Patent Application
20110292968
1. Field of the Invention
The present invention relates to a thermoelement for measuring the temperature in gaseous or fluid media by means of one or more thermocouples, each comprising wires of different metals welded together, which give off a resulting electrical voltage when heated, and are configured as a measuring insert arranged in an insulating rod inserted in a heat-resistant protective tube that can be connected to a connection head, in which case the protective tube is wholly or partially surrounded by a holding tube.
2. Description of the Prior Art
Thermoelements of this kind are familiar in numerous different embodiments and have proven effective in practice for measuring the temperature in thermal process systems. Although the protective tube and/or also the holding tube are manufactured from more or less heat-resistant materials, according to the particular application, the heat input into the contact surfaces of the protective tube and/or the holding tube is considerable, especially at the connection head. This results in impairments and therefore inaccuracies in the measuring result, with the effect that incorrect temperature data must be accepted.
It is therefore the object of the present invention to provide a thermocouple of the aforementioned type in which a high input of heat, which has an unfavourable effect on the temperature measurement, is avoided. Instead, it is attended to ensure that the connection head is insulated against heat to a large extent, so that incorrect temperature measurements are practically excluded and that the thermoelement is not sensitive to thermal shocks. The construction complexity in order to achieve this should be kept low, whilst nevertheless providing high measuring accuracy with a simple design.
In accordance with the present invention, this is achieved in a thermoelement of the aforementioned kind in that the holding tube is supported against the protective tube at a radial distance from the protective tube, a heat-resistant trace and, preferably, an insulating material are disposed between the protective tube and the holding tube, and the holding tube is attached to a connection head and/or the protective tube in one, or both, end areas with thermal insulation.
The trace preferably is made from a heat-resistant or ceramic material and arranged in a helical profile between the protective tube and the holding tube. In addition, the trace is attached to the outer jacket surface of the protective tube and/or the holding tube, and preferably glued onto it/them, in order to prevent the trace from shifting its position during operation.
Moreover, it is appropriate for an air gap between the protective tube and the holding tube, which also functions as a thermal insulator, to be closed at both ends in order to hold the trace or, alternatively for it to be constricted to result in a clearance that is smaller than the diameter of the trace.
To avoid damage during installation of the thermoelement due to excessively hard contact between a support leg and the corresponding component of the thermal process system and, in accordance with a different embodiment, there is provision for the holding tube arranged between the connection head and the support leg to be divided into two sections, and for a coil compression spring disposed between the two sections such that the coil compression spring is supported against the sections, in which case the end areas of the coil compression spring is firmly connected to the two sections, preferably by means of crimping.
The trace in this embodiment is only to be provided in the section of the holding tube attached to the connection head and, in the end areas, to be firmly connected to the connection head and the corresponding section, e.g. by means of crimping, or glued onto the section or the protective tube.
According to a further embodiment, there is provision for the holding tube to be provided on the side facing the measuring insert with a radially projecting support leg configured as a flange and to attach it to this in a thermally insulating manner by means of one or more insulating or sealing discs inserted between the support leg and the measuring insert. Also, the holding tube should be connected to the connection head on the side facing the latter by means of one or more insulating or sealing discs located between the connection head and the holding tube with thermal insulating properties.
Furthermore, it is advantageous for the holding tube to be supported against the protective tube on the end facing the connection head in a torsionally rigid arrangement. The holding tube is therefore provided with a partially open flange with one or more grooves into which the protective tube engages with an axially projecting shoulder for each groove located in the outer edge area.
Due to this embodiment, the protective tube and/or the holding tube can be made from a gas-tight, heat resistant material, preferably, of silicon carbide, with the effect that it is insensitive to thermal shock.
If a thermoelement is configured in accordance with the present invention, the heat input into the connection head via the holding tube is practically excluded although the holding tube can be manufactured from silicon carbide and, as a result, falsifications of the measuring results are to all intents and purposes ruled out. The thermally insulating arrangement of the protective tube in relation to the holding tube, as well as the thermally insulating attachment of the holding tube on the connection head ensures that the connection head is not influenced by conducted heat. Also, because the holding tube is supported on the protecting tube in a torsionally rigid arrangement and because it can be configured in sections, this provides for an operationally reliable construction, as well as installation of the thermoelement, without damage. Accordingly, with little complexity, a thermoelement is created which permits accurate measurements of temperature to be taken over long periods even in excess of 1200° C., without susceptibility to thermal shocks, for example in mobile measuring positions.
The drawings show a sample embodiment of a thermoelement configured in accordance with the present invention, the details of which are explained below. In the drawings,
The thermoelement 1 shown in
In order to avoid a high level of heat input into the connection head 6, the holding tube 21 is arranged with a radial distance from the protective tube 11, with the result that an air gap 30 is formed between them. A trace 31 made from a heat-resistant or ceramic material arranged in a helical profile in the air gap is wrapped around the protective tube 11 and is glued onto it and/or the holding tube 21, and the trace 31 supports the holding tube 21 on the protective tube 11. The air gap in this case acts as a thermal insulator. If necessary, insulating material 33 can be filled in the air gap 30 as well, as is shown in
The holding tube 21, which like the protective tube 11, can also be manufactured from silicon carbide, is configured in one piece in the embodiment shown in
On the side facing the measuring insert 2, the protective tube 11 furthermore has a radially projecting flange 23 configured as a support leg 22, with a sealing and insulating disc 24 attached to the flange 23 by means of a flange plate 25 and screws 26. Also, a sealing and insulating disc 27 is provided between the flange 28 and the connection head 6, with the effect that the holding tube 21 is connected to the support leg 22 in both end areas in a thermally insulated manner, firstly on the connection head 6 and secondly on the flange plate 25 to which the support leg 22 is connected.
The heat input into the connection head 6 via the holding tube 21 and the protective tube 11 is therefore slight, and as a result the temperature values measured by the measuring insert 2 are not unfavourably impaired with the effect that incorrect temperature measurements are avoided.
In the embodiment of the thermoelement 1 shown in
The support leg 22 is therefore placed on the protective tube 11 in a manner which permits restricted movement, with the effect that damage to the thermoelement 1, and in particular to the brittle protective tube 11, e.g. by hard contact between the support leg 22 and the corresponding component of a thermal process system, is largely avoided.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10162481.5 | May 2010 | EP | regional |
