MEASURING DEVICE

Description

[0001] The invention relates to a device for determining and / or monitoring a process variable of a medium. The medium is preferably located in a container, for example, in a tank or in a pipeline.

[0002] Such field devices are used to monitor and / or determine at least one process variable, for example, a chemical or physical one, of a medium. For the purposes of this application, field devices essentially refer to all measuring devices that are used close to the process and that provide or process-relevant information, including remote I / Os, wireless adapters, and generally electronic components located at the field level. A large number of such field devices are manufactured and distributed by companies in the Endress + Hauser Group.

[0003] Typically, a field device comprises at least one sensor unit that comes into contact with the process at least partially and at least temporarily, and an electronics unit that serves, for example, for signal acquisition, evaluation, and / or power supply. At least the electronics unit of the respective field device is typically arranged in a housing with a housing inlet for introducing at least one connection cable to the field device.

[0004] Examples of field devices include level measuring devices, flow measuring devices, pressure and temperature measuring devices, pH and / or pH-redox potential measuring devices, or conductivity measuring devices, which are used to record the respective process variables of level, flow, pressure, temperature, pH value, redox potential, or conductivity. The underlying measuring principles are well known from the state of the art and will not be listed individually here. Flow measuring devices include, in particular, Coriolis, ultrasonic, vortex, thermal, and / or magnetic inductive flow measuring devices. Level measuring devices, in turn, include, in particular, microwave, ultrasonic, time domain reflectometric (TDR), radiometric, capacitive, conductive, and / or vibronic level measuring devices. Pressure measuring devices, on the other hand, are, for example, so-called absolute, gauge, or differential pressure devices.

[0005] Without limiting its generality, the following description focuses on field devices in the form of thermometers. The following considerations are transferable to other field devices, in particular to thermal flowmeters for determining the flow rate and / or flow velocity of a medium through a pipeline, which also comprise at least one sensor unit with a temperature-sensitive sensor element, for example, in the form of a temperature sensor.

[0006] Thermometers in a wide variety of designs have become known in the art, and their underlying measuring principles have also been described in detail. For example, there are thermometers that use the expansion of a liquid, gas, or solid with a known coefficient of expansion to measure temperature, or those that relate the electrical conductivity of a material to temperature, such as when using resistance elements or thermocouples. In contrast, radiation thermometers, especially pyrometers, utilize the thermal radiation of a substance to determine its temperature.

[0007] A temperature sensor in the form of a so-called thin-film sensor, particularly a resistance temperature detector (RTD), uses a sensor element provided with connecting wires and applied to a carrier substrate. The back of the carrier substrate is usually coated with metal. The sensor elements used are so-called resistance elements, which are provided, for example, by platinum elements, and are also commercially available under the designations PT10, PT100, and PT1000, among others.

[0008] The resistance elements are often inserted into a sensor head, for example, a sensor tip, using a soldering process, particularly SMD soldering, and in particular onto the inner base of a sleeve made of stainless steel, for example. Methods for producing such a solder connection for a thermometer are known, for example, from published patent applications DE102006048448A1 or DE102015112199A1. The production of a solder connection is advantageously associated with high mechanical stability of the respective thermometer. However, the solder connection also has a significant influence on the thermal properties of the thermometer, particularly on the thermal coupling between the resistance element and the sensor head.

[0009] This particularly applies to the quality of the respective solder joint and its reproducibility. For example, it should be ensured that the same amount of solder is always used for each solder joint. With regard to quality, the wetting of the solder on the respective surface plays an important role. Furthermore, the stability of the solder joint and the geometric distribution of the solder between the two components are of key importance. It should be noted that this list is by no means exhaustive. Rather, it provides examples of some possible aspects that could negatively influence the thermal properties of the thermometer.

[0010] The present invention is therefore based on the object of providing a device which has a high mechanical stability.

[0011] This object is achieved by a device for determining and / or monitoring at least one process variable of a medium, comprising at least one sensor element and a unit comprising at least partially a material with anisotropic thermal conductivity. According to the invention, the unit is non-positively connected to the sensor element and is non-positively attached to a surface of the sensor element.

[0012] The use of units comprising materials with anisotropic thermal conductivity has become known, for example, from DE102017100267A1 in connection with a device in which two sensor elements in a single sensor head are kept in thermal equilibrium at all times. A similar idea is pursued in DE102017116408A1 in connection with a thermal flow meter. Both applications are incorporated by reference with regard to the unit. Within the scope of the present invention, however, such a unit is utilized to ensure good mechanical stability of the device, in particular while simultaneously maintaining good thermal properties. The unit comprising the material with anisotropic thermal conductivity serves to provide a force-fitting connection for the sensor element and also ensures uniform heat distribution, in particular ensuring thermal equilibrium.The solution according to the invention also advantageously significantly reduces thermally induced mechanical stresses, which may arise, for example, from different thermal expansion coefficients of the different materials used. The invention relates to a device for determining and / or monitoring a process variable of a medium according to claim 1.

