GB688653A - Improvements relating to photo-electric measuring apparatus - Google Patents

Abstract

688,653. Photo-electric particle counting apparatus. LOESCHCKE, H.H., and WEVER, R. Aug. 21, 1950 [Aug. 22, 1949], No. 20685/50. Class 40 (iii). Measuring apparatus for estimating the number of discrete particles contained in suspensions or emulsions in a transparent or translucent medium, comprises means for passing a beam of light through the medium so as to produce a divergent beam of diffracted or scattered rays in addition to the main beam, and a light-sensitive cell arranged to respond to an annular portion of the diffracted beam surrounding the main beam but shielded or otherwise rendered irresponsive to the main beam and the central portion of the diffracted beam. Although generally applicable the invention is primarily concerned with estimating the number of corpuscles in .blood and is adjustable to give satisfactory results with such particles even when these vary in size considerably. The apparatus may consist of a light-tight box 21 in which is placed a lamp 1 the light from which after passing through colour filter 3 is focused on a small hole in screen 5 by lens 4. Light from the hole is made parallel by lens 6 and passes through small holes in two further screens 7 and 8 before impinging on a transparent vessel 9 containing the suspension or emulsion under investigation. The particles scatter or diffract part of the light to form a cone-like beam and, while the main beam is stopped by the central disc 11b of a screen having an annular hole cut in it some of the diffracted light passes through the annular hole and impinges on photo-cell 12. On the further side of lamp 1 there is a further colour filter 17, a ground glass plate 18 and an adjustable diaphragm 19 and a compensating light-sensitive cell 20. In use the photo-cells are arranged with their outputs in opposition and the diaphragm 19 adjusted until there is zero electrical output as shown by a measuring instrument such as a galvanometer, the adjusting arm of the diaphragm co-operating with a scale calibrated to show the number of particles per unit volume directly. It is shown with reference to a graph, Fig. 2 (not shown), that if the semiapex angle of the cone based on the inner edge of the annular opening in the screen 116 and having its apex at the cell 9 is 4 degrees and the semi-apex angle of a similar cone based on the outer edge of the annular opening is 30 degrees then, using yellow light, particles ranging in size between 5Á and 9Á can be counted. Other ranges of sizes will require different angles which may be similarly determined. If the photo-cell 12 is made removable the diffraction pattern can be inspected on a ground glass screen 14, normally covered with a light-tight cover 15. By further slight alterations the apparatus may also be used for absorption tests.