GB755568A - Improvements in or relating to welding control - Google Patents

Abstract

755,568. Control systems for resistance welders. FORD MOTOR CO., Ltd. (Ford Motor Co.). May 27, 1954, No. 15730/54. Class 38 (4). To ensure that flow of welding current, and the timing thereof, is initiated only when the electrodes are making good contact with the work, the contactor, or ignitrons 17 through which the welding transformer 15 is supplied is shunted by an impedance, such as a transformer 18, the change of voltage across which, when the electrodes firmly engage the work, is sufficient to operate means for effecting closure of the welding contactor, or opening up of the ignitrons. In the arrangement shown, transformer 18 applies an A.C. " turn-on " voltage of adjustable value to the grid of a thyratron 20 which is normally held non-conducting by an adjustable D.C. bias obtained over a rectifier and potentiometer 21 from a transformer 23. The " turn-on " and bias voltages are so adjusted that the thyratron fires only when the electrodes are in good engagement with the work and the primary winding of the welding transformer 15 consequently presents little impedance in series with transformer 18. Firing of thyratron 20 operates a relay 25 which controls the contactor, or ignitrons 17.