Thermal flow meter and method for operating a thermal flow meter

Abstract

Device (1) for determining and / or monitoring a volumetric flow rate, mass flow rate and / or a flow velocity of a flowable medium (M) through a pipe (2), comprising a heating element (4) which heating element (4) is at least partially and / or temporarily in thermal contact with the medium (M) and which heating element (4) can be acted upon at least temporarily by means of a heating signal (P), and a first temperature sensor (5) which serves to detect a temperature, in particular at least one component of the device (1) or the temperature of the medium (M), and which first temperature sensor (5) can be acted upon at least temporarily by means of a first temperature signal, wherein the heating element (4) and the first temperature sensor (5) are arranged outside an internal volume (V) of the tube (2) through which the medium (M) flows, characterized by that the device (1) has at least one coupling element (3) which coupling element (3) is at least partially in thermal contact with the heating element (4), the first temperature sensor (5) and / or a part of the tube (2) and serves to ensure thermal coupling between the heating element (4) and the first temperature sensor (5) and between the heating element (4) and the medium (M), wherein the coupling element (3) consists at least partially of a material with anisotropic thermal conductivity, and wherein the coupling element (3) is designed in the form of a layer, a coating or a thin-walled film.

Description

[0001] The invention relates to a device for determining and / or monitoring the volume flow, mass flow and / or flow velocity of a flowable medium through a pipeline and to a method for operating a device according to the invention. The device comprises at least one heating element and a first temperature sensor. The heating element is at least partially and / or temporarily in thermal contact with the medium and can be acted upon at least temporarily by a heating signal. The first temperature sensor, in turn, serves to detect a temperature of at least one component of the device or a temperature of the medium and can be acted upon by a first temperature signal. The invention further comprises a method for operating such a device.

[0002] Thermal or calorimetric flowmeters are widely used in process and / or automation technology. The applicant manufactures corresponding field devices in a wide variety of designs and markets them under the names t-switch, t-trend, t-mass, or Flowphant. The underlying measurement principles are also well known from the prior art. For example, DE 34 19 504 A1 discloses a thermal flowmeter. US 2013 / 0 098 150 A1 and EP 0 131 318 A1 also disclose a thermal flowmeter.

[0003] Fundamentally, flow can be determined in two different ways. Within the context of the present invention, the term "flow" includes both volume flow and mass flow of the medium. The flow velocity of the medium can also be determined.

[0004] According to a first measuring principle, a sensor element is exposed to a medium flowing through a pipeline and heated such that its temperature remains essentially constant. If the medium properties are known and at least temporarily constant, such as the medium temperature, its density or composition, the mass flow of the medium through the pipeline can be determined based on the heating power required to maintain the temperature at a constant value. The medium temperature is understood to be the temperature that the medium has without additional heat input from a heating element. In an alternative measuring principle, however, the heating element is operated with constant heating power and the temperature of the medium is measured downstream of the heating element. In this case, the measured temperature of the medium provides information about the mass flow.

[0005] In the case of both measuring principles described, a second sensor element, for example a temperature sensor, can also be used to measure the temperature of the medium, especially when the medium temperature is variable.

[0006] WO 2010 / 023 255 A1 relates to a temperature measuring device for measuring the temperature of an animal or human body, in which temperature sensors are embedded in a composite material. The composite material of the embedding body comprises aligned polymer chains to achieve anisotropic thermal conductivity.

[0007] The heating elements of thermal flowmeters are often designed as resistance heaters. For example, so-called resistance elements, such as RTDs (Resistance Temperature Detectors), particularly platinum elements, are used, which are also commercially available under the designations PT10, PT100, and PT1000. The resistance elements are heated by converting the electrical power supplied to them, e.g., as a result of an increased current supply.

[0008] The determination and / or monitoring of volume flow, mass flow, and / or flow velocity is fundamentally based on the thermal contact resistance between the respective sensor element and the flowing medium changing with the prevailing flow velocity. If, for example, there is no flow in the pipeline, the heat is dissipated from the heating element via thermal conduction, thermal radiation, and possibly also via free convection within the medium. To maintain a certain temperature difference according to the first of the two measuring principles described, a temporally constant amount of heat is then required. In the presence of flow, however, the sensor element is additionally cooled by the passing, particularly colder, medium. Additional heat transport occurs due to forced convection.Accordingly, increased heating power must be supplied as a result of flow in order to maintain a fixed temperature difference to the medium temperature. Similar considerations apply to the second of the two measurement principles described.

[0009] The functional relationship between the heating power or measured temperature and the flow rate and / or flow velocity of the medium through the pipeline can also be expressed using the so-called heat transfer coefficient. In addition, various thermophysical properties of the medium as well as the pressure prevailing in the pipeline influence the measured flow rate. To also account for the dependence of the flow rate on these variables, various thermophysical properties are stored, for example, in the form of characteristic curves or as components of functional determination equations within an electronic unit of the flow meter.

[0010] Thermal contact between the heating element and the flowing medium is fundamentally crucial for high measurement accuracy. For example, a change in the thermal resistance of the heating element, which leads to a change in the heat transfer from the heating element to the medium under otherwise constant flow conditions, can cause significant measurement errors. Such a change in thermal resistance is also referred to as sensor drift.

