GB653972A - Improvements relating to air flow interlock switch for electrical apparatus having acooling means - Google Patents

Abstract

653,972. Thermal switches. BRITISH THOMSON-HOUSTON CO., Ltd. July 28, 1948, No. 20140. Convention date, July 29, 1947. [Class 38(v)] [Also in Groups XIII and XL(a)] A protective device included in a cooling system comprises a thermally expansible member situated in the flow path of a coolant, operating means mechanically connected to the expansible member for actuating a control mechanism through a plurality of control positions dependent upon the temperature of the member, and means for heating the member by an electric current passing therethrough to a predetermined temperature at which the control mechanism is actuated to one of the control positions in the absence of coolant flow, the operating means actuating the mechanism to another control position in response to the cooling effect on the member produced by a flow of the coolant in the path. As shown a resistance wire 7 having a substantial temperature coefficient of expansion is contained in a perforated housing 4 extending into the air duct 2. One end of the wire 7 is attached to an actuating contact arm 10, of spring material. The wire 7 is electrically heated by a battery 28 connected through a switch 36 and a variable resistance 30 and may be adjusted by the screw 11 so that in the absence of air flow through the duct the expansion of the wire opens. the contacts 13, 14, to de-energize the relay 33, which may for example, control the power supply for the high power air cooled thermionic valves of a transmitter.