MEASURING DEVICE AND METHOD FOR DETERMINING ABRASION

Description

[0001] The invention relates to a measuring device, a process engineering system and a method for determining abrasion.

[0002] Measuring devices are known from process automation that are used to monitor process properties of the medium. Common process properties include flow volume and velocity, mass flow, pH value, pressure and temperature of the medium. An example of a frequently used measuring device is a magnetic-inductive flowmeter. Depending on the application, the medium for the measuring tube can have abrasive properties. To ensure the longest possible service life of the measuring device, special housings, measuring tube bodies or linings are provided for the measuring tube. When linings are used, the user can replace them if increased abrasion occurs. It can be advantageous to predict the time at which the lining needs to be replaced without interrupting the process.

[0003] Magnetic-inductive flowmeters are used to determine the flow velocity and volumetric flow of a flowing medium in a pipeline. A magnetic-inductive flowmeter has a magnet system that generates a magnetic field perpendicular to the flow direction of the flowing medium. Individual coils are usually used for this purpose, less frequently permanent magnets. To create a predominantly homogeneous magnetic field, additional pole pieces are shaped and attached to the measuring tube so that the magnetic field lines run across the entire pipe cross-section essentially perpendicular to the transverse axis or parallel to the vertical axis of the measuring tube. A pair of measuring electrodes attached to the outer surface of the measuring tube taps an electrical measuring voltage or potential difference in the medium that is perpendicular to the flow direction and the magnetic field. This potential difference occurs when a conductive medium flows in the direction of flow when a magnetic field is applied.Since the measured voltage depends on the speed of the flowing medium according to Faraday's law of induction, the induced measuring voltage can be used to calculate . U the flow rate u and, with the addition of a known pipe cross-section, the volume flow V̇ be determined.

[0004] Magnetic-inductive flowmeters are widely used in process and automation technology for fluids with an electrical conductivity of approximately 5 µS / cm and above. The applicant markets corresponding flowmeters in a wide variety of designs for various applications, for example, under the name PROMAG.

[0005] Due to the high mechanical stability required for measuring tubes of magnetic-inductive flowmeters, these usually consist of a metallic support tube of predeterminable strength and width, which is internally lined with an electrically insulating material of predeterminable thickness, the so-called liner. For example, DE 10 2005 044 972 A1 and DE 10 2004 062 680 A1 each describe magnetic-inductive measuring sensors that comprise a measuring tube that can be inserted into a pipeline and has a first end on the inlet side and a second end on the outlet side, a non-ferromagnetic support tube as an outer casing of the measuring tube, and a tubular lining made of an electrically insulating material, housed in a lumen of the support tube, for guiding a flowing medium that is electrically insulated from the support tube.

[0006] The lining, which is usually made of a thermoplastic, thermosetting, and / or elastomeric plastic, serves, among other things, to chemically insulate the support tube from the medium. In magnetic-inductive measuring sensors where the support tube has a high electrical conductivity, for example when using a metallic support tube, the lining also serves to electrically insulate the support tube from the medium, preventing the voltage induced in the medium from short-circuiting via the support tube. By appropriately designing the support tube, the strength of the measuring tube can be adapted to the mechanical stresses present in the respective application, while the lining can be adapted to the electrical, chemical, and / or biological requirements applicable to the respective application.

[0007] A so-called support body embedded in the lining is often used to secure the lining. For example, in patent EP 0 766 069 B1, a perforated sheet metal tube welded to the support tube serves as the support body. The support body is connected to the support tube and embedded in the lining by applying the lining material internally to the support tube. Furthermore, a measuring tube with a metal housing is known from patent US 4,513,624 A for mechanical stabilization and electrical shielding. The metal housing surrounds a pipe carrying the medium specifically for this purpose.

[0008] Furthermore, magnetic-inductive flowmeters are known that have a measuring tube body made of an electrically insulating material—e.g., plastic, ceramic, and / or glass. Such measuring tubes do not require an insulating coating.

