Casella CEL CEL-393 - Manual (Page 84)

To ensure accurate calibration using the pistonphone, it is important that
the following procedure be followed, otherwise significant errors may be
introduced into the system. These instructions assume that the piston-
phone produces a nominal level of 124dB, although there are some
devices available that generate 114dB.
Switch the CEL-393 ON and allow it to reach its correct operating
conditions, checking that the battery voltage is adequate in the process.
Select the 70dB range (7R), fast time constant (F), linear frequency
weighting (L) with filters switched off, and the SPL display mode (F key).
Place the 13.2mm coupler supplied with the pistonphone over the
microphone, ensuring that it fully bottoms against the shoulder in the
coupler.
Offer the pistonphone cavity up to the microphone and coupler assembly,
ensuring once again that the microphone remains correctly in the coupler
and that it in turn is accurately seated in the calibration cavity.
Caution
Do not allow the weight of the pistonphone to hang
on to either the microphone or preamplifier assem-
blies.
The sound level meter and pistonphone assembly should be placed upon
a suitable table or flat surface (free from significant shock or vibration)
to avoid putting undue stress on to the CEL-393 preamplifier connector.
Switch the pistonphone ON, checking that its batteries are serviceable
in accordance with its instructions. Return the pistonphone to its calibra-
tion mode and note the reading on the CEL-393.
The nominal calibration level for the pistonphone is 124dB, but this varies
from unit to unit, the exact level being noted on the calibration certificate
supplied with each pistonphone. This calibration level needs to be
/80. 393 Handbook