Patent GB-500871-A (GB)
Title: Improvements in or relating to timing arrangements for the control of electromagnetic switches controlling alternating current circuits
IPC: B23K11/24
Filed: 1937-08-11
Abstract: 500,871. Valve circuits. IGRANIC ELECTRIC CO., Ltd. Aug. 11, 1937, No. 22094. Convention date, Aug. 15, 1936. [Class 40 (v)] [Also in Groups XXXV and XXXVII] In an arrangement for timing the duration of closure of an electromagnetic switch 25 controlling an A.C. circuit for short or long periods so that the switch always opens at a predetermined point in the A.C. cycle, means are provided which control the point in the cycle at which the switch coil is energized for one type of timing period, and which control the point in the cycle at which the switch coil is de-energized for the other type of timing period. In a welding control system the primary 26 of the welding transformer is connected to supply L<2>, L<3> through a switch 25 the coil 25 a of which is energized from a rectifier 1 under the control of a push button 19 and a gas discharge valve 20. Short period closure is obtained with a switch 23 in the position shown in which on 'closure of the button 19, the coil is in series with a condenser 29 and the valve 20. The grid of valve 20 is negatively biassed from a potentiometer and rectifier arrangement 7, 8, 9, 10 but conduction is initiated at a predetermined point in the cycle when a switch 12 opens and introduces a resistance in the grid circuit. The resistance 15 is connected across a peaking arrangement comprising a glow discharge tube 16, and condenser 18 and resistance 17 connected to A.C. supply through an adjustable phase shifting transformer 5 determining the instant of conduction of valve 20. The switch 12 is controlled by a valve 11 shunted by a condenser 13 and connected to D.C. supply over a resistance 14 and switch 19 so that the valve 11 conducts only after the switch 19 has been firmly closed. The duration of the current flow through the coil 25a is adjustable and is determined by the charging time of the condenser 29. The condenser 29 may be adjusted with the inductance of the circuit so as to produce oscillations whereby the valve 20 is extinguished at the first zero point and the duration of current flow is limited to less than one half cycle of the A.C. supply. By adjusting the phase shifter 5 and condenser 29 the switch 25 may be caused to open at the zero point of the A.C. cycle. A condenser 22 across the valve 20 prevents premature conduction of the valve. For long-period operation the switch is moved to the left. In this position coil 25a is connected to D.C. supply only over condenser 29 and shunt resistances 28, 24 when the button 19 is pressed. The initial current surge closes the switch and resistances 28, 24 permit holding current to flow. The time duration is now determined by the charging time of condenser 13 controlled by a resistance 30 so that after a predetermined time, valve 11 conducts, switch 12 operates and valve 20 conducts at a predetermined point in the A.C. cycle so as to increase the p.d. across resistance 24 and de-energize the switch coil 26a. Only one welding period is permitted for each operation of the button 19. Discharge resistances 27, 31 are provided for condensers 29, 13.