental values until one of them exceeds its HIGH value thus moving out of the Span range This completes the acceleration runup phase In the second phase the procedure corresponds to a negative slope condi tion and the deceleration coastdown is begun As the RPM and Speed decrease such that one or both values fall within their Span range data will be autostored at negative incre mental values of RPM and Speed until either of them falls below the corresponding LOW value at which time the autostorage sequence is stopped If neither the
340. ity or sound power with greater frequency resolution than provided by 1 3octave bands With the Model 2900 sound intensity measurements can be performed using FFT analysis Setup the 2900 as described above for 1 3 octaves but instead of 1 3 octave fil ters select the number of lines desired for the FFT analysis 100 200 400 or 800 Hanning weighting and the baseband full scale frequency desired for the analysis When using FFT analysis for sound intensity the normaliza tion procedure must be performed from the Cross Mode as described in Chapter 19 8 When the normalization has been completed return to the Intensity Mode to perform sound intensity measurements Note that the normalization proce dure must be performed for the same set of analysis parame ters frequency range time weighting window and baseband full scale frequency to be used for the subsequent measure ments To avoid problems it is best to repeat the normaliza tion prior to utilizing the FFT analysis mode for sound intensity analysis Definition of Surface Area m for the Power Calculation Sound Intensity Measurements The intensity measurement produces a spectrum represent ing values of acoustic power flowing through a unit surface area perpendicular to the direction of alignment of the inten sity probe The linear units of intensity are Watt square meter The intensity level in logarithmic units is expressed as dB relative to 1 pW m 1 0 x 10 12 w m
341. key labels from the active memory file The message Overwrite ALL SET UPS on the upper right of the screen warns the user that the recall will result in the loss of the user defined setups presently active in the Setup Menu Press YES A to continue with the recall Press NO C to abort the recall operation The message RECALL Setups N on the upper right indicates that the Nth Setup record from the active memory file has been recalled The message recall data on the lower right of the screen indicates that the horizontal arrow keys can be used to page through the Setup records available within the file As each record is recalled the set of softkey labels will change to correspond with the data in that record Storage and Recall of Instrument Setups When the desired setup record has been recalled either press the appropriate softkey to change the analyzer setup or exit from the Setup Menu by pressing EXIT 12 3 2900 MANUAL 12 4 Storage and Recall of Instrument Setups 13 Storing and Recalling Non Autostore Data Files Operations This chapter discusses the file and record structure used for the storage of data in the analyzer the transfer of files between the internal memory and the optional floppy disk and the storage and recall of normal non autostored data blocks The storage and recall of autostored data blocks is discussed in Chapters 15 and 16 Accessing the Files Menu Data measured or gener
342. l be stored and the system will now seek another spectrum whose interval of RPM is 50 or more greater than 1 058 The values of t Amax and s Amax are used for situations where the Tach or Speed values change so rapidly that the interval values of Tach Speed for which data storage actually occur could become unacceptably greater than those speci fied by t Amin and s Amin Or there could be spikes on the Tach Speed inputs which would result in data storage corre sponding to the values produced by these spikes t Amax and s Amax are defined to limit on the high side the acceptable range of increments for Tach and Speed Data storage requires that the measured spectrum have incremental val ues of Tach and or Speed with respect to those of the spec trum last stored falling within these minimum and maximum values Consider the case of a vehicle acceleration where the Tach interval values have been set to t Amin 5 and t Amax 10 After each autostorage operation a spectrum with a value of Tach falling between these limits must occur if the autostor age is to continue in a regular manner Suppose that a spec trum was stored having a Tach value of 4 000 and that due to a particularly rapid acceleration the next spectrum produced corresponded to a Tach value of 4 015 No spectrum storage would occur until the driver slowed the vehicle sufficiently that a spectrum was measured having a Tach value between 4 005 and 4 010 He could then resume the
343. l indi cate the presently active averaging time for that averaging type Select the Menu corresponding to the desired averaging type using the softkey A Then press one of the softkeys along the bottom row to select the desired averaging time and press EXIT to return to the Tachset Menu The linear averaging times are expressed in units of seconds The exponential averaging times specify the averaging time constant by its corresponding equivalent base 2 exponent value 1 to 64 In general the user should select as small an averaging time as possible as long as stable trigger operation is obtained The main detrimental effect of averaging is that the averaged value will lag behind the instantaneous value by a degree related to the amount of averaging and the slew rate of the tacho pulse rate As a result the tacho and speed values stored along with the spectra will be slightly different than the true values occurring at the instant of storage When the averaging of the Tach Speed signals has been defined press EXIT to return to the Tachset Menu Autostore by Tach From the Autostore Menu enable Autostore byTach by press ing byTACH J The message bTACH will appear on the left of the screen to indicate that the Autostore byTach mode is active Press R S to initiate operation If the complete test sequence variation of RPM Speed corre sponding to the choice of the Slope parameter proceeds as described earlier the
344. l remain displayed within th ewin dow to indicate to the user the state of the autostore func tion Individual Data Display Windows The control of the Run Stop function is performed by clicking on STATE which opens a window providing the options RUN STOP and RESET Clicking on the desired choice will per form that function and the window will then close Note that when the state is STOP upon clicking on STATE the mouse pointer will be aligned with RUN which means that a double click will change the analyzer from STOP to RUN Similarly when the state is RUN upon clicking on STATE the mouse pointer will be aligned with STOP meaning that a double click will stop the analyzer Display Type These four windows appear without headings above each data display whether one two or four are being used This means that the parameters selected via these windows may be different for each data display The upper left parameter window for each display window presents a choice of display types which depend upon the Analysis mode which is presently active and in the case of Cross the filter type which is active as well For example if the Analysis Mode is Intensity then the choice of display types available for each display window will be Intensity Quality Sound Pressure Level and Particle Velocity If the Analysis Mode is Cross and if FFT filtering has been selected there will be 24 choices available in the MASTER window at the
345. layed The message THRESHOLD NOT MET NO RT60 means that for at least one frequency band the condi tion described in 1 above has occurred and therefore in at least one band an RT60 value of zero will occur in the dis play Even when this message appears and the zero value occurs for one or more frequency bands for all the frequency bands where the curvefit has been successfully applied RT60 values will be stored in the RT60 register and they will appear in the RT60 display As the cursor is moved across the RT60 display the RT60 value for the indicated frequency will be displayed digitally on the right of the screen 8th line down along with the number of averages used to calculate the RT60 value At this instant since the RT60 was reset before beginning the message will read FAVE OT for all bands having a non zero value of RT60 In those cases where the automatic curvefit has failed to pro vide a non zero value of RT60 it is recommended that the user examine the decay curve to determine why this has hap pened In extreme conditions it may be necessary to utilize a manual curvefit between cursors for each troublesome fre quency band to determine a meaningful RT60 value and to store it in the RT6O register For statistical accuracy it is common to make multiple decay measurements at each microphone position and to average the RT60 values determined for each decay together in the Rt60 register When the RT60 register alre
346. linear units such as m sec g etc After entering this linear value it will then be displayed in the Frequency Trigger Menu as a decibel level consistent with the calibration of the instrument To input the trigger level press level P which will produce the message TRIGGER LEVEL XX X on the upper right of the screen Type in the desired value using the numeric key pad and press EXIT Frequency Domain Trigger Setup for the SLM Mode Arming and Disabling The previous description for establishing the trigger criteria applies when the instrument is in the Single or Dual channel Frequency Analyzer Mode When the instrument is in the SLM Mode of operation there is no softkey EF TRIG M avail able in the Main Menu Instead access the Autostore Menu by pressing AUTOSTR P from which the F TRIG M soft key is available When the Model 2900 is in the SLM Mode of operation when paging upwards through the frequency bands in order to set the Trigger Frequency the steps beyond the highest fre quency will sequentially produce the different SLM parame ters prior to reaching Spectrum 2 11 6 The Frequency Domain Trigger is enabled as soon as the Fre quency Trigger Menu is accessed and displayed indicated by the message TRIG on the left axis of the screen To disable this function press OFF Ol before exiting from this Menu VVith the instrument in the Standard storage mode pressing the R S key will initiate fr
347. locked menus identical to the softkey menus which appear on the LCD screen of the Model 2900 It is assumed that the user has become familiar with the operation of the Model 2900 using the front panel hardkeys and softkeys before beginning to work with the color monitor mode of instrument operation Each simulated key appearing on the monitor may have upper and lower labels or alphanumeric characters Note that when the Control Window is open the mouse pointer cannot be moved outside the boundaries of the window To press a key move the mouse until its pointer is located within the rectangle of the desired key Click the left button to initiate the activity associated with the lower level label or click the right button to initiate the activity associated with the upper 24 4 Use of External Color Monitor for Display and Instrument Control Selecting the Number of Display Windows 2900 MANUAL level label Clicking the middle key will close the Control Win dow To select the number of data display windows to be open on the external monitor access the System Menu from the Main Menu by clicking on SYSTEM then access the Color Menu by clicking on COLOR Select the number of display windows by clicking on one of the following SINGLE DUAL or QUAD In certain operations it may be desirable to display on the exter nal monitor the same display which is shown on the 2900 LCD screen This is selected by clicking on LC System Operati
348. lom s 2 tie RP hinge eedem ree n ids 13 9 Setup MOMMA OM abe eco iiti dont Qu sul ERE RR 13 9 crm IE 13 9 Recall and Display of Data Records Non autostored from Memofy 13 9 Analyzer Setup for Recall eese nennen nennen 13 10 Recall Operatori da cnet oe o ete emu 13 10 Record Type and Number Indication enn 13 11 Note Presentation cielo dee tener AAA edu E n ak a mai 13 11 Changing Displayed Record Number 13 11 Oe Een eate thee aree ess CM OM es niet ae 13 11 Deleting Stored Records A 13 12 Block Averaging of Stored Records sse nnne 13 12 Block Maximum of Stored Records n 13 12 Block Summation of Stored Records Re eee eee eee aye seooossaaoosssononsasosososoonn 13 13 Waterfall Display of Stored Records sess enne 13 14 Exiting from the Recall Mode sss neret nnne 13 15 Memory Requirements Non autostore Records A 13 16 Annotation of Data Blocks J J J J 14 1 Annotation of Data BIOCKS AA 14 1 Autostore by TIME vision koi u UI aaa n kk a kk m kn RA AN 15 1 Setup for an Autostore Sequence taa eee ee a yaa oo entente trennen nenas 15 1 Accessing the Autostore Men 15 1 Defining Delta Time and End Time 15 2 Delta Time Blut LEE 15 2 Selection of Spectral Type to be Autostored
349. longer than that it is best to correct the open cir cuit sensitivity of the microphone for the effect of the cable lengths when performing the calibration Contact Lar son Davis for further information When using a transducer such as an accelerometer most users prefer to measure in units such as g m s m s etc rather than decibels Since the default unit is decibels change the scale by pressing SHIFT Y AXIS B followed by LIN LIN A or LIN LOG C depending upon whether the scaling of the vertical axis is to be linear or logarithmic The uses of different units is described in more detail in Chapter 19 Control of Display Formats After a unit name has been assigned to the channel to be calibrated the desired integra tion or differentiation defined and that channel has been selected using the keypad press mV cal F The message Enter mV unit XXX will prompt the user for a numerical entry Use the keypad to type the sensitivity in mV unit and press EXIT With an accelerometer having a sensitivity of ymV g and wishing to have the instrument read in units of g select the name G for the units name No differentiation or integration is required and the value of sensitivity to be entered will be x 9 5 2900 MANUAL Calibration Based on a Reference Signal The sensitivity value to be entered must correspond to the units name assigned to that channel When the units name is the same as the units utilized in express
350. lor Monitor for Display and Instrument Control 24 13 2900 MANUAL The definition naming and storing of the setups from the color display requires the use of the Control Window Displaying in the vsRPM Speed Format Selecting the vsRPM Speed Format In Chapter 17 vsRPM Graphics it is explained how the 2900 can be used to measure and present spectral data in a vsRPM or vsSpeed format using either the Real time Graphics mode or the Graphics from byTach Autostored records The proce dure used to relate pens to trace numbers when using the color monitor is also described 24 14 In order to set up a color display using the vsRPM Speed for mat set the MODE Parameter to Standard Then using the MASTER window select vs Tach This will produce a dis play as shown in Figure 24 5 External Monitor vsRPM Speed Display Note that when multiple windows are being used some may be set for the vsRPM Speed display mode while others are in the normal vs frequency or order display mode Figure 24 5 External Monitor vsRPM Speed Display STATE MODE FILTER MASTER SCH WIND STORE STOP Standard LYS ws Tach Z Single KNOB AVERAGING AVG TIME BASE FREG RECALL crsr 286 EXPONENTIAL lt 14 25 0 Hz MACROS RANGE RUTOSTR TRACK MODE PEN STAT CH FREQUENCY 140 off NORMAL O10n 1 15 31 5 Hz SETUPS lam v amp Tach RPM 1400 64 l WU Hu 01 04 1000 112 0 2 02 62 7 5 05 VZOOM 1 10350 61 0 s 73 0 54 0 6 06
351. lter type selected Octave or FFT When the Analysis Mode is selected by pressing one of these three softkeys System Menu will remain active on the dis play However when exiting from the System Menu the sys tem will proceed to the analysis Menu corresponding to the selected analysis mode Octave Frequency Analysis FFT Frequency Analysis 2900 Instrument Setup Via The System Menu The octave filters 1 1 and 1 3 operate only in real time Therefore increasing the number of active channels has the effect of reducing the maximum frequency of the analysis Table 4 1 Effect of Number of Channels on Octave Bandwidth Frequency Ranges Hz Number of Bandwidth Channels 1 1 Octave 1 3 Octave 1 1 0 16k 0 8 20k 2 1 0 8k 0 8 10k A baseband FFT analysis can always be configured to use any of the available full scale frequeney values 2 5 kHz 5 kHz 10 kHz or 20 kHz for each channel regardless of the num ber of input channels selected Hovvever the larger the num ber of channels selected the lower will be the frequency range for which the analysis is performed in real time The maximum baseband full scale frequency for real time analy sis is 20 kHz N where N number of active channels 4 3 2900 MANUAL Table 4 2 Baseband Full Scale Frequencies for which real time analysis is obtained as a function of the number of channels Number of Channels N 20k N Real time Full Scale Frequ
352. m a single acoustic source The display form DIFF Ph XX Sn YY indicates that the diffuse field method is active while the format FREE Ph XX Sn YY indicates that the free field method is active The units of loudness level is phones The selection of which form of the Loudness function is to be calculated is done from the Digital Display Menu accessed by pressing the softkey sequence DISPLAY F Dig WGT I To select the desired form of loudness press one of the follow ing Softkeys Softkey Functions Zw FREE A Free field Loudness Zw DIFF B Diffuse field Loudness After one of these keys have been pressed the loudness in sones from which the loudness level is being calculated is displayed as a function of critical bands as shown in Figure 6 2 Figure 6 2 Loudness versus Critical Bands B FEB 16 01 44 Zw FREE Zw DIFF SPL 1 9458 EXPONENTIAL Dual LINEAR 20 2 20 STOP 07 FEB 97 15 58 24 FILTER 50 1 B8kHz L73 Channel 1 of 2 2wickery Sone Wa FREE PHONS 70 0 TACH 8 8 SPEED 4 6 Zwicker crs Although the cursor will move through each critical band and display the amplitude the frequency values are only given to the nearest 1 3 octave band center frequency When the ana lyzer is running a real time display of loudness is provided When stopped the display is for the last spectrum in the data buffer Analysis Menus Selection Of Measurement And Display Parameters 6 5 2900 MANUAL Cr
353. m the Files Menu List the records on the right side of the screen move the highlight to the desired Macros Data record and press KEEP H to perform the recall Control of Display Formats Cross Channel Normalization and Use of Key Macros 20 Sound Intensity Measurements Sound Intensity Measurements Selection of the sound intensity operating mode permits the Model 2900 equipped with OPT 80 and used with the Lar soneDavis Model 2260 Sound Intensity probe to determine the flow of acoustic energy between the two microphones in a direction parallel to the axis between them During the mea surement sound pressure data are being sampled at each microphone in a synchronized manner The sound intensity is then calculated in software based upon a knowledge of the spacing between the microphones and the temperature and static pressure of the medium The intensity display depends upon the filters selected for the analysis 1 1 and 1 3 octave or 100 200 400 or 800 line FFT When exponential weighting using a short time constant has been selected the probe can be moved and rotated to probe around a sound source permitting the user to observe in real time the changes in the intensity spectrum This can be useful for rapidly identifying the physical location of domi nant sound radiators Most often the parameter of interest is the acoustic power flowing across a selected surface element determined by multiplying the surface area b
354. m the Signal Generator by pressing PULSE L 2900 Instrument Setup Via The System Menu Interface Operations 2900 MANUAL Figure 4 15 Pulse Generator ut 05 05 POSZNEG T on T off LEUEL REAL 58 Note PULSE SIGNAL 04 COUNT REPERT 1 Dual LINEAR 1Hz 28kHz STOP 38 an Ti 82 43 34 TIME 1718m5 mE vTime s 1 664 E 06Z Base Fresuencuz 66 6668 8 80 SPEED 4 8 solid crsr D I B 90 aa INITIRL A series of either positive or negative pulses can be generated from this menu The status of the generator is indicated briefly by a message on the upper right of the screen when ever one of the keys is pressed The key POS NEG B will toggle the polarity between positive and negative going pulses as indicated on the upper right of the screen The time increment for which the pulse is Positive or Negative in milliseconds is set by pressing T on C entering a value using the numeric keypad and pressing ENTER The time increment for which the pulse is to have a zero value in milli seconds is set by pressing T off C entering a value using the numeric keypad and pressing ENTER The LEVEL E key is used to set the output in the same manner as explained in the preceding sections When using the analyzer to measure and display the wave form generated using the pulse generator Cross Mode FFT Analysis Count Averaging Time display the effect of even the lowest frequency highpass filter
355. med UP LFT UP RGT LOW LFT AND LOW RGT The intensity of each AREA is measured and the data is stored in eight Intensity records as depicted in Table 20 1 JOB Named MACHINES Table 20 1 JOB Named MACHINES RECORD PART NUMBER NAME UP LFT UP RGT LOW LFT LOW RGT UP LFT UP RGT LOW LFT LOW RGT To display the power spectrum of the measurement associ ated with the labels MACHINE REAR UP LEFT from the Intensity Analysis Menu recall the intensity spectrum from record number 5 because it has those particular label names Then access the Power Summation Menu and copy the labels into the Power Search Field by pressing S JOB I S gt PART J and S gt AREA K The Power Search Field will now read MACHINE REAR UP FRONT Press Power A to perform and display the summation spectrum which in this case is not really a summation because only record 5 satisfies the search field criteria To calculate and display the power spectrum representing the sum of all the measurements made on the PART named FRONT from the Intensity Analysis Menu recall record 1 2 3 or 4 because any of these have stored with them the desired JOB and PART labels MACHINE and FRONT To perform the summation access the Power Summation Menu and press S gt JOB I and S gt PART J so that the Power Search Field now reads MACHINE FRONT Pressing Power A will calculate the summation of the intensity spectra stored in re
356. mely non linear the accelerometer signals measured in both channels will have the same frequency as the generator By selecting the Max display mode as the sweep progresses the displayed curves will represent the measured level as a function of frequency If properly implemented at the conclu sion of the test the trace displayed for Channel 1 should be flat as a result of the autolevel control and the trace for Channel 2 will represent the frequency response of the test accelerometer Like any circuit the feedback loop has a finite response time which means that if the level of the reference channel changes too rapidly the modification of the output level may not be fast enough to maintain the reference level within 4 19 2900 MANUAL Pink Noise Generator Wideband or Bandlimited 4 20 desired limits This is largely controlled by the sweep rate For instance when the frequency is sweeping through a sharp resonance if the trace of the reference channel shows an increase during the test the sweep rate should be reduced Another source of instability in the feedback loop could be the existence of a time delay between the excitation and the response For example when generating a sine signal in a room there could be a significant delay between the gen eration of the signal and its detection by a measuring micro phone due to the time required for the signal to propagate between the source and the microphone In the signal gener
357. mine the weighted broadband level versus time in addition to unweighted spectral data the SLM Mode should be used with the autostore function In that case the SLM function can be A or C weighted while the analyzer function is left unweighted Autostore by Time When the 2900 is in the Wide Dynamic Range Sound Level Meter Mode after pressing DATA M the measured parame ters can be displayed as a function of time in the following order using the right hand arrow to page upwards through the list SLOW SLOW MIN SLOW MAX FAST FAST MIN FAST MAX IMPULSE IMPL MIN IMPL MAX Leq SEL PEAK 15 11 2900 MANUAL When the 2900 is in the SLM A Mode after pressing DATA M the measured parameters can be displayed as a function of time in addition to the data for each frequency band While using the right arrow key to page upwards through the frequency bands after the highest band is reached continue presses will display additional data in the following order SLOW SLOW MIN SLOW MAX FAST FAST MIN FAST MAX IMPULSE IMPL MIN IMPL MAX Leq SEL PEAK and Spectrum X If these data were taken in the Dual Channel SLM A Mode use the hardkeys CH1 and CH2 to select the channel for which the data are to be stored Displaying the Same Frequency of Another Record Suppose a number of autostore records have been stored possibly representing reverberation decays measured at a number of different points within a room and the u
358. mmercially available 1 3 octave analog filters were based on a 6 pole design In instances where it is desired that the result of the measurement match as closely as possible the results which would have been obtained using one of these older analog fil ters the Short filter is recommended The Long and Short digital filter algorithms are designed to provide a fast rise time and slow decay time For the mea surement of rapid time decays a reversed filter algorithm has been implemented which provides a slower rise time but a faster decay time The Reverse filter selected by pressing reverse H provides a decay time approximately ten times faster than that of the Short filter With regard to IEC Publication 225 1966 all these filters sat isfy the requirements The filter algorithm is selected by pressing either LONG F SHORT G or REVERSE H When octave and fractional octave filters are active this is indicated on the right side of the display right end of the fifth line down in the format of a letter L for Long S for Short or R for Reverse followed by the symbol and a number 1 or 3 which represents the fraction of an octave used for the bandwidth While in the Filter Menu the bandwidth and the filter type may be changed independently by simply pressing the appropriate softkey Return to the System Menu by pressing EXIT There are three parameters which must be defined to perform a baseband FFT analysis the number of
359. n 23 8 As an example consider the custom printout illustrated in Figure 23 6 Example of Custom Printout Figure 23 6 Example of Custom Printout le MIN e SEL DISPLAY mote DETECTR ent Time 17 NOV 93 17 03 02 Ge me WASTLES o s 2 yun eret toa n esent LARSON DAVIS 2900 RTA A4 15 Recalled from file TEST 1 record 3 Run Time 25 4250 etector EXPONENTIAL 1 8 Input LINEAR20Hz 20kHz trum Time 17 NOV 93 16 10 22 A THC 18 St 949 Tacl eh 0 0 Speed 0 0 sdotlad us Job Part Area me USER DEFINED PRINTOUT 90 M HIGH SPEED TEST TR AL 8 0100000 e ie ES KI 2 BO 40 10 0kHz E A 32 E 776 1 3 OCTAVE BANDWIDTHS MAJOR TONE SPL IN DECIBELS This particular example includes two separate graphic areas a direct reproduction of the LCD display from the analyzer itself and a scaled custom graphic at the bottom of the page The text strings printed on the upper portion of the printout describe parameters associated with the measurement of the data all of which are stored as part of the data block in the analyzer and available for printout under user control The various other text lines such as USER DEFINED PRINT OUT SPL IN DECIBELS 1 3 OCTAVE BANDWIDTHS HIGH SPEED TEST TRAIL 8 and MAJOR TONE are user defined text strings The location size and orientation of each of the measurement setup te
