GB599674A - Improvements in and relating to continuous interrupters for electric circuits - Google Patents

Abstract

599,674. Thermal switches. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 16, 1943, No. 19065. Convention date, Nov. 19, 1942. [Class 38(v)] [Also in Group XXXV] Switching control. - A device for intermittently energising a load 10, such as an electrically heated flying suit which it may be required to maintain at a uniform temperature under conditions of varying ambient temperatures, comprises a switch arm 15 pivoted at 17 and actuated by an electromagnet 22, 23, the arm controlling contacts 13, 14 in the load circuit and contacts 30, 31 in the magnet circuit. Contact 31 is carried by a resilient extension of arm 15 and contact 30 is mounted on the free end of a bimetallic strip 25, secured at 26 and provided with a heater 28 which is energised over contacts 30, 31 and through rheostat 35. With the starting switch 34 open, the circuits of the magnet coil, heater 28 and load 10 are open and the arm 15 is biased by spring 18 against an adjustable stop 20. The contacts 30, 31 remain closed when the arm is in this position and the bimetallic strip cold. Closure of the starting switch immediately energises the magnet coil and heater 28, the magnet then attracting the switch arm to close the load circuit at 13, 14 and to increase the contact pressure at 30, 31. Load current flows until flexure of the bimetallic strip by the heat developed in 28, which may be regulated by 35, causes contacts 30, 31 to separate. When this occurs the circuits of 28 and the magnet coil are broken so that the switch arm snaps back against stop 20, interrupting the load circuit, and heater 28 starts to cool. As cooling proceeds contact 30 again engages 31 and the cycle repeats itself. Ambient temperature variations affect the strip 25 in such a way that the period of closure of contacts 30, 31 increases with decreasing temperature and vice versa, so that the energy supplied to the load varies inversely as the ambient temperature and, in the case of a heating load, an approximately constant temperature may be maintained in the load. Rheostat 35 may so control the current in heater 28 that the load circuit is maintained open above a low ambient temperature limit.