G.R.A.S. 50AI User manual

Instruction Manual
Sound Intensity Probe Type 50AI
G.R.A.S.
Sound & Vibration
Skovlytoften 33, 2840 Holte, Denmark www.gras.dk

Revision 6 June.2014
Sound-intensity Probe Type 50AI

G.R.A.S. Sound & Vibration
CONTENTS
1. Introduction and Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Main Components..................................................4
Microphones .............................................................4
Preampliers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Available Versions..................................................6
2. Input Channels ..................................................9
2.1 PreamplierInputsAandB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Sound-intensityAxis ................................................9
3. Output Socket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1 UsewithPowerModuleType12AB ...................................11
4. Handling and Assembling the Probe ...............................12
4.1 TheMicrophones .................................................12
4.2 Probe Design ....................................................12
4.3 PhysicalStrength .................................................12
4.4 Assembling the Probe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.5 UsingtheWindscreen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5. Specications ..................................................16
5.1 All versions:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.2 VersionB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.3 Version C .......................................................16
5.4 Version D .......................................................17
5.5 Version HP ......................................................17
5.6 Version LD ......................................................17

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 4
1. Introduction and Description
TheSound-intensityProbeType50AI(Fig.1.1)isatwo-microphonesoundintensityprobe.It
hasapairofG.R.A.S.phase-matched½″microphonesType40AI(Fig.1.2),twoG.R.A.S.¼″
microphonepreampliersType26AA,solidspacers,remotecontrolhandleandconnection
cable.Theprobeisadjustable,durableandfullycomplieswiththefollowingrequirements:
• IEC61043,Electroacoustics-InstrumentsfortheMeasurementofSoundIntensity-Meas-
urementswithPairsofPressureSensingMicrophones,1993forClass1Sound-intensity
probes.
Fig. 1.1 The Sound-intensity Probe Type 50AI

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Sound-intensity Probe Type 50AI - Page 5
Fig. 1.2 The type of carrying case delivered with the Type 50AI
1.1 Main Components
ThemaincomponentsoftheSound-intensityProbeType50AIare:
• SoundIntensityMicrophonePairType40AK
• TwoMicrophonePreampliersType26AA
• Foursolidspacersofvariouslengthsandaspacercup(seeFig.1.5)
• Remote-controlhandlewith(whereapplicable)uptotwopushbuttonsforcontrollingmeas-
urements
SeealsoFig.1.8.
TheType50AIisdeliveredinacarryingcasesimilartotheoneshowninFig.1.2,completewith
microphones,preampliers,standardaccessoriesandaremote-controlhandle.
1.1.1 Microphones
Themicrophones(Fig.1.3)arehighsensitivity,free-eld½″condensermicrophoneswitha
uniquely-designedpressureequalizationsystemthatensuresextremelywelldenedphase
characteristics.Themicrophonesandpreampliersaremountedontheendofthetelescopic
armoftheRemote-controlhandle.Tocoverthefullfrequencyrangefrom50Hzto10kHz,the
Type50AIisdeliveredwithfoursolidinterchangeablespacersforspacingthemicrophonesat
12mm,25mm,50mmand100mm.

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Sound-intensity Probe Type 50AI - Page 6
1.1.2 Preampliers
Thesmall¼″diameterand40mmlongmicrophonepreampliers(Fig.1.4)arehousedin
robust,stainlesssteelcasingswhichenablenovelprobedesignsthatreducedisturbancesto
thesoundeldotherwisebroughtaboutbytheeffectsofshadowsanddiffraction.Symmetryof
designenablesreliablecalibrationsasdescribedintheproposedstandard(ISO/DIS9614-2)for
soundpowermeasurementsusingsound-intensitymeasurements.
Fig. 1.3 Showing similar pairs of phase-matched ½″ microphone cartridges
Above: Type 40AK, which includes spacers and three adapters for
¼″ preampliers as supplied with the Type 50AI.
Below: Type 40AI, which includes cartridges only
Fig. 1.4 Pair of ¼″ Preampliers Type 26AA supplied with the Type 50AI
Fig. 1.5 Showing the various spacers and the spacer cup supplied with the Type 50AI
RA0263
100 mm spacer
RA0264
50 mm spacer
RA0265
25 mm spacer
RA0266
12 mm spacer
GR0040
Spacer cup

