ABSTRACT
This chapter discusses the methods for the on-line measurement of particle size by classifying them into several groups: direct classification, permeability, optical, electrical, acoustic, and other methods. The direct method is based on the particle size classification technique, and indirect methods utilize various phenomena, such as the pressure drop of air flowing through a powder bed. The optical method has the feature that it is extremely sensitive, nearly instantaneous, and does not require physical contact with the measured particles. Particles passing through a corona discharge field are electrically charged by ions existing in the field. The amount of charge on any particle can be determined by the particle size and the conditions of corona discharge. Acoustic emission caused by particle movement will also be utilized in the measurement of particle size. There are two types of acoustic method, one for the measurement of aerosol particles and the other for bulk solids.