360. n 1 is negative the measurement array does not sat isfy the requirements of the standard N 1 1 2 YES eq 6 where 7 is the mean value of M short time average samples 1 Of 1 calculated from the equation M 1 22127 eq 7 kel m the previous section Power Summation it is shown how the sound power can be determined over a surface area named Part by performing a two level search using the field JOB PART The search identifies all the intensity measurements stored in the database which correspond to the Area elements which together makeup the larger surface area named Part From the Power Summation Menu the indicators defined above can also be determined and dis 20 21 2900 MANUAL 20 22 played as a function of frequency over the same surface area by pressing the following keys Softkeys Softkey Functions F2 P I B F2 Surface Pressure intensity Indicator F3 NPP C F3 Negative Partial Power Indicator F4 FNU D Field Non uniformity Indicator The resulting display will resemble Figure 20 5 F2 Display Figure 20 6 F3 Display and Figure 20 7 F4 Display below Figure 20 5 F2 Display 23 MAR 15 47 22 Power F2 P I F3 NPP F4 FNU note Note SPEAKER TEST 4 880808 LINERR SINGLE 4 60668 ual LINEAR 26Hz 26kHz RESET 24 FEB 94 16 53 57 Fie TER 20 z LAS set See tu dz 6 7 dB ala Saddam JOB_ SPEAKER PART FRONT AREA 7777777 z dotted crsnr 52 SSP
361. n the two cursor frequencies rather than between the analog input filters With a displayed spectrum which is not uni form note that moving the two cursors together across the screen will result in amplitude variations of these two broad band levels as more or less energy falls between them 8 2 When FFT filtering is being used and the horizontal frequency axis is linear it is possible to use the display to investigate possible harmonic relationships between peaks in frequency domain functions Place the active cursor solid or dotted at a frequency which might be the fundamental frequency of a series of harmonically related spectral peaks and from the Cursor Menu press HARMNIC L Superimposed upon the spectral data will be a series of very finely dotted vertical lines each located at one of the frequencies representing a harmonic integer multiple of the fundamental frequency Note that the horizontal arrow keys continue to control the active cursor With the Harmonic Cursors active shift the position of the active cursor and note that the harmonic cur sors follow in order to maintain their relative positions at har monic frequencies To turn off the harmonic cursors simply press HARMNIC L a second time Repeated pressing HARMNIC L toggles the harmonic cursors on and off Cursor Control Fixing Cursor Positions 2900 MANUAL When examining a spectrum which does indeed contain a number of peaks which are harmonically r
362. n On or Off the noise in all 1 3 octave bands simultaneously The On Off status of the noise in individual bands can also be set on a band by band basis using the keys ON C and OFF D to set the status of the band indicated by the active cursor In this manner noise can be generated for any combination of 1 3 octave bands contiguous or not When using the ana lyzer to measure the spectrum of the noise generated the user should bear in mind the effect of filter selectivity due to filler skirts not being perfectly vertical on the measured spectrum For example with noise generated in a single band the measurement will produce a spectrum indicating noise in the two adjacent sidebands at levels approximately 17 dB lower This phenomenon is associated with the mea surement process only and does not represent the much more accurate bandlimited noise actually being produced To return to the Wideband Pink Noise Menu press WIDE A m the Bandlimited Pink Noise mode the autolevel feature is used to improve the noise spectrum in a test room for the purpose of making sound decay measurements Because the sound absorption of room surfaces tends to increase vvith fre quency it usually happens that the spectrum of a room excited with pink noise will fall off greatly with increasing fre quency This makes it difficult to measure the decay of all bands in real time because the levels in the higher frequency bands are not sufficiently greater than
363. n immediately upon pressing that key There are two formats available for the presentation of the waterfall plots In the two dimensional format produced by pressing DRAW 1 C the spectra are simply overlaid one at a time without any offsets in the vertical and horizontal Storing and Recalling Non Autostore Data Exiting from the Recall Mode Storing and Recalling Non Autostore Data 2900 MANUAL directions This produces a graphic as shown in Figure 13 4 Waterfall Menu 2D Format In the three dimensional format produced by pressing DRAW 2 D an offset in both the vertical and horizontal directions is added to each successive spectrum curve pro viding perspective to the view Figure 13 5 Waterfall Menu 3D Format 25 RPR 16 18 23 DRAW 1 DRAW 2 START END DELTA Although the record type which was recalled from memory was determined by some aspects of the analyzer setup at the time of recall there are other setup parameters which may be different between the recalled records For example within the records classified as Normal some may use FFT filtering and others 1 3 octave In addition a variety of different aver aging methods and times may have been used for the differ ent measurements Suppose the user had the analyzer configured for FFT analysis at the time the recall was initi ated and that during the recall operation a record measured using 1 3 octave was recalled and displayed It will be noticed that whe
364. n the 1 3 octave record was recalled the setup parameters on the screen changed from those associ ated with FFT analysis to those associated with 1 3 octave analysis The user has two options as to which setup the ana lyzer will be configured after exiting from the recall operation To have the 2900 return to the setup which was active at the time the recall operation was initiated press EXIT The dis play of the recalled data block will be lost when this is done since the setup which had been active prior to the recall oper ation may not be the same as that corresponding to the pres ently displayed data block To have the 2900 remain in the setup configuration shown on the screen based on the record last recalled press KEEP H It is necessary to follow this procedure if the recalled data block is to remain on the screen In either case the 2900 will then return to the SLM or Ana lyzer Menu 18 15 2900 MANUAL Memory Requirements Non autostore Records Each point of a data block spectrum time record RT60 data etc requires 2 bytes for storage Complex spectra require two points per filter band The note field requires 64 bytes 13 16 Storing and Recalling Non Autostore Data 14 Annotation of Data Blocks Annotation of Data Blocks Annotation of Data Blocks It is possible to annotate a data block such as adding a test number comments concerning the measurement process the test procedure etc
365. n working with data in the vsRPM Speed format the user can define as many as 32 pens each representing a specific Classification Class Lines Optional Feature Accessing the Class Lines 2900 MANUAL channel number and frequency band or order number as described in Chapter 17 When performing the class lines function the additional rows appearing in the first column below the Ch 1 and Ch 2 rows denoted Pn N N 1 2 3 permit the class lines to be applied to each of the curves cor responding to each pen number as well as to the two chan nels of data displayed on the analyzer itself Although these pens were originally defined for use with the multi window display capability when operating the analyzer with an exter nal color monitor via the Model 2500 Color Display Adaptor it is not necessary to actually use the external display when performing the class lines function in this manner The ability to classify a test item according to different classi fication criteria in a single operation is of great practical importance Suppose for example the test object is a motor which is used in a variety of different machines and the major concern of the machine manufacturer is that the radiated noise be within acceptable limits In many cases the noise radiation by the machine associated with the motor will depend predominantly upon the vibration spectrum of the motor the transfer function of the vibration between the motor mo
366. nce in the vsTime display mode the overload message will no longer appear when the FREQ M softkey is used to change the fre quency band of the display The initial indication of an over load should be sufficient to warn that the effects of the overload will influence the data in any of the frequency bands for time values greater than that for which the overload first occurred Leq Measurements in the vsTime Display Mode 15 10 When data is being displayed in this mode there are three values of Leq indicated digitally on the lower right of the screen as shown in Figure 15 5 Figure 15 5 Leq Data in vsTime Display se pya 90 17 31 RT6B REPLACE AVERAGE Auto RE Auto DU note Note SPL 6 16068 EXPONENTIAL 1 64 Dual LINEAR 26Hz 26kHz STOP 36 AUG 90 00 16 55 DATA 1 G6kHz L 3 Channel 1 of 2 vsTIME e 3 d 8 1606 3 8 do INITIRL lthresh hthresh R Preu R Hext DATA SOLID DOTTED B From left to right these represent the following Leq for the entire record Denoted by the symbols 1 1 above Leq for the portion of the record outside the two cursors Denoted by the symbols above Autostore by Time Changing the Displayed Frequency Band 2900 MANUAL Leq for the portion of the record between the two cursors Denoted by the symbols 1 1 above Broadband Level versus Time The frequency band which the displayed amplitude time curve represents is indicated on the right of the display ju
367. nce spectrum Because we are now displaying the same spectrum which was selected as the reference spec trum a spectrum relative to itself all points will have zero amplitude resulting in a horizontal line Figure 19 4 Shift Menu uiis 93 14 38 X AXIS Y AXIS U SCRLE U OFSET H SCRLE H OFSET 200 ENT 6 6008 E m Ehear Be 2 kHz TE los FEB 98 83 14 34 ac opt D sch 23 0 E 38 5 ES PHONS 68 2 dotted cran LI SetREF vsREF Control of Display Formats Cross Channel Normalization and Use of Key Macros 19 3 2900 MANUAL Dual Channel Measurements Any spectra now displayed whether just measured or recalled from memory remember to press KEEP H when exiting from the Recall Menu will be displayed relative to the reference spectrum If the message Reference may not match appears on the upper right of the screen this indi cates that the displayed and reference spectra have different bandwidths and a display of this spectrum versus the present reference spectrum is not appropriate Returning to Normal Display Format When the Model 2900 is configured for dual channel analy sis the data block to be used as a reference will represent a dual channel measurement and the spectra for channels 1 and 2 will in most cases be different However the spectrum for only one of these two channels can be displayed at the time the reference spectrum is defined By pressing sameREF N the displayed spectrum will
368. ndwidths 0 707 Fe 1 3 Octave Bandwidths 0 23 Fe Sound Intensity Measurements 20 9 2900 MANUAL Entering Label Names 20 10 To assign the labels to each measurement press each of the following keys and respond to the prompt on the upper right of the display by typing the desired name using the keypad and pressing EXIT Softkeys Softkey Functions job I The total envelope surface being measured It is composed of PART surfaces part J A subset of the total envelope surface It is com posed of AREA surfaces area K A subset of the JOB surface AREA has both a label and a numerical value of surface area After the label has been typed and entered an entry field will open at the upper right of the screen for input of a numerical value of surface area as indicated by the message SQUARE METERS XXXXX The value XXXXX in the field will be taken from the AREA field on the lower right If the value is to be the same simply press EXIT otherwise input a new value from the keypad before pressing EXIT As each label is entered it will appear on the lower right of the display alongside the appropriate designation JOB PART or AREA The numerical value of surface area for the AREA label can be edited without changing the AREA label by pressing meter2 M inputting a new value and pressing EXIT Be sure to store each measurement after defining the labels and making the measurement The user is not obliged to assign lab
369. ne spectrum then overlaid upon that another spectrum then another etc Access the Recall Menu by pressing RECALL and use the A Prev N and A Next O keys to recall the record number from which the spectra are to be displayed Then press W Fall A which will bring up the Waterfall Menu shown in Figure 15 6 Waterfall Menu Figure 15 6 Waterfall Menu ER ig 65 88 34 DRAW START END DELTA Hote H recall data COMPUTER On the right of the screen we see a table indicating the present values of START END and DELTA These represent the first and last spectra in sequence which are to be dis played and the incremental record number between dis played spectra respectively For example using the following combination START 0010 END 0020 DELTA 0002 The spectra displayed will be numbers 10 12 14 18 and 20 in sequence To edit any of these numbers press START E END F or DELTA G This will produce the message W FALL sSXXXX eXXXX dXXXX with a flashing cursor to denote where inputs from the key pad will begin The only difference between initiating this input with the START E END F or DELTA G softkeys is that the flashing cursor will be positioned for immediate edit ing of the START END or DELTA values respectively Use the numeric keypad and the horizontal arrow keys to edit the values as required and press EXIT The display sequence will begin immediately upon pressing that key
370. neeeeeesenceeeeeeseneeeseesseneesesesenaeeseeseeneeeeeenenaas 19 14 Salle Me fee c aa te ee eae 19 14 Recall n Maeros acti ttti ida et tat end ote um emitte 19 14 Chapter 20 Sound Intensity Measurements U J J J 20 1 Sound Intensity Standards U n rene nnns nenas 20 2 Instrument Standards zu e Eee eee entere dee ones 20 2 Application Standards sese aaa aaa nnn senes 20 3 Setup and Calibration of the Measurement System 20 3 Sound Pressure Level Calibration eene nnne 20 3 Setup for 1 3 octave Intensity Measurement enne enne 20 3 Pressure Temperature and Spacer Length Input 20 4 Amplitude and Phase Normalization 1 1 1 3 Octave Measurements 2222 20 4 2900 MANUAL Chapter 21 Sound Intensity using Narrow Band FFT Analysis a 20 7 Definition of Surface Area m2 for the Power Calculation esee 20 7 Job Part Area Labele nennen ss esa ise rs as sa akaqa s snas ens 20 8 Guer 20 10 Selection of Display Parameters eene 20 11 Selecting Displayed Parameter 20 11 Readout of Broadband Levels eceeecceeeeeeeeceeeseceneeeeeeeeeeeeeeeeeaeeeenesaaeeseseeeeeeseeeneseenenenee 20 11 Reducing the Frequency Display Range enne eene 20 11 Reducing the Amplitude Display Range essen nennen 20 12 Performing the Intensity Measurement
371. nent is the default value of the Ranging Aperture This value may be changed from the Input Menu by pressing AUTO RA E and entering a new value When the Ranging Aperture is small with respect to the variability of the input signals the autor anging may be unable to find a stable setting If this occurs increase the Aperture The speed with which the autorange responds is related to the response of the input modules which in turn depends upon the values of highpass filters which are active For the 7 3 2900 MANUAL fastest autoranging operation select a frequency range hav ing a 20 Hz lower limit After the autoranging process has stabilized to the proper gain setting press RANGE to turn off the autoranging func tion and put the range under manual control Response Time of Digital Filters In the case of frequency analysis using digital filters when the analysis is initiated following a STOP RESET sequence there is a time delay associated with the output of each filter The lower frequency filters which have the narrowest band widths have the longest response time Because the filter lev els are not displayed until valid data are available the upper frequency filter levels will appear before those of the lower fre quency filters Once the filters are running however and the measurement is stopped by pressing R S without a reset the frequency analysis function continues to run in the back ground When the R S k
372. ng the measurement The result is a single intensity spectrum which has been averaged both in time and spatially over the defined measure ment area Scanning can be combined with either of the aver aging methods described in the above paragraphs Storage and Recall of Intensity Spectra To store the displayed Intensity spectrum press STORE which will produce the message STORE INTENSITY n on the upper right of the screen to indicate that the spectrum Sound Intensity Measurements 20 13 2900 MANUAL has been stored into the active file as the nth record of type Intensity Both the Intensity and the SPL spectra are stored along with the JOB PART and AREA names the surface area associated with the AREA and the setup as displayed on the right of the screen The Quality and Particle Velocity spec tra are calculated from the Intensity and SPL spectra so it is not necessary to store them Intensity spectra are recalled from the Intensity Menu by pressing RECALL which will produce the message RECALL Intensity N on the upper right of the screen to indicate that the Nth record of type Intensity has been recalled and is being displayed The message recall data on the lower right of the screen indicates that the horizontal arrow keys are in control of the recall process Pressing the left arrow key will sequentially recall records lower in number than the one presently recalled while the right arrow key will sequentially recall
373. nge Input Attenuator Control V Offset Vertical Display Window Control H Offset Horizontal Pan Control When Using an Expanded X Axis recall Data Block Recall Control contrast Screen Contrast Control new data Control of independent parameter during a paging process such as selecting the fre quency value for the display of vsTime records lifter Control of time domain editing while display ing liftered spectrum noise Control of Noise Generator Output Level MEMORY Files Menu controlling Memory File Listing Highlight Position DISK Files Menu controlling Disk File Listing Highlight Position RECORDS Files Menu controlling Records Listing High light Position 1 19 2900 MANUAL Noise Floor 1 20 The noise floor of the Model 2900 was measured by placing a LarsoneDavis Model ADOO5 dummy microphone on the microphone preamplifier which provides a shunt capacitance equal to that of an actual 1 2 inch microphone 18 pF and shorting the input Figure 1 7 Noise Floor in dB re 1 microvolt 1 3 octave bandwidths 15 DV 12 07 12 NORMRL Lea MIN MAX SEL DISPLAY note DETECTR Note SHORTED INPUT 60 000A H a I Tu LINEAR SINGLE 60 aaa neut 1 LINEAR 1Hz 2 kHz 15 94 12 05 OP NOU 94 kusa gr e eg e oe o o o o o o o oo o o so o o o o o o o FILTER 30 1 66kHz LAJ Dag 1 of 1 NORMAL d 4 PHONS SPL Loc 8 80 SPEED 4 6 30 Purr
374. nits Units Data Stored macros Macros Data Custom Print Setups stored from Print Menu Print Setup Classification Lines stored from Class Lines Setup Menu Class Setup Field Indicators stored fromIntensity Power Summation Menu Field Ind The user must bear in mind that ONLY the displayed data block is stored For example in the Standard Analysis Mode spectra for Normal Leq Max Min and SEL are calculated for each input channel If the 2900 is set for dual channels stan dard analysis and the display mode is set for Normal then pressing STORE will result in the storage of one record of type Normal which contains a Normal spectrum for both channels If the user wishes to store the Leq spectra as well the display must be changed to LEQ mode and the STORE key pressed again resulting in the storage of one data record of type Leq which contains an Leq spectrum for each of the two channels Similarly storage of the Max Min and SEL Storing and Recalling Non Autostore Data Storage Verification 2900 MANUAL spectra require selection of each of these display modes and a press of STORE In the case of complex data blocks the data block is stored in the format of the display real imaginary or magnitude phase If the user wishes to be able to recall and display the data block in both the rectangular and polar coordinate rep resentations he must display and store the block twice using each of the coordinate systems Setu
375. nment Menu had been aligned with channel 2 it is possible that the line for channel 1 will not be seen on the table In that case use the T G soft key to bring that line back down into the table Manual Judgement of a Displayed Spectrum using a Softkey 22 10 NOTE As above press the softkey corresponding to the hardkey O until its label is USE KEY O Return to the System Menu or the Main Menu and either make a new measurement or recall and keep a previously stored measurement Display the spec trum which is to be judged channel 1 or channel 2 then access the Class Lines Menu and press m JUDGE P which will produce the message Select class to judge on the upper right of the screen Upon pressing a softkey representing one of the named class line families a selection of softkeys will be presented at the top of the screen each one representing one line of the family selected There will only be as many lines represented as were defined for that family originally Press any one of these not ing that only that particular line of that family is displayed permitting visual comparison of the spectrum with that line However at this point the set of softkeys representing differ ent lines of that family remains along the top of the screen enabling the user to continue to select any particular line of that family for visual comparison against the displayed spec trum At this particular point in the sequence we are desc
376. nn n on the upper right of the screen Use the numeric keypad to enter a value which will define the end of the curvefit time interval as the instant when the sound has decayed to nnn n dB below the highest value which had occurred during the measurement In the example above this would be 020 0 dB Press EXIT to accept the value which will then appear as XX X in the text field AutoTH Max XX X YY Y on the right of the screen To perform automatic curvefitting access the RT60 Menu from the vsTime Menu by pressing RT60 B If this is to be the first curvefit made vvith this set of decay records press the softkey sequence RESET D YES A to reset the RTGO register The automatic curvefitting process may be applied to a lim ited number of frequency bands if desired This is done by positioning the solid and dotted cursors along the frequency axis such that they enclose just those frequency bands for which the curvefit is to be performed Use the softkeys SOLID N DOTTED O and BOTH P along with the hori zontal arrow keys to define this region the CURSOR hardkey will not function from the RT60 Menu The frequency range between the cursors is indicated digitally on the right of the screen 5th line down by the message Af XX YY where XX is the lower frequency limit and YY is the upper frequency limit If it is desired to apply the curvefit to the entire set of frequency bands place the cursors at the two extreme limits
377. nnns 12 2 Storage of User defined Setups ener 12 2 Recall of User defined Setups AA 12 3 Exiting from the Setup Men 12 3 Storing and Recalling Non Autostore Data 13 1 FilesOperaflions va sove yo A X Ras 13 1 2900 MANUAL Chapter 14 Chapter 15 Accessing the Files 2 2 ietininkai nandaan trennen nnne nnne invia la 13 1 Files information alii a aad aa ba Dei us 13 1 Gfe e 13 2 Renaming Files u a atete nE de duse eet edd oct dira dE 13 2 Dee ing FIlGS u M gn 13 3 Formatting a Floppy DISK u y t y S tu S a kaa asss 13 3 File Transiore torom DISK cerei tie iege piede a Lopes bi cede gegen 13 3 Selection of the Active File 13 4 Record Operations from the Files Men 13 4 Classification of Record Types uit el ERR RUE had rin dos ban c dad 13 4 Hecords Listilrig iiio ee a eR eom alo nua 13 5 Note Editing s asa cie Dee ae tel aan aed eee Ld KA A eee t 13 5 Dee ime Records Ee EU een tus 13 5 Recalling a Record from the Files Men 13 5 Storage of Normal Non autostored Data to Internal Memory seen 13 6 Storage of RENE Te 13 6 Record Classification eg menani aa tcd be nu ce Eie t D edat exe Pe mace Ee E tin 13 6 Storage VerifICat
378. note Multi i SPL 5 7300 EXPONENTIAL 1 8 Dual A WEIGHT STOP 24 MAR 97 16 19 35 FILTER 14 25 0 Hz L KE ech 1 of 2 HOFMRL DIFF PHONS MET TACH 6 6 SPEED 6 6 Hz Be dotted crsr INT Dig WGT BWNORM Figure 10 2 Display Menu Standard Mode with FFT 24 TAR 16 23 27 al fr AVERAGE sun SETUSER note Multi SPL 2 6488 9e EXPONENTIAL 178 Dual A WEIGHT STOP 24 MAR 97 16 22 15 T FREQ a G6BAHz H4AA 1 Channel 1 of ORMI 6 6 3 50 REM TRCH 6 6 5 6 6 a E dotted crsr INT Di9 WGT BWNORM Digital Display including Broadband Acoustic Frequency Weighting User defined Frequency Weighting and Integration of FFT Spectra 10 1 2900 MANUAL Selecting Bandwidth for Display of 1 3 Octaves Display of the Average Spectrum When the measurement has been made using 1 3 octave fil ters the display may be presented in either 1 1 or 1 3 octave format The user makes this selection by pressing one of the following softkeys 1 1 A or 1 3 B as shown in Figure 10 1 The 1 1 octave levels are obtained by summing the three 1 3 octave levels contained within each 1 1 octave band Selecting Integration When the analyzer is in the dual channel Standard Analysis Mode with 1 1 or 1 3 octave filters it is possible to display the average spectrum calculated from the spectra measured for channel 1 and 2 The default state is to display either the channel 1 spectrum or the channel 2 spectrum
379. nt the Normal window will display data but there will be no valid data shown in the other windows Upon stopping the mea surement data will be displayed in these windows as well The upper right parameter window for each display window permits the user to select the channel whose data is to be displayed Click on this window and select either 1 or 2 To exit without making a selection click on EXIT Selection of Broadband and Highpass lowpass Filters Selection of Units The parameter window farthest to the left on the lower level is for the selection of Broadband weighting and selection of Highpass lowpass filters Click on this window to select a broadband weighting filter A or C or to select a frequency range defined by highpass and lowpass filters inserted into the input path While this selection changes the analog filters used in the measurement the frequency range of the display will remain the same 1 Hz 20 kHz as in the 2900 itself 24 10 The parameter window farthest to the right on the lower level is for the selection of units For the creation of user defined units the pop up Control Window must be opened Click on SYSTEM and then UNITS Once defined these will appear among the choices available within the Units parameter win dow Use of External Color Monitor for Display and Instrument Control 2900 MANUAL Cursor Control and Selection of Graphic Display Parameters Cursor Control There are two cu
380. nteger steps can be cal culated using either 1 1 or 1 3 octave bandwidth Statistical values are calculated for each frequency band and in the SLM mode all the sound level meter parameters An Ln value from a set of measurements represents the amplitude level which was exceeded n percent of the time over the measure ment period For example suppose that the level in the 250 Hz frequency band has been sampled 1 000 times and that the value calculated for Log is 85 dB This means that 9006 of the samples 900 samples had level values above 85 dB In the Model 2900 Ln values are determined in integer steps from Lo to Log over a user positioned measurement range of 120 dB Autoranging must be utilized to obtain this large measurement range since the dynamic range of the 2900 is approximately 80 dB Other statistical values which are cal culated for each frequency band are the maximum value the minimum value the median value the mean value and the standard deviation In the SLM and single channel Standard mode the resolution of the statistics is 0 5 dB In the dual channel Standard mode the resolution of 1 0 dB Statistics and Ln Calculations Statistical analysis can be performed with the 2900 in either the SLM or the Analyzer Mode In the Analyzer Mode statis tics are calculated in 1 1 or 1 3 octave frequency band widths In the SLM Mode statistics are calculated for the sound pressure level both Slow and Fast response in ad
