Abstract
Count variance and instrument-to-instrument variability of optical particle counters are investigated experimentally. In order to compare counts of the same particles by two counters, two commercial counters with some necessary modifications are connected in series. Statistical analysis of the series count data reveals that difference between the threshold size of the counters and the typical size of sample particles is the major parameter determining magnitude of both the count variance and the instrument-to-instrument variability. In addition, the former is shown to originate mainly from uncertainty of size discrimination of sample particles whose sizes locate near the threshold, and the latter from difference in size resolution of the OPC's.
