GB515537A - Improvements in and relating to control systems for arrangements employing electric discharge devices - Google Patents

Abstract

515,537. Supply systems for resistance welding etc.; converting. BRITISH THOMSON-HOUSTON CO., Ltd. June 2, 1938, No. 16556. Convention date, June 2, 1937. [Classes 38 (ii) and 38 (iv)] Thermionic control.-A pair of reversely paralleled valves 7, 8, which determine the supply from an A.C. network 1 to a load circuit 2, e.g., a welding circuit, are controlled from circuits 63, 12 and 47 such that (a) periodic impulses are supplied to the load circuit, successive impulses commencing in half cycles of the supply of opposite polarity, or (b) periodic impulses are supplied to the load circuit, successive impulses commencing in half cycles of the supply of similar polarity, or (c) a single impulse is supplied, the arrangement being preset after an impulse so that the next impulse when required commences in a half cycle of the supply of opposite or of similar polarity. Peaked grid control voltages for the valves 7, 8 are derived from the circuit 47 which comprises a transformer 57 having a centre tapped primary winding 58, 'fed from the transformer 48 through diodes 53, 54 and a valve 55 grid controlled from the circuit 12. The supply to the transformer 48 is through a phaseshifting transformer 52 to enable the power transmitted by the valves 7, 8 to .be adjusted by control of themoment of ignition. The circuit 12, for controlling the valve 55, is a parallel type inverter .comprising a pair of parallel paths, each consisting of a valve 20 or 23 and an impedehce 21, 22 or 24, 25. The control potentials of the valves 20, 23 are obtained from a transformer 37 a switch 43 being provided to enable the grid of the valve 23 to be energized either in phase or 180 degrees out of phase with the energization of the grid of valve 20 so that the voltage impulses across the resistance 32 for controlling the valve 55 would occur successively in half cycles of the control potential of similar or opposite polarity respectively. A further switch 64 is also provided to enable a control circuit 63, comprising a glow discharge tube 69 in series with a condenser 70 and resistance 71 across the D.C. supply, to be included in the grid circuit of the inverter 12 to give control as defined in (c) above in dependence on the actuation of a switch 76. In a modification the valves 7, 8 are of the immersion igniter type, the circuit 47 is omitted and the anodes of the valves 20, 23 are connected to a centre tapped transformer which supplies control potentials to grid controlled valves which supply the ignition electrodes of the main valves. Specification 514,004 is referred to.