381. nterpolation function OFF simply press INTERP N a second time Creating a User Weighting Curve from a Measured Spectrum After a spectrum has been measured and it is being dis played it can be made into a user weighting curve by press ing MAKE M At the right of the display there will be a prompt MAKE USER ZERO AT 000 0 which permits the user to add a dc offset in creating the user weighting curve from the spectrum Use the keypad to enter the desired off set then press EXIT For no offset simply press EXIT directly without typing a value Digital Display including Broadband Acoustic Frequency Weighting User defined Frequency Weighting and Integration of FFT Spectra 10 5 2900 MANUAL The Active Register There is an active register associated with user weighting This register holds one user weighting curve for each of the following bandwidths 1 1 octave 1 3 octave and FFT which together make up a set of user curves Whenever the Setuser Menu is accessed the user weighting curve in the active register corresponding to the present analyzer band width will be displayed When the user clears creates and edits a user curve as described in the preceding section he is modifying the user weighting in the active register associated with that bandwidth When originally accessing the Setuser Menu the user weight ing curve displayed is whatever happened to be in the active file for that bandwidth at that time Thi
382. nuities in the curves the values of t max and s Amax are also used to define the maximum vsRPM Graphics Control of Trace Status 2900 MANUAL increment of RPM Speed for which a new point is to be gen erated The incremental amplitude value required for the generation of a new point is set by pressing Alevel B which results in the message ENTER dB THRESHOLD XXX X on the upper right of the screen Use the numeric keypad to enter the desired value and press EXIT Suspending Color Monitor Updates The 2900 allows 4 kilobytes of memory to the generation of the traces in the Real time vsRPM Graphics mode These are divided among the number of traces which are active Each point requires 6 bytes 2 each for the trace amplitude the RPM value and the Speed value To make a trace inactive previous to a test in order to increase the amount of memory available for the remaining pens access it via the numerical keypad and press STATUS I The letter U denoting Unassigned will appear to the left of an inactive trace in the parameter table Repeated presses of STATUS I will toggle the status between active and unassigned Any combination of traces may be made inactive Performing a Test Because the color monitor can be dealing with up to 32 differ ent pens and up to four different display windows the gener ation of the Real time vsRPM Graphics may be slower when the color monitor is active Pressing VIDEO E will
383. o define it as such for the calculation Then recall the Test Room background spectrum and press BACK GD O to define that for the calculation In some cases a user may be confident that the Test Room spectrum is sufficiently above the background spectrum that no correc tion will be necessary and they do not wish to measure the background spectrum In this case simply press CLR BG to reset the levels of the background spectrum to be used for the calculation to zero dB in all frequency bands To define the RT60 record to be used for the calculation press RT60 F to access the RT60 Menu If the desired record is already in that buffer simply press EXIT to return to the Rooms Menu Otherwise press RECALL YES A use the horizontal arrow keys to recall the desired record then press EXIT Select the standards organization whose standards you wish to follow for the determination of the impact sound insulation parameters by pressing either ASTM I or ISO J Room Acoustics Measurements Pressing ASTM I will produce the ASTM Rooms Menu as shown in Figure 21 5 The standard ASTM E1007 90 Field Measurement of Tapping Machine Impact Sound Transmission Through Floor Ceiling Assemblies and Associated Support Structures describes the procedure for determining the Normalized Impact Sound Pressure Level Ln from the measured data Another stan dard ASTM E492 90 Impact Noise Isolation Laboratory is appropriate for laboratory measuremen
384. o the Main Menu to run 4 28 2900 Instrument Setup Via The System Menu Key A and Key B Control 2900 MANUAL Opto isolator In 2900 Instrument Setup Via The System Menu The pins 9 10 11 13 14 and 15 are used to implement a pair of opto isolated inputs and a pair of opto isolated out puts as shown in Figure 4 20 Opto isolated Connections Figure 4 20 Opto isolated Connections mA OutA mB Opto isolator OutB Out Common Common Anode Emitter The most common use of this is in conjunction with the LarsoneDavis Model 2250 Acoustic Intensity Probe which has two buttons thumb and forefinger actuated on the han dle and a plug on the analyzer end of the cable for connection to the above mentioned receptacle A separate control box for use with this receptacle is also available from Larson Davis Laboratories These two keys are then programmed such that a press of each of these keys simulates a press of one of the softkeys or hardkeys of the 2900 Programming of the acoustic intensity probe keys is done from the I O Menu To program the forefinger actuated key press KEY A D which will produce the message PRESS EXIT THEN THE KEY on the upper right of the screen Pro ceed by pressing EXIT followed by whatever softkey or hard key is to be simulated by a press of Key A Program the thumb actuated key by similarly pressing KEY B E EXIT then the softkey or hardkey which KEY B is to simulate In many cas
385. o the connector on the top panel nearest the edge To select the microphone input press CH1 or CH2 Sound Level Meter Operating Modes Selecting the Frequency Weighting 2900 MANUAL To set the microphone bias voltage press the key sequence SYSTEM INPUT K and one of the following OV A 28V B or 200V C The factory default bias voltages 200 volts Press EXIT twice to return to the WDR SLM menu Sound Level Meter Operating Modes The frequency weighting is selected as follows Softkeys Softkey Functions A WGT A A Weighting C VVGT B C Weighting 20 20k C 20 Hz highpass 20 kHz lowpass The active frequency weighting is indicated on the lower right of the screen 3 25 2900 MANUAL 3 26 Sound Level Meter Operating Modes 4 2900 Instrument Setup Via The System Menu System Menu At any time the setup and operational status of the analyzer are indicated on the display as described in Chapter 1 LCD Display Parameter Presentation Format It is possible that the 2900 will bootup to exactly the setup desired but that is highly unlikely unless the bootup configuration has been modified by the user to match his requirements exactly Usu ally the user will move immediately to the System Menu from which he may recall and possibly modify a setup previously created and stored or he may proceed to create a complete new setup He will then exit to one of the Analysis Menus for instrument operation If one
386. ock on the cus tom printout The Trace Legend is applicable only with the vsRPM Speed display format of the analyzer where multiple 23 9 2900 MANUAL LCD Graphic Printout curves are displayed simultaneously The trace legend is a table indicating the line type used for each of the different curves as well as the level at the cursor position for each curve If turned ON for other display formats nothing differ ent will be seen on the Custom Printout The next message Print CLASS LINES prompts you to decide whether or not the class lines are to be included on the custom graphic printout Select YES A or NO C Measurement Parameter Text Strings A reproduction of the LCD display on the analyzer as part of the custom printout can be configured by pressing SCREEN B If YES messages on the upper right of the screen will prompt for input of the origin width and height of the portion of the printout to be used for the reproduction of the LCD display in the same manner as the parameters for the custom graphic were input If NO this function will be turned OFF for the custom printout 23 10 Press TEXT C to access the Text Menu shown in Figure 23 7 Text Menu Figure 23 7 Text Menu Le DV 19 43 88 NOTE PRECALL 1 5 PR TIME MDETCTR INPUT Note SPL EXPONENTIAL Input 1 LINEAR 20 2 208 STOP 17 NOU 93 15 33 54 FILTER 854 2 S0kHz_ 125 v Channel 1 of 1 NORMAL dz 58 1 A 63 7
387. of the A Weighted total energy is indicated in the format A XX X N2 Both Cursors Active With both cursors active the values displayed along with the X and A represent the total energy between the two cursors rather than between the analog filters as is the case with either the dotted or solid cursor active Introduction Location O Loudness Level Location P Data from Tacho or Order Tracking Boards Location Q Status of the Horizontal Arrow Keys Introduction 2900 MANUAL When the Model 2900 is in the Standard Analysis Mode using 1 3 octave filters this location will display the loudness level in units of phons and the Loudness in sones as specified by ISO Recommendation R523 Method B The message PHONES VVGT indicates that an analog broadband weighting filter A or C weight has been selected in the input path making the measurement of Phones impos sible With any other configuration of the 2900 this location will be blank There are two inputs on these boards to accept pulse train signals from external transducers The software scaled values of the frequencies of these pulse trains are displayed in the format TACH XXX X SPEED XXX X This location indicates the assigned role of the horizontal arrow keys Possible messages are as follows dotted crsr solid crsr Dotted Cursor Control Solid Cursor Control both crsr Control Both Cursors Together OFF Cursor Control Off ra
388. om the upper right corner in a direction corresponding to a continuation of the diagonal between the lower left and the upper right corners of the front panel When making a measurement of a specific noise source whether the instrument is handheld or mounted on a tripod the front panel should be approxi mately horizontal and the instrument aligned such that the main boom element is aimed at the noise source to be mea 3 5 2900 MANUAL SLM Standards sured Thus sound waves emanating from that source will impinge the instrument case along the front panel diagonal from the upper right corner to the lower left corner IEC 651 1979 The two major standards establishing performance specifica tions for sound level meters are ANSI S1 4 1983 and TEC 651 1979 In the United States the ANSI standard is most generally utilized while the IEC standard is usually followed in other countries particularly in Europe While the Model 2900 meets the specifications for Type 1 according to both standards the selection of microphone type and orientation during a measurement may be different depending upon the standard being followed ANSI S1 4 1983 The approach of the IEC standard is that the sound level to be measured is the result of a vvell defined noise source whose position in space is known and that the effects of reflections and other noise sources on the measured sound pressure level are secondary compared to the effect of the dire
389. ompatible floppy disk drive pow ered from the 2800 2900 is available as an option Supports high density 1 44 MB and low density 720 KB format disks Noise Generator The optional noise generator provides pink and white broad band random noise with the On Off synchronized with byTime autostore for automatic measurement of sound decay in rooms It can also provide a sequence of digitally repeat able one millisecond duration noise bursts with the repeti tions rate user adjustable Digital Output and Control Printer Output CentronicsTM Parallel Port for use with a Hewlett Packard compatible laser printer or an Epson compatible printer with graphics capability Also used for communication with Model 2500 Color Video Adapter Computer Interface RS 232 ntroduction 1 25 2900 MANUAL Analog Outputs AC output 5 volt full scale DC Output 0 5 Volts Display Characteristics Internal LCD Type Flat panel supertwist with anti reflective treatment Backlighting Electroluminescent Contrast Adjustable dark to full sunlight Size Height 2 6 inch 6 60 cm Width 9 3 inch 23 62 cm Resolution 128 X 489 with full graphics and alphanumer ics External Color Display Color Video Adapter required 1 2 or 4 display windows using EGA VGA or SuperVGA Monitor Environmental Operating Temperature 13 to 122 F 10 to 50 C Storage Temperature 13 to 158 F 25 to 70 C Relative Hum
390. on There can be a problem in the case where the entire memory of the instru ment is used for a single file That file cannot be deleted since it is the only one yet the user cannot create a new file because there is no memory available to store it The solution is to delete one or more records within that file until there is sufficient memory available 256 bytes to create a new file and thus delete the other one as desired The highlighted disk file can be similarly deleted by pressing the softkey delete N File Transfers to from Disk Place the disk to be formatted into the floppy disk drive Note that any data already stored on this disk will be lost as a result of this operation Press format F which will produce the message Enter volume 2900 Data with a flashing cur sor over the 2 This prompts the user to input a volume name for this disk Use the keypad to type in the desired name and press EXIT It is not obligatory that a volume name be entered the user may choose to clear the entry field using the CLEAR key and enter the blank field as the name Upon entering the volume name the message OK to format this disk will appear on the right of the screen requesting verification of the formatting operation To continue press YES A To abort the formatting operation press NO C Storing and Recalling Non Autostore Data Only complete files can be transferred between the internal memory and a formatted floppy d
391. on Without the Control Window Global Configuration Windows Much of the instrument control and selection of display parameters can also be performed with the mouse using pop up windows overlaid on the data display windows without the need to open the Control Window Whenever one of these windows is opened the user will be presented with number of options based on the particular window which was opened The user must point the mouse at one of these and click either the left or right button to make a selection Once the window is open a selection must be made Base Frequency Regardless of the number of data windows open 1 2 or 4 the upper portion of the video display will always look as shown in Figure 24 4 Most of the instrument setup and some of the video display functions are controlled by the following windows each of which is labeled in green STATE MODE FILTER MASTER CH WIND KNOB AVERAGING AVG TIME BASE FREQ RANGE and AUTOSTR The selected parameter of each is indicated in white in the lower portion of each window The selections made within each of these windows applies to all data display windows whether one two or four have been opened When using FFT filters and operating the instrument from the front panel keypad the analysis zoom function generates the zoom analysis about the frequency of the active cursor It is not possible to have the instrument zoom about one of the cursors on the colo
392. on of a custom printout the user establishes the portion of the available height and width of the printout which is to be used for the graphic pre sentation of the data by defining the coordinates of the origin lower left corner and the height and width of the graphic Similarly the user defines the origin of each printed text string the character size and the orientation vertical or hori zontal It is recommended to begin by using a copy of one of these worksheet to sketch an approximation of the desired custom printout 2900 Printing Data Screen Displays and Tables 2900 MANUAL 2900 Printing Data Screen Displays and Tables 23 5 2900 MANUAL Figure 23 4 Portrait Worksheet CLLLLLLLLLLLLLLLLLLLLLLLL Ds SAAT REAR EDENN 2900 Printing Data Screen Displays and Tables X Coordinate mm Portrait orientation M H 8MHH HHHHHHHHHHHHHHHHS User defined printout worksheet e O Q E EE EE Re S S S S Sas o o iii el gl gt st als 23 6 2900 MANUAL Figure 23 5 Landscape Worksheet 08 88 AN 75 7710 eee ae eee 2507555 NX ee 7 E 5 75 7 5 75 9 7 5 g 5 2 5 o 2 57P 7 5 2 755 5 7 7OC 7 7 En Enn 7 5 77 17 71 70 75 5 U75 7 7 7 5 5 Be E 5282775 260 2900 Printing Data Screen Displays and Tables 23 7 2900 MANUAL General Descriptio
393. ong with the indication that the 2900 is in the ARMED state on the right of the display A subsequent press of R S will initiate the autostorage sequence beginning with the next spectrum to arrive from the processor Pressing OFF P from the Frequency Trigger Menu will take the 2900 out of this particular mode of manual triggering 15 4 The Frequency Trigger is used when the user wishes to ini tiate the autostorage sequence based on the amplitude of one of the frequency bands measured on Channel One The Fre quency Trigger Menu shown in Figure 15 2 Frequency Trig ger Menu is accessed from the Autostore Menu by pressing F TRIG M Figure 15 2 Frequency Trigger Menu JAN 80 05 14 gt 4 29 800 Hz 80 0 i SEL a baba 6872523570 2 anve ke E peut UA SAI AM bee EXPONENTIAL 1764 4 Input 1 LINEAR 28Hz 28kHz 1 RESET 05 JAN 96 00 05 00 TEES FILTER 852 1 66kHz 15 TRIG i channel 1of1 AREAL KREE bari chute EE PH0NS 53 6 u Loc I I TO ZI 32 43 Trigger TEST_1 A gt SLOPE SL PE lt MANUAL RE ARM OFF level Note that the message TRIG appears on the left of the dis play to indicate that the Frequency Trigger Mode is active The setup of the Frequency Trigger function is described in Chapter 11 After the setup of the Frequency Trigger pressing the R S key will put the 2900 in the ARMED state as indicated by the message on the right of the display At the same time the measurement and display
394. ons A SPECT A Auto Spectrum each channel C SPECT B Cross Spectrum ch 2 vs ch 1 X FER C Transfer Function ch 2 vs ch 1 Repeated presses display H1 H2 or H3 COHER D Coherence ch 2 vs ch 1 A second press will display Coherent Output Power INVERSE E Inverse Transfer Function ch 2 vs ch 1 An asterisk indicates a complex parameter In the Cross Analysis Mode using Octave filters these are only available in the magnitude phase format Thus the softkey P lt gt R will not appear in the Menu Otherwise the selection of channel number form of transfer function and magnitude or phase display is as explained in the proceeding section Analysis Menus Selection Of Measurement And Display Parameters 6 9 2900 MANUAL Intensity Analysis Display of Broadband Data The Intensity Analysis Menu which appears after setting up the analyzer and exiting from the system Menu is shown in Figure 6 6 Intensity Analysis Menu Figure 6 6 Intensity Analysis Menu a BER 12 43 46 POWER INTNSTY QUALITY SPL P VELOC DISPLAY note DETECTR 2 98058 25 8 Hz 500 Hz 18 0kHz Z A INT job Part area prob meter2 SETUP FILES AUTOSTR dotted crsr To select the desired display parameter press one of the fol lowing Softkeys Softkey Functions INTNSTY B Intensity Spectrum QUALITY C Quality Spectrum Intensity SPL of Ch 1 SPL ID SPL Spectrum of Channel 1 P VELOC E Particle Velocity 2900 Intensity parame
395. ons of the acoustic parameters done within the Model 2900 can be performed according to either ASTM or ISO standards Airborne Sound Transmission Loss Measurements Room Acoustics Measurements The determination of the airborne sound transmission loss either in a laboratory or the field requires a noise source typically a loudspeaker within one room which is designated the Source Room The adjacent room designated the Receiv ing Room will be excited acoustically by energy transmitted through the wall or partition element between the two rooms In many cases the loudspeaker will be excited to produce broadband noise typically pink noise With the speaker oper ating the space averaged 1 3 octave sound pressure level spectra are measured within both the Source and the Receiv ing Room The space averaged spectrum may be determined by making a number of separate measurements at different locations within the room and performing a block average operation Another technique is to mount the microphone and preamplifier on a rotating microphone boom and perform a linear single average over a time interval which represents several complete rotations of the boom If using a Model 2900 it is possible to make measurements in the Source and Receiving Rooms simultaneously by utilizing two micro phones In addition to the Source Room and Receiving Room spectra a measurement of the background noise in the Receiving Room is performed without exc
396. or Video Adaptor MOUSE o o Joo Ojos ANALOG OUT DIGITAL OUT LINE ACTIVITY Analog Out Connector Use this to connect a VGA or Super VGA monitor to the hard ware module Digital Out Connector Use this to connect an EGA monitor to the hardware module Mouse Connector Use this connect a bus mouse trackball or other similar type control device to the hardware module Use of External Color Monitor for Display and Instrument Control 24 1 2900 MANUAL Printer Out Because the Centronics interface on the Model 2900 will be connected to the hardware module use this connector for the printer Digital Out Connector This LED indicator is illuminated when the hardware module is connected to line voltage and turned on Line This LED indicator flashes whenever data transfer between the Model 2900 and the hardware module is taking place Figure 24 2 Hardware Module Rear Panel I LARSON DAVIS 77 PROVO UT MADE IN USA O ANALYZER IN MONITOR LINE Analyzer In Use this to connect the 2900 Centronics interface to the hardware module using a standard Centronics interface cable Voltage Set Set this to correspond to the local AC line voltage Power Line Connectors The connector on the far right of the hardware module rear panel is for the line or mains connection of the hardware module The connector to the left of that one is designed to power the external monitor although it is not necessary to use it The monitor
397. or accuracy 7 2 Press the hardkey RANGE to put the input range under the control of the horizontal arrow keys which will be indicated by the message range on the lower right of the display This message also indicates the full scale value of the screen Pressing the right horizontal arrow key increases the full scale value in 10 dB steps decrease gain and pressing the left horizontal arrow key decreases the full scale value increase gain in 10 dB steps The upward and downward vertical arrow keys can also be used to change the gain although there is no indication on the lower right of the screen to indicate this function Press ing the upward vertical arrow key increases the full scale Performing a Measurement Offsetting Gain Between Channels 2900 MANUAL value and pressing the downward vertical arrow key decreases the full scale value Autorange of Input Gain If there is a great difference between the signal levels at the different inputs it may happen that one channel will be near overload while another will have such a low signal level as to represent only a fraction of the available dynamic range of the input In such a case it may be necessary to set an offset between the channels such that there is a difference between the full scale values In the Model 2900 the channel 2 gain can be offset with respect to the channel 1 gain from the Input Menu by press ing ARANGE P which will produce the message
398. or annotating data records and press EXIT 23 1 2900 MANUAL Selecting Printer Type Press TYPE G to select the printer type which is to be used for the printout Use the keys T B and J J to scroll the printer listing vertically until the desired printer is high lighted Many printers use an interrupt communication with the printer which permits the analyzer to continue drawing while the printer is printing which we refer to as FAST mode Pressing the key L will toggle the softkey label between FAST and COMPAT Set this to FAST when using a printer which supports the interrupt communication and to COM PAT for those which do not When in doubt try FAST and if this does not work select COMPAT When the printer has been selected as described above press EXIT to return to the Print Menu Printing the LCD Screen Display Printing a Data Table To obtain a printout of the display presently on the LCD screen press screen A Because three screen display print outs will fit onto a single sheet the actual printout will not occur until the third of a sequence of display printouts is ini tiated To obtain a screen display printout on a single sheet press eject N following screen D To obtain a printout in tabular form of the data which is being displayed on the LCD screen press table B In the tabular printout the measured data values will be printed under the column labeled RMS dB When Digital Display
399. ored byTime Hecorde 15 15 Waterfall Display of Autostored Records AA 15 16 Autostore DY Tach Uu aaa aa dA aaa yaaa 16 1 Tachometer Input TACH 22 22 nennen nennen tenter aaa eee ara yaa nnns alan 16 1 Second Tachometer Input SPEED sse 16 1 TACH SPEED Display in Intensity Mode eene nnns 16 1 EELSTEN Ee TEE 16 2 Setting the Tacho Parameters a Ai EEN d dedu Leid a T e A 16 2 Tach Speed SCaling EE 16 3 Interval and Span Geittngs sse entente enr a rennes 16 4 Influence of Slope on Test Procedure entente 16 6 BR ee Be lee ET 16 7 Trigger Smoothing EE 16 8 Enabling Autostore Dby T ach e eere ate et pe 16 9 Recall of Data Autostored T ach 16 10 Displaying Individual Gpecha nennen nnne 16 11 Channel Selection cs ves deze da qtu cet redd SP eaten ba eta ce OS UD sd Eed 16 11 16 11 Averaging of Autostore 805 16 11 Block Maximum of Autostored Records 16 13 Waterfall Display of Autostored Records AAA 16 14 Ve Ee e 16 15 2900 MANUAL Chapter 17 vsRPM QGraphics I UI U I aa aa cra ria inan AR anasan kk az uzuk a urandan 17 1 Realtime yS RPM Grap OS wi sousi esd koton kok na yi ee ray ka ad BWE pri se kon olarm OE B gr aaa aqa 17 2 Color Monitor Pen Format A 17 2
400. ortion of this chapter which deals with setup parameters directly related to the measurement pro cess Pressing EXIT will return the system to the Analysis Menu corresponding to the Analysis Mode last selected while in the System Menu Operation of the Noise Generator OPT 10 Required The Noise Menu shown in Figure 4 7 Noise Menu is accessed from the System Menu by pressing NOISE J Figure 4 7 Noise Menu 15 RPR 15 32 25 N FF ONZRUN FF RUN BURST ka WHITE NOISE IS OFF SPL 6 60668 27105 EXPONENTIAL i Dual LINEAR 28Hz 28kHz RESET 15 RPR 93 15 29 23 T bere its FILTER 1 88 H LAS Z i Channel 1 of 2 NORMAL i d 23 0 34 7 58 Fd TEE PHONS 88 7 LOC a TRCH 8 8 SPEED 0 0 R 2 noise 088 INITIAL PINK WHITE DELAY LEVEL The status of the noise generator is indicated by the message on the upper right of the screen indicating the spectral con tent of the noise pink or white and the operational status 4 14 2900 Instrument Setup Via The System Menu Connection Selecting Spectral Content Selecting Operational Mode 2900 Instrument Setup Via The System Menu 2900 MANUAL ON OFF ON RUN or OFF RUN Pink noise has equal energy content per percentage bandwidth and is usually used with octave bandwidth measurements White noise has equal energy content per constant bandwidth and is most often used in conjunction with FFT analysis The connector for the noise source outpu
401. oss Analysis Cross Analysis of FFT Filters The Cross Menu which appears after setting up the analyzer and exiting from the System Menu will depend on the filter type octave or FFT which was selected because FFT filters measure both time domain and frequency domain functions while octave filters measure only frequency domain func tions 6 6 The Menu which is first displayed when Cross Analysis and FFT filtering have been selected is shown in Figure 6 3 FFT Cross Analysis Menu 1 Figure 6 3 FFT Cross Analysis Menu 1 MAG SPL SPL 16 6488 L VN EXPONENTIAL 1 78 Dual LINEAR 28Hz 28kHz FREN a AER 37 12 37 07 co T n FRI aGB6Hz H4AA Cross Spectrum D 2 dz 41 9 73 1 50 IX Base Freauenc y aa Bl GER 12 38 29 H SPECT C SPECT X FER COHER TIME DISPLAY note DETECTR REM TRCH 8 80 SPEED 4 6 aa dotted crsr INT ALTERN BWNORM P 3R T TRIG SETUP FILES AUTOSTR There are more parameters which can be measured and dis played when doing Cross Analysis with FFT filters than can be presented in one screen Menu so two forms of this Menu are available Pressing the softkey DISPLAY F will toggle the Cross Menu from the form shown above to the one shown below which offers a different set of parameter choices Figure 6 4 FFT Cross Analysis Menu 2 801 APR 12 39 27 A CORRE C CORRE IMPULSE INVERSE CEPSTRM DISPLAY note DETECTR SPL SPL 16 6460 EXPONENTIAL 1 8 Dual LINEAR
