Magnetic inductive flowmeter

Abstract

The invention relates to a magnetic inductive flowmeter (1) comprising: - a measuring conduit (8) for conducting a medium, wherein the measuring conduit (8) comprises an electrically insulating measuring conduit body (32), - a device (5) for generating a magnetic field, which penetrates the measuring conduit body; - a device (9) for detecting an induced voltage, which is related to a flow rate; - a reference electrode (33); - an electrode assembly (34) for detecting a damage of the measuring conduit body (32), wherein the electrode assembly (43) is electrically insulated from the reference electrode (33) and / or the medium by the measuring conduit body (32); - a measuring circuit (11) configured to measure a variable related to an electrical impedance between the electrode assembly (34) and the reference electrode (33).

Description

Technical Field

[0001] This invention relates to an electromagnetic flowmeter, and more particularly to a magnetic induction flowmeter for measuring the volumetric or mass flow rate of a fluid or a flowable solid substance, wherein the fluid flows through the instrument in a continuous flow manner. Background Technology

[0002] Magnetic induction flow meters are used to determine the flow rate and volumetric flow rate of a medium flowing in a pipeline. A magnetic induction flow meter has a magnet system that generates a magnetic field perpendicular to the flow direction of the medium. A single coil is typically used for this purpose; permanent magnets are less common. To achieve a predominantly uniform magnetic field, pole pieces are additionally formed and attached to the measuring pipe such that the magnetic field lines extend substantially perpendicular to the transverse axis or parallel to the vertical axis of the measuring pipe across the entire pipe cross-section. Measuring electrodes attached to the side surface of the measuring pipe tap an electrical voltage or potential difference in the medium, which is perpendicular to the flow direction and perpendicular to the applied magnetic field, and appears when the conductive medium flows in the flow direction as the magnetic field is applied. Because, according to Faraday's law of induction, the tapped measuring voltage is a function of the velocity of the flowing medium, i.e., the flow rate u, and given a known pipe cross-section, the volumetric flow rate... It can be determined based on the induced voltage U.

[0003] Magnetic induction flow meters are commonly used in fluid processes and automation engineering, and have a conductivity of approximately 5 μS / cm. The applicant sells corresponding flow meters in various embodiments for various applications, for example, under the name Promag.

[0004] Because the measuring pipe of a magnetic induction flowmeter requires high mechanical stability, the pipe is typically constructed of a metal carrier tube of predetermined strength and width, with the interior of the metal carrier tube lined with an electrically insulating material of predetermined thickness, known as a liner. For example, DE 102005 044 972A1 and DE 10 2004 062680A1 each describe a magnetic induction measuring sensor, which includes a measuring sensor and a tubular liner. The measuring sensor can be inserted into the pipeline and includes a first end on an inlet side and a second end on an outlet side. The non-ferromagnetic carrier tube serves as the outer sheath of the measuring pipe, and the tubular liner, constructed of electrically insulating material, is housed within the inner cavity of the carrier tube to guide the flow process medium electrically insulated from the carrier tube.

[0005] Liners, typically made of thermoplastic, thermosetting, and / or elastomeric plastics, are particularly used for chemical insulation between the support tube and the process medium. In magnetic induction measurement sensors where the carrier tube has high conductivity, for example when a metal carrier tube is used, the liner also serves for electrical insulation between the carrier tube and the process medium, preventing short circuits caused by voltages induced in the process medium via the carrier tube. Therefore, the corresponding design of the support tube allows the strength of the measuring pipe to adapt to the mechanical stresses present under the corresponding application conditions, while the liner enables the measuring pipe to be adapted to the electrical, chemical, and / or biological requirements of the corresponding application conditions.

[0006] Typically, a so-called support body embedded in the liner is used to secure the liner. For example, in patent specification EP0 766 069B1, a perforated pipe welded to a carrier pipe serves as the support body. The support body is attached to the carrier pipe and embedded in the liner by applying the material used to manufacture the liner into the interior of the carrier pipe. Furthermore, a measuring pipe with a metal shell is known from patent specification US 4 513 624A for mechanical stabilization and electrical shielding. For this purpose, the metal shell surrounds the conduit leading to the medium.

