NON-INVASIVE THERMOMETER

Description

[0001] The invention relates to a device for determining and / or monitoring the temperature of a medium in a container in automation technology. The container is, for example, a tank or a pipeline.

[0002] Thermometers are known in a wide variety of designs from the prior art. For example, there are thermometers that use the expansion of a liquid, gas, or solid with a known coefficient of thermal expansion to measure temperature, or those that relate the electrical conductivity of a material or a derived quantity to temperature, such as electrical resistance when using resistance elements or the thermoelectric effect in the case of thermocouples. In contrast, radiation thermometers, especially pyrometers, utilize the thermal radiation of a substance to determine its temperature. The underlying measurement principles of each have been described in numerous publications.

[0003] Temperature sensors in the form of resistance elements include thin-film and thick-film sensors, as well as thermistors (also known as NTC thermistors). In a thin-film sensor, particularly a Resistance Temperature Detector (RTD), a sensor element with connecting wires is applied to a substrate, the back of which is typically coated with metal. These sensor elements are resistance elements, such as platinum elements, which are commercially available under designations like PT10, PT100, and PT1000.

[0004] In thermocouple temperature sensors, the temperature is determined by a thermoelectric voltage generated between thermocouple wires made of different materials connected at one end. Thermocouples conforming to DIN standard IEC 584, such as types K, J, N, S, R, B, T, or E, are typically used for temperature measurement. However, other material pairs, particularly those exhibiting a measurable Seebeck effect, are also possible.

[0005] The accuracy of temperature measurement is highly dependent on the specific thermal contacts and the prevailing heat conduction. The heat flows between the medium, the container holding the medium, the thermometer, and the process environment play a crucial role. For reliable temperature determination, it is essential that the temperature sensor and the medium are essentially in thermal equilibrium for at least a certain period of time required to measure the temperature. The time it takes for a thermometer to respond to a temperature change is also known as the thermometer's response time.

[0006] High measurement accuracy can be achieved particularly when the temperature sensor is immersed in the medium. Numerous thermometers are known in which the temperature sensor is brought into more or less direct contact with the medium. This allows for a comparatively good coupling between the medium and the temperature sensor.

[0007] For various processes and many containers, especially small vessels or pipelines, non-invasive temperature measurement is more advantageous. Thermometers that can be attached externally or internally to the container holding the medium are also known. Such devices, also called surface thermometers or contact sensors, are disclosed, for example, in documents such as DE102014118206A1 and DE102015113237A1. With these types of measuring devices, the temperature sensors are not in direct contact with the process. This necessitates that various additional aspects be considered to ensure good thermal coupling. For example, the mechanical and thus also the thermal contact between the container and the thermometer is crucial for the achievable measurement accuracy. Insufficient contact makes accurate temperature determination impossible.

[0008] Surface or skin-point thermometers often use thermocouple temperature sensors that are welded directly to the outer surface or skin of the pipe or container. However, replacing the thermocouples in such cases can be a time-consuming and costly process, especially since it may require temporarily shutting down the process and / or application. To overcome these drawbacks, embodiments of such thermometers that allow for easy replacement of the temperature sensors have been disclosed, for example, in US Patent No. 5382093 and the as-yet-unpublished European patent application No. 18198608.4.

[0009] Furthermore, numerous different designs of thermometers for non-invasive temperature measurement have become known, such as in the

[0010] Documents US2016 / 0047697A1, DE102005040699B3, EP3230704B1 or EP2038625B1 are described. Also noteworthy are the following documents: US 2014 / 334517 A1, DE 10 2009 003848 A1, DE 20 2006 003903 U1, DE 31 26 931 A1, DE 10 2015 112425 A1 and DE 10 2017 100267 A1. In particular, US 2014 / 334517 A1 discloses a temperature sensor strip for detecting the temperature of a workpiece during welding, comprising a carrier material and a plurality of temperature sensors embedded in an insulating material, the insulating material being configured to thermally insulate the temperature sensors. Furthermore, DE 31 26 931 A1 discloses a device for attaching and holding a temperature sensor on a tubular object, comprising a cuff made of two layers of a glass fiber tape. The temperature sensor is arranged on a thin copper foil between the two layers of the cuff.Finally, DE 42 44 189 C2 discloses a contact temperature sensor for determining the surface temperature of a measuring object, consisting of a rubber-elastic rubber material in cylindrical form and a contact plate vulcanized to the end face of the cylinder with retaining or barbed hooks, so that the rubber-elastic retaining system and the contact plate interlock to form a firm connection. The contact plate protrudes slightly from the rubber-elastic rubber material, allowing for unimpeded contact with the object surface. A thermocouple is attached to the inside of the contact plate with thermally conductive adhesive.