402. ound level As the measure ment proceeds the sound pressure level will be traced across the screen as a function of time in a manner analogous to a strip chart recorder The elapsed time of the measurement is indicated in seconds on the right side of the screen first line down from the top Repeatedly pressing the R S key after beginning a measure ment will pause then restart the measurement without reset ting the data buffer Thus the elapsed time will continue to increase and the integrated levels will represent data mea sured since the last reset of the instrument To reset the data buffers and set the elapsed time to zero press RESET Sound Level Meter Operating Modes The hardkeys with the upward and downward vertical arrow symbols are used to control the input attenuators and thus the vertical scaling of the display Pressing the upward verti cal arrow key will increase the full scale amplitude and press ing the downward vertical arrow key will decrease it One can also use the horizontal arrow keys to adjust the input gain by first pressing RANGE The gain can be changed with the 2900 in either the RUN or the STOP mode Whenever the gain is changed the data buffer is reset and the elapsed time ini tialized to zero for another measurement One would typically decrease the full scale value until the sound level trace is clearly visible preferable in the upper half of the screen if possible without overloading the input
403. oved by the American National Standards Institute ANSI while in other countries most users will fol low standards approved by the International Electrotechnical Commission IEC and the International Standards Organiza tion ISO All of these standards are intended to provide sound intensity measurements in one third octave bands or octave bands There are no standards which define the measurement of sound intensity in narrow band FFT frequency format 20 2 ANSI S1 9 1996 Instruments for the Measurement of Sound Intensity IEC 1043 1993 Instruments for the measurement of sound intensity Instruments which measure intensity with pairs of pressure sensing microphones Both of these standards address the accuracy requirements of the sound intensity measurement system in terms of the pressure residual intensity index They also define the requirements for the following devices 1 Residual intensity testing device 2 Sound intensity calibrator When calibrated as recommended in this manual the combi nation of the Model 2900 analyzer and the Model 2260 Sound Intensity probe meets or exceeds the specifications of both these standards for a sound intensity measurement system The LarsoneDavis Model CAL291 Residual Intensity Calibra tor meets or exceeds the specifications as a residual intensity testing device as defined in both these standards To drive the Model CAL291 the Model 2900 must be equipped with either the 2800 OPT
404. p Information Following the storage operation the message STORE XXXX N will appear on the upper right of the display XXXX denotes the type classification of the stored record and N is an integer indicating that this particular record is the Nth record of that particular type which has been stored into the active file Records of each type are numbered sequentially within a file in the order of their storage Notes When the data block represents measured data such as a spectrum or a time waveform block complete setup informa tion of the analyzer Analysis mode averaging type and time autostore or not etc at the time of the acquisition of the data block is stored in the data record Information contained in the note field at the time of storage of the data block is also stored in the data record The Note Menu is accessed by pressing the softkey note G The user should thus create the desired note before storing the data block as described in more detail in Chapter 14 The user can also add a note to a record after it has been stored as described earlier in the section Record Operations from the Files Menu of this chapter Recall and Display of Data Records Non autostored from Memory Storing and Recalling Non Autostore Data This section refers to the recall of non autostore records from one of the operational menus of the 2900 Recall of records from the Files Menu was discussed earlier in this chapter Record
405. play weighting status wil be whatever it had been when the Setmenu was accessed Thus if it had been something other than USER it will be necessary to change to USER or USER before the newly created user weighting curves will have an influence on the displayed data If USER or USER had been active at the time of accessing the Setuser Menu the effect of the newly created user weighting curve will be immediately apparent A second press of EXIT will exit from the Display Weighting Menu to the active Analysis Menu 10 8 Digital Display including Broadband Acoustic Frequency Weighting User defined Frequency Weighting and Integration of FFT Spectra 11 Time domain Triggering Trigger Functions The 2900 can be put into a mode whereby signal averaging is initiated by the satisfaction of certain trigger criteria There are two types of trigger functions available time domain trig gering for use with FFT filtering only and frequency domain triggering Trigger Level Time domain triggering requires that FFT filtering be selected for use with Cross Analysis and that Count Averaging be active As the name implies the Time Trigger is based upon the input signal as sampled in the time domain e g the value of the digitized sample measured by the analog digital con verter Only the signal applied to Channel 1 can be used for the Time Trigger The Time Trigger Menu shown in Figure 11 1 Time Trigger Menu is accessed from the Cross
406. pper right of the screen To enter a number into the field click on the center mouse but ton to open the Global Configuration Window and use the mouse to click character by character the number The individual characters will appear on the upper right of the display as they are clicked The items PREV and NEXT can also be used When the desired number has been entered click on EXIT and then close the window by clicking the cen ter mouse button The master display type is selected by clicking on MASTER The choices available depend upon the selected Analysis Type and filtering as follows Standard Analysis with Octave or FFT Filters Normal Leq Lmin Lmax SEL and vsTach Cross Analysis with FFT Filters Auto Spectra Auto Correlation Real Imag Auto Correlation Mag Phase Inverse Transfer Function Real Imag Cross Spectrum Mag Phase Cross Correlation Real Imag Cross Correlation Mag Phase Transfer Function H1 Real Imag Transfer Function H1 Mag Phase Transfer Function H2 Real Imag Transfer Function H2 Mag Phase Transfer Function H3 Mag Phase Impulse Response Real Imag Use of External Color Monitor for Display and Instrument Control 24 7 2900 MANUAL Impulse Response Mag Phase Coherence Mag Power Weighted Time Time Magnitude Cepstrum Liftered Spectrum Cross Analysis with Octave Filters Auto Spectra Inverse Transfer Function Real Imag
407. press EXIT The entered value will be displayed upon the screen and the cursor will move to the next filter band It is necessary to press edit P each time before entering a value for a frequency band However the numerical value in the entry window when it opens is the same as the value previously entered so a horizontal weight ing line can be entered by repeatedly pressing the key sequence edit P EXIT Rather than enter the amplitude of each band one by one one may choose to define a section of the user weighting curve where the amplitude values of successive bands are to fall along a straight line values are interpolated from a straight line To do this move the cursor to the frequency band which represents the low frequency limit of the section and press INTERP N The message AUTO INTERPOLATION IS ON will appear on the upper right of the display Press edit P and use the keypad to type in the amplitude for this frequency band and press EXIT Now move the cursor to the frequency band which represents the high frequency limit of the section to be defined press edit P type the amplitude value for that band and press EXIT The amplitudes of all bands between these two bands will fall along a straight line drawn between them If the cursor is now moved to a higher frequency and an amplitude entered another straight line interpolated section will be defined because the interpolation function is still ON To turn the i
408. printing of that particular text string in the custom printout select NO C in response to the original prompt message Print string parameter You can con figure all of these text strings as desired yet select individu ally whether each is to appear on the final printout The eight softkeys below the screen on the Edit Menu are used to define user defined text strings which may be up to twenty five characters in length These are configured much the same as the measurement setup text strings described above Upon pressing any one of these the message Print USER TEXT n indicates that you are addressing the nth user defined text string Press YES A to print that text Sub sequent messages will prompt you to input the origin size and orientation of the printed string The final message Enter text prompts you to input the actual text string using the alphanumeric keypad the press EXIT The symbol will appear to the left of the label for each user defined text string which has been set ON and which will be printed Selecting NO C in response to the original message Print USER TEXT n will turn OFF the printing of that particu lar string When the text string has been set to OFF the sym bol will not appear to the left of its softkey label Storing a Custom Printout Setup to a Softkey 2900 Printing Data Screen Displays and Tables From the Print Menu press SETUPS J to access the Cus tom Print Setup Menu
409. quency Hz Sound Pressure Level Measurements Dual Channel Sound Level Meter with Frequency Analysis SLM A Mode Two Microphones Setup The Dual Channel Sound Level Meter with Frequency Analy sis Mode provides much of the functionality of the Single Channel Sound Level Meter with Frequency Analysis Mode for both Channels 1 and 2 simultaneously Due to the addi tional signal processing demands of the dual channel mode only 1 1 and 1 3 octave spectra are measured and the high est frequency filter is limited to 10 kHz This does not affect the ability of the SLM function to meet the Type 1 sound level meter standards 3 22 From the Main Menu access the System Menu by pressing SYSTEM Select the SLM A mode by pressing SLM A B Press the key Chanls A until the message Channel 1 of 2 NORMAL appears on the right side of the screen 6th line down If the notation of the right side of the screen third line down is not Dual it could be Input 1 or Input 2 press INPUT IK and Inputs G to change it to Dual The operation in this mode is essentially the same as for the Single Channel Sound Level Meter with Analyzer Mode Hovv ever the frequency weighting is selected individually for each channel these need not be the same Press the appropriate channel key CH1 or CH2 prior to selecting the frequency weighting for that channel as indicated by the message Channel 1 of 2 NORMAL or Channel 2 of
410. r and Signal Gener ator Post processing Order Tracking 17 11 Power Battery 1 9 DC 1 10 Primary Indicator Range 3 14 printing 23 1 Pulse see Signal Generator Q QUALITY 6 10 20 11 Quality 6 10 20 11 R Range control 1 5 3 11 7 2 offset between channels 7 3 RC Noise Rating Curves 21 22 Real imaginary display 6 8 Recall byTach autostored records 16 10 25 39 byTime autostored records 15 7 25 39 Ln Traces 18 6 Macros 19 14 non autostore records 13 10 25 38 RT60 21 12 setups 12 3 Statistics table 18 7 Units 9 7 user weighting curves 10 7 10 8 Records 13 5 classifying 13 4 13 6 2900 MANUAL editing or deleting 13 5 listing 13 5 recalling 13 5 reference spectrum 19 3 Remote Control Module 4 24 Reset 12 2 Reverberation Time 21 4 room acoustics 21 1 S SEL 6 3 Setup 12 1 13 10 default 3 2 3 17 4 7 for autostore 15 1 16 2 for recall 13 11 labeling and assigning 12 2 recall of setup 12 3 reset 12 2 statistical analysis 18 1 storing a setup 12 2 via system menu 4 1 Signal Generator 4 16 25 40 Pink Noise 4 20 25 43 Pulse 4 22 25 47 Sine Dual Tone 4 18 25 42 Sine Single Tone 4 16 25 41 White Noise 4 22 25 45 Signal Type periodic 5 7 stationary 5 5 transient 5 7 Sine VVave see Signal Generator SLM SLM A dual channel 3 22 SLM A single channel 3 2 SLM wide dynamic range 3 24 Softkeys 1 4 changing setup 12 2 labeling and assigning 12 2 menu concept 2 1 software upgrade 1 7 Sound Intensity
411. r and the printer To abort a printout simply press abort P In cases where the printer has a buffer memory the printing cannot be stopped until the buffer has been printed and the analyzer is again in communication with the printer 23 15 2900 MANUAL 23 16 2900 Printing Data Screen Displays and Tables 24 Use of External Color Monitor for Display and Instrument Control Model 2500 Color Video Adaptor required The Model 2500 Color Video Adaptor permits the Model 2900 to communicate with an external color monitor EGA VGA or Super VGA via the Centronics interface The user can select to have one two or four data display windows open simulta neously on the external monitor screen The system also includes a three button mouse which connects to the hard ware module for control of the analyzer and selection of dis play parameters on the monitor screen Utilization of an external color monitor will reduce slightly the display update rate of the 2900 LCD display resulting in a somewhat more jerky action to the movement of the dis played lines or bars However this does not affect the inter nal signal processing so no additional errors in the data values are produced Hardware Considerations The front panel of the Model 2500 Color Video Adaptor is shown in Figure 24 1 Hardware Module Front Panel below Figure 24 1 Hardware Module Front Panel DC IN LARSON DAVIS 9 15V 1 5A Model 2500 Q PRINTER OUT Col
412. r display So this window is used via the Use of External Color Monitor for Display and Instrument Control 24 5 2900 MANUAL Selection of Analysis Type mouse to adjust the center frequency of the zoom analysis Unless the instrument is set to FFT analysis with the zoom factor greater than unity the mouse will not be able to change the base frequency number Selection of Filter Type The selection of the analysis type is performed by clicking on MODE and clicking on either SLM to select the Sound Level Meter Mode Standard 1 Standard 2 Cross or Intensity When utilizing the SLM Mode with the color monitor the 1 3 octave filter bandwidth should also be selected The resulting display will consist of the spectrum on the left 2 3 of the screen and the sound level values in bargraph format on the right 1 3 of the screen As a cursor is moved over these bars the readout field level value from left to right in the following sequence Slow Slow Min Slow Max Fast Fast Min Fast Max Impulse Impulse Min Impulse Max Leq SEL and Peak To exit without changing the mode selection click on Exit Selection of Detector Type The filter type is selected by clicking on FILTER and clicking on the parameters displayed in the window which opens Since only one click may be made on an open window it may require several operations with this window to set the filters as desired For example selection of FFT could require on
413. r function This function is also described in Chapter 3 Because the Single and Dual Channel Sound Level Meter with Analyzer Modes provide frequency analysis in parallel with the sound level meter function a brief description of a few of the most fundamental aspects of the frequency analy sis function also appear However if the user is to fully appre ciate all of the features of the frequency analysis function he should become familiar with the remaining chapters of the 2 3 2900 MANUAL Shift Menu manual In some cases the setup of the analysis function is best performed within the analyzer mode after which the 2900 can be returned to the SLM mode for measurement When the 2900 has been placed in the SLM mode it can be returned to the single channel Standard Analysis mode to which it originally boots up by pressing the key combination SYSTEM STAND 2 4 There is one more softkey Menu which is not accessed from one of the other Softkey Menus We shall refer to this as the SHIFT Menu and it is accessed by pressing the SHIFT hard key When this is done the SHIFT Menu will appear on screen for about 4 seconds during which time the user may press one of the softkeys When exiting from this Menu or if no softkeys have been pressed within 4 seconds the instru ment will return to the Menu which had been previously dis played A complete set of softkey Menus for the Model 2900 is pre sented in Chapter 25 Menu Stru
414. rT sse D WOU nuoJA dm s sourT Sept sdm s kay dm s o UPN USISSY 19 92 snue N exyos 17 92 JANDIJ d JAASA N Hawoues N AqM urms opour wny ds S ouueyo yore Joy s ouueyo poq OSu9 19J 1 L SNSIOA SoouoaioJoi se en ds 10 Se ake dsip APS youueq Buipuodsa1100 os umn roeds p zeydsip es T L3AV LS IN DX 443914 f LIVAN UI dOLS IN H OHNISAS skoy Surumure130Jq OIW ut s S yu oummnsur e dsiqq 8t Sc ams A LHSHO H A IIVISH A LHSHO D ATVOSA gq SIXVA V SIXV X y sno ejuozuoU onuoo 10329 298 y sHo VOTIAOA Onuoo 10329 BOS jeUuLIOJ e dsrp sofeos So pue on s y BJUOZIIOY jo9 q e1uozuoujoo og 5 0 810071 0 1971 RONADA 199 9S sixe 4 19 T S o S 30 144 LJIHS Aoxprey ssa1q DU T LATHS 29 92 snu W Aayyos 8r S JANDIJI d 5DO nOS D DO T NTI d DO T DO I V NTINTI ILIS 801 ALI 801 ILIS 801 SUI VOS 1eourT sun 1eourT porenbs Sur ur suun 3071 sun re ur1 Lp SZ 010814 NUN LATAS Woy nuo SIXV A A Index A A CORRE 6 7 A SPECT 6 6 6 9 A D Inputs 4 27 AC output 1 11 Accelerometer Connection 1 11 Acoustic Intensity Probe 4 3 Acoustic Intensity see Intensity Amplitude phase display 6 8 Analysis Mode 4 1 Cross 4 3 6 6 Intensity 4 3 6 10 Standard 4 2 6 1 Annotation 14 1 Arrow Keys 1 5 Auto Correlation
415. ractional octave filters and those along the bottom apply to FFT 4 4 2900 Instrument Setup Via The System Menu Selection of Octave and Fractional Octave Filters 2900 Instrument Setup Via The System Menu 2900 MANUAL Only one of these two filter types can be active at one time Select the filter bandwidth by pressing one of the following Softkeys Softkey Functions 1 loct A for full octave bandwidth 1 3 oct B for one third octave bandwidth The effective bandwidth for the 1 1 octave filters is 0 707 1 f where f is the filter center frequency The effective band width for the 1 3 octave filters is 0 2316 f The maximum permissible input voltage is 10 Vrms corresponding to the maximum permissible input voltage to the instrument with the range selected appropriately to avoid overload External ambient sound fields have no effect on the performance of the digital filters In North America the applicable standard for this type of fil ter is ANSI S1 11 1986 Specification for Octave Band and Fractional Octave Band Analog and Digital Filters In this standard filters are specified by both a Type number and a Sub Type letter as shown in the following tables Table 4 3 ANSI S1 11 1986 Tables White Noise Bandwidth Type Error millibel Number 10 0 lt 25 1 x41 2 or 3 depends on passband ripple Criteria for selecting Type Number Composite Bandwidth Sub Type Error milli
416. rameter displayed on the right of the screen rd line down to either Input 1 or Input 2 Select the input channel to which the measurement microphone is con nected by pressing either CH1 and CH2 and EXIT Perform the measurement as usual using the hardkeys CH1 and CH2 to select which of the two SLM A analysis is being dis played If different requency weightings have been used the corresponding weighting displayed on the lower right of the screen near the digital SPL readout will change as well Sound Pressure Level Measurements using the Wide Dynamic Range Sound Level Meter WDR SLM function Accessing the WRD SLM Menu In this mode the two A D convertors usually used for each of the two microphone inputs are used together offset to mea sure a single channel providing a primary indicator range in excess of 80 dB This means that the Type 1 specifications corresponding to ANSI S1 4 1983 and TEC 651 and IEC 804 are met over the entire 80 dB dynamic range of the instru ment Frequency analysis is not provided in this mode of operation Sound Level Meter Operating Modes To access the WDR SLM menu as shown in Figure 3 14 press the hardkey SLM 3 23 2900 MANUAL Figure 3 14 WDR SLM Menu 29 RUS 05 38 17 A WGT C WGT 28 28k note SPL 19 1688 Input 1 E STOP 29 AUG 96 05 37 09 aa 70 o UNES EEG ANNE LL EP Ee z REM FRST D D D a H mist EXES ANN ANN Min 53 7 Max 8
417. range of intensity measurements it may be desirable to select a smaller display range 80 dB when viewing intensity The amplitude display range is changed from the Shift Menu by pressing V SCALE C and making a selection as described in detail in Chapter 19 Performing the Intensity Measurement 20 12 The most common standards which define the procedure to be followed in performing a measurement of the sound power radiated by a noise source based on sound intensity mea surements are the following e ISO 9614 1 Acoustics Determination of sound power lev els of noise sources using sound intensity Measurement at discrete points ISO 9614 2 Acoustics Determination of sound power lev els of noise sources using sound intensity Part 2 Mea surement by scanning e ANSI S12 12 1992 Engineering method for the determina tion of sound povver levels of noise sources using sound intensity The ANSI American National Standard Institute standard is typically follovved in the United States vvhile the ISO stan dard is more commonly followed in countries other than the United States Each of these standards are very detailed and complex It is strongly recommended that the user become familiar with the complete standard appropriate to their mea surement situation as it is outside the scope of this manual to cover all the aspects of these standards Since both of these standards call for the use of 1 1 or 1 3 octave bandwidths
418. rate for the 800 X 600 resolution is 56 Hz which may produce flicker on some monitors Some newer monitors may not sup port this scan rate in which case the 800 X 600 resolution cannot be utilized To turn off the color monitor mode of operation press OFF A Use of External Color Monitor for Display and Instrument Control 24 3 2900 MANUAL System Operation Using Pop Up Control Window The middle mouse button is used to open and close a pop up Control Window in the center of the monitor screen as shown in Figure 24 4 External Monitor Main Menu below Figure 24 4 External Monitor Main Menu STATE MODE FILTER MASTER SCH WIND STORE STOP Standard L Normal KNOB AVERAGING AVG TIME BASE FREG RECALL dotted crsr EXPONENTIAL ESE MACROS RANGE AUTOSTR 140 off SETUPS Normal Channel 1 Lmax Channel 1 1400 DIR ICP LINEAR 20 20kHz SPL 2 135 4 150 0 DIRAICP LINEAR 20 20kHz SPL E 135 4 1300 1100 90 6 YO LEFT NORMAL Leq MIN M SEL DISPLAY note DETECTR SYSTEM PRINT ROOMS vsRPM STAT Mx Spec F TRIG SETUP FILES AUTOSTR 5 1 4 2 LOCAL CHANL 1 CHANL 2 CHANL 3 CHANL 4 MACRO RANGE STORE 12 RUNASTP CHANL 5 CHANL 6 CHANL 7 CHANL 8 KNOB KNOB RECALL mm 100 0 i 00 00 a 24 250 Hz HZOOM 2 VZOOM 1 38 6 30kHz an 14 25 0 Hz HZOOM 1 200 1 43 20 0kHz 31 1 25kHz 24 250 Hz A 28 630 Hz 24 250 Hz A e i UV et enr SO 1 uam Under mouse control there is a network of inter
419. recall intensity spectra autostored vsRPM set the 2900 to the Intensity Mode with vsRPM autostore active and press RECALL Use the A Prev M and A Next N softkeys to recall the desired record number of that type In this case the vsRPM Graphics Menu will look somewhat different as shown in Figure 17 2 vsRPM Graphics Menu Intensity Data Figure 17 2 vsRPM Graphics Menu Intensity Data a9 gan 22 29 13 SLOPE alevel TRGBHRS X SPAN VIDEO RPM SPD note PKWIDTH S 27e 5 70 crsr 268 a 06 18088 6000 RPM 5 INITIAL STATUS HIDE SPL INT REDRAW PEN selvint FR G In this mode the user can select to graph either intensity or sound pressure level spectra In the graphic parameter table the column beneath the C will no longer represent the chan nel number Instead there will appear either an S or an I to represent Sound Pressure Level or Intensity respectively The softkey spl int O will toggle the value for the selected trace between these two When the selected value is I an upward or downward vertical arrow will appear to the right of the amplitude value in the first column to represent positive upward or negative downward intensity corresponding to the alignment of the intensity probe The softkey SPL INT L will toggle the graphic between a dis play of sound pressure level versus RPM Speed and a display of intensity versus RPM Speed When the display represents sound pressure level the units in
420. red into the table Statistics and Ln Calculations For reasons of clarity the user may wish to display only one or several of the six traces at a time Any trace may be hidden by addressing it and pressing HIDE F When this is done the curve corresponding to that trace will not appear on the screen The status of a hidden trace is indicated by an aster 18 5 3200 MANUAL OPT 42 Clearing the Statistics Table isk to the left of the trace number Any number of traces may be hidden at one time To unhide or to again include a trace in the set of curves being displayed simply address that trace and once again press HIDE F The asterisk will then disappear to denote that the trace is no longer hidden Storing the Ln Trace Repeated presses of the R S key will simply start and stop the analysis there will be no reset of the Statistics Table Whenever the analyzer is running the Statistics Table will continue to be updated and will represent the statistical characteristics associated with all measurements since the Statistics mode was turned on or was last cleared In order to clear the Statistics Table to begin a new independent mea surement sequence press R STAT D which will produce the message ARE YOU SURE on the upper right of the screen To continue and clear the Statistics Table press YES A To abort the clearing operation and preserve the active Statistics Table press NO C Storing the Statistic
421. reen when the wrong menu is being displayed when attempting to execute a macro A macro can also be executed via the opto isolated ports such as from one of the keys on the intensity probe When Control of Display Formats Cross Channel Normalization and Use of Key Macros 19 13 2900 MANUAL Delayed Macro Execution programming the role of Key A or Key B from the I O Menu use the key sequence SPACE digit 0 91 For example to program the Key A to execute the macro 3 use the sequence KEY A D SPACE 3 Storing Macros In order to schedule the execution of a macro at a future time press SHIFT McSTART L which will bring to the upper right of the screen the message Macro M on DD at HH MM SS M is the number of the macro to be executed DD is the day for the execution and HH MM SS is the time for the execution The letter M will be flashing to indicate that the cursor is centered on that letter waiting for an entry Recalling Macros To store a set of up to eight macros which are active in the analyzer press the key sequence MACRO STORE The message Macros Data N on the upper right of the screen will indicate that these macros are stored in the Nth record of type Macros Data In order to differentiate between the stored Macros Data records it is recommended that the note field be used to tag each with a descriptive word or phrase 19 14 Records of type Macros Data are recalled fro
422. reen will be POWER in units of dB re 1 pW dBpW on the screen rather than the units INTENSITY in Sound Intensity Measurements Storage of Power Spectra 2900 MANUAL dB re 1 pW per square meter dBpW m on the screen which appear when in the Intensity Main Menu As with other spectrum displays the frequency and ampli tude corresponding to the cursor position are displayed digi tally on the right of the screen when the SOLID or DOTTED cursor is active When the BOTH cursor mode is active the digital display will indicate the total power between the cur sor frequencies in both unweighted to the right of the sum mation sign and A Weighted to the right of the letter A formats and the cursors will move together in response to presses of the horizontal arrow keys The level displayed to the right of the delta symbol on the right of the screen is the difference between the amplitude corresponding to the dotted cursor position and that corresponding to the solid cursor position The ability to readout the power associated with a frequency range larger than a single frequency bandwidth is important when studying the characteristics of broadband noise sources Recall of Power Spectra Power spectra are stored from the Power Summation Menu by pressing STORE which will produce the message STORE Povver N on the upper right of the screen to indicate that the displayed spectrum has been stored into the active file as the Nth re
