Casella CEL Microdust 880 IS real time dust monitor - Manual (Page 42)

Microdust 880nm & WinDust Application Software
Handbook HB3255-03
Page 42 of 51
5. Continue sampling for a time period which will allow the collection of sufficient sample
mass.
6. At the end of the sampling period, stop the sampling pump and note the Microdust’s T.W.A
value. Where applicable, stop the internal data logger.
7. The filter should be conditioned and re-weighed to establish the collected mass. The
gravimetric density during sampling period can be established by dividing the mass increase
by the total volume sampled.
The calibration correction factor is calculated as;-
Correction factor = Gravimetric Concentration
Microdust TWA Concentration
This correction factor should be applied to the value indicated on top of the optical calibration filter.
Insert the calibration filter into the probe and adjust the ‘Span’ control such that the displayed
concentration represents the adjusted filter value.
Example;-
Filter mass increase = 3.21mg
Volume Sampled = 0.75m
3
Gravimetric density = 3.21 / 0/75 =4.28 mg/m 3
Microdust’s T.W.A indication over period = 3.45 mg/m
3 (ie, the Microdust read low)
Correction factor = 4.28 / 3.45 =1.24
Value shown on the calibration filter = 12 (centre of indicated range)
Insert the calibration filter into the probe and adjust the ‘Span’ control for an indication of
1.24 x 12 = 14.88 mg/m
3
In the above example, increasing the instruments sensitivity (Span) will ensure optimal
accuracy between the Microdust indication and the true gravimetric concentration.
Whenever the Microdust is used to measure this specific dust, the correction factor should be
applied to the value shown on the calibration filter.