Sensor for determining the concentration of oxidizable...

Details Sensor for determining the concentration of oxidizable... Sensor for determining the concentration of oxidizable...

1999-03-22

2001-01-16

Warden, Sr., Robert J. (Department: 1744)

Chemistry: electrical and wave energy

Apparatus

Electrolytic

C204S426000, C204S291000

Reexamination Certificate

active

06174421

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a sensor for measuring the concentration of oxidizable constituents in a gas mixture, in particular for measuring one or more of the gases NO
x
, CO, H
2
, and preferably unsaturated hydrocarbons.
BACKGROUND INFORMATION
Elevated concentrations of oxidizable constituents, in particular, of NO
x
, CO, H
2
, and hydrocarbons, can occur in the exhaust gases of spark-ignition and diesel engines, internal-combustion machines and incineration plants, e.g. as the result of a component malfunction such as an injection valve or as the result of incomplete combustion. To optimize the combustion reaction, it is therefore necessary to determine the concentration of these exhaust gas constituents. A method for measuring oxidizable gases is described in Unexamined Japanese Patent Application No. 60-61654, in which a stoichiometric reaction with oxygen takes place at a first measuring electrode made of platinum-class metals, and quasi-equilibrium states are established at one or more additional metallic measuring electrodes with reduced catalytic activity for the oxygen equilibrium reaction. Nernst voltages E1 and E2 are measured between the measuring electrodes and a reference electrode, which is exposed to a reference gas having a constant oxygen partial pressure, and the concentrations of the gas constituents calculated from the difference between these voltages on the basis of calibration curves.
SUMMARY OF THE INVENTION
A sensor according to the present invention provides greater miniaturization, a simplified design, and more cost-effective production than a conventional sensor. This is achieved according to the present invention by the fact that the solid electrolyte is porously sintered. The molecules of the measuring gas can thus diffuse through the solid-electrolyte pores and reach the reference electrode, where thermodynamic equilibrium is established. This exposes the reference electrode to an oxygen partial pressure which corresponds to the thermodynamic equilibrium. It is therefore not necessary to supply a reference gas, which greatly simplifies the sensor layout.
The thermodynamic equilibrium can also be advantageously established even in the solid electrolyte by selecting a catalytically active solid electrolyte material. A particular advantage of this is that it enables the gases interfering with the reference signal to be selectively oxidized, simplifying signal analysis or even making it possible in the first place. Not only the solid electrolytes but also the measuring electrodes can be suitably porous, which further improves the diffusion of the measuring gas molecules to the reference electrode.
Mixing additives made of the same substances as the electrodes into at least one layer of the solid electrolyte which lie adjacent to the electrodes improves electrode adhesion and thus also the service life of the sensor. It is also especially advantageous to construct the measuring electrodes from semiconductors, which can significantly increase selectivity toward the individual gas constituents to be detected.


REFERENCES:
patent: 5520789 (1996-05-01), Takahashi et al.
patent: 5630920 (1997-05-01), Friese et al.
patent: 5814719 (1998-09-01), Suzuki et al.
patent: 6022464 (2000-02-01), Schumann

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