[0011] With regard to the thermal resistance in a flowmeter, a distinction is made between internal and external thermal resistance. The internal thermal resistance depends, among other things, on individual components within the sensor element, e.g., within the sleeves. Sensor drift can be caused by defects in solder connections due to tensile stress caused by material expansion or the like. The external thermal resistance, on the other hand, is influenced by the formation of deposits, material removal, or material transformation (e.g., corrosion) on the surfaces of the respective sensor element that come into contact with the medium. A change in the external thermal resistance is therefore particularly relevant during long-term operation and / or when in contact with aggressive media.In the case of gaseous or vaporous media, the measurement of the mass flow or flow velocity can also be impaired by condensation on at least one of the temperature sensors.

[0012] To measure the volume flow, mass flow, and / or flow velocity, the heating element is brought into thermal contact with the medium, at least temporarily and / or partially. For this purpose, the heating element is typically at least partially inserted into the pipeline or integrated into a sensor head that can be installed into an existing pipeline. By integrating the respective sensor element into the pipe, a fast response time and high measurement accuracy of the measuring device can be ensured, since any change in the thermal contact resistance between the heating element and the flowing medium can be detected essentially immediately.

[0013] However, for certain applications, it can also be disadvantageous if the sensor unit protrudes into the process. This applies, on the one hand, to the installation or replacement of the measuring device, which requires intervention in the respective process. Furthermore, a sensor unit protruding into the process also influences the flow behavior of the medium in the pipe.

[0014] Non-process-contact measuring devices for determining flow have become known, for example, in the form of clamp-on ultrasonic flow meters. In such devices, the sensor unit can be attached to the outside of the pipe and does not protrude into the respective process. One such device is described, for example, in US Pat. No. 6,883,369 B1. Such measuring devices are also manufactured by the applicant and sold, for example, under the name Proline Prosonic. Using the thermal or calorimetric measuring principle, such a setup is significantly more difficult to implement without direct contact with the process. For example, the respective media-carrying pipe and the external environment of the pipe, in particular the ambient temperature, have a significant influence on the thermal behavior of the measuring device, or on the heat flows between the heating element, medium and, if applicable, the temperature sensor.For example, the positioning of the sensor unit of a thermal or calorimetric flow meter results in a reduced response time to flow changes and possibly also in a lower measurement accuracy compared to a device in contact with the process.

[0015] Based on this, the object underlying the present invention is to provide a thermal flow meter with high measuring accuracy, which can be installed and replaced in a particularly simple manner.

[0016] This object is achieved by the device according to claim 1 and by the method according to claim 14.

[0017] With regard to the device, the object underlying the invention is achieved by a device for determining and / or monitoring a volume flow, mass flow and / or a flow velocity of a flowable medium through a pipe. The device comprises a heating element, which heating element is at least partially and / or temporarily in thermal contact with the medium and which heating element can be acted upon at least temporarily by a heating signal, and a first temperature sensor which serves to detect a temperature, in particular at least one component of the device or temperature of the medium, and which first temperature sensor can be acted upon at least temporarily by a first temperature signal. The heating element and the first temperature sensor are further arranged outside an internal volume of the pipe through which the medium flows.According to the invention, the device further comprises at least one coupling element, which coupling element is at least partially in thermal contact with the heating element, the first temperature sensor and / or a partial region of the pipe and serves to ensure thermal coupling between the heating element and the first temperature sensor and between the heating element and the medium. The device according to the invention is therefore a measuring device in which the sensor unit does not protrude into the respective process. In this way, an influence on the flow profile of the medium through the pipe can be avoided. According to the invention, the coupling element consists at least partially of a material with anisotropic thermal conductivity and the coupling element is designed in the form of a layer, a coating or a thin-walled film.

[0018] In particular, the coupling element is a flat element, particularly one adapted to the contour of a pipe wall. The coupling element can, for example, have a triangular, square, round, or even elliptical cross-sectional area.

[0019] For applying the heating signal and the first temperature signal to the heating element and the first temperature sensor, the device comprises, for example, at least one electronic unit. The heating element and the first temperature sensor can be controlled either coupled or independently of each other. Furthermore, both pulsed and continuous heating signals and first temperature signals are conceivable.

[0020] Any heating element and temperature sensor known to those skilled in the art can be used. For example, the heating element can be a resistance element, as already mentioned in the introduction to the description. The temperature sensor can also be designed as a resistance element. Alternatively, a temperature sensor in the form of a thermocouple is also conceivable.

[0021] To determine and / or monitor the mass flow and / or flow velocity of the respective medium, the heating element is brought into contact, particularly thermal contact, with the medium. Heat exchange occurs between the device and the medium. The thermal contact resistance between the respective sensor element and the flowing medium changes with the prevailing flow velocity. Thus, heat propagation or heat flow occurs from the heating element to the medium.

[0022] However, since the heating element is located outside of the internal volume of the pipe through which the medium flows, heat is not only transferred from the heating element to the medium, but also from the heating element to the components surrounding the heating element, for example components of the measuring device or the measuring point, which are in contact with the heating element, particularly mechanical or thermal contact, as well as heat is transferred to the pipe or even to the environment. This, in turn, can lead to significant measurement error. In practice, the thermal contact resistance therefore depends not only on the flow of the medium, but also, in principle, on the measuring point, the design of the measuring device, and the respective mechanical or thermal contacts of the respective components.It goes without saying that a multitude of other influences can also lead to a falsification of the determined thermal contact resistance and can also play a central role.