[0007] Furthermore, magnetic induction flowmeters are known to have a measuring pipe body formed of an electrically insulating material such as plastic, ceramic, and / or glass. With such a measuring pipe, the need for an insulating coating is eliminated.

[0008] It has been shown that despite the use of heavy-duty materials, the electrically insulating liner and the measuring pipe body formed by the electrically insulating material are still susceptible to corrosion. In particular, solid particles such as sand, gravel, and / or rock cause wear on the liner or the measuring pipe body. Wear or deformation of the liner or the electrically insulating measuring pipe body alters the flow profile of the measuring sensor. As a result, the measuring equipment provides incorrect measurements of volumetric or mass flow rates. Furthermore, when the measuring pipe has an internal liner, the chemical or electrical insulation between the process medium and the carrier pipe is lost.

[0009] WO 2010 / 066518A1 discloses a measuring device for determining the volumetric flow rate and / or mass flow rate of a process medium flowing through a measuring conduit. The measuring conduit includes: a carrier tube having an inner liner comprising a first layer and a second layer; and a monitoring electrode embedded between the first and second layers and configured to detect damage to the second / first layer. However, a disadvantage of this approach is the limited impact of monitoring on the measurement of the volumetric flow rate and / or mass flow rate. Summary of the Invention

[0010] Therefore, the object of the present invention is to provide an alternative solution for magnetic induction flow meters that can detect damage to the lining and / or electrically insulated measuring pipe body caused by wear without compromising measurement performance.

[0011] According to the present invention, this objective is achieved by a magnetic induction flowmeter.

[0012] The magnetic induction flowmeter according to the present invention comprises:

[0013] - Measuring pipes used to guide the medium.

[0014] The measuring pipeline includes a main body, which is electrically insulated in sections.

[0015] - A device for generating a magnetic field that penetrates the body of the measuring pipe;

[0016] - A device for detecting an induced voltage that is related to the flow rate;

[0017] -Reference electrode;

[0018] - Electrode assembly, which is used to detect and measure damage to the main body of the pipeline;

[0019] The electrode assembly is connected to a reference electrode and / or dielectric via a measuring conduit body.

[0020] Insulation; and

[0021] - Measurement circuit, which is configured to measure variables related to the impedance between the electrode assembly and the reference electrode.

[0022] Section-wise electrical insulation of the measuring pipe body can be achieved by applying an electrically insulating liner to the interior of the metallic and therefore conductive carrier pipe. Alternatively, the measuring pipe body can be formed of electrically insulating plastic, ceramic, and / or glass.

[0023] Impedance—also known as AC resistance—is the resistance in AC technology, and in the case of two-pole network elements, impedance represents the ratio of voltage to current intensity. This term is used particularly when there is a phase shift between the two variables, so the ratio differs from the resistance determined by direct current. Impedance is advantageously expressed as a complex function of frequency. Impedance is a combination of the ratio of the amplitude of a time-varying AC voltage to the amplitude of a time-varying AC current and the displacement of the phase angle between these two variables (time-varying AC voltage and time-varying AC current). These two properties (the ratio and the displacement) are mathematically combined by expressing impedance as a complex variable, specifically by combining the real value, apparent resistance, and imaginary part of the complex impedance, the imaginary part being expressed as an exponential function of the phase shift angle—which can take values ​​between 0° and 90°—with imaginary units and an exponential form. In other words, impedance has real and imaginary parts. The phase shift component is frequency-dependent; the non-phase-shifted component can be frequency-dependent, but at least for the frequency range used in electronic devices, the non-phase-shifted component is generally frequency-independent.

[0024] The measurement circuit is configured to apply a time-varying excitation signal, particularly an excitation signal having at least one excitation frequency, to the electrode assembly. The excitation signal is generated using a voltage source on the electrode assembly relative to a reference potential—preferably relative to ground potential. Furthermore, the measurement circuit is configured to measure the measurement signal on the electrode assembly.

