Method for determining a nitrogen oxide concentration

• US 6,645,367 B1
• Filed: 10/30/2000
• Issued: 11/11/2003
• Est. Priority Date: 04/30/1998
• Status: Expired due to Fees

• Current Assignee: Continental Automotive GmbH (Continental AG)
• Original Assignee: Siemens AG
• Inventors: Rössler, Jürgen, Zhang, Hong
• Primary Examiner(s): TUNG, TA HSUNG
• Application Number:
  US09/699,599
• Time in Patent Office: 1,107 Days
• Field of Search: 204/421-429, 205/781, 205/783-785
• US Class Current: 205/781
• CPC Class Codes: G01N 27/4175 Calibrating or checking the analyser

Abstract

The NO_x concentration in a gas is determined with a thick-film measuring sensor which has two measuring cells. The raw measured value of the measuring sensor is corrected by a multiplicative correction value and an additive correction value, which are both taken from a characteristic map. The characteristic map depends on the oxygen-ion pumping current in the second measuring cell, the measured gas temperature, and the measuring sensor temperature.

Claims

1. A method of determining a NO_x concentration in a gas, which comprises:

providing a measuring sensor with a first measuring cell and a second measuring cell connected to the first measuring cell;

introducing a portion of a gas into the first measuring cell and adjusting a first oxygen concentration with a first oxygen-ion pumping current;

inroducing gas at the first oxygen concentration from the first measuring cell into the second measuring cell and adjusting a second oxygen concentration in the second measuring cell with a second oxygen-ion pumping current;

decomposing NO_x present in the gas at the second oxygen concentration within the second measuring cell;

pumping oxygen present in the gas after decomposition of NO_x form the second measuring cell with a third oxygen-ion pumping current;

measuring a NO_x concentration with a measuring electrode in the second measuring cell by measuring the third oxygen-ion pumping current to obtain a measured value of the NO_x concentration; and

correcting the measured value of the NO_x concentration by the following equation;

2. The method according to claim 1, which comprises exposing the sensor to exhaust gas of an internal combustion engine and measuring the NO_x concentration in the exhaust gas of the internal combustion engine.

3. The method according to claim 1, which comprises defining the characteristic map in a test bed measurement of the measuring sensor and thereby varying at least one parameter selected from the group consisting of a NO_x concentration, a rate of change of the NO_x concentration, an O₂ concentration, and a rate of change of the O₂ concentration.

4. The method according to claim 1, which comprises defining the characteristic map in a test bed measurement of the measuring sensor under predetermined test gas conditions with the second oxygen-ion pumping current being adjusted over a certain range.

5. The method according to claim 1, wherein the correction values in the characteristic map are also dependent on a temperature of the measuring sensor.

6. The method according to claim 5, which comprises equating the temperature of the measuring sensor with the temperature at the second measuring cell.

7. The method according to claim 1, wherein the correction values in the characteristic map are also dependent on a temperature of the gas to be measured.