TSI Incorporated PORTACOUNT PRO+ 8038, Руководство по эксплуатации и обслуживанию

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82 Appendix B
How the PortaCount Pro Fit Tester Counts Particles
The PortaCount Pro fit tester is based on a miniature, continuous-flow
Condensation Nucleus Counter (CNC), also known as a Condensation
Particle Counter (CPC). A CNC takes particles that are too small to be
easily detected, grows them to a larger, easily detectable size, and then
counts them.
The idea of CNCs/CPCs is not new. As early as 1888, Aitken
described a dust counter that grew particles to detect them. In 1943
the Nolan-Pollack photoelectric CNC was described. In the 1950s and
1960s, commercial, automatic CNCs were available. However, none
were of the continuous-flow type, and the PortaCount Respirator Fit
Tester is the first highly portable continuous-flow CNC.
The concept of using a condensation nucleus counter (CNC) for the
purpose of quantitative respirator fit testing was first demonstrated in
1981 by Dr. Klaus Willeke of the University of Cincinnati.
Reference: Willeke, K., H.E. Ayer, J.D. Blanchard. “New
Methods For Quantitative Respirator Fit Testing With
Aerosols,”
American Industrial Hygiene Association
Journal, Feb. (1981).
The PortaCount Pro
Respirator Fit Tester grows submicron particles
to supermicron alcohol droplets and then measures the concentration
of the alcohol droplets. This makes the PortaCount Pro Fit Tester
sensitive to particles with diameters as small as 0.015 microns, but
insensitive to variations in particle size, shape, composition, and
refractive index. Thus, quantitative fit testing can be performed with
virtually any aerosol, including ambient air.
Aerosol is drawn through the instrument by a diaphragm vacuum
pump operating at a flow rate of 1.0 liter per minute. The flow enters
the instrument through either the ambient port or the sample port. The
switching valve determines which port is used. The outlet of the
switching valve leads to the saturator end cap, where the flow splits.
A flow rate of 0.35 liters per minute enters the saturator and passes
through the condenser, nozzle, and sensing volume. The remaining
flow passes through the excess airline and is recombined with the
sampled flow down-stream of the sensing volume.