GB440282A - Improvements in circuit arrangements for automatically timing the operation of electric relays and contactors or other devices - Google Patents

Abstract

440,282. Control systems for resistance welding. DANNATT, C., 39, Marlborough Road, BRAILSFORD, F., 9, Kenwood Road, both in Stretford, Manchester, and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Crown House, Aldwych, London. Aug. 15, 1934, No. 23568. [Class 38 (iv)] [See also Group XL] An automatic timing circuit for use on A.C. mains, of the kind in which a relay or other device is actuated by a gas-filled discharge tube, comprises a condenser charged in the anode circuit of the tube and discharged in the control grid circuit to maintain the tube in conducting condition for a given period. The figure shows a tube I supplied from A.C. mains 5, 6 the anode circuit including the operating coil 8 of a relay, a condenser 9 and series resistance 14. The coil 8 has connections brought to a double-pole push-button switch 12, in the undepressed condition of which contacts 13 and 16, and 10 and 15 are connected. The coil 8 is thus shortcircuited and the condenser 9 is charged up from the source 5, 6 in series with the valve 1. Resistance 14 limits the charging current at this stage. Depression of the push-button connects contact 13 to 18 and 10 to 17 thereby including the coil 8 in the anode circuit of 1 and simultaneously connecting condenser 9 in the grid circuit. The relay operates by virtue of the grid potential of valve 1 being swung positive by condenser 9 ; when the push-button 12 is depressed, the grid also derives a negative bias potential from circuit 21, 22, 23, 24. The time period of discharge of 9 is determined by its capacity and resistance 20 ; one or both these valves may be variable. On cessation of discharge the coil 8 is de-energized and the circuit resumes its initial aspect, the condenser 9 becoming negatively charged from the biassing circuit 21, 22, 23. Shunt resistance 28 prevents chattering of the relay armature. The circuit 21, 22, 23, 24 shifts the phase of the grid voltage of valve 1 to compensate for phase shift of anode potential due to coil 8 and resistance 14. The invention is specially applicable to control circuits for spot welding apparatus to ensure exact equality of duration of each weld. The contactor device 12 may be manually or automatically actuated.