[0011] A key problem with non-invasive temperature measurement is heat dissipation from the process to the environment. This results in a significantly higher measurement error than if the temperature sensor were directly integrated into the process.

[0012] Therefore, the invention aims to provide a thermometer for non-invasive temperature measurement, which is characterized by high measurement accuracy.

[0013] This problem is solved by the device for determining and / or monitoring a process variable, in particular the temperature or flow rate, of a medium in a container, in particular a vessel, a container or a pipeline, according to claim 1. The device according to the invention comprises a temperature sensor for detecting the temperature and a flexible, thermally conductive support element, which support element can be arranged on an outer wall of the container, wherein the temperature sensor is attached to the support element.

[0014] The support element is designed in such a way that it can be adapted to the contours of the container. For example, the support element can be arranged, at least partially, around the wall of the container. An arrangement along a circumferential line based on a cross-sectional area perpendicular to the longitudinal axis of the container is particularly preferred in the case of a container in the form of a pipe.

[0015] The temperature sensor is preferably attached to the support element in a region of the support element facing away from the container in its installed state. The device is brought into thermal contact with the container from an outer region of the container. The temperature of the medium is thus determined indirectly via a wall of the container. Heat is transferred from the process to the at least one temperature sensor by means of the thermally conductive support element, which is therefore essentially in thermal equilibrium with the process. The temperature sensor is thus essentially exposed to the process temperature, even though it is located outside the container.

[0016] This in turn leads to increased measurement accuracy of the device.

[0017] The device may optionally include electronics. Alternatively, the electronics can be a separate component that can be connected to the device. Furthermore, the temperature sensor is advantageously provided with at least one connecting wire for electrical contact.

[0018] One design involves the temperature sensor being a resistance element or a thermocouple.

[0019] The device may also include more than one temperature sensor, with all temperature sensors used being attached to the support element.

[0020] A further embodiment includes the device comprising at least one reference element for in-situ calibration and / or validation of at least the temperature sensor, which is mounted on the support element, and which reference element consists at least partially of at least one material for which, in the temperature range relevant for calibrating the first temperature sensor, at least one phase transition occurs at at least one predetermined phase transition temperature, and for which phase transition the material remains in the solid phase. In this respect, reference is made to EP02612122B1.

[0021] The temperature sensor and the reference element are advantageously always in thermal equilibrium relative to each other due to the use of the thermally conductive support element, regardless of their exact arrangement on the support element.

[0022] In another embodiment, the device includes a heating element attached to the support element. The heating element allows the device to be heated to a predefined temperature. Again, the thermally conductive support element ensures that all components of the device attached to it are essentially exposed to the predefined temperature.

[0023] Furthermore, the heating element can be used to determine the flow rate according to the thermal flow measurement principle, which is well known from the state of the art.

[0024] Accordingly, the flow rate can be determined in two different ways. Within the scope of the present invention, the term flow rate encompasses both volumetric flow rate and mass flow rate of the medium. Likewise, the flow velocity or flow rate of the medium can be determined.

[0025] According to the first measuring principle, a sensor element is exposed to a medium flowing through a pipeline and heated in such a way that its temperature remains essentially constant. Given known and at least temporarily constant medium properties, such as the medium temperature, density, or composition, the mass flow rate of the medium through the pipeline can be determined from the heating power required to maintain the temperature at this constant value. The medium temperature is defined here as the temperature the medium would have without any additional heat input from a heating element. In contrast, the second measuring principle involves operating the heating element at a constant power and measuring the temperature of the medium downstream of the heating element. In this case, the measured temperature of the medium provides information about the mass flow rate.

[0026] The heating element can, for example, be in the form of a resistance heater.

[0027] For example, so-called resistance elements, such as RTD resistance elements (Resistance Temperature Detectors), especially platinum elements, are used, as they are also commercially available under the designations PT10, PT100, and PT1000. The resistance elements are heated by the conversion of electrical power supplied to them, e.g., as a result of an increased current supply.

