| 摘要 |
1,178,417. Automatic temperature control systems. GENERAL ELECTRIC CO. April 24, 1967 [May 26, 1966], No. 18730/67. Heading G3R. The heating unit 12 of a self-cleaning electric oven is controlled by the circuit shown in which the contacts 10 of a hot wire relay 11 are respectively closed or opened by the continuous energization or de-energization of a heated wire actuator 13, which energization is dependent on the action of a unijunction transistor 17 and a silicon controlled rectifier 16 whose conductivities are controlled by a voltage divider including a temperature responsive resistor 23 sensitive to the oven temperature. During cooking operations a switch 42 is set to connect the resistor 23 to resistors 24, 25 and the temperature is controlled at a value set by adjustment (through a control knob) of the resistor 24. For heat cleaning the switch 42 is set to connect resistor 23 to an impedance network 28 and the temperature is controlled at a value determined by the setting of a calibrating resistor 30 and by the other members 31, 32, 33 of the network 28. The heat generated by a resistor 34, which is in parallel with the unit 12 but thermally isolated therefrom and from the oven, is indicative of the average power delivered to the unit 12. By suitable choice of the resistor 31, of the resistor 32 which has a negative temperature co-efficient of resistance and is responsive to the ambient temperature of resistor 33, and of the resistor 33 which has a positive temperature co-efficient of resistance and is responsive to the heat generated by the resistor 34, the magnitude of the combination 31, 32, 33 is arranged to be indicative solely of the average power delivered to the unit 12. The design of the network 28 also ensures that the final heat cleaning temperature is reached without overshoot, and the behaviour of the circuit is described for a typical heat cleaning operation, Fig. 3 (not shown). Temperature control at the cooking or the heatcleaning temperature is produced by the members 11, 16, 17 which are arranged so that the conduction of transistor 17 during a positive half cycle of the supply V 0 fires the controlled rectifier 16 to (fully) energize the actuator 13 and close contacts 10, the latter remaining closed during the-succeeding negative half cycle due to the mechanical inertia of the relay 11. The functioning of the circuit for a typical cooking operation is described, Fig. 2 (not shown). Rapid cycling of the contacts 10 is prevented by the self-heating of the resistor 23 which occurs during the whole of each positive half cycle when the transistor 17 does not conduct. The controlled rectifier 16 may be replaced by a pair of cascaded transistors, Fig. 4 (not shown). |
