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

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. [phone] Fax [phone]
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 PreamplierType26HG .............................................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. Specications ..................................................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.
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

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)
andconsistsof:
• ½-inchLow-noiseLevelMicrophoneSystemType40HT.
• PowerModuleType12HF.
Note:thepowermodulemustbeorderedseparatelyandthetripodandtripodadapterare
optionalextras.
1.1 Microphone Type 40AH
TheType40AHisaspecialhigh-sensitive½-inchmicrophone.Itisexternallypolarizedwith
aspeciallyreducedinherentnoiseoorinordertoachieveahighdynamicrangeandwide
frequencyrange.
1.2 Gain and Filter Unit Type 26HT
ThebodyoftheUnithasanoverload-warningLED,(Fig.1.1),whichisrepeatedonthefront
panel of the chosen power module (see Fig. 2.1).
Thesignalofthemicrophoneisampliedby20dBintheGainandFilterUnitType26HT.
Thetwocompensationltersgivethesystemtwoparalleloutputswhichcorrespondto:
a) linearpressure-frequencyresponse.
b) linearfree-eldfrequencyresponseatanangleof0°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
Thechoiceofwhichfrequencyresponsetouseismadeviaatwo-positionswitchmarkedPres-
sure / Free Field on the front panel of the chosen power module (see Fig. 2.1).
Fig.1.4showstheresponsesofthetwocompensationltersaswellasthefree-eldresponse
for0°incidence.Note:free-eldcorrectionsareaddedtothelowestcurve.
Fig.1.5showswhatthesefree-eldcorrectionsareforvariousanglesofincidence.
Fig.1.6shows,foracompletelow-noisemeasuringsystem,atypicalnoiseoorin⅓-octave
bands for both the linear and A-weighted cases.
1.3 PreamplierType26HG
SimilartothestandardG.R.A.S.Type26ACbutwith40GΩinputimpedancetoenablelow-level
andlow-frequencynoisemeasurements.
Thepreamplierhasanintegrated3metrelightweightcableterminatingina7-pinLEMOcon-
nector (which plugs in to the Gain and Filter Unit Type 26HT).
A¼”to½”adapter,GR0010,isincluded,sothatitcanalsobeusedwithG.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
Decibelsre.levelat250Hz
- 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
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. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HT and Type 12HF - Page 9
• 7-pinLEMOEGA3071BinputsocketfortheLEMOplugonthecableoftheGainand
Filter Unit Type 26HT. Wiring diagram shown in Fig. 2.2.
• BNCoutputsocketfortheselected(Pressure / Free Field) output signal.
2.2 Rear Panel
The rear panel has the following features (see Fig. 2.3)
• Twist/releaseholderfor315mAfast-blowfuse.
• Inputsocketforanexternalvoltagesupplyof6V-20VDC;centrepin+terminal.Usethe
Mains/line Adapter AB0010 supplied with the Type 12HF.
• Lockingscrew
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
Inputforexternal
Power Supply
6V-20VDC
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
Togainaccesstothebatterypack,unscrewthelockingscrewontherearpanel(Fig.2.3)and
slide the base plate off towards the rear. Pull out the battery pack See Fig. 2.4.
Thebatterypackconsistofabatteryholderand4xLR14(C)standardalkalinecells.When
replacingthebatteries,replaceallofthemmakingsurethatthepolarityisasindicatedonthe
battery holder.
Fig. 2.4 Showing the battery pack of the Power Module Type 12HF

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Sis 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. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HT and Type 12HF - Page 12
Fig. 3.2 Pistonphone tted with Coupler RA0090 and the microphone
inserted into the Coupler
6. Mount the microphone of the Type 40HT in the Coupler as shown in Fig. 3.2 and switch the
Pistonphone on.
7. Adjusttheanalysertoindicate94dB*re.20μPa.
3.2 Measurements
1. Assemble the system as shown in Fig. 1.3.
2. Connect the output from the Power Module to an analyser.
3. Switch both Power Module and analyser on.
4. Calibrate the set up via one of the methods described in section 3.1.
5. Select which microphone operation to use via the switch on the front panel of the Type
12HF marked Pressure / Free Field.
AtthispointyoucanmakeyourmeasurementsbutkeepaneyeontheoverloadwarningLEDs
to avoid overloading the system and invalidating the measurements.
* Plus any corrections for barometric pressure. See pistonphone manual.

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HT and Type 12HF - Page 13
4. Specications
4.1 ½-inch Low-noise Microphone System Type 40HT
Low-noise Microphone System Type 40HT comprising:
½-inchMicrophone: Type40AH
Preamplier:  Type26HH(with3mcableandLEMOFGA.1B.307plug)
Frequency response:
12.5 Hz - 10 kHz ±1.0 dB
10Hz-16kHz:  ±2.0dB
6Hz-20kHz:  +2.0dB,–3.0dB
Nominal sensitivity:
System:   800mV/Pa±2dB
Microphone polarization voltage:
200 V
Dynamic range:
Upperlimit:  113dBre.20µPa
Lowerlimit:  6.5dBAre.20µPa(inherentnoise)
Microphone capacitance:
20 pF
4.2 Single-channel Power module Type 12HF (separate order)
Input channel:
7-pinLEMOEGA1Bconnector
Outputs channel:
BNC socket
Output impedance:
30Ω
Polarization voltage:
200 V
Power supply:
internal:  6Vfrom4xLR14(C)standardalkalinecells
external:  6V-20VDCviaincludedMainsAdapterAB0010
Dimensions:
height:  132.6mm(5¼in)
width:  34.6mm(1.3in)
depth:  196.0mm(7.7in)

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HT and Type 12HF - Page 14
Weight:
620 g (1.3 lbs)
Accessories included:
Batteries:   4xLR14(C)standardalkalinecells
Mains/lineAdapter:  AB0010
4.3 Common
Temperature range:
    –20°Cto+60°C
Accessories available:
Powermodule(1ch.): Type12HF
Powermodule(10ch.): Type12HM
Windscreens(setof5): AM0069
Pistonphone:  Type42AA
PistonphoneCoupler: RA0090(for94dBre.20µPa)
Tripod:   AL0006
TripodAdapter:  RA0096
3mExt.cable:  AA0046
10mExt.cable:  AA0047
30mExt.cable:  AA0048
WEEEdirective:
2002/96/EC
CEmarkingdirective:
93/68/EEC
Manufacturedtoconformwith:
RoHSdirective:
2002/95/EC