[0009] It has been shown that the electrically insulating lining, as well as the measuring tube body made of an electrically insulating material, is subject to erosion despite the use of durable materials. In particular, media containing solid particles – such as sand, gravel, and / or rock – cause abrasion of the pipeline lining or the measuring tube body. As a result of the abrasion or deformation of the lining or the electrically insulating measuring tube body, the flow profile of the sensor changes. As a result, the measuring device delivers erroneous measured values ​​for volume or mass flow. Furthermore, in measuring tubes with an internal lining, the chemical or electrical insulation between the medium and the carrier tube is lost.

[0010] US 6 946 855 B1 discloses a device for monitoring the effect on a material exposed to a fluid. The device contains a sensor element which is exposed to the fluid and is designed as a ring made of the material, which is mounted coaxially in the pipe section but is electrically insulated from it. Changes in the electrical resistance of the sensor element can thus be monitored. Furthermore, the device also has a reference element which is electrically insulated from the pipe, electrically connected in series with the sensor element and protected from contact with the liquid. The elements can both be made of the same material as the pipe and, since they are contained in the pipe, are subject to the same temperature and pressure fluctuations as the pipe. In this way, a change in the resistance of the sensor element caused by corrosion or erosion by the fluid accurately indicates the degree of corrosion or erosion.Erosion of the pipe carrying the fluid.

[0011] WO 2010 / 066518 A1 discloses a measuring device for determining a volume and / or mass flow rate of a medium flowing through a measuring tube. The measuring tube comprises a support tube with an internal lining comprising a first layer and a second layer, and a monitoring electrode embedded between the first layer and the second layer and configured to detect damage to the second / first layer. A disadvantage, however, is the influence of the monitoring on the measurement of the volume and / or mass flow rate.

[0012] The invention is based on the object of providing an alternative measuring device and method for determining abrasion, which remedy the problem.

[0013] The object is achieved by the measuring device according to claim 1 and the method according to claim 13.

[0014] The measuring device according to the invention comprises: a measuring tube for conducting a flowable medium, the measuring tube having an inner surface, the inner surface being electrically insulating at least in sections; at least one monitoring electrode, the at least one monitoring electrode being arranged in contact with the medium on the electrically insulating section of the inner surface; an abrasion detection device configured to determine at least one value on the at least one monitoring electrode that corresponds to abrasion of the monitoring electrode.

[0015] Known monitoring electrodes are metallic foils or pin electrodes embedded in the liner, at which a measuring circuit of the abrasion detection device measures electrical resistance against a reference electrode in contact with the medium. According to the invention, the monitoring electrode is in contact with the medium and thus directly exposed to the abrasive medium.

[0016] An abrasion detection device is a device designed to determine or measure values ​​of the quantity to be measured (e.g., electrical resistance, current, voltage, or variables dependent thereon) at the monitoring electrode. This can be done either contactlessly or by contact.

[0017] According to the invention, the layer system comprises at least two electrically conductive layers, each comprising different materials.

[0018] Stainless steels, CrNi alloys, ZnAl alloys, platinum, or titanium are preferred as coating materials. Stainless steels 1.4435 and 1.4462 are suitable for a wide range of applications. The use of at least two layers of different materials has the advantage that abrasion rates for different materials can be derived from the measured values. Accordingly, the abrasion detection device is configured to determine a first abrasion rate for the first layer and a second abrasion rate for the second layer. The second abrasion rate is only determined once the first layer has been removed and the values ​​of the measured values ​​deviate from a target range.

[0019] Advantageous embodiments of the invention are the subject of the subclaims.

[0020] According to the invention, the at least one monitoring electrode is designed as a selectively applied at least partially conductive layer system, wherein, according to one embodiment, the layer system comprises at least one conductive polymer layer and / or at least one metal layer and / or at least one doped semiconductor layer.

[0021] The layer system is preferably formed as a thin film and can have layer thicknesses of several nanometers down to a few millimeters.

[0022] Such thin layer systems have the advantage that their size, in particular the electrical resistance, determined by means of an abrasion detection device, depends significantly on the change in layer thickness and thus also indirectly on the abrasion by the medium.

[0023] One embodiment provides that the at least two layers each have an electrical resistance, wherein the at least two layers are arranged such that the respective electrical resistances decrease in the radial direction, in particular in the direction of a measuring tube center point.

