GB580179A - Improvements in electric timing circuits - Google Patents

Abstract

580,179. Electric timing control circuits. GUMMING, W. R., YOUNG, W. F., and ROSE STREET FOUNDRY & ENGINEERING CO., Ltd. Oct. 33, 1943, No. 17480. [Class 38 (iv)] A timing circuit, particularly for use with spot welding machines, comprises a grid controlled electronic valve 28 having in its anode circuit the winding 24 'of a relay which has normally open contacts 52 in a circuit 54 to be controlled and normally closed contacts 38 in the charging circuit for a grid timing condenser 40. The valve is energized from a potentiometer 10, 12 connected across a smoothing condenser'16 charged from an alternating current supply through a rectifier 14. With the timing condenser and grid 44. negatively biassed by the potentiometer tapping 18, timing is initiated by closing a switch 34 thereby allowing the grid to assume a positive potential. The valve then becomes conducting but the inductance of relay winding 24 delays flow of anode current and thereby allows the grid to reach a higher potential. When anode current flows, contacts 52 close to complete the controlled circuit 54 and contacts 38 open to prevent further rise in grid potential. Condenser 40 then commences to discharge through resistances 46, 48 and when its potential has reached a low value the valve becomes non-conducting and the relay contacts assume their initial position. The discharge time of condenser 40 is controlled by potentiometer tapping 18 and switch 50. In order that discharge shall not commence until welding current flows, a normally open switch 56, closed by a winding 58 under the control of primary or secondary current flowing in the welding transformer, is arranged in the grid circuit of the valve.