Electrical resistors – Resistance value responsive to a condition – Ambient temperature
Patent
1990-03-22
1993-04-13
Lateef, Marvin M.
Electrical resistors
Resistance value responsive to a condition
Ambient temperature
338308, 156 89, 427101, H01C 304
Patent
active
052026655
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a temperature sensor with a temperature-sensitive layer containing platinum placed on a support substratum, as well as a process for the production of a temperature sensor in which a layer containing platinum is placed on a support substratum.
BACKGROUND ART
Temperature sensors having a temperature-sensitive element with platinum are known which are produced in thin-film technology in which platinum on a support substratum is diffused in layers of a few atoms. In maintaining a corresponding geometric structure such as meander form, there may be obtained with thin enough layers of a few atom layers a high enough ground resistance which, for such a temperature sensor, must lie in the range of 100 ohms. These thin-film sensors can only be used at lower temperatures in the range up to 400.degree. C., and below 600.degree. C. in any case since platinum vaporizes at higher temperatures. By this alone, there is a considerable change of resistance so that no reproducible results are longer possible because of the layer thickness of only a few atom layers.
Platinum wires have also been used as temperature sensors. To reach the large enough ground resistance, the wire would have to have a considerable length which even with winding in coil form would lead to a sensor with considerable outer dimensions which cannot be used in many areas where there is miniaturizing. Thick-layer pastes containing platinum are also known which have organic binders and solvents as other components. These are used as thick-film heating elements and reach their sufficient resistance based on the length of the heating element, and are used for pressure-setting temperatures usual in heating. Aside from the low specific resistance which would also lead only to very large sensor elements, these could not be used at temperatures higher than 600.degree. C. since there would no longer be reproducibility. In both cases, it is true that platinum is in a red glow from about 800.degree. C., but can no longer be used as a temperature sensor.
The applicant has found that no miniaturized temperature sensors are known for high temperature uses. Thermo elements which work with thermovoltages are used. A disadvantage here is that a definite surrounding temperature must be used as a reference temperature or a microprocessor be used. Such temperature coolers are expensive.
SUMMARY OF THE INVENTION
The invention, therefore, addresses the problem of providing a sensitive high-temperature sensor stable with time in miniaturized design which can be used in a versatile way.
According to the invention, the problem is solved by a temperature sensor distinguished by the fact that a layer in ceramic oxide contains finely divided metallic platinum. For the production of such a temperature sensor according to the invention, there is proposed a process which is distinguished by the fact that platinum powder, oxides and binder are mixed together, and after applying the layer on the support substratum tempered with the latter.
The temperature-sensitive layer of the temperature sensor according to the invention may have between 60 and 90% by weight metallic platinum, and is preferably distinguished by the fact that it contains platinum in a proportion of about 70 to 85% by weight. As the oxide part, preferably a mixture of silicon, aluminum and alkaline earth oxide, especially calcium oxide, is used. The aluminum oxide part is provided by the fact that, as a rule, the support substratum is aluminum oxide. In the case that the support substratum consists of another oxide, the aluminum oxide might be replaced by the material of the corresponding support substratum. Based on tempering, silicon oxide provides a quartz or vitreous nature, and forms an inert material which is especially suitable for the desired high temperature uses. As an alkaline earth oxide, calcium oxide is preferable. Instead of this, strontium and barium oxides may be used, but calcium oxide has proved more stable. The oxide mixture forms a eutectic of which
REFERENCES:
patent: 4805296 (1989-02-01), Jinda et al.
patent: 4906968 (1990-03-01), Gershenfeld et al.
patent: 5010315 (1991-04-01), Fedter et al.
Lateef Marvin M.
Roth-Technik GmbH & Co.
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