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

A method of measuring a concentration of NOx as a gas component of a measurement gas, comprising the steps of:

• introducing the measurement gas containing the NOx component from an external measurement-gas space into a first internal space under a first diffusion resistance;
• controlling an amount of oxygen in the measurement gas within said first internal space to produce an atmosphere which does not substantially affect measurement of the NOx component and which does not substantially reduce or decompose NO;
• introducing said atmosphere from said first internal space into a second internal space, under a second diffusion resistance, to contact an NOx reduction or decomposition catalyst contained in said second internal space;
• reducing or decomposing NO present in the atmosphere in said second internal space as a result of contact between NO and said reduction or decomposition catalyst, and pumping out oxygen produced upon reduction or decomposition, by an oxygen pumping action of an electrochemical cell;
• and
• detecting a pumping current flowing through said electrochemical cell, so as to calculate the concentration of the NOx component in the measurement gas, on the basis of said pumping current.

A method of measuring a concentration of NOx as a gas component of a measurement gas, comprising the steps of:

• introducing the measurement gas containing the NOx component from an external measurement-gas space into a first internal space under a first diffusion resistance;
• regulating an oxygen partial pressure in said first internal space by an oxygen pumping action of a first electrochemical cell, to produce an atmosphere having a predetermined level of oxygen partial pressure, which level does not allow reduction or decomposition of NO at a first temperature of the first internal space;
• introducing said atmosphere from said first internal space into a second internal space under a second diffusion resistance;
• regulating an oxygen partial pressure in said second internal space by pumping out oxygen due to an oxygen pumping action of a second electrochemical cell, so that the oxygen partial pressure is regulated to a predetermined level which allows reduction or decomposition of NO at a second temperature of the second internal space as a result of contact with an NOx reduction or decomposition catalyst contained in said second internal space, said second electrochemical cell further pumping out oxygen produced upon reduction or decomposition of NO and
• detecting a pumping current flowing through said second electrochemical cell, to calculate the concentration of the NOx component in the measurement gas, on the basis of said pumping current.

A sensing device for measuring a concentration of NOx as a gas component of a measurement gas, comprising:

• means for defining a first internal space which communicates with an external measurement-gas space where the measurement gas is present;
• first diffusion means for introducing the measurement gas containing the NOx component from said external measurement-gas space into said first internal space under a first diffusion resistance;
• first oxygen pumping means comprising an electrochemical cell having a first oxygen-ion conductive solid electrolyte and a pair of electrodes formed thereon, for effecting an oxygen pumping action with respect to said first internal space, so that an oxygen partial pressure of an atmosphere in the first internal space is regulated to a predetermined level which does not substantially allow reduction or decomposition of NO;
• means for defining a second internal space which communicates with said first internal space;
• second diffusion means for introducing the atmosphere from said first internal space into said second internal space under a second diffusion resistance;
• a catalyst disposed in said second internal space for reducing or decomposing NO to remove oxygen therefrom;
• second oxygen pumping means comprising an electrochemical cell having a second oxygen-ion conductive solid electrolyte and a pair of electrodes formed thereon, for pumping out oxygen from an atmosphere in said second internal space, so that an oxygen partial pressure of the atmosphere in the second internal space is regulated to a predetermined value which allows reduction or decomposition of NOx as a result of contact with said catalyst, whereby the NO present in the atmosphere in the second internal space is reduced or decomposed, said second oxygen pumping means further pumping out oxygen produced upon the reduction or decomposition;
• and
• current detecting means for detecting a pumping current flowing through said second oxygen pumping means.

