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Summary of Contents for G.R.A.S. 12HM
- Page 1 G R A S SOUND & VIBRATION Skovlytoften 33, 2840 Holte, Denmark www.gras.dk gras@gras.dk...
- Page 2 Power Module Type 12HM Revision 05 12 2012...
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Page 3: Table Of Contents
G.R.A.S. Sound & Vibration CONTENTS Introduction and Description ........3 Polarization Voltage . -
Page 4: Introduction And Description
With these, sound-power measurents of low-noise products, such as disk drives, can be made under anechoic and/or semi-anechoic conditions according to IEC 3745:1977. The Type 12HM provides: • polarization voltages (200 V) for 10 condenser microphones • voltage supplies (± 15 V) for powering 10 microphone preamplifiers • individual response setting, Pressure or Free field, for each channel • individual gain adjustment of ± 3 dB for each channel Polarization Voltage Polarization voltages of 200 V are supplied via the 7-pin LEMO EGA 307 1B sockets on the front panel. 1.2 Preamplifier Voltage Supplies Preamplifier voltage supplies of ±15 V are supplied via the 7-pin LEMO EGA 307 1B sockets on the front panel. Input/Output Each channel of the Type 12HM has a 7-pin LEMO EGA 307 1B input socket for the G.R.A.S. microphone preamplifiers mentioned above, viz. Types 26HF, and 26HH. Fig. 2.3 shows the wiring diagram of this input socket. The output of each channel is available via a standard BNC socket for direct use with analyzers, voltmeters, oscilloscopes etc. Fig. 1.1 Power Module Type 12HM Power Module Type 12HM - Page 4... -
Page 5: Power Supply
G.R.A.S. Sound & Vibration Power Supply The Type 12HM can run from a nominal mains/line supply of either: • 115 V AC or • 230 V AC A voltage tap is provided on the rear panel for selecting one or the other. On delivery, it is set to 230 V AC. Power Module Type 12HM - Page 5... -
Page 6: External Features
For selecting a frequency response corresponding to either pressure-microphone opera- tion or free-field microphone operation: Pressure - to select the output of the compensating filter (in the preamplifier) which gives the system a linear pressure-frequency response. Free Field - to select the output of the compensating filter (in the preamplifier) which gives the system a linear free-field frequency response at 0 ° incidence. Overload warning LED • Lights instantaneously and only while there is an overload; synchronised with the one on the preamplifier (Type 26HF or Type 26HH). • Level Adjustment switch and potentiometer On - enables the level-adjustment potentiometer; use a small screwdriver on the potenti- ometer to adjust the gain in signal level (± 3 dB) Off - disables the level-adjustment potentiometer. In either case, the signal level will already have been raised by 20 dB by the preamplifier to yield a nominal system sensitivity of: • 1.1 V/Pa with the 1-inch preamplifier and microphone, or • 0.9 V/Pa with the ½-inch preamplifier and microphone • Preamplifier Input 7-pin LEMO EGA 307 1B input socket for microphone preamplifier. Wiring diagram shown in Fig. 2.3 Ouput • BNC socket for the output signal either via signal conditioning or directly from the micro- phone preamplifier. Power Module Type 12HM - Page 6... -
Page 7: Rear Panel
Level adjustment potenti- ometer; enabled when level adjustment is switched On Overload LED (instantaneous) Preamplifier input Output Fig. 2.2 Front-panel details for each channel of the Power Module Type 12HM Fig. 2.3 7-pin LEMO EGA 307 1B input socket (exter- nal view) Rear Panel The rear panel has the following features (see Fig. 2.4) • AC Mains 50 - 60 Hz, 35 VA Input socket for mains/line AC power supply. Centre pin is earth/ground. - Page 8 G.R.A.S. Sound & Vibration AC Mains/line input socket 50 - 60 Hz 35 VA Mains Voltage Selector: 230 V AC or Pull-out fuse box, for 2 fuses, 115 V AC 1 active (innermost); 1 spare Fig. 2.4 Rear panel of the Power Module Type 12HM Power Module Type 12HM - Page 8...
