| 摘要 |
PROBLEM TO BE SOLVED: To constantly maintain the temperature of a detection part at a high temperature especially by a heater while absorbing a leakage current caused by the deterioration in an insulation plate with a guard heater. SOLUTION: A guard heater 40 for preventing leakage current is arranged adjacently at the side of an auxiliary heater 32 between a main heater 30 and the auxiliary heater 32 being arranged at an insulation plate for maintaining a detection part, for example, at 400 deg.C. A supply voltage to a first bridge circuit 18 and a main heater 30 is controlled by a first amplifier 24 based on the output of the first bridge circuit 18 including the auxiliary heater 32, a first resistor 12, a second resistor 14, and a third resistor 16. A second amplifier 52 performs control so that the voltage of a connection point 50 to a guard heater 40 is equal to that of a connection point 13 to the auxiliary heater 32 based on the output of a second bridge circuit 44 including the auxiliary heater 32 and the guard heater 40. The first amplifier 24 connects an inverted input terminal to the connection point 13, connects a non-inverted input terminal to a connection point 17 between the second resistor 14 and a third resistor 15 and connects an output terminal to the base or gate of a first transistor 20 that supplies a supply voltage to a main heater 30. |
