Method and apparatus for particle counting and counter calibration

Abstract

A system for counting particles entrained in a flowing fluid and for automatically calibrating the counting system is disclosed. A conduct through which a fluid carrying particles flows has a transparent section. A narrow light beam, such as a laser light beam, is passed through the transparent section to a detector, such as a photodiode, that detects light scattered by the particles. The scattering pattern is useful in counting the flowing particles and measuring other particle characteristics, such as size. The measurement system can be calibrated by passing the light beam through a transparent slide bearing a standard particle array to a detector, either the measurement detector or a second detector. The slide is moved at the same rate as the fluid flows, so that the scattering produced by the standard array is useful in calibrating the measurement of the flowing particles in a conventional manner. The calibration may be accomplished by deflecting, such as with a movable mirror, the light beam through the moving slide to a second detector or the body containing the conduit can be moved out of the way so that the slide can be moved across the original light path. A multiple solenoid valve may be provided to selectively direct the particle bearing fluid through the conduit, direct reverse flow of clean water or a gas, such as air, through the conduit to clean the conduit or remove any particle contamination or jams.