4
The complete system would require the purchase of the static air sampling enclosure ( Part
number 176170D ), plus the following additional items:-
Microdust P
ro
,
Apex Standard or Pro Sampling Pump with charger or Apex Lite Sampling pump
Apex starter kit or suitable Flow Meter Kit
Pre weighed GFA filters. (See ordering Information section 7)
The key component to this accessory is the sampling inlet which utilises PUF size-selective filter
techniques. Size-selective filters were originally developed for operation in the Conical Inhalable
Sampler (CIS) as detailed within the Health and Safety Executive publication MDHS 14/3. The
foam filter specifications and dimensions determine the desired aerosol size selection
characteristics and eliminate particle sizes greater than PM
10,
PM
2.5
or Respirable (4 mm) as
appropriate. The larger particles become trapped and collect within the foam matrix, whilst all
particles below these “cut-off points” pass through the PUF filters and enter the measurement
chamber, where the real time mass concentration is established.
After passing through the Microdust
pro
, particulate matter is deposited on a 25 or 37mm filter
which may be used for gravimetric or chemical analysis.
Remember however, although the Dust Detective system has been designed to monitor
particulate fraction concentrations in a variety of environments, it does have some operating
limitations. The instrument is not designed to operate continuously out of doors for long periods
over 19 hours.
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 instrument 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.
Any application requiring this type of monitoring regime, will need a particulate monitor with
internal heater, to drive off any water vapour within the incoming air stream, thus eliminating
erroneous readings. The Casella Ambient Particulate Monitor (APM950) is considered the best
tool for this job and can run continuously and unattended for months at a time. Please contact
CASELLA CEL or your distributor for more information.
System Overview
The internal configuration of the Dust Detective is shown in Figure 1. The system incorporates an
Apex 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 of 3.5 L/min. 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). PUF filter adaptors
are described in Figures 3 and 4. A nozzle on the mounting block is a push fit into the inlet fitting
on the case lid.
Power Supply
The Microdust
Pro
is powered via either internal rechargeable NiMh cells (2.1Ah) or via AA sized
dry cells. This allows the unit to run for typically 19 hours.
The Apex Lite pumps are powered via 4 x AA Alkaline cells. Other Apex (Standard and
pro
)
pumps use rechargeable NiMh cells.(1.7Ah) and must be fully charged before use.
