GB882942A - Improvements in or relating to thermostats - Google Patents

Abstract

882,942. Automatic temperature control systems. GALLENKAMP & CO. Ltd., A. June 12, 1958 [June 12, 1957], No. 18565/57. Class 38 (4). A thermostat for controlling the temperature of a furnace, oven, heat bath or the like comprises two elements, 1, 20 which are liquid filled and connected to a bellows 2, the first element 1 being situated in the device to be heated whilst the element 20 is remote from the device and is provided with a heating member such as an electric heating coil 19, movement of the bellows 2 operating a micro-switch 5, the position of which is adjustable by means of a threaded spindle 11, ambient temperature compensation being provided by securing the bellows 2 to a member 14 which is supported on two further bellows 15. In operation, the device to be heated is heated electrically and the supply thereto and to the coil 19 is controlled by the switch 5. When the supply is switched on the coil 19 rapidly heats the element 20-which has little heat inertia-but the bellows 2 does not operate the switch 5 to remove the supply until the device is hot enough to cause the combined responses of the two elements 1, 20 to expand the bellows 2 to operate the switch. Upon removal of the supply the element 20 rapidly cools, whereupon the bellows 2 contract and the switch 5 operated to replace the supply. Thus the element 20 plays a predominant role ,in the control of the heated device and the temperature of the device is controlled within narrow limits. Slight variations in the response of the element 1 causes variations in the cycling of the element 20; the coil 19 of which may be wound for differing wattages. In an alternative arrangement the heating of the device and the element 20 may be done by gas burners and the elements 1, 20 may comprise metal rods only, either solid or tubular.