Method of measuring a gas component and sensing device for measuring the gas component

• US 6,196,053 B1
• Filed: 05/05/2000
• Issued: 03/06/2001
• Est. Priority Date: 04/21/1994
• Status: Expired due to Term

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: Kato, Nobuhide, Nakagaki, Kunihiko
• Primary Examiner(s): LARKIN, DANIEL SEAN
• Application Number:
  US09/565,401
• Time in Patent Office: 305 Days
• Field of Search: 73/310.5, 204/425, 204/426, 204/427
• US Class Current: 73/31.05
• CPC Class Codes: F02D 2041/1468 the characteristics being an ammonia content or concentration of the exhaust gases
• 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 and a sensing device of measuring a concentration of a gas component of a measurement gas, which method includes the steps of: introducing the measurement gas containing the gas component, from an external measurement-gas space into a first internal space, under a diffusion resistance; controlling an amount of oxygen in the measurement gas within the first internal space, so as to produce an atmosphere which does not substantially affect measurement of the gas component and which does not convert the gas component; introducing the atmosphere from the first internal space into a second internal space, under a diffusion resistance; and measuring the concentration of the gas component present in the atmosphere in the second internal space.

Claims

1. A method of measuring a concentration of NOx as a component of a measurement gas, using a sensing device including (a) means for defining an internal chamber which communicates with an external measurement-gas space, (b) diffusion means for introducing said measurement gas into said internal chamber under a predetermined diffusion resistance, (c) first oxygen pumping means having a first pair of electrodes disposed within and outside said internal chamber, respectively, for controlling an oxygen partial pressure of an atmosphere in said internal chamber, (d) second oxygen pumping means having a second pair of electrodes disposed within and outside said internal chamber, respectively, for pumping out from said internal chamber oxygen which is produced by decomposition or reduction of the NOx component of the measurement gas, and (e) current detecting means for detecting an amount of electric current flowing through said second oxygen pumping means, said method comprising the steps of:

selecting a material of one of said pair of electrodes of said first oxygen pumping means which is disposed within said internal chamber, and/or controlling at least one of a temperature and the oxygen partial pressure in said internal chamber, such that an ability of said one of said first pair of electrodes as a catalyst to decompose or reduce NO is lower than that of one of said second pair of electrodes which is disposed within said internal chamber; and

controlling said first oxygen pumping means to effect an oxygen pumping action with respect to said internal chamber, such that a pumping current corresponding to the concentration of said NOx component of said measurement gas flows through said second oxygen pumping means, and so that the oxygen partial pressure of the atmosphere in said internal chamber is regulated to a predetermined level.

2. A method according to claim 1, wherein said predetermined level of the oxygen partial pressure of the atmosphere in said internal chamber is selected within a range between 10⁻

4 atm and 10<sup>−

10</sup> atm.

3. A method of measuring concentration of NOx as a component of a measurement gas, using a sensing device including (a) means for defining a first internal space which communicates with an external measurement-gas space, (b) first diffusion means for introducing said measurement gas into said first internal space under a predetermined diffusion resistance, (c) first oxygen pumping means having a first pair of electrodes disposed within and outside said first internal chamber, respectively, for controlling an oxygen partial pressure of an atmosphere in said first internal space, (d) means for defining a second internal space communicating with said first internal space, (e) second diffusion means for introducing the atmosphere whose oxygen partial pressure has been controlled in said first internal space, into said second internal space under a predetermined diffusion resistance, (f) second oxygen pumping means having a second pair of electrodes disposed within and outside said second internal space, respectively, for pumping out from said second internal chamber oxygen which is produced by decomposition or reduction of the NOx component of the measurement gas, and (g) current detecting means for detecting an amount of electric current flowing through said second oxygen pumping means, said method comprising the steps of:

selecting a material of one of said first pair of electrodes of said first oxygen pumping means which is exposed to said atmosphere within said first internal space, and/or controlling at least one of a temperature and the oxygen partial pressure in said internal chamber, such that an ability of said one of said first pair of electrodes as a catalyst to decompose or reduce NO is lower than that of one of said second pair of electrodes which is exposed to an atmosphere within said second internal space; and

controlling said first oxygen pumping means to effect an oxygen pumping action with respect to said first internal space, such that pumping current corresponding to the concentration of said NOx component of said measurement gas flows through said second oxygen pumping means, and so that the oxygen partial pressure of the atmosphere in said first internal space is regulated to a predetermined level.

4. A method according to claim 3, wherein said predetermined level of the oxygen partial pressure of the atmosphere in said first internal space is selected within a range between 10⁻

4 atm and 10<sup>−

10</sup> atm.