Instrument Operation
3-5
Table 3-1
Front Panel Indicator Conditions
Indicator Particle Status
Flow
Liquid
Off
No particles
Instrument off
Pump off
Drain
reservoir full
and water
injections
stopped
Slow Flashing
Particles
detected
Instrument not
at operating
temperatures
Low flow rate
Drain
reservoir full
Fast Flashing
Particles
detected
Laser off or not
at required
power
High flow rate
Growth tube
wick is dry
On
Particle
concentration
is over about
5.0 #/cm
3
Normal
operation
Normal flow
rate
Normal
operation
A i r - F l o w S y s t e m
A pair of pumps draw aerosol into the UWCPC and provide the
sheath flow. These pumps can be turned on or off by pressing the
Pump button on the front panel. The UWCPC saves this on or off
condition so when the instrument is turned on, it will resume that
state after the warm-up cycle. The Flow indicator light on the front
panel provides an indication of the pump and flow status. When
operating, a flashing Flow indicator results from the inability of the
pumping system to maintain the calibrated flow. This may be the
result of excessive pressure variations at the sample inlet.
Inlet flow is feedback controlled to maintain a steady calibrated
value of 0.6 L/min volumetric flow rate. The sheath flow is feedback
controlled to a value of 0.3 L/min and the difference between these
flows is the aerosol flow rate which is nominally 0.3 L/min. The
feedback controls includes a measure of the inlet absolute pressure
to continuously compensate for pressure changes. There is an
internal purge flow (~10% of sheath) that draws air out of the
sheath flow loop to minimize any reentrainment of particles into the
sample stream during changes in inlet pressure. This maintains the
instruments’ response time and zero-count performance. The