Optical instrument for measurement of particle size distribution

Optics: measuring and testing – For size of particles – By particle light scattering

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250574, 350162SF, G01N 1502

Patent

active

042459095

ABSTRACT:
A method for measurement of the size distribution of particles suspended in a gas or in a liquid. The particle suspension is illuminated by a collimated beam of nearly monochromatic light. Part of the light scattered by the particles is collected by a lens and is passed through a spatial filter placed in the focal plane of the lens. The light transmitted by the filter is measured by a photodetector. The photodetector output is measured as different spatial filters are switched in place. A computer, microprocessor, or analog device acts on the measured values and produces the particle size distribution as an output. The data reduction algorithm consists of a linear transformation of the measured data vector, followed by the construction of a linear combination of basis functions for the size distribution. The spatial filters consist of transparencies with non-uniform transmittance functions. The average scattering angle is not restricted, but for broad polydisperse particle distributions near back scatter is preferred, in order to avoid an ill-conditioned data reduction problem. One of the spatial filters has a uniform transmittance for the purpose of background light subtraction, and to provide a bias in order to allow effectively indefinite filter transmittance functions.

REFERENCES:
patent: 3469921 (1969-09-01), Taylor
patent: 3873206 (1975-03-01), Wilcock
patent: 4037965 (1977-07-01), Weiss
patent: 4052600 (1977-10-01), Wertheimer
Malvern Instrument Ltd. Division of Precision Devices and Systems, Malvern, Worcestershire, England, "Particle and Droplet Size Distribution Analyzer Type ST 1800".

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