GB493374A - Improvements in and relating to electric circuits employing discharge devices - Google Patents

Abstract

493,374. Control systems for consumption apparatus ; valve relays. BRITISH THOMSON-HOUSTON CO., Ltd., KNIGHT, H. DE B., and HIGGINS, B. G. April 6, 1937, No. 9804. [Class 38 (iv)] [Also in Group XL] Current from an A.C. supply 1 to a load 2 is controlled by a pair of reversely con nected valves 10, 20 a relay 70 being pro vided so that when the valve 10 has conducted an overriding negative bias is applied to its grid and is not removed until the valve 20 conducts current. This prevents pulsating D.C. from being supplied in the event of the valve 20 breaking down. The relay 70 has two positions, engaging the contact 72 to connect the control circuit 14 to the grid 13, and engaging the contact 73 to connect the negative biassing potential from a battery 76 to the grid 13, operation of the relay being effected by current flow in the main circuit, the relay winding 74 being connected across an impedance 75 in series therein. Alternatively it may be supplied through a current transformer or connected in series with an inductance across the load circuit. Where the control of the valve 20 is dependent on the operation of the valve 10, one relay as shown is sufficient. Where however both valves are controlled from an external source a control relay is needed for each. In a modification, in which the valves 10, 20 are of the immersion igniter type controlled through auxiliary valves, the control relay 70 operates in the grid circuit of one of the auxiliary valves either directly on the control grid or on a screen grid. The Specification states that in welding operations this arrangement ensures that the valve conducting at the close of a welding operation will not conduct first at the commencement of the next operation.