| 摘要 |
<p>The sensing unit (3) of a heating-type sensor is kept at a constant high temperature by a main heater (30) and an auxiliary heater (32). A leakage current caused by the deterioration of an insulating board (2) is absorbed by a guard heater. The sensing unit which can be kept at a high temperature, for instance 400 DEG C, and a heat conducting insulating board or film (2) on which the main heater and auxiliary heater are provided closely to each other are included. Or, a leakage current preventive guard heater is provided adjacent to the auxiliary heater side between the main heater and the auxiliary heater. A bridge circuit (18) has the auxiliary heater on its one side and has a 1st resistor (12), a 2nd resistor (14) and a 3rd resistor (16) on the other three sides. A heating control circuit has an amplifier or a voltage follower (20) and an amplifier (24) whose reverse input terminal is connected to a series connection point between the 1st resistor and the auxiliary heater, whose non-reverse input terminal is connected to a series connection point between the 2nd resistor and the 3rd resistor and whose output terminal is connected to the control input terminal of the voltage follower. The amplifier controls a voltage applied to the bridge circuit and the main heater in accordance with output of the bridge circuit. A 2nd amplifier (52) controls the voltage at a connection point (50) to the guard heater (40) so as to be equal to the voltage of a connection point (13) to the auxiliary heater in accordance with the output or a 2nd bridge circuit (44) including the auxiliary heater and the guard heater (40). <IMAGE></p> |
