Patent GB-727134-A (GB)
Title: Improvements in or relating to electrical counting apparatus
Inventor: BAREFORD CHRISTOPHER FREDERIC
IPC: G06M11/04
Filed: 1951-03-06
Abstract: 727,134. Particle counting by radiation beams. MULLARD RADIO VALVE CO., Ltd. March 6, 1952 [March 6, 1951], No. 5473/51. Class 40 (3). Particle counting apparatus comprises means such as a cathode-ray tube for scanning a sample of the particles, means such as a photocell co-operating with the scanning means for producing a signal which is an indication of the presence of a particle, and a number of position memory units for remembering the positions along a line of scan of the interception of a particle by a spot until corresponding positions are reached in the succeeding scanning line and means associated with these units for registering the number of times a particle is remembered and counting means for giving a total count of the number of particles. General operation (Fig. 1).-The scanning generator 1 comprises a cathode-ray tube on the face of which is produced a rectangular raster by saw-tooth " line " and " frame " time bases. A sample of the particles to be counted or a photographic reproduction is inserted between the tube and the " pick-up " unit 2 which is a photo-electric cell. Alternatively the cell may receive light reflected from a photographic print. When the scanning of the first line commences the first particle in the line produces a pulse in the photo-cell 2 which is passed through a main route control switch 3 to the first of a number of channel selector switches 4 and then to a "position memory unit " 12. The position memory unit is triggered to " remember " where the particle occurred in the scan and sends a pulse back to the first channel selector 4 which is operated so that the next pulse in the line is sent to channel selector 5 which in turn is joined to selector 6. Thus each successive particle in the first line is registered on a different position memory device. During the scanning of the next line, immediately before the beam reaches a position corresponding to the first particle encountered, position memory unit 12 restores channel selector 4, opens the route control switch 3 and closes memoryoperated switch 8. Thus, if the first particle is again encountered the output of the cell is fed direct to the first channel. If the first particle is a small one, i.e. it does not extend across two scanning lines, after an inspection period memory-operated switch 8 opens and the main control switch closes, the channel selector being left in its original position. When the scanning beam reaches the second particle, which extends across two lines, position memory 13 restores channel selector 5, opens main control switch 3 and closes the memory-operated switch 9 so that the expected pulse from the large particle is directed to memory unit 13 which is reset so that a similar check is made in the third line. A new particle encountered in the third line will register in the now vacant first channel. The main control switch (Fig. 2), comprises a pair of valves V18, V19, of which V18 is initially conducting. A negative pulse received from the photo-cell blocks V18 which in turn unblocks V19 on its suppressor grid. The negative pulse from the anode of V19 is passed to valve V1 in the first channel selector switch and the positive pulse produced at the anode of V18 is passed to all the memory-operated switches. The control grid of V19 is also connected to all the memory-operated switches. The channel selector switches:-The negative pulse from V19 is passed through a valve V1 to the suppressor grids of a pair of valves V2, V3, both of which are blocked at their suppressor grids, V2 being also blocked at its control grid. A further pair of valves V4, V5 constituting a bi-stable multivibrator, is provided, the anode of V4 being connected to the grid of V2 and the anode of V5 to the grid of V3. The negative pulse from V 19 opens V3 and the negative pulses from the anode of V3 alter the stable position of valves V4, V5 and is fed to the particle completion unit and a sizing adder. When V4, V5 change over the potential of the control grid of V3 is lowered and that of V2 is raised. Hence, both V2 and V3 are cut off and a following pulse from the main switch is directed to the next channel selector. The position scanning unit (Fig. 2) comprises a condenser CM, one pole of which is connected to the line scanning potential of the cathode-ray tube time base. The other pole is held at earth potential by a clamp comprising valves V6, V7 and is connected to the grid of a cathode coupled pair of valves V8, V9. When the pair of valves V4, V5 in the channel selector triggers, the potential drop at the anode of V5 is used to open the clamp. Thereafter the pole of the capacitor follows the descending sawtooth of the line scan voltage until on the flyback it causes valve V8 to conduct and V9 to block. As the sawtooth potential falls in the subsequent scanning line a point is reached at which, if potentiometer 20 is correctly