Casella CEL Microdust Pro real time dust monitor - Manual (Page 26)

MicroDust Pro Aerosol Monitoring System
26 Casella CEL
The MicroDust Pro instrument’s use of a narrow forward scattering angle
minimises these effects, but for optimal accuracy when measuring a specific
particulate type, you should perform gravimetric calibration.
Optional gravimetric and respirable adapters incorporate 25 mm or 37 mm
filter cassettes and provide a convenient method of gravimetrically calibrating
the MicroDust Pro instrument. Refer to section 6.1 “
Gravimetric adapters ” on
page 37 for information about these adapters.
Standard gravimetric techniques can be used to provide a cross-check between
readings of the MicroDust Pro and a weighed example. This is achieved by
collecting two average measurements over the exposure period – one from the
filter (the gravimetric value) and the other from the instrument’s averaging
function. If there are differences between the gravimetric value and the
instrument’s reading, a user-defined correction factor can be entered for the
relevant particulate type. This correction factor can then be applied
automatically to any measured values to provide optimal measurement
accuracy.
Calibration procedure
During the calibration, you must use the MicroDust Pro instrument’s logging
feature to record the particulate concentration measured by the instrument.
1. Adjust the instrument’s zero and span settings as described in
“ Adjusting the zero and span settings ” on page 23.
This returns the instrument to the default calibration set by the factory
so that all user-defined calibrations are relative to this setting. This is an
absolute calibration that is not affected by changes to the correction
factor.
2. Fit the gravimetric or respirable adapter onto the instrument’s probe
and load a pre-weighted filter into the cassette holder.
See section 6.1 “
Gravimetric adapters ” on page 37 for a description of
the optional gravimetric or respirable adapters.
3. Adjust the sampling pump to provide the appropriate flow rate.
• The respirable adapter requires a flow rate 0f 2.2 litres/minute.
• For isokinetic sampling, the flow rate is calculated from the
sample velocity and cross-sectional area of the gravimetric inlet
tube (200 mm²).
• For general Total Suspended Particulate (TSP) measurements,
the actual flow rate is not critical, but will affect the mass of the