Size Analysis in the Sub-sieve Range by Electronic Counter

Abstract

THE electronic apparatus for the rapid measurement of particle content and size distribution, known as the Coulter counter¹, is finding increasing application in many fields. A known volume of an extremely dilute suspension of particles in a conducting fluid flows through a standard interchangeable aperture having an immersed electrode on either side. The particles traverse the aperture substantially one at a time, causing an attendant change in electrical resistivity proportional to the volume of the particle passing through the aperture. The amplified signals pass through a gate circuit which ensures that only pulses greater than a pre-selected threshold value are counted; thus, the pulse count records the number of particles greater than a certain size. A typical count requires about 5–25 sec and is performed at a rate up to 600 particles/sec. A size range of about 500–0.5µ can be covered, therefore overlapping with sieving, microscope and sedimentation methods.