[0023] To avoid such problems associated with a thermal flowmeter that does not extend into the respective process, the coupling element according to the invention is provided. Since the coupling element ensures thermal coupling between the heating element and the first temperature sensor and thermal coupling between the heating element and the medium, heat propagation or heat flow from the heating element to other components of the measuring device, or the measuring point, to the pipe, especially away from the measuring device, or even to the environment is minimized. Accordingly, unwanted distortion of the determined thermal contact resistance is also significantly reduced or minimized.

[0024] Numerous possibilities are conceivable for the design of the coupling element, all of which fall within the scope of the present invention. The exact design depends, among other things, on various specifications relating to the measuring device and also on the respective geometric situation. For example, the heating element and the first temperature sensor can be arranged one above the other or next to each other, which requires different arrangements of the coupling element depending on the case. In any case, the coupling element ensures thermal coupling between the heating element and the first temperature sensor and between the heating element and the medium. In addition to the coupling element, the wall of the pipe can also be arranged between the heating element and the medium. In this case, the coupling element is applied to the pipe. However, the coupling element can also be integrated into a section of the pipe.For this purpose, the coupling element can be designed as a partial section of the pipe.

[0025] Finally, in a further embodiment, the coupling element can also provide a direct thermal coupling between the first temperature sensor and the medium.

[0026] The coupling element is preferably made of a material with high thermal conductivity. For example, it can be a metallic material.

[0027] A preferred embodiment includes that the coupling element consists at least partially of a carbon-containing material or of hexagonal boron nitride.

[0028] In a further development, the carbon-containing material is graphite.

[0029] In this regard, reference is made to the subsequently published DE 10 2017 100 267 A1, which describes the use of a corresponding material in connection with thermometers, and to the also subsequently published DE 10 2017 116 408 A1, which describes the use of a corresponding material in connection with thermal flowmeters. Both applications are incorporated by reference in their entirety within the scope of the present invention.

[0030] In one embodiment, the device comprises a measuring tube that can be integrated into an existing pipeline, with at least the heating element, the first temperature sensor, and the coupling element arranged on or in a wall of the measuring tube. Alternatively, it is conceivable for the device to be designed so that it can be attached to a pipe from the outside. In the second case, it is a clamp-on measuring device.

[0031] Regardless of whether the device comprises a measuring tube or is designed as a clamp-on measuring device, it is advantageous if the device comprises a fastening unit for, in particular detachably fastening, at least one component of the device to the tube or the measuring tube.

[0032] A preferred embodiment of the device includes the coupling element being arranged at least partially between the heating element and the first temperature sensor, particularly in the region of the first temperature sensor facing away from the medium. In this case, the temperature sensor is attached to or inserted into the pipe or measuring tube. The coupling element, followed by the heating element, is located on the side of the temperature sensor facing away from the pipe or measuring tube.

[0033] An alternative preferred embodiment includes the heating element and the first temperature sensor being arranged next to one another essentially in one plane, with the coupling element being arranged between the medium and the first temperature sensor and the heating element. In this case, the coupling element is accordingly attached to or inserted into the pipe or measuring tube. On the side of the coupling element facing away from the pipe or measuring tube, the heating element and the first temperature sensor are arranged next to one another.

[0034] It is advantageous if the coupling element is arranged on the pipe or on / in the measuring pipe in such a way that an imaginary connecting line between the first temperature sensor and the heating element has a predeterminable angle to a longitudinal axis through the pipe and / or wherein a width and / or a thickness of the coupling element is variable at least in sections along a length of the coupling element and / or wherein the coupling element is made from a first material at least in a first partial region and from a second material at least in a second partial region different from the first partial region. Through these or similar measures, the thermal coupling by the coupling element can be adapted to the respective conditions of an application.The coupling element is adapted to the respective application in terms of its shape, its orientation relative to the flow direction and the pipe, and the choice of materials used to ensure the best possible thermal coupling. This allows for the different materials and wall thicknesses of different pipes, the different physical and chemical properties of different media, and different ranges for the expected flow velocities and flow profiles within the pipe to be accommodated.

[0035] In a preferred embodiment, the coupling element is at least partially designed and / or arranged in such a way that when the heating element is subjected to the heating signal by means of the coupling element, a first predeterminable amount of heat flows from the heating element to the first temperature sensor and a second predeterminable amount of heat flows from the heating element to the medium. The dimensioning and design of the coupling element therefore also depends on the respective heating signal used, or the heating signal can be adapted according to the design of the coupling element. If necessary, the pipe is also arranged between the coupling element and the medium. In this case, the heat is transported from the heating element via the coupling element and at least a partial area of ​​the pipe to the medium.

[0036] A first portion of the heat output introduced by the heating element flows from the heating element via the coupling element to the first temperature sensor, and a second portion of the heat output introduced by the heating element flows from the heating element via the coupling element via the pipe or measuring tube to the medium. If the flow velocity changes, the first and second preset heat quantities change. If the heating element is operated with a constant heat output, the temperature determined by the first temperature sensor changes. The temperature change is then a measure of the flow rate. If the device is operated with a variable heating cable, the heat output required to maintain a preset temperature of the first temperature sensor changes.

