GB779160A - Improvements in or relating to particle-counting systems - Google Patents

Abstract

779,160. Photo-electric particle counters. CINEMA-TELEVISION, Ltd. Aug. 11, 1955 [Aug. 12, 1954], No. 23429/54. Class 40 (3). In an apparatus for counting particles in which an area comprising the particles is scanned, for example by a travelling light spot, to derive signals corresponding to the presence of an object in order to produce pulses which have only two possible valves the scanning spot is traversed in at least one direction in a succession of substantially instantaneous transitions from one position to an adjacent position separated by pulses of finite duration at each of the positions. As shown, a transparency B comprising the objects to be counted is positioned in front of a photo-cell 5 which produces impulses when the light beam is intercepted by such an object. The output pulses are amplified at 6, recorded on a rotating magnetic track 8 by a head 7 and applied to an anticoincidence circuit 10. Signals previously recorded on the track are read in known manner by the same head and the anti-coincidence circuit, which may be as described in Specification 778,288, delivers a pulse to a counter 11 only when the scanning spot encounters a transparencing for the first time. Also recorded on the magnetic drum are 200 sinusoidal signals in a track 13 which signals are read by head 12 and used to control the " line " defiection of the scanning spot through a scanning generator 18 and the intensity of the spot through a device 14. Scanning generator 15 is such that each negative-going peak of the applied sinusoidal signal produces a movement of the scanning spot from one position to an adjacent position while during positive excursion of the signal the spot is stationary. Thus the waveform of generator 15 is a " staircase ". Device 14 causes the spot to appear only during the positive going peaks of the sinusoidal signal. A signal produced in generator 15 during the fly-back at the end of each line is applied to a dividing circuit 16 which produces a signal having the frame frequency and sychrons a scanning generator 17 to generate a frame saw-tooth. Alternatively a third head 18 may receive a signal 19 of line frequency recorded on drum 8 and fed to the divider 16. Specification 778,289 also is referred to.