GB833160A - Electronically controlled time delay apparatus - Google Patents

Abstract

833,160. Control systems for arc-welding apparatus. AIR REDUCTION CO. Inc. May 9, 1958 [May 9, 1957], No. 14899/58. Class 38 (4). [Also in Group XL (c)] A time delay device comprises an electron discharge tube 5 in series with a relay 10 and an initiating device having two normally open pairs of contacts and one normally closed pair, a capacitor 17 being connected between the grid and, via one normally opened pair, to the negative supply terminal the side of the capacitor 17 remote from the grid being connected via a charging path such as R1 to the positive terminal. A variable resistance R2 in series with the other normally opened pair is connected between the grid and the positive terminal, the normally closed pair being connected between the grid and the negative terminal. As shown, the contacts of an initiating relay 13 first charge capacitor 17 via resistor R 1. The timed period is started by energizing the initiating relay 13 by means of a switch, not shown, so that the cathode is connected to the negative supply terminal. Capacitor 17 now discharges at a rate determined by the setting of resistor R2 and tends to recharge in the reverse direction so that the angle of incidence between the discharge curve and the critical voltage is large. When the critical grid voltage is reached, the gas-filled or vacuum tube fires or conducts, energizing relay 10 which closes a load circuit 18. The circuit is reset by releasing the initiating relay 13 so that the tube is cut off and the capacitor recharges. The device may be used to control the length of an arc welding period.