[0037] A further preferred embodiment includes the device comprising at least the first and a second temperature sensor. The second temperature sensor can be used to increase measurement accuracy or to ensure redundancy, for example, in the event of a defect in one of the two temperature sensors. Like the first temperature sensor and the heating element, the second temperature sensor is also located outside an internal volume of the pipe through which the medium flows and thus does not come into contact with the process.

[0038] In this regard, it is advantageous if the coupling element is at least partially designed and / or arranged such that, by applying the heating signal to the heating element via the coupling element, a third predeterminable amount of heat flows from the heating element to the second temperature sensor. This configuration is analogous to the case where only one temperature sensor is present.

[0039] It is also advantageous if at least a first partial area of ​​the coupling element or a first coupling element is arranged between the heating element and the first temperature sensor, in particular in the area of ​​the first temperature sensor facing away from the medium, and wherein at least the second temperature sensor is arranged next to the first temperature sensor and the heating element, wherein at least a second partial area of ​​the coupling element or a second coupling element is arranged between the medium and the second temperature sensor and is in thermal contact with the first temperature sensor and the heating element.

[0040] Alternatively, the heating element and the two temperature sensors can be arranged side by side along a common connecting line, or the heating element and the first temperature sensor can be arranged along a first connecting line, and the second temperature sensor and the heating element can be arranged along a second connecting line, with the first and second connecting lines having a predeterminable angle to one another. In this case, the coupling element can be configured, for example, as square, U-shaped, L-shaped, or T-shaped, with the heating element and the two temperature sensors being arranged at different positions along a surface of the coupling element.

[0041] Finally, it is also advantageous if the device has at least a first and a second coupling element, wherein the first coupling element is at least partially designed and / or arranged such that, when the heating element is subjected to the heating signal by means of the first coupling element, a first predeterminable amount of heat flows from the heating element to the first temperature sensor, and wherein the second coupling element is at least partially designed and / or arranged such that, when the heating element is subjected to the heating signal by means of the second coupling element, a third predeterminable amount of heat flows from the heating element to the second temperature sensor. The two coupling elements are then also thermally coupled to one another, in particular in the region of the heating element.

[0042] The object underlying the invention is also achieved by a method for operating a device according to the invention for determining and / or monitoring a volume flow, mass flow, and / or flow rate of a flowable medium through a pipe. In the method, a heating element is at least temporarily acted upon by a heating signal, and a first temperature sensor is at least temporarily acted upon by a first temperature signal. Furthermore, a statement is made regarding the volume flow, mass flow, and / or flow rate and / or temperature of the medium.

[0043] The first temperature sensor can be used to determine and / or monitor the flow rate. However, it is also conceivable to determine the temperature of the medium additionally or alternatively. Depending on the application, both process variables can be determined simultaneously, periodically alternating, or at essentially specific, predefined times. For example, the flow rate can be determined essentially continuously while the temperature of the medium is determined at certain predefined times. It is advantageous if, at a time when the temperature of the medium is being determined, the heating element is not being supplied with a heating signal in order to avoid falsifying the determined medium temperature due to additional heating power.

[0044] To determine the respective process variable flow or temperature, it is also conceivable that changes in the respective process variable are determined or that measured values ​​are compared with characteristic curves stored in the device.

[0045] It should also be noted that the heating signal and temperature signal can be either a pulsed signal or a continuous signal.

[0046] A preferred embodiment of the method involves at least one second temperature sensor being at least temporarily exposed to a second temperature signal. For example, a statement about the volume flow, mass flow, flow rate, and / or temperature of the medium is made based on a first temperature determined by the first temperature sensor and / or a second temperature determined by the second temperature sensor.

[0047] The use of at least two temperature sensors enables different configurations. For example, the first temperature sensor can provide information about the flow rate, and the second about the temperature. Both temperature sensors can also be used to determine and / or monitor flow rates. In this case, the temperature values ​​measured by both temperature sensors can be compared. For example, a difference between the measured values ​​measured by both temperature sensors can be calculated and evaluated.

[0048] It should be noted that the embodiments explained in connection with the device are also applicable mutatis mutandis to the proposed method and vice versa.

[0049] The invention is explained in more detail with reference to the following drawings. It shows: Fig. 1: a schematic representation of a clamp-on flowmeter according to the invention with a heating element and a single temperature sensor arranged next to the heating element, Fig. 2: a schematic representation of a clamp-on flowmeter according to the invention with a heating element and a single temperature sensor arranged between the heating element and the pipe, Fig. 3: various possible embodiments of a flow meter according to the invention with a heating element and a first temperature sensor arranged next to the heating element, Fig. 4 different possible embodiments of a flow meter according to the invention with a heating element and two temperature sensors, and Fig. 5 a schematic representation of the heating power and the respective flowing heat quantities to clarify the measuring principle underlying the present invention.

[0050] In the figures, identical features are identified by identical reference numerals.

