G.R.A.S. 12HM User manual

Instruction Manual
Power Module Type 12HM
Skovlytoften 33, 2840 Holte, Denmark
www.gras.dk [email protected]
SOUND & VIBRATION
G R A S
...
.

Revision 05 12 2012
Power Module
Type 12HM

G.R.A.S. Sound & Vibration
CONTENTS
1. Introduction and Description ......................................3
1.1 Polarization Voltage ................................................3
1.2 PreamplierVoltageSupplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Input/Output ......................................................3
1.4 PowerSupply .....................................................4
2. External Features ................................................5
2.1 Front Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Rear Panel .......................................................6
3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 PowerSupply .....................................................8
3.2 Calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Based on Channel Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Pistonphone .............................................................8
3.3 Measurements ....................................................8
4. Service and Repair ..............................................10
5. Specications ..................................................11

G.R.A.S. Sound & Vibration
Power Module Type 12HM - Page 4
Fig. 1.1 Power Module Type 12HM
1. Introduction and Description
TheG.R.A.S.PowerModuleType12HM(Fig.1.1)isa10-channelpowersupplyforthefollow-
ingtypesofG.R.A.S.preampliersandmicrophoneswhenmakinglow-noisemeasurements:
• 1-inchPreamplierType26HFwith1-inchMicrophoneType40EH
• ½-inchPreamplierType26HHwith½-inchMicrophoneType40AH
Withthese,sound-powermeasurentsoflow-noiseproducts,suchasdiskdrives,canbemade
underanechoicand/orsemi-anechoicconditionsaccordingtoIEC3745:1977.
TheType12HMprovides:
• polarizationvoltages(200V)for10condensermicrophones
• voltagesupplies(±15V)forpowering10microphonepreampliers
• individualresponsesetting,PressureorFreeeld,foreachchannel
• individualgainadjustmentof±3dBforeachchannel
1.1 Polarization Voltage
Polarizationvoltagesof200Varesuppliedviathe7-pinLEMOEGA3071Bsocketsonthefront
panel.
1.2 PreamplierVoltageSupplies
Preampliervoltagesuppliesof±15Varesuppliedviathe7-pinLEMOEGA3071Bsocketson
the front panel.
1.3 Input/Output
EachchanneloftheType12HMhasa7-pinLEMOEGA3071BinputsocketfortheG.R.A.S.
microphonepreampliersmentionedabove,viz.Types26HF,and26HH.Fig.2.3showsthe
wiringdiagramofthisinputsocket.
TheoutputofeachchannelisavailableviaastandardBNCsocketfordirectusewithanalyzers,
voltmeters,oscilloscopesetc.

G.R.A.S. Sound & Vibration
Power Module Type 12HM - Page 5
1.4 Power Supply
TheType12HMcanrunfromanominalmains/linesupplyofeither:
• 115VACor
• 230VAC
Avoltagetapisprovidedontherearpanelforselectingoneortheother.Ondelivery,itissetto
230 V AC.

G.R.A.S. Sound & Vibration
Power Module Type 12HM - Page 6
2. External Features
2.1 Front Panel
2.1.1 Power Switch
See Fig. 2.1.
• Power OnLED(green)
ThegreenLEDlightsupwhenevertheunitisswitchedonviatheOn/Off(I/0)toggle
switch.
• Mains/linetoggleswitchOn/Off(I/0)
Formains/lineACsupply.Power OnLEDilluminatedwhenpowerisswitchedon.
Fig. 2.1 On/Off (I/0)switch on front panel
2.1.2 Channel Details
Front-paneldetailsforeachchannelareasshowninFig.2.2.
• Pressure or Freeeldswitch
Forselectingafrequencyresponsecorrespondingtoeitherpressure-microphoneopera-
tionorfree-eldmicrophoneoperation:
Pressure-toselecttheoutputofthecompensatinglter(inthepreamplier)whichgives
thesystemalinearpressure-frequencyresponse.
Free Field-toselecttheoutputofthecompensatinglter(inthepreamplier)whichgives
thesystemalinearfree-eldfrequencyresponseat0°incidence.
• OverloadwarningLED
Lightsinstantaneouslyandonlywhilethereisanoverload;synchronisedwiththeoneon
thepreamplier(Type26HForType26HH).
• Level Adjustmentswitchandpotentiometer
On-enablesthelevel-adjustmentpotentiometer;useasmallscrewdriveronthepotenti-
ometertoadjustthegaininsignallevel(±3dB)
Off-disablesthelevel-adjustmentpotentiometer.
Ineithercase,thesignallevelwillalreadyhavebeenraisedby20dBbythepreamplierto
yieldanominalsystemsensitivityof:
• 1.1V/Pawiththe1-inchpreamplierandmicrophone,or
• 0.9V/Pawiththe½-inchpreamplierandmicrophone
• PreamplierInput
7-pinLEMOEGA3071Binputsocketformicrophonepreamplier.Wiringdiagramshown
in Fig. 2.3
• Ouput
BNCsocketfortheoutputsignaleitherviasignalconditioningordirectlyfromthemicro-
phonepreamplier.
Mains/lineOn/Off
toggleswitch
Power on
LED(green)

