GB749815A - Improvements in and relating to control systems for resistance welding apparatus - Google Patents

Abstract

749,815. Control systems for resistance weiders. BRITISH THOMSON-HOUSTON CO., Ltd. May 5, 1953 [May 6, 1952], No. 11418/52. Drawings to Specification. Class 38 (4). A control circuit for back-to-back resistance welding ignitrons comprises means for deriving a sequence of square pulses from the A.C. supply, a multi-cathode counter tube for counting, after closure of an initiating switch, a predetermined number of pulses during which a gating valve is maintained non-conducting to prevent firing of the ignitrons, and a second similar counting tube which then becomes effective to count another predetermined number of pulses during which the gating valve is maintained open to allow firing of the ignitrons for this period. A further valve may become effective upon the second tube counting out to re-start the cycle of operations, which will then continue to repeat for so long as the initiating switch is maintained closed. The phase of the sequence of pulses may be adjustable with reference to the supply voltage wave so as to allow control of the phase of the pulses from the gating valve when it is conducting and thus provide for heat control in the welding circuit. A further counting tube may be provided to count a predetermined number of pulses corresponding to a desired number of " on " and " off " periods of welding current and to terminate the welding operation when this number has been counted.