[0051] In Fig. 1 shows a thermal flow meter 1 with a coupling element 3, a heating element 4, and a first temperature sensor 5. This meter 1 is mounted on a wall W of a pipe 2 through which the medium M flows in the direction indicated by the arrow. Different variants are possible for attaching the device 1 to the pipe. Fig. 1, the measuring device 1 is designed as a clamp-on measuring device that can be attached to the pipe 2 from the outside. For this purpose, all fastening methods well known to those skilled in the art are conceivable and fall within the scope of the present invention. In another embodiment, not shown, the heating element 4, the first temperature sensor 5 and the coupling element 3 are integrated into a measuring tube, which in turn can be introduced into an existing pipeline. In this case, the coupling element 3, the heating element 4 and the first temperature sensor 5 can also be integrated into the wall of the measuring tube. In any case, the device 1 is designed such that the sensor unit, i.e. at least the heating element 3 and the first temperature sensor 4, do not come into contact with the process.This means that the heating element and the first temperature sensor (as well as any additional temperature sensors 8 present) are arranged outside the internal volume V of the pipe 2 through which the medium M flows. They are therefore at least substantially flush with an inner wall of the pipe 2, or are mounted in the wall W or on the outer wall of the pipe 2.

[0052] The heating element 4 is arranged next to the first temperature sensor 5. Both the heating element 4 and the first temperature sensor 5 are further arranged on the coupling element 3 and are in thermal contact with each other and with the medium M via the coupling element 3.

[0053] In other embodiments of the present invention, the device may also have several heating elements 4, several temperature sensors 5, 8 or several coupling elements 3. The heating element 4 and the first temperature sensor 5 are connected to an electronics unit 7 by means of connecting wires 6, which serves for signal acquisition, evaluation, and power supply. It should be noted that the number of connecting wires 6 used can vary from design to design. The electronics unit 7 is also adapted to the design of the measuring device 1.

[0054] The heating element 4 is at least partially and / or temporarily in thermal contact with the medium M by means of the coupling element 3. In continuous operation, the heating element 4 can be heated to a predeterminable temperature T to determine the flow rate or the flow rate, for example by supplying a variable heating power P, or can be operated at a variable temperature T by supplying a constant heating power P. Basically, there is an exchange of heat between the measuring device 1 and the medium M, or a propagation of heat or a flow of heat from the heating element 4 to the medium M. The thermal contact resistance between the heating element 4 and the flowing medium M changes with the prevailing flow rate v.

[0055] The coupling element 3 effects both a thermal coupling of the heating element 4 and the first temperature sensor 5 and a thermal coupling to the medium M. In particular, the coupling element 3 ensures that a first predeterminable amount of heat flows from the heating element 4 to the first temperature sensor 5 and a second predeterminable amount of heat flows from the heating element 4 to the medium M. A heat flow emanating from the heating element 4 can be specifically influenced by means of the coupling element 3, in particular with regard to the direction of propagation of the respective amount of heat and its distribution in different directions. In order to specify the respective amounts of heat flowing from the heating element 4 to the first temperature sensor 5 or to the medium, the coupling element can therefore simply be designed and arranged to suit the requirements. Examples of such possible configurations are given in the following figures.The coupling element 3 is preferably made of a material with high thermal conductivity, for example, a metal. The use of graphite, but also other materials, is also conceivable.

[0056] The first temperature sensor 5 can be used to determine and / or monitor the flow rate and / or flow velocity. Additionally or alternatively, the first temperature sensor can also be used to determine the temperature T of the medium M.

[0057] A second possible embodiment of a measuring device 1 according to the invention is the subject of Fig. 2. As in Fig. 1, for example, is a clamp-on measuring device. This embodiment also applies that the device 1 can be attached to the pipe 2 using any fastening means well known to those skilled in the art. A corresponding embodiment can also be realized using a separate measuring tube (not shown).

[0058] As opposed to Fig. 1, the first temperature sensor 5 and the heating element 4 are in Fig. 2 arranged one above the other. The temperature sensor 5 is attached to a wall W of the pipe 2. On the side of the first temperature sensor 5 facing away from the pipe 2 is the coupling element 3, followed by the heating element 4. In another embodiment [not shown], a second coupling element can also be arranged between the first temperature sensor 5 and the wall W of the pipe 2. For the embodiment shown, the cross-sectional areas of the heating element 4 and the coupling element 5 are essentially the same size. It should be noted that the heating element 4 and the coupling element 3 can also be dimensioned differently in other embodiments.

[0059] In Fig. 2, the connecting wires 6 and the electronic unit 7 are not shown. The control of the heating element 4 and the first temperature sensor 5, or the application of a suitable heating signal and temperature signal, is carried out analogously to Fig. 1.

[0060] Numerous variants are possible for the design of the coupling element 3 and for the arrangement of the heating element 4 and the first temperature sensor 5 relative to the coupling element 3 and the pipe 2 and are covered by the present invention. Without limiting the generality, various possible variants for a device according to the invention are outlined below by way of example.

