Dust Detective
6
Due to the light scattering principle used within the instrument, any moisture which individual particles attract
at periods of high humidity or temperatures approaching
“dewpoint” will be “seen” by the instru
ment as
larger particles. This biases results towards greater concentrations. Also, during these periods, any air being
drawn through the instrument which is high in humidity may condense on the optics and distort the light
beam, producing spurious results.
The system incorporates an Apex2 sampling pump to draw the sample air through the inlet pipe at a user
selected flow rate. PUF filters are designed to operate at a flow rate up to 3.5 L/min, but running at 2L/min is
adequate for the system. The inlet head is designed to prevent the ingress of insects and other large foreign
objects. A dust cap is provided to seal the inlet port on the case lid whenever the inlet tube is removed for
transit purposes.
Size selection of the sample stream is performed by passing the sample through a PUF foam filter appropriate
to the chosen sampling strategy, (PM
10,
PM
2.5
or Respirable).
