CONTROL METHOD FOR ELECTRIC HEATER

PROBLEM TO BE SOLVED: To prevent the excessive temperature rise of a heater by controlling a molten metal temperature to a set temperature without turning heater output ON/OFF and controlling a heater temperature to be equal to or less than the set temperature (upper limit temperature) as well. SOLUTION: The temperature T1 of molten metal 130 and the temperature T2 of the heater 40 are respectively detected and control output S1 and S2 based on the deviation from the respective set temperatures with thermometer 21 and 22 are outputted. By a selection circuit 60, the smaller (or larger) control output S (=S1 or S2) of the control output S1 and S2 is inputted to the thyristor unit 70 of characteristics for reducing supply power P to the heater 40 as the inputted control output S becomes small (large).