Metrolab Blog

Particle Counters Knowledge Hub 2

Did you know? “Equivalent Area Diameter”

A particle is a 3-dimensional object, and only if it is spherical can its exact size be determined by its diameter. The size of particles measured on a witness plate or by an instrument vanes according to the method used. The particle size is normally measured by microscopy or by an equivalent optical measurement system, and in both of these systems a 2-dimensional silhouette of the particle is observed.
Equivalent diameter is normally based on the physical properties measured, such as light scattering, where the amount of light scattered by a particle is related to the size of the particle. In order to ensure particle sizes in particle counters, synthetic particles such as PSL’s (polystyrene latex) are widely used in industry. With exact diameter, PSL’s are helping us to simulate particle light scattering so we can get particle counters calibrated based on this data and set equalent particle diameter as reference diameter. 

Equalent Area Diameter