[0025] According to one embodiment, the excitation signal is an AC voltage signal, particularly a multi-frequency voltage signal. The excitation signal is designed as an AC voltage signal because DC voltage signals ensure interruption of flow measurement. It is advantageous if the frequency of the AC voltage signal is in the range of 1 Hz to 10 kHz. For a multi-frequency voltage signal, the voltage value changes periodically at at least two frequencies. Advantageously, the AC voltage signal has a first frequency during a first time interval, and then the frequency of the AC voltage signal is changed during a subsequent second time interval.

[0026] The function of the reference electrode is to ensure potential equalization between the fluid and the measuring sensor. The reference electrode is typically a grounding plate and / or electrode disposed on the end face. This grounding plate and / or electrode is usually a needle electrode, mushroom-shaped electrode, or brush electrode and is disposed in an opening within the measuring pipe sleeve, typically in contact with the medium and located in the same measuring plane as the measuring electrode. Typically, the reference electrode is electrically connected to the housing of the measuring electronics in the pipeline. The housing is usually connected to protective ground. Magnetic induction flow meters are commercially available, and their reference electrodes are not grounded.

[0027] A measurement circuit is a combination of electrical or electromechanical components—such as amplifiers, terminals, analog-to-digital converters, transistors, batteries, switches, displays, etc.—that form a functional arrangement. A circuit becomes usable because current flows through its components; therefore, at least one electrical energy source is required to be contained within the circuit in a closed circuit. This at least one electrical energy source can be implemented internally as a battery or an external power source. A measurement circuit can have individual functional elements capable of performing logical operations.

[0028] Advantageous embodiments of the present invention are as follows.

[0029] One embodiment specifies that the electrode assembly includes at least one monitoring electrode.

[0030] The monitoring electrode has a longitudinal direction.

[0031] The monitoring electrode has a material thickness D.

[0032] The material thickness D of the monitoring electrode in the longitudinal direction preferably increases at least partially in a gradual manner.

[0033] The advantage of partially increasing the material thickness is, for example, that in cases of particularly uniform wear of the monitoring electrode, the contact surface of the monitoring electrode in contact with the dielectric current increases. This is reflected in the measurement signal, and as a result, it is possible to determine how much of the liner has been removed based on the changing measurement signal or on variables related to impedance.

[0034] The existence of a stepwise increase in material thickness has the following advantages: in the case of monitoring electrode wear, the contact surface with the medium increases discretely rather than continuously, which in turn affects the measurement signal. Therefore, the degree of wear or the remaining lining thickness can be determined based on the stepwise changes in the measurement signal.

[0035] One embodiment specifies that at least one monitoring electrode is at least partially hollow cylindrical or annular.

[0036] One embodiment specifies that the measuring pipe body has a longitudinal direction.

[0037] At least one of the monitoring electrodes is oriented coaxially with the measuring pipe body and is arranged to be offset relative to the reference electrode in the longitudinal direction of the measuring pipe body.

[0038] At least one monitoring electrode is preferably arranged on the input and / or output side, such that the measurement pipeline has a section in which a device for detecting an induced voltage in the medium, which is related to the flow rate, is arranged, but this section does not contain a monitoring electrode. This has the advantage that the measurement of the voltage applied to the device for detecting the flow rate-related induced voltage is minimized in the event of wear-related short circuits occurring at several points on the monitoring electrode.

[0039] Furthermore, this configuration has the following advantages: damage to the pipe body or lining can be detected not only locally and therefore selectively, but also over a larger area.

[0040] One embodiment specifies that the reference electrode extends through the body of the measuring conduit.

[0041] At least one of the monitoring electrodes has an opening.

[0042] The reference electrode is configured to electrically connect the dielectric to a reference potential.

[0043] The reference electrode extends through the opening.

[0044] This embodiment forms a simple and advantageous alternative to the solutions for monitoring and measuring equipment taught in WO 2010 / 066518A1. This embodiment is particularly suitable for detecting wear caused by particles such as, for example, suspended matter, sand, concrete, plaster, and gravel, which tend to settle and continuously wear away the surface of the lining or body of the measuring pipe when the medium is directed. This is typically not selective, but rather occurs over a larger area on the underside of the measuring pipe where a reference electrode is also arranged. If the measurement signal determined between the reference electrode and the monitoring electrode deviates from the setpoint value, the probability of uniform wear increases.