[0024] This has the advantage that an abrasion rate can be determined based on the temporal change in electrical resistance. In an intact layer system, the current flow through the layer with the lower resistance dominates. If this layer is removed, this is reflected in the values ​​of the parameter to be determined. The abrasion rate is a material-specific parameter that provides information about the removal - expressed as a length, an area or a volume - over a period of time. The abrasion rate can be used to determine the time for replacing measuring device components that come into contact with the medium, such as liners or measuring electrodes. The different electrical resistances can be adjusted by selecting materials with different specific resistances or by using layers with different thicknesses.

[0025] One embodiment provides that the at least two layers each have a layer thickness, wherein the at least two layers are arranged such that the respective layer thicknesses increase in the radial direction, in particular in the direction of a measuring tube center point.

[0026] This also makes it possible to create layer systems with layers made of a soft and therefore quickly ablated layer material - such as polymers - which have a higher electrical conductivity than thinner metallic layers.

[0027] One embodiment provides that the at least two layers each have a hardness, wherein the at least two layers are arranged such that the respective hardnesses decrease in the radial direction, in particular in the direction of a measuring tube center point.

[0028] This has the advantage that hardness-specific abrasion rates can be determined, which can then be used to draw conclusions about maintenance intervals for other measuring device components made of materials of similar hardness. The term hardness refers to the mechanical resistance that a material offers to mechanical penetration by another body—namely, the substances in the flowing medium causing the abrasion. Different types of hardness are distinguished depending on the type of impact. Hardness, for example, is not only the resistance to harder bodies, but also to softer bodies of equal hardness. Hardness is also a measure of the wear behavior of materials.

[0029] One embodiment provides that the layer system has at least one electrically insulating layer which separates two electrically conductive layers of the at least two layers from one another.

[0030] This prevents effects due to inhomogeneous abrasion. If the electrical contact between one of the contacting agents and the first layer is broken, only the electrical resistance of the second layer is measured. This resistance remains essentially constant until the insulating layer is removed. Only when the second layer is removed—and the insulating layer is therefore at least partially removed—does the electrical resistance of the layer system change again. This can be used to separate the different abrasion rates of the individual layers.

[0031] One embodiment provides that a layer of the layer system touching the inner surface is at least partially annular and / or has an electrical resistance R 1, with R 1 ≤ 10 -6 < Ω m , in particular R 1 ≤ 5 · 10 -7 < Ω mand preferred R 1 ≤ 10 -7 < Ω m .

[0032] This has the advantage that the monitoring electrode is also suitable for grounding the medium to be conveyed, which is particularly advantageous for magnetic-inductive flowmeters where a lack of grounding leads to a shift in the measuring point.

[0033] One embodiment provides that the abrasion detection device is configured to measure the at least one variable in a first time interval, wherein the abrasion detection device is configured to connect the layer system to a ground potential at least in a second time interval.

[0034] One embodiment provides that the abrasion detection device has a contacting arrangement for electrically contacting the monitoring electrode, in particular comprising a first contacting means and a second contacting means, wherein the abrasion detection device is configured to measure an impedance, in particular an electrical resistance, at the at least one monitoring electrode and to determine the at least one variable at least as a function of the impedance, in particular as a function of the temporal change in the impedance.

[0035] One embodiment provides that the contacting arrangement has a first contacting means and a second contacting means, wherein the contacting arrangement has a third contacting means and a fourth contacting means, wherein the third contacting means and the fourth contacting means are arranged in particular in a circumferential direction of the measuring tube between the first contacting means and the second contacting means, wherein the abrasion detection device is designed to allow an electrical current to flow between the first contacting means and the second contacting means, wherein the abrasion detection device is designed to measure an electrical voltage between the third contacting means and the fourth contacting means, wherein the abrasion detection device is designed to determine a surface resistance and to determine the at least one variable at least as a function of the surface resistance, in particular as a function of the change in the surface resistance over time.

[0036] Such a design has the advantage that contact resistances between the contacting means and the layer system are reduced and thus even very small changes in the electrical resistance of the layer system can be detected.

[0037] One embodiment provides that one variable of the at least one variable describes a material-dependent abrasion rate and preferably another variable of the at least one variable describes a further material-dependent abrasion rate.

[0038] Once material-dependent or hardness-dependent abrasion rates are known, it is possible to determine the maximum running time until further components in the measuring device or in the process plant need to be replaced.