[0013] One embodiment of the invention provides that the sensor element is a temperature sensor. In this case, the device is, for example, a thermometer or a flowmeter operating according to the thermal measurement principle.

[0014] However, a device according to the invention can also have more than one sensor element. In this case, at least two sensor elements are preferably frictionally connected to a single unit comprising a material with anisotropic thermal conductivity. In this case, the at least two sensor elements are advantageously always in thermal equilibrium. This can be advantageously ensured, in particular, even if the at least two sensor units cannot be arranged directly together within the device, for example, due to design restrictions.

[0015] It goes without saying that not only multiple sensor elements, but also at least one sensor element and at least one other component can be non-positively connected to a single unit. For example, in addition to a sensor element, a heating / cooling element and / or a reference element, particularly for in-situ calibration of the sensor element, can also be non-positively attached to the same unit.

[0016] The unit is designed, in particular, in the form of an elongated element, wherein the thickness of the element is small compared to the length and / or width of the element. Thus, in one embodiment of the device according to the invention, the unit is a thin-walled film, which film consists at least partially of the material with anisotropic thermal conductivity. A unit designed in this way can be incorporated into a sensor unit of a field device in a particularly space-saving manner.

[0017] One embodiment of the device includes the material with anisotropic thermal conductivity being a material containing at least some carbon, in particular graphite, or hexagonal boron nitride. Preferably, the unit preferably has a higher thermal conductivity along its longitudinal axis than perpendicular to it.

[0018] One embodiment of the invention includes at least one hole in the unit. The hole allows the unit to be connected to the at least one sensor element in a force-locking manner.

[0019] A further embodiment provides that the unit, at least in a first partial region in which the force-locking connection with the sensor element can be established, has a first diameter that is smaller than a second diameter of the unit in a second partial region that differs from the first partial region. In particular, the first diameter is smaller than a diameter of the sensor element in the remaining regions.

[0020] In one embodiment, the device comprises fastening means for establishing the force-locking connection.

[0021] In this regard, it is advantageous if the fastening means comprise a screw, a rivet, or a clamp. For example, in the case of a unit with a hole, the fastening means can serve to fasten the unit to the sensor element through the hole. Similarly, in the case of a unit with a reduced diameter in some sections, fastening around the unit is conceivable, for example, by means of a suitably designed clamp.

[0022] An alternative embodiment involves the fastening means comprising a solder, in particular consisting of a solder. In addition to a conventional solder connection of the unit to the sensor element, it is also conceivable for the solder, in the case of a unit with a hole, to extend through the hole and achieve an effect comparable to that of a rivet, or for the solder, in the case of a unit with a reduced diameter, to act like a clamp. Such embodiments are particularly advantageous when the sensor element and / or the unit have a comparatively low wettability, so that a conventional solder connection cannot lead to a reliable, force-fitting connection. These considerations also apply analogously to a fastening according to the invention, in this case in comparison to a conventional adhesive connection, which is based on the development of an adhesive force between the components to be connected.

[0023] One embodiment of the device includes that the unit is designed in the form of a, in particular thin-walled, flexible, film, wherein the unit is fastened to the sensor element in a first end region.

[0024] In this context, it is advantageous if the film is arranged and / or designed such that, starting from the first end region fastened to the sensor element, it surrounds the sensor element, in particular is wound around the sensor element. In this case, the film serves to establish thermal equilibrium in a volume surrounding the sensor element by heat flowing in a direction parallel to the film. When the sensor element with the unit is introduced into a sensor housing, in particular a sensor head, the winding of the unit around the sensor element causes a restoring force of the unit, which leads to stable positioning within the housing or sensor head. Such a sensor housing can in particular be a protective tube for a thermometer.

[0025] It is further advantageous if the unit is non-positively fastened in a second end region to another component of the device, in particular in a sensor housing in which the sensor element is arranged, or to a carrier element on which the sensor element is arranged. The sensor housing can be a sensor head, for example. In the case of a thermometer, the sensor housing can be a protective tube. In the case of a carrier element, it can be a flat element on which at least the sensor element is arranged and by means of which the sensor element can be fastened to a container containing the medium.