A sensing device for measuring a concentration of NOx as a gas component of a measurement gas, comprising a sensing element including an oxygen-ion conductive solid electrolyte as an integral part thereof, said sensing element comprising:

• means for defining a first internal space which communicates with an external measurement-gas space where the measurement gas is present;
• first diffusion means for introducing the measurement gas containing the NOx component from said external measurement-gas space into said first internal space under a first diffusion resistance;
• means for defining a second internal space communicating with said first internal space;
• a catalyst disposed in said second internal space;
• second diffusion means for introducing an atmosphere in said first internal space into said second internal space under a second diffusion resistance;
• a heater for heating said first and second internal spaces to first and second temperatures, respectively;
• first oxygen pumping means comprising an electrochemical cell having the oxygen-ion conductive solid electrolyte and a pair of electrodes formed thereon, for effecting an oxygen pumping action with respect to said first internal space, so that an oxygen partial pressure of the atmosphere in the first internal space is regulated to a predetermined level which does not substantially allow reduction or decomposition of NO at said first temperature;
• second oxygen pumping means comprising an electrochemical cell having the oxygen-ion conductive solid electrolyte and a pair of electrodes formed thereon, for pumping out oxygen from an atmosphere in said second internal space, so that an oxygen partial pressure of the atmosphere in the second internal space is regulated to a predetermined value which allows reduction or decomposition of NO at said second temperature, whereby the NO present in the atmosphere in the second internal space is reduced or decomposed as a result of contact with said catalyst, said second oxygen pumping means further pumping out oxygen produced upon the reduction or decomposition;
• and
• current detecting means for detecting a pumping current flowing through said second oxygen pumping means.

A sensing device for measuring a concentration of NOx as a gas component of a measurement gas, comprising:

• means for defining a first internal space which communicates with an external measurement-gas space where the measurement gas is present;
• first diffusion means for introducing the measurement gas containing the NOx component from said external measurement-gas space into said first internal space under a first diffusion resistance;
• first oxygen pumping means comprising an electrochemical cell having a first oxygen-ion conductive solid electrolyte and a pair of electrodes formed thereon, for effecting an oxygen pumping action with respect to said first internal space, so that an oxygen partial pressure of an atmosphere in the first internal space is regulated to a predetermined level which does not substantially allow reduction or decomposition of NO;
• means for defining a second internal space which communicates with said first internal spaces
• second diffusion means for introducing the atmosphere from said first internal space into said second internal space under a second diffusion resistance;
• a catalyst disposed in said second internal space, for reducing or decomposing NO to disassociate oxygen therefrom;
• second oxygen pumping means comprising an electrochemical cell having a second oxygen-ion conductive solid electrolyte and a pair of electrodes formed thereon, for pumping out oxygen from an atmosphere in said second internal space, so that an oxygen partial pressure of the atmosphere in the second internal space is regulated to a predetermined value which allows reduction or decomposition of NO as a result of contact with said catalyst, whereby NO present in the atmosphere in the second internal space is reduced or decomposed, said second oxygen pumping means further pumping out oxygen produced upon the reduction or decomposition;
• and
• current detecting means for detecting a pumping current flowing through said second oxygen pumping means,
• wherein at least one electrode exposed to said first and second internal spaces includes an alloy comprising Au and the balance being an element selected from the platinum group.

A sensing device for measuring a concentration of a gas component of a measurement gas, said gas component having bonded oxygen, comprising:

• a solid electrolyte body;
• a narrow, flat chamber formed within said solid electrolyte body, said chamber having a first internal space in communication with an external measurement gas space via a first diffusion resistance means, and a second internal space in communication with said first internal space via second diffusion resistance means;
• first oxygen pumping means comprising a pair of electrodes formed on a portion of said solid electrolyte body such that one of said electrodes is exposed to said first internal space, said first oxygen pumping means effecting an oxygen pumping action with respect to said first internal space, so that an oxygen partial pressure of an atmosphere in the first internal space is regulated to a predetermined level which does not substantially allow reduction or decomposition of the gas component;
• second oxygen pumping means comprising a pair of electrodes formed on a portion of said solid electrolyte body such that one of said electrodes is exposed to said second internal space, said second oxygen pumping means pumping out oxygen from an atmosphere in said second internal space so that an oxygen partial pressure of the atmosphere in the second internal space is regulated to a predetermined value which allows reduction or decomposition of the gas component, whereby the gas component present in the atmosphere in the second internal space is reduced or decomposed, said second oxygen pumping means further pumping out oxygen produced upon the reduction or decomposition;
• and
• current detecting means for detecting a pumping current flowing through said second oxygen pumping means.