423. ribing the entire set of lines of the families not yet selected do appear along with the single line of the selected family Upon exiting from this Menu the message Select class to judge will again appear on the upper right of the screen However if previous to exiting a single line of one family had been displayed as a result of a previous selection then only this single line of that family will continue to be displayed At this point the user can select another family and proceed as described above to display only one line of that family The result will be that one line only for each of these two different Classification Class Lines Optional Feature 2900 MANUAL families are displayed along with the spectrum in addition to the entire set of lines for the families not yet selected Con tinuing until one line from each of the families has been selected the user can visually compare the spectrum with any single line from any or all of the four possible families Automatic Judgement Based on Stop State of Analyzer For this particular mode of operation press the softkey corre sponding to the hardkey O until its label is AT STOP O In this mode it is not necessary to access the Class Line Menu to perform a judgement which makes it ideal for on line applications Exit to either the System Menu or the Main Menu and press R S to begin a measurement As soon as the measurement is stopped either by pressing the R S ke
424. rizontal and right horizontal play a very important role in the operation of the Model 2900 The lower pair of keys denoted by the left and right horizontal arrow symbols can perform a variety of functions which are user assigned by pressing particular hardkeys or softkeys At any time the assigned role of these horizontal arrow keys is indicated on the lower right of the display by a message preceded by an asterisk When the analyzer boots up the message will read dotted ersr Use the horizontal arrow keys to move the cursor across the screen Single presses advance the cursor a single step in the direction indicated by the symbol on the key Holding the key down will produce a series of cursor move ments as if the key were being pressed repeatedly Pressing the SHIFT key along with an arrow key invokes the action associated with the double headed arrow symbol on the upper portion of the key label In this case the first cursor movement will be larger than for the single headed arrow and each subsequent movement will be even larger With 1 1 and 1 3 octave filters it may not be necessary to use the dou ble headed arrow keys but with the large number of filters associated with FFT analysis it is best to use the double headed arrow keys to move the cursor near to the desired position then use the single headed arrows for exact place ment of the cursor The horizontal arrow keys are also used for paging through stored data records a
425. rojs gS WOUJ JIXA Surio LAJ ure NUAN S SATEUV SSO1J 6 Gc SNUSW Aoyyos 8 92 34 91 ST ST Amt GC 9T C aS GI SZ m l d ALSOLAV O SA TIJ N anLas YL Aq urLAq nuoJA dnjos rezApeuv ar10 s0 ny dm SOL SS900Yy GEET 0T SZ 913r Eyl egare f ued T qof H ALDALAA t t gaIy pue Jed gor 101 soureN oqe T nduy JojoureJeq pue dAL SULSET AV PAPS la dotaAqa ql 4S 121 ALITWNO t t Jejourereq Aejdsiq AS IN aam 1 Bory ooejIns 10 anfeA ynduy D atou t PIH SION WPT 8 ALSNINI t T dsppd t Jooedg pue onssoJq JO son eA Mdu 61 Z m r 3 AV IdSId t jnopeos pueqpeorg pue SunusroA TENSIA PAS V WHMOd t nus uorneulung SS V Aysuoju Sun y s Jaye T Z mr MWAN urojs Sg WOUJ JIXA nuo SISATEUV A suU 01 92 snu W Aayyos 6 S 34 91 d f Tds I H 1949 D A d 182 Am sur peugop sy sun pueq an gA uoneuq yeo an eA uoneuq yeo H ST 199 9S 148 P S ATigp ers p lpolpuqo yaxar 10A P induy Yumn Au e 3ndug 0 on peA eourounu e ynduy a a 27 o 7 V T 9poIN IN IS Sjru p un p 9110 1 UTES kay sirun o uonegISso u IO S 9 9 JOO SION 10dut SEIWERT 9 9400 dye JWEN UBISSY UOnBLUJIIJJIQ 109 2S SZ m rn NUWIN Wa sAS Wo
426. rr UT Y0c 0c DA 307 1 1 ISuucuo s ouueyo uloq o SINY o yoodsar YIM Sunusro p f s A ddy ssedmorT ssedyZrH JO 51049 21900942 195 O SUDuS19AA IeourT 129 og f LOMO D 4 H LSHL 3 VX OLAV O A 007 g A8C Yo uonouny SUDusroA 1S9 10 JABM S OA serg ououdodor q 129 og pueqpeodg VAS renbs ZH ogueojny 19S HHO NO 213830 SZ m rn n fy ur 3s4AS Wouj nuon ndul GL GZ snu W Aayyos yl gc FTANDII r r IOUO 10102 uo Kejdsiq 421 eieordnq X avn fl Tvad_ Il ATONIS a 009 X008 1 08 X 0F9 LAlost X 9 1 144 ke dsiq 10703 uonnjosa 109 2s pue JOJIUOJN 10102 SAODUIA JO JoquinN VAS JOJIUOJA 10 02 peux UO ung HO UnL T Sz Im3r n yy urojs g OU nuon e dsiqq 10 0J 91 8Z snu W Aayyos 91 92 34 913 d f I TInVHAQ 5 30u dm s dnjog PPIH 930N p un p r sr alas j n T9 T PAS Jpg s1e217 H LOO H 4MOLS lal anLas A g oureu dnjos pouyop dnjog p un p r sn o sdmos pouyop kay dm s o Jos 0 dn 100g dm 1uosaud a1018 PSN PVS oureN USISSY O JozAfeuy USISSY 8 pue 9 Z s m3ri snus SISAJBUY n Jo ouo JO 1 Z AMFI NUAN Wo sAS OI nuoJv dm 11 92 snuey Aayyos 91 52 34 013 O eureuo1 N al 4 IN wou rki 4810 r 4810 UMOq ISS Kiouro A o SILA ASI PAYSIMYBTH eureuew Dous VPA pIS IETA PaAYSMYBTH 2 ai r
427. rrection 1000 10000 Frequency Hz 90 Degree Incidence CO CH O NN Q vs PT oo o Correction dB Ger k S AE od tab ooh fal o 10 UB WN eo 000 10 0 11 0 12 0 1000 10000 Frequency Hz 3 10 Sound Level Meter Operating Modes Position of Operator 2900 MANUAL Making a Sound Level Measurement When making a measurement it is recommended that the observer be positioned as far behind and to the right of the instrument front panel as possible to minimize interference of the sound field at the microphone resulting from body reflec tions Note that the viewing angle of the LCD screen may be adjusted to optimize viewing by an operator in this position If possible the instrument should be mounted on a tripod dur ing a measurement If the instrument is to be handheld dur ing the measurement the user should hold the instrument as far away from his body as possible and as far as possible to the left of his body centerline Adjusting the Input Gain Pressing the RA key Run Stop will start and stop a mea surement The sound pressure level corresponding to the SLM setup is displayed digitally on the lower right of the screen in large numbers The height of the vertical bar near est to the center of the screen is an analog indication of the same sound pressure level and it will move up and down in response to variations in the s
428. rsors for each data display window and a number of graphic display parameters which are selected independently for each Vertical Display Range Control The frequency and amplitude corresponding to the location of the yellow blue cursor is indicated by the yellow blue num bers below each data display window For octave filters the ANSI filter number is also presented To move the yellow or blue cursor point the mouse so it is within the parameter window containing the cursor data of the desired color Each press of the left mouse button will move the cursor one fre quency band to the left and each press of the right mouse button will move it one frequency band to the right Holding either the left or the right mouse button down and moving the mouse to the left or right will move the cursor continuously in the same direction The numbers in the parameter window to the right of the blue cursor data window denoted by the delta symbol represent the difference between the level for the yellow cursor and the level for the blue cursor When the mouse is pointed within this window the cursors can be moved together using the mouse buttons as described in the preceding paragraph Horizontal Display Range Control To shift the vertical display range for a particular data display window point the mouse within the grey area surrounding the vertical scale values Each press of the left mouse button will shift the scale down and each pres
429. rve which is to be used for the determination of the slope of the decay and from that the value of RT60 for that frequency as shown in Figure 21 1 Typical Decay Curve When either the solid or the dotted cursor is active the level and the relative time with respect to the beginning of the autostore record of the cursor intersection with the displayed curve are displayed on the right of the screen When both cursors are active the level and time differences between the intersections of the two cursors are displayed Although the overall form of the early decay curve is linear there will always be statistical variations of the measured curve with respect to a straight line In the 2900 a linear regression is made using the points on the decay curve between the cursors to determine a curve and the slope of that straight line is used for the determination of the RT60 The result is displayed on the right of the screen in the for mat RT60 XX XX ctr Y YY where XX XX is the decay time and Y YY is the time corresponding to the center of the por tion of the curve used for the extraction of the decay time Both are in units of seconds If the RT60 register has not been cleared before beginning this sequence of curvefitting and evaluation of RT60 access the RT60 Menu by pressing RT60 B and press RESET D Respond to the message Erase RT60 database by pressing YES A unless you have made an error in which case abort the cle
430. ry 2900 MANUAL cates that this set of Custom Print Setups have been stored as the Nth record of the type Print Setup in memory NOTE Default Custom Printout Setups To recall a Print Setup from memory press RECALL The message Overwrite ALL SETUPS on the upper right of the screen warns that upon recall all the custom print setups presently stored in the eight labeled softkeys will be lost If these are of importance they should be stored as described in the proceeding paragraph prior to recalling another set from memory Press YES A to continue with the recall oper ation or press NO C to abort the recall operation Upon pressing YES A the message RECALL Print Setup N on the upper right of the screen will indicate that the Nth Print Setup consisting of eight setup softkeys has been recalled If this is not the record number corresponding to the Print Setup desired use the left and right arrow keys to page through the sequence of record numbers until the desired record number is displayed then press EXIT While paging through the sequence of Print Setup records the softkey labels stored with that record number will appear on the screen making it easy to determine when the desired Print Setup record has been accessed 2900 Printing Data Screen Displays and Tables Two pre defined user setups one in portrait format and one in landscape format are included to assist you in the cre ation of custom printouts
431. s Power Summation 2900 MANUAL keypad and pressing EXIT To return to the Recall Menu press EXIT another time At this time the modified parame ters will replace the original parameters To return to the Intensity Menu press EXIT one more time Accessing Power Summation Menu Stored along with each measurement are the following 1 The labels for JOB PART AREA blank if not assigned 2 A numerical value of surface area corresponding to the measurement for purposes of power calculation 3 The measured intensity spectrum 4 The SPL spectrum for Channel 1 The Quality and Particle Velocity are not stored because they can be calculated from the intensity and average SPL spectra Search Field Concept To perform summations of the stored power spectra from the Main Menu press POWER A which will access the Power Summation Menu shown in Figure 20 3 Power Summation Menu Figure 20 3 Power Summation Menu 23 yon 19 42 18 Power F2 P I F3 HPP F4 FNU note 327777777 7777777 7777777 P 0080 5a EELER LINEAR SINGLE 4 Dual LINEAR 28Hz 2 kHz RESET 23 MAR 94 15 41 29 16 FILTER 14 25 6 Hz 125 RESIDE A aR l 1 vy POWER I d 13 8mm d 27 44 200 Dn 5a NEE 41 5 64 A 39 Y AdBrll JOB_ SPEAKER LOC PART FRONT w w n w w n n n n n n n n n n n n n n n n n n AREA 25 0 Hz 508 Hz 10 kHz A dotted crsr SPER
432. s sm m s s s s s s s s s s WIDTH Pick 1 Sum as SOURCE IS TACH INPUT 6 9000 ang W W W W W W W W W W W W W w n n n w W w nn n n n n n n n n n n n n n n n n nn n n nn ng ng EXPONENT I AL ua LINEAR 28Hz 28kHz RESET 687 JAN 96 23 55 59 T W W W w w wan A a W A W EH o W W o ng elle PEH LEUEL FREQUENCY gt 01 16 1 66 2 02 11 1 25 5a w a W W w a W W a W w W W W W n W a w n cc cc D 3 s 1 2 1 60 4 04 15 2 00 LOC 5 05 14 2 56 a c ne 5 o 5 1 5 o WE UN ee ece o o c s o o eke 6 06 1 5 3 15 1000 6000 RPM crsr 01 INITIRL sum 2 sum 3 sum 4 sum 5 sum 6 sum 7 sum 8 sum 9 The choices of the Peak Hunt parameter are represented by the row of softkeys above the screen pick 1 A pick 3 B pick 5 C pick 7 D With pick 3 selected the program examines the amplitude of not only the frequency band which is calculated to represent a particular order but also those of each adjacent sideband Of these three bands the one whose amplitude is the largest is taken to represent that order With pick 5 the search includes the two adjacent bands on each side and with pick 7 the three adjacent sidebands on each side With pick 1 no sidebands are examined Note that when this analysis is being performed from autostored spectral data the user can generate a variety of vsRPM Speed graphics using differ
433. s Table To store the data associated with the statistics parameter table presently displayed including hidden traces can be stored to the active memory file by pressing STORE This will be sufficient data to regenerate the curves presently dis played on the screen The message displayed on the upper right of the screen STORE Ln Trace N indicates that this data have been stored as the Nth record of type Ln Trace in the active memory file It is recommended that a descriptive note be created before storage of the Ln Trace Although the Ln Trace notes are not displayed during the recall procedure the record listing in the Files Menu will permit the user to observe the notes attached to each stored Ln trace record Recalling Ln Traces The complete Statistics Table can be stored to memory by pressing STO TBL I Note that storage of the Statistics Table requires a large amount of memory in excess of 22 KB It is recommended that a descriptive note be created prior to storing the Statistics Table Although the Statistics Table notes are not displayed during the recall procedure the record listing in the Files Menu will permit the user to observe the notes attached to each stored Statistics Table record 18 6 To recall an Ln Trace from the Statistics Menu press RECALL The message on the upper right of the screen Statistics and Ln Calculations Recalling a Statistics Table 3200 MANUAL OPT 42 RECALL Ln Trace N
434. s are recalled from the active memory file whose name is indicated on the lower left of the screen If this is not the file from which it is desired to recall records it is necessary to return to the Files Menu highlight the desired file and then exit to make that the active file If the desired file is on a floppy disk that file must be transferred to the analyzer 13 9 2900 MANUAL Analyzer Setup for Recall memory and made the active file before recall can be per formed Recall Operation An explanation of the classification of records at the time of storage was presented above In order to recall a particular type of record the 2900 must be placed in a setup configura tion which corresponds to the type of record to be recalled Examples 1 With the 2900 in the Standard Analysis mode and the nor mal storage mode and the selected display parameter Leq then the recall operation will recall only records of the type Leq Change the display parameter to Maximum and only Maximum type records will be recalled Both FFT and octave bandwidths can be recalled With the 2900 in the Cross Analysis mode normal storage mode and the selected display parameter Coherence only records classified Coherence will be recalled Both FFT and octave bandwidths can be recalled If the display parameter is changed to Impulse only impulse response records measured with FFT filtering will be recalled With the 2900 in the auto
435. s is why the clear operation is recommended before creating a new user curve The clear operation only clears the user curve in the active register which corresponds to the active bandwidth not the entire set of user curves Suppose that the 2900 is configured to a 1 1 octave band width the Setuser Menu is used to create a user curve and without any specific storage operation the user exits from the Setuser Menu reconfigures the 2900 to a 1 3 octave band width accesses the Setuser Menu and creates a user curve Then he exits from the Setuser Menu reconfigures for an FFT bandwidth accesses the Setuser Menu and creates a user curve Although no storage operation has been per formed all three of these user curves or a set are contained in the active register Should the user exit from the Setuser Menu and reconfigure to another bandwidth upon returning to the Setuser Menu the user weighting curve which is in the active register for that bandwidth will be displayed Storing the Active Register into Storage Registers There are 4 nonvolatile storage registers available into which the set of user weighting curves in the active register can be stored This is done by pressing STR USR I The message on the upper right of the screen USER 1 4 TO STORE X with a flashing cursor on the X prompts the user to input a register number between 1 4 using the numeric keypad and press EXIT The data in these registers will remain in
436. s of the right mouse button will shift it up Directly beneath each data display window is a message VZOOM N where N 1 2 4 or 8 This indicates that the present vertical display range is equal to 80 N dB Unless this has already been modified by the user the value of N will be unity To increase the vertical display resolution point and click the mouse within this parameter window The window which opens will present the user with a choice of values Use the mouse to select the one desired Directly beneath each data display window is a message HZOOM N where N 1 2 4 or 8 This indicates that the horizontal axis presently used for the display represents 1 N of the total range of the data block Unless this has already been modified by the user the value Use of External Color Monitor for Display and Instrument Control 24 11 2900 MANUAL Line Type of N will be unity To increase the graphic resolution of a data display window in the horizontal axis move the yellow cursor to the center of the portion of the display which is to be the center of the expanded display Point and click the mouse in the parameter window containing the message and select the desired value The values of the horizontal axis parameters corresponding to the left and right limits of each data display window are indi cated in the parameter windows just below each end of the horizontal axis These will change as the horizontal displa
437. s part of a data recall Range Control If the horizontal arrow keys are assigned to some function other than controling the cursor pressing the hardkey CURSOR will assign these keys to control whichever cursor was last under the control of these keys Pressing the CURSOR key while these keys are already assigned to control the cursor will bring to the screen the Cursor Menu for the selection of cursor type Introduction Pressing the hardkey RANGE will assign the horizontal arrow keys to control the input range by changing the input attenu ators indicated by the message range XXX on the lower 1 5 2900 MANUAL Instrument Boot up Procedure right of the screen where XXX is the full scale amplitude Each press of the left arrow key will decrease the full scale level by 10 dB while presses of the right arrow key will increase the full scale level by 10 dB increments Although there is no message indication on the screen to indicate it the vertical arrow keys can also control the range setting each press producing a 10 dB change It is necessary to observe the displayed amplitude indicators on the left of the display to determine the modification of the full scale level in response to presses of these two keys Upon pressing the hardkey ON the Model 2900 will go through a boot up procedure during which the following mes sage will appear briefly on the screen Press boot reset RAM disk RS23
438. s stored each time the STORE hardkey is pressed This data block is stored as a single record into the active memory file whose name is dis played on the lower left of the screen If the indicated file name is not the one into which it is desired to store the data block it is necessary to return to the Files Menu and high light the desired file before exiting so that it becomes the active file 13 6 The classification of the records into types is based on the setup of the analyzer and the specific parameter which is being displayed These are as follows Sound level data measured using the Wide Dynamic Sound Level Meter Mode and stored using the normal storage mode SLM Sound level and spectral data measured using the Sound Level Mode and stored using the normal storage mode Normal SLM Leq SLM Minimum SLM Maximum SLM SEL SLMJ MaxSpec SLM Storing and Recalling Non Autostore Data Storing and Recalling Non Autostore Data 2900 MANUAL Sound Level and Spectral data measured using the Sound Level Mode and stored using the Autostore byTime or byTach mode byTime SLM byTach SLM Spectral data measured using the Normal Analysis mode and the normal storage mode Normal Leg Minimum Maximum SEL or MaxSpectrum depending on which of these parameters is being displayed Spectral data measured using the Cross Analysis mode and the normal storage mode FFT and Octave band widths Au
439. scale between logarithmic and linear Control of Display Range In the default condition the measured data block will be dis played such that the frequency or time range used for the measurement extends completely across the screen from left to right This represents a horizontal scale factor of unity The user can change this value When a scale factor of eight is selected for example the total horizontal width of the data block is multiplied by eight so that only one eighth of the width of the block can be seen at one time but the screen resolution will be eight times greater than with unity scale factor This is done from the Shift Menu Accessed from the Analysis Menu by pressing SHIFT by pressing H SCALE E which will bring to the screen the Horizontal Scale Menu shown in Figure 19 7 Horizontal Scaling Menu Figure 19 7 Horizontal Scaling Menu 22 OCT 17 45 62 100 SELECT Horizontal Scale Hote 6 9008 L sa IRL 1 PREAMP LINEAR _ 20 18kHz RESET 22 OCT 91 16 38 24 60 FILTER 8166 38 3 Hz L712 v Channel 1 of 1 NORMAL d 8 0 Ze 28 5 dotted crsr Select the Horizontal Scale Factor by pressing the corre sponding softkey Only a portion of the total data block will be visible at one time when the horizontal scale factor is greater than 1 In order to be able to pan the displayed portion horizontally from the Shift Menu press H OFSET F which will produce the message H Offset xx on the lower righ
440. se the vertical arrow keys to select as low a value of full scale ampli tude as possible without overloading the input Press R S to stop the measurement Change the detector to a one minute linear single average by pressing DETECTR H LIN S A AV TIME H 2 HI EXIT EXIT Perform a one minute measurement by press ing R S and waiting until the instrument state changes from RUN to STOP The data on the screen will be the residual intensity of the measurement system without normalization Internally the Model 2900 is measuring the transfer function between the signals at the two microphone inputs Because a residual intensity testing device is being used as the acoustic source for both microphones we know that they are exposed to 20 4 Sound Intensity Measurements Sound Intensity Measurements 2900 MANUAL equal amplitude signals with zero phase difference between them within the limits of the standard for the residual inten sity calibrator Thus any variation of the magnitude of the transfer function from unity 0 dB and of the phase from zero is the result of errors in the measurement system which includes the microphones intensity probe electronics and the analyzer Having measured the transfer function a cor rection function can be generated which can be used to improve the precision of measured cross channel data such as sound intensity We refer to this procedure as normaliza tion To perform the amplitude and
441. se values simply place the mouse pointer within the window depress the left mouse button and slide the mouse left or right Or use single presses of the left and right mouse buttons for sin gle step changes in the value Use of External Color Monitor for Display and Instrument Control 2900 MANUAL Selecting Band Tracking As explained in Chapter 17 when the data have been mea sured in the vsRPM Speed mode using normal frequency analysis postprocess order tracking can be used to calculate and display the data as orders rather than frequency based on the RPM or Speed value attached to the spectrum In order to select band tracking click the mouse pointer in the TRACK MODE window and select BAND TRK When in the BAND TRK mode the ORDER window will now assign order numbers to the pens instead of frequency values To switch back to a display of frequency bands use the TRACK MODE window to select NORMAL Use of External Color Monitor for Display and Instrument Control 24 17 2900 MANUAL 24 18 Use of External Color Monitor for Display and Instrument Control Softkey Menus Softkey Menus c Sc SNUSW Aoyyos LG JANDIJ LI SZ 91 62 81 57 mr Sam C Gc am 1 4 90814 dl SLASTA O SATA N anLas IN nuoJA nuoJA sdnjos rezApeuy JOJIUO N 10102 JosaY SS V Salt s922 V I e 2o3 pue a101S dm 1 ST on314 GE SZ AMBY 30 21 42 mr 11 92 m lq yy C om3 T pop 4 L
442. ser wishes to examine how the amplitude vs time curves for a particular frequency vary from record to record He begins as described above recalling a record selecting a frequency band with the cursor and displaying the amplitude time curve by pressing vsTIME C If he now presses A Prev K the amplitude time curve for the same frequency but calcu lated from the record stored previously will be displayed Similarly pressing A Next L will produce the amplitude time curve for the record stored after the one which was pre viously displayed The key DATA M and the horizontal arrow keys can still be used to change the desired frequency band while examining amplitude time curves from the vari ous stored records Displaying and Storing Leq MIN MAX SEL and Mx Spec Spectra 15 12 During a byTime autostore measurement sequence the Leq MIN MAX SEL and Mx Spec spectra are also calculated for the total time of the autostore sequence Although the autostored spectra are automatically stored at the conclusion of sequence the Leq MIN MAX SEL and Mx Spec are not automatically stored If the user wishes to examine these it is important that this be done immediately following the data acquisition before the data buffer is reset For example if a recall operation is performed immediately following the acquisition in order to examine the autostored data records the data buffer will be reset and these other spectra will no longer be
443. shown in Figure 23 8 Setups Menu 23 11 2900 MANUAL Figure 23 8 Setups Menu 17 DV 15 44 51 NAME RESET STORE PORTDEF LRNDDEF SPL 16 4925 T I T EXPONENTIAL Input 1 LINEAR 268Hz 28kHz d STOP 17 NOU 93 15 33 54 s OM W W W W W n n W W n n n W W n n n n n n n n on n n n n n n n nn d FILTER 34 2 5OkHz LAS v Channel 1 of 1 NORMAL dz 58 1 A 63 7 PHONS 78 1 TACH 6 6 SPEED 4 6 50 mol o PPS LOC 18 TIPP cH H dotted crsr GD Hz Hz d d Az TEST 1 SET 1 undef undef undef undef undef undef undef When delivered all eight of the softkey labels the screen will read undef to indicate they are as yet undefined Before storing a custom print setup assign a label identifying the custom printout setup to one of the softkeys as follows Press NAME A The message Push Setup To Name will prompt you to press the softkey to which the label is to be assigned The message Enter setup name will then prompt you to input the label name using the alphanumeric keypad and press EXIT The newly entered name will now appear as the label of that softkey To store the custom print setup presently active press STORE C and respond to the message Store in this setup by pressing the softkey to which the setup name has been assigned Up to eight different custom print setups can be stored by name one for each softkey To delete all the setups previously stored and to return all the softkey
