Casella CEL CEL-450 - Manual (Page 37)

4. ACOUSTIC CALIBRATION CHECK
4.1 Start Acoustic Calibration Check
It is recommended that a calibration check of the microphone be made
both before and after a measurement run. A record of the last calibration
before the run and the first calibration after the run are stored. This gives
the confidence that the microphone remained calibrated throughout the
measurement period.
In addition to storing a “before” and “after” calibration with
every measurement, the instrument saves the last four calibrations,
which can be viewed on the instrument screen.
At the end of a calibration check, the user is offered the option of
saving the new calibration, or not saving it and reverting to the previous
calibration.
If any runs have been completed since the the previous
calibration, ensure that only a calibration with the correct level be saved,
as this calibration will be saved as the first calibration after a run and
once stored it cannot be changed. Saving a new calibration will also
calibrate the “next” measurement. However, the user always has the
option of performing another calibration immediately before any future
run is started.
The calibration level indicated by the instrument will depend on
the microphone response set. Therefore, an acoustic calibration check
should be performed only when the microphone response is correct for
the required task. When the calibration is known to be acceptable, press
once to obtain a Measurement screen or twice to obtain the Main
menu that gives access to all settings and stored data.
It is recommended that an acoustic calibration check
be performed both BEFORE and AFTER a measurement run.
Perform the calibration check using a CEL-110/1 (or 284/2)
Class 1 Calibrator for sound level meters with Class 1 accuracy (WS2)
and a CEL-110/2C (or CEL-282) Class 2 Calibrator for Class 2 instruments
(WS3). All of these calibrators provide a nominal level of 114.0 dB at 1
kHz, while the CEL-110/1 can also supply a calibration level of 94 dB.
However, the exact value to which the instrument must be calibrated
will depend on the microphone type in use, its response and the local
atmospheric conditions.
CEL-450/490 Operators Handbook - Page 37
Acoustic Calibration Check