Casella CEL CEL-281 - Manual (Page 128)

pressure, the CEL calibrators generates a nominal 1 kHz signal
with a level of 114.0 dB at the microphone. The dosimeter dis-
play should indicate 114.0 dB (A) in the following format:
: dBA
However, with a replacement microphone, the level may well
be several dB different, so that the digital section of the instru-
ment must be re-trimmed before an accurate calibration can be
achieved.
16. Use the and keys to change the display so that the
trimming range of the microphone can be determined.
These keys give +0.05 dB or -0.05 dB increments respectively,
over a total correction range of
±2 dB. However as the display
resolution is 0.1 dB, two key presses are needed to produce an
observable change in the displayed value. In calibration mode
these keys have an automatic repeat function when held down.
For example, these keys may be found to change the display
from 115.3 to 119.3 dB.
17. Use the and keys to set the display in the exact
centre of this range.
117.3 dB in the example.
The digital section has now been trimmed for the replacement
microphone.
Caution
DO NOT touch the prominently positioned
potentiometer located beside the display on
the upper circuit board
Technical Information
CEL-281 Operator's Handbook - Page 119