[0039] A process plant according to the invention, comprising: a pipeline, a measuring device according to the invention, wherein the measuring device is connected to the pipeline, wherein the monitoring electrode has an electrode material and / or a coating arranged on the inner circumferential surface has a coating material, wherein a variable of the at least one variable is specific to the electrode material and / or the coating material, a system component which, at least in a section in contact with the medium, also has the electrode material and / or the coating material, a monitoring device, wherein the monitoring device is designed to output a warning for the system component and / or to determine a remaining operating time until a maintenance measure for the system component, at least as a function of the variable and preferably a threshold value assigned to the system component.

[0040] A method according to the invention for determining abrasion of a medium-contacting electrically insulating coating of a measuring tube of a measuring device according to the invention comprises the method steps: Measuring a surface resistance on a monitoring electrode, in particular one in contact with a medium, wherein the monitoring electrode is designed as a layer system; determining a test variable dependent on a layer thickness of the layer system using the measured surface resistance; determining whether abrasion is present based on the test variable.

[0041] The inventive method is suitable for thin-film electrodes whose electrical resistance depends on the layer thickness. Even minimal changes in the layer thickness affect the measured resistance. The abrasion rate can be derived from the change in resistance over time.

[0042] The invention is explained in more detail with reference to the following figures. It shows: Fig. 1 : a longitudinal section of a measuring device according to the invention; Fig. 2 : a perspective view of a partially sectioned embodiment of the measuring device according to the invention; Fig. 3 : a section of a longitudinal section of an embodiment of the measuring device according to the invention; Fig. 4 : a section of a longitudinal section of a further embodiment of the measuring device according to the invention; Fig. 5 : a section of a longitudinal section of a further embodiment of the measuring device according to the invention; Fig. 6 : a section of a longitudinal section of a further embodiment of the measuring device according to the invention; Fig. 7 : a section of a longitudinal section of a further embodiment of the measuring device according to the invention; Fig. 8 : a section of a longitudinal section of a further embodiment of the measuring device according to the invention; Fig. 9 : a longitudinal section of a magnetic-inductive flowmeter; and Fig. 10 : a view of part of a process plant.

[0043] The Fig. 1 shows a longitudinal section of a measuring device 1 according to the invention. The measuring device 1 shown comprises a measuring tube 6 for conveying a flowable medium. The measuring tube 6 consists of a metallic support tube 3 and a liner 4 made of an electrically insulating material, such as plastic. The liner 4 serves to insulate the support tube 3 from the medium. Due to the liner 4 applied to an inner surface of the support tube 3, the inner surface 20 of the support tube 3 is designed to be electrically insulating, at least in sections. Furthermore, the measuring device 1 has two monitoring electrodes 7, 26, which extend annularly on the inlet and outlet sides on the electrically insulating section of the inner surface 20, in contact with the medium. A measuring device 2 for determining a process property of the medium to be conveyed is part of the measuring device 1.An abrasion detection device 9 is configured to determine at least one variable on one of the two monitoring electrodes 7, 26, which corresponds to abrasion of the monitoring electrode 7. Alternatively, the abrasion detection device 9 can be connected to both monitoring electrodes 7, 26, wherein one of the two values ​​of the determined variable can serve as a reference value. The abrasion detection device 9 is configured to determine a sheet resistance of the monitoring electrode 7 and to determine the at least one variable at least as a function of the sheet resistance, in particular as a function of the temporal change in the sheet resistance. The metallic support tube 3 is electrically insulated from the abrasion detection device 9. The determined variable is a material-dependent abrasion rate, which represents the specific material of the two monitoring electrodes 7, 26.The two monitoring electrodes 7 are each formed as a selectively applied conductive layer system 8, wherein the layer system 8 comprises at least one conductive polymer layer and / or at least one metal layer and / or at least one doped semiconductor layer. Furthermore, the layer system 8 has a width b and a thickness layer system thickness . d Both of which, in addition to the material-dependent specific resistance, are decisive for the magnitude of the sheet resistance of the layer system 8. The abrasion detection device 9 can also be configured to measure the at least one variable in a first time interval and to connect it to a ground potential in a second time interval. Thus, in addition to detecting abrasion by the medium, the monitoring electrodes 7, 26 also serve to connect the flowable medium to a controlled potential.

