GB684508A - Improvements in or relating to spectrophotometers - Google Patents

Abstract

684,508. Photo-electric spectrophotometers. EVANS ELECTROSELENIUM, Ltd., and COLLINS, G. C. May 24, 1951 [May 24, 1950], No. 13036/50. Class 40 (iii). The colour content of a surface is determined by means of a portable unit placed on the test surface, the unit comprising a light source directing light on to the surface, a photo-cell receiving this light reflected from the surface and a filter carrier with a number of filters, any one of which may be placed in front of the cell. As shown, the unit comprises a base 7 of insulating material on which is mounted between side-plates 11 an inclined partition 10 carrying a light source 3 and a photo-electric cell 1. Light from the source passes through an aperture 8 in the base and is reflected from the surface of the test material, on which the base 7 rests, to the photo-electric cell. The lamp-holder is supported on three springs 36 on screwed rods 34. The height of the lamp-holder is adjusted by knurled nuts 37. A boss 14 in the partition 10 carries a lens 4, to focus the light on to the test surface, and a sheet of heat-absorbing glass 15. The photo-cell 1 (Fig. 4) is supported in recesses in insulating blocks 38 in which it is clamped by a block 40. A spring 43 between block 40 and the top of the cell provides one of the cell connections. The cell is mounted above the aperture in the base on pillars 39. The filters are carried in a holder 5 which rotates on a pin 20 passing through the partition. There may be nine narrow band spectrum filters or a different holder carrying three " Tristimulus " filters may be used. To enable withdrawal of a holder the partition has a slot 18. At the end of the slot is a recess 19 in which the head 22 of pin 20 engages. A spring 24 compressed between the filter holder and the other end of the pin 20 normally holds the filter holder in frictional engagement with the partition. When withdrawing the holder, the head 22 is pressed out of its recess and the pin slid out along slot 18. The head 22 is provided with two flats which slide in the slot 18. The edge of the filter holder is knurled and projects through the casing 17 enabling selection of any filter. A spring- loaded ball engages depressions in the underface of the disc thereby locating successive filters accurately in the light path. To divide the instrument reading by two, a neutral filter is provided. This filter is mounted in a plate 25 which is spring-loaded so that the filter normally lies in the light path but may be moved out of it 'by an extension of plate 25 which projects to the outside of the casing.