| 摘要 |
PROBLEM TO BE SOLVED: To provide a nitrogen oxide concentration detector capable of efficiently controlling sensor temperature with a simple structure and capable of accurately detecting NOx concentration even if the sensor temperature is changed. SOLUTION: This NOx sensor 2 is provided with the first measuring chamber 20 communicated with the measured gas side via a diffusion rate controlling layer 4d and the second measuring chamber 26 communicated with the first measuring chamber 20 via diffusion limiting layers 6d, 22d. When the first pump current IP1 is controlled so that the output of a Vs cell 6 becomes the reference voltage VC0, the oxygen concentration of the measured gas flowing into the second measuring chamber 26 from the first measuring chamber 20 is controlled constant. A constant voltage is applied to the second pump cell 8, the NOx component in the second measuring chamber 26 is decomposed to pump out oxygen, and the NOx concentration is detected based on the second pump current IP2. The sensor temperature is detected from the internal resistance of the Vs cell 6, and the excitation current quantities of heaters 12, 14 are controlled. When the temperature of the measured gas is abruptly changed, the sensor temperature is changed, and the detected second pump current IP2 is corrected in response to the drift of the detected sensor temperature from the target value. The NOx concentration can be detected with high accuracy. |