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 7
Fig. 1.6 Showing the markings and external features on the remote-control handles of the various
versions of the Type 50AI
1.2 Available Versions
VariousversionsoftheType50AIareavailablefordirectusewithawiderangeofgeneral-pur-
posefrequencyanalysersaswellasspecialisedsoundintensityanalysers.Fig.1.6showsthe
mainexternalfeaturesofthevariousversions.
Type 50AI version B
Hasbuilt-inremote-controlfunctionsfordirectconnectionto,andcontrolof,sound-intensity
measuringsystemsfromawiderangeofsupplierssuchas01dB,Müller-BBMandNeutrix-
Cortex.
CanbeuseddirectlywiththeG.R.A.S.IntensityModuleType12AB(seealsosection3.1),
whichprovidesallnecessaryvoltagesfortheremote-controlfunctionsandpoweringthepream-
pliers.
TheIntensityModuleType12AB(whichisbattery-operated)hastwostandardBNCoutput
socketsforconnectingtoanalysersthatdon’thavespecialmicrophone-preamplierinputsand
a9-pinD-subsocketwiredupforconnectingdirectlytotheRS232portofacomputer(Fig.3.2);
thusenablingsoftwaretobecontrolledbytheremotecontrolfacilitiesofthisversionofthe
Sound-intensityProbe.
UsewiththeType12ABenablesdirectusewith01dBSoundIntensitysystems.
Type50AI
version HP
Type50AI
version C
Type50AI
versionB
version D
version LD

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Sound-intensity Probe Type 50AI - Page 8
Type 50AI version C
Canbeconnecteddirectlytoanyanalyserwithtwostandard7-pinLEMOmicrophone-preampli-
erinputs.
CanbeusedwiththefollowingG.R.A.S.PowerModules,whichprovideallnecessaryvoltages
forpoweringthepreampliers:
• IntensityModuleType12AB(seedescriptionaboveunderversionB)
• PowerModuleType12AA
(viatheincludedadaptercableAC0003,whichsplitstheoutputfroma12-pinLEMOsocket
intotwo7-pinLEMOplugs)
ThePowerModuleType12AA(whichisbattery-operated)hastwostandardBNCoutputsock-
etsforconnectingtoanalysersthatdon’thavespecialmicrophone-preamplierinputs.
Type 50AI version D
SimilartoversionBbutusesaninternal9-Vbattery(alreadyttedondelivery)forenablingits
remote-controlfunctions.Fig1.7showshowtogainaccesstothebattery.
Type 50AI version HP
Hasbuilt-inremote-controlfunctionsfordirectconnectionto,andcontrolof,Hewlett-Packard
analyserssuchasthetypesHP3569AandHP35670AOptUK4.
BothoftheseanalyserswillsupporttheLEDsmarkedOVERLOADandMEASURING as well as
thecontrolbuttonmarkedSTART/GATE.
Type 50AI version LD
Hasbuilt-inremotecontrolfunctionsfordirectuseandcontrolofLarsonDavisanalyserssuch
asthetypesLD2900andLD3000.
Fig. 1.7 Access to the 9 -V battery located inside the remote-control handle of the
Type 50AI version D. The battery should be disconnected / reconnected
while inside the remote-control handle
Unscrewand
remove
Slidecover
back

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 9
Fig. 1.8 Showing the main components of the Sound-intensity Probe Type 50AI prior to assembly
RA0263 100 mm spacer
RA0264 50 mm spacer
RA0265 25 mm spacer
RA0266 12 mm spacer
GR0040 Spacer cup
RA0003 Straightadapter
PairofType26AA ¼″preampliers
Type40AI Pairofphase-matched½″microphones
Pair of RA0001 Right-angledadapters
OutputsocketRemote-controlbuttonsTelescopicarmPreamplierinputsSwivelhead

G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 10
2. Input Channels
TheType50AIhastwoinputchannels,one
foreachmicrophonepreamplier.Thechan-
nelsaremarkedAandBontheremote-control
handle,seeFig.2.1.
2.1 PreamplierInputsAandB
AandBrefertothetwochannelsoftheprobe.
ChannelAisreservedfortheleadingmicro-
phone,i.e.themicrophonerststruckbyan
acousticwavefront(seeFig.2.2).Whenthis
happens,thisshouldbeinterpretedasaposi-
tivecomponentofthesoundintensityinthe
directionfrommicrophoneAtomicrophoneB.
2.2 Sound-intensity Axis
Fig.2.2illustratestheoriginanddirectionof
positivesound-intensityvectors.Thispositive
directionisalwaysfrommicrophonesAtoB.
Theoriginofthesound-intensityaxisliesonthe
geometric centre of the pair of probe micro-
phones.
Fig. 2.1 Showing the inputs and markings for
the two preamplier inputs
InputforchannelB
InputforchannelA
Markingsforchan-
nelsAandB