Calibration and Verification
45CA-1 and 45CA-2
Before calibration, the microphone and preamplifier must be removed from the 45CA. To get a
good hold on the microphone, cover plate and insert must be removed.
45CA-1 - with 1” microphone
1.
Remove the GR1085 cover plate. Remove the four bolts using the 2 mm Allen key.
2.
Remove the GR0970 Insert by loosening the screw at the bottom and pulling it out.
3.
Using the 2,5 mm Allen key, loosen the two grub screws at the side of the head.
1.89 mm
Insert
GR0970
Grub screws for holding the
microphone in position.
Use Allen key, 2.5 mm, YY0016
Fig. 10.
The microphone can be removed for calibration when the insert and cover plate have been re
-
moved. When reinstalled, it must be located precisely as shown, protruding 1,89 mm at the horizontal center
line.
4.
Pull out the microphone.
You are now ready to calibrate. The GRAS RA0023 Coupler for 1” microphones must be used, it is
included with the 42AP and an optional accessory for 42AA.
The correction factor is 0.0 dB, and therefore you analyzer should read 114 dB +/- correction for
the static ambient pressure.
Refer to your pistonphone manual for detailed calibration instruc
-
tions.
Instruction Manual
2 4 | GRAS 45CA Headphone/Hearing-protector Test Fixture