| 摘要 |
PURPOSE: To reduce preheating time by detecting a physical amount representing ohmic resistance of at least one preheating plug during off period of the preheating plug and comparing it with a desired value so as to control the current-conducting time of the preheating plug corresponding to a deviation obtained in the comparison. CONSTITUTION: A switching device 2 of a field effect transistor or the like is connected in series to a preheating plug 1, and a casing terminal 7 of the preheating plug 1 is connected to an earth terminal of a voltage source UB. A resistor bridge circuit 4 is composed of an ohmic resistor R4 of the preheating plug 1 and other ohmic resistors R1 to R3. The node between the resistors R1 and R3 is connected to the voltage source UB via an assistant switching device 5 of a field effect switching or the like. Then, a reference potential is provided to one terminal of the resistor R2, and a voltage lowering in the resistors R2 and R4 is inputted to an adjustment circuit 10 and compared so as to making each of the switching device 2 and 5 perform switching control corresponding to the difference or the ratio obtained by the comparison.
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