Casella CEL Airborne particulate monitor (AMS950-IS) - Manual (Page 14)

AMS950IS -Aerosol Monitoring System
Handbook HB3235-03
6. Calibration.
6.1. Zero
adjustments.
To check the instruments zero, slide the collar over the inlet to the measurement chamber.
Ensure the range and time averaging switches are set to 0-20mg/m3 (for 0-200 version) or 0-
200mg/m3 (for 0-2000 version) and 1 second respectively. Attach the hand pump to the probe
(fig. 3 shows two inputs) and squeeze the bulb several times to force clean air into the chamber.
This will also dislodge any dust settlement from the forward lens. The user will see the display
reading increase and then decrease toward zero.
Ensure that the rubber cap is fitted to one of the purge inlets while the other 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 time for the display to stabilise, adjust the potentiometer with the screw
driver provided so that the display indicates zero to + 0.01mg/m3 Clockwise rotation of the
potentiometer will increase the displayed value.
Ensure that both rubber caps are re-fitted to the purge inlets, when these are not in use check the
instruments zero, slide the collar over the inlet to the measurement chamber.
Note: The purge inlet marked with a single dot indicates the handle end lens.
6.2. Offset.
Before any offset adjustment is made, check and if necessary set the zero as previously
described. Move the range switch to 0-200mg/m3 (0-200 version) or 0-2000mg/m3 (0-2000
version) setting and watch the display reading drop to zero. If the reading shows a value other
than zero, adjust the potentiometer clockwise or anti-clockwise depending on the offset error.
Moving the range switch to the lowest mg/m3 should not show a change in the zero reading of
more than
± the least significant digit.
6.3. Span adjustment.
The instrument span is set during factory calibration.
Issue 3/NOV 95 Page 14