Patent ID: 8308925

Claim:
a gas sensor for measuring NOx concentration in a measurement gas, comprising: (a) a sensor element including an oxygen control part arranged and adapted to control oxygen concentration in the measurement gas, and a measuring part arranged and adapted to measure NOx concentration by detecting an amount of oxygen in the measurement gas while generating oxygen by resolving NOx in the measurement gas after being passed through said oxygen control part; and (b) a control device for controlling said sensor element including a detection element arranged and adapted to detect current oxygen output characteristics in said sensor element, and a correction element arranged and adapted to correct a change rate of sensor output with respect to detection of NOx in the measurement gas by determining a difference between the current oxygen output characteristics of the sensor element and initial oxygen output characteristics of the sensor element or a reference sensor element to determine an effect of sensor degradation on the current oxygen output characteristics, and correcting said change rate of sensor output with respect to detection of NOx in accordance with the difference between the initial oxygen output characteristics and the current oxygen output characteristics of the sensor element; wherein said oxygen output characteristics are relationships between said sensor output and said oxygen concentration, wherein said correction element is arranged and adapted to correct a change rate of Q of sensor output with respect to a change of NOx concentration on the basis of a change rate P and a change rate P 0 , said change rate P being a change rate of sensor output with respect to a change of oxygen concentration and representing said current oxygen output characteristics, and said change rate P 0 being a change rate of sensor output with respect to the change of oxygen concentration and representing said initial oxygen output characteristics, and wherein said correction element is arranged and adapted to obtain a change rate Qc on the basis of a proportional calculation: Qc=(P/P 0 )×Q, said change rate Qc being a change rate after said change rate Q is corrected.