PURPOSE: To prevent the deterioration of an oxygen sensor and the degradation in the sensitivity thereof the constituting the sensor of an oxide sintered body of the type in which electrical conduction is accomplished partly by ion conduction, and using an AC power source for the power source thereof.
CONSTITUTION: An AC oscillator 11, a titania sensor 21 and a thermistor 31 are connected in series to form a closed circuit, and the voltage generated across both input and output terminals of the thermistor 13 is put into an AC amplifier circuit 4, the output whereof is further put into an AC-DC conversion circuit 5, by which it is converted from AC to DC. The DC output thereof is inputted to a comparator 6. On the other hand, a closed circuit is formed with a DC power source 12 and a resistance 22, and said output is conducted through this to the comparator 6 for comparison voltage of a constant voltage. In the comparator 6, the output voltage based on the resistance change of the titania sensor 21 and the comparison voltage are compared.
YOSHIDA AOGU
SAKANO KOUJI
