GB530105A - Improvements in and relating to electric valve circuits - Google Patents

Abstract

530,105. Supply systems for resistance welding &c. BRITISH THOMSON-HOUSTON CO., Ltd. (General Electric Co.). March 31, 1939, No. 10180. [A Specification was laid open to inspection under Sect. 91 of the Acts, Oct. 2, 1939.] [Class 38 (iv)] Apparatus for effecting periodic energization of a load such as a welding circuit 1 from an A.C. supply 2 through a pair of reversely connected valves 4, 5 of the immersion igniter type associated with a transformer 3 comprises a pair of valves 12 through which are supplied ignition impulses to the igniter electrodes of the valves 4, 5 under the control of a valve 25 which is in turn controlled by impulses derived from a circuit 74 comprising a condenser 75 arranged to be periodically discharged through a valve 76 in dependence upon the duration but independently of the magnitude of a control voltage applied to its grid. The apparatus also includes (1) a phase-shafting transformer 32 in the anode supply to the valve 25 whereby the amount of energy supplied to the load during the operative periods may be controlled, (2) a polarity selecting arrangement 33 whereby the load may be energized during half-cycles of the same or opposite polarity of the A.C. supply 2 as described in Specification 515,537, and (3) a lock-out circuit 91 which may be brought into operation at will to terminate energization of the load after a single period or after a predetermined number of periods. A three-position switch 123 associated with the control circuits enables the apparatus to be pre-set for (1) energization of the load for a single interval of time at each operation for spot welding, (2) energization of the load for a pre-determined number of final intervals at each operation for interrupted spot welding, and (3) energization of the load for an indefinite number of time intervals for seam welding, the lock-out circuit in this case being inoperative. Each energization may comprise a fraction of a halfcycle, a complete half-cycle or a definite number of complete or fractional half-cycles of current. Specifications 514,004 and 515,528 also are referred to.