NOX DETECTOR

PROBLEM TO BE SOLVED: To provide a NOx detector for suppressing the lowering of NOx detection accuracy even if the concentration of oxygen in measuring object gas varies. SOLUTION: This NOx detector 1 starts a NOx pumping motion (pumping-out motion) from a gas detection chamber 19 (S170) when a first electromotive force Vs1 comes to an oxygen criterion value (positive determination at S150). Because of this, oxygen concentration in the detection chamber 19 at a NOx discharge starting time point (time t1) by a gas pump cell 11 becomes a constant concentration corresponding to the criterion value used at S150 without being affected by a change in the oxygen concentration in exhaust gas. The NOx detector 1 can accurately detect NOx concentration even if oxygen concentration in the exhaust gas varies, since the NOx detector 1 starts NOx discharge under the condition that the oxygen concentration in the detection chamber 19 becomes a constant concentration and detects the NOx concentration based on the time (first elapsed time TD1) required for the NOx discharge. COPYRIGHT: (C)2007,JPO&INPIT