DE2427992A1 - METHOD OF MEASURING HIGH TEMPERATURES WITH THERMOCOUPLES - Google Patents

Description

KKT "Dlpl.-Ing. R. H. Bahr == 5?

8000 Manchen Elsenacher StraBo P »t.-Anw. B *! Z! * R

Dipl.-Phys. Eduard Betzier Dip Wng. W. Harimann-Trentepohl

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Bavarian Verelnsbenk monks S5? is Dresdner Bank AQ Herne 7-520 499 Postscheckkonto Dortmund 558 6G-467

2A27992

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Method of measuring high temperatures with thermocouples

The invention relates to thermocouples and, more particularly, to hot junction thermocouples ^{suitable for measuring temperatures in the range of 1200 °} C. or above. A special application of the elements according to the invention is the determination of the immersion temperature of molten metal baths.

The invention also relates to dn. A method for measuring temperature and a method for producing a

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Element with a hot connection point.

Thermocouple devices are available for temperature measurements up to 1800 ⁰ C and more. At temperatures below approx. 1000 C, basic metals and their. Alloys are used for d.io thermocouple wires, but if the measurements are in the range of 1200 C and above, the wires of the hot junction elements must be made of platinum, rhodium, tungsten or rhenium.

When using noble or precious metals such as platinum, local considerations require that the Thermocouple wires are as thin as possible.

Even so, thermocouples made from valuable metals only have a limited lifespan and are relatively expensive. Usually can only carried out a single temperature measurement with the known elements at the upper end of their temperature range will. For certain industries, such as the steel industry, where a large number of high temperature measurements have to be carried out, this results in high annual material costs. Furthermore Thermocouples are particularly difficult to manufacture from valuable metals, especially the coupling of the thin wires difficult to produce at the hot connection point.

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so that the error rate of these elements is quite high.

When making thermocouples with a hot junction, which are suitable for immersion, the wires of the thermocouples must usually be welded together in order to do so to form the hot junction. When using precious metals, the wires used have a diameter below 0.1 mm and after welding, the connection must be ga ~

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be annealed so that it is flexible enough to insert the wire pair into the female refractory Enable coat. Such a process is time consuming and difficult as it is costly. In addition, has the use of alloys in welded thermocouple wire pairs have their own problems and difficulties. So need special Alloys are used which allow the formation of a weld joint, thereby reducing the area of the problem coming thermocouple pairings was limited, as the wires were not more in terms of their weldability have been selected for maximum thermal effect or optimal service life. When using high temperatures often a diffusion effect occurs at the hot junction with a tendency for the alloys to dissolve to adjust, whereby the thermal effect is changed.

A change can also be due to partial evaporation of alloy components occur at high temperatures, so that again after a certain time Thermocouple gives incorrect values.

Because of the above difficulties, the known thermocouples with a hot connection point for measuring high temperatures (e.g. molten steel) designed so that they can only be used for a single measurement.

It has heretofore been considered necessary that the electrical connection between the thermocouple wires be at the hot The connection point must be a permanent bond, either directly between the thermocouple wires or via a middle conductive bridge takes place.

The use of a conductive bridge made of powder!

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Material was suggested in U.S. Patent 3,477,122, however , the powder was then melted together by induction heating in order to achieve a permanent bond. In contrast, it has now been found that an improved hot junction thermocouple can be formed can if the conductivity bridge consists of a powder that remains in powder form at the temperatures to be measured.

According to one aspect of the invention, the method consists of measuring temperatures in the range of 1200 ° C. and above by determining the potential difference between two different ones Thermocouple wires that are electrically connected to each other, the connection point being in the to measuring area is in that the electrical connection is achieved by means of a conductive bridge, the consists of a finely divided material located between the ends of the thermocouple wires. A preferred one electrical bridge is made of powdered tungsten. Another made of graphite or tungsten carbide powder.

The grain size of the powder can vary within wide limits. Grain sizes were found to be below 500 microns and preferably used below 100 microns.

