Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Means for analyzing gas sample
Patent
1992-06-19
1994-08-02
Warden, Robert J.
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Means for analyzing gas sample
422 88, 338 34, 338229, 73 3106, G01N 2704, H01C 102, H01C 700
Patent
active
053343506
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The invention is based on a generic resistance probe. Such resistance probes are known, for example, from German Patent 2,908,916, in which a heating conductor, electrodes, a semiconductor layer as well as a gas-permeable cover layer, separated by insulating layers, are applied in multi-layer technology onto a ceramic carrier plate. Experiments have shown that such protective layers do not exhibit satisfactory characteristics with respect to adhesion and reproducibility.
ADVANTAGES OF THE INVENTION
In contrast thereto, the resistance probe according to the invention comprises the following layers: an insulating ceramic substrate, a superposed pair of electrodes, a superposed semiconductor layer, a superposed ceramic covering, and at least one covering sheet disposed on the pair of electrodes and containing at least one recess in which the semiconductor layer with the ceramic covering is disposed on the pair of electrodes and which allows a gas mixture to pass through to the ceramic cover. The semiconductor layer functions as a gas sensor and is in electrical contact with the pair of electrodes. The ceramic covering is configured as an engobe protective layer with a plurality of pores which allow the gas mixture to pass through to the semiconductor layer.
A second embodiment of the invention comprises the following layers: an insulating ceramic substrate, a superposed pair of electrodes, a superposed semiconductor layer, and a superposed ceramic covering. The semiconductor layer functions as a gas sensor and is in electrical contact with the pair of electrodes. The ceramic covering is configured as a protective layer structure produced by thick-film technology in the form of a pattern of regions covering the semiconductor layer and with openings which allow access for the gas mixture to the semiconductor layer. The Invention has the advantage of its layer structure having sufficient stability under permanent stress. On the one hand, the structure according to the invention delays chemical aging of the resistance layer in that corrosion of the resistance layer, that is configured as a semiconductor layer, due to contaminants from the exhaust gas is prevented and, on the other hand, mechanical aging caused by abrasion of the resistance layer due to particles in the stream is also delayed. Even after long periods of operation, release of the semiconductor layer from the carrier is not observed.
Moreover, the application methods for the porous engobe protection layer, namely screen-printing, insertion of a porous sintering film or dripping in a suspension, are less expensive than the plasma spraying method employed in the past.
The method according to the invention is distinguished in that initially a sensor carrier body equipped with electrodes and an integrated heating element is prefabricated and sintered at high temperatures, whereupon a semiconductor layer is then applied as the resistance layer. This layer possibly carries an engobe protective layer and is sintered in together with the latter at lower temperatures. The advantage of this method is that the engobe protective layer is unable to react with the semiconductor layer during the sintering process as well as during later operation of the sensor and is therefore sufficiently stable.
Another advantageous method includes the application of a protective layer structure provided with openings only in certain regions so as to ensure access of the measuring gas to the semiconductor layer. The adhesion of the protective layer structure can be further improved by pressing it into the semiconductor layer before the sintering.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
Two embodiments of the invention are illustrated in the drawings and will be discussed in greater detail in the description below.
FIG. 1 depicts the structure of a resistance probe according to a first embodiment of the invention.
FIG. 2 depicts an alternative to the first embodiment.
FIG. 3 depicts the layout of a resistance probe according to the invention.
FIG. 4 depic
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Friese Karl-Hermann
Gruenwald Werner
Hoetzel Gerhard
Wiedenmann Hans-Martin
Robert & Bosch GmbH
Trembley T. A.
Warden Robert J.
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