METHOD AND APPARATUS FOR DETECTING DUST PARTICLES BY PARTIAL EMBEDMENT IN A LAYER WHOSE SURFACE IS DEFORMED BY THE PARTICLES AND MEASURING RADIATION SCATTERED BY THE PARTICLES WITH A SCHIEREN OPTICAL SYSTEM

摘要

A method and apparatus for detecting and measuring the number and/or size of dust particles on a support plate having a planar surface. The method comprising flowing a liquid layer over the support to wet the particles and controlling the layer thickness so that particles form deformations in the layer surface due to surface tension of the liquid and then measuring,by means of a Schlieren or phase contrast optical system, the amount of light scattered by those particles causing the deformations. The measured intensity is then compared with calibration curves derived empirically from measurements of dust particles of known size embedded in liquid layers of different known thicknesses to determine the number and/or size of the particles under measurement. The apparatus comprises a dust proof chamber into which the support plate with the particles embedded in a liquid layer is introduced, the chamber including a light source for illuminating the liquid layer and a Schlieren optical system for measuring the light scattered from the particles. The optical system includes a photoelectric transducer which is connected to an evaluation system not forming part of the housing to provide an indication of the number and/or size of the particles under measurement.