[0028] In another embodiment of the device, the temperature sensor comprises a temperature-sensitive sensor element which is electrically contacted via at least a first and a second connecting lead, wherein the first connecting lead is divided into a first and a second section, the first section facing the sensor element being made of a first material, and the second section facing away from the sensor element being made of a second material different from the first, the second connecting lead being made of the second material, and wherein the first section of the first connecting lead and at least a part of the second connecting lead form a first differential temperature sensor in the form of a thermocouple. In this context, reference is made to the hitherto unpublished German patent application with file number 102018116309.6.With this type of temperature sensor design, it is possible to detect heat dissipation in the sensor's vicinity. Precise knowledge of the heat dissipation further increases the device's measurement accuracy. When determining flow rate, higher flow rates of the medium in the container can be detected as heat dissipation decreases, thus extending the device's measuring range.

[0029] Preferably, the at least one temperature sensor, as well as the reference element and / or heating element, which may also be present, are all attached to the support element in a region of the support element facing away from the container in the state in which they are arranged thereon. All conceivable arrangements of the aforementioned components of the device on the support element are possible, particularly geometric arrangements, and fall within the scope of the present invention.

[0030] According to the invention, the support element consists of a metallic fabric or mesh, particularly using copper. However, other metals besides copper can also be used to manufacture a support element according to the invention in the form of a metallic fabric or mesh, and these also fall within the scope of the present invention. The support element is preferably a planar structure with definable geometric dimensions. A fabric is understood to be a structure made of two different flexible metal strands or wires – warp and weft – of the respective metal used, which regularly intersect at a specific angle, while a mesh consists of several intertwined flexible metal strands or wires.

[0031] According to the invention, the device comprises a thermal insulation unit that at least partially surrounds the support element. In particular, the thermal insulation unit surrounds the support element at least partially in an area facing away from the process when the support element is attached to it. The insulation unit serves to thermally insulate the support element and the at least one temperature sensor attached to it from the environment. In this way, unwanted heat dissipation to the environment is avoided, which would lead to an undesirable temperature gradient, especially in the area of ​​the device.

[0032] It is advantageous if the thermal insulation unit consists at least partially of silicone or silicone foam.

[0033] According to the invention, the temperature sensor is arranged between the support element and the thermal insulation unit.

[0034] In a further embodiment, the device comprises at least one guide for guiding at least one connecting cable of at least the temperature sensor. The use of a guide serves to mechanically stabilize the connecting cables and prevents them from breaking off. If a thermal insulation unit is present, the guide is designed and arranged such that the at least one connecting cable can pass through the insulation unit. The guide is, for example, a sleeve or a channel. The number of guides used depends on the number of connecting cables and the number of components attached to the support element, such as additional temperature sensors, a heating element, or a reference element.

[0035] In a particularly preferred embodiment, the temperature sensor is attached to the support element by means of a flexible adhesive. This ensures consistent mechanical and thermal contact between the temperature sensor and the support element, regardless of the outer radius of the container along which the support element is positioned. Advantageously, no air gaps form between individual sections of the temperature sensor and the support element.

[0036] However, fastening by means of an adhesive is by no means necessary within the scope of the present invention. Rather, all conventional fastening methods can be used to attach a temperature sensor. In particular, in other embodiments of the invention, the temperature sensor can, for example, also be soldered onto the carrier element.

[0037] In a particularly preferred embodiment, the support element consists of at least two flexible layers arranged one above the other. Configuring the support element with several flexible layers arranged one above the other also serves to prevent air gaps between individual sections of the temperature sensor and the support element. In the case of such a support element, the use of a flexible adhesive is not strictly necessary.

[0038] A further embodiment includes fastening means for attaching the device to the container, in particular in a detachable manner. In this respect, all fastening means customary and suitable for those skilled in the art, such as pipe clamps, are eligible and fall within the scope of the present invention.

[0039] It is advantageous if the fastening elements are designed to ensure a predefined contact pressure of the support element against the container. This ensures good and reproducible thermal contact between the container wall and the support element.

[0040] It is also advantageous if the fasteners have at least one elastic element, in particular a spring. With an elastic fastener, the same fastener can be used to accommodate different outer radii, especially diameters, of the containers used.

[0041] In particular, essentially the same contact pressure can be guaranteed regardless of the outer radius.

[0042] Another embodiment involves the container being a pipeline, with the support element being designed in such a way that it can be arranged around the pipeline perpendicular to the longitudinal axis through the pipeline.

