PURPOSE: To prevent a heater element from getting damaged and control the generation of defective products to the minimum by sensing voltage variation on the primary or secondary side of a transformer with its primary side constant current controlled and sensing the abnormality of the heater element.
CONSTITUTION: The actually measured value on the secondary side voltage of a transformer 4 sensed by a sensing means on the secondary side and the allowance range of secondary voltage of the transformer 4 computed by a computing means corresponding to the set value of the primary side current of the transformer 4 are compared with each other by a comparison means. As the primary side of the transformer 4 is controlled to have a constant current and the secondary side current of the transformer applied to a nozzle section 40 is also constant, the measured value of secondary side voltage of the transformer is varied according to the condition of the nozzle section 40, and when the measured value is out of the allowance range, a signal showing the abnormality of the nozzle section 40 is generated from the comparison means. An electric resistant heater element 6 installed on the nozzle section 40 is thereby prevented from getting damaged, and the generation of defective products can be controlled to the minimum.
YAMAMOTO SHIGEYUKI
KANAYAMA SHIYOUJI
FUJIMOTO HAJIME
NAKANO ISAO
SAITO TADAYOSHI
