Nox measurement device, nox sensor self-diagnosis device, and self-diagnosis method thereof

摘要

Apparatus for measuring NOx concentration comprises a NOx sensor element having an oxygen partial-pressure detection cell 3 which detects oxygen concentration of an analyte gas in first measurement chamber 5, first oxygen pump cell 1 across which a current corresponding to oxygen concentration of analyte gas ("a first oxygen pump current") flows by pumping oxygen from inside to outside of first measurement chamber 1, second measurement chamber 6 into which gas is introduced from first measurement chamber 5 via second diffusion resistance 8, and second oxygen pump cell 2 across which a current corresponding to NOx concentration ("a second oxygen pump current") flows by transferring oxygen dissociated by decomposition of nitrogen oxide in second measurement chamber 6; and first diagnostic means 30a for diagnosing the apparatus as normally functioning if the second oxygen pump current Ip2 or a predetermined voltage Vp2 applied to second oxygen pump cell 2 is within a predetermined range, whereas as not normally functioning if the current Ip2 or the voltage Vp2 is outside predetermined range.