[0045] One embodiment specifies that the electrode assembly has at least two monitoring electrodes.

[0046] At least two monitoring electrodes can be electrically connected to and communicate with the measurement circuit, or electrically connected to each other. The first-mentioned embodiment has the advantage that monitoring can be performed in a spatially resolved manner.

[0047] The second embodiment mentioned has the following advantages: it can be easily implemented and can be implemented using the measurement circuit of a known magnetic induction flowmeter.

[0048] One embodiment specifies that the first monitoring electrode of at least two monitoring electrodes has a first inner diameter.

[0049] The second monitoring electrode of the at least two monitoring electrodes has a second inner diameter.

[0050] The first inner diameter deviates from the second inner diameter.

[0051] If at least two monitoring electrodes are electrically connected to the measurement circuit respectively, and the measurement circuit is configured to determine the measurement signals on the at least two monitoring electrodes, the degree of wear and the remaining thickness of the liner can be determined by the selection of the inner diameter.

[0052] One embodiment specifies that at least two monitoring electrodes are arranged to be offset from each other, particularly coaxially, in the longitudinal direction of the measuring conduit.

[0053] This embodiment provides an alternative to a monitoring electrode with a stepped monitoring electrode body, and enables wear to be determined in a spatially resolvable manner.

[0054] One embodiment specifies that the first monitoring electrode is surrounded by the second monitoring electrode in the radial direction, at least in a portion of the section.

[0055] If the length of the second monitoring electrode in the longitudinal direction deviates from the length of the first monitoring electrode in the longitudinal direction, the remaining thickness of the liner can be determined based on the measurement signal. As wear increases, current contact is first established between the medium and the first or second monitoring electrode, and subsequently between the second or first monitoring electrode and the medium. This is reflected in the measurement signal, regardless of whether the at least two monitoring electrodes are mated together or measured individually by the measurement circuit.

[0056] One embodiment specifies that the measuring circuit is configured to signal the presence of a defect—particularly wear on the pipe body or lining—in the event of a deviation in a variable related to impedance—particularly from a setpoint value or a phase shift from the acceptable range. Attached Figure Description

[0057] The invention will be explained in more detail with reference to the following figures, but not limited to the figures themselves. The following figures illustrate:

[0058] Figure 1 This is a cross-sectional view of a magnetic induction flow meter based on existing technology;

[0059] Figure 2 This is a first embodiment of an electrode assembly for detecting damage to the measuring pipe body of a magnetic induction flowmeter;

[0060] Figure 3 This is a second embodiment of the electrode assembly;

[0061] Figure 4 This is a third embodiment of an electrode assembly having at least one stepped monitoring electrode;

[0062] Figure 5 This is a fourth embodiment of an electrode assembly having at least three monitoring electrodes;

[0063] Figure 6 This is the fifth embodiment of the electrode assembly;

[0064] Figure 7 This is the sixth embodiment of the electrode assembly; and

[0065] Figure 8 This is the seventh embodiment of an electrode assembly having at least two monitoring electrodes. Detailed Implementation

