Particle counter

A particle counter is an instrument that detects and counts physical particles; either ionising or non-ionising.

Ionising particles are detected used such as a Geiger Counter, whilst non-ionising particles are detected by such as optical techniques. This page deals with non-ionising detectors, see Particle detector for ionising particle detection.

The nature of particle counting is based upon either light scattering, light obscuration, or direct imaging. A high intensity light source is used to illuminate the particle as it passes through the detection chamber. The particle passes through the light source (typically a laser or halogen light) and if light scattering is used, then the redirected light is detected by a photo detector. If direct imaging is used, a halogen light illuminates particles from the back within a cell while a high definition, high magnification camera records passing particles. Recorded video is then analyzed by computer software to measure particle attributes. If light blocking (obscuration) is used the loss of light is detected. The amplitude of the light scattered or light blocked is measured and the particle is counted and tabulated into standardized counting bins. The image to the right shows a light scattering particle counter diagram. More information about types of particle counters and types of particle detection follow in this article.

Direct imaging particle counting employs the use of a high resolution camera and a light to detect particles. Vision based particle sizing units obtain two dimensional images that are analyzed by computer software to obtain particle size measurement in both the laboratory and online. Along with particle size, color and shape analysis can also be determined.

Applications of particle counters are separated into three primary categories:

Aerosol particle counters are used to determine the air quality by counting and sizing the number of particles in the air. This information is useful in determining the amount of particles inside a building or in the ambient air. It also is useful in understanding the cleanliness level in a controlled environment. A common controlled environment aerosol particle counters are used in is a cleanroom. Cleanrooms are used extensively in semiconductor device fabrication, biotechnology, pharmaceutics, disk drives, aerospace and other fields that are very sensitive to environmental contamination. Cleanrooms have defined particle count limits. Aerosol particle counters are used to test and classify a cleanroom to ensure its performance is up to a specific cleanroom classification standard. Several standards exist for cleanroom classification. The most frequently referred to classification is from the United States. Though originating in the United States, the standard Federal Standard 209E was the first and most commonly referred to. This standard was replaced in 1999 by an international standard, but Federal Standard 209E remains today the most widely referenced standard in the world.

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