ELEMENT RESISTANCE DETECTING METHOD FOR GAS CONCENTRATION SENSOR, AND GAS CONCENTRATION DETECTING DEVICE

摘要

PROBLEM TO BE SOLVED: To precisely detect an element resistance value irrespective of various kinds of factors such as detection timing of a current change accompanied to a voltage change and a time constant. SOLUTION: An A/F sensor 10 has an element part. using a solid electrolyte, and makes a sensor current flow in response to an oxygen concentration in exhaust gas in the accompaniment of voltage impressing. A bias control circuit 30 switches an impressed voltage to the A/F sensor 10 to an element resistance detecting voltage with a prescribed time constant when element resistance is detected, so as to detect a sensor current value flowing at that time. A comparison circuit 40 determines the fact that a variation of the voltage with the prescribed time constant reaches to a prescribed value. A timing determining circuit 20 determines to detect a voltage change and a current change for detecting the element resistance in the timing of the determination by the comparison circuit 40. A data output circuit 50 measures the current change correponding to the voltage change, according to the timing determination by the timing determining circuit 20.