[0061] In Fig. 3 shows different configurations for a device with a heating element 4 and a first temperature sensor 5. In Fig. 3a, the heating element 4 and the first temperature sensor 5 are arranged side by side and positioned on the coupling element 3, which in turn is attached to the wall W of the pipe 2. The imaginary connecting line a between the heating element 4 and the first temperature sensor 5, for example a connecting line a running through the respective center points or corresponding edges, runs parallel to the longitudinal axis through the pipe 2 and parallel to the flow direction of the medium M. It goes without saying that the order of the heating element 4 and the first temperature sensor 5 parallel to the flow direction can vary in different embodiments. It is therefore possible for the first temperature sensor 5 to be arranged upstream of the heating element 4 or downstream of the heating element 4 in the flow direction.It should also be noted that other geometric shapes for the coupling element 3 are also conceivable, which also fall within the scope of the present invention. For example, the coupling element 3 can also be oval, circular, or even triangular.

[0062] The design of Fig. 3b differs from that of Fig. 3a in that the connecting line a has an angle of approximately 45° to the longitudinal axis through the tube 2. In the variant according to Fig. 3c, the angle between the connecting line a and the longitudinal axis L is 90°. It should be noted that other values ​​for the angle between the connecting line a and the longitudinal axis L are also possible within the scope of the present invention. By adjusting the angle between the connecting line a and the longitudinal axis L, the thermal coupling between the coupling element 3, the medium 2, the heating element 4, and the first temperature sensor 5 can be specifically adjusted and adapted.

[0063] However, other measures are also possible to adjust the thermal coupling. For example, the coupling element 3 can be designed such that its width b is variable along the length l of the coupling element. For this purpose, a continuous variation of the width b is conceivable, as shown in Fig. 3d, or a step-like variation of the width b [not shown].

[0064] A further possible measure for adapting and / or adjusting the thermal coupling consists in manufacturing the coupling element 3 at least in a first partial area 3.1 from a first material and at least in a second partial area 3.2 different from the first partial area 3.1 from a second material, as shown by way of example in Fig. 3e shown.

[0065] Another possible measure is to vary the thickness d of the coupling element along the longitudinal axis l, as shown in the figures Fig. 3f and Fig. 3g. In Fig. 3f the thickness d increases continuously from a value d1 to a value d2, while in Fig. 3g the thickness varies stepwise and the coupling element 3 has a thickness d1 in a first partial area and a thickness d2 in a second partial area.

[0066] In addition to the described measures, numerous other possibilities for adapting and / or adjusting the thermal coupling mediated by the coupling element 3 are possible and also fall within the scope of the present invention. It should also be noted that the various possible measures can be combined with one another as desired. Corresponding measures for a configuration of the device 1, as shown in Fig. 2 is possible.

[0067] A further preferred embodiment of a flow measuring device 1 according to the invention is the subject of Fig. 4. Here, the device 1 comprises, in addition to the coupling element 3, the heating element 4, and the first temperature sensor 5, a further temperature sensor 8. A first predeterminable amount of heat is transported from the heating element 4 to the first temperature sensor 5, while a second predeterminable amount of heat flows from the heating element 4 to the medium M, and a third predeterminable amount of heat flows from the heating element 4 to the second temperature sensor 8. As in the case of the preceding figures, a corresponding device 1 can be designed either as a clamp-on measuring device 1 or with a separate measuring tube. The possibilities are just as diverse as in the case of the figures. Fig. 1 and Fig. 2. Only the second temperature sensor 8 needs to be added, although there are numerous options available for this as well.

[0068] In this respect, Fig. The variants shown in Figure 4 are the same as in the case of Fig. 3 is to be considered as an example. The present invention is in no way limited to the variants shown. According to Fig. 4a, the heating element 4 and the first 5 and second 8 temperature sensors are mounted side by side along a common imaginary connecting line a on the coupling element 3, which in turn is mounted on the wall W of the tube 2. In contrast to Fig. 4a is in Fig. 4b the heating element 4 is arranged between the two temperature sensors 5 and 8.

[0069] In Fig. 4c, the first temperature sensor 5, the coupling element 3.3 and the heating element 4 are analogous to the variant according to Fig. 2. In contrast to Fig. 2, the heating element 4, the coupling element 3.3 and the first temperature sensor 5 are not attached directly to the wall W of the pipe 2, but rather on the further coupling element 3. The coupling elements 3 and 3.3 can each be made of the same material or of different materials. In addition to the heating element 4, coupling element 3.3 and first temperature sensor 5, the second temperature sensor 8 is also arranged, which is also located on the coupling element 3. In another embodiment, not shown, the two temperature sensors 5, 8 and the heating element 4 can all be arranged one after the other, in particular one above the other. The coupling element 3 is then attached between at least two of the components. However, several coupling elements 3 can also be used, which can be attached, for example, between two components each.

[0070] For the adaptation and adjustment of the thermal coupling mediated by the coupling element 3, numerous further measures are possible, even in the case of two temperature sensors 5, 8. For example, the shape and / or dimensioning of the coupling element 3 or the relative arrangement of the heating element 4 and the two temperature sensors 5, 8 can be suitably selected. Thus, the coupling element 3 is Fig. 4d rectangular, while in Fig. 4e a U-shaped, in Fig. 4f a T-shaped, and in Fig. 4g, a V-shaped coupling element 3 is shown. In all these configurations for the shape of the coupling element, the heating element 4 and the first temperature sensor 5 are positioned along a first imaginary connecting line a1, and the second temperature sensor 8 and the heating element 4 are positioned along a second imaginary connecting line (a2), wherein a suitable angle can be set between the two connecting lines a1 and a2. This arrangement is similar to that shown in Figures Fig. 3b and Fig. 3c for the case of a single first temperature sensor 5.