444. signed value is displayed Either press ENTER to keep the same value or modify the value using the numeric keypad and then press ENTER The value can range from a maximum of 9999 to a minimum of 0000 The maximum value will produce a volt age output of approximately 3 Vrms and other values will produce a proportionally lower output voltage The softkey ATT G will attenuate the output level by 20 dB each time it is pressed up to a maximum attenuation of 60 dB With attenuation in effect the softkey ATT H will reduce the attenuation by 20 dB each time it is pressed until there is no attenuation in effect A message on the upper right of the screen will indicate the status of the attenuation whenever either of these keys is pressed To obtain the optimum performance from the digital to ana log converter DAC try to keep the level value as large as possible by using the 20 dB attenuator steps rather than continue reducing the level For example once the level is below 0999 the same output voltage can be obtained by increasing the attenuation by 20 dB and setting the level back to 9999 With the sine generator set for a single tone activate the dual tone mode by pressing 2 tone N The first word in the mes sage appearing briefly on the upper right of the screen will be 2tone Repeated presses of this key toggles the status betvveen single and dual tone The Dual Tone Generator Menu is shown in Figure 4 10 Dual tone
445. ss over a single averaging cycle When BT Exp or BT Lin are selected the averaging times of the lower frequency filters are longer than those of the higher frequency filters because they have narrower bandwidths This means that the averaged values of the lower frequency filter bands will be updated less frequently than the higher frequency band averaged values At the end of any given Delta Time interval it is only necessary to store the values corresponding to frequency bands whose averages have been updated since the last data storage operation This is a much more efficient storage procedure than storing a full spectrum for each time interval which optimizes the use of the data memory It is therefore recommended that one of these be used when it is necessary to store as many spectra as possi ble over a long time interval Recall and Display of Autostored Data Autostore by Time Pressing the hardkey RECALL while the 2900 is in the autostore byTime mode will recall one of the By Time type records from the Active Memory File whose name is listed on the lower left of the screen The message RECALL By Time N on the upper right of the screen will indicate that the Nth record of the type By Time has been recalled If the 2900 is in the SLM Mode the message will be RECALL ByTime SLM N In most cases this will be the record number which was last stored or recalled To determine how many By Time 15 7 2900 MANUAL Displa
446. sse 9 3 ere eco EUR E 9 4 Calibration Based on a Transducer Sensitivity Value a li si i ii i l 9 4 Logarithmic Units Calibration dBAolt sess 9 4 Logarithmic Units Calibration Microphone K factor sss 9 5 Linear Units Galibratloric coiere Ree ee ENEE 9 5 Calibration Based on a Reference Gong 9 6 Calibration Using the Test Signal n a 9 7 Storage and Recall of Units Information I 9 7 storage Or Units RE EE 9 8 Recall ot Units DACA ke iie eee tiered edie eat utente iei ose 9 8 2900 MANUAL Chapter 10 Digital Display including Broadband Acoustic Frequency Weighting Us Chapter 11 Chapter 12 Chapter 13 er defined Frequency Weighting and Integration of FFT Spectra 10 1 Accessing the Display Mem 10 1 Selecting Bandwidth for Display of 1 3 10 2 Display of the Average AA Ae eee yam iaraa yaa ee a eiaa aieiaa 10 2 Selecting Integration 10 2 Digital Display Weighting essen 10 3 Accessing the Digital Weighting Menu 10 3 Exiting From Display Weighting enne 10 4 User Ee Lu E 10 4 Creating a User Weighting Curve sse entente nennen 10 5 Interpolation Function
447. ssed for a period of four minutes It turns on again as soon as a key is pressed Press EXIT to exit from the Screen Menu Introduction Beeper Control 2900 MANUAL Color Monitor The Model 2900 can produce an audio output or beep corre sponding to the following conditions 1 The press of a hardkey or softkey 2 An overload condition at one of the inputs 3 An error condition 4 Any combination of the above three The beeper function can be programmed by the user from the I O Menu as explained in Chapter 4 The default condition is that all of the above activities result in a beeper output Power Supply Battery Power Display of analyzer setup and data blocks on the color moni tor is described in Chapter 24 along with an explanation of the mouse trackball control of the analyzer Introduction The Model 2900 can operate for up to four hours in the Run mode using the removable NiCd battery pack supplied with the instrument When it is On but not Running the power consumption is reduced by 4096 The current drain of the instrument is too high for it to work effectively with alkaline batteries The supply voltage is displayed on the upper right of the screen for approximately eight seconds whenever the hardkey SYSTEM is pressed When operating on batteries this will be the battery voltage When connected to an exter nal DC power supply this will be the power supply voltage The voltage will then be displaye
448. st above the indication of the displayed channel To examine the amplitude time curve corresponding to another frequency band without returning to the spectrum display and selecting another frequency band press DATA M The horizontal arrow keys assignment message on the lower right will become new data As these keys are pressed the indicated frequency band on the right of the display will change and the amplitude time curve corresponding to that indicated frequency will be displayed This permits the user to display the amplitude time curve for any frequency band using the horizontal arrow keys to scroll through the frequency bands one by one SLM Data versus Time While changing the displayed frequency band in the versus time display mode if the right horizontal arrow key is used to move one increment beyond the highest frequency band then the displayed curve will be that of the broadband level versus time as indicated by the phrase spectrum instead of a bandwidth center frequency on the fifth line down on the right of the screen Although the digital display weighting can be used in order that the autostored spectra be weighted before display the broadband level is calculated before the effect of the display weighting is included Thus the user cannot take a series of autostored spectra and use digital weighting in order to obtain a curve of weighted broadband level e g dBA versus time If the user wishes to exa
449. st way to become familiar with the creation of a single class line is to experiment Until one becomes quite familiar with the method the recommended technique is to sketch the desired pattern on paper with coordinates and generate the line using a simple series of points created sequentially from left to right Classification Class Lines Optional Feature In most noise and vibration applications of this technique the desirable result of a test is that noise or vibration spec trum levels be as low as possible In terms of the class lines this might correspond to the desire that the spectrum levels remain below a single classification line or that they cross as few lines in the upward direction as possible We refer to this as the Max mode of operation and when a family of class lines is created they are numbered sequentially in the verti cally upward direction beginning with O see section below The higher the number associated with the classification of a spectrum using the Max mode the more severe the rating because it is associated with increasingly higher spectrum levels or at least at one frequency The class lines also support a Min mode In terms of a single class line a classification of O indicates that the spectral lev els are all above the line and a classification of 1 denotes that in at least one frequency band the level is below the class line A family of lines created from the Min mode are num bered sequ
450. sted at the bottom of the internal memory file listing and it will also be highlighted Note that when typing the file name the hardkey CLEAR may be used to clear the entry field and the horizontal arrow keys can be used for editing 13 2 The highlighted internal memory file name can be renamed by pressing rename J In response to the prompt on the right of the screen type a new name and press EXIT The new name will then appear in place of the former name in the listing If after selecting to rename the file it is desired to abort that operation simply use the CLEAR hardkey to clear the entry field and press EXIT The message Invalid name will appear on the right of the screen and the file name will be unchanged Storing and Recalling Non Autostore Data Deleting Files 2900 MANUAL The highlighted disk file name can be similarly changed using the softkey rename O Formatting a Floppy Disk The highlighted internal memory file can be deleted by press ing delete I The message Delete highlighted file on the right of the screen prompts verification of the delete operation by the user who will press YES A to proceed with the dele tion or NO C to abort the deletion operation The files management of the Model 2900 requires that there always be at least one defined file so when there is only a single file defined it cannot be deleted In such a case simply create another file prior to making the deleti
451. store By Time storage mode regardless of the Analysis mode only By Time records will be recalled These may be FFT or octave bandwidths With the 2900 in the RT60 Menu only RT6O records will be recalled With the 2900 in the SLM Mode set for normal storage and the selected display parameter Leq then the recall operation will recall only data records of the type Leq SLM Change the display parameter to Normal and only records of the type Normal SLM will be recalled In either case both SLM and spectral data will be recalled However the time history line analogous to a strip chart recording which was drawn during the original measure ment is not stored with the measurement so it will not appear after a recall In order to store a time history of the sound pressure level and the spectrum the vsTime autostorage function must be used This is described in Chapter 15 18 10 Data Records are recalled from the active memory file by pressing RECALL This will result in the display of the Recall Menu shown in Figure 13 3 Recall Menu Storing and Recalling Non Autostore Data Record Type and Number Indication 2900 MANUAL Figure 13 3 Recall Menu 25 BER 15 59 23 W Fall B RUE B MAX de KEEP Note i SPL 3 1575 sa e w won n a w on n w a n a NM wa n a n o o EXPONENTIAL i Input 1 LINEAR 1Hz 28kHz i RESET 22 APR z L 68 f w w u w w u a u w u wonn u a w u
452. t O will page the recall procedure continually towards the last record stored in that file 15 8 Once the desired record has been recalled presses of the hor izontal arrow keys will page through the individual spectra contained in the autostore record bringing them sequentially to the screen Each spectrum is tagged with the time it was stored relative to the initiation of the autostore sequence This is displayed on the right of the screen first line down An exception is when count averaging was used in which case this field will show the spectrum number rather than a time value Presses of the left horizontal arrow key will produce a paging backwards in sequence toward the first spectrum stored When there are many spectra in the record pressing the Autostore by Time Cursor Control 2900 MANUAL SHIFT key along with the horizontal arrow key will produce a jump of more than a single spectrum which is useful when seeking a spectrum far in sequence from the one being dis played Use the keys CH1 and CH2 to select the displayed channels If during the data acquisition an overload condition occurs at one or more of the inputs the inverse video message OVER LOAD will appear on the screen However the overload con dition may not have affected all the inputs and may not have been in effect during the complete time period of the acquisi tion meaning that some of the individual spectra in the autostored record may be
453. t a time without any offsets in the vertical and horizontal directions This produces a graphic as shown in Figure 16 8 Waterfall Menu In the three dimensional format produced by pressing DRAW 2 D an offset in both the vertical and horizontal directions is added to each successive spectrum curve pro viding perspective to the view Figure 16 9 Waterfall Menu 3D Format 38 JAN 83 43 15 DRAW 1 DRAW 2 START END DELTA 6 9058 NENTIAL 1 64 LINEAR 28Hz 28kHz T 26 JAN 95 23 37 18 ER 814 25 0 Hz L S hannel 1 of 2 HORMRL FRLL OT INITIAL Usually one begins by displaying all the spectra within the record using a large enough spectral increment number that the drawing does not take too long Then based on the obser vations of the display sequence the range of spectra is reduced to a sequence of particular interest with a smaller increment to produce more details of the spectral changes over that range of spectra Autostore by Tach The 2900 provides a unique vsRPM Graphic capability which can be used with byTach autostored data This permits the generation and display of a number of curves in the format amplitude versus RPM or Speed where each curve corre sponds to a specific channel and frequency or order 16 15 2900 MANUAL 16 16 When octave bandwidths or standard FFT spectra have been autostored the graphic may be in the form of frequency ver sus RPM Speed or order versus RPM Speed The latter is
454. t only data within small frequency regions of the total analysis frequency range are of interest making it desirable that the Amplitude Frequency data presented in the tabular printout cover only that range The data presented in the tabular printout represent only those frequency bands shown in the display Thus by modifying the horizontal display range as described in Chapter 19 the frequency range of both the tab ular printout and the screen display will be reduced accord ingly Setting the Microphone Bias Voltage 4 12 To select the microphone bias voltage and define the input signal path to the analyzer from the System Menu press INPUT K which will bring to the screen the Input Menu shown in FFigure 4 6 Input Menu Figure 4 6 Input Menu 14 96 09 23 51 BU 28 U 200 U RUTO RR Ineuts TEST SPL 6 9000 108 002000 EXPONENTIAL 1 8 H Dual A WE IG RESET 14 OCT 97 09 12 19 ou FILTER 14 25 8 Hz L73 v Channel 1 of 2 NORMAL de 36 9 Ze ea LAA W EA DIFF Ph WGT Sn REM 8 8 SPEED 0 0 25 0 Hz S35 Hz Z UkHz FF TL TRRD A WGT 1 20k 20 20k 1 18k 20 18k SAME RANGE Upon accessing the Input Menu the value of the microphone bias voltage presently active will be displayed on the upper right of the screen for approximately 4 seconds To change the polarization voltage press one of the following Softkeys Softkey Functions O V A Bias voltage OFF for use with ele
455. t the averaging will continue until the R S is pressed again This will pause the averaging the run time will cease to increase and the operational status will change to STOP Should R S be pressed again averaging will recommence the operational status will return to RUN and the run time will pick up the count from the time displayed when the averaging had been previously paused If in Standard Mode the Max Min Leq and SEL data will include contributions from all signals applied to the inputs during all time intervals when the oper ational status was RUN beginning from the original initiation of the averaging process To reset the data buffer in order to begin a new averaging period containing no prior signal data press RESET SHIFT then RESET This will clear the data buffers set the run time to zero and change the operational status to RESET Caution Do not press SHIFT and OFF simultaneously as this will produce a hard reset and reboot of the instrument 7 1 2900 MANUAL Finite Length Time Averaging Input Gain Control If the averaging type has been selected to be Linear Single Count Single or Count Manual and if the R S key is not pressed again the averaging will continue until such time as the selected averaging time number of spectra has been reached The operational status will then change to STOP and the run time will display the same value as the averaging time shown on the line dire
456. t by pressing R S again after the vehicle has passed by press Mx Spec L to recall the Max Spectrum and then press STORE to store the spectrum The user can per form a data reset operation while the measurement is in progress which will initialize the Leq Minimum Maximum SEL and Max Spectrum values to zero and begin the calcula tions again 6 4 When the Model 2900 is configured for dual channel mea surements in the Standard Analysis Mode it is possible to Analysis Menus Selection Of Measurement And Display Parameters Loudness Measurement 2900 MANUAL display the spectra for both channels simultaneously in a side by side configuration From the Main Menu presses of the softkey sequence DISPLAY F Multi H will toggle between the single and the dual channel display formats This function is described in more detail in Chapter 19 Con trol of Display Formats When in the Standard Analysis Mode with 1 3 octave filter ing the Loudness in sones and the Loudness Level in phons corresponding to ISO Recommendation R523 Method B sometimes referred to as Zwicker loudness after the researcher who developed the method are calculated and displayed on the lower right of the screen There are two forms which correspond to measurements made in diffuse acoustic fields where energy is from all directions such as inside a reflective space and measurements made in the free field where the sound is radiated without reflection fro
457. t is located on the top panel of the instrument as indicated by the rear panel label The load impedance should be at least 6 KQ The spectral content of the noise is selected by pressing either PINK M or WHITE N Pressing ON A or OFF B will cause the generator to be continually ON or OFF Pressing ON RUN C will engage the noise generator when the analyzer is in the run mode Con versely pressing OFF RUN D will disengage the noise gen erator when the analyzer is in the run mode Changes in the operational status or the spectral content will bring the appropriate message to the upper right of the screen A typical application of the OFF RUN mode is the measure ment of reverberation time A room is filled with acoustic energy and then the energy decay is measured after the sound source is turned off With the 2900 configured to per form 1 3 octave analysis using the autostore measurement mode pressing the R S key initiates RUN which turns off the noise generator and begins the autostorage of spectra during the decay process During the initial interval of analysis there will be a finite time before data is available from each of the filters The lower the frequency of the filter the longer the interval before the appearance of data from the filter There fore it is convenient to delay the shutoff of the noise genera tor until data is being produced from all the filters of interest The user sets this delay time by pressing
458. t of the screen indicating that the horizontal offset of the displayed portion of the horizontal axis is now under control of the horizontal arrow keys A second press of H OFSET F will reset the horizontal offset to zero 19 8 Control of Display Formats Cross Channel Normalization and Use of Key Macros 2900 MANUAL Normalization of Amplitude and Phase Between Channel 1 and Other Channels When using the Cross Analysis Mode channel 1 is the refer ence channel Each cross channel measurement such as cross spectrum transfer function and coherence are made between channels 1 and 2 In order to minimize the effect of amplitude and phase mismatch between the channels a nor malization procedure can be utilized to correct for such mis matches When the Model 2900 is used in the Intensity Analysis Mode cross spectrum measurements are used for the determina tion of intensity so normalization to correct for mismatch between channels may also be desirable to obtain the best possible accuracy for intensity measurements The procedure is to input the same broadband noise into both input channels and measure the transfer function between them Any variation from a unity value of magnitude and a zero value of phase represents the effect of mismatch Once measured this transfer function can then be used to build a correction function which will normalize the cross channel data taken in subsequent measurements to correct for these errors
459. tact unless the nonvolatile memory is reset or the data in the reg isters are overwritten by recall of a User Curve record as described later in this chapter Since the active register con tains a complete set of user weighting curves one each for 1 1 1 3 and FFT bandwidths the storage register will there fore contain these same four user curves 10 6 Digital Display including Broadband Acoustic Frequency Weighting User defined Frequency Weighting and Integration of FFT Spectra Recalling from Storage Registers 2900 MANUAL Adding Registers To recall a set of user weighting curves from a storage register back into the active register press RCL USR J The mes sage on the upper right of the screen USER 1 4 TO RECALL X with a flashing cursor on the X prompts the user to input the number of the storage register whose curves are recalled using the numeric keypad and press EXIT Since these are recalled into the active register the user weighting curve based on the presently active bandwidth which was in the storage register will be displayed Subtracting Registers The user can add the set of user curves in any of the four storage registers to the set in the active register by pressing ADD K The message USER 1 4 TO ADD N prompts the user to input a storage register number using the numeric keypad and press EXIT The user weighting curve resulting from the addition is displayed User curves
460. tely 15 hours for a full recharge Caution Because of the charging voltage applied to the bat tery pack within the instrument under DC operation only rechargeable batteries should be used For rapid recharging of 2800 2900 battery packs external to the instrument Larson Davis offers the optional Model 2829 EC This smart charger unit provides a regulated charge rate to optimize battery life and avoid overcharging A dis charged battery pack can be fully recharged by the Model 2829 EC in 3 5 hours 1 10 Screw the microphone firmly onto the microphone preampli fier 900B or 910B and use the short length of microphone cable supplied with the 2900 EC1 5 to connect the micro phone preamplifier to one of the microphone input connec tors on the top panel of the 2900 Then while holding the preamplifier such that it is aligned with the microphone holder with the connector end toward the cylindrical microphone holder back it slowly into the holder until it is firmly in place with the cable passing through slot If the microphone boom is not used the user should be aware of the potential for error associated with improper microphone placement and take appropriate measures when designing an alternative microphone placement system such as using an external tripod mount Introduction Alternative Inputs 2900 MANUAL Accelerometers with Internal Electronics Charge coupled Accelerometers The Larson Davis Model 950B
461. ters are measured between channel 1 and channel 2 See Chapter 20 for a more detailed discussion of intensity measurements and analysis 6 10 Regardless of the Analysis Type there are two vertical bars on the right of the spectrum display whose height represents broadband data calculated from the spectra data The one with the summation symbol beneath it is the total energy cal culated from the spectral data being displayed This could be referred to as the linear or overall level The one with the A beneath it represents the same spectral data with the A weighting correction included so it can be referred to as the A weighted level If it is desired to accurately measure the energy between two frequencies other than the available combinations of lower and upper frequencies use the Both Cursor readout format and place the two cursors at the desired frequency limits as described in Chapter 8 When analog A or C weighting has been selected at the input of the frequency analysis function the A bar will show no data However since an analog weighting function is being used and the broadband data is calculated from the spec trum itself the summation band now includes the effect of the analog weighting and thus represents the A or C weighted level Analysis Menus Selection Of Measurement And Display Parameters 2900 MANUAL A digital readout of the broadband level is presented on the right of the screen seventh lin
462. the user can access the RT60 Menu to display the RT60 values Using the cursor both the average value of RT60 and the number of averages upon which the value is based are dis played for the frequency corresponding to the cursor position Automatic Determination of RT60 Using Fixed Thresholds 21 10 This procedure is exactly the same as that described above with the exception that the upper and lower threshold values used to define the portion of the time decay curve over which the curvefit is to be performed are actual levels of the decay curve rather than the difference between the decay curve level and maximum noise level previous to the decay process For example one could select to perform the curve fit over the time interval during which the level decays from 90 to 70 dB To select the Fixed Threshold mode from the RT60 Menu press Auto TH K until the message on the right of the dis play 10th line down reads THRESHOLDS XX X YY Y and press Exit Select the upper threshold by pressing hthresh J which will produce the message ENTER THRESHOLD Max nnn n Use the numeric keypad to enter a value which will define the beginning of the curvefit time interval as the instant when the sound level equals nnn n dB In the example above this would be 090 0 dB Press EXIT to accept the value which wil then appear as YY Y in the text field THRESHOLDS XX X YY Y on the right of the screen Select the lower threshold in th
463. the background noise to make a good measurement In well equipped test laborato ries a 1 3 octave spectrum shaper is often used to shape the frequency spectrum of the electrical excitation to the ampli fier driving the speaker such that a flatter sound spectrum is obtained in the room As with the sine wave autoleveling function the signal measured in channel 1 is used as the ref erence Upon pressing Auto L L the level difference between each frequency band of the measured signal and that of the frequency band having the lowest level is noted Then the output level for each of these higher level frequen cies is decreased by that amount in order to produce a spec trum which will more nearly approximate a flat 1 3 octave spectrum inside the room Unlike the autolevel in the sine mode this is not a feedback operation but simply a single 4 21 2900 MANUAL White Noise Generator Wideband or Pseudo Pulse Generator 4 22 correction to the output spectrum which takes place when the key is pressed The Wideband White Noise Menu shown in Figure 4 13 Wideband White Noise is accessed from the Signal Generator Menu by pressing WHITE K White noise has equal energy per constant bandwidth e g narrowband FFT analysis Wideband white noise can be used with either digital filters or FFT analysis The LEVEL El lt ATTEN G and gt ATTEN H keys are used in the same manner as described above for the pink noise generator Fi
464. the disk drive is also indi cated One of the files names displayed on each side of the screen will be highlighted by a horizontal black background strip The user can shift the list of internal memory files up and down past the highlight using the softkeys T C and J K Similarly the list of floppy disk files can be shifted up or down using the softkeys T E and J M When the Files Menu is first displayed presses of the hori zontal arrow keys will result in an up or down paging of the internal memory files on the left of the screen However whenever any of the up or down arrow softkeys have been used for vertical shifting of the files on either side of the screen presses of the horizontal arrow keys will result in paging of the files on that same side of the screen In most of the file manipulations operations are performed on the file which is highlighted Thus the use of these verti cal arrow softkeys and the horizontal arrow keys are funda mental in selecting a particular file The paging of the files up and down is also necessary when there are more files than can be displayed on the screen at one time Renaming Files A new internal memory file is created by pressing create A The message Enter new name on the right of the screen accompanied by a blinking cursor will prompt the user to type in a file name of up to eight characters using the keypad and then press EXIT The new file information will then be li
