Casella CEL Microdust 880 IS real time dust monitor - Manual (Page 15)

Microdust 880nm & WinDust Application Software
Handbook HB3255-03
Page 15 of 51
In Microdust models incorporating the optional logger facility, the internal clock will be
automatically programmed using the P.Cs time and date. (please refer to logger section for more
details)
Making dust measurements
The display is a 2 line alpha-numeric L.C.D. with the readings updated every second. The position of
the decimal point indicates the working range. If the instrument ‘over ranges’ due to a high dust
concentration, readings will be limited to the ranges full scale value (ie, 2.5, 25, 250 mg/m3 etc).
Checking the instruments calibration - Zero and Span
Before making any dust measurements it is necessary to confirm that the instrument is correctly
zeroed and that its span control (sensitivity) is correctly adjusted.
Adjusting the ‘Zero’ control
From the ‘Configuration’ menu, ensure that the instruments ‘Range’ is set to either ‘Automatic’ or
‘Low’. It is generally easier and quicker’ to perform zero adjustments whilst the ‘Averaging
period’ is set for 1 second.
Slide the probe collar over the inlet to the measurement chamber leaving only a small hole from
which the purge air can vent. Attach the hand pump to one of the probes purge inlets (Please refer to
Probe diagram on page 50) and rapidly squeeze the bulb 5-6 times on each inlet position. This action
will inject clean air into the sample chamber and will remove possible contamination which may
have settled on the surface of optical components within the probe. The user will normally see the
indicated concentration increase and then decrease towards zero.
Ensure that the rubber cap is fitted to one of the purge inlets whilst the other inlet is in use, otherwise
any dislodged dust particles will move to the opposite end of the probe instead of being expelled
through the measurement chamber.
After allowing sufficient settling time for the display to stabilise, adjust the ‘Zero’ control (located
on the top panel) using the screw driver provided such that the display indicates zero + 1 digit.
Clockwise rotation of the potentiometer will increase the displayed value.
Ensure that both rubber caps are re-fitted to the purge inlets.
Note: The purge inlet marked with a single dot identifies the emitter lens (handle end). Purging
of this inlet generally has the most influence on achieving a successful zero adjustment.
For sensitive instrument versions operating on the 0-2.5 and 0-25mg/m
3
ranges, it is important to
purge the probe with clean air prior to checking or performing any zero adjustments. Fine dust