| 摘要 |
PURPOSE:To hold temperature constant by using detecting elements which output temperature information signals of a temperature-controlled body heated by a heater, and a control circuit turning on and off the heater and a breaking circuit turning on and off a powers source according to the said output signals and their difference signals. CONSTITUTION:When thermistors 7 and 8 added to a temperature-controlled body (e.g., electric pan) are normal, their output voltage signals S1 and S2 are equal to each other, so the output Vw of a differential amplifier 17 is within the operation range of a window comparator circuit 18. A thyristor 4, therefore, turns on by the gate output of a control circuit 19, when the temperature of the pan is low, the S1 and S2 are lower than the reference voltage Vs of comparator circuits 11 and 12, so control circuits 13 and 14 are driven to turn on thyristors 2 and 3, thereby putting the AC power source of a pan heater 1 between terminals 5a and 5b to work for heating. When the pan temperature rises and, for example, the S1 exceeds the Vs, the thyristor 2 turns off and the S1 drops owing to the deterioration of the thyrsitor 7; if the Vw goes beyond the operation range of the circuit 18, the thyristor 4 turns off to turn off the heater 1. |