465. the frequency range of interest 20 24 Sound Intensity Measurements 21 Room Acoustics Measurements Sound Decay Measurements Room Acoustics Measurements One of the most common acoustics tests performed for the evaluation of room acoustics is the measurement of reverber ation time or early decay time This is done by injecting acoustic energy into the room usually with loudspeakers an exploding balloon or a starter pistol and then examining the decay of the sound pressure level as a function of time One generally wishes to evaluate the reverberation time in 1 3 octave frequency bands since the result of the measurement can be used to determine the sound absorption in the room which is a function of frequency To make such a measurement with the 2900 it should be configured for Standard Analysis using 1 3 octave filtering and with the Autostorage Mode active so that a series of spec tra are measured and stored during the sound decay at regu lar time intervals which are short with respect to the reverberation time to be measured Typical values of rever beration times are 0 1 to 3 s The time decay process is a statistical one such that there will be a variation of results between tests measured at the same position in the room using apparently identical sound excitation and between tests made at different measurement points in the room To achieve good statistical accuracy numerous tests are generally performed with
466. the full scale frequency will be limited as a means to improve resolution 4 9 2900 MANUAL 4 10 The frequency resolution of the FFT analysis can be increased substantially by utilizing the zoom analysis mode Essentially this means that the number of lines selected for the analysis are used over a narrower frequency range than originally chosen for the baseband analysis Access the Zoom Menu Figure 4 5 Zoom Menu from the Filter Menu by pressing FFTZOOM M Figure 4 5 Zoom Menu Bl D 12 27 52 2 4 8 16 32 64 3 4868 NENT IAL LINEAR 20 2 20 81 APR 37 12 26 46 1537 5080 H4AA annel 1 of 2 NORMAL 73 3 Ze 88 7 REM TACH 6 6 SPEED 4 6 DOG DUM dotted crsr INT 128 256 512 BRSE Hz The zoom multiplier is selected from 2 to 512 binary sequence by pressing the key above or below the desired number Selecting 1 produces a baseband analysis The total frequency range covered by the zoom analysis will be equal to the full scale frequency of the baseband analysis divided by the zoom multiplier For example when a zoom multiplier of 16 is used after a O 20 kHz baseband analysis the total width of the zoom analysis will be 1250 Hz 20 kHz 16 Using 800 lines the frequency resolution would then be 1 56 Hz per band 1250 800 The cursor position at the time the zoom analysis is initiated defines the center of the zoom frequency range the use of the cursor is explained in Chapter 7 Continuing the abov
467. the lower right of the display seventh line down just below the channel num 8 1 2900 MANUAL ber indication The letter s indicates that the solid cursor is being read and the letter d indicates that the dotted cursor is being read The two vertical bars at the right of the display represent the Summation and A Weighted broadband levels designated by the symbol for summation S and the letter A below respectively With either of these cursors active these broad band levels representing the Summation and A Weighted Lev els correspond to the energy between 1 Hz and 20 kHz Solid and Dotted Cursors Moving Together Harmonic Cursors If the key BOTH N is pressed the two cursors will move together under control of the horizontal arrow keys main taining a constant spacing between them as they move across the display The message will be both crsrs The frequency readout fifth line down will be indicated by the symbol A and the values of the frequencies corresponding to both solid and dotted cursors will be indicated in that order in the form solid freq dotted freq The amplitude readout indicated by the symbol A on the seventh line down will display the difference between the amplitude corresponding to the solid cursor and the ampli tude corresponding to the dotted cursor The displayed broadband levels representing the Summation and A Weighted Levels will now represent the energy betwee
468. the next spectrum to be produced Spectra are produced from the math processor at discrete time intervals When fractional octave filtering is used the Tach and Speed values are read at 2 5 ms intervals Using FFT filtering these values are read at the same rate as the FFT spectral blocks are produced 100 line 10 ms 200 line 20 ms etc For this reason it is not possible to ensure that data storage will take place at precisely defined intervals of Tach or Speed because no spectra might appear which hap pen to have exactly these Tach or Speed values For this rea son we define both minimum and maximum values of the increments of Tach and Speed for which data storage is to occur t Amin and s Amin represent the increments of Tach and Speed for which we would like data storage to occur t Amax and s Amax represent maximum acceptable values of Autostore by Tach Autostore by Tach 2900 MANUAL these intervals for which the autostorage is to continue in a normal manner Consider a case where we have set t Amin to 50 RPM and t Amax to an extremely high value such that it is unlikely ever to occur such as 50 000 RPM We have set the Slope to and the last data storage was at 1 000 RPM The next spec trum stored will be the first one for which the RPM value is 1 050 OR GREATER unless it exceeds 50 000 It may be that the first spectrum satisfying that condition will corre spond to an RPM of 1 058 in which case that spectrum wil
469. the number of bits of resolution that method of integration is invalid for frequen cies below 196 of the full scale frequency The method utilized here while restricted to FFT spectra measured using the Standard Analysis Modes is valid over the complete fre quency range The integration of octave bandwidth spectra is invoked from the Units Menu as described in Chapter 9 10 2 Digital Display including Broadband Acoustic Frequency Weighting User defined Frequency Weighting and Integration of FFT Spectra Digital Display Weighting Accessing the Digital Weighting Menu 2900 MANUAL The display weighting is digital and independent from the input signal analog weighting selected from the input menu Its effect is to weight the spectral data before presentation on the display Display weighting is not available when the Cross Analysis Mode is active The Model 2900 offers two types of digital display weighting 1 Broadband Acoustic Weighting corresponding to the A and C filters 2 User defined Weighting From the Display Menu access the Digital Weighting Menu shown in Figure 10 3 by pressing Dig Wgt I Figure 10 3 Digital Display Weighting a1 BER 12 46 18 Zw FREE Zw DIFF SPL 3 2606 EXPONENTIAL 1 8 Dual LINEAR 26Hz 26khHz STOP 021 APR 9 12 44 26 d P 88 DIFF PHONS 88 7 TACH 6 6 SPEED 4 6 o Hz GO H A Lk H dotted crsr INT NO WGT A USER R C USER Note that the softkeys associated with
470. the sum of the deficiencies above the curvefit line as described in the standard Parameter Index Noise Reduction NR Noise Isolation Class NIC Normalized Noise Normalized Noise Isolation Class Reduction NNR NNIC Transmission Loss TL Sound Transmission Class STC Field Transmission Loss Field Sound Transmission Class FTL FSTC ISO Airborne Sound Transmission Parameter 21 16 Pressing ISO J will produce the ISO Rooms Menu as shown in Figure 21 7 Figure 21 6 ISO Rooms Menu 11 MBR 17 17 53 D R DnT 110 Pe ee ee ee ee ey I SPL 6 0008 L Hs EXPONENTIAL 178 Dual LINEAR 28Hz 28kHz RESET 11 MAR 97 Los 125 51 Fa FILTER 814 25 6 v Channel 1 of 2 NORMAL X d a R 34 7 iss ees DIFF PHONS 52 5 REM 1 TACH 8 8 SPEED 8 0 25 0 Hz 500 Hz 10 0kHz H dotted crsr ROOMSTST L n L nT The following lists a set of parameters which are defined by the standard ISO 140 4 1978 Field measurements of air borne sound insulation between rooms Another standard ISO 140 3 1978 Laboratory measurements of airborne sound insulation of building elements defines sound reduc tion index R but in most cases this will be the same as the Room Acoustics Measurements Room Acoustics Measurements 2900 MANUAL apparent sound reduction index R defined in 140 4 Thus we use the symbol R to represent both for these calculations Parameter Standard Apparent Sound Reduction Index ISO 140
471. the time between samples is calculated from the relationship BT 1 which is the fastest rate at which statistically independent samples can be taken There fore the time between samples is a function of the baseband full scale frequency the number of lines used for the analy sis and the zoom factor The following formula can be used to determine the time between samples NE 2566 Time between samples in seconds Fy Baseband full scale frequency before zooming Z Zoom multiplier 1 for baseband analysis Using a full scale of 10 kHz and no zoom 1 P See IUE M To determine the total delay time multiply T by the number of delay samples 11 3 2900 MANUAL Channel 2 Delay Arming and Disabling The Trigger Delay as set above applies to all channels In some measurement situations it is desirable to delay the beginning of sample storage in the buffer for channel 2 an additional number of samples This is the Channel 2 Delay which is defined as a delay with respect to Channel 1 The Channel 2 Delay is set by pressing 2 DELAY O and using the horizontal arrow keys as was done to set the Time Delay The value of the Channel 2 Delay is indicated on the screen by the message Ch2 xx where xx is the delay in number of samples This value will always be positive Frequency Domain Triggering 11 4 When the parameters have been entered and the user exits back to the Analysis Menu the trig
472. this does produce the flattest frequency response When the source is moving with respect to the microphone such as during a vehicle passby measurement this angle cannot be maintained for all positions so a vertical microphone alignment is preferable Figure 3 4 2900 free field response using Model 2541 free field microphone 4 2 04 EXIST m 0 LOA JA 30 2 tn MA 4 T Angles of Incidence MNA m e PARCI e Ek 8 N 40 zi 90 180 12 N 150 120 400 1200 2000 2800 3600 4400 5200 6000 6800 7600 Frequency Hz 3 7 2900 MANUAL 3 8 dB Relative SPL dB Figure 3 5 2900 free field correction at calibration angle of incidence using Model 2560 random incidence microphone o o o o A 0 2 Frequenc x A L m Figure 3 6 2900 free field response using Model 2560 random incidence microphone 24 TAN 04 ae 2 NI 309 Angles of Incidence 4 2 1 60 6 8 10 90 4 180 12 1209 150 144 Wes SS SES SS SSS HE SSS SSS BSS Tee Sk aR See Se SSS eset atte 0 Frequency Hz Sound Level Meter Operat
473. thresholds the upper threshold will always be below the initial noise level so the only instance where the calculation of the RT60 at a particu lar frequency would be aborted will be when the decay curve reaches the background noise level before the lower thresh old condition is met Averaging of Autostored Time Decay Records Room Acoustics Measurements Rather than calculating RT60 values for each time decay curve and averaging these together one might prefer to aver age together the original time decay curves measured for a number of tests in order to obtain a single averaged decay curve and then use this curve to calculate RT60 values A general description of the averaging of autostore records is presented at the end of Chapter 15 It must be remembered that the data in the different autostore records are averaged together bin by bin This means first of all that the spectral storage rate DELTA used during the acquisition must be the same for all records Also the beginning of the decay for each record should occur at approximately the same number of time intervals from the beginning of the record This can be done by using the noise generator in the OFF RUN mode and using the same value of Delay Time since this deter mines the instant of the shut off of the noise generator rela tive to the beginning of each autostore sequence If a large number of decays are to be measured over a single testing period typically a n
474. tially stored records of the same type and bandwidth to determine the maximum amplitude which occurred in each frequency band over the entire set of sequential records From the 13 12 Storing and Recalling Non Autostore Data 2900 MANUAL Recall Menu press B MAX C which will bring to the upper right of the screen the following message Last N MAXIMUM 0001 0002 Use the numeric keypad and the horizontal arrow keys to enter values representing the first and the last of the sequence of record numbers over which the block maximum operation is to be performed Upon pressing EXIT the opera tion is performed and the resulting spectrum is displayed Note that the word MAXIMUM appears on the right of the screen 2nd line down in place of the elapsed time usually displayed with a measured spectrum to indicate that this spectrum is the result of the Block Maximum operation Fol lowing the Block Maximum operation the spectrum is not automatically stored To store this spectrum press STORE The record number into which the spectrum has been stored will be indicated on the upper right of the screen If the records contained within the specified range are not all of the same type and bandwidth the Block Maximum opera tion will not be completed and the message NOT SIMILAR DATA will appear on the upper right of the screen Block Summation of Stored Records Storing and Recalling Non Autostore Data Sequentially stored records of the
475. ticular reset indicated Softkeys Softkey Functions R MEMRY A Reset of RAM Memory loss of stored data R UNTTS B Reset of User Defined Units R SETUP C Reset of User Created Setups R RT60 D Reset of RT60 Register R USER E Reset of User Weighting R MACRO F Reset of Macros R STATS G Reset of Ln Statistics Table In each case upon pressing the softkey a message on the upper right of the screen will request user verification of the reset operation To continue the reset operation press YES A To abort the reset operation press NO C To exit from the Reset Menu press EXIT 4 81 2900 MANUAL Remaining System Softkeys The softkeys appearing in the System Menu which have not been described in this Chapter are explained in detail in later chapters as follow Softkeys COLOR M SETUP N FILES O 4 32 Softkey Functions This softkey is used to access the Color Menu for multi window color data display and total instrument control via mouse or trackball using an external EGA VGA or Super VGA color monitor See Chapter 24 This softkey is used to access the Setup Menu for creation storage and recall of user created setups of the Model 2900 See Chapter 12 This softkey is used to access the Files Menu for creation and manipulation of data files and records associated with the internal memory and the floppy disk of the Model 2900 See Chapter 13 2900 Instrument Setup Via The System Menu 5
476. tion of the decay curve over a time interval where the curve is linear the early decay portion then extrapolates this to calculate the time which would be required for a 60 dB decay For example if the slope of the early decay portion of the curve is 33 dB s the RT60 is 1 8 s 21 4 There is an RT60 register in the 2900 which can store a value of reverberation time for each frequency band There are a number of ways by which reverberation time values can be calculated and stored into this register It is possible to per form averaging in this file such that a newly calculated value is averaged together with the previously stored value The RT6O file may be stored to non volatile memory Room Acoustics Measurements Reading Current RT60 2900 MANUAL Manual Entry of RT60 Values The RT60 Menu shown in Figure 21 2 is accessed from the vsTime display of a byTime autostore record by pressing RT60 B Figure 21 2 RT60 Menu 25 BPR 16 15 08 RESET Ruto RE Ruto RU note Note 1 5 8 0508 1 s c vCe MT EXPONENTIAL 1 64 bT ME Dual LINEBR S liz 20kHz RESET 25 FEB 94 1 KASAYA CPI AEG erre esa eg af 86 6 3 15kHz 173 x ET68 TA b l RT66 2 00 RUG i ButoTH Max 25 0 5 8 TACH SPEED P z Et solid crsr ROOMS lthresh hthresh Ruto TH SOLID DOTTED edit The display indicates the values last stored in the RT60 regis ter The cursor can be used to read the value of RT60
477. toSpectrm CrossSpectrm Transfer Fn or Coherence depending on which of these parameters is being displayed Spectral and time domain data measured using the Cross Analysis mode and the normal storage mode FFT band widths only AutoCorrel CrossCorrel Impulse Time Wavefm Cepstrum or Lifter depending on which of these parameters is being dis played Spectral data measured using the Intensity mode and the normal storage mode Intensity or Power depending on which of these parameters is being displayed Spectral data measured using the Autostore By Time storage mode By Time Standard Analysis mode By Time Crs Cross Analysis mode By Time Int Intensity mode Spectral data measured using the Autostore By Tach stor age mode By Tach Standard Analysis mode By Tach Crs Cross Analysis mode By Tach Int Intensity Analysis mode Curves generated using Ln and Statistics using the Stan dard Analysis WDR SLM or SLM A mode and the normal storage mode Ln Trace Ln Table 13 7 2900 MANUAL 13 8 Level versus RPM curves generated and displayed from the vsRPM Graphics Menu vsRPM Trace Decay Time curves displayed from the RT60 Menu RT60 Cross channel normalization curves generated by the normalization procedure to minimize cross channel amplitude phase mismatch Normalizatn User Weighting Curves generated and displayed from the Set User Menu User Curves 2900 Setups stored from the Setup Menu Setups U
478. ts If any of these are changed after the normaliza tion has been done the normalization must be redone Therefore setup the analyzer accordingly FFT normalization curves are always measured using 100 line resolution If during a subsequent analysis a larger num ber of lines is selected the correction function will be extrap olated from the one created using 100 lines Selection of Baseband Full Scale Frequency Noise Generator Setup The system memory permits the measurement and storage of a unique normalization function for each permissible value of baseband full scale frequency Following the normalization procedure with normalization active during subsequent measurements the 2900 will utilize the stored normalization function which corresponds to the value of baseband full scale frequency selected for the analysis Thus it is best to measure and store a normalization curve for each permitted baseband full scale frequency to be certain that the results will be correct for any value of full scale frequency which may be selected Otherwise there may be normalization curves in memory which do not correspond to the measurement being made Measurement 19 10 Set the noise generator to white noise and turn it on White noise is used because its equal energy per constant band width spectrum produces a nominally flat spectrum shape with FFT filtering Set the analyzer to Count Single Averaging and a sufficiently large
479. ts but the actual cal culation of the Normalized Impact Sound Pressure Level is the same as used in the field The standard ASTM 989 89 Impact Isolation Class describes the determination of Field Impact Insulation Class FIIC from the Normalized Impact Sound Pressure Level using a curvefitting technique The same calculation is applied to the laboratory measurements to obtain the Impact Insulation Class IIC To determine these ASTM parameters simply press Ln I to obtain a display similar to Figure 21 9 If a message WARNING High Background appears on the upper right of the screen this means that the difference between the Test Room spectrum and the Test Room back ground spectrum levels at one frequency or more is less than 5 dB In such a case the corrected spectrum can only be 21 19 2900 MANUAL used as an estimate of the upper limit of the impact noise level and this should be noted in the report Figure 21 8 Normalized Impact Sound Pressure Level Display 11 MBR 17 23 12 NR NNR TL FTL 1868 i Hote TRPPING 6 9308 sa EXPONENTIAL 178 Dual LINEAR 20 2 20 n STOP 11 MAR 37 17 21 28 yonn ooo oo oo oo EE FILTER 28 166 Hz LAS Normalized Impact SPL d 64 7 E FIIC 52 def 29 REM TACH 8 8 SPEED 6 8 190 Hz Z A dotted crsr ST ROOMST ISO Impact Isolation Pressing ISO J will produce the ISO Rooms Menu as shown in Figure 21 7 The following parameters are
480. ts nennen nensi nter enr senes 19 4 Returning to Normal Display Format essen 19 4 Control of Vertical Display 19 4 Control of Display Range iiie tte ie tco atti t tte pe t ee 33 2L IEEE HER PARERE REL SERERA 19 5 Bandwidth Compensation Power Spectral Density 22 19 7 Control of Horizontal Display 19 8 Selection of Logarithmic Linear Formatl nennen nens 19 8 Control of Display Hange ennt nnns entren nnns nennen 19 8 Normalization of Amplitude and Phase Between Channel 1 and Other Channels 19 9 Connection of the Noise Generator 19 9 Normalization in Cross Mode Using FFT Filtering 2 19 10 Selection of 100 Line Resolution nennen nennen nns 19 10 Selection of Baseband Full Scale Frequency ss eee e e eee ee aai ise ii il l 19 10 Noise Generator Setup A 19 10 MEE 19 10 Klee e RE 19 11 Toggling Normalization ON and OFF n n 19 11 Normalization in the Cross Mode using Octave Bandwidths 19 12 Key Macros E 19 12 Gr ating MaCTOS im iret be va Zoe bl a tente m ete ert te ifo ose ecce ooo i 19 12 McSTOP and McWAIT and 5 19 13 Resetting Macr s ura a cd dec Ete Lose a dak Xe on a E NEEN 19 13 Exec ting RE Lee 19 13 Delayed Macro Execution ccccscecceeeeeeencceteeeee
481. tudies there is much more information to be obtained from the time history of the level in each band than just the rever beration time such as the timing of arrivals of reflections the existence of flutter echoes etc The 2900 is ideally suited for these tests as well 21 3 2900 MANUAL Evaluation of Reverberation Time RT60 Register A typical decay curve will resemble Typical Decay Curve on page 4 Figure 21 1 Typical Decay Curve 22 11 15 88 RT6 REPLACE AVERAGE Auto RE Ruto RU note Hote NOISE DECAY EXPONENTIAL 1 64 PREAMP LINEAR 180 10 2 RESET 22 OCT 91 10 37 04 FILTER 850 1 006 2 L 3 Channel 1 of 1 vsTIME v Ld 38 3 Td 1 28808 RT66 00 30 ctr 1 1000 THRESHOLDS 60 8 85 8 0500 2 18808 new frea TL TEST lthresh hthresh R Prev A Next FREQ SOLID DOTTED BOTH In this log amplitude versus time format the major portion of the curve will be linear with some variations especially over the first 10 to 20 dB of the decay Eventually the level will approach the background noise level of the room which will limit the actual dB range over which the level will decay The value which is referred to as the reverberation time RT60 is by convention the time which would be required for the level to decay by 60 dB In most cases there is not a sufficient dif ference between the initial level and the background level for a 60 dB decay to be measured In practice one measures the slope of the upper por
482. tup Softkeys 22 13 Turning Off the Class Lines Function 22 13 Chapter 23 2900 Printing Data Screen Displays and Tables 23 1 Accessing the Print Menu enn 23 1 Initializing the EE 23 1 Creating the LOGO vize m tern i e tested teet te bap opt este ilo fave ii 23 1 selecting Printer NEIE cate eto edt eat nues 23 2 Printing the LCD Screen Dieplay enne 23 2 Printing a Data Table RR Ee Hee e daeeueu eeu 23 2 Printing LCD Screen Display and Data Table 23 2 Print t Screen HS FUNCION as zeen Fete e teo eya ra e e trt eoe P i oreet qe Hs pa ka ki ce vets 23 2 Abor ng a PEIDEOUL celeriter eth str dote ee dit dem uet 23 3 Ejecting a Sheet of Paper or Making a Form Feed 23 3 Printing the Color Monitor Display 23 3 Block Printing of Stored Data Hecorcde 23 3 G storm B Tas LEE 23 4 Accessing the Custom Printout Module 23 4 2900 MANUAL Scaling of the Custom Printout A 23 4 General Descriptionzz tenete eter eem He OR eiue Pots 23 8 Custom Graphic Configuration I ener ennt en 23 9 ECD Graphic PriritoUt ua cores ile UL adore S m ee 23 10 Measurement Parameter Text Gring 23 10 KE le EE 23 11 Storing a Custom Printout Setup to a Softkey 23 11 Recalling a Custom Print Setup from a 5
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484. ues of the individual traces and hide traces exactly as was done with the graphic produced in the Real time vsRPM Graphic mode vsRPM Graphics In the Real time vsRPM Graphics mode the only data which are stored in the graphics memory buffer are those associ ated with the specific channel numbers and frequencies assigned to the traces previous to performing the test Once the graphic has been created it cannot be modified with the exception that traces can be hidden With the vsRPM Graphics based on autostored records the entire set of complete spectra for each channel are available for use in the graphics routine Thus the user can now mod ify most of the graphics parameters such as the channels and frequencies or orders defined for each trace the hori zontal axis endpoints the slope parameter and switch between Frequency and Orders in those cases where this is consistent with the data type Simply press REDRAW M after modifying the parameter table as desired 17 9 2900 MANUAL Storage and Recall of Trace Records Intensity Mode Data The storage and recall of the displayed vsRPM graphic is per formed exactly as explained for the Real time vsRPM Graph ics Because of the versatility of this routine for displaying data using different combinations of channel and frequency or order for each trace the user may choose to generate and store a variety of graphic displays as vsRPM Trace records 17 10 To
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486. umber of decays at each of a num ber of microphone positions there may not be sufficient memory in the 2900 to store an autostore record for each It may be desirable from a memory utilization standpoint to measure multiple decays at each microphone position aver age these together then delete the original decay records and save only the averaged decay curve for later calculation of RT60 values for each microphone position This block averag ing of decay curves followed by record deletion can be done much more rapidly in the field than evaluating and storing RT60 values for each decay before deleting the autostore records which is another alternative for the efficient use of memory 21 11 2900 MANUAL Storage and Recall of RT60 Data Recall of RT60 When a set of RT60 values have been determined and saved in the RT60 register using one of the methods described pre viously store the register to memory from the RT60 Menu by pressing STORE This will produce the message STORE RT60 N on the upper right of the screen indicating that it has been stored into the active file as the Nth record of type RT60 Do not forget that a note field may be created and stored with each RT60 record which may be very useful later for differ entiating between different stored records To recall an RT60 data block from the active memory file the 2900 must be in the RT60 Menu Pressing RECALL will pro duce the message Overwrite ALL
487. umbers shall be made the same as the trace numbers If upon accessing the table the pen numbers do not corre spond to the trace numbers modify them to do so as follows Access each trace and press PEN N Use the horizontal arrow keys to modify the pen number until it corresponds to the trace number Frequency Band Selection After accessing the desired trace number press CHANNEL O repeatedly and note that this will toggle between channels 1 and 2 Use this method to obtain the desired input channel number for each trace 17 4 After accessing the desired trace number press FREQ P and use the horizontal arrow keys to sequence through the filter center frequencies corresponding to the analysis type presently active for the 2900 Beyond the highest center fre quency will appear SUM which represents the summation of the energy contained in all the frequency bands Set the fre quency in the table to the desired value vsRPM Graphics Order Selection 2900 MANUAL If instead of FREQ P the softkey ORDER P is displayed press B FREQ L to change it to FREQ P before selecting the frequency band RPM Speed Selection Whether the 2900 has been configured for octave bandwidths or standard FFT filtering it is possible to present the vsRPM curves in the form of orders rather than frequency To do this press B ORDER L to change the parameter repre sented by the last row of the table from FREQUENCY to ORDER Set t
