TSI Incorporated PORTACOUNT PRO+ 8038, Operation And Service Manual

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Appendix D
Calculating Particle Concentration
Particle concentration is calculated by counting the number of
particles passing through the sensor in a given period of time. Since
the flow rate is known (5.83 cm
3
/sec), the particle concentration can
be determined.
In 1-Second Count Mode the equation is:
sec / 83 . 5 sec) 1 (
ion Concentrat Particle
3
1
cm
N

where N
1
is the number of particles counted in a 1-second period
Note that the total flow rate of air through the PortaCount
®
Pro is a
nominal 16.7 cm
3
/sec. The reason that we use 5.83 cm
3
/sec. in the
calculations above is because the flow path inside the PortaCount
P
RO
is divided into two branches, the sensor flow and the bypass
flow. The sensor flow is set at precisely 5.83 cm
3
/sec and the bypass
flow is approximately 10.8 cm
3
/sec.
Using the equation above, you can see that the minimum measurable
concentration is 0.17 particles per cm
3
in 1-Second Count Mode.
The equations above can also be used to determine the minimum
measurable mask concentration that can be measured in Fit Test
Mode given the mask sample time that is used. For example, with a
40 second mask sample (factory setting), the minimum measurable
concentration is 0.004 particles per cm
3
.