CESVA CB004, User Manual

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3. OPERATION
3.1. Checking method
1) Insert the instrument into the calibrator, introducing the microphone into the checking
cavity. Make sure the microphone reaches the bottom of the cavity and is parallel to the
calibrator axis. This may require a little effort since the sound level meter must fit exactly
into the calibrator. Insert the instrument gently; otherwise you might damage the
microphone. Also ensure that the small bleed-hole next to the microphone cavity is not
blocked as this could cause damage to the microphone.
2) Turn on the calibrator by pressing the power button (1). The indicator will illuminate to
show that the unit is operating.
3) Wait until the sound pressure level generated by the calibrator is stabilized, typically 3
seconds.
4) Turn on the instrument to be checked. Where applicable, adjust the sensitivity of the
instrument to obtain a correct reading of the effective checking level, (level generated by
the cali correction factors).
5) The effective checking level is obtained by correcting the level generated by the
calibrator (94 dB) with the following factor:
a. Pressure to free field correction of the microphone at 1 kHz factor: This factor
must be applied when the instrument to be checked is designed to measure in
free field. It is not necessary for instruments designed for measuring in a
pressure field. This factor is equal to changing the sign to the pressure to free
field correction at 1k Hz that is indicated in the user’s manual of the instrument.
The following table shows the factors to apply to some
microphones
and for two microphones commonly used in laboratory tests.