Teledyne API Ultrafine Particle Monitor - Model 651Particle Counting
C o n c e n t r a t i o n M e a s u r e m e n t
The Model 651 can report particle concentration values in the following ways:
∙On the
∙On the Totalizer display.
∙Using the data communications ports.
Particle concentration is presented as particles per cubic centimeter (p/cm3). The following parameters are important for calculating particle concentration:
∙The number of particle pulses counted (measured internally by the Model 651).
∙The sample time (measured internally by the Model 651).
∙The sample flow rate (always assumed to be 0.120 L/min, or (120 cm3/min).
The basic calculation for the number of particles per volume of air is:
Concentration = N
Q × t
where:
Concentration is the particle concentration in #/cm3
Nis the number of particle counted
tis the sample time (corrected for
The number of particles in the measured sample is one of the limiting factors of how low a particle concentration can be precisely determined. To calculate low particle concentrations, the Totalizer uses the elapsed time as the sample time in the above calculation.
The formula for this statistical precision is:
σ N = 
NN ×100%
where:
σN is the relative standard deviation in percent
Nis the number of particle counts in the sample
For a sample of 10,000 particles, the statistical precision is 1% (greater accuracy than that of the instrument). At 100 particles, the statistical uncertainty increases to 10% and becomes a significant factor in determining the aerosol concentration. The Totalizer allows
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