G.R.A.S. Type 40HT - 1 Introduction and Description

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HT and Type 12HF - Page 4
* Tripods and Tripod adaptors are available from G.R.A.S.
1. Introduction and Description
The ½-inch Low-noise Microphone System Type 40HT (Fig. 1.1) can measure noise levels
below the threshold of human hearing.
ItsspecicationsaresimilartotheType40HHbutcanalsobeusedinconnedspaces,e.g.:
• intheKEMARHeadType45DA
• intheHearing-protectorTestFixtureType45CA
when these are to be used for measuring very low noise levels.
TheType40HTcomprises:
• ½-inchHigh-sensitiveMicrophoneType40AH.
• ¼-inchHigh-impedancePreamplifierType26HG
• ¼to½-inchAdapterGR0010(includedwithTypeType26HG)
• GainandFilterUnitType26HTwithtwobuilt-incompensationltersandanoverload-
warningLED.
Tocompletethesystem,aspecialsingleor10-channelpowermoduleisrequiredandisavail-
ablefromG.R.A.S.,i.e.
• Type12HFforsingle-channelmeasurements,seeFig.1.2(left).
Or
• Type12HMformulti-channel(1to10)measurements,seeFig.1.2(right)
Thechosenpowermoduleprovidesallnecessaryvoltagesforpoweringthepreamplier(s)as
well as polarizing the microphone(s).
Fig. 1.1 ½-inch Low-noise Measurement Microphone System Type 40HT
Gain and Filter Unit Type 26HT.
Withoverload-warningLEDto
indicate when the measured
sound pressure level overloads
the system’s electronics
Frontendcomprising:
• ½-inchHigh-sensitiveMicro-
phone Type 40AH
• ¼to½-inchAdapterGR0010
• ¼-inchHigh-impedance
PreamplierType26HG
Tripod Adapter
RA0096 *
To Power Module Type 12HF
(or Type 12HM for multi-chan-
nel set-ups). see Fig 1.3
Preamplier’s
LEMOconnector