Element impedance detection device and the oxygen concentration detecting device of the oxygen concentration sensor

摘要

PROBLEM TO BE SOLVED: To provide an element-impedance detecting device, for an oxygen concentration sensor, by which the element impedance of the oxygen concentration sensor can be detected precisely although its constitution is simple. ;SOLUTION: In a device, a sensor current before changing an applied voltage to an air-fuel ration sensor AFS is detected, a sensor current after the elapse of a prescribed time after an operation to change the applied voltage is detected, and the element impedance of the sensor AFS is found. The device is provided with an operational amplifier OP1 which outputs the voltage of its + terminal to one terminal AF1 of the sensor AFS, an operational amplifier OP5 which outputs a prescribed voltage V1 to the + terminal of the operational amplifier OP1 via a resistance R15 and transistors Tr1 (Tr2) and resistances R16 (R17) which are connected across a signal route up to the operational amplifier OP1 from the resistance R15 and a voltage which is different from the prescribed voltage. The transistors Tr1 (Tr2) are turned on and off, and the applied voltage is changed. As a result, the sensor current after the elapse of the prescribed time is detected surely on the basis of a change in the applied voltage, and the element impedance can be detected surely.;COPYRIGHT: (C)1999,JPO