[0026] The unit serves both to mechanically fasten the sensor element to the other component and to ensure optimal, particularly even, heat distribution from the process. This ensures an easily implemented, force-locking connection between the sensor element and the other component that does not adversely affect the thermal properties. Furthermore, mechanical stresses and forces acting on the sensor element can be minimized or even eliminated by using the unit to create the force-locking connection. In an alternative embodiment, the unit is designed in the form of a, particularly thin-walled, flexible, film, with the unit being attached to the sensor element in a central region.

[0027] In this context, it is again advantageous if the film, starting from the central region attached to the sensor element, is arranged on two opposite sides of the sensor element, at least partially around the sensor element. Similar to the case of attachment in an end region of the unit, this allows the unit to achieve uniform heat distribution in a volume surrounding the sensor element. In particular, the unit can be used to achieve thermal equilibrium between the sensor element, the unit, and at least one other component of the device.

[0028] In summary, the present invention can reduce thermal contact resistance within a field device while simultaneously ensuring high mechanical stability. In particular, mechanical stresses that otherwise occur due to different thermal expansion coefficients of different materials can be avoided.

[0029] The invention is explained in more detail with reference to the following drawings. It shows: Fig. 1 : a schematic representation of a thermometer with a sensor element arranged in a sensor head in the form of a temperature sensor according to the prior art, Fig. 2 : two embodiments of a device according to the invention with (a) a unit fastened to a sensor element in an end region and (b) in a middle region; Fig. 3 : preferred embodiments for producing a force-locking connection with the aid of a solder; and Fig. 4 an embodiment of a device according to the invention with a unit attached to a sensor element and to a sensor housing.

[0030] In Fig.1 is a schematic illustration of a thermometer 1 with an immersion body or a protective tube 2, a measuring insert 3, and electronics 4 according to the prior art. The measuring insert 3 is inserted into the immersion body 2 and comprises a sensor element 5, which in the present case is a temperature sensor in the form of a resistance element, which is electrically contacted via the connecting lines 6 and connected to an electronics 4. However, the sensor element 5 does not necessarily have to be part of a measuring insert 3. In other embodiments, the electronics 4 can also be arranged separately from the measuring insert 3 and immersion body 2. Also, the sensor element 5 does not necessarily have to be a resistance element, and the number of connecting lines 6 used does not necessarily have to be two. Rather, a different number of connecting wires 6 can be used depending on the measuring principle applied.

[0031] The sensor element 5 is firmly attached by a solder joint in an internal volume of the measuring insert 2 to a bottom surface B of the measuring insert 2 facing the medium M. As already explained in the introduction, such a connection is associated with high manufacturing requirements. The quality and reproducibility of the solder joint significantly influence the thermal properties of the device 1.

[0032] In order to provide high mechanical stability with good thermal properties at the same time, a unit 8 comprising a material with anisotropic thermal conductivity is connected to the sensor element 3 in a force-fitting manner, as shown for two exemplary embodiments of a device according to the invention in Fig. 2 illustrated. In both embodiments, as well as in the following embodiments, the unit 8 is manufactured, without limitation of generality, in the form of a thin-walled foil made of a material with anisotropic thermal conductivity, for example, graphite.

[0033] For the design according to Fig. 2a is unit 8 in Fig. 2a in an end region E1 attached to the sensor element 5 and wound around the sensor element 5. In the Fig. 2b In the embodiment shown, however, the unit 8 is attached to the sensor element 5 in a central region MB and surrounds the sensor element 5 on two opposite sides. In both cases, the unit 8 is arranged at least partially around the sensor element 5 and at least partially surrounds the sensor element 5. In this way, rapid heat transfer from the medium M to the sensor element 5 and thus homogeneous heat distribution within the protective tube 2 can be ensured; in particular, a region of the protective tube 2 facing the medium M, the unit 8, and the sensor element 5 are in thermal equilibrium.

[0034] To establish the force-locking connection between the unit 8 and the sensor element 5, fastening means 10, 11 can be used, as shown in Fig. 3 is illustrated by example.

[0035] For those in the figures Fig 3a-3c In the embodiments shown, the unit 8 has a hole 9, which in this case is arranged, for example, in the end region E1. The force-locking connection can be established through the hole. Fastening means 10, 11 can be used to establish the connection, as in Fig. 3b in the case of a lot 10 and in Fig. 3c shown for the case of a rivet. In this case, the solder 10 acts like a rivet 11. Alternatively, it is also conceivable for the unit E1 in a first partial area T1 to have a smaller first diameter d1 than a second diameter d2 of the unit in a second partial area T2. In this case, the fastening means 10, 11 can be designed, for example, in the form of a clamp [not shown], which is clamped around the unit 8 in the first partial area T1. The diameters d1 and d2 can be constant in the two partial areas T1 and T2 or also variable at least in sections.

