FI71986C - Koaxialröruppställning. - Google Patents

Description

71 986

Coaxial tube arrangement - Koaxialröruppställning

The invention relates to a coaxial tube arrangement as defined in the preamble of claim 1.

DE-A-2 709 717 discloses a solution as set out in the preamble of the claim, by means of which it is possible to keep the temperature of the liquid or gaseous medium substantially constant. For this purpose, an electric heating element is placed either longitudinally or threaded on the outer surface of the innermost tube. The heating element comprises two electrodes placed in an insulating layer, which in turn is coated with a metal coating. The heating element is attached to the outer surface of the inner tube with ties. Further, the outer surface of the heating element has two separate layers of polyurethane foam and an outer plastic coating. Such a structure is relatively complex and requires several manufacturing steps. In addition, the heating effect is not uniform on the outer surface of the pipe but is strongest at the heating element. This results in an uneven temperature distribution on the outer circumference of the inner tube.

It is an object of the present invention to provide a coaxial tube fitting 20 which can prevent the effects of external temperature variations on the medium contained in the tube and / or heat the medium. One particular purpose is to keep the temperature of the medium contained in the tube constant despite external temperature fluctuations.

The solution according to the invention has several application areas. One possible area of application is pressure transmitters used in control technology. Such pressure transmitters, the so-called capillary tubes, transmit information about the state and control of the process as pressure changes in the medium contained in the capillary tube. The medium contained in the tube may be gaseous or liquid and there may be flow in the tube when the transfer medium is 2 71986 gaseous and the medium may be stationary, especially when the medium is liquid. In practical instrumentation situations, such capillary tubes used for the transmission of pressure signals also have to be placed in places where they are exposed to the effects of ambient temperature fluctuations. Since the properties of gases and liquids, e.g. viscosity and density, are temperature dependent, the above-mentioned placement of the capillary tube results in the problem that the pressure message may be distorted by changes in ambient temperature, for example due to process information. There is no satisfactory solution to this problem and thus the measuring and control devices installed in such conditions do not work satisfactorily.

Another area of application in which the coaxial tube according to the invention can be used is in general the transfer of liquids and gases. Such applications may be, for example, fuel or oil transfers, pneumatic and hydraulic systems in which the pressure medium is transferred. Thus, the invention encompasses 20 medium transfer needs in which the medium must be kept substantially constant despite external temperature fluctuations and / or heating the medium.

To achieve the object of the invention, the coaxial pipe arrangement is mainly characterized in that a layer of 25-resistance material surrounds the pipe containing the medium and that electrical supply conductors are arranged on the inner and outer surface of the layer of resistance material.

The above arrangement provides a preferred solution to the present problem previously described. The power losses in the resistive material are transferred through the tube to the medium. On the other hand, the protective layer prevents the heat generated in the resistor from conducting outwards and thus reduces the need for power.

3,71986

According to a preferred embodiment, the resistance material is selected from a material or combination of materials whose resistance is temperature-dependent, so that the heat loss in the resistance material decreases with increasing temperature and vice versa. Such a solution achieves a coaxial tube arrangement whose temperature remains very constant. In this case, no separate temperature sensors are required to control the power, but the material or combination of materials is selected on the basis of the resistance properties so that the temperature-10 dependence curve is suitable for the conditions in which the coaxial tube arrangement is used. Such materials and combinations of materials with temperature-dependent resistance are known per se and are commercially available.

According to a further preferred embodiment, the tube is made of an electrically conductive material. Such a tube, in particular a metal tube, can be used as a supply conductor on the inner surface of the resistance layer.

According to a further feature, the tube is a non-electrically conductive material. In this case, a supply conductor is placed on the surface of the tube on the inner surface of the resistive layer.

The above embodiments with material choices are always performed according to the need for use and the conditions that the coaxial tube is intended to achieve.

According to a further embodiment, the at least second supply conductor is a network structure surrounding a layer and / or a pipe of resistive material. With such a solution, the heat losses are evenly distributed in the resistance material.

According to a further embodiment, the protective layer consists of an inner layer of heat-insulating material and an outer layer of plastic material. In this case, the inner layer has a thermal insulating effect and the outer layer acts as a mechanical and / or moisture barrier.

