GB875077A - Improvements in and relating to automatic temperature control systems - Google Patents

Abstract

875,077. Automatic temperature-control systems. MACLAREN & CO. Ltd., ROBERT, MACLAREN, I. G., and ADAM, I. R. Dec. 29, 1958 [Dec. 30, 1957], No. 40252/57. Class 38 (4). [Also in Group XXXVII] A thermally sensitive device controlling a main switch in series with an electric heater also controls a switch in a circuit including two auxiliary heaters which modify the effect of the thermally sensitive device when the main switch is open and closed respectively, the main switch opening and closing intermittently to maintain a constant temperature. In an automatic temperature-control system, e.g. for a room or furnace, a rod and tube expansion device 22, Fig. 1, responsive to the temperature, operates a lever 20 so that when the temperature rises to a value determined by the setting of a screw 28 a switch 26 is closed to energize, as shown in Fig. 2, an auxiliary heater 19 causing expansion of a tube 18. The movement of lever 20 and the expansion of tube 18 combine to open a snap-action switch 10 and thus interrupt the supply to the room or furnace heater 10a. The supply to auxiliary heater 19 is also interrupted by the opening of switch 10 so that tube 18 cools and permits switch 10 to re-close. Heater 10a is thus energized intermittently with the ratio of the on to off periods variable to maintain the desired temperature. A high-resistance heater 17 which is energized when switch 10 is open causes expansion of an adjustable tube 14 to assist reclosing of switch 10 thus reducing the temperature differential of switch 10.