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

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HT and Type 12HF - Page 8
2. Power Module Type 12HF
SincethemicrophonesignalisampliedintheGainandFilterUnitType26HTby20dB,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Supplyis0.8VRMS,themicrophone
isbeingsubjectedto94dBre.20μPa.
TheactualsensitivityisquotedontheindividualcalibrationchartsuppliedwitheachType40HT.
Important!
The Single-channel Power Module Type 12HF (available from G.R.A.S.) is a dedicated module.
Under no circumstances should any other Power Module (apart from the multi-channel Power
Module Type 12HM - also available from G.R.A.S.) be used with the ½-inch Low-noise Level
Microphone System Type 40HT.
2.1 Front Panel
Thefrontpanelhasthefollowingfeatures(seeFig.2.1):
• PowerswitchwithtwoLEDs:green“OK”,red“Batt.Low”.
Ifthepowersupplyiscorrect,thegreenLEDlightsup.IftheredLEDlightsup,eitherthe
batteriesarelowandshouldbechanged(seesection2.3)ortheexternalDCsupplyvolt-
age is too low.
• Two-positionswitchforselectingfrequencyresponse,Pressure microphone operation or
Free Fieldmicrophoneoperation:
Pressure-toselecttheoutputofthecompensatinglterwhichgivesthesystemalinear
pressure-frequencyresponse.
Free Field-toselecttheoutputofthecompensatinglterwhichgivesthesystemalinear
free-eldfrequencyresponseat0°incidence.
• Overload-warningLEDsynchronisedwiththeoneontheGainandFilterUnitType26HT
(see Fig. 1.1).
Fig. 2.1 Front panel of the Power Module Type 12HF
Power switch
GreenLED
powerOK
RedLEDBatt.
Low
Input 7-pin
LEMOsocket
Output BNC
socket
OverloadLEDindicates
when the measured
sound pressure level
overloads the system’s
electronics
Switch for
selecting either
pressure micro-
phone opera-
tionorfree-eld
microphone
operation

G.R.A.S. Type 40HT Specifications

General

Brand	G.R.A.S.
Model	Type 40HT
Category	Measuring Instruments
Language	English