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According to a further embodiment, the resistive material is selected from a material or group of materials with little or no temperature dependence, whereby the power of the power supply is adjusted. This solution also achieves a coaxial tube arrangement in which the medium remains substantially constant or its temperature can be raised, because fluctuations in power demand due to changes in conditions are caused by changing the voltage and / or current in the circuit. In this case, for example, a temperature sensor is required, which measures the ambient and / or medium temperature and controls the power taken from the power supply.

The invention is further illustrated in the following description with reference to the accompanying drawings. In the drawings, Figures 1 and 2 schematically show some embodiments of a coaxial tube-15 arrangement according to the invention, the layers belonging to the coaxial tube being separated to illustrate the structure.

Figure 1 shows the so-called A capillary tube application used as a pressure transmitter. In the fitting-20, the innermost tube 1 is of electrically conductive material and comprises a small hole 2 in which the medium is located. A substantially radially strong layer of resistive material 3 is formed around the tube 1. Further, a feed conductor 4 is placed on the outer surface of the layer 3, which is preferably a reticulated conductor structure surrounding the outer surface of the resistor 25 layer, e.g. Such an Fe sock improves the mechanical strength of the arrangement and protects the inner layers from damage. Furthermore, a uniformly strong thermal insulation layer 5 is placed on the outer surface of the layer 4 in a suitable radial direction for several minutes. Several materials can be used as the thermal insulation layer 5, e.g.

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According to the invention, supply conductors are connected to the inner and outer surfaces of the layer 3 of resistive material, which are connected to the power supply 7. The heat losses generated in the resistive material 3 are transferred by conduction to the medium contained in the tube 1.

In the embodiment according to Fig. 1, a pipe 1 can be used as a supply conductor on the inner surface of the resistive material 3.

Figure 2 shows an embodiment in which the tube 1 'is a non-electrically conductive material. In this case, the second supply conductor 8 is placed between the layer 3 of resistive material and the pipe 1 10. Preferably, the supply conductor 8 is a network-like conductor surrounding the pipe 1, which surrounds the pipe 1 '. As the supply conductor, the same type of Fe sock can be used as the supply conductor 4 placed on the outer surface of the layer 3 of resistance material. In this case, the power supply 7 is, of course, connected to the supply conductor 8. The other layers substantially correspond to the embodiment of Fig. 1 and are denoted by the corresponding reference numerals.

The layer of resist material is preferably selected from a material or combination of materials whose resistance is temperature-dependent so that the heat loss in the resist material decreases with increasing temperature and vice versa. In this case, a self-adjusting coaxial tube arrangement with a heating power is obtained, the temperature of which remains very very constant when the material or combination of materials of the layer 3 used as a resistance material is selected on the basis of resistance properties so that the temperature dependence curve is suitable. Such materials and combinations of materials are known per se and one skilled in the art will be able to select a suitable material or combination of materials from these.

It is also conceivable for an embodiment in which the layer 3 used as a resistance material is selected from a material or group of materials which has little or no temperature dependence. In this case, the power of the power supply is adjusted. In this case, however, it is necessary to use, for example, a temperature sensor which measures the ambient and / or medium temperature and controls the power taken from the power supply.

Claims (8)

A coaxial tube arrangement comprising a tube (1, 1 ') containing medium and a bearing structure about the same for protecting the medium inside the tube (1, 1') from external temperature changes and / or for heating the medium to a desired temperature. temperature comprising arrangement: a layer (3) of resistive material, in contact with the resistive material (3), standing electrical conductive trades (1, 8, 4) connected to a power source (7) to cause heat loss to develop in the resistive material (3) and around the layer (3) of resistive material provide a protective layer (4, 5, 6) providing thermal insulation and mechanical protection and / or moisture protection, characterized in that the pipe (1, 1 ') containing medium is surrounded by the layer (3) of resistance material, the electrically conductive trees (1, 8, 4) are located on the inner and outer sides of the layer of resistance material. 2. Arrangement according to claim 1, characterized in that the resistance material (3) is of such material or combination of material having such a temperature dependent resistance that the heat loss generated in the resistance material is reduced as the temperature is raised and the opposite. 3. Arrangement according to claim 1, characterized in that the pipe (1) is of electrically conductive material.