| 摘要 |
PROBLEM TO BE SOLVED: To provide a device capable of accurately detecting the element impedance of an oxygen concentration sensor. SOLUTION: A device 1 obtains the element impedance of an air-fuel ratio sensor AFS by detecting a sensor current before changing an impressed voltage to the sensor AFC and a sensor current after a predetermined period of time from the changing operation of the impressed voltage. The device 1 is provided with a multiplexer 8 to impress each voltage of input terminals X1 to X3 alternatively on the positive-side terminal AF+ of the sensor AFS. Then a microcomputer 2 outputs a reference voltage Vpr for air-duel ratio detection and voltages (Vpr+ΔV) and (Vpr-ΔV) different from the voltage Vpr in advance from the output terminals DAC1 to DAC3 of a D/A converter incorporated in the microcomputer 2 to the input terminals XI to X3 of the multiplexer 8 and switches a selection signal to the multiplexer 8 to change an impressed voltage to the positive-side terminal AF+. As a result, it is possible to detect a sensor current reliably after a predetermined period of time from the change of the impressed voltage. |
