GB551775A - Improvements in systems for maintaining constant power consumption in a.c. circuits subject to voltage variation - Google Patents

Abstract

551,775. Control systems for resistance welding etc.; automatic regulation. BUDD MANUFACTURING CO., E. G. Jan. 26, 1942,. No. 1085. Convention date, Dec. 31, 1940. [Class 38 (iv)] Thermionic control.-To obtain an automatic adjustment of the time during an A.C. cycle in which current flows to a load, such as a resistance welding circuit 12, to prevent a change in power consumption due to variation in supply source voltage, the phase shifting means controllihg'the timimg of a gaseous discharge device 14, 16 through which the load is supplied comprises a phase shifting impedance 64 varied by means automatically responsive to the variations of supply voltage. Ignitrons 14, 16 are controlled by screen grid gaseous tubes 20, 22 the grids of which receive timing impulses compounded of voltages from a peaking transformer 36, a " hold-off" transformer 44 and a timer controlled transformer 28 neutralizing the second. Welding current is determined by a resistor 54 in a phase shifting circuit supplying the peaking transformer which is connected between taps 56, 58 in parallel. phasing circuits containing the primary winding, of a transformer 64 the impedance of which is determined by the conductivity of electron tubes 66, 68. The negative grid voltage of these tubes increases with fall in supply voltage being compounded of a constant voltage from a potentiometer 92 and a smaller opposed voltage from a potentiometer 82, varying with the supply volts. The potentiometers 82, 92 receive rectified voltages from a transformer 78 subject to supply voltage variations.