G.R.A.S. Type 40HT Bedienungsanleitung
Instruction Manual
Single-channel Low-noise Measuring
System consisting of:
½-inch Low-noise Level Microphone
System Type 40HT and
Power Module Type 12HF
G.R.A.S.
Sound & Vibration
Skovlytoften 33, 2840 Holte, Denmark Tel. +45 45 66 40 46 Fax +45 45 66 40 47
To Analyser
Type 12HFType 40HT
Revision 7 September 2012
Single-channel
Low-noise Measuring System
consisting of:
½-inch Low-noise Level Microphone System Type 40HT
Power Module Type 12HF
G.R.A.S. Sound & Vibration
CONTENTS
1. Introduction and Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Microphone Type 40AH .............................................4
1.2 Gain and Filter Unit Type 26HT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 PreamplierType26HG .............................................5
2. Power Module Type 12HF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1 Front Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Rear Panel .......................................................8
2.3 Battery Pack ......................................................9
3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1 Calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Based on System Sensitivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Pistonphone ............................................................10
3.2 Measurements ...................................................11
4. Specications ..................................................12
4.1 ½-inch Low-noise Microphone System Type 40HT .......................12
4.2 Single-channel Power module Type 12HF (separate order).................12
4.3 Common . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
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.
ItsspecicationsaresimilartotheType40HHbutcanalsobeusedinconnedspaces,e.g.:
• intheKEMARHeadType45DA
• intheHearing-protectorTestFixtureType45CA
when these are to be used for measuring very low noise levels.
TheType40HTcomprises:
• ½-inchHigh-sensitiveMicrophoneType40AH.
• ¼-inchHigh-impedancePreamplifierType26HG
• ¼to½-inchAdapterGR0010(includedwithTypeType26HG)
• GainandFilterUnitType26HTwithtwobuilt-incompensationltersandanoverload-
warningLED.
Tocompletethesystem,aspecialsingleor10-channelpowermoduleisrequiredandisavail-
ablefromG.R.A.S.,i.e.
• Type12HFforsingle-channelmeasurements,seeFig.1.2(left).
Or
• Type12HMformulti-channel(1to10)measurements,seeFig.1.2(right)
Thechosenpowermoduleprovidesallnecessaryvoltagesforpoweringthepreamplier(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.
Withoverload-warningLEDto
indicate when the measured
sound pressure level overloads
the system’s electronics
Frontendcomprising:
• ½-inchHigh-sensitiveMicro-
phone Type 40AH
• ¼to½-inchAdapterGR0010
• ¼-inchHigh-impedance
PreamplierType26HG
Tripod Adapter
RA0096 *
To Power Module Type 12HF
(or Type 12HM for multi-chan-
nel set-ups). see Fig 1.3
Preamplier’s
LEMOconnector
G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HT and Type 12HF - Page 5
Fig. 1.3 shows a Single-channel Low-noise Measuring system (as described in this document)
andconsistsof:
• ½-inchLow-noiseLevelMicrophoneSystemType40HT.
• PowerModuleType12HF.
Note:thepowermodulemustbeorderedseparatelyandthetripodandtripodadapterare
optionalextras.
1.1 Microphone Type 40AH
TheType40AHisaspecialhigh-sensitive½-inchmicrophone.Itisexternallypolarizedwith
aspeciallyreducedinherentnoiseoorinordertoachieveahighdynamicrangeandwide
frequencyrange.
1.2 Gain and Filter Unit Type 26HT
ThebodyoftheUnithasanoverload-warningLED,(Fig.1.1),whichisrepeatedonthefront
panel of the chosen power module (see Fig. 2.1).
Thesignalofthemicrophoneisampliedby20dBintheGainandFilterUnitType26HT.
Thetwocompensationltersgivethesystemtwoparalleloutputswhichcorrespondto:
a) linearpressure-frequencyresponse.
b) linearfree-eldfrequencyresponseatanangleof0°incidence.
Fig. 1.2 Power modules available from G.R.A.S. for Type 40HT,
Left: Single-channel Power Module Type 12HF
Right: 10-Channel Module Type 12HM
Fig. 1.3 A Single-channel Low-noise Measuring System as described
in this document, shown here with Tripod and Tripod Adapter
(both available from G.R.A.S.)
To Analyser
Type 12HFType 40HT
G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HT and Type 12HF - Page 6
Thechoiceofwhichfrequencyresponsetouseismadeviaatwo-positionswitchmarkedPres-
sure / Free Field on the front panel of the chosen power module (see Fig. 2.1).
Fig.1.4showstheresponsesofthetwocompensationltersaswellasthefree-eldresponse
for0°incidence.Note:free-eldcorrectionsareaddedtothelowestcurve.
