Casella CEL CEL-269 - Manual (Page 4)

FIELD ACCURACY CHECK
(ACOUSTIC CALIBRATION)
Perform a field accuracy check (acoustic
calibration) using a CEL-282 or CEL-284/2
Acoustical Calibrator immediately before and after
measurements are made as follows.
1. Remove the microphone cover.
2. Fit the CEL-4725 Microphone Coupler on to
the calibrator.
3. Push the calibrator and coupler on to the
microphone, with the label at the top as
shown.
4. Slide the RANGE switch to A HI (high range).
5. Slide the RESPONSE switch to F (fast) to
switch the instrument on.
6. Wait approximately 20 s for the instrument to
stabilise.
The software version number will be indicated
at the start of this period, then the micropro-
cessor performs a series of test routines after
which the instrument is ready for use.
It always starts with sound pressure (S PL )
measurement selected, which is the mode
used for calibration.
When is displayed, the batteries should be
changed. The battery voltage can be shown on
the display by pressing the MODE button
several times until B ATT is indicated.
7. Press the bottom of the calibrator switch to
obtain 114 dB at 1 kHz.
Early units had to be set to the 114.0 dB
calibration level. However, due to minor
changes in the ¼" microphone assembly, the
calibration level for later units is 113.6 dB.
If this instrument has a serial number XX6XXX...
or higher, or a replacement CEL ¼"microphone
supplied after 1-1-96, use the 113.6 dB level.
8. If necessary, carefully adjust the CAL control
with the screwdriver provided until the
indication is correct.
The CAL control uses 4 turns to give 12 dB of
adjustment.
9. Switch the calibrator OFF, when not in use.
Other calibrators may be used, but the correct
indication will depend upon the volume of the
acoustic coupler used, the operating frequency,
and the calibration level. Pistonphones operating
at 250 Hz may be used, however the instrument
must be switched to C-weighted operation. It is
recommended that the calibration be verified at at
least every year. Contact the CASELLA CEL
Service Department at Bedford for details.
OPERATION
1. Insert batteries as described above.
2. Calibrate the instrument.
3. Switch the calibrator OFF.
4. Remove the calibrator and microphone coupler.
5. Hold the instrument comfortably in the hand
and point the microphone at the suspected
noise source.
6. Range Selection
Select A HI or C HI (high) ranges.
These ranges cover sound levels between 65
and 135 dB.
Select A LO or C LO (low) ranges when the
indicated sound level falls below 80 dB. A
constant reading of 65 dB may also indicate
that LO range should be selected.
If is indicated during a measurement, select
one of the HI ranges.
If is indicated during a measurement, select
one of the LO ranges.
7. Mode Selection
S PL (sound pressure level) mode is selected
automatically when the test routines are
completed. In this mode the current sound
pressure levels are displayed with a resolution
of 0.1 dB, and updated every half second.
If S
PL
is not being indicated, or another mea-
surement mode is required, press the MODE
button several times to cycle the instrument
through the measuring modes until the
relevant mode is displayed.
When M AX (Maximum Hold) mode is chosen,
The instrument captures and holds the
maximum noise levels for long periods using
ANY of the time weightings and ranges.
Press the RESET button to clear the M AX
display for the next measurement.