Importance

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Abstract

Apparatus and a method are disclosed for determining the sizes of particles entrained in a fluid over a relatively wide range of sizes and determining the distribution of particles in a plurality of size increments. A sample of particles is fed into a drop tube, allowing the particles to be distributed at a relatively low density and fall through a sensing region defined at an intermediate point in the drop tube. A laser diode produces coherent light that is focused with a lens, forming a sheet of coherent light that is directed transversely through transparent sides of the drop tube toward a lens that focuses the sheet of coherent light on a photodetector. A laser intensity control circuit maintains a constant light intensity output from the laser diode when no particle is present in the sensing region and compensates for ambient light. When a particle in the size range of 32.mu. to 4000.mu. falls through the sensing region, a chord around the particle is illuminated by the relatively thin sheet of coherent light, and the level of an electrical signal produced by photodetector is reduced in direct proportion to the portion of the sheet of coherent light that is occluded by the particle. A peak value of the pulse is thus a measure of the size of the particle. A pulse discrimination circuit detects pulses produced by a plurality of particles in the sensing region, preventing such multiple particles from being analyzed or counted. After the size of a particle is determined, a counter increments the count in an appropriate channel, each channel corresponding to one of plurality of different successive ranges that together cover the total size range of the particle analyzer.

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First Claim