[0044] The Fig. 2 shows a perspective view of a partially sectioned embodiment of the measuring device 1 according to the invention. The monitoring electrode 7 shown is ring-shaped and consists of a layer system 8 with a conductive layer 11. The ring can be closed or open. The contacting arrangement 13 has a first contacting means 14, a second contacting means 15, a third contacting means 16, and a fourth contacting means 17. The third contacting means 16 and the fourth contacting means 17 are arranged in a circumferential direction of the measuring tube 6 between the first contacting means 14 and the second contacting means 15. The contacting means 14, 15, 16, 17 are evenly distributed around the circumference of the measuring tube.The adjacent contacting means are each spaced substantially equally apart, with the distance being greater than the thickness of the layer system 8. The abrasion detection device 9 is configured to allow an electrical current to flow between the first contacting means 14 and the second contacting means 15 and to measure an electrical voltage between the third contacting means 16 and the fourth contacting means 17. Depending on the magnitude of the electrical current and the measured voltage, a sheet resistance for the monitoring electrode 7 results. The at least one variable can be determined at least as a function of the sheet resistance, in particular as a function of the change in the sheet resistance over time.

[0045] The Fig. 3 shows a detail of a longitudinal section of an embodiment of the abrasion detection device 9 of the measuring device according to the invention. In this variant, the liner 4 can have a size of less than 2.5 mm, preferably less than 1.5 mm. For example, a liner can also be introduced into the support tube 3 as a coated, comparatively thin material. Alternatively, the liner can also be a lacquer layer or a plasma coating. Particularly advantageously, the liner thickness of the liner 6 can be from 50 µm to 1.5 mm, in particular between 200 µm and 1.3 mm. On the side facing the medium, the measuring tube 2 has an electrically conductive layer 10. This can preferably be a metallic coating. The electrically conductive layer 11 can preferably be applied as an electrically conductive lacquer, as an electrically conductive powder coating and / or as an electrically conductive plasma coating.Preferred thicknesses for the electrically conductive layer are between 40 µm and 1 mm, preferably between 50 µm and 800 µm. These thicknesses ensure that the layer is sufficiently stable even under mechanical stress and, at the same time, that a contacting agent can be contacted from the measuring tube side. The contacting agent is in . Fig. 3 as a pointed pin electrode 27. Of course, other electrode shapes can also be realized within the scope of the present invention, whereby this electrode shape has proven to be particularly suitable for contacting the metallic coating. In the case of plastic measuring tubes, an electrode shape such as that in WO 2009 / 071615 A1 can alternatively be used, which does not require an additional anchoring device. In terms of production technology, the pin electrode 27 can be inserted from the outside, i.e. beyond the lumen of the measuring tube 1, through a bore in the measuring tube 1 or simply in the support tube 3 until contact is made with the electrically conductive layer 11. It is also possible and easy to realize to first position the pin electrode 27 and then apply the electrically conductive layer 11.An electrically insulating inner lining 32 is provided in the bore of the measuring tube 1 or the support tube 3 of the measuring tube 1, which advantageously prevents contact between the metallic support tube 3 and the pin electrode 27. The electrically conductive layer 11 can be used in any type of measuring tube, but is particularly advantageous for measuring tubes with a small inner diameter (DN100 or less) and in measuring tubes with a reduced and / or modified cross-section in the area of ​​the magnet system, as described, for example, in WO 2016 / 102168 A1. On the side of the measuring tube 1 facing away from the medium, an anchoring system 28 for the pin electrode 27 is provided. This comprises two arms 29 projecting obliquely from the outer wall of the measuring tube 1 and converging towards one another, and a platform 31 which is radially spaced from the outer wall of the measuring tube and which has a bore for the pin electrode 27 to pass through.This form of the anchoring system 28 can also be used as a centering aid and as a stop when preparing the bore for the electrode in the support tube 3, so that a drill is guided and drills the bore at a defined height. Furthermore, the anchoring system 28 serves to secure the pin electrode 27 against rotation. Additional connection layers can be provided between the electrically conductive layer 11 and the measuring tube 1. However, and advantageously, the electrically conductive layer 11 can also be applied directly to the inside of the measuring tube 1, in particular to the surface of the liner 4. The electrically conductive layer 11 is location-selective. The material of the electrically conductive layer 11 can preferably be steel, but can also be other corrosion-resistant metal. Stainless steel of class 1.4435, which is approved for drinking water applications, can be used with particular preference.The arms 29 of the anchoring system 28 can be welded to the support tube 3.

