| 摘要 |
PROBLEM TO BE SOLVED: To perform a careful temperature control in the midst of temperature control by multi-valued control which is different from binary-valued control, and to reduce a variation of current (a flicker value). SOLUTION: The temperature of an object to be heated by a heater is divided into four temperature ranges divided by three threshold values Ta, Tb and Tc. On the other hand, one period of an alternating current of power source is made to include three half-waves, and four wave forms such as the first wave form of full-wave, the second wave form with deletion of one half-wave, the third wave form with deletion of two half-waves, and a no conduction are prepared, and they are allocated to the four temperature ranges from low temperature side in above sequence respectively. When the temperature of the heater is controlled, the temperature of the object to be heated is detected one after the other, and judged whether to which temperature range out of above four temperature ranges the detected temperature belongs, and the heater is controlled by the wave form corresponding to the temperature range to which, the temperature of the object to be heated belongs.
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