[0071] In Fig. 4h, on the other hand, the device 1 comprises a first coupling element 3.4 and a second coupling element 3.5. The coupling elements 3.4 and 3.5 are arranged side by side, and the heating element 4 is positioned along an interface between the two coupling elements 3.4 and 3.5 such that it is in thermal contact with both the first coupling element 3.4 and the second coupling element 3.5. By applying the heating signal to the heating element 4, a first predeterminable amount of heat is transported from the heating element 4 to the first temperature sensor 5 and a third predeterminable amount of heat is transported from the heating element 4 to the second temperature sensor 8 by means of the first coupling element 3.4. Heat is transported from the heating element 4 to the medium M by means of both coupling elements 3.4 and 3.5.

[0072] Another example of a possible measure is, similar to the case of the figures Fig. 3f and Fig. 3g to vary the thickness d of the coupling element 3 along its longitudinal axis l, as shown in Figures Fig. 4i, Fig. 4k and Fig. 4l. Just as in Fig. 3 the thickness d can be varied continuously or stepwise.

[0073] As in the case of an embodiment with a single, first temperature sensor 5, the different Fig. 4 shown variants can be combined with each other as desired. Also in connection with Fig. The variants shown in Figure 3 can be applied analogously to the case of a device 1 with two temperature sensors 5,8, as in Fig. 4, and vice versa. It should also be noted that the Fig. The possibilities shown in Figure 4 are by no means exhaustive. Rather, numerous other examples are conceivable, which also fall within the scope of the present invention.

[0074] A schematic representation of the measuring principle underlying the present invention is finally the subject of Fig. 5. In Fig. 5a is a device according to the invention as in Fig. 2a, for which the respective heat quantities Q1 and Q2 are indicated. By applying a heating signal P to the first temperature sensor 5, the second predeterminable heat quantity Q2 flows from the heating element 4 to the medium M, and the first predeterminable heat quantity Q1 flows from the heating element 4 to the first temperature sensor 5. The sizes of the predeterminable heat quantities Q1 and Q2 depend on the geometric configuration of the device 1, the materials used, the pipe 2, and also the medium M itself and its flow velocity v.

[0075] In Fig. Figure 5b is a schematic representation of a heating signal P in the form of rectangular pulses (solid line), as well as the second predeterminable heat quantity Q2 for two different flow velocities v1 (dotted line) and v2 (dashed line) of the medium M, each shown as a function of time t. The heating signal P is constant over time for the duration of a pulse. It should be noted that the heating signal P shown here is to be understood as an example. In other embodiments, the heating signal P can be sinusoidal, trapezoidal, or sawtooth-shaped, for example. The temperature T of the medium is identical for both flow velocities v1 and v2 and constant over time. v1>v2 applies. The predeterminable heat quantities Q1 and Q2, or their proportions to the total heat quantity Q ges=Q1+Q2 depend on the flow velocity v of the medium M. For example, if the flow velocity v increases from the lower value v2 to the higher value v1, Q2 increases because more heat is transported from the heating element 4 to the medium M. The second predeterminable heat quantity Q1 decreases accordingly. As a consequence, a lower temperature T is measured by the first temperature sensor 5, whereby the temperature change ΔT of the temperature measured by the first temperature sensor 5 is proportional to the change in the flow velocity v of the medium M.

[0076] This connection is in Fig. 5c is illustrated again using a schematic representation of the first predeterminable heat quantity Q1 and the first v1 (dotted line) and second flow velocity v2 (dashed line), each as a function of time t. If, for example, the flow velocity v increases from the lower value v2 to the higher value v1, Q1 decreases, since more heat is transported from the heating element 4 to the medium M. As a consequence, a lower temperature T is measured by the first temperature sensor 5, as in connection with Fig. 5a already described.

[0077] The temperature T measured by the first temperature sensor 5 is, in principle, a measure of the first predeterminable heat quantity Q1. Again, the temperature T of the medium M is constant, so that any influence of a variable medium temperature T on the quantities measured by the device 1 can be ruled out. It goes without saying that the described relationships also apply in principle to the case of a variable medium temperature T. Analogous considerations also apply if at least a second temperature sensor 8 is provided. List of reference symbols 1 flow meter 2 pipes 3.3.1-3.5 Coupling element 4 heating element 5 First temperature sensor 6 connecting wires 7 Electronics unit 8 Second temperature sensor M Medium W wall of the pipe V Internal volume of the raw material T Temperature of the medium v, v1, v2 flow velocity a Imaginary connecting line between heating element and temperature sensor L Longitudinal axis through the pipe l Length of the coupling element b, b1-b2 Width of the coupling element d, d1-d3 thickness of the coupling element Q, Q1, Q2, Q ges Heat quantities P heating signal

