Mineral-insulated supply line

Electricity: conductors and insulators – Conduits – cables or conductors

Reexamination Certificate

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Details

C174S07400A, C174S11000P, C174S1130AS, C174S116000, C174S126400

Reexamination Certificate

active

06300571

ABSTRACT:

The invention relates to a mineral-insulated supply line for a sensor, comprising a sleeve and at least one internal conductor arranged in the sleeve, with one end of the internal conductor connected with a sensor element or its supply line and with the sleeve containing a mineral powder as insulation material. The invention relates further to the use of such a supply line.
A wide variety of this type of supply line is known in the art. For example, a mineral-insulated supply line for a temperature sensor is described in DE 43 30 447 A1. This supply line exhibits an internal conductor made of a nickel-chrome alloy material. A similar supply line in which the internal conductor consists of wires made of a precious metal, which are surrounded by a sleeve made of a nickel-chrome or nickel-chrome-iron alloy, is known from DE 69942. Similar supply lines are known from DE 40 22 051 A1 and from U.S. Pat. No. 4,590,669.
These mineral-insulated supply lines are used for resistance thermometers or as thermoelectric cell wires. They utilize a property of the measuring element, whereby its electrical resistance or thermoelectric voltage depends on the temperature of the material.
For purposes of temperature measurement, the conductors described above are operated virtually without current. However, applications for mineral-insulated supply lines with other sensors, such as gas sensors, are becoming increasingly conceivable. Such sensors include sensor elements with supply and discharge lines for current; these sensors are operated live instead of without current. A mineral-insulated supply line in which the internal conductor operates live is known from WO 95/18965. However, this creates problems in connection with the use of known supply lines, as these lines corrode very easily in an energized state, particularly at higher temperatures such as those which predominate in combustion exhaust gases. In addition, these known materials are relatively difficult to mold precisely, as an unwanted elastic effect takes place. As the materials themselves exhibit low conductivity, they become additionally heated by the flow of current. This is also undesirable or disadvantageous.
Consequently, the objective of this invention is to provide a mineral-insulated supply line whose internal conductors are also suitable for use as high temperature-resistant and corrosion-resistant connection materials for sensors, particularly for gas sensors, when in an energized state.
According to the invention, this objective is solved in that at least one internal conductor is made of a metal from the group consisting of tantalum, titanium, niobium, molybdenum, vanadium, zirconium, rhenium, and osmium, or of an alloy based on at least one of these metals. This type of supply line is highly resistant to high temperatures and corrosion, so that, advantageously, it can even be designed and is suitable for use as a supply line for a heater which, if applicable, is surrounded by a gas sensor, and where the supply line is directly exposed to the hot exhaust gas and its corrosive effects. Surprisingly, it has been demonstrated that such internal conductors are also very resistant when in a charged state. If such a heater line (as an anode) is made of titanium, which may be preferable for cost reasons or for reasons of high temperature stability, the second internal conductor (cathode) should preferably be made of a known iron-chrome-nickel alloy. A different material can be selected for the cathode if, for example, tantalum is used as the anode.
For certain applications, it is advantageous for at least one internal conductor to have a coating which is catalytically active for reducing gases, with this coating preferably consisting of a precious metal or precious metal alloy. This coating can serve as a catalyst for reducing gases (hot exhaust gases), especially H
2
. It is also advantageous for the sleeve to be closed at both ends and only to exhibit openings for the internal conductors, of which there is at least one, so that the insulation material is protected.
According to the invention, the mineral-insulated supply line can be used for a gas sensor for measurement of gaseous components in a gas compound and, especially, as the supply line of a heater of the gas sensor.


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