Sensor for measuring nitrogen oxide

• US 6,306,271 B1
• Filed: 01/24/2000
• Issued: 10/23/2001
• Est. Priority Date: 05/16/1996
• Status: Expired due to Term

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: Ina, Noriyuki, Kato, Nobuhide
• Primary Examiner(s): TUNG, TA HSUNG
• Application Number:
  US09/490,046
• Time in Patent Office: 638 Days
• Field of Search: 204/421-429, 205/781, 205/783.5, 205/784, 205/784.5, 205/785
• US Class Current: 204/425
• 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 sensor 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: means for introducing the gas to a first inner space under a first diffusion resistance and connected with an external space, means for 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, means for 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 means for 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 NOx sensor for measuring nitrogen oxide (NOx) in a gas which comprises:

a first inner space and a first diffusion resistance for introducing a gas to be measured from outside the sensor to said first inner space,

a main electrochemical pump cell for controlling the oxygen partial pressure in said first inner space,

a means for applying a control voltage to said main electrochemical pump cell in order to effect oxygen pumping thereby,

a second inner space connected to said first inner space via a second diffusion resistance,

an electrical signal conversion means for effecting decomposition or reduction of nitrogen oxide on an internal electrode in said second inner space and measuring the amount of oxygen produced by the decomposition or reduction by producing an electrical output corresponding to the amount of oxygen produced, and by controlling at least the oxygen partial pressure of the atmosphere in said first and second internal spaces such that the concentration of the NOx component to be determined of the atmosphere in said second internal space by means of said electrical signal conversion means corresponds to a concentration of the NOx component in said measurement gas,

a second electrochemical pump cell arranged for adjusting oxygen concentration in the gas which has passed through said first inner space into one of either

(a) said second inner space, or

(b) a third inner space of said sensor arranged in series connection between said first and second inner space and connected to said first inner space by a third diffusion resistance, said second electrochemical pump cell having an internal electrode in said second or third inner space,

a means for applying electrical power to effect pumping of oxygen by said second electrochemical pump cell and for obtaining thereby an electrical measurement output dependent on the oxygen concentration at said internal electrode thereof,

a means for adjusting said control voltage applied in said main electrochemical pump cell in dependence on said measurement output of said second electrochemical pump cell so as to maintain said measurement output of said second electrochemical pump cell at a constant level.

2. A sensor according to claim 1, wherein said internal electrode of said second electrochemical pump cell is arranged in said second space.

3. A sensor according to claim 1, wherein a porous protective layer is disposed on said internal electrode of said electrical signal conversion means to constitute said second diffusion resistance, thereby forming said second inner space at the surface of said electrode, and said second electrochemical pump cell is arranged to adjust oxygen concentration of gas in said second inner space adjacent said protective layer.

4. A sensor according to claim 1, wherein said third inner space is provided, and said second electrochemical pump cell contacts gas in said third inner space.

5. A sensor according to claim 4, wherein said first, second and third inner spaces and said first, second and third diffusion resistances are provided by a flat and narrow slot in said sensor.