GB565302A - Improvements relating to starting switches for electric discharge devices - Google Patents

Abstract

565,302. Supply systems for discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd. April 2, 1943, No. 5284. Convention date, April 4, 1942. [Class 38 (iv)] [Also in Group XXXVII] A thermal switch for starting discharge lamps is constructed to cease to act after a certain number of unsuccessful attempts and to de-energize the circuit of the starting switch so that a manual operation is necessary before the switch can again function. The Figure shows the circuit including the discharge lamp 30 with electrodes 31. The thermal switch 6 and lock-out switch 20, 21 are shown apart, but are mounted on opposite sides of an insulating partition in the switch enclosure. Spaced contacts 11, 16 are alternatively engaged by a double contact 10 on the end of reversely mounted bimetallic strips 7, 8 welded together at 9. On switching on, a heating current through the electrodes 31 passes through the strips 7, 8, contacts 10, 11 and heater 14 near the lower strip 8 and also through another bimetal strip 21, the bent-over end of which retains contact with a spring 20, a high resistance heater 22 being in circuit as shown. On 7, 8 heating up contacts 10, 16 engage, a current surge passing through the electrodes and also through heater 22. Cooling of the strips 7, 8 then breaks the circuit and the lamp should start. If it fails to start, successive attempts result in the two-part bimetal floating between contact 11 and the mid-space, without making contact with 16. Moreover, sufficient heat by this time from heater 22 causes strip 21 to bend away and release spring 20, thereby opening the circuit of the starting switch. A push-button is provided to return spring 20 into engagement with strip 21 on cooling.