Claims

[1] Device (1) for determining and / or monitoring a volume flow, mass flow and / or a flow rate of a flowable medium (M) through a pipe (2), comprising a heating element (4), which heating element (4) is at least partially and / or temporarily in thermal contact with the medium (M) and which heating element (4) can be acted upon at least temporarily by means of a heating signal (P), and a first temperature sensor (5) which serves to detect a temperature, in particular of at least one component of the device (1) or the temperature of the medium (M), and which first temperature sensor (5) can be acted upon at least temporarily by means of a first temperature signal, wherein the heating element (4) and the first temperature sensor (5) are arranged outside an internal volume (V) of the tube (2) through which the medium (M) flows, characterized by that the device (1) has at least one coupling element (3), which coupling element (3) is at least partially in thermal contact with the heating element (4), the first temperature sensor (5) and / or a partial area of ​​the pipe (2) and serves to ensure a thermal coupling between the heating element (4) and the first temperature sensor (5) and between the heating element (4) and the medium (M), wherein the coupling element (3) consists at least partially of a material with an anisotropic thermal conductivity, and wherein the coupling element (3) is designed in the form of a layer, a coating or a thin-walled film. [2] Device (1) according to claim 1, wherein the coupling element (3) consists at least partially of a carbon-containing material or of hexagonal boron nitride. [3] Device (1) according to claim 2, wherein the carbon-containing material is graphite. [4] Device (1) according to at least one of the preceding claims, wherein the device (1) comprises a measuring tube which can be integrated into an existing pipeline, wherein at least the heating element (4), the first temperature sensor (5) and the coupling element (3) are arranged on or in a wall of the measuring tube or wherein the device (1) is designed to be attachable to a pipe (2) from the outside. [5] Device (1) according to at least one of the preceding claims, wherein the coupling element (3) is arranged at least partially between the heating element (4) and the first temperature sensor (5), in particular in the region of the first temperature sensor (5) facing away from the medium (M). [6] Device (1) according to at least one of claims 1-4, wherein the heating element (4) and the first temperature sensor (5) are arranged next to one another substantially in one plane, and wherein the coupling element (3) is arranged between the medium (M) and the first temperature sensor (5) and the heating element (4). [7] Device (1) according to at least one of the preceding claims, wherein the coupling element (3) is arranged on the tube (2) or on / in the measuring tube in such a way that an imaginary connecting line (a) between the first temperature sensor (5) and the heating element (4) has a predeterminable angle to a longitudinal axis (L) through the tube and / or wherein a width (b) and / or a thickness (d) of the coupling element (3) is variable at least in sections along a length (l) of the coupling element (3) and / or wherein the coupling element (3) is made from a first material at least in a first partial region (3.1) and from a second material at least in a second partial region (3.2) different from the first partial region (3.1). [8] Device (1) according to at least one of the preceding claims, wherein the coupling element (3) is at least partially designed and / or arranged such that by applying the heating signal (P) to the heating element (4) by means of the coupling element (3), a first predeterminable heat quantity (Q1) flows from the heating element (4) to the first temperature sensor (5) and a second predeterminable heat quantity (Q2) flows from the heating element (4) to the medium (M). [9] Device (1) according to at least one of the preceding claims, comprising at least the first (5) and a second temperature sensor (8). [10] Device (1) according to claim 9, wherein the coupling element (3) is at least partially designed and / or arranged such that by applying the heating signal (P) to the heating element (4) by means of the coupling element (3), a third predeterminable amount of heat flows from the heating element (4) to the second temperature sensor (8). [11] Device (1) according to claim 9 or 10, wherein at least a first partial region of the coupling element (3) or a first coupling element (3.3) is arranged between the heating element (4) and the first temperature sensor (5), in particular in the region of the first temperature sensor (5) facing away from the medium (M), and wherein at least the second temperature sensor (8) is arranged next to the first temperature sensor (5) and the heating element (4), wherein at least a second partial region of the coupling element or a second coupling element (3) is arranged between the medium (M) and at least the second temperature sensor (8) and is in thermal contact with the first temperature sensor (5) and the heating element (4). [12] Device (1) according to claim 9 or 10, wherein the heating element (4) and the two temperature sensors (5, 8) are arranged next to one another along a common connecting line (a), or wherein the heating element (4) and the first temperature sensor (5) are arranged along a first imaginary connecting line (a1) and the second temperature sensor (8) and the heating element (4) are arranged along a second imaginary connecting line (a2), and wherein the first (a1) and the second connecting line (a2) have a predeterminable angle to one another. [13] Device (1) according to claim 9 or 10, comprising at least a first (3.4) and a second coupling element (3.5), wherein the first coupling element (3.4) is at least partially designed and / or arranged such that by applying the heating signal (P) to the heating element (4) by means of the first coupling element (3.4), a first predeterminable amount of heat flows from the heating element (4) to the first temperature sensor (5), and wherein the second coupling element (3.5) is at least partially designed and / or arranged such that by applying the heating signal (P) to the heating element (4) by means of the second coupling element (3.5), a third predeterminable amount of heat flows from the heating element (4) to the second temperature sensor (8). [14] Method for operating a device (1) for determining and / or monitoring a volume flow, mass flow and / or a flow rate of a flowable medium (M) through a pipe (2) according to at least one of the preceding claims, wherein the heating element (4) is at least temporarily acted upon by means of a heating signal (P), wherein the first temperature sensor (5) is at least temporarily acted upon by a first temperature signal, and wherein a statement is made about the volume flow, mass flow and / or the flow velocity and / or the temperature (T) of the medium (M). [15] Method according to claim 14, wherein a second temperature sensor (8) is at least temporarily acted upon by a second temperature signal.

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