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Page 9: Operation
• 1.1 V/Pa with the 1-inch preamplifier and microphone, or • 0.9 V/Pa with the ½-inch preamplifier and microphone Correspondingly (if Level Adjust is swithched Off - see Fig. 2.2), when the measured RMS output voltage from the channel is 1.1 V or 0.9 V, the microphone in question is being subjected to 94 dB re. 20 μPa. Based on this information, proceed as follows: Connect the channel output to the analyzer to be used and switch both units on. Adjust the analyzer to indicate 94 dB re. 20 μPa for an RMS input of S volts; where S is the sensitivity (1.1 V/Pa or 0.9 V/Pa, see above) of the channel in question. 3.2.2 Pistonphone A G.R.A.S. Pistonphone Type 42AA fitted with a G.R.A.S. Coupler RA0090 can be used to pro- duce 94 dB re. 20 μPa on a microphone. Note: a Pistonphone fitted with a normal 1-inch coupler (RA0023) cannot be used because this will overload the channel with a level of 114 dB re. 20 μPa. Proceed as follows: Connect the channel output to the analyzer to be used and switch both units on. Unscrew and remove the normal coupler of the Pistonphone. Screw the Coupler RA0090 to the Pistonphone, see Fig. 3.1. Insert the microphone of the channel in question in the Coupler as shown in Fig. 3.2 and switch the Pistonphone on. Note: for a ½-inch microphone, use the adapter GR0619 sup- plied with the Coupler RA0090. Adjust the analyzer to indicate 94 dB re. 20 μPa. Measurements Connect the preamplifier (with microphone) to the LEMO EGA input of the channel in ques- tion. Connect the output from the channel to an analyzer Power Module Type 12HM - Page 9... - Page 10 G.R.A.S. Sound & Vibration Switch on both units Calibrate the set up via one of the methods described in section 3.2. Select which microphone operation to use via the switch on the front panel marked Pres- sure / Free Field (see Fig. 2.2). At this point you can make your measurements but keep an eye on the relevant overload warn- ing LEDs (one on the front panel for each channel and one on the preamplifier) to avoid over- loading the system and invalidating the measurements. Fig. 3.1 Pistonphone without its normal coupler and ready to accept the Coupler RA0090 Fig. 3.2 Pistonphone fitted with Coupler RA0090 and the microphone inserted into the Coupler Power Module Type 12HM - Page 10...
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Page 11: Service And Repair
G.R.A.S. Sound & Vibration Service and Repair Repairs should be carried out only by qualified personal. The Power Module Type 12HM should not be dismantled with power on because of high-voltage circuits. Power Module Type 12HM - Page 11... -
Page 12: Specifications
Microphone: 90 mV/Pa Microphone polarization voltage: 200 V Channel separation: 20 Hz - 20 kHz: >90 dB Output impedance: 30 Ω Output voltage: Max: ±10V Power supply: Mains/line: 115 V or 230 V AC (nominal) Power consumption: With 10 G.R.A.S preamplifiers 35 VA Fuse: 315 mA (Slow) for 115 V AC mains/line supply, or 160 mA (Slow) for 230 V AC mains/line supply Operating temperature range: -10 °C to +50 °C Power Module Type 12HM - Page 12... - Page 13 G.R.A.S. Sound & Vibration Dimensions: Height: 132.6 mm (5¼ in) Width: 420.0 mm (16½ in) Depth: 196.0 mm (7.7 in) Weight: 5.5 kg (12.1 lbs) Accessories included: Mains/line cable Accessories available: Type 26HF 1-inch preamplifier Type 40EH 1-inch microphone Type 26HH ½-inch preamplifier Type 40AH ½-inch microphone Manufactured to conform with: CE marking directive: 93/68/EEC WEEE directive: 2002/96/EC RoHS directive: 2002/95/EC Power Module Type 12HM - Page 13...