The wires of the thermocouple can be any thermocouple suitable for measuring temperatures above 12C0 ° C. A preferred pair is made up of pure Volfram wire on one side and pure platinum wire on the other.

The pure metal ladder will not change subject to their composition by diffusion or evaporation and the elements can therefore be re-

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gets used. Even if one or both of them were using Head alloys are (e.g. if a platinum-rhodium alloy instead of tungsten in the example above is used), the diffusion does not have to influence the service life of the thermocouple, as the alloys can be selected so that the evaporation effects can be minimized and the ends of the Conductors are physically linked by the conductive bridge.

In accordance with another aspect of the invention, the hot junction thermocouple is a distinct one thereof Insert thermocouple wires in a fire-proof, electrically insulating jacket surrounding them and inside the Sheath are electrically connected to one another, characterized in that the sheath is an electrical bridge of contains finely divided conductive material which has a melting point above the measurement temperature, the Wires are in electrical communication across the particles of the bridge.

The manufacture of the thermocouple with a hot connection point according to the invention is largely simplified, since no welding is required between the wires, which in itself is a great advantage. Furthermore, brittle welded joints are avoided, which have to be annealed and which often break when the conductor is inserted into the jacket. Thermocouple wires can also be selected which previously could not be selected because of the difficulty in coupling the wires at the hot connection point. A thermocouple according to the invention is manufactured so that

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preferably the powdered material for the electrical Bridge is first placed in a tubular jacket (e.g. in the form of a U-tube) and then the wires are inserted into the jacket so that the opposite ends of the wires are in the powdery electrical bridge are embedded. Alternatively, the wires can be put into the jacket first and the powder that makes the electrical Bridge shapes around the ends of the wires to be stuffed.

At the working temperature of the element the powder forms a completely equivalent electrical contact between the wires of the thermocouple.

The invention will now be described in more detail with reference to the drawings, all three figures being different Show embodiments of the thermocouple according to the invention.

According to Fig. 1 is a quartz tube 1 bent in itself that two legs 2 and 3 with a U-shaped chamber 4 at the end are formed. The chamber 4 is located below a drawn-in area 5 of the legs 2 and 3. One piece Pure platinum wire 6 runs through the bore of leg 2 and a piece of pure tungsten wire 7 runs through the bore from leg 3. The lower chamber 4 contains a certain amount of tungsten powder 8 and the lower ends of the wires 6 and 7 dip into the powder. The rest of the space of chamber 4 is taken up by crushed quartz powder 9. Plug 10 (e.g. an epoxy resin) seal the upper ends of legs 2 and 3.

Although there is no direct contact between wires 6 and 7 (and therefore no permanent bond between them) because of the properties of the bridge formed by the powder

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a good electrical contact at the measuring temperature.

The element with hot junction of FIG. 1 may be to temperature measurements in the range yon 1200 ⁰ C to 16oo ° C used to (the melting point of the tungsten 3387 ° C) and up to 30 A-diving operations in molten steel can be performed. v / ground without damaging the element. To protect the pipe 1, it can be covered with a thin layer of graphite cement, this layer being able to be renewed from time to time between immersion in the molten metal.

The embodiment according to FIG. 1 has the typical dimensions 48 mm for a, 1.5 mm for b, 5 to 6 mm for c, d and e and 2 to 3 mm for f. The pipe 1 can be a have an inner diameter of 1.4 mm and an outer diameter of 2.29 mm. The particle size of the tungsten powder can be in the range of 5 to 10 microns. Powdered graphite, carbon or tungsten carbide can be used instead of the tungsten powder 8 can be used.

The embodiment of FIG. 2 is formed by concentric tubes 12 and 13 made of quartz, a lower chamber 14 is located below a constriction 15 in the outer tube 12. A thermocouple wire 16 (e.g. platinum) is located in the annular space between the tubes 12 and 13. The other wire 17 (e.g. platinum-rhodium alloy) runs within the bore of the tube 13. An electrical contact between the wires in the chamber 14 is via the conductive Bridge made of powder 18 ensured, which remains in powder form, even at the measurement temperatures. A bed of crushed Quartz 19 is over the bridge from tungsten powder 18

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layered to hold this in place and to keep air contact of the bridge 18 to a minimum.

