GB463561A - Improvements in electric timing circuits - Google Patents

Abstract

463,561. Supply systems for resistance welding. BRITISH THOMSON-HOUSTON CO., Ltd., and WHITELEY, A. L. Oct. 1, 1935, No. 27089. [Class 38 (iv)] An electric circuit is energized for a predetermined interval of time from an A.C. source by means of a relay associated with a gridcontrolled discharge tube which is rendered conductive on the actuation of the control device, the period of conductivity being determined by the time taken to charge a condenser in the grid circuit so that it prevents further conduction through the discharge tube. The welding transformer 3 is supplied with A.C. from the mains 1 when the contactor 4 is closed by the relay 5 which is then supplied with rectified A.C. from the mains 1 through the grid-controlled discharge tube 6. Secondary 14 of the transformer 11 heats the cathode while secondary 10 in conjunction with rectifier 12 and smoothing condenser 13 maintains a difference of potential between points A, B and across condenser 9. The cathode is connected to the points A, B through a potentiometer 15 so that the tube is normally rendered non- conducting by a negative grid potential. A weld is initiated by closure of contact 19 which is connected to the electrodes. The consequent current through relay coil 21, while condenser 20 is being charged, closes contacts 22 and discharges condenser 9, thus applying a positive potential to the grid. The tube 6 being thus rendered conductive energizes relay 5 which closes contactors 4 and starts the welding operation. Contactor 23 is opened by the closing of contactor 4 so that condenser 9 is recharged through resistance 16<a> and when the grid potential is sufficiently negative, tube 6 is rendered nonconducting and the welding interval terminates. Specification 435,193 is referred to.