5-4 Model 3775 Condensation Particle Counter
has a flow rate of 0.3 L/min. TSI’s Model 3020 CNC was replaced in 1988
by the Model 3022A, which was replaced again in 2005 by the Model 3775
CPC. Both the Model 3775 CPC and the 3785 Water-based Condensation
Particle Counter use the photometric mode of operation to monitor high
particle concentrations up to 10
7
particles/cm
3
. These CPCs are general-
purpose instruments suitable for a wide variety of applications.
The Model 3025 Ultrafine Condensation Particle Counter (UCPC) was
developed in 1989 and was replaced by the Model 3776 UCPC in 2005.
The 3776 has a lower size detection limit and a higher aerosol flow rate
compared to the 3025A. Both the 3776 UCPC and 3786 UWCPC utilize
sheath-air-flow design to lower the size detection limit. When growing the
particles in the condenser chamber, 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. Using sheath air, the UCPC confines
the aerosol to the centerline of the condenser tube where level of
supersaturation is the highest. The result is very high detection efficiency
for small particles. The high sensitivity of the Model 3776 UCPC and the
Model 3786 UWCPC makes them the only instruments of their kind that
can detect particulates down to 2.5 nm. This makes them useful for atmos-
pheric studies, nucleation, cleanroom monitoring, and basic aerosol
research, etc. The sheath-air-flow design of the two CPCs also significantly
reduces the response time for particle detection and particle diffusion
losses. This occurs because aerosol particles are routed directly from the
inlet to the condenser and optics, not through the saturator.
The Model 3781 WCPC is a small size and light weight instrument that
detects particles down to 6 nm and operates in single count mode for
concentrations up to 5 10
5
particles/cm
3
.
The Model 3007 CPC was developed in 2001. It is a hand-held, battery
powered instrument with a size detection limit of 10 nm. It uses isopropyl
alcohol as the working fluid.
Currently, five CPCs (Models 3772, 3775, 3776, 3785, and 3786) are also
commonly used with submicron size-distribution measurement systems
such as the Scanning Mobility Particle Sizer
TM
(SMPS
TM
) Spectrometers
(TSI Model 3936).
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