Casella CEL CEL-414 - Manual (Page 24)

CEL-192, CEL-250 or CEL-230 are
used. (The display should read 94 dB
when an MK-301 is fitted.)
The calibration of the instrument may
have changed, for example due to
the use of an extension cable, or
because of variations in the ambient
conditions. For altitude and environ-
mental information refer to the
calibrator ins truction sheet.
8. If necessary, using the trimtool pro-
vided to avoid damage, carefully
adjust the CAL control, accessed via
the small hole at the top of the
switch panel, until the displayed
sound level is 114.0 dB (or 94 dB
when an MK-301 is fitted).
This control is a multi-turn potentio-
meter, with 5 turns giving an adjust-
ment range of approximately 15 dB.
Rotate the control clockwise to
increase the indication.
Other calibrators may be used with
these sound level meters, but the
correct display indication will depend
upon the volume of any acoustic
coupler used, operating frequency,
and calibration level.
If a pistonphone such as the RFT
05 001 is used, set the A-L-FA-FL/
A-C-FA-FL switch to L (Linear
response) on A, B and CEL-493/3, or
C-response on C, D & E versions, or
to FL (Linear plus filter) when an
external filter set is used (and set
the filter to All Pass).
This prevents incorrect levels from
being displayed, which would occur
if the low frequencies produced by a
pistonphone were measured with
an A-weighted circuit.
When an external filter set is used, it
is also good practice to make a field
accuracy check (perform an acoustic
calibration) of the sound level meter
both alone, and with the filter set, to
isolate any faults.
9. When finished, switch the calibrator
OFF, and carefully remove it (and
the coupler) from the microphone.
Many measurement protocols require
laboratory verification of the complete
measuring system. It is recommended
that such verification be performed at in-
tervals between one and two years. Full
details are available from your local CEL
Agent, or from the CEL Service Depart-
ment at Hitchin.
These instruments have a wide range of
measurement applications. Their design
is particularly suited to the measurement
procedures specified in the following
standards (and their international and na-
tional equivalents).
BS 3425 Motor Vehicle Pass By
Noise Tests,
BS 4142 Industrial Noise Impact
on Residential Areas,
BS 5228 Construction Site Noise
Measurement,
BS 5330 Assessment of Industrial
Deafness Risk.
The instruments may also be used for the
measurement methods and codes of
6. OPERATION
Page 20 - General CEL Sound Level Meters Handbook