Patent GB-766342-A (GB)
Title: Method and apparatus for automatic counting and sizing of particles
Inventor: PHILLIPS JAMES WILLIAM
IPC: G06M11/04
Filed: 1953-05-07
Abstract: 766,342. Photo-electric particle counter. COAL INDUSTRY (PATENTS), Ltd. Aug. 5, 1954 [May 7, 1953], No. 12789/53. Class 40 (3). Apparatus for counting and sizing particles in a collection comprises two or more light sensitive scanning heads arranged in a line and each connected through a signal channel to an electronic counter common to all channels, each signal channel including switching means whereby the presence of a signal in one channel prevents the independent passage to the counter of an overlapping signal in an adjacent channel, thus preventing multiple counting of a particular particle. An enlarged image of the area to be examined produced by a projection microscope or a flying spot microscope in which the picture appears on the screen of a cathoderay tube is moved across the line of scanning elements by inserting a moving deflector, e.g. a prism into the optical system for projecting the image. Part of the image may be used for monitoring. Fig. 1 shows an arrangement for counting only signals derived from the output of five detector heads I-V placed side by side perpendicular to the direction of scanning. As shown in Fig. 5, head III encounters the particled image first and a positive signal is passed to the control grid of the left-hand triode of the lower double triode in channel III. The left-hand triode conducts, its current passing through the right-hand side of the upper double triode because of its higher grid potential and operating a counter 12 common to all channels. The negative pulse at anode B is passed to the left-hand grid of the same triode pair and locks it so that the right-hand side continues to conduct as long as the pulse from the scanning head persists. When the left-hand side of the lower triode conducts, the right-hand upper triode of neighbouring channels II and IV are cut off. As scanning proceeds head II produces an output pulse but the current through the upper triode runs " to waste " through anode F. However, the adjacent left-hand channel I is disabled but the pulse is insufficient to close channel III which is locked open. If channel V which constitutes a guard channel receives a pulse when channel IV has not been tapped the signal runs " to waste" from anode F. If channel IV has already detected the particle however the righthand triode conducts and a negative counter connected to anode K cancels the count already registered by one of channels I-IV. Thus particles which overlap the left-hand border are counted as are those contained entirely in channels I-IV. Those overlapping the left-hand border are not. Fig. 3 shows an arrangement for sizing particles by measuring the total intercept of all the scanning heads with one particle. This is done by locking to a single integrator all channels receiving signals due to the interception of one particle. As shown, each scanning head feeds a ladder of electronic switches each comprising double triodes 21-24, seven channels are described of which channels IV, V and VI are main channels I, II and III border channels and VII a guard channel. The function of the guard channel is to cancel the count if a particle overlaps it. The channels are interconnected at each level but only the interconnections at the third level are shown. One of integrators I1 to I4 is connected to the left-hand anode of each of the double triodes in each channel. Supposing a first pulse to be received at channel VI the left-hand side of triode 21 in this channel is opened and the signal passes to the integrator I1. The potential developed at the anode connected to integrator I cuts off the right-hand triode, thus blocking the path of the pulse to the integrator, and opens the left-hand side of the adjacent double triodes in channels V and VII. Thus subsequent pulses produced by particle interception in neighbouring channels are also passed to integrator I1 which thus adds the total current caused by all the intersections of the particular particle. When the integrator I1 receives a pulse, it delivers a pulse through condensers 31 to block the lefthand triodes of all except adjacent valves at the same level. Thus, pulses produced at these heads represent a different particle and are passed to the next integrator I2. If channel V is energized before channel IV the pulses are assumed to originate from the same particle. Valve 21 of channel IV is reset and signals received on this channel are passed to integrator I1. Guard channel VII passes a current to waste until a signal is received on the right-hand grid of valve 20. It then passes a signal to integrator I1 unless valve 21 in the channel can be switched to the " through " position by a negative pulse received from integrator I1 in which case the signal is passed to valve 22. If channel VI is passing a signal to integrator I1 when a signal is received in channel VII valve 21 will have been primed by an over-riding negative pulse received at the control grid of its right-hand triode from valve 21 in channel VI. The signal in channel VII will be passed to integrator I1 and will cancel the count as described with reference to Fig. 4 (below). All of channels I-VI are connected to integrating condenser C1. Signals from border channels I, II and III are stored in C1 until a gas-filled valve V5 fires due to a signal in one of main channels IV-VI which render V8 non-conductive triggering V5. The charge on V1 is now shared between C1 and C2. When no further signals are received these three cut off. Relay V1, V2 turns over, applies a positive pulse to V6 which fires subsequently followed by V4 which receives a pulse immediately afterwards. The discharge through V6 generates a signal at the counter through conductor 35 and a pulse amplitude short sorter (not shown), which is proportional to the peak charge of Cl and C2 that is to the sum of the signal. If guard channel VII is energized V9 triggers V7 discharging both C1 and C2 so that no signal is passed to the counter.