Research was undertaken to test whether different particle counters yield the same particle count and size distribution information, to assess the possibility of using particle concentration standards from other applications in the water industry, and to develop and test a concentration standard for use in the water industry. Five particle counters were used,including duplicates of each of two manufacturers' light-obscuration instruments (commonly used in the water industry)and one electrical sensing zone (ESZ) instrument. On all types of samples (latex spheres,a commercially available fine test dust used as a standard in other industries, and water treatment plant samples),the light-obscuration instruments consistently measured far fewer particles in the smallest sizes (2-5μm) than the ESZ instrument, and evidence is presented that suggests the ESZ instrument is more correct. Recommendations for standards to use with light-obscuration instruments include using a multimodal count standard using latex spheres of two sizes, with those sizes being in the middle of standardized size ranges; using separate sizing standards at the boundaries of the size ranges; and avoiding any use of particle counters for regulatory purposes at this time.
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