5-4 Model 3022A Condensation Particle Counter
grow to about 10 to 12 micrometers. The droplets are counted by a
single-particle-counting optical detector. For high-concentration
measurements, a classical photometric light-scattering technique is
used. The first commercial version of this type of CNC (TSI Model
3020) used n-butyl alcohol as the condensing fluid and has a
flowrate of 0.3 liter per minute. Other versions include cleanroom
CNCs (TSI Model 7610 and Model 7620, formerly Model 3760 and
Model 3761), U.S. patent no. 4,790,650) and a respirator-fit test
CNC (TSI Model 8010). The Model 3022A CPC is patterned after
these.
Looking at the flow path in the CPC, the highest saturation ratio
occurs on the centerline of the flow-stream at some distance down
the condensing tube (Stolzenburg [1988]). Although the saturation
ratio is not uniform across the flow profile due to thermal gradients,
the lower size-sensitivity can still be predicted and measured.
Nearly 100 percent of particles greater than 0.02 micrometer are
detected with a gradual drop-off in detection efficiency below that
size. Another version of the CPC confines the aerosol to the
centerline of the condenser tube where supersaturation is the
highest. The result is higher detection efficiency for small particles
down to 3 nanometers and faster response time, but with an
increase in the complexity of the instrument and a reduction in
sample flowrate. This enhanced version for ultrafine particle
detection is TSI’s Model 3025A Ultrafine CPC.
The wide dynamic range of both the Model 3020 CNC and
Model 3022A CPC has made them useful in four areas: measuring
filter efficiency, atmospheric studies, cleanroom monitoring, and
basic aerosol research. These are the detectors most commonly
used with submicron size-distribution measurement systems such
as the diffusion battery (Sem et al. [1980]) and differential electrical
mobility classifier (Keady et al. [1983]).
Design of the CPC
The basic instrument consists of three major subsystems: the
sensor, the microprocessor-based signal-processing electronics,
and the flow system.
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