GB558814A - Improvements in and relating to control systems for electric welding and other circuits - Google Patents

Abstract

558,814. Control systems for resistance welding &c. BRITISH THOMSON-HOUSTON CO., Ltd. June 18, 1942, No. 8353. Convention date, June 19, 1941. [Class 38 (iv)] Thermionic control.-An impulse of current is obtained from an inductance, such as the primary winding of a transformer feeding a welding circuit, by interrupting unidirectional current flowing in the inductance when the current in an A.C. supply circuit furnishing it has reached a predetermined value. A valve 34 is maintained non- conductive by a grid bias voltage derived from a potentiometer 42 in shunt with a voltage stabilizing glow discharge tube 40 supplied from a D.C. source comprising a condenser 30. When a switch 51 is opened a coil 32, energized across a resistance 39 in series with the tube 40, is deenergized and a relay 19 operates to connect the inductance 17 to a polyphase rectifier circuit 3. As the current rises in the inductance a current transformer 45 superposes an alternating voltage on the grid of valve 34 which, accordingly, becomes conducting at a current value predetermined by the potentiometer tap and energizes the coil 32 to cause the relay 19 to interrupt the current through the inductance. The rectifiers may have immersion-ignitor control members and the voltage of the D.C. furnished may be determined by controlling or adjusting the timing of the impulses supplied by the exciting circuit 15 to these members.