488. und level measurements Sound Level Meter Operating Modes Calibration 2900 MANUAL In the default setup of the Model 2900 as delivered from the factory at the completion of the bootup sequence the fre quency analysis function is configured as follows Microphone input Channel 1 Analog Filtering 20 Hz highpass and 20 kHz lowpass filters Digital Filtering 1 3 Octave Bandwidths Averaging Type Exponential Averaging Time 1 8 second corresponds to SLM Fast Units SPL sound pressure level Sound Level Calibrator Calibration Procedure The subject of calibration of the Model 2900 for sound and vibration measurements is dealt with in detail in Chapter 9 of this manual However for the purpose of quickly calibrating the Model 2900 for a sound level measurement the following description is provided It is the usual practice in the acoustics field to utilize a sound level calibrator to perform the calibration of a sound level meter This device fits over the grid cap of the microphone and exposes the microphone to a known sound pressure level at a fixed frequency Although the calibration may be per formed using calibrators providing various combinations of signal level and frequency the sound level meter standards require that the manufacturer recommend a specific refer ence level and reference frequency for calibration Lar son eDavis recommends calibration be done using a reference level of 94 0 dB at a frequenc
489. und Level Meter Operating Modes To take the signal from either the Channel 1 or the Channel 2 microphone input connector press either CH1 or CH2 The active input will be indicated by the message on the right side of the screen third line down from the top 3 3 2900 MANUAL Changing the SLM Analog Filters In the default setup the A weighting filter is active The SLM Input Menu shown in Figure 3 2 used to change the micro phone bias voltage is also used to select the analog filters for use in the signal path of the sound level meter Press the key sequence SYSTEM INPUT K to access this menu To change the analog weighting press one of the following Softkeys Softkey Functions A WGT I Inserts an A Weighting filter in the sound level meter signal path C VVGT J Inserts a C Weighting filter in the sound level meter signal path 1 20k K Inserts a 1 Hz highpass filter and a 20 kHz low pass filter in the sound level meter signal path 20 20k L Inserts a 20 Hz highpass filter and a 20 kHz lowpass filter in the sound level meter signal path 1 10k M Inserts a 1 Hz highpass filter and a 10 kHz low pass filter in the sound level meter signal path 20 10k N Inserts a 20 Hz highpass filter and a 10 kHz lowpass filter in the sound level meter signal path Note that the choice of analog filter selected for the sound level meter function is displayed on the lower right of the screen To return to the SLM Menu press EXIT tw
490. und spectrum to be used for the calculation to zero dB in all frequency bands To define the RT60 record to be used for the calculation press RT60 F to access the RT60 Menu If the desired record is already in that buffer simply press EXIT to return to the Rooms Menu Otherwise press RECALL YES A use the horizontal arrow keys to recall the desired record then press EXIT Select the standards organization whose standards you wish to follow for the determination of the airborne sound trans mission parameters by pressing either ASTM I or ISO J ASTM Airborne Sound Transmission Parameters Room Acoustics Measurements Pressing ASTM I will produce the ASTM Rooms Menu as shown in Figure 21 5 Figure 21 4 ASTM Rooms Menu 11 MAR 17 16 11 NR HHF TL FTL SPL 8 0000 an 2202200 EXPONENTIAL Dual LINEAR 28Hz 28kHz RESET 11 MAR 97 16 12 51 T FILTER 14 25 8 Hz LAS v Channel 1 of 2 NORMAL d 25 0 34 7 5a 12020 E ILE DIFF PHONS 52 5 REM g 1 TACH 8 8 SPEED 0 0 25 0 Hz 500 Hz 10 0kHz H dotted crsr ROOMSTST Ln The following lists a set of parameters which are defined by the ASTM standards Parameter Standard Noise Reduction NR ASTM E90 90 and E336 90 Normalized Noise Reduction NNR ASTM 336 90 Transmission Loss TL ASTM E90 90 Field Transmission Loss FTL ASTM E336 90 To perform the calculation and display the result as a func tion of frequency on the analyzer
491. unos pue joedui peziprepuejg pue TPA ounssauq PUNOS 1 pozi epurio0N Posi 9 9 2INSSA1J punog Joedu pozrprepuejg ojenp eAq 9A9 AINSSI punog joedui pozi epurioN INLAT 0 a al A v q uon np i punos pozirepue1s Ju mddvy urge uone nsu punog ou1oq1ry pue p JUSI AA put POYSIOM pue v r yiq punos pays juoreddy JIOUTIJJI 2A9 T JJeNJLAJ paziprepue1S ojenjeAq x pul uononpoyz pumos VIZ SZ 21NB1q NUI suioos n Wouj nuo OSI 92 92 snu W yilos ec 86 FTANDIJ d 4 a C E O oot pajedIPUI 10 Iojoureded 4999S ouuey 12o og 1 TAIL 9 I SZ m lu N Nada N TV VII SI4440 8 1 LASHOVL SIojoureed jas ydeis NARASA 10 nuon ure s 0 IN VAS Iojoure Jed 159 9S poodg uoe ssoooy t Jan I SALVIS H HLAIM D 30u 4 SIXV X Jen pojoo os IWI Sup oe1 Iop1O PIIA SION poods Wd oprqu Jo p H p f s yo 88900 4 1804 npaq r U99A 9q SIX SNIS PS e UOZLIOU 91330 jung Yea 1 9 eg A OACIA q ueds x D SAVIDVL g 949 V V 4430718 440 NO p ds yydyq 840 Keyds p Suppen 7 kejdsip SIXE ejUOZLIOQ sIeqZeL 8301 ouin eo1 yo dofs 19 S 10709 o S 30 10 Syrum 19g ATATISU S pmrdury S SZ mu NUN SISA eUY paepuejgou WOU nu N INdRASA
492. unt and the sound radiating surfaces of the machine and the radiation efficiency of the machine surface in converting surface vibration into acoustically radiated energy Thus the actual noise radiated by a particular machine will depend on both the parameters of the motor and those of the machine itself The design of one machine may make it particularly suscepti ble to motor vibrations at a particular frequency yet rather insensitive to those at other frequencies Stated another way when the goal of the test program is to minimize the noise radiated by a machine utilizing that motor then the classifi cation of a motor in terms of its vibration spectrum must in some way reflect the vibration transmission noise radiation characteristics of the machine itself Simply said with this classification technique using four different classification curve families one for each of four different machine designs the motors could be sorted or classified in terms of accept ability for use in any of these four different machine designs by a single test The fact that two channels can be measured and classified at once permit the user to classify the sound or vibration of one motor at two positions or to test two motors on different test lines at the same time Classification Class Lines Optional Feature Class lines are only applicable to spectra measured in the Standard Analysis Mode STAND 1 or STAND 2 so the ana lyzer must first be conf
493. ured Cross Analysis Frequency and Time Domain FFT only data are measured for each input channel and also cross channel parameters are measured between channels 1 and 2 Intensity Analysis Spectral data corresponding to acoustic intensity are measured This implies a cross channel mea surement between channel 1 and 2 Since these are very different we will discuss each within a separate section of this chapter Control of the display for mats such as linear amplitude scales logarithmic frequency scales for FFT combining percentage bandwidths to obtain larger bandwidths and the readout of the broadband A Weight and Linear levels will be discussed later Standard Analysis After having setup the analyzer for Standard Analysis Single or Dual Channel in the System Menu upon exiting from that Menu the Standard Analysis Menu will be displayed as shown in Figure 6 1 Standard Analysis Menu This Menu will be the same for either type of frequency analysis Octave or FFT Figure 6 1 Standard Analysis Menu 29 ud 84 34 40 NORMAL SEL DISPLAY note DETECTR SPL 3 6488 eye laa sab alles DRM NE EXPONENTIAL 178 Dual LINEAR 20Hz 20kHz STOP 29 JAN 98 04 34 05 Da OO FILTER 25 315 Hz L73 v Channel 1 of 2 NORMAL d 65 9 2 69 9 Lm EE 9 Bd o FREE Ph 76 4 Sne 12 57 TACH 8 8 SPEED 8 8 b t Hz A OKAZ dotted crsr VSRPM STAT Mx Srec F TRIG SETUP FILES AUTOSTR Analysis Menus Selection Of Measur
494. use during its execution until the analyzer is in the STOP state at which time the execution will continue This is useful for defining macros which will initiate a mea surement and also perform operations after the measure ment has been completed This implies the use of an averaging method where the measurement sequence stops without the requirement of manual intervention e g linear single or count single or an autostore measurement The softkey McWAIT J is used to provide a wait state dur ing the execution of a macro Upon pressing this key a menu wil offer the user a choice of wait periods in a binary sequence beginning with 0 25 second The softkey McREPT K is used to generate a repeat of the macro When this is used the macro will continue to be repeated until the analyzer is stopped manually by pressing the hardkey SPACE Executing Macros From the Reset Menu pressing R MACRO F will clear all the macros presently active To execute a macro simple press MACRO to display the Macro Menu followed by the softkey corresponding to the desired macro The message MACRO Executing N where N is the letter I P of the softkey corresponding to the macro being executed will appear on the upper right of the screen When executing a macro the menu displayed on the screen must be the same one which was displayed when the macro was created The message MACRO MENU MISMATCH will appear on the upper right of the sc
495. utor nu yv 1 515AA WTS f LOM I LOM V t t g LOM V LOM V t t G Gc SNUSW Aoyyos vy Sc 34 91 g6I Sc mr d N AONM 9 I LOM 20 440 nuspy BUDYBIEM Aeyds q 23131 ss y uonesuoeduio Qprepueg 213301 C 6c am 22 92 90314 5 910u 5 edg x q g LVIS V INdzISA PIPIA SION urnn ds xew nuoJA nuo sorude npa re n Aeyds q 52115114 ssoooy INdMS s222 V T ST 210817 n yy WTS oul nuo Aejdsiq WTS 9 Gz SNUSW Aoyyos ST ST mr d ALSOLAV t qoe q ourr q o101s01ny dm CI SZ OMIT 12 42 m r N Aus N OTALA T ds xiy sdm JOSS 9 9 pueqpeoJq T ZATEUV kouanbol1q tunurxeu ou TIeooq 91o1sS o Surpuods i11oo wnnoads Avydsiq 61 S7 21n31q 101 Jou 4 AV IdSIG t t PPIH XON jnopeos pueqpeorg pue UPH SUDUST AL PRSIA PAPS 9 92 34 91 11 42 91 57 BINS O STTIH t S H ssoooy IZ ST ONS EZ SZ am 22 92 m r MN LVLS r NASA I SWOON nuoJA nua NUI sonsnejg sonder sonsnooy SS V INd ISA uoo SS V SS V la ras a XVIN DININ aq b rq 4 Jrejourereq Ae dsi VAS c ANVIS 10 1 ANVIS Suno l s Jonge Uer n yy WAISAS uio xq sjouueyD pue nus sisAjeuy prepueig Aquo SINY 247120 Oc Sc oar H ALOALAA t lojoureTeq pue adAL Buide1oAY jospeg V TVINSION t G SNUSW Aoyyos 9 92 34 91 CC m ri LI S
496. ve 2900 AC Outputs RTA Mode SLM Mode Out 1 RTA In Ch 1 Out 1 In Ch 1 Qut 2 SLM Out 1 RTA In Ch 2 Out 2 In Ch 2 dud SEM 1 28 ntroduction 2 Menu Structure For Instrument Operation Softkey Menu Concept Analyzer Mode The main user interface of the Model 2900 consists of an interlinked network of displayed softkey Menus each of which has associated with it a set of softkey labels As explained in the Introduction when the user presses a par ticular softkey the result may be a direct action or it may result in the display of a different softkey Menu We refer to a particular softkey using the format XXXX Y where XXXX is the softkey label and Y is the lower alphanumeric character imprinted on the associated hardkey For example AUTOSTR P would refer to the key on the far right of the row below the display which has the character P imprinted on it and the label AUTOSTR displayed on the screen directly above it References to front panel hardkeys are made using bold capi tal letters without any brackets such as SYSTEM To invoke the upper character of a hardkey press SHIFT before press ing the key Menu Structure For Instrument Operation When the Model 2900 has completed its bootup sequence it is configured as a single channel frequency analyzer We say that it is in the analyzer mode and the set of softkeys which are displayed represent the Analyzer Menu Because of the analysis flex
497. ve the text cursor to the left margin of the next line down Multiple presses of this key will move the text cur sor down by a number of lines equal to the number of key strokes 14 1 2900 MANUAL 14 2 When a sequence of characters have been typed onto the screen the horizontal arrow keys may be used to move the blinking text cursor forward and backward through the text Pressing the CURSOR hardkey on the lower right of the front panel will delete the character highlighted by the text cursor All following characters will be scrolled backwards to fill in the space created by the deletion of the character When the text cursor is within a text string typing additional charac ters will cause them to be inserted to the left of the cursor position Note that there is a space key on the right of the front panel When the text cursor is within a text string and the RANGE key is pressed the portion of the string to the right of and including the character highlighted by the cursor will be shifted vertically downward and to the left margin to begin a new line Repeated presses will move the cursor further downward Pressing CLEAR will clear the entire text string In most cases when the note G key is pressed the previously entered or recalled text string will appear Use the CLEAR key to erase the previous note before beginning a new one unless the new note will be sufficiently similar that editing would be more efficient After cr
498. veraging process is begun again this repeats until manually stopped Exponential produces a running time averaging process sim ilar to an RLC analog circuit This averaging must be stopped manually Constant Confidence averaging produces a running time averaging with a different effective averaging time for each fil 5 2 Selection of Averaging Parameters Averaging Time 2900 MANUAL ter such that the same statistical accuracy for a noise signal is obtained for each frequency band The Exp or Lin refer to the algorithm used to calculate the averaged value This aver aging method must also be stopped manually In Spectral Single averaging the individual spectra are aver aged together until a specified number of spectra is reached then averaging is stopped A check for overloads is performed as each spectrum is produced overloaded spectra are rejected from the averaging process With Spectral Repeat the detector is reset and the spectrum averaging begun again until a manual stop Spectrum averaging with Manual Accept is mainly used when measuring structural frequency response functions with an instrumented hammer The data generated from each individ ual hammer blow is examined and if satisfactory accepted manually for inclusion in the spectrum averaging process This continues until the desired number of spectra have been averaged together or until manually stopped Note that the averaging type message displayed on the
499. xt on the 10th line down on the right side of the screen reads AutoTH Max XX YY then the Max based Threshold mode is already active If the message reads THRESHOLDS XX YY then the Fixed Thresholds described in the following section are active To modify the mode of the thresholds access the RT60 Menu by pressing RT60 B and note that repeated presses of AutoTH K toggles the threshold mode between Max based and Fixed as indicated by the text on the right of the screen Select the Max based mode and press EXIT to return to the vsTime Menu The beginning of the portion of the decay curve used for the curvefit is defined by the upper threshold Select the upper 21 7 2900 MANUAL 21 8 threshold by pressing hthresh J which will produce the message ENTER THRESHOLD Max nnn n on the upper right of the screen Use the numeric keypad to enter a value which will define the beginning of the curvefit time interval as the instant when the sound level has decayed to nnn n dB below the highest value which had occurred during the mea surement In the example above this would be 005 0 dB Press EXIT to accept the value which will then appear as YY Y in the text field AutoTH Max XX X YY Y on the right of the screen The end of the portion of the decay curve used for the curvefit is defined by the lower threshold Select the lower threshold by pressing lthresh I which will produce the message ENTER THRESHOLD Max n
500. xt strings and the user defined text strings are under user control so the general form of a custom printout could be very different from this example However certain of these items fall into groups and are either set ON or OFF when con figuring a custom printout Referring to Figure 23 3 the soft key GRAPH A is pressed to initiate the configuration of the custom graphic portion of the printout If this has been selected to be an active part of the present configuration turned ON there will be a small symbol w displayed to the left of the softkey label If this symbol is not displayed it indi cates that the custom graphic portion of the printout is turned OFF and it will not be printed 2900 Printing Data Screen Displays and Tables Custom Graphic Configuration 2900 MANUAL Press the softkey SCREEN B to configure the position size and orientation of the printout reproducing the LCD display on the analyzer screen You may set this to ON or OFF Press the softkey TEXT C to configure the location size and orientation of the measurement setup text strings stored with the data block in the instrument There are fourteen of these and each may be turned ON or OFF independent of the oth ers The softkey FRAME D turns ON or OFF the printing of a frame outlining the page of the printout The softkey ORIENT H selects either portrait or landscape orientation of the printout 2900 Printing Data Screen Displays and Tables
501. y a second time or waiting until a linear single average or a count single average is completed the judgement is performed and the judgement table automatically displayed on the right of the screen Press EXIT to return to the System or Main Menu and R S to initiate a new measurement preparatory to performing another judgement as described above Classifications Requiring Line Crossings at Multiple Frequencies Classification Class Lines Optional Feature In the preceding descriptions the classification of a spectrum was based upon the farthest penetration of any one spectrum level into a family of class lines either in the upward direc tion for Max mode or in the downward direction for Min mode The numerical classification was simply the number of lines crossed at the frequency representing the furthest pene tration Another classification scheme could involve the requirement that the line of maximum penetration be crossed at multiple frequencies This is done from the Editing Menu by pressing qualify D and in response to the message Points to qualify nn on the upper right of the screen typ ing in a number using the numeric keypad and pressing EXIT In the example shown in Figure 22 10 Judgement Example using qualification 3 a value of 03 has been entered as the qualification value for the family CURV 1 Figure 22 10 Judgement Example using qualification 3 29 DEC 17 86 25 t 90 4 Upon performing a judgement of
502. y of 1 kHz which can be pro vided by the LarsoneDavis Model CAL200 Sound Level Cali brator The CA200 begins producing the calibrated sound level upon pressing the button on the side When equipped with fully charged batteries the sound will remain on for a period of at least one minute As the batteries become weaker the cali brator will shut off sooner than one minute but the level and frequency will remain correct during the time it is operating Sound Level Meter Operating Modes We will assume that the Model 2900 has just been turned on and it has booted up to the default setup as delivered from the factory The frequency analysis function will be config ured for 1 3 octave analysis with flat weighting over the fre quency range 20 Hz 20 kHz This is indicated on the third line down on the right of the screen at the right end of the line If the weighting is different due to a boot up modifica 3 17 2900 MANUAL 3 18 tion access the Weighting Menu and press 20 20k D to select flat weighting with those values of analog lowpass and highpass filters at the input of the frequency analysis func tion If the microphone bias voltage is to be different than the default 200 volts change that as described at the beginning of this chapter Access the sound level meter function by pressing SLM place the calibrator over the microphone switch it ON and press the R key to begin a measurement Use the upward and downwar
503. y range is changed Linear and A Weighted Data Pointing and clicking the mouse within the general data dis play area will open a window offering a choice of line types Select the one desired for that data window Line Bar Line for Bar and Outlined Bar are simply different graphic presentations of single channel data When the Stan dard Analysis Mode has been selected along with two input channels the selection of Multiline for Line Type will permit the display of both channels in the same display window When Multiline is selected a window will open listing Chan nel 1 in blue letters and Channel 2 in green letters Point ing the mouse at either of these channel numbers and clicking will toggle the state of that line between On and Off When either is Off the color blue or green will be replaced by black To exit without making a change click on Exit When the Cross Analysis Mode has been selected all param eters with the exception of Autospectra and Time are cross spectra and therefore cannot have a different display for each channel In those cases the selection of Multiline will indicate Channel 2vs1 in blue to show that this is a cross channel data type and no dual channel display is possible In the Intensity Mode no parameters can be displayed which have different values for each channel so no multiline dis play can appear 24 12 The overall values of the data within each data display win dow are in
504. y the average intensity mea sured in the direction normal to the surface In a typical project one measures the acoustic power associated with many separate area elements which together form an enve lope in space totally enclosing the device under test Once the intensity at each point has been measured and stored along with the area value then power values can be calculated not only for each area element but for groups of elements which together make up larger sections of the overall surface To offer maximum flexibility in these calculations the individual elements are denoted by AREA names Groupings of these AREAs which together make up larger surface areas are denoted by PART names Finally the totality of PARTs are denoted by a JOB name When ByTime or ByTach autostore are used with the 2900 in the Intensity Analysis Mode both Intensity and SPL spectra will be stored simultaneously Upon recall either of these data types may be displayed in the vsTime or vsRPM format as explained in Chapters 15 and 16 20 1 2900 MANUAL Sound Intensity Standards Instrument Standards There are two types of applicable standards for sound inten sity instrument standards which present minimum perfor mance requirements for the instruments to be used to perform the measurement and application standards which provides a methodology to be followed in order to obtain accurate results In North America most users will follow standards appr
505. ying Individual Spectra records have been stored in a particular record and to exam ine their note fields use the Files Menu If the desired record is in another file it will be necessary to access the Files Menu change the Active Memory File and exit before performing the recall operation At the same time the Recall Menu shown in Figure 15 3 Autostore Recall Menu will be displayed Figure 15 3 Autostore Recall Menu 25 APR 16 18 53 W Fall B RUE B MRX vsTIME N KEEP 168 RECRLL Bs Time 1 Hote SPL a 1000 EXPONENTIAL Ine H TRCH 6 6 SPEED 4 6 50 Hz H l OEH recall data TEST 1 DELETE A Prev R Next and the message recall data on the lower right of the screen will indicate that the horizontal arrow keys are assigned to recall the individual spectra from the recalled record To recall an autostored record stored earlier previous to the one which has been recalled press A Prev N and note that the index N in the message on the upper right has been decreased by one indicating that the previous record has now been recalled Repeated presses of A Prev N will page the recall procedure continually towards the first record stored in that file Similarly pressing A Next O will result in the recall of the autostored record which was stored later after the one which had originally been recalled as indicated by a unity increase in the value of N in the message on the upper right Repeated presses of A Nex
506. ypically be used with a free field microphone left and with the microphone aligned vertically such as would be used with a random incidence microphone right Figure 3 12 Complete instrument being excited instrument being excited Acoustic Response to Vibration with complete Acoustic Response to Vibration with complete instrument being excited 90 80 70 60 50 40 30 20 10 o e 20 4 50 63 31 5 100 N o 200 D A 315 oo oo 4 630 o o e Excitation Frequency Hz m dB 4 Reference Level 90 80 70 dB Reference Level 1000 60 Reference 50 Microphone und 40 y 30 20 10 0 e Reference Microphone B o oo oo o o e e a xo D songs a D do oo L oo DN Oc Hz 31 5 125 160 1000 Excitation Frequency Sound Level Meter Operating Modes Figure 3 13 presents similar data measured when the micro phone and preamplifier only are excited in the vertical direc tion as indicated with the instrument stationary 3 21 2900 MANUAL Figure 3 13 Microphone only being excited Acoustic Response to Vibration with microphone being excited m dB Reference Level Reference icropl men 4 L u 110 Q OO D o L o m x QN OQ o s 10 OO O Excitation Fre
507. ys Turning Off the Class Lines Function To perform this operation press RECALL The message Overvvrite all setup on the upper right of the screen warns that the setups being recalled will replace those presently active under all softkeys and that unless they have already been stored as a Class setup they will be lost Press YES A to continue with the recall or NO C to abort the recall When YES A has been pressed the message RECALL Class setup n will appear on the upper right of the screen to indi cate that the nth record of type Class setup has been recalled At the same time the labels of the eight softkeys along the bottom of the screen will indicate the names used to store each set of four class line families At this point before exiting the left and right horizontal arrow keys can be used to page backwards and forwards through all the stored records of type Class setups As this is done the value of the record number in the message on the upper right and the softkey labels will change accordingly When the desired Class setup record has been recalled press EXIT to cease the recall process and return to the Class Lines Setup Menu Classification Class Lines Optional Feature To turn off the Class Line function from the Class Lines Menu press C OFF F 22 13 2900 MANUAL 22 14 Classification Class Lines Optional Feature 23 2900 Printing Data Screen Displays and Tables Accessing the
508. z 18kHz 16 45 12 Channel 1 CURUS 1 CURUS 2 CURUS 3 CURUS 4 PHONS 53 6 0 SPEED 4 6 data Lac INITIRL Utilize the softkeys T E and J M to align the highlighted line with either Channel 1 or Channel 2 this being the input channel to which the class line families are to be assigned Repeatedly pressing any one of the softkeys named for a par ticular family of class lines in Figure 22 8 these are named CURVS 1 A CURVS 2 B CURVS 3 C and CURVS 4 D will cause the name to alternately appear and disappear along the row associated with that channel number All the names appearing along the row at the time of exiting from the Assignment Menu are assigned to that channel Once these are assigned whenever a judgement or comparison is made between a spectrum measured for that channel and the class lines the comparison will be made simultaneously using all the class line families whose names appear in the row associ ated with that channel In this manner different combina tions of the four possible class line families may be assigned to the two input channels Automatic Judgement of Spectra all channels Using a Softkey Classification Class Lines Optional Feature In order to perform a judgement of spectra based on class lines using a softkey it is first necessary to press the softkey corresponding to the hardkey O until its label is USE KEY O Since measurements cannot be m

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