G.R.A.S. Sound & Vibration
Power Module Type 12HM - Page 7
2.2 Rear Panel
Therearpanelhasthefollowingfeatures(seeFig.2.4)
• AC Mains 50 - 60 Hz, 35 VA
Inputsocketformains/lineACpowersupply.Centrepinisearth/ground.
• Fuse
Pull-outfuseboxfortwofuses,oneactive(innermost)andonespare.Fuserating:
315mA(Slow)for115VACmains/linesupply,or
160mA(Slow)for230VACmains/linesupply
• Mains Voltage Selector
VoltagetapformatchingtheType12HMtotheavailableACpowersupplyvoltage,select.
• 230foranACmains/linepowersupplyofnominally230VAC,or
• 115foranACmains/linepowersupplyofnominally115VAC
Fig. 2.3 7-pin LEMO EGA 307 1B input socket (exter-
nal view)
Fig. 2.2 Front-panel details for each channel of the Power Module Type 12HM
Leveladjustmentpotenti-
ometer;enabledwhenlevel
adjustmentisswitchedOn
Preamplierinput
OverloadLED(instantaneous)
Responsesettingswitch
Leveladjustmentswitch
Output

G.R.A.S. Sound & Vibration
Power Module Type 12HM - Page 8
Fig. 2.4 Rear panel of the Power Module Type 12HM
ACMains/lineinputsocket
50-60Hz35VA Mains Voltage
Selector:
230 V AC or
115 V AC
Pull-outfusebox,for2fuses,
1active(innermost);1spare

G.R.A.S. Sound & Vibration
Power Module Type 12HM - Page 9
3. Operation
Note:thischapterassumesthattheType12HMisbeingusedwitheitherofthefollowing
G.R.A.S.preampliers(nootherscanbeused):
• 1-inchPreamplierType26HFwith1-inchMicrophoneType40EH
• ½-inchPreamplierType26HHwith½-inchMicrophoneType40AH
3.1 Power Supply
BeforeconnectingtheType12HMtoanACmains/linesupplyandswithcingiton,makesure
the Mains Voltage Selectorontherearpanel(seeFig.2.4)matchesthelocalACvoltage
supply.Select:
• 230foranACmains/linepowersupplyofnominally230VAC,or
• 115foranACmains/linepowersupplyofnominally115VAC
Checkalsothatthecorrectfuseisinplaceandnotblown(seeFig.2.4).
3.2 Calibration
3.2.1 Based on Channel Sensitivity
SincethemicrophonesignalisampliedinthePreamplierby20dB,thenominalsensitivityat
theoutputofthechannelinquestioncorrespondsto:
• 1.1V/Pawiththe1-inchpreamplierandmicrophone,or
• 0.9V/Pawiththe½-inchpreamplierandmicrophone
Correspondingly(ifLevel AdjustisswithchedOff-seeFig.2.2),whenthemeasuredRMS
outputvoltagefromthechannelis1.1Vor0.9V,themicrophoneinquestionisbeingsubjected
to94dBre.20μPa.
Basedonthisinformation,proceedasfollows:
1. Connectthechanneloutputtotheanalyzertobeusedandswitchbothunitson.
2. Adjusttheanalyzertoindicate94dBre.20μPaforanRMSinputofSvolts;whereSis the
sensitivity(1.1V/Paor0.9V/Pa,seeabove)ofthechannelinquestion.
3.2.2 Pistonphone
AG.R.A.S.PistonphoneType42AAttedwithaG.R.A.S.CouplerRA0090canbeusedtopro-
duce94dBre.20μPaonamicrophone.
Note:aPistonphonettedwithanormal1-inchcoupler(RA0023)cannotbeusedbecausethis
willoverloadthechannelwithalevelof114dBre.20μPa.
Proceedasfollows:
1. Connectthechanneloutputtotheanalyzertobeusedandswitchbothunitson.
2. UnscrewandremovethenormalcouplerofthePistonphone.
3. ScrewtheCouplerRA0090tothePistonphone,seeFig.3.1.
4. InsertthemicrophoneofthechannelinquestionintheCouplerasshowninFig.3.2and
switchthePistonphoneon.Note:fora½-inchmicrophone,usetheadapterGR0619sup-
pliedwiththeCouplerRA0090.
5. Adjusttheanalyzertoindicate94dBre.20μPa.
3.3 Measurements
1. Connectthepreamplier(withmicrophone)totheLEMOEGAinputofthechannelinques-
tion.
2. Connecttheoutputfromthechanneltoananalyzer

G.R.A.S. Sound & Vibration
Power Module Type 12HM - Page 10
3. Switchonbothunits
4. Calibratethesetupviaoneofthemethodsdescribedinsection3.2.
5. SelectwhichmicrophoneoperationtouseviatheswitchonthefrontpanelmarkedPres-
sure/Free Field(seeFig.2.2).
Atthispointyoucanmakeyourmeasurementsbutkeepaneyeontherelevantoverloadwarn-
ingLEDs(oneonthefrontpanelforeachchannelandoneonthepreamplier)toavoidover-
loadingthesystemandinvalidatingthemeasurements.
Fig. 3.1 Pistonphone without its normal coupler and ready to accept the
Coupler RA0090
Fig. 3.2 Pistonphone tted with Coupler RA0090 and the microphone
inserted into the Coupler