Fig.1.5showswhatthesefree-eldcorrectionsareforvariousanglesofincidence.
Fig.1.6shows,foracompletelow-noisemeasuringsystem,atypicalnoiseoorin⅓-octave
bands for both the linear and A-weighted cases.
1.3 PreamplierType26HG
SimilartothestandardG.R.A.S.Type26ACbutwith40GΩinputimpedancetoenablelow-level
andlow-frequencynoisemeasurements.
Thepreamplierhasanintegrated3metrelightweightcableterminatingina7-pinLEMOcon-
nector (which plugs in to the Gain and Filter Unit Type 26HT).
A¼”to½”adapter,GR0010,isincluded,sothatitcanalsobeusedwithG.R.A.S.½”micro-
phones. See separate data sheet.
Fig. 1.4 Typical frequency response curves of Type 40HT
G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HT and Type 12HF - Page 7
Fig. 1.5 Free-eld corrections for various angles of incidence on the ½-inch Microphone Type 40AH.
Fig. 1.6 Typical noise oor of Type 40HT for system and microphone. Shown in ⅓-octave bands for
both the linear and A-weighted cases
100 kHz10 kHz1 kHz100 Hz
Decibelsre.levelat250Hz
- 6
- 4
- 2
0
2
4
6
8
10
180 º
Random incidence
150 º
120 º
0 º
30 º
60 º
90 º
0 º
90 º
120 º
- 8
14
12
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
SincethemicrophonesignalisampliedintheGainandFilterUnitType26HTby20dB,the
nominal system sensitivity at the output of the Power Module corresponds to 0.8 V/Pa. In other
wordswhenthemeasuredoutputvoltagefromthePowerSupplyis0.8VRMS,themicrophone
isbeingsubjectedto94dBre.20μPa.
TheactualsensitivityisquotedontheindividualcalibrationchartsuppliedwitheachType40HT.
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
Thefrontpanelhasthefollowingfeatures(seeFig.2.1):
• PowerswitchwithtwoLEDs:green“OK”,red“Batt.Low”.
Ifthepowersupplyiscorrect,thegreenLEDlightsup.IftheredLEDlightsup,eitherthe
batteriesarelowandshouldbechanged(seesection2.3)ortheexternalDCsupplyvolt-
age is too low.
• Two-positionswitchforselectingfrequencyresponse,Pressure microphone operation or
Free Fieldmicrophoneoperation:
Pressure-toselecttheoutputofthecompensatinglterwhichgivesthesystemalinear
pressure-frequencyresponse.
Free Field-toselecttheoutputofthecompensatinglterwhichgivesthesystemalinear
free-eldfrequencyresponseat0°incidence.
• Overload-warningLEDsynchronisedwiththeoneontheGainandFilterUnitType26HT
(see Fig. 1.1).
Fig. 2.1 Front panel of the Power Module Type 12HF
Power switch
GreenLED
powerOK
RedLEDBatt.
Low
Input 7-pin
LEMOsocket
Output BNC
socket
OverloadLEDindicates
when the measured
sound pressure level
overloads the system’s
electronics
Switch for
selecting either
pressure micro-
phone opera-
tionorfree-eld
microphone
operation
G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HT and Type 12HF - Page 9
• 7-pinLEMOEGA3071BinputsocketfortheLEMOplugonthecableoftheGainand
Filter Unit Type 26HT. Wiring diagram shown in Fig. 2.2.
• BNCoutputsocketfortheselected(Pressure / Free Field) output signal.
2.2 Rear Panel
The rear panel has the following features (see Fig. 2.3)
• Twist/releaseholderfor315mAfast-blowfuse.
• Inputsocketforanexternalvoltagesupplyof6V-20VDC;centrepin+terminal.Usethe
Mains/line Adapter AB0010 supplied with the Type 12HF.
• Lockingscrew
Unscrew to remove base plate and gain access to the battery pack (see section 2.3).
Fig. 2.2 7-pin LEMO EGA 307 1B input socket
(external view)
Fig. 2.3 Rear panel of the Power Module Type 12HF
Inputforexternal
Power Supply
6V-20VDC
Fuse 315 mA fast
blow
Locking screw for
base plate
G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HT and Type 12HF - Page 10
2.3 Battery Pack
Togainaccesstothebatterypack,unscrewthelockingscrewontherearpanel(Fig.2.3)and
slide the base plate off towards the rear. Pull out the battery pack See Fig. 2.4.
Thebatterypackconsistofabatteryholderand4xLR14(C)standardalkalinecells.When
replacingthebatteries,replaceallofthemmakingsurethatthepolarityisasindicatedonthe
battery holder.
Fig. 2.4 Showing the battery pack of the Power Module Type 12HF
Dieses Handbuch passt für folgende Modelle
4
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