[0066] Figure 1A magnetic induction flowmeter 1, known from the prior art, is shown. The structure and measurement principle of the magnetic induction flowmeter 1 are known in principle. A conductive medium is guided through a measuring pipe 2. The measuring pipe 2 can be designed as, for example, a carrier pipe formed of metal, with an inner lining applied inside the carrier pipe, or the measuring pipe 2 comprises a measuring pipe body formed substantially of an electrically insulating material such as plastic, ceramic, glass, and / or concrete. A device 5 for generating a magnetic field is attached to the measuring pipe 2 such that the magnetic field lines are oriented substantially perpendicular to the longitudinal direction defined by the axis of the measuring pipe. A pole shoe or saddle coil with mounted coils and coil cores is preferably suitable as the device 5 for generating the magnetic field. When the magnetic field is applied, a potential distribution is generated in the measuring pipe 2, which is tapped by a device 8 for measuring the induced measurement voltage, preferably two measuring electrodes attached to the inner wall of the measuring pipe 2. Typically, these two measuring electrodes are arranged radially and form an electrode axis or intersect a transverse axis extending perpendicular to the magnetic field lines and perpendicular to the axis of the measuring pipe. Based on the measured measurement voltage U and taking into account the magnetic flux density, the flow rate of the medium can be determined, and taking into account the cross-sectional area of ​​the pipe, the volumetric flow rate can be determined. To prevent the measurement voltage applied to the first and second measuring electrodes from dissipating through the metal carrier tube, an electrically insulating liner, the so-called lining, is provided on the inner wall of the carrier tube. The magnetic field established by the device—for example, an electromagnet used to generate a magnetic field—is generated by a DC current of alternating polarity timed by means of an operating circuit. This ensures a stable zero point and makes the measurement insensitive to the effects caused by electrochemical interference. The measurement circuit 23 is configured to read the measurement voltage applied to the first and second measuring electrodes. The evaluation circuit is configured to determine the flow rate and / or volumetric flow rate of the medium and output the medium to the user, for example, via a display 38. The commercially available magnetic induction flowmeter 1 has additional electrodes besides the measuring electrodes. First, the filling level monitoring electrode ( Figure 1 (Not shown in the image) – optimally attached to the highest point in the measuring pipe 2 – is used to detect partial filling of the measuring pipe 2 and is configured to transmit this information to the user and / or take the fill level into account when determining the volumetric flow rate. Additionally, the reference electrode is typically attached radially relative to the fill level monitoring electrode or at the lowest point of the pipe cross-section to ensure adequate grounding of the medium.

[0067] Figure 2A first embodiment of an electrode assembly 34 for detecting damage to the measuring pipe body of a magnetic induction flowmeter 1 is shown. The magnetic induction flowmeter 1 includes a measuring pipe 2 for guiding a medium through a measuring pipe body 32, which is segmentally electrically insulated. In the depicted embodiment, the measuring pipe body 32 is formed by a carrier tube 3 and an electrically insulating liner 4 disposed inside the carrier tube 3, the electrically insulating liner 4 extending inside the carrier tube 3 along the longitudinal direction of the measuring pipe body. A reference electrode 33 extends through an opening provided in the carrier tube 3 and through the liner 4. The reference electrode 33 is designed to contact the medium and is configured to electrically connect the medium to be guided to a reference potential. Alternatively, the reference electrode 33 may also be completely embedded in the liner or in the electrically insulated measuring pipe body, as in the electrode assembly 34. These embodiments each show a reference electrode 33 designed as a needle electrode. In applications with highly abrasive media, a brush electrode, preferably made of steel, is also used. According to the invention, the electrode assembly 34 for detecting damage to the measuring pipe body 32 is arranged on the measuring pipe 2. According to a first embodiment, the electrode assembly 34 includes monitoring electrodes 35 arranged on the input side and / or output side. The monitoring electrodes 35 are electrically insulated from the reference electrode 33 and the dielectric via the measurement pipe body 32. This is achieved by embedding the monitoring electrodes 35 within an electrically insulating liner 4. At least one monitoring electrode 35 shown is hollow cylindrical or annular and is oriented coaxially with the measurement pipe 2, particularly with the carrier pipe 3. It has a longitudinal direction of the monitoring electrode and a constant material thickness D in the longitudinal direction of the monitoring electrode. Furthermore, the monitoring electrodes 35 are arranged offset from the reference electrode 33 in the longitudinal direction of the measurement pipe body. The reference electrode 33 is arranged in the measurement pipe section without the electrode assembly 34, particularly at the location of at least one monitoring electrode 35. The electrode assembly 34, particularly at least one monitoring electrode 35, is electrically connected to a measurement circuit 11, which is configured to measure a variable related to the impedance between the electrode assembly 34 and the reference electrode 33 in the case of at least one monitoring electrode 35. The variable related to the impedance may be the phase shift between the excitation signal and the measurement signal. The electrode assembly 34 can be electrically connected via an electrical conductor (not shown), which is also embedded in the liner and extends through the provided opening to the measuring circuit 11 arranged outside the measuring pipe 2.

