GB1089875A - Control circuit of an electric hotplate - Google Patents

Abstract

1,089,875. Control circuits for electric heating elements; thermal switches; automatic circuit breakers. LICENTIA PATENT-VERWALTUNGS-G.m.b.H. Dec. 2, 1964 [Dec. 2, 1963], No. 48976/64. Headings H2B and H2H. Control circuits for electric heating elements.- To provide increased power for a certain time during the " warm-up " or " steady cooking " operation of an electric hot-plate heating element 1 whose control circuit elements 2 ... 7 are generally similar in identity and function to those of Specification 908,530, elements 8 ... 11 are connected to the circuit as shown in Fig. 2, contact 8 being in series with a low value resistor 9 and contact 10 being controlled by a bimetal member 11. Contacts 8, 10 modify the effect produced by the members 3, 4 on the regulating switch 2, 6, and after manual closure of contacts 8, 10, the contact 8 remains closed for a predetermined period during which the contact 10 is cycled on and off by the member 11 until a timing mechanism permanently opens both contacts. Means are provided to override the timing mechanism so that the contacts may be opened at any instant during the predetermined period. Thermal switches; automatic circuit breakers.- The above-described operation of contacts 8, 10 may be obtained by the switch construction shown in Fig. 4 in which depression of a switching bar 31 permanently closes contacts K1 and initially closes contacts K2, the bar 31 being latched against action of its return spring 41 by having teeth 35 engaging the wheel 36 of a cam 37 which alternately engages the arms of an armature 40 linearly movable by a bi-metal strip 11 against the action of a spring 39. Heating and cooling of the strip 11 allows step-wise return of the bar 31 whose shaped rack 32 produces alternate opening and closing of the contacts K2, and finally permanent opening of contacts K1, K2. Members 35, 36, 37 may be dispensed with by providing the bar 31 with teeth alternately engaging the arms of the armature, Fig. 5 (not shown). In another embodiment, Fig. 3 (not shown), the switching bar (16) is latched in one fixed position to maintain contacts K1 closed while a normally-closed snap-action switch constituting the contacts K2 is actuated by heating and cooling of the strip 11, each heating movement of the strip producing a one-step rotation of a toothed wheel (26) which turns a coaxially mounted cam (25), so that after a predetermined number of rotary steps by the wheel (26) the cam (25) unlatches the bar (16). The bar (16) controls further contacts (27) in series with the snap-action switch and the heating resistor of the bi-metal member 11, which contacts (27) are respectively opened or closed when the bar (16) is unlatched or latched. Means are provided to unlatch the switching bar at any point in its travel so that the time mechanism is over-ridden.