7
LI0196 – 19 July 2017
Using the 42AG
Microphone Calibration
Adapter Selection
From the factory, the 42AG has a 1” calibration coupler mounted with an adapter for the 1/2”
microphone typically used with Sound Level Meters.
If you are going to calibrate a 1” microphone, remove the 1/2” adapter. For 1/4” and 1/8”
microphones, mount the appropriate adapter, RA0049 or RA0069. These are included in the
delivery.
Calibration
The microphone must be placed in the acoustic coupler of the calibrator before the calibrator is
switched ON
.
If you are going to calibrate a sound level meter, turn it on and let it stabilize before
calibration. At least three minutes are required.
1. Place the microphone to be calibrated in the coupler of the calibrator. Use a suitable adapter, if
necessary.
Use a slow movement, since a fast movement may create an excessive pressure which
temporarily may change the sensitivity of the microphone. Wait a few seconds for the pressure
equalization to stabilize.
2. Press
. Wait for the LED above the
dB
button to change from red to green.
The level and frequency is indicated in the display of the calibrator. After powering the sound
calibrator, the first combination of frequency level is 94 dB re. 20µPa and 1 kHz. Select the
appropriate level and frequency for your calibration by pressing
dB
or
Hz
, respectively.
Normally the background level should be more than 20 dB lower than the level from the
calibrator in order to not influence the reading. Therefore it is considered good practice to
notice the indicated sound level before the sound calibrator is switched on.
3. Press
Hz
to switch frequency. Press
dB
to switch level.
4. Press the
Met
to display the environmental conditions: air pressure, temperature and humidity.
The temperature and humidity is measured in the acoustic coupler. Note that due to heat
generated by the calibrator’s electronics the temperature may rise above the ambient condition
after longer time of operation (typically one degree ˚C) affecting both the temperature and the
humidity indication.
It is therefore considered good practice to measure the conditions shortly after powering the
unit. The temperature may be displayed in centigrade (Celsius) or in degree Fahrenheit. The
rising temperature does not affect 42AG's output.
5. Press
Met
again for returning to the sound calibrator mode.
