IEST addresses liquid-borne particle counting

Published: 3-Nov-2011
Analysis

Releases a new Recommended Practice (RP)


A new Recommended Practice (RP), IEST-RP-CC042.1: Sizing and Counting of Submicrometer Liquid-Borne Particles Using Optical Discrete-Particle Counters, is now available from the US Institute of Environmental Sciences and Technology (IEST).

Liquid-borne particle measurement involves many technical challenges that can affect results in both sizing and counting of particles.

This first-edition RP, published by the IEST Contamination Control Division, is a single source of information, and provides a handy reference for professionals in this field.

A liquid-borne particle counter (LPC) uses light to detect particles suspended in a liquid medium. This RP focuses on LPCs that use a light-scattering technology to measure the amount of light scattered by particles to obtain information on the concentration and the size distribution of those particles. This technology is predominantly used to detect low concentrations of particles ranging in diameter from 0.05µm to 20µm. Typical applications are in the semiconductor, flat-panel display, and data storage industries.

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,” said Huaping Wang, chair of IEST Working Group CC042, which developed the RP.

“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.

  • Companies:
  • IEST Institute of Environmental Sciences and Technology
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