6-1
CHAPTER 6
Particle Counting
This chapter discusses specific aspects of particle counting and
particle count measurements performed using the Model 3775
Condensation Particle Counter (CPC).
The Model 3775 CPC has two modes for particle counting:
Concentration mode, where data is presented as particle
concentration in p/cc, updated each second on the display (the
maximum time resolution is tenth of a second).
Totalizer mode, where total particle counts are accumulated and
presented each second.
Concentration mode is commonly used for most applications.
Totalizer mode is used at very low particle concentrations. Particles
can be accumulated until a desired statistical accuracy is achieved.
Refer to the section below discussing total count accuracy.
In the concentration mode, the CPC operates in the single count
mode between 0 and 5 × 10
4
particles per cubic centimeter and
operates in photometric mode for concentrations in the range from
5 × 10
4
to 10
7
particles per cubic centimeter. It employs continuous,
live-time coincidence correction in the single counting mode.
Optical Detection
Submicrometer particles are drawn into the counter and enlarged
by condensation of a supersaturated vapor into droplets that
measure several micrometers in diameter. The droplets pass
through a lighted viewing volume where they scatter light. The
scattered-light pulses are collected by a photodetector and
converted into electrical pulses. In single counting mode, the
electrical pulses are counted and their rate (live-time corrected) is a
measure of particle concentration. In photometric mode, the total
scattered light is converted into particle concentration based on a
calibration curve in the instrument.
To Next Page
Loading...
Need help?
General
