What Is A Particle Counter

By Dr. Hans-Walter Motzkus and Joe Gecsey

A particle counter is an electronic instrument that detects and counts airborne or liquid particles. Particles are detected using laser based optical systems that shine a powerful light through a detection chamber. The detection chamber has collection optics that produces a signal which is processed to determine particle quantity and size in a given volume. There are two main detection methods in common use:

• Light Scatter: As the particles pass through the detection chamber then light energy is either absorbed by the particle or reflected. Off axis electronic sensors measure how much light is scattered in order to calculate how many particles have passed through the chamber. Typically used for counting smaller particles in either air or liquid. eg 0.1 to 25μm diameter

• Light Obscuration: As larger particles pass through the detection chamber they directly obscure the laser light and the electronic sensor measures the drop in order to count the particles. Typically best for counting larger particles in liquids. eg 0.5 to 600μm diameter