Patent GB-732662-A (GB)
Title: Apparatus for counting particles
Inventor: WALTON WILLIAM HENRY
IPC: G06M11/04
Filed: 1951-12-17
Abstract: 732,662. Particle counting apparatus. COAL INDUSTRY (PATENTS), Ltd. March 16, 1953 [Dec. 17, 1951; Sept. 22, 1952], Nos. 29460/51 and 23720/52. Class 40 (3). In apparatus for determining the number and/or distribution of sizes of particles in a collection wherein the collection is scanned along a series of parallel lines by a radiation beam, the electric signal produced each time a beam traverses an element is temporarily recorded on a magnetic track so that a count may be made either of the number of pulses produced during the scanning of each particle or only when the scanning of each ,particle is completed. As shown, the pulses produced by the scanning head are applied through an amplifier RA2 to a recording head R which transfers the signal to a magnetic track on the periphery of a rotating drum D. This drum performs a single revolution in the time taken to scan two lines of the sample. The signal from the scanner is simultaneously applied to a mixing circuit M2. A little more than half-way round the drum is a pick-up head P also feeding the mixing circuit. The signal is erased at E before reaching the scanning head. If a pulse is received at the mixing circuit from the scanner at the same time as one is delivered from pick-up P, the mixing circuit is not operated. Thus only on the line following the final scanning line does the pick-up head deliver a pulse to mixing circuit M2 which then operates a counter C2. A suitable circuit is described with reference to Fig. 6. The input from the scanner is amplified at VI, operates a recording head R and is applied to a flip-flop circuit comprising V3 which blocks on its right-hand side. The pulse from pick-up head P, amplified at V5 and V6, is then applied to the grid of valve V4 which is in series with the right-hand side of V3, hence a pulse is produced at the anode of valve V4 only if no pulse is simultaneously applied from the scanner to valve V3. In the arrangement of Fig. 4, drum D carrying on its periphery two tracks T1, T2 (shown concentric), rotates once during each line scan. The output of the scanner is simultaneously recorded on both tracks by heads R1, R2. both tracks being subsequently read by pick-ups P1, P2. P1 feeds a mixing circuit M4 through an amplifier A41 while P2 feeds this circuit through an amplifier A42 and pulse shaper PS4. The mixer feeds counters C4 and, through a delay circuit D4, an erasing head E2. In operation mixer M4 feeds a pulse to counter C4 and delay circuit D4 only if a pulse is received from track T2 but not from T1. At a further point in the drum rotation erasing head E1 removes track T1. Then each time the drum rotates and the scanning beam encounters the particle, signal T1 is re-recorded while signal T2 merely increases in width to the maximum intercept of the scanning beam with the particle. When the scanning beam misses the particle, track T2 only carries a signal and mixing circuit M4 feeds counter C4 and delay circuit D4 also. The delay circuit operates erasing head E2 to remove the signal on track T2. Counter C4 includes a device for converting the width variations of the signals on track T2 into amplitude variations which are then passed to a pulse amplitude analyser of known type. The mixing circuit is as described with reference to Fig. 6 but a suitable delay circuit is also described with reference to Fig. 8 (not shown). In an arrangement described with reference to Fig. 10 (not shown), the line scan intercepts are added together to obtain a measure of the area of each particle. In this arrangement the drum has three tracks. The output of the scanner is recorded on one track and is passed through an adding circuit and recorded on a second. Operation is as for the arrangement described with reference to Fig. 4 except that during the rotation the signal from the second track is transferred by means of a pick-up, amplifier and recording head to the third track. This third track is read when it reaches the initial recording position by a further pick-up head applied to the adding circuit where it is added to the incoming signal from the scanner and again recorded on track T2. The signal on the third track is erased. Thus when the line following the particle is scanned the pulse passed to the counter is proportional to the area of the particle scanned. In the arrangement of Fig. 11 (not shown), a number of tracks equal to the maximum number of scanned lines in the largest particle is provided. The first interception is recorded on the first track which during rotation of its drum is transferred to a second track, an erasing head deleting the signal from the first track. During the next revolution the signal is transferred to the third track while a subsequent pulse is recorded on the first track. When the first signal reaches the outer track, it operates an electric switch and registers itself on a counter at the same time so that all the pick-ups on previous tracks are connected to individual counters; each counter representing a number of interceptions of the scan by a particle. In a modified version of Fig. 11 (Fig. 12, not shown), a single helical track is used, the pick-up and recording heads being moved by one pitch of the helix each revolution. In this arrangement the drum must be stopped and the signals erased between each scan. A system is described with reference to the drawing accompanying Provisional Specification 23720/52 in which the signals are impressed on a single track around which are positioned a number of pick-up heads and an erasing head. The signals from the head are passed to a " multiple coincidence unit " the arrangement being that only when the first signal arrives at the last pick-up is the first counter operated, and the circuit prepared for operation of the second counter by the next pulse. The second signal operates the second counter and prepares the third and then operates the first counter again. Thus after a complete scan the difference between the various counter readings give an indication of particle size. If all pick-up heads are receiving a sig simultaneously the count is cancelled impulsing all the counters in the reverse di tion or an oversize counter may be operated