Method and apparatus for measuring NOx gas concentration

摘要

A nitrogen oxide concentration detector has a first measurement chamber (2) into which is introduced a measurement gas via a first diffusion resistance (1); an oxygen concentration detection electrode (7a) for measuring the oxygen concentration in the measurement gas in said first measurement chamber (1); a first oxygen ion pump cell (6) for pumping out oxygen in the measurement gas from said first measurement chamber (2) based on the potential of said oxygen concentration detection electrode (7a); a second measurement chamber (4) into which the gas is introduced from said first measurement chamber (2) via a second diffusion resistance (3); and a second oxygen ion pump cell (8) having a pair of electrodes (8a,8b) across which a voltage is applied to decompose NOx in the second measurement chamber (4) to pump out dissociated oxygen to cause a current Ip2 corresponding to the NOx concentration to flow in the second oxygen ion pump cell (8). Variation of NOx concentration is a function of variation of Ip2. The concentration obtained based on the Ip2 is corrected responsive to the oxygen concentration in the measurement gas. Particularly, a coefficient of the variation of the Ip2, gain, in said function is corrected responsive to the oxygen concentration in the measurement gas .