adjusted, V8 blocks and V9 again conducts. At this moment the clamp is closed by using the change of potential at the anode of V9 which change is fed back to valve V5 through condenser C3 to reset the channel selector switch and hence the clamp V6, V7. This change is also used to set a " width " unit and a particle completion unit to indicate whether a particle has been totally counted or not. V8 blocks a little previously to the point at which it did so in the previous line, thus providing an anticipation interval. The width unit comprises a further clamp V10, V11 and valves V12, V13 forming a multivibrator. The clamp holds one pole of a width capacitor CW at earth potential, the other pole being connected to the line scan. The negative pulse from V9 cuts off V13, the positive anode pulse being communicated through link A to the memory operated switch V20, V21 and opening valve V12. V12 opens the clamp V10, VII and the suppressor grid potential of V12 falls with the line scan until after an interval to allow for the appearance of a pulse produced as a result of the second scanning of a particle V12 is again suppressed. The pulse appearing at the anode of V12 when V9 cuts off V13 is passed to the memory operated switch through link D. Particle completion unit (Fig. 2).-The purpose of this unit is to indicate when the scan of a particular particle has been completed when it may be registered on an appropriate counter. It comprises valves V15, V16 of which V15 initially conducts and V16 is blocked. The negative pulse produced at V9 when the memory switch is again opened to receive a second pulse from a particle scanned in a previous line, cuts off V15 which in turn opens V16, the potential on the screen grid of which falls. At the end of the " width " period during which a second pulse should arrive, the anode of V13 falls in potential, this fall being applied to the suppressor grid of V16 so that all the valve current is carried by the screen grid, the potential of which falls. The rise of potential at the anode of V10 unblocks V15 which in turn unblocks V16 and the screen grid potential rises. If a particle pulse is received during the width period from valve V3, link E, valve V16 is cut off at its control grid, hence screen grid potential does not fall. This difference in screen grid potential according as a pulse is received during the width period or not is utilized to actuate a sizing adder. Memory operated switches (Fig. 1).-Each memory operated switch comprises a pentode V20 and a diode V21. The suppressor of V20 is connected to the anode of V18 in the main control switch, its control grid being connected to V13 in the position memory unit. V20 is initially at off on both its suppressor and control grids. The cathode of diode V21 is connected to the anode of V12 in the position memory switch and its anode, in common with all the diodes in the memory operated switch are connected to the grid of V19. During the second scanning line the position memory 12 operates at the appropriate moment, at the commencement of the width period lowering the cathode potential of diode V21 (link D) and cutting off valve V19 at its control grid. At the same time the position memory raises the control grid potential of V20 (link A) so that the expected pulse on its suppressor grid can cause the valve V20 to conduct. When this pulse arrives it opens valve V20 which delivers a pulse to V1 in the channel selector. Hence the main control switch is opened and the memory operated switch closed whenever one of the position memory units operates to commence a " width inspection " period. Thus the memory operated switch ensures that a pulse in the width period is delivered into the channel in which it is registered. Sizing adder (Fig. 4).-Each time a particle it scanned a small pulse is produced by the particle completion unit until in the first scan in which the particle is not detected a larger pulse is given out. The small pulses are added in the circuit of Fig. 4 in which valves V22, V23 form a cathode coupled pair. The negative pulses received through link E block V22 and open V23. These valves restore after a period determined by condenser C9 and resistor 36. The positive pulse from the anode of V4 is fed through the diode pump circuit (diodes V24 V25, capacitor CP). The output of the ring circuit is delivered via diode V30 to a kick sorter of the type described in Proc. I.E.E., Part III, No. 97 (March, 1950), pages 108-120, which sorts the pulses according to amplitude. Associated with the pump circuit is a multivibrator V27, V28. To the grid of V27 is fed the pulse developed at the screen grid of V16 in the particle completion unit. Successive pulses produced as the particle is scanned in each line are integrated on capacitor CP, but in the line in which the particle does not appear the large pulse produced at the screen grid or V16 (line F) blocks V27, and V28 conducts, hence capacitor CP discharges through diode V29 and resistor 37. A negative pulse appears at the cathode of V26, the amplitude of