The below HTML version provides a quick overview.

This paper defines the most common terminology used in particle counting.

Accumulative (Cumulative) Counts The summed or total counts for all particles in the specific channel as well as particles in the larger channels.

Aerosol Particles suspended in air or water-vaporized air.

Brownian Motion This is the random movement of small particles due to collisions with molecules. Generally, Brownian motion influences particles equal to or smaller than 0.1 micron (µm) diameter.

Capillary A transparent, small-diameter conduit through which sample fluid passes. Laser light passes through the capillary and illuminates the fluid to scatter light from particles. Commonly, the capillary’s shape is a cylinder, made from glass or sapphire, and the diameter is about 0.7 mm (700 µm).

Channel A predefined storage bin designed for specific particle sizes. Channels are calculated by measuring a particle’s scattered light and creating thresholds, which correlate the amount of particle scatter to the particle size. Example: particle counters display common channels as 0.2 µm or 0.3 µm.

Class (i.e.: Cleanroom Class) Cleanrooms or clean environments are often categorized in classes that define the quality of a cleanroom. Using the (obsolete) FS-209e standard, a cleanroom class was expressed as the maximum number of 0.5 µm particles per cubic foot; in the ISO standard, a cleanroom class is expressed as the maximum number of 0.1 µm particles per cubic meter.

Coherent Light This is a beam of light whose photons have the same optical properties (wavelength, phase, and direction). Coherent light is essential for particle detection because particles illuminated by different light sources will size differently.

Coincidence Loss When two or more particles are within a light source (e.g. laser) at the same time, a particle counter may not differentiate between the two particles and instead, assume there is one large particle present. This is called coincidence loss and is characterized by a distribution shift in particle data.

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