FAQ - ×ÜÀà

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What is counting efficiency?

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Counting efficiency is an expression of the probability that a particle counter will sense and thus count a particle passing through the particle counter's sample volume. This probability is a function of size up to a certain critical size above which all particles are normally sensed and counted.

The figure displayed here shows three plots of counting efficiency versus particle size. Curve A (the vertical line) shows a counting efficiency curve for a hypothetical particle counter with "perfect" sizing resolution, curve B shows the curve for a real-world particle counter with "good" resolution, and curve C shows the curve for an particle counter with "poor" resolution. Percent resolutions selected to illustrate "good" and "poor" are 10% and 25% respectively.

Note that while the signal produced by the particles is distributed symmetrically about the nominal most sensitive threshold, the exponential relationship between particle size and signal returned causes the counting efficiency curve to be asymmetrical. The discussion of 50% counting efficiency is deferred until after the section on Sensor Resolution because it relies on an understanding of particle counter resolution.

For more information, see our paper Particle Counting Efficiency and Resolution in Particle Counters

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