G.R.A.S. Sound & Vibration
Power Module Type 12HM - Page 6
2.
External Features
2.1
Front Panel
2.1.1 Power Switch
See Fig. 2.1.
•
Power On
LED (green)
The green LED lights up whenever the unit is switched on via the On/Off (
I
/
0
) toggle
switch.
•
Mains/line toggle switch On/Off (
I
/
0
)
For mains/line AC supply.
Power On
LED illuminated when power is switched on.
Fig. 2.1 On/Off (
I/0
)switch on front panel
2.1.2 Channel Details
Front-panel details for each channel are as shown in Fig. 2.2.
•
Pressure
or
Free field
switch
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 Adjust
ment 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.
Mains/line On/Off
toggle switch
Power on
LED (green)