[0068] Impedance-related variables are determined by applying an excitation signal with at least one frequency to the monitoring electrode 35. A measurement signal is determined at the monitoring electrode 35 relative to the reference electrode 33. The measurement circuit is configured accordingly.

[0069] The monitoring electrode 35 can be embedded as a separate component in the form of a metal ring within the liner or the measuring pipe body, or alternatively, it can be achieved by local doping of the plastic liner or by applying conductive plastic.

[0070] All features, regardless of the number, shape, and location of the monitoring electrodes, can also be applied to subsequent embodiments.

[0071] Figure 3 A second embodiment of the electrode assembly 34 is shown, which is particularly suitable for detecting a continuous decrease in the liner thickness due to wear. For this purpose, the monitoring electrode 35 has a material thickness D that increases at least partially continuously in the longitudinal direction of the monitoring electrode. According to the depicted embodiment, the material thickness D of the monitoring electrode 35 increases continuously from the outermost monitoring electrode cross-section along the direction of the centrally oriented monitoring electrode cross-section. The monitoring electrode 35 gradually tapers in the direction of its center point located on the longitudinal axis of the monitoring electrode.

[0072] These three characterizations illustrate an idealized development of wear, where the thickness of the liner and the thickness of the monitoring electrode decrease uniformly. As wear increases, the thickness of the liner decreases from the contact surface between the monitoring electrode and the medium, which becomes apparent in the determined impedance. Depending on the material of the monitoring electrode, it may also be worn away due to wear. In this case, the variable material thickness D of the monitoring electrode 35 results in a similar increase in the contact surface area.

[0073] Figure 4 A third embodiment of an electrode assembly 34 having at least one stepped monitoring electrode 35 is shown. The depicted monitoring electrode 35 has a material thickness D that gradually increases in the longitudinal direction of the monitoring electrode. The depicted variant of the monitoring electrode 35 has three steps. In the case of uniform wear of the liner and possibly the monitoring electrode 35, the variable related to impedance changes abruptly. Based on this change, the degree of wear of the liner or the remaining thickness can be determined.

[0074] Figure 5 A fourth embodiment of the electrode assembly 34 with at least three monitoring electrodes 35, 36, and 37 is shown. The at least three monitoring electrodes 35, 36, and 37 are arranged on the input and / or output sides of the measuring pipe, and the inner and outer diameters of the at least three monitoring electrodes 35, 36, and 37 are different in each case. Furthermore, the at least three monitoring electrodes 35, 36, and 37 are offset in the longitudinal direction of the measuring pipe and are arranged according to the size of the inner diameter. All monitoring electrodes are electrically connected to the measuring circuit 11.

[0075] Alternatively, monitoring electrodes 35, 36, and 37 may have substantially the same outer diameter, but in each case different inner diameters, i.e., different material thicknesses. When monitoring electrodes 35, 36, and 37 are arranged coaxially, these electrodes can be electrically connected to each other. With increasing wear, the total contact surface between the electrode assembly and the medium also increases, whereby the total contact surface is generated by the individual contact surfaces of monitoring electrodes 35, 36, and 37.

[0076] Figure 6 A fifth embodiment of an electrode assembly 34 with a monitoring electrode having an opening 39 through which a reference electrode 33 extends. The reference electrode 33 extends through a measuring conduit body 32 and is configured to electrically connect a medium to a reference potential. The monitoring electrode 35 has a material thickness D that gradually increases along the longitudinal direction of the monitoring electrode. In the depicted embodiment, the monitoring electrode 35 has exactly two steps, each of which is formed with a different material thickness in cross-section.

[0077] As in Figure 3 In the three characterizations, an idealized progression of wear is shown, where the thickness of the lining and the thickness of the monitoring electrode decrease uniformly. As wear increases, the contact surface between the monitoring electrode and the medium increases, which becomes evident in the detected impedance.

[0078] Figure 7 A sixth embodiment of an electrode assembly 34 having a monitoring electrode 35 is shown. (Compared to...) Figure 6 The difference is that the material thickness D increases in the direction of the longitudinal axis of the monitoring electrode. The monitoring electrode 35 has a triangular longitudinal cross-sectional area in the longitudinal section.

