This application claims priority to German Patent Application No. 10 2013 112 493.3, filed Nov. 13, 2013, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to an improved temperature sensor.
2. Background of the Invention
An embodiment of the invention is based on a temperature sensor having the features listed in the claims. Prior art temperature sensors are known from U.S. Pat. No. 6,617,956 B1 and U.S. Pat. No. 7,233,262 B2.
U.S. Pat. No. 6,617,956 B1 and U.S. Pat. No. 7,233,262 B2 disclose temperature sensors comprising a platinum resistor that is arranged on a substrate and covered by a protective ceramic layer of Al2O3. The thin protective layer is covered by a thicker covering layer that is a mixture of Al2O3, MgO and Si2O. The known temperature sensors can only be used at temperatures up to 1000° C. and show significant resistance drift after extended use at such elevated temperatures.
An object of the present invention is to show how the temperature resistance of such sensors can be improved and resistance drift lowered. This problem, and other problems, may be solved by a temperature sensor according to the claims. Further advantageous refinements of the invention may be the matter of the dependent claims.
An increase in temperature resistance is achieved with a temperature sensor comprising a substrate, a platinum resistor arranged on the substrate, a protective layer covering the platinum resistor, and a cover layer covering the protective layer in that the cover layer contains Al2O3, Si2O, and Y2O3. By adding Y2O3 to Al2O3 and Si2O a cover layer can be provided that results in significantly reduced layer diffusion. The cover layer is thus less prone to pore formation and can provide a reliable seal up to higher temperatures. Moreover, reduced layer diffusion means that contact between material of the cover layer and the platinum resistor can be prevented up to higher temperatures and thus resistance shift reduced.
A rather small amount of Y2O3 is sufficient to improve the heat resistance of a layer that consists predominantly of Al2O3 and Si2O. For example, the cover layer may contain 5% by weight of Y2O3 or more. In an embodiment of the invention, the cover layer may contain 10% by weight of Y2O3 or more. Increasing the concentration of Y2O3 beyond 30% by weight does not improve the cover layer significantly and may not be economical. An embodiment of the invention may be that the cover layer contains less than 20% by weight of Y2O3.
Another embodiment of the invention may be that Si2O and Al2O3 together add up to at least 50% by weight of the cover layer, for example 60% by weight or more.
Another embodiment of the invention may be that the cover layer contains more Si2O by weight than Al2O3. For example, the cover layer can contain twice as much Si2O by weight than Al2O3 or more.
Another embodiment of the invention is that the cover layer contains less Y2O3 by weight than Al2O3. Another embodiment of the invention is that the cover layer contains more Si2O by weight than Y2O3.
The cover layer may contain at least 30% by weight of Si2O, for example 40% by weight or more. A Si2O content of more than 70% is usually not advantageous.
The cover layer may contain at least 15% by weight of Al2O3, for example 20% weight or more. An Al2O3 content of more than 30% is usually not advantageous.
The cover layer may also contain B2O3, e.g. up to 25% by weight. For example, in an embodiment of invention the cover layer may contain 1% by weight to 20% by weight of B2O3. The cover layer may also contain additional additives, especially other oxides besides Si2O, Al2O3, Y2O3 and B2O3. In a possible embodiment of the invention, the content of any additional additives may be less than 20% by weight in total, for example not more than 10% by weight.
The accompanying drawings illustrate the invention. In such drawings:
An embodiment of a temperature sensor shown in
The cover layer 5 may be a glass ceramic or glaze layer. The cover layer 5 contains Si2O, Al2O3, and Y2O3. For example, the cover layer 5 may contain 40 to 60% by weight of Si2O, 20 to 25% by weight of Al2O3, and 10 to 19% by weight of Y2O3. The cover layer 5 may also contain up to 20% by weight of B2O3, e.g. 5% to 20% by weight of B2O3, and up to 20% by weight of other components, especially other oxides. Such a temperature sensor can be used for measuring temperatures up to 1200° C.
The protective layer 4 can be applied by a vapour deposition method or as a green foil that is later fired. The cover layer 5 can be produced by a screen-printing method, for example. In the embodiment of
Although several embodiments have been described in detail for purposes of illustration, various modifications may be made to each without departing from the scope and spirit of the invention. Accordingly, the invention is not to be limited, except as by the appended claims.
Number | Date | Country | Kind |
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10 2013 112 493.3 | Nov 2013 | DE | national |