| 摘要 |
PURPOSE:To make it possible to control the temperature of a sensor to be constant without using an AC generator by feeding an output of a differential circuit positively back to the differential circuit to accomplish oscillation utilizing resistance changes due to changes in the concentration of oxygen and in the temperature, ON/OFF opera tion of a heater or the like. CONSTITUTION:One end of an oxygen sensor 30 is connected to a power source and the other end thereof to an inverting input terminal of an operational amplifier 31. The output of the amplifier 31 is connected both to its inverting input terminal through a resistor R1 and to its noninverting input terminal through resistor R2. A resistance (r) and an impedance R3 of the sensor 30 vary slightly with changes in the concentration of oxygen in an exhaust gas and in the temperature and oscillation is accomplished when RsXR2=R1Xr is met. As no oscillation occurs when the temperature of the sensor 30 is low, the output of the amplifier 31 comes under a reference value and an output of a comparator 36 moves to be at a low level to energize a heater 38 electrically. As the temperature rises, the oscillation occurs and conversely, the output of the comparator 36 goes to be at a high level to stop the energization of the heater 38. By repeating the operation, the temperature of the sensor 30 is controlled to be constant thereby eliminating an AC generator. |
