Casella CEL Airborne particulate monitoring system - Manual (Page 46)

HB3256-03 Page 44
Probe Calibration.
The probe is factory calibrated against a known dust (Arizona road dust) using wind tunnel
facilities.
An optical filter is provided with the system and is used to generate a stable reference signal
from the probe. The signal processing circuitry may be adjusted to display the reading obtained
during factory calibration. If gravimetric results have been used to determine local conditions, it
is possible to apply a correction factor to the filter's reference value.
By equating a real time data set to a corresponding gravimetric result, it is possible to optimise
overall measurement accuracy to suit local measurement conditions.
Zero adjustments.
The signal processing circuitry may be zeroed using the procedure detailed in the 'Operation'
section of this manual.
Span adjustment.
The instrument span is set during factory calibration.
Adjustments will be necessary if re-calibration to a different dust composition is required.
To check the factory setting.
Turn the instrument on and allow approximately five minutes warm up time.
following the 'Zero' check, remove the probe from heater assembly as described in servicing
section of this handbook. Insert the calibration filter into the probes measurement chamber
ensuring the arrow points towards the probe handle. Adjust the span potentiometer until the
control unit display corresponds with the filter value.
To use gravimetrically corrected filter value.
The P.C. software provides a span correction value based upon comparison of real time and
gravimetric results. This is explained within the software section of the manual.