Particle Measuring Systems

Improved Particle Counting Accuracy in Manifold Monitoring

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Courtesy of Particle Measuring Systems

Abstract

Many particle counter users are unaware that – during traditional manifold sampling – the monitor undercounts the ambient particle concentration. Because of the additional vacuum created by the manifold pump, the particle concentration is substantially lower in the air sampled than in the ambient cleanroom air. Unless the system adjusts appropriately, this lower-than-expected particle density causes a 7 – 17% under-reporting of particle concentrations.

Historically, different particle counters have used different methods of compensating for this undercounting. To date, none of these compensation techniques have resulted in truly accurate numbers; some have lead to additional errors, such as particle mis-sizing, which in turn caused 40% underreporting in the first channel.

Particle Measuring Systems has now developed a system where these counting errors are automatically eliminated. When used with the Aerosol Manifold II, the Lasair® III counter's proprietary system for pressure monitoring and flow control makes it possible for the first time to correctly normalize the raw counts and calculate accurate cleanroom particle concentrations.

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