Improvements in or relating to apparatus and methods for limiting the duration of anelectric current to a period of time not exceeding one-half cycle of an alternating current mains supply

摘要

548,236. Control systems for resistance welding &c. FERRANTI, Ltd., and ATKINSON, L. June 18, 1941, No. 7695. [Class 38 (iv)] Switching and thermionic control. Current is supplied from A.C. mains for a period limited to a half-cycle through an ignition 7, the ignition electrode 10 of which is in the charging and discharging circuits of a condenser 12. During negative half waves of potential on the anode of the ignition the condenser is charged through a half wave rectifier 15. A gas filled relay valve is arranged to discharge the condenser during a single positive half wave of potential on the ignition. As shown the relay valve 18 requires excitation of both of two control electrodes 21, 28 to become conductive. The valve 18 fires when the condenser potential through the potentiometer 20 sufficiently excites electrode 28 and when a switch 26 is opened to permit the peaky wave output of a transformer 25 to excite electrode 21. The instant of ignition is determined by a phase shifting circuit (not shown) supplying the transformer 25 and the current period is terminated by the reduction of anode potential on the ignition. In an alternative arrangement the switch 26 is placed in series with the potentiometer 20.