Methods and apparatus for measuring nox gas concentration, for detecting exhaust gas concentration and for calibrating and controlling gas sensor

Abstract

A nitrogen oxide concentration detector has a first measurement chamber into which is introduced a measurement gas via a first diffusion resistance an oxygen concentration detection electrode for measuring the oxygen concentration in the measurement gas in said first measurement chamber a first oxygen ion pump cell for pumping out oxygen in the measurement gas from said first measurement chamber based on the potential of said oxygen concentration detection electrode a second measurement chamber into which the gas is introduced from said first measurement chamber via a second diffusion resistance and a second oxygen ion pump cell having a pair of electrodes across which a voltage is applied to decompose NOx in the second measurement chamber to pump out dissociated oxygen to cause a circuit Ip corresponding to the NOx concentration to flow in the second oxygen ion pump cell Variation of NOx concentration is a function of variation of Ip The concentration obtained based on the Ip is corrected responsive to the oxygen concentration in the measurement gas. Particularly, a coefficient of the variation of the Ip gain, in said function is corrected responsive to the oxygen concentration in the measurement gas.