GB521970A - Improvements in and relating to methods of and apparatus for regulating electric resistance heating apparatus - Google Patents

Abstract

521,970. Thermal switches. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 29, 1938, No. 34792. Convention date, Nov. 30, 1937. [Class 38 (v)] [Also in Group XXXV] In electric resistance heating apparatus the current is regulated by steps with intermediate regulation between steps by means of mechanism c o ntrolled by a single operating member arranged to produce the step regulation when in predetermined positions and to effect progressive regulation while being moved between the predetermined positions. The operating handle, Fig. 1 (not shown) rotates an axle on which is fixed a drum carrying contact members which co-operate with fixed contacts 4, 5, 7-9, Fig. 6, connected respectively to the line wires, a mercury interrupter 11, and resistance elements A, B the arrangement being such that the switch contacts have three positions corresponding respectively to " off," element A heated, and elements A and B connected and heated in parallel. A bimetallic strip 15, Fig. 8; mounted adjajcent to a current-carrying heater coil 16 is adapted, when actuated, to bend upwardly against the lower end of a pivoted rocker arm 18 carrying the mercury interrupter 11, which opens the circuit through the elements when titled from its horizontal position. Movement of the bimetallic strip 15 is controlled by a cam 23 on the end of the axle 2, so that after element A is brought into circuit by an initial rotary movement of the controlling handle, the duration of the periods of current supply to the element is increased progressively by rotating the cam 23 into its higher positions, until the bimetallic strip and the end of the rocker arm are held so far apart that the contact-breaker is inoperative and element A is heated continuously. Further rotation of the operating handle to insert elements A and B in parallel may either reintroduce the interruptor or, as in the example, maintain it inoperative, so that the two. elements are heated continuously. A locating device to hold the rotary switch drum in a set position comprises a cam disc mounted on the axle 2, and co-operating with a roller which is carrier on a spring-controlled lever. When element A alone is energized, as shown in Fig. 6, it is shunted by the thermostat heater coil 16 in series with elements B, the combined resistance of these latter being such that the heating effect of'B is negligible.