FAQ - General

Pregunta
How will counting efficiency affect data for actual particle distributions in cleanrooms as compared to data from monosized calibration particles?

Respuesta

Most actual particle distributions are much broader than the distributions of monosized particles, and much broader than the particle size range spanned from 0% to 100% counting efficiency for particle counters. Since this is the case, the slope of the distribution becomes important in predicting the effect of the counting efficiency of a particle counter on the reported distribution.

Particle counters with imperfect resolution tend to overcount in distributions where the concentration increases rapidly with decreasing particle size. Because the resolution particle counter counts a larger fraction of the smaller particles in the relatively higher concentration area than does the "good" resolution OPC, the "poor" resolution OPC overcounts at a significantly higher rate. To calculate the expected total difference in counts between the two particle counters, it would be necessary to integrate the product of the concentration and the counting efficiency across the size range from 0% to 100% counting efficiency for both particle counters.

To compensate for the effects of imperfect resolution, final calibration of particle counters manufactured by Particle Measuring Systems is done with reference to a standard particle counter while both instruments are sampling diluted ambient air.

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

Contact us if you need more information or have questions.