| 摘要 |
PROBLEM TO BE SOLVED: To sustain the temperature at a sensing part at a high constant level by means of a main heater while preventing the generation of leak current due to the deterioration of an insulating board. SOLUTION: A main heater 30 comprising first and second heating parts 30a, 30b, and an auxiliary heater 32 are arranged on an insulating board which can sustain a sensing part at 400 deg.C, for example. The first grounded heating part 30a is arranged between the second heating part 30b and the grounded auxiliary heater 32 contiguously there. Supply voltage to a bridge circuit 18 and the main heater 30 is controlled by an amplifier 24 based on the output from the bridge circuit 18 comprising the auxiliary heater 32, and, first, second and third resistors 12, 14 and 16. The amplifier 24 has an inverted input connected with a joint 13, an noninverted input connected with the joint 17 of the second and third resistors 14, 16 and an output connected with the base of the gate of a transistor 20 for supplying a voltage to the main heater 30. The ratio of resistance between the first and second heating parts 30a, 30b is set equal to that of the third and second resistors 16, 14. |
