Except for ideal spherical particles, the particle size (diameter) of any actual particle sample measured on any particle size testing instrument is equivalent particle size (diameter), that is, the particle diameter given by the instrument is not the actual diameter of the particle, because a non spherical particle does not have a real "diameter" at all. The equivalent particle size of a particle refers to the diameter of a homogeneous sphere that has similar geometric or physical properties to the particle in some aspect. So, what is the relationship between equivalent particle size and the actual external dimensions of particles? This should be of interest to the majority of particle testing workers. Laser particle size analyzer is a widely used particle size testing instrument today. Rod shaped and sheet-like particles are two typical types of particles that deviate significantly from the spherical shape. This article studies the equivalent particle size (distribution) of these two types of particles in a laser particle size analyzer.

The laser particle size analyzer referred to in this article is a measurement system that calculates the particle size of scatterers (particles) by measuring the angular distribution of scattered (diffracted) light. It consists of an optical part, an electronic part, and a computer. Only the optical part related to this article will be introduced here.