Patent ID: 6372120
Filing Date: 2002-04-16
Classification: G01N

Abstract:
A method of determining a NOx concentration in a gas, which comprises:providing a measuring sensor with a solid electrolyte, a first measuring cell with a first electrode, a second measuring cell with a second electrode, a diffusion barrier separating the first measuring cell from the second measuring cell, an exterior electrode, and a reference elect rode exposed to ambient air; connecting a first controller to the first electrode and the external electrode for controlling a current therebetween; connecting a second controller to the second electrode and the external electrode for controlling a current therebetween; allowing a gas to pass via a diffusion barrier into the first measuring cell, measuring an oxygen concentration in the first measuring cell via a first Nernst voltage between the first electrode and the reference electrode, and regulating the oxygen concentration to a first oxygen concentration with a first oxygen-ion pumping current between the first electrode and the external electrode with the first controller by using a measured value of the first Nernst voltage for controlling the first oxygen-ion pumping current; measuring an oxygen concentration in the second measuring cell via a second Nernst voltage between the second electrode and the reference electrode, and regulating the oxygen concentration in the second measuring cell to a second oxygen concentration with a second oxygen-ion pumping current between the second electrode and the external electrode with the second controller; also measuring the NOx concentration with a measuring electrode in the second measuring cell; and correcting an error occurring in the measured value of the first Nernst voltage due to a transitional resistance between the first electrode and the solid electrolyte by the following steps: providing a third controller using a prescribed value of the second oxygen-ion pumping current as a reference variable and a current value of the second oxygen-ion pumping current in order to provide a correction value approximating the transitional resistance at least partially as a controlled variable; multiplying the correction value and the first oxygen-ion pumping current to provide a product value; and using the product value to correct the measured value of the first Nernst voltage.