[0046] The Fig. 4 shows a section of a longitudinal section of a further embodiment of the abrasion detection device of the measuring device according to the invention. Fig. 4 represents a modified embodiment of a carrier tube 3 made of plastic. This therefore requires no liner and no electrically insulating bore lining. The electrically conductive layer 11, the pin electrode 27 and the anchoring system 28 can be analogous to Fig. 3 be trained.

[0047] The Fig. 5 shows a section of a longitudinal section of a further embodiment of the abrasion detection device of the measuring device according to the invention. The electrode variant has a first conductive layer 11 and a second conductive layer 12, which preferably completely covers the first conductive layer 12 towards the medium. The material of the first conductive layer 11 differs in its conductivity from the material of the second layer 12. The second layer 19 can, for example, consist of a more corrosion-resistant material than the first layer 11. For example, steel, in particular stainless steel, for example material class 1.4435 for drinking water applications, can be used as the material of the second layer 12, and copper, a conductive plastic, or a conductive semiconductor can be used as the material of the first layer 11. Here, too, the erosion of the second layer 12 can be monitored, e.g.by changing a resistance value, and an indication of imminent failure. Nevertheless, the measuring function of the electrode remains intact here too due to the presence of the first layer 11. Location-selective direct coatings can be applied, for example, using a plasma coating process and are already known from, among others, ecoCOAT GmbH. By applying a layer in this way, an electrode surface can be created which protrudes only to a negligible extent into the lumen of a tube, in particular a measuring tube of a magnetic-inductive flowmeter. This reduces or even completely prevents turbulence or similar on the electrode surface.In addition, a thin liner thickness can be selected for measuring tubes with metallic support tubes, since the electrode heads were previously partially pressed into the liner material to avoid turbulence, which required a certain liner thickness, which is no longer necessary. The pin electrode 27 and the anchoring system 28 can be designed analogously to . Fig. 3 be trained.

[0048] The Fig. 6 shows a section of a longitudinal section of a further embodiment of the abrasion detection device of the measuring device according to the invention. Two pin electrodes 27 and 33 are arranged one behind the other in the flow direction A in the electrically conductive layer 11 and in the measuring tube. If the front or upstream area of ​​the layer 11 is ablated, this can be detected by comparing the voltages and / or resistances of the respective electrodes 27 and 33 relative to a reference electrode, and an imminent failure can be signaled. Repair can be carried out relatively easily by simply recoating the inside of the support tube 3 in a location-selective manner.

[0049] The Fig. 7 shows a detail of a longitudinal section of a further embodiment of the abrasion detection device 9 of the measuring device according to the invention. The layer system 8 consists of four individual layers, each with a different electrical resistance, wherein the electrical resistances are selected such that they decrease in the radial direction, in particular towards a measuring tube center. Alternatively, individual layers can each have different hardnesses, wherein the hardnesses decrease in the radial direction, in particular towards a measuring tube center. Alternatively, the layers can each have different layer thicknesses, wherein the layer thicknesses are selected such that they increase in the radial direction, in particular towards a measuring tube center.In addition to the electrically insulating layers, the layer system 8 has at least one electrically insulating layer 10 which separates two electrically conductive layers 11, 12 from each other.

[0050] The Fig. 8 shows a section of a longitudinal section of a further embodiment of the abrasion detection device 9 of the measuring device according to the invention. Alternative to the embodiment according to Fig. 2 with contacting means distributed around the circumference of the support tube. The contacting means 14, 15, 16, 17 are evenly distributed in the direction of flow. The layer system is not necessarily designed as a ring strip, but can be designed as The adjacent contacting means are each at a substantially equal distance from one another, wherein the distance is in each case greater than the thickness of the layer system 8. The abrasion detection device 9 is designed to allow an electrical current to flow between the first contacting means 14 and the second contacting means 15 and to measure an electrical voltage between the third contacting means 16 and the fourth contacting means 17. A surface resistance for the layer system results from the magnitude of the electrical current and the measured voltage.The at least one quantity can be determined at least as a function of the surface resistance, in particular as a function of the change in the surface resistance over time.