[0043] The invention is explained in more detail using the following figures. They show: Fig. 1 : a state-of-the-art non-invasive temperature measurement thermometer; Fig. 2 : a first embodiment for a thermometer with a single temperature sensor; Fig. 3 : a second embodiment for a thermometer with two temperature sensors, a heating element and a reference element; Fig. 4 : a third embodiment for a thermometer according to the invention with a thermal insulation unit; Fig. 5 : a fourth embodiment with a fastening unit comprising an elastic element; and Fig. 6 : a support element made up of several layers.

[0044] In the figures, identical elements are each marked with the same reference symbol.

[0045] In Fig. 1Figure 1 shows a schematic diagram of a thermometer 1 according to the prior art, comprising a measuring insert 3 and electronics 4. The thermometer 1 serves to measure the temperature T of a medium M, which is located in a container 2, here in the form of a pipeline. For this purpose, the thermometer 1 does not protrude into the pipeline 2, but rather is attached to a wall W of the pipeline 2 from the outside for non-invasive temperature determination. The measuring insert 3 includes a temperature sensor 5, which in this case comprises a temperature-sensitive element in the form of a resistance element. The temperature sensor 5 is electrically contacted via the connecting leads 6a, 6b and connected to the electronics 4. While the thermometer 1 shown is designed in a compact form with integrated electronics 4, in other thermometers 1 the electronics 4 can also be arranged separately from the measuring insert 3.Furthermore, the temperature sensor 5 does not necessarily have to be a resistive element, and the number of connecting leads 6 does not necessarily have to be two. Rather, the number of connecting leads 6 can be selected appropriately depending on the measuring principle used and the temperature sensor 5 employed.

[0046] As already explained, the measuring accuracy of such a thermometer 1 depends to a large extent on the materials used for the thermometer and on the respective, especially thermal, contacts, particularly in the area of ​​the temperature sensor 5. The temperature sensor 5 is in indirect thermal contact with the medium M, i.e., via the measuring insert 2 and the wall W of the container 2. Heat dissipation from the medium M to the environment also plays a significant role in this context, which can lead to an undesirable temperature gradient in the area of ​​the temperature sensor 5.

[0047] To adequately address these problems, an alternative embodiment for a non-invasive thermometer 1 is proposed within the scope of the present invention, as shown in the following figures with reference to some preferred, exemplary embodiments.

[0048] A first embodiment of a thermometer 1 is in Fig. 2The thermometer 1 comprises a flexible, thermally conductive support element 7, which is arranged on an outer wall W of the container 2. In the example shown here, with a container 2 in the form of a pipe, the support element 7 is arranged perpendicular to the longitudinal axis of the pipe 2 around the outer wall W of the pipe 2. The support element 7 is thus adapted to the contours of the container 2. It should be noted that a device 1 according to the invention can also be used in connection with tanks, containers, or other types of containers. The support element 7 is in each case arranged on the outer wall W of the container 2 used and adapted to its contour within a predefinable area.

[0049] The temperature sensor 5 is attached to the support element 7. The temperature sensor 5 is mounted on the support element 7 in a region facing away from the process and thus from the outer wall W of the container 2. During continuous operation, the support element 7 serves to conduct heat from the respective process, i.e., from the medium M, from the wall W of the container 2 to the temperature sensor 5. Because the support element 7 is positioned along its surface against the wall W of the container 7, there is good thermal contact with the wall W and thus with the process or the medium M. Therefore, the temperature sensor 5 is essentially in thermal equilibrium with the medium M, resulting in high measurement accuracy for the respective device 1.

[0050] In addition to the temperature sensor 5, the device 1 may also have other components, as exemplified in Fig. 3 illustrated. Compared to the one in Fig. 2In the embodiment shown, the device 1 additionally comprises a heating element 8, a reference element 9 and a further temperature sensor 10.

[0051] At the in Fig. 4In the embodiment shown, the thermometer 1 further comprises a thermal insulation unit 11, which here, by way of example, completely surrounds the support element 7. In other embodiments, an insulation unit 11 that partially surrounds the support element 7 would also be conceivable. The temperature sensor 5 is arranged between the thermal insulation unit 11 and the support element 7. The insulation unit 11 serves to insulate against the environment and to prevent heat conduction from the support element 7 and / or the temperature sensor 5 to the environment. Furthermore, the device 1 here, by way of example, includes two guides 12 for guiding connecting leads 6 of the temperature sensor 5, which are also guided through the insulation unit 11.It should be noted that the guides 12 can also be used in conjunction with configurations without an insulation unit 11, and that the number of guides 12 used depends on the number and arrangement of the connecting lines 6 of the device 1. The configuration shown here is therefore to be understood merely as one possible example.

