GB901465A - An arrangement for digitally counting electric pulses - Google Patents

Abstract

901,465. Electric selective signalling systems. LICENTIA - PATENT - VERWALTUNGS - G.m.b.H. Feb. 13, 1959 [Feb. 14, 1958; Jan. 15, 1959], No. 5068/59. Class 40 (1). [Also in Groups XIX and XXXVI] Apparatus for digitally counting electrical pulses of a train during a predetermined time interval and for indicating the count comprises two electronic counting circuits each comprising bi-stable flip-flops and a timing device for controlling the operation of the counters, the system being such that one electronic counting circuit counts the incoming pulses while the other electronic counting circuit stores the value counted during the predetermined time interval and supplies the stored value to an indicating device. In Fig. 2, positive-going input pulses, derived e.g. from intermittent illuminations of a photocell through a perforated disc driven by a motor whose speed is to be measured, pass through a pulse shaper 18 to two alternately-operating decade counters 14, 15 and 16, 17 (see Group XIX), which prepare corresponding units and tens indicating instruments 19, 20. A crystal oscillator 60 of e.g. 20 kc/s. energizes a pulse shaper 61 and four successive frequency dividers 62, 63, 64, 65 to produce a pulse train at 2 kc/s. continuously changing over a crossconnected bi-stable transistor flip-flop circuit 23 supplying alternately weak and strong negative bias voltages to the bases of transistors 66, 68 connected in other bi-stable flip-flop circuits 21, 22 with respective transistors 67, 69, so that transistors 66, 68 alternately block and conduct and 67, 69 conduct and block in succession. When 66 or 68 blocks, a negative bias is applied over resistor 70 or 71 in super-imposition in the input pulse train to bias back the input of first decade counter 14 or 16 and to thus disable it from counting the input pulses while also biasing gate transistors 72, 73 or 74, 75 to correspondingly open the circuits connecting indicating currents from the decade counters 14, 15 or 16, 17 to the common units and tens indicating instruments 19, 20. Thus for a given time interval, the input pulse train is being counted by units and tens counter 14, 15 whose indicating current circuits are disconnected from measuring instruments 19, 20, while the latter are connected to produce indications responsive to the count during the preceding time interval recorded on units and tens counters 16, 17. For subsequent equal time intervals counters 16, 17; 14, 15 are alternately connected to count the input pulses and to display the count by deflection of the units and tens instruments 19, 20. Fig. 5 shows apparatus for comparing the speeds of two motors, e.g. generating pulse trains at e.g. 1000 pulses per revolution at terminal 8 (not shown). The first pulse train is shaped at 82 and frequency reduced by a ratio of, e.g., 1: 1000 in frequency divider 83 to operate control stage 84 to pulse once per revolution. The second pulse train is applied over terminal 99 and pulse shaper 96 through gate circuit 97 to counting decades 86, so that the count represents, e.g., the number of revolutions of the second motor per 1000 revolutions of the first. After the latter have been completed, control stage 84 is pulsed to operate transfer circuits 91 to 94 through pulse amplifier 85 to transfer the accumulated count to decade indicators 87 to 90, and to pulse the cancelling circuit 95 to zeroize the counting decades in readiness for a succeeding count. Gate circuit 97 is closed in response to control stage 84 during the transfer to prevent spurious indications arising from input pulses arriving during the transfer time. If a pulse sequence proportional to time is applied to terminal 99 and an input pulse train to terminal 81, the indication represents time for a given number of pulses, while if these inputs are transposed, it represents the number of pulses per unit time.