In the embodiment of FIG. 2, the tube 12 could be a outer diameter from 5 "to 6 mm, an inner diameter from 4 to 5 mm and tube 13 could have an outer diameter of 3 mm and an inner diameter of 1.2 mm. Typical dimensions would be 48 mm for g and 5 to 6 minutes for h and j.

The embodiment of FIG. 3 is formed by an outer tube 22 and a solid quartz rod 23, which is in the tube runs. The thermocouple wires and 27 made of platinum and a platinum-rhodium alloy are melted into the rod 23, so that these run over the entire length of the rod inside the same. A chamber 24 is closed The end of the tube 22 is formed by means of a constriction 25.

A bed of ¥ olefin powder 28 with a particle size below 10 microns forms an electrical bridge for the exposed ends of wires 26 and 27 which go into the Dip powder. Above the tungsten powder is a layer of crushed quartz 29.

Since the wires 26 and 27 run inside the rod 23, they can be very thin (a diameter of 30 microns is typical - although smaller diameters are also possible are possible), whereby expensive material is saved and a robust construction is achieved.

The length of the element shown in Fig. 3 can range from a few millimeters to 2 m and typical dimensions are 0.7 mm for k, 0.5 min for m, 0.34 mm for ρ and 0.2 mm

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for n.

The elements shown in the drawings can be used in conjunction with a known immersion lance which both supports the element and provides electrical connection to the upper ends of the thermocouple wires and switches them into the measuring circuit. The embodiment according to FIG. 3 is also suitable for use in the field of miniature thermocouples.

An advantage of the invention is that the production of the elements by simply plugging together the individual Components can be made without complicated welding procedures on the thermocouple wires are required.

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Claims (8)

Patentan's fractions 1J method of measuring temperatures in the range of 1200 C or above by measuring the potential between two different electrically connected thermocouple wires arises when this is brought with its connection point in the range of the temperature to be measured, characterized in that the electrical connection is made by means of a conductive bridge finely divided material (8, 18, 28) takes place, which is located between the ends of the Tnermoelementdrähtε (6, 16, 26, 7, 17, 27). 2. A thermocouple with different thermocouple wires, which are surrounded by a fireproof, electrically insulating jacket and electrically with one another within the jacket are connected, characterized that the jacket (1, 12, 22) is an electrical bridge made of -particulate! contains conductive material (8, 18, 28), which? has a melting point above the measuring temperature, and that the wires (6,16,7,17,27) are electrically connected via the particles of said bridge. 3. Thermocouple according to claim 2, characterized in that the bridge made of tungsten, graphite, carbon or tungsten carbide powder is formed. 4. "Thermocouple according to claim 2, characterized in that the powder has a particle size below 100 microns. - 11 - 509811/0656 COPY 5. Thermocouple according to claim 4, characterized in that the powder has a particle size below 10 microns. 6. Thermocouple according to claim 2, characterized in that the thermocouple wires (2b, 27) in embedded in a rod (23) made of refractory, electrically insulating material and located within the jacket dip the bare ends of the wires into the bridge. 7 «Method of making a thermocouple using the ends of two different thermocouple wires are brought into a fire-proof, electrically insulating jacket surrounding them, characterized in that that the ends of the wires (6, 16, 26, 17, 27) are embedded in a chamber (4, .14, 24) at a certain distance from one another, containing a conductive bridge of particulate material (8, 18, 28) and sealing the chamber around the wires is. 8. The method according to claim 7, characterized in that the jacket is closed at one end Tube (12, 22) is made of quartz and the bridge of particulate material (18, 28) is at the closed end and. the wires (16, 26, 17,27) 'run within a quartz part which is inserted into the tube so far that it ends immediately at said closed end, the wire ends protruding from the part in the small-shaped Immerse the material of the bridge. ■ x- * * * B0981 1/0656 COPY Blank page