GB802372A - Improvements relating to means for controlling the power dissipation in electric heaters - Google Patents

Abstract

802,372. Automatic control systems for electric heaters. SIMPLEX ELECTRIC CO., Ltd. Aug. 2, 1956 [July 1, 1955], No. 19032/55. Class 38 (4). [Also in Group XI] In a control having a regulator effecting a cyclic variation in current supply to an electric heater R1 having, in thermal communication with the heater as primary control R4 for the regulator, a resistor of a material with a resistance changing with temperature, e.g. a nickel strip and heating means R3 for a thermal responder 14 (e.g. a bimetallic strip) with contacts Sl in parallel with the primary control R4, a ballast resistor R5 for the control R4 is so disposed relatively to the heater R 1 that the ballast resistor R5 does not contribute significantly to the heat developed in the controlled heater R1, but is placed to heat a part of the heated apparatus separate from the controlled heater R1. Thus a cast-iron hotplate with a central plate 10 carrying in grooves the heater R1 and the nickel strip R4 is closely surrounded by an annular plate 11 carrying a heater R6 directly connected through a manual switch S2 to the supply terminals t1, t2. The annulus 11 fits closely in a rectangular plate in one or more parts 12, 13. The ballast resistor R5 may be attached to the outer plate 12 for keeping a saucepan warm or may be used in a warming compartment of a cooker, e.g. for warming plates. The innermost hotplate 10 may carry further heating resistors subject each to a similar control with a separate ballast resistor; and if four such heaters are used, a ballast resistor may be placed in each corner of the rectangular plate 12. The innermost plate 10 may also carry resistors not subject to these controls. The current variation in the controlled heater may result purely from the change in resistance of the nickel resistor R4 and in this case the control is thermostatic; or the current variation may be compounded of a cyclic variation corresponding to that which the regulator imposes on the current for the heater, e.g. by connecting the parallel combination of nickel resistor and heating means for the responder in series with the regulator, together with a superimposed component of the variation derived purely from resistance changes in the nickel strip, and in this case the control will comprise an energy regulating characteristic with a superimposed thermostatic characteristic. Two nickel strips may be connected with two ballast resistors to form a bridge circuit across opposite points of which is connected the heating resistor R3. Specification 710,560 is referred to.