GB811445A - Improvements in or relating to electric heating apparatus - Google Patents

Abstract

811,445. Automatic temperature control systems. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Sept. 19, 1955 [Sept. 28, 1954], No. 26691/55. Class 38 (4). In an automatic temperature control system for an electric heating element, reverse current through rectifying means, having a negative temperature coefficient, associated with or forming part of the element and being coextensive therewith, controls the energization of the element. Temperature changes of a blanket or clothing incorporating a heater 16, Fig. 2, supplied from an A.C. source 17, 18, are detected by change in the back resistance of rectifier material, e.g. selenium, copper oxide, germanium or silicon 14 (see also Fig. 1), between strip conductors 13, 13a wound on a flexible core 10 of jute or flax to form a cable, having a plastic covering 12, which is also incorporated in the blanket or clothing. When the temperature rises to a predetermined value, rectifier 14 passes sufficient reverse current through a rectifier 24 and a bimetallic element 27 to open a switch 19 and disconnect heater 16 until the temperature falls. In a modification, Fig. 3, conductors 13, 13a also constitute the heater, current to which is normally supplied through rectifiers 40 and 14. When the temperature rises to a predetermined value, however, reverse current through rectifier 14 provides sufficient energization of a heater 43 through a rectifier 42, to open a thermallyoperated switch 41 to interrupt the heating circuit. Alternative forms of temperaturesensitive rectifier cable, e.g. in which conductors 13, 13a are concentric and may surround a central core, are described.