[0051] The Fig. 9 shows a longitudinal section of a magnetic-inductive flowmeter according to the invention, which can be connected to a process line via flanges 5. The measuring device of the magnetic-inductive flowmeter has a magnetic field generating device 18 for generating a magnetic field penetrating the measuring tube 6, which is arranged on an outer surface of the measuring tube 6. The magnetic field generating device 18 can, for example, comprise at least one saddle coil or at least one coil with a pole piece. In addition, the measuring device has an electrode arrangement 19 for tapping a flow velocity-dependent measured variable inductively generated in the medium. This generally consists of at least two diametrically arranged measuring electrodes. The electrode arrangement 19 is arranged in a measuring section, and a monitoring electrode 7 is applied to the liner 4 as a layer system 8, offset in the direction of flow from the measuring section.The layer system 8 is connected via an abrasion detection device 9 to a measuring circuit configured to carry out the method according to the invention. The monitoring electrode 7, the abrasion detection device 9, and the measuring circuit together form the monitoring device 25.

[0052] The Fig. 10 shows a view of a part of a process plant 30, which comprises a pipeline 23, a measuring device 1 according to the invention, a plant component 24, and a monitoring device 25. The measuring device 1 is connected to the pipeline 23 and has a monitoring electrode that has an electrode material and / or a coating material that the plant component 24 also has. The monitoring device 25 is configured to issue a warning for the plant component 24 and / or to determine a remaining operating time until a maintenance measure for the plant component 24, at least as a function of at least one variable that is specific to the electrode material and / or the coating material, and preferably a threshold value assigned to the plant component 24. Bezugszeichenliste

[0053] Measuring device 1 Measuring device 2 Support tube 3 Liner 4 Flange 5 Measuring tube 6 Monitoring electrode 7 Layer system 8 Abrasion detection device 9 Insulating layer 10 First layer 11 Second layer 12 Contacting arrangement 13 First contacting means 14 Second contacting means 15 Third contacting means 16 Fourth contacting means 17 Magnetic field generating device 18 Electrode arrangement 19 Inner shell surface 20 Outer shell surface 21 Process plant 22 Pipeline 23 Plant component 24 Monitoring device 25 Monitoring electrode 26 Pin electrode 27 Anchoring system 28 Arm 29 Process plant 30 Platform 31 Inner lining 32 Pin electrode 33

Claims

1. A measuring device (1), comprising: - A measuring tube (6) for conducting a flowable medium, wherein the measuring tube (6) has an inner lateral surface (20), wherein the inner lateral surface (20) is designed to be electrically insulating at least in sections, - at least one monitoring electrode (7), wherein the at least one monitoring electrode (7) is arranged on the electrically insulating section of the inner lateral surface (20) in such a way that it is contact with the media, - a measuring apparatus (2) for determining a process property of the medium; - an abrasion detection device (9), which is configured to determine at least one variable on the at least one monitoring electrode (7), which corresponds to an abrasion of the monitoring electrode (7), wherein the at least one monitoring electrode (7) is configured as a selectively applied conductive layer system (8); characterized in that the layer system (8) comprises at least two electrically conductive layers (11, 12) each having different materials.

2. The measuring device (1) as claimed in the preceding claim, wherein the layer system (8) comprises at least one conductive polymer layer and / or at least one metal layer and / or at least one doped semiconductor layer.

3. The measuring device (1) as claimed in claim 1 or 2, wherein the at least two layers (11, 12) each have an electrical resistance, wherein the at least two layers (11, 12) are arranged in such a way that the respective resistance decreases in a radial direction, in particular in the direction of the center of the measuring tube.

4. The measuring device (1) as claimed in one of the preceding claims, wherein the at least two layers (11, 12) each have a layer thickness, wherein the at least two layers (11, 12) are arranged in such a way that the respective layer thickness increases in a radial direction, in particular in the direction of the center of the measuring tube.

5. The measuring device (1) as claimed in at least one of the preceding claims, wherein the at least two layers (11, 12) each have a hardness, wherein the at least two layers (11, 12) are arranged in such a way that the respective hardness decreases in a radial direction, in particular in the direction of the center of the measuring tube.

