| 摘要 |
PURPOSE:To detect the temperature even if a bidirectional power control element is used, by controlling an energizing means so that power supply to a heater is stopped temporarily synchronously with an AC power source. CONSTITUTION:A temperature control circuit of a heater 4 consists of a safety circuit 2, a control means 3, a relay 5 of the bidirectional power control element, a detecting line 6, a sensor 7, a converting means 8 which converts a temperature signal current to a voltage, an energizing means 9 of the relay 5, a zero crossing pulse generating circuit 10, a power supply/non-supply state detecting circuit 12, etc., and performs the bidirectional power control of the heater 4. In this case, a timer means 11 which stops the energizing means 9 temporarily during power supply to open the relay 5 and sets the heater 4 to the power non-supply state to detect the temperature. Since the electric field is distributed uniformly throughout the sensor 7 when the temperature is detected (the relay 5 is opened), the temperature signal current accompanied with the change of the impedance of the sensor 7 is detected.
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