Achieving particle counting accuracy

ISO 21501 offers standard methodology for calibrating optical particle counters

By Tony Harrison and Bob Latimer, Hach Ultra Analytics, Inc.

ISO 21501 is a new family of standards describing the instruments and calibration requirements for determining particle size distribution using light interaction methods. It represents the culmination of work by instrumentation manufacturers and industry users and comes at a critical time for the life science industry with the increasing trend for real-time air particle monitoring in cleanrooms using light scattering air particle counters.

The ISO 21501 family of standards extends beyond air particle counters to include both scattering and extinction type liquid particle counters. The standard is split into four parts and all are available from ISO at

ISO 21501, Determination of particle size distribution


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