| 摘要 |
PURPOSE:To prevent erronous operation by holding high reliability and high accuracy over a long period of time, by freely checking the deterioration in the capacity of a gas sensor in an actual use state at every arbitrary time. CONSTITUTION:The operational temp. of a heater part 3 is changed from rated operational temp. to predetermined temp. lower than said temp. The operational temp. of the heater part 3 is changed from the rated operational temp. to the predetermined temp. lower than said temp. for a short time before the required time from the change point of time to the point of time when the output signal of a gas sensor 1 beings to oscillate is detected by a detection circuit 7 and subsequently again returned to the rated operational temp. The degree of the deterioration in the capacity of the sensor 1 is judged corresponding to the degree of the change in the required time from the use initial stage of the sensor 1 and, by successively resetting a reductive gas detection level to one of first detection levels, the deterioration in the capacity of the sensor 1 can be self-corrected by a self-correction circuit 9. By this method, erroneous operation can be prevented.
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