| 摘要 |
PROBLEM TO BE SOLVED: To realize a temperature control having a high accuracy by preventing erroneous arc firing or extinction of a switching means for applying AC voltage to a heater. SOLUTION: In response to the heater output request values, the power applying method to the heater is switched between an ordinary phase control and an intermittent phase control, further, the pulse width of ON signal to a switching means for applying the AC voltage to the heater is set to a width permitting definitely to turn ON the switching means and to a minimum value, thereby preventing the erroneous arc firing or extinction and preventing the erroneous firing or extinction thereby permitting accurate temperature control and heater output in a wide range.
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