Method for measuring nitrogen oxide

• US 6,036,841 A
• Filed: 05/12/1997
• Issued: 03/14/2000
• Est. Priority Date: 05/16/1996
• Status: Expired due to Term

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: Kato, Nobuhide, Ina, Noriyuki
• Primary Examiner(s): TUNG, TA HSUNG
• Application Number:
  US08/854,746
• Time in Patent Office: 1,037 Days
• Field of Search: 204/421-429, 205/783.5, 205/784, 205/784.5, 205/785, 205/781
• US Class Current: 205/781
• CPC Class Codes: G01N 27/4074 for detection of gases other than oxygen
• CPC Class Codes: G01N 27/419 Measuring voltages or currents with a combination of oxygen pumping cells and oxygen concentration cells

Abstract

A method for measuring nitrogen oxide (NOx) in a gas by decomposing NOx in the gas and measuring an amount of oxygen generated by the decomposition includes: introducing the gas to a first inner space under a first diffusion resistance and connected with an external space, controlling an oxygen partial pressure in an atmosphere in the first inner space to be a predetermined low value at which NO is not decomposed substantially by a main pump means, introducing a controlled atmosphere of the first inner space into a second inner space which is connected with the first inner space and which is under a second diffusion resistance, and converting the atmosphere into an electric signal corresponding to the quantity of oxygen generated by decomposition or reduction of NOx contained in the atmosphere by an electric signal conversion means. A first oxygen concentration detecting means is disposed for detecting an oxygen partial pressure in the second inner space, and a control voltage to be applied to the main pump means is adjusted on the basis of an output of the first oxygen concentration detecting means.

Claims

1. A method for measuring nitrogen oxide (NOx) in a gas by decomposing NOx in the gas and measuring an amount of oxygen generated by the decomposition, using a sensor comprising:

a main pump means including an electrochemical pump cell comprising a substrate comprising an oxygen ion conductive solid electrolyte and an inner pump electrode and an outer pump electrode formed on the inner surface and outer surface of the substrate, respectively, and said main pump means treating oxygen contained in the measuring gas introduced from an external space by pumping processing on the basis of a control voltage applied between said inner pump electrode and said outer pump electrode, and

an electric signal conversion means for generating an electric signal corresponding to the quantity of oxygen generated by decomposition or reduction of NOx contained in the measuring gas after having been treated by the pumping processing by said main pump means, said electric signal conversion means having a pair of detection electrodes where one of the electrodes is on the side where the measuring gas that was treated by pumping processing by said main pump means is introduced;

said method for measuring nitrogen oxide (NOx) comprising the steps of;

introducing the gas to a first inner space under a first diffusion resistance and connected with said external space,

controlling an oxygen partial pressure in an atmosphere in the first inner space to be a predetermined low value at which NO is not decomposed substantially by said main pump means,

introducing a controlled atmosphere of the first inner space into a second inner space which is connected with the first inner space and which is under a second diffusion resistance,

detecting an oxygen partial pressure in said second inner space with an electrochemical pump cell which is located for detecting an oxygen partial pressure in the second inner space,

adjusting said control voltage applied in said main pump cell in dependence on the measurement output of said electrochemical pump cell to maintain the measurement output of said electrochemical pump cell constant, and

generating an electric signal corresponding to the quantity of oxygen generated by decomposition or reduction of NOx contained in said atmosphere by said electric signal conversion means.

2. A method for measuring nitrogen oxide according to claim 1, wherein said control voltage applied to the main pump means is adjusted on the basis of an integral value of an oxygen partial pressure of the second inner space for a predetermined period of time.

3. A method for measuring nitrogen oxide according to claim 1, wherein said electrochemical pump cell for detecting an oxygen partial pressure in the second inner space for controlling the oxygen partial pressure in said first inner space to be a predetermined value, has one of a pair of electrodes being exposed in the second inner space.

4. A method for measuring nitrogen oxide (NOx) in a gas by decomposing NOx in the gas and measuring an amount of oxygen generated by the decomposition, using a sensor comprising:

a main pump means including an electrochemical pump cell comprising a substrate comprising an oxygen ion conductive solid electrolyte and an inner pump electrode and an outer pump electrode formed on the inner surface and outer surface of the substrate, respectively, and said main pump means treating oxygen contained in the measuring gas introduced from an external space by pumping processing on the basis of a control voltage applied between said inner pump electrode and said outer pump electrode, and

an electric signal conversion means for generating an electric signal corresponding to the quantity of oxygen generated by decomposition or reduction of NOx contained in the measuring gas after having been treated by the pumping processing by said main pump means, said electric signal conversion means having a pair of detection electrodes where one of the electrodes is on the side where the measuring gas that was treated by pumping processing by said main pump means is introduced;

said method for measuring nitrogen oxide (NOx) comprising the steps of;

introducing the gas to a first inner space under a first diffusion resistance and connected with said external space,

controlling an oxygen partial pressure in an atmosphere in the first inner space to be a predetermined low value at which NO is not decomposed substantially by said main pump means,

introducing a controlled atmosphere of the first inner space into a second inner space which is connected with the first inner space and which is under a second diffusion resistance,

detecting an oxygen partial pressure in a third inner space, connected with the first inner space by means of a third diffusion resistance, with an electrochemical pump cell which is located for detecting an oxygen partial pressure in said third inner space,

adjusting said control voltage applied in said main pump cell in dependence on the measurement output of said electrochemical pump cell to maintain the measurement output of said electrochemical pump cell constant, and

generating an electric signal corresponding to the quantity of oxygen generated by decomposition or reduction of NOx contained in said atmosphere by said electric signal conversion means.

5. A method for measuring nitrogen oxide according to claim 4, wherein said control voltage applied to the main pump means is adjusted on the basis of an integral value of an oxygen partial pressure of the third inner space for a predetermined period of time.

6. A method for measuring nitrogen oxide according to claim 4, wherein said electrochemical pump cell for detecting an oxygen partial pressure in the third inner space for controlling the oxygen partial pressure in said first inner space to be a predetermined value, has one of a pair of electrodes being exposed in the third inner space.

7. A method for measuring nitrogen oxide according to claim 4, wherein the second inner space is connected to the first inner space by means of the third inner space.