[0052] In the Fig. 5In the embodiment shown, the device 1 has fastening means 14, which here, by way of example, comprise an elastic element in the form of a spring. The device 1 can be attached to containers 2 with different outer radii by means of the fastening means 14. In the present case, as in the preceding figures, containers 2 in the form of pipes with different diameters d1 and d2, where d2 > d1, have been selected in Figures 5a and 5b. The fastening means 14 serve to ensure consistent and good thermal contact between the support element 7 or the temperature sensor 5 and the wall W of the container 2, or with the medium, regardless of the container used. By using a fastening means 14 with an elastic element, ensuring a predefinable contact pressure of the support element 7 against the wall W of the container is particularly easy to achieve.Nevertheless, numerous other fastening methods are known which are also applicable within the scope of the present invention.

[0053] To ensure consistent thermal contact between the temperature sensor 5 and the carrier element 7, the temperature sensor 5 is attached to the carrier element 7 by means of a flexible adhesive 13 in the illustrated embodiment. The adhesive conforms to the curvature of the carrier element 7, which in turn is adapted to the outer wall W of the container 2.

[0054] However, such consistent contact between the temperature sensor 5 and the carrier element 7 can also be achieved through a multi-layered structure of the carrier element 7, as finally shown in Fig. 6The support element 7 shown here is composed of four superimposed layers 7a-7d. It goes without saying that the number of layers used can vary from one embodiment to another. In the case of using a multilayer support element 7, a rigid adhesive 13 can also be used to attach the temperature sensor 5 to the support element 7. Reference symbol list

[0055] 1 Device 2 Container 3 Measuring insert 4 Electronics 5 Temperature sensor 6 Connecting wires 7 Support element 8 Heating element 9 Reference element 10 Additional temperature sensor 11 Thermal insulation unit 12 Guide 13 Adhesive 14 Fasteners Medium, temperature, container wall

Claims

1. A device (1) for determining and / or monitoring a process variable, in particular the temperature (T) or flow, of a medium (M) in a container (2) comprising: A temperature sensor (5) for detecting the temperature (T), and a flexible, thermally conductive carrier element (7) consisting of a metallic fabric or mesh, with it being possible to arrange said carrier element (7) on an outer wall (W) of the container (2), and wherein the temperature sensor (5) is fastened to the carrier element (7), comprising a thermal insulation unit (11), which at least partially surrounds the carrier element (7), wherein the temperature sensor (5) is arranged between the carrier element (7) and the thermal insulation unit (11).

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

3. The device (1) as claimed in claim 1 or 2, comprising at least one reference element (8) for the in situ calibration and / or validation of at least the temperature sensor (5), which is fastened to the carrier element (7), and said reference element (8) at least partially consisting of at least one material, for which material in the temperature range relevant for the calibration of the first temperature sensor (5) at least one phase transition occurs at at least one specified phase transition temperature, for which phase transition the material remains in the solid phase.

4. The device (1) as claimed in at least one of the preceding claims, comprising a heating element (9) which is fastened to the carrier element (7).

5. The device (1) as claimed in at least one of the preceding claims, wherein the metallic fabric or mesh contains copper.

6. The device (1) as claimed in at least one of the preceding claims, wherein the thermal insulation (11) consists at least partially of a silicone or silicone foam.

7. The device (1) as claimed in at least one of the preceding claims, comprising at least one guide (12) for guiding at least one connection cable (6) of at least the temperature sensor (5).

8. The device (1) as claimed in at least one of the preceding claims, wherein at least the temperature sensor (5) is fastened to the carrier element (7) using a flexible adhesive (13).

9. The device (1) as claimed in at least one of the preceding claims, wherein the carrier element (7) consists of at least two flexible layers (7a-7d) arranged on top of each other.

10. The device (1) as claimed in at least one of the preceding claims, comprising fastening means (14) for fastening the device (1) to the container (2), in particular in such a way that it can be released.

11. The device (1) as claimed in claim 10, wherein the fastening means (14) are configured to ensure that the carrier element (7) exerts a specifiable contact pressure on the container (2).

12. The device (1) as claimed in claim 10 or 11, wherein the fastening means (14) have at least one flexible element, in particular a spring.

13. The device (1) as claimed in at least one of the preceding claims, wherein the container is a pipeline (2), wherein the carrier element (7) is configured so that it can be arranged around the pipeline (2) in such a way that it is perpendicular to the longitudinal axis through the pipeline (2).