GB783261A - Improvements in or relating to electrical resistance heating apparatus - Google Patents

Abstract

783,261. Current supply for resistance heaters. METROPOLITAN - VICKERS ELECTRICAL CO., Ltd. May 24, 1955 [Feb. 25, 1954], No. 5578/54. Class 39(3) [Also in Group XXXV] In electrically heated apparatus having a heat capacity in such relation to the heating power that the normal operating temperature is attained only after a considerable interval after switching on, e.g. a hotplate, contacts 7, 8 of a thermal time delay means are connected with the heater sections 2, 3 so that when the relay is cold the supply terminals L, N are connected for rapid heating of the apparatus, and when the relay is hot the sections 2, 3 are connected in series for normal operation, the relay means having a heater 10 which is connected with the terminals L, N in circuit with the contacts of a main switch 4 or regulator for the apparatus so that the heater 10 is energized at all times when the apparatus is switched on and to change the heater sections from the first connections to the second connections after a time delay, and thereafter to maintain the second connections until the main switch or regulator is turned off. The thermal time delay means comprises a bimetallic strip 9 carrying a contact 7 and a heater 10, and is so designed or has thermal insulation so arranged that the time for the delay means to cool down to the temperature at which the second connections are made (for normal operation) corresponds to the time taken for the heating apparatus to cool down to the temperature at which the second connections can be made. The contacts 7, 8 of the delay means are arranged so that when the delay means is cold, one section 2 of the heater is short-circuited and another section 3 is connected across the terminals L, N. Alternatively in Fig. 3 (not shown) the sections 2, 3 are connected first in parallel and then the thermal relay after delay switches to series connection. A variable heat switch or energy regulator 20 may be connected in circuit with the heating apparatus and has contacts 21, 22 which are open in the "off' position of the regulator but when closed connect the heater 10 of the delay means to the supply conductors L, N. The energy regulator may be a "Simmerstat" (Registered Trade Mark) made according to Specifications 517,538 and 587,947 [both in Group XXXVII]. The auxiliary contacts 21, 22 may be employed with a variable heat switch controlling the connectors of a plurality of hot-plate heater sections. Specification 783,262 also is referred to.