GB586593A - Improvements in or relating to temperature control systems for electric heating devices - Google Patents

Abstract

586,593. Control systems for heating resistances. BRITISH THOMSONHOUSTON CO., Ltd. Aug. 25, 1943, No. 13837. Convention date, Aug. 26, 1942. [Class 38 (iv)] [Also in Group XXXVII] An electric heating device, such as a blanket 10, has its temperature controlled in accordance with atmospheric temperature by a bimetallic element 25 controlling a snap-action switch 20 in series with the heating element 12. The element 25 moves the actuating member 24 of the switch as its temperature increases, regulation being provided by an adjustable stop 29. In the closed position of the switch 20, as shown, the element 12 and a resistance 30 for heating the element 25 are energized, whereby intermittent action of the switch 20 occurs. To render the apparatus inoperative in the event of folding or such misuse of the blanket as to cause an abnormal increase in its temperature, two oppositely flexing bimetal elements 32, 33 are hingedly coupled by a bridge 35, carrying a contact 36, and are heated respectively in proportion to the supply circuit voltage and the current in the element 12 when the switch 20 closes. An increase in the supply voltage will not disturb the balance of the forces exerted on the bridge 35, but abnormal heating of element 12 so changes its resistance as to cause contact 36 to engage a contact 39, whereby current is supplied through the switch arm 21 to a contact 23 in the next " off " position of the switch arm and heats portions of the heaters 30, 37 to maintain the-switch 20 in its " off " condition and contacts 36, 39 in engagement. Specification 554,987, [Group XXXVII], is referred to.