Name: G.R.A.S. Type 40HT
Brand: G.R.A.S.
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G.R.A.S. Sound & Vibration

Single-channel Low-noise Measuring System consisting of: Type 40HT and Type 12HF - Page 11

3. Operation

3.1 Calibration

3.1.1 Based on System Sensitivity

Sincethemicrophonesignalisampliedby20dBintheGainandFilterUnitType26HT,the

nominal system sensitivity at the output of the Power Module corresponds to 0.8 V/Pa. In other

wordswhenthemeasuredoutputvoltagefromthePowerModuleis0.8VRMS,themicrophone

isbeingsubjectedto94dBre.20μPa.

Theactualsystemsensitivityisquotedontheindividualcalibrationchartsuppliedwitheach

Low-noise Microphone System Type 40HT.

Basedonthisinformation,proceedasfollows:

1. ConnecttheType40HTviaitsLEMOplugtotheLEMOinputsocketoftheType12HF

(see Fig. 1.3).

2. Connect via a suitable cable the BNC output of the Type 12HF (see Fig. 1.3) to the ana-

lyser to be used and switch both Power Module and analyser on.

3. Adjusttheanalysertoindicate94dBre.20μPaforanRMSinputofSvolts;whereS is the

systemsensitivityoftheType40HTasquotedonthecalibrationchart.

3.1.2 Pistonphone

APistonphoneType42AAttedwithaCouplerRA0090(bothavailablefromG.R.A.S.)canbe

usedtoproduce94dBre.20μPaonthemicrophoneoftheType40HT.

Note:aPistonphonettedwithanormal½-inchcouplercannotbeusedbecausethiswillover-

loadthesystemwithalevelof114dBre.20μPa.

Proceedasfollows:

1 ConnecttheType40HTviaitsLEMOplugtotheLEMOinputsocketoftheType12HF

(see Fig. 1.3).

2. Connect via a suitable cable the BNC output of the Type 12HF (see Fig. 1.3) to the ana-

lyser to be used and switch both Power Module and analyser on.

3. Unscrew and remove the normal coupler of the Pistonphone.

4. ScrewtheCouplerRA0090tothePistonphone,seeFig.3.1.

5. Pushtthe½-inchadapterGR0619shownFig.3.1totheentranceofthecouplerRA0090.

Fig. 3.1 Pistonphone without its normal coupler and ready to accept the

Coupler RA0090

GR0619

Adapter for ½-inch microphone

G.R.A.S. Type 40HT User Manual

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