Casella CEL Airborne particulate monitoring system - Manual (Page 42)

HB3256-03 Page 40
C
ALIBRATION
Calibration check.
The APM950 uses an optical measurement technique and must be routinely calibrated to ensure
accurate and reliable performance.
Allow the system to operate for 30 minutes and stabilise.
Firstly check the instruments zero using the following procedure.
Zero Check.
Whilst the APM950 system performs an automatic zero check every hour, it is possible to trim
the zero dust signal level to counteract the effects of long term drift. The probe signal voltage
may be measured using the 'Special' -'Test' option within the APM950 operating software.
The probes zero output signal level should be checked every 6 -12 months. Carefully remove the
optical sampling probe from the sampling line. This is achieved by removing the filter holder
and sliding the support assembly downwards (after loosening the two retaining wing nuts).
Slide the cover over the sample chamber aperture. Using the APM software, check the probe
voltage is less than ±50mV. If necessary adjust the zero control located adjacent to the analogue
output socket on the signal processing unit.
Span.
The span adjustment is used to equate the instruments real time response to that obtained by
gravimetric results. The span adjustment procedure is detailed within the software section of this
manual.
Filter body assembly.
To remove the complete filter holder assembly, first disconnect the suction tube from the
underside and then pull down from the optical sensor support block while gently rotating against
the o-ring friction.
To remove the filter holder assembly 03-153050A it is only necessary to unscrew the locking
ring, the filter holder assembly can then be lifted from the lower body.