[0036] It is also conceivable to arrange several similar or different sensor elements 5, or at least one sensor element 5 and at least one further component, for example a heating / cooling element and / or a reference element for in situ calibration of at least one sensor element 5, in different areas of the unit 8. It should also be noted that the sensor element 5 and the unit 8 do not necessarily have to be arranged in an immersion body 2. For example, it is also conceivable for the unit 8 and the at least one sensor element 5 to be arranged on a carrier element [not shown here]. In this case, it is also conceivable for the unit 8 and the at least one sensor element 5 to be non-positively connected to the unit 8 and the carrier element.

[0037] One option for stabilization, protection, and / or further thermal insulation is to coat the fastener used at the respective connection point. The coating can be, for example, an elastic coating, a potting compound, or an adhesive.

[0038] A further design is in Fig. 4 shown. In this embodiment, the unit 8 is also designed in the form of a thin-walled film. It is non-positively connected to a sensor element 5 in a first end region E1 and to a bottom surface of a protective tube 2 in which the sensor element 5 is arranged in a second end region E2. Alternatively, it can also be connected to a side wall of the protective tube 2 or to another component of the device 1. Bezugszeichenliste

[0039] 1Thermometer 2Protection tube 3Measuring insert 4Electronic unit 5Sensor element 6Connecting cables 7Solder connection according to the state of the art 8Unit with a material with anisotropic thermal conductivity 9Hole 10Solder 11Rivet BBottom area of ​​the protective tube d1, d2Diameter of the unit T1, T2Partial areas of the unit E1, E2End areas of the unit MBMiddle area of ​​the unit MMedium TTemperature

Claims

1. A device (1) for determining and / or monitoring at least one process variable of a medium (M) comprising at least one sensor element (5) and a unit (8) made at least partly of a material with anisotropic thermal conductivity, wherein the unit (8) is secured to a surface of the sensor element (5) by means of a force-fit connection, and wherein the unit (8) is a thin film, said film consisting at least partly of the material with anisotropic thermal conductivity and wherein the film serves for the force-fit connection of the sensor element, and also ensures an even distribution of the heat, in particular ensures a thermal equilibrium.

2. The device (1) as claimed in claim 1, wherein the sensor element (5) is a temperature sensor.

3. The device (1) as claimed in at least one of the preceding claims, wherein the material with anisotropic thermal conductivity is a material containing at least some proportion of carbon, in particular graphite, or hexagonal boron nitride.

4. The device (1) as claimed in at least one of the preceding claims, wherein at least one hole (9) is made in the unit (8).

5. The device (1) as claimed in at least one of the preceding claims, wherein the unit (8) has a first diameter (d1) at least in a first section (T1), in which the force-fit connection to the sensor element (5) can be created, said first diameter being smaller than a second diameter (d2) of the unit (8) in a second section (T2).

6. The device (1) as claimed in at least one of the preceding claims, comprising additional mounting materials (10, 11) arranged on the unit (8) for creating the force-fit connection.

7. The device (1) as claimed in claim 6, wherein the mounting materials (10, 11) comprise a bolt, a rivet (11) or a clamp.

8. The device (1) as claimed in claim 6, wherein the mounting materials (10, 11) comprise a solder (10), in particular consist of a solder (10).

9. The device (1) as claimed in at least one of the preceding claims, wherein the unit (8) is configured in the form of an, in particular thin and flexible, film, and wherein the unit (8) is secured to the sensor element (5) in a first end area (E1).

10. The device (1) as claimed in claim 9, wherein the film (8) is arranged and / or configured in such a way that it surrounds the sensor element (5), in particular is wound around the sensor element (5), starting from the first end area (E1) secured to the sensor element (5).

11. The device (1) as claimed in claim 9, wherein the unit (8) is secured to another component (2) of the device (1) by means of a force-fit connection in a second end area (E2), in particular one with a sensor housing (2) in which the sensor element (5) is arranged, or a carrier element on which the sensor element (5) is arranged.

12. The device (1) as claimed in at least one of claims 1 to 8, wherein the unit (8) is configured in the form of an, in particular thin and flexible, film, and wherein the unit (8) is secured to the sensor element (5) in a central area (MB).

13. The device (1) as claimed in claim 12, wherein the film (8) is arranged on two opposite sides of the sensor element (5), at least partly around the sensor element (5), starting from the central area (MB) secured to the sensor element (5).