6. The measuring device (1) as claimed in at least one of the preceding claims, wherein the layer system (8) has at least one electrically insulating layer (10), which separates two electrically conductive layers (11, 12) of the at least two layers (11, 12) from each other.

7. The measuring device (1) as claimed in at least one of the preceding claims, wherein a layer (11) of the layer system (8) in contact with the inner lateral surface (20) is at least partially annular and / or has an electrical resistance R1, where R1 ≤ 10-6 Ωm, in particular R1 ≤ 5 · 10-7 Ωm and preferably R1 ≤ 10-7 Ωm.

8. The measuring device (1) as claimed in at least one of the preceding claims, wherein the abrasion detection device (9) is configured to measure the at least one variable in a first time interval, wherein the abrasion detection device (9) is configured to connect the layer system (8) with an earth potential at least in a second time interval.

9. The measuring device (1) as claimed in one of the preceding claims: wherein the abrasion detection device (9) has a contacting arrangement (13) for electrically contacting the monitoring electrode (7), in particular comprising a first contacting medium (14) and a second contacting medium (15), wherein the abrasion detection device (9) is configured to measure an impedance on the at least one monitoring electrode (7) and to determine the at least one variable at least as a function of the impedance, in particular as a function of how the impedance changes over time.

10. The measuring device (1) as claimed in at least one of claims 1 to 8, wherein the contacting arrangement (13) has a first contacting medium (14) and a second contacting medium (15), wherein the contacting arrangement (13) has a third contacting medium (16) and a fourth contacting medium (17), wherein the third contacting medium (16) and the fourth contacting medium (17) are arranged between the first contacting medium (14) and the second contact medium (15), in particular in a circumferential direction of the measuring tube (6), wherein the abrasion detection device (9) is configured to allow a electric current to flow between the first contacting medium (14) and the second contacting medium (15), wherein the abrasion detection device (9) is configured to measure an electrical voltage between the third contacting medium (16) and the fourth contacting medium (17), wherein the abrasion detection device (9) is configured to determine a sheet resistance and to determine the at least one variable at least as a function of the sheet resistance, in particular as a function of how the sheet resistance changes over time.

11. The measuring device (1) as claimed in at least one of the preceding claims, wherein a variable of the at least one variable describes a material-dependent abrasion rate and preferably a further variable of the at least one variable describes a further material-dependent abrasion rate.

12. The measuring device (1) as claimed in at least one of the preceding claims, wherein the measuring apparatus comprises a magnetic field generating device (18) for generating a magnetic field which penetrates the measuring tube (6), wherein the magnetic field generating device (18) is arranged on an outer lateral surface (21) of the measuring tube (6), wherein the measuring apparatus comprises an electrode arrangement (19) for measuring a flow velocity-dependent measured variable inductively generated in the medium, wherein the electrode arrangement (19) is arranged in a measuring section, wherein the at least one monitoring electrode (7) is arranged in the measuring tube (6) on the inlet side and / or on the outlet side and preferably at a distance from the measuring section.

13. A process plant (22), comprising: - A pipeline (23), - a measuring device (1) as claimed in one of the preceding claims, wherein the measuring device (1) is connected to the pipeline (23), wherein the monitoring electrode (7) has an electrode material and / or a coating arranged on the inner lateral surface has a coating material, wherein a variable of the at least one variable is specific to the electrode material and / or the coating material, - a plant component (24), which also has the electrode material and / or the coating material at least in a section in contact with the medium, - a monitoring device (25), wherein the monitoring device (25) is configured to issue a warning for the plant component (24), at least as a function of the variable and preferably a threshold value assigned to the plant component (24) and / or to determine a remaining operating time until a maintenance measure on the plant component (24).

14. A method for determining an abrasion of an electrically insulating coating of a measuring tube (6) of a measuring device (1) in contact with the medium as claimed in one of claims 1 to 12, comprising the process steps: - Measuring a sheet resistance at a monitoring electrode (7) in contact with the medium, wherein the monitoring electrode (7) is configured as a layer system (8); - Determining a test variable dependent on a layer thickness of the layer system (8) by means of the measured sheet resistance, - Determining whether abrasion is present based on the test variable.