THE MEASUREMENT OF PARTICLE-SIZE DISTRIBUTION USING THE METHOD OF OPTICAL INCOHERENT SPACE-FREQUENCY ANALYSIS

Optically incoherent spatial frequency analysis is used to determine p article-size distribution. The optical system used for this purpose in cludes a liquid crystal (LC) modulator which is illuminated by means o f a condenser, a micro-objective lens acting as a Fourier transformati on lens, and a point light defector which consists of a micro-diaphrag m and a photomultiplier. A personal computer (PC) controls the LCD, th e detection of light intensities and the piezoelectric x-y stage for i nternal beam alignment. A sample feeding device helps to lead rest mat erial across the beam path. Measured values are accumulated during thi s passage. An evaluation program implemented on the PC calculates part icle-size distribution in the form of proportions within to a maximum of 30 particle-size ranges. The results obtained with incoherent optic al space-frequency analysis are compared with the results achieved by means of particle-size analysers working on the basis of laser diffrac tion. This provides a simple method for particle-size analysis which l ends itself especially to applications at the production level.