GB758971A - Improvements in or relating to devices for controlling the welding times and intervals in resistance welding apparatus - Google Patents

Abstract

758,971. Control systems for resistance welding. PHILIPS ELECTRICAL INDUSTRIES, Ltd. May 14, 1954 [May 18, 1953], No. 14193/54. Class 38 (4). A circuit for generating across a resistor 24 voltage pulses for controlling the lengths of the " on " and " off " periods of a resistance welding machine comprises a thyratron relaxation oscillator 1, 3, 6 generating pulses having an interval between them equal to the sum of the two periods, a second similar oscillator 13, 15, 17, for determining the ratio of the two periods, subject to control both by the pulses of the first oscillator (applied over pulse transformer 7) and by mains frequency pulses (injected by transformer 27), and a trigger circuit controlled by the second oscillator over pulse transformer 16 and comprising thyratrons 18, 19, the anode circuit of 19 of which includes the resistor 24 which also forms part of the grid circuit of the second oscillator and so controls the standing D.C. bias on its thyratron 13 according as to whether or not thyratron 19 is conducting. The arrangement is such that the discharge in thyratrons 18, 19 switches from one tube to the other each time the second oscillator pulses transformer 16 and the magnitude of the mains frequency pulses supplied by transformer 27 is such that they are unable to trip tube 13 when tube 19 is conducting and resistor 24 providing hold-off bias. Tube 13 is, however, tripped by the larger amplitude pulse supplied by transformer 7, whereupon tube 19 becomes non- conducting, the bias on tube 13 is removed and that tube then comes under the control of transformer 27. Tube 13 thus fires alternately under the control of transformer 7 and transformer 27.