6
LI0055 – Revision 25 June 2012
Calibration and Verification
Note
: For complete calibration information, see the pistonphone instruction manual. The
instructions here explain the specific details related to the 67AX.
G.R.A.S. recommends calibration prior to each use to ensure the accuracy of your
measurements. Verification is performed in situations where you need to check that the
microphone is functioning in its setup and cannot check it properly in the laboratory.
Important
: The pistonphone calibration adapter and the pistonphone field-verification
adapter are designed for use with a 250 Hz pistonphone, such as the G.R.A.S. 42AP
Pistonphone. Do not use them with any other calibrator or verification device. The
250 Hz pistonphone can be used for both calibration and daily verifications.
Calibrating the microphone
To calibrate the microphone in the 67AX, remove it from the mounting plate.
1. Set the pistonphone in an upright position, preferably using a calibration stand
for stability.
2. Mount the pistonphone calibration adapter (RA0221) on the pistonphone.
3. Insert the microphone into the adapter on the pistonphone. Press gently to
ensure that the microphone is inserted as far as it can go.
4. Turn on the pistonphone and calibrate as described in the instruction manual for
the pistonphone.
Verifying the microphone
1. Mount the field-verification adapter (RA0216) onto the pistonphone.
2. Hold the pistonphone steady while centering the opening in the adapter over the
microphone.
3. Gently press the pistonphone with adapter over the microphone, ensuring that
the microphone is as far in the pistonphone as it will go.
Note
: Due to the setup conditions for the microphone, you may not be able to hold the
pistonphone steady. As a result, measurements may not be ideal and cannot be used
for calibration purposes. These measurements can only be used for verifying that the
measurement chain and the microphone especially is functioning as expected.
Important
: When performing verification in the field on a microphone with the grid
removed, be extremely cautious during measurements. The membrane is vulnerable
without the grid and can be easily damaged.