[0079] Figure 8 A seventh embodiment of an electrode assembly 34 with two monitoring electrodes 35, 36 is shown, each of which radially surrounds a reference electrode 33. The first monitoring electrode 35 and the second monitoring electrode 36 each have an opening. The reference electrode 33 extends through the corresponding opening. Alternatively, the first monitoring electrode 35 may also extend through the opening of the second monitoring electrode 36, resulting in the first monitoring electrode 35 being radially surrounded by the second monitoring electrode 36 at least in a partial segment. In the depicted embodiment, the first monitoring electrode 35 is arranged offset from the second monitoring electrode 36 in the direction of the longitudinal axis of the monitoring electrode. The first monitoring electrode 35 and the second monitoring electrode 36 may each be electrically connected to a measurement circuit, allowing for the determination of when the monitoring electrodes 35, 36 come into contact with a medium, respectively.

[0080] For clarity, Figures 2 to 8 No device is described for generating a magnetic field that penetrates the body of the measuring pipe or for detecting induced voltages in the medium that are related to the flow rate.

[0081] List of reference numerals

[0082] Magnetic induction flowmeter 1

[0083] Measuring Pipe 2

[0084] Carrier tube 3

[0085] Lining 4

[0086] 5. Device for generating a magnetic field

[0087] Device for measuring induced voltage 8

[0088] Measurement circuit 11

[0089] Measurement circuit 23

[0090] Casing 31

[0091] 32 measuring pipe body

[0092] Reference electrode 33

[0093] Electrode assembly 34

[0094] First monitoring electrode 35

[0095] Second monitoring electrode 36

[0096] Third monitoring electrode 37

[0097] Monitor 38

[0098] Opening 39

[0099] Contact surface 40

Claims

1. A magnetic induction flow meter (1), comprising: - Measuring pipe (8) for guiding the medium, The measuring pipe (8) includes a measuring pipe body (32), which is electrically insulated in sections. -A device (5) for generating a magnetic field that penetrates the body of the measuring pipe (32); - A device (9) for detecting an induced voltage in the medium, the induced voltage being related to the flow rate; -Reference electrode (33); - Electrode assembly (34), the electrode assembly being used to detect damage to the measuring pipe body (32), The electrode assembly (34) is electrically insulated from the reference electrode (33) and / or the dielectric through the measuring pipe body (32); - Measurement circuit (11), the measurement circuit being configured to measure a variable relating to the impedance between the electrode assembly (34) and the reference electrode (33), In this embodiment, at least one monitoring electrode (35) is at least partially hollow cylindrical or annular. The measuring pipe body (32) includes the longitudinal direction of the measuring pipe body. The at least one monitoring electrode (35) is oriented coaxially with the measuring pipe body (32) and is arranged to be offset relative to the reference electrode (33) in the longitudinal direction of the measuring pipe body. The electrode assembly (34) has at least two monitoring electrodes. The first monitoring electrode of the at least two monitoring electrodes has a first inner diameter. The second monitoring electrode of the at least two monitoring electrodes has a second inner diameter. Wherein, the first inner diameter deviates from the second inner diameter.

2. The magnetic induction flowmeter according to claim 1, The electrode assembly (34) includes the at least one monitoring electrode (35). in, The at least one monitoring electrode (35) has a monitoring electrode longitudinal direction. Wherein, the at least one monitoring electrode (35) has a material thickness D, The material thickness D of the at least one monitoring electrode in the longitudinal direction increases at least partially in a stepwise manner.

3. The magnetic induction flowmeter according to claim 1 or 2, in, The reference electrode (33) extends through the measuring pipe body (32), The at least one monitoring electrode (35) has an opening (39). The reference electrode (33) is configured to electrically connect the dielectric to a reference potential. The reference electrode (33) extends through the opening (39).

4. The magnetic induction flowmeter according to claim 1, in, The at least two monitoring electrodes are arranged to be coaxially offset from each other in the longitudinal direction of the measuring pipe body.

5. The magnetic induction flowmeter according to claim 1, in, The first monitoring electrode is surrounded by the second monitoring electrode in at least a portion of a section in the radial direction.

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