Patent ID: 8512536

Claim:
A NOx sensor comprising a sensor element equipped with first and second pumping cells to define first and second measurement chambers so that gas under measurement first flows into the first measurement chamber and then from the first measurement chamber into the second measurement chamber, the first pumping cell being capable of exerting an oxygen pumping action against the first measurement chamber to adjust the concentration of oxygen in the gas under measurement in the first measurement chamber to a given level, the second pumping cell being capable of exerting an oxygen pumping action against the second measurement chamber to produce a pumping cell current in accordance with the concentration of NOx in the gas under measurement, wherein, when the moisture content of the gas under measurement changes from 2 vol % to 8 vol %, the NOx sensor allows a variation of a NOx concentration detection value based on the pumping cell current in such a manner that the NOx concentration detection value reaches a transient peak value of 20 ppm or smaller and converges to ±5 ppm of a reference value within 5 seconds.