Casella CEL Microdust 880 IS real time dust monitor - Manual (Page 17)

Microdust 880nm & WinDust Application Software
Handbook HB3255-03
Page 17 of 51
Adjusting the ‘Span’ control.
The sensitivity or ‘Span’ of the instrument is calibrated at the factory using Arizona fine calibration
dust.
All light scattering instruments can have some sensitivity to a particulates refractive index, size,
shape and colour. The Microdust uses a narrow forward scattering angle to minimise these effects but
for optimum calibration to a specific dust type, gravimetric calibration and adjustment of the
instruments span control may be required. Gravimetric calibration is discussed later in this manual,
for now we will simply check the factory calibration point.
Checking the factory calibration
An optical calibration filter is provided with each instrument and is used to create a fixed optical
scattering effect within the probe. This fixed reference signal can be used to confirm the factory
calibration point.
To check the factory calibration point, firstly turn the instrument on and perform the ‘Zero’
adjustment as detailed on page 15. Insert the calibration filter in the measurement chamber with the
arrow pointing towards the probe handle. The operating range should be set to either ‘Automatic’ or
‘High’.
The instrument should display a value within the range indicated on the calibration element unless
the span setting was previously adjusted to compensate for a specific dust composition.
Turning the span potentiometer clockwise will increase the displayed value.
Normal Operation.
Before carrying out monitoring, the ‘zero‘ and ‘span‘ checks discussed previously should be
performed. Select the ‘Averaging period’ and ‘Range’ appropriate to the monitoring application.
With the measurement chamber aperture exposed, slowly move the probe through the aerosol or rely
on natural air movement. Measurements can be taken with the probe either attached or detached from
the display unit. For static monitoring applications the use of an aspirator system is preferred (refer to
‘Sampling Accessories’ section).
In addition to the basic real time dust indication, the Microdust is able to calculate and display
other useful data values including:-
Maximum Value