Measuring and testing – Instrument proving or calibrating – Gas or liquid analyzer
Reexamination Certificate
1999-10-05
2001-07-31
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Instrument proving or calibrating
Gas or liquid analyzer
C073S001030, C073S023320, C204S427000, C205S784500
Reexamination Certificate
active
06266993
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for testing a measuring sensor for the determination of an oxygen concentration in a gas mixture.
BACKGROUND INFORMATION
Measuring sensors are known. By determining the oxygen concentration in the exhaust gas of internal combustion engines, such measuring sensors specify the setting of a fuel-air mixture for the operation of the internal combustion engine. The fuel-air mixture can lie in the “rich” range, that is, the fuel is in stoichiometric excess, so that only a small quantity of oxygen is present in the exhaust gas in comparison to other partly unburned components. In the “lean” range, in which atmospheric oxygen predominates in the fuel-air mixture, an oxygen concentration in the exhaust gas is correspondingly high.
“Lambda probes” are known for determining the oxygen concentration in exhaust gas; these detect a lambda value >1 in the lean range, a lambda value <1 in the rich range, and a lambda value =1 in the stoichiometric range. A Nemst measuring cell of the measuring sensor supplies in known fashion a detection voltage, which is supplied to a circuit arrangement.
In a known design of the measuring sensor, one electrode of the Nernst measuring probe is exposed to the gas mixture (exhaust gas) being monitored, a second electrode to a reference gas. The electrodes here are arranged on opposite sides of a solid electrolyte. As a result of the oxygen concentration present in the gas mixture being measured, a difference in oxygen concentration arises between the electrodes. A constant current is passed through the Nernst measuring cell, so that a certain detection voltage is set up on the electrodes as a result of the difference in oxygen concentration present. If there is a rise or fall in the oxygen concentration in the gas mixture being measured, the detection voltage decreases or, respectively, increases.
It is known to fabricate such measuring sensors as “thick-film” planar broadband lambda probes. Here, the individual functional elements of the measuring sensor are arranged and structured in layers one atop another. This layer construction is obtained, for example, by film casting, stamping, screen printing, laminating, cutting, sintering, or a like method. It has turned out that reference gas can be consumed to various extents as a result of manufacturing-related contaminants in a reference compartment of the measuring sensor. Because, however, a consumption of reference air has a substantial effect on the detection voltage with regard to generating an accurate detection voltage during the intended use of the measuring sensor, measuring sensors fabricated by the same manufacturing steps are subject to a variation in their output signal.
SUMMARY OF THE INVENTION
The method according to the present invention for testing a measuring sensor offers the advantage that measuring sensors can be exactly classified after manufacturing. Because the Nernst measuring cell is exposed to a constant test voltage and a gas mixture with a well-defined oxygen concentration, and a measuring current of the Nernst measuring cell that comes into being over time is evaluated, the consumption of reference air due to contaminants in the reference compartment can be determined in a simple fashion.
By determining the contaminants in the reference compartment of the measuring sensor, which can originate, for example, from grease deposits, stamping oil, hand sweat, or the like, oxidation of this contamination upon subsequent heating, in particular in the intended use of the measuring sensor, can be predicted. The test according to the present invention very advantageously permits in-process monitoring of any reference-air consumers (contaminants) that may be present, batch release, or material selection. Any contaminants that may be present can be divided into various categories on the basis of the test current that comes about for a constant test voltage and constant oxygen concentrations of the gas mixture present. These can preferably be classified as permanent consumers and exhaustible consumers. If such reference-air consumers (contaminants) are determined, the batch tested can be selected out and declared rejected if they are classified as permanent consumers. If they are classified as exhaustible consumers, the exhaustible reference-air consumer can be eliminated, for example by “torching,” so that the measuring sensors can subsequently be released for use. Further, the test for any reference-air consumers (contaminants) present makes it possible to infer any possible causes for the occurrence of these contaminants, which can be eliminated from the manufacturing process once they are known.
During the reference-air consumption test, a well-defined heat energy is applied to the measuring sensors. In this way, the later service conditions of the measuring sensor can be simulated, especially if the measuring sensors are used as lambda probes in motor vehicles for detecting the oxygen concentration in exhaust gases. Further, the ionic conductivity of the solid electrolyte is set.
REFERENCES:
patent: 5080765 (1992-01-01), Wang et al.
patent: 5221445 (1993-06-01), Wang et al.
patent: 5780710 (1998-07-01), Murase et al.
patent: 5804700 (1998-08-01), Kwon et al.
Bareiss Alexander
Diehl Lothar
Kenyon & Kenyon
Larkin Daniel S.
Robert & Bosch GmbH
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