Recommended Practice (RP), IEST-RP-CC042.1: Sizing and Counting of Submicrometer Liquid-Borne Particles Using Optical Discrete-Particle Counters covers liquid-borne particle counters (LPCs) that use a light-scattering technology to obtain information on particle concentration and size distribution. This technology is predominantly used to detect low concentrations of particles ranging in diameter from 0.05 µm to 20 µm. Typical applications are in the semiconductor, flat-panel display, and data storage industries.

Liquid-borne particle measurement involves many technical challenges that can substantially affect results in both sizing and counting of particles. This first-edition RP is intended as a single source covering those challenges and solutions and provides a handy reference for professionals in this field.

IEST-RP-CC042.1 explains the use of channels to record particle counts within specified size ranges. Channels are established by means of voltage thresholds that match particle light-scattering intensity to particle size. The RP dispels the common misconception that the first channel counts only 50% of the particles in that size range, while the other channels count 100% of the particles in those size ranges.

“As a result of that misconception, some users unnecessarily discard first-channel data,” says Huaping Wang, Chair of IEST Working Group CC042, which developed the document. “In fact, all channels are calibrated in the same way, at the median of their corresponding PSL calibration standards.”

The RP discusses various categories of LPCs, including:
  • Volumetric vs. non-volumetric design, based on the effective sampling volume.
  • Monitor, spectrometer, or counter, depending on size resolution and the number of size channels.
  • Batch type vs. in-line type, based on how the sample is introduced into the sensor.
First printing October 2011


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