Casella CEL CEL-440 - Manual (Page 22)

It is recommended that an acoustic calibration check
be performed both before and after a measurement run.
Perform the calibration check on the sound level meter using a
CEL-284/2 (Class 1) Calibrator for instruments with Type 1 accuracy and
a CEL-282 (Class 2) for Type 2 instruments. These calibrators provide a
nominal level of 114.0 dB at 1 kHz. However, the exact value to which
the instrument must be calibrated will depend on the microphone type in
use, the microphone response and local atmospheric conditions.
DO NOT remove the protective metal grid from
Type 1 microphones.
With a Type 1
instrument (i.e. 1/2"
microphone), fit the
CEL-284/2 Calibrator
directly on to the
microphone, making sure it
is pushed firmly into
contact with the shoulder in
the calibrator cavity
(Figure 5).
With a Type 2
instrument (i.e. 1/4"
microphone), fit the
CEL-4725 Coupler, supplied
with the calibrator, into the
cavity of the CEL-282 (or CEL-284/2) Calibrator making sure it is pushed
firmly into contact with the shoulder in the calibrator cavity (Figure 5).
Then fit the calibrator complete with coupler on to the instrument
microphone, again ensuring that it is pushed firmly into contact with the
shoulder in the coupler cavity.
DO NOT lay the sound level meter and calibrator on a
horizontal surface during calibration, as the combined
weight will cause the microphone to move inside the
calibrator cavity and produce an incorrect level.
Support the sound level meter and calibrator in an upright
position. To aid removal, the coupler flange does not fit tightly against
the calibrator housing.
Calibrator
Boss
980017
1/4" Microphone &
Preamplifier Unit
'O' Ring
Shoulder
1/2"
Microphone
Microphone
Coupler
Figure 5: Fitting the acoustic calibrator
Page 22 - CEL-440/480 Operators Handbook
Preliminary Operations