GB466577A - Improvements in circuit arrangements for automatically timing operation of electric apparatus - Google Patents

Abstract

466,577. Supply systems for resistance welding. BRAILSFORD, F., and METROPOLITAN - VICKERS ELECTRICAL CO., Ltd. Dec. 2, 1935, No. 33379. [Class 38 (iv)] [Also in Group XL] A timing circuit for electric welding or the like comprises a gas discharge tube having a condenser and resistance in the anode circuit coupled to the grid circuit of a similar tube. Means are provided to apply to the anode circuits alternating current voltages of predetermined phase and to the control electrode of the first tube a voltage of peaked wave form to ensure operation at the maximum point in the wave and so that a predetermined number of voltage impulses are applied to the second tube and the latter operated for the predetermined number of cycles. The Figure shows a timing discharge tube 46 with the anode and grid energized from two phases of a three-phase supply which effects the charging of condenser 49 through resistance 37 when contact 50 is open and contact 57 is closed. The resistance 37 in the grid circuit of a discharge tube 24 controls this tube. A second tube 25 passes current in the half cycle succeeding a half cycle in which the tube 24 is energized as transformer 18 is energized and charges condenser 44. In this way a single impulse from the timing contacts applies a complete cycle to the primary of transformer 18. The secondaries 19, 20 of this transformer control the discharge tubes 6, 7 in the circuit of the primary 5 of a welding transformer. The tubes 6, 7 may be Ignitrons " in which the discharge is initiated by a starting electrode in contact with one of the main electrodes. The discharge devices may have time delay relays in the supply circuit to enable the filaments to be pre-heated while resistance 62 of material which is conductive only at high voltages, may be provided to prevent surges. In addition a protective spark-gap in series with a condenser may be connected across the control electrode and cathode of each power circuit discharge tube. A switch 63 may be provided to prevent operation of the tube 6 when the load circuit is required to operate only for one half cycle,