| 摘要 |
PROBLEM TO BE SOLVED: To detect the abnormality and the life of a sensor element by monitoring the change of an internal impedance of the gas sensor element and comparing with a preliminarily determined value. SOLUTION: When an abnormality judgment operation starts at a start time or at a regular or irregular confirmation time, an operation CPU 4 switches a switch 2 to B to connect an output of a gas sensor element to an internal impedance measurement circuit 5. The circuit 5 measures an internal impedance seen from an output terminal of the element 1 and sends the result to the CPU 4. A predetermined time later, the CPU 4 compares the internal impedance value of the element 1 with a plurality of preliminarily determined, abnormality judgment threshold values on the basis of a map stored therein beforehand, and judges the abnormality of the element 1. When the element 1 is judged as abnormal, the fact is displayed at a display part. When the element 1 is not judged to be abnormal or to be expired the judgment operation is terminated and the switch 2 is switched to A to enter a normal operation. A judgment condition for deterioration and life of the element is set so as to judge it as abnormal and expiration of the life when the impedance exceeds a threshold value or 0 Ω. |
