Patent GB-701598-A (GB)
Title: Improvements in or relating to record card controlled statistical machines
Inventor: ENGLISH FRANCIS GUY SYDENHAM
Filed: 1951-04-04
Abstract: 701,598. Statistical apparatus. POWERS-SAMAS ACCOUNTING MACHINES, Ltd. Feb. 25, 1952 [April 4, 1951], No. 7863/51. Class 106 (1) A record card magnetic sensing means comprises for each column on the card a sensing head having a narrow-gapped ferro-magnetic cored inductor supported with its air gap in close proximity with the path through which the card is fed. The data is recorded on the record card by means of a marking material having ferromagnetic properties whereby location of a mark across the air gap varies the electrical inductance of the sensing head to change the output voltage from its circuit. The sensing means also includes an amplifier to amplify the output voltage and electronic gating means to select a utilization circuit in accordance with the value of the mark sensed on the card. Cards 1 are fed from a magazine 4 by a picker 5 in known fashion to feed rolls 67, and thence under a narrow gapped sensing head 15, Fig. 1. Each of the narrow-gapped sensing heads comprises a ferromagnetic core, Figs. 5, 8 in two halves 13 with a gap 15. Two coils 14 are mounted on each half core 13. When a magnetic mark 2, Fig. 8, is aligned beneath the gap 15 the inductance of the head is changed sufficiently to be detected by a bridge circuit, Fig. 6. The bridge detecting circuit comprises two inductive ratio arms SH and DH and two resistance arms shown as 470 ohms each. The bridge is fed with 1.5 volts A.C. at 4,000 cycles per second, the output being taken from the junction of a 80 milli-henry choke and a 5 Á f condenser as shown. The two inductive arms are comprised by the sensing head SH, and a dummy head DH which is not located for sensing but being identical with the sensing head serves to cancel out variation in inductance due to changes in temperature or humidity. The output from the bridge is fed to the control grid of a three stage amplifier 31, 32, 33. The output of the amplifier is fed to a line 36 common to twelve gas-filled tetrodes 35, all the control grids of the tetrodes 35 being returned to the line 36, thus when a positive pulse is received on line 36 from the amplifier any of the tetrodes which has been conditioned to fire will conduct and send an actuating current through its associated solenoid winding 19 which solenoid winding is arranged to operate for example a punch selecting member. Conditioning of the tetrode gate valves 35 so that they are able to fire when a positive pulse is received on line 36 is carried out by switching the suppressor grid 39 of each tetrode in timed sequence to earth thus removing for each in turn the standing negative bias supplied by line 38 common to all the tetrodes. The earthing of the suppressor grids is arranged in timed sequence by a distributer contact arrangement 40 operating between pairs of contacts 46, 47. The moving contact 40 is shown also in Fig. 1 and is driven by gearing from the main shaft the timing of the contact 40 being arranged in a manner well known in the art so that the appropriate tetrode is conditioned for firing'at the time that the particular index position is under the sensing head. The movement of the card is synchronized with the machine cycle by a card stop 48 which arrests each card in turn with the first data representing position beneath the sensing heads. The stop 48 is then withdrawn to allow the card to proceed, when the contact 40 is engaging the first pair of brushes 46, 47. At the end of each cycle contacts 51, 52 are opened by a cam which causes associated contacts 57, 58 to open and remove the positive voltage from the anodes of the tetrodes thus restoring any that have fired and are conducting, to their normal non-conducting state.