Patent GB-528967-A (GB)
Title: A method of and means for colour comparison
IPC: G01J3/42
Filed: 1939-04-25
Abstract: 528,967. Photo-electric testing apparatus. LEMON, C. G. April 25, 1939, No. 12413. [Class 40 (iii)] Relates to apparatus for comparing the " colour " of a specimen with that of a standard by their alternate action on a beam of light from a source of light to a photo-electric cell, whereby the relative degree of whiteness or blackness or of the tint of the specimen is determined. According to the invention, the apparatus comprises a revolving circular double compartment cage 12, 11, Fig. 1, with peripheral windows 8, a photo-electric cell 10 adjacent said cages, a light source 3, means for bifurcating the light to the two cages for example a double reflector 5 two reflectors 6 and two prisms 7, electric amplifying means for the alternating electric output of the photo-electric cell, and adjusting devices to control the light path to the standard material in the cage 12 to enable the alternating electric output to be annulled and thereby indicating the relative "colour" of the specimen. The alteration is produced by staggering the windows of the cages 11, 12 as shown in Fig. 4, or by deflecting one of the light beams relatively to the other, the staggering or deflection producing a phase displacement of 180 degrees on the photo-electric cell, so that no alternating output occurs from the cell when the light beams coming thereon from the two cages are equal. The cages are griven by a synchronous motor 27, the speed of which together with the pitch of the recurrent windows 8 determines the frequency of the alteration of the beams on the cell. The output of the cell is amplified by the circuit, Fig. 6, which includes a filter 66 tuned to pass only the frequency of the beams. The output is indicated by a measuring instrument or detected by a sound reproducer 65. Zero adjustment is made by means of a slidable light wedge 56 which is set by a screw 57 to annul the cell output when both cages 12, 11 contain the same material. Then in actual use, the cage 12 is charged with the standard material and the cage 11 with the material to be tested ; and while the cages are rotating, the beam of light to the standard material in the cage 12 is controlled by a disc 43 carrying colour filters 45 or by an obscurating wedge disc 28 and a set of obscuring plates 30 on a disc 30 until the cell output is annulled. These devices may also be used in conjunction with the sliding wedge 56 when making the initial adjustment. The discs 28, 30, 43 are rotated by side knobs 32, and are connected to graduated wheels visible through windows 39. Spring pawls engage notched discs 40, 43 to stop the discs 29, 43 with each pane 30, 45 thereof in correct position in the light beam. The cages 12, 11 shown are intended especially for powdered materials which are pressed uniformly by centrifugal force against the windows 8. The cages may also be adapted to contain liquids. When it is desired to examine materials through which light passes, cylindrical reflecting or diffusing walls are inserted in the cages and the materials are inserted in the annular spaces between these walls and the windows. In another modification, the materials may be charged in capsules 67 detachably inserted behind the windows 8. Stray light is screened off by means of flaps 62 held in position by springs against fixed stops.