Patent GB-782750-A (GB)
Title: Improvements in or relating to apparatus for enumerating objects
Inventor: GALPIN HAROLD HENRY ALBERT
IPC: G06M11/04
Filed: 1954-12-13
Abstract: 782,750. Photo-electric counting arrangements. CINEMA-TELEVISION, Ltd. Dec. 12, 1955 [Dec. 13, 1954], No. 36003/54. Class 40 (3). The invention relates to particle counters of similar type to that described in Specification 733,562 wherein the field containing the particles is scanned by a light spot traversing a raster of adjacent paths, each path being composed of a linear movement and a rectangular waveform type movement causing alternate parts of two adjacent scanning lines to be viewed. The scanning is arranged such that a particle of minimum size is encountered several times by paths passing across it. Means responding to the impingement of the light on a particle to give an electric signal are provided and the signals are separated into two trains in accordance with whether they were received during scanning of the upper or the lower scanning line. According to the invention one of these signal trains is delayed a time equal to one half of the periodicity of the rectangular waveform movement and the two trains are then combined to give an output signal only when a particle is encountered for the first or last time. The output signals are counted, preferably after integration, to provide an indication as to the number of particles. In the embodiment described the light beam is obtained from the screen 5 of a cathode-ray tube 1 which is scanned over a rectangular area under the influence of line and frame deflection current generators 7 and 8. Further deflection current generator 9 has a square waveform and causes the scanning spot to move abruptly from one line to an adjacent line and back so that it travels its own width along each of the two lines in turn. Light from the screen 5 is focused upon support 12 on which are supported the objects to be counted. Light passing through the support is directed to photo-electric cell 15 to produce an electrical output signal varying between two values in accordance with whether the light beam is passing over an object or not. The output signal is fed through trigger-circuit amplifier 16 to electronic switch 17 operated by signals from generator 9 and directing all the signals corresponding to the parts of the scan along one of the adjacent lines through delay device 21 to anticoincidence device 20. The train of signals corresponding to the scan along the other of the lines is fed directly to device 20 and the delay introduced at 21 is one half of the period of generator 9. Device 20 gives an output only when it receives an input directly from switch 17 and not from delay means 20. These output signals are fed to an integrator 22 which moves on counter 23 only on receipt of a sequence of at least two successive signals. The counter thus moves on only when a fresh object is encountered. Where the light beam scans substantially across the middle of an object only one (or no) output pulse is fed to the integrator which does not operate the counter and likewise the scanning of the " trailing " edge of an object already counted is ineffective (Fig. 2, not shown). In some cases it may be found desirable to arrange that the counter is not operated until a larger number than two inputs signals from circuit 20 have been integrated. Recording separately the numbers of trains of input signals of different lengths applied to the integrator gives some measure of the size distribution of the objects.