Magnetic inductive flowmeter and method for operating a magnetic inductive flowmeter

Abstract

The invention relates to a magnetic-inductive flowmeter, which can be inserted into a pipe through which a medium flows, comprising: a housing, wherein the housing has a housing wall; at least a first measuring electrode and a second measuring electrode, which form galvanic contact with the flowing medium and are positioned on the housing wall; at least one magnetic-field generating device for generating a magnetic field through the housing wall, wherein the magnetic-field generating device is positioned in the housing and comprises a measuring circuit which is designed to determine at least one first measuring variable, and wherein the measuring value of the first measuring variable is measured between the two measuring electrodes or at the measuring electrodes relative to a reference potential, in particular ground potential. The flowmeter is characterized in that: an evaluation circuit is designed to determine the Reynolds number and / or the kinematic viscosity value of the medium in the pipe by means of the measuring value of the first measuring variable and the measuring value of a second measuring variable which is different from the first measuring variable, wherein the measuring value of the second measuring variable is determined between the two measuring electrodes or at one of the measuring electrodes relative to a reference potential, in particular ground potential; and the measuring electrodes are positioned on the housing wall in such a way that the quotient of the current measuring value of the first measuring variable and the current measuring value of the second measuring variable during a test measurement corresponds bijectively to the Reynolds number of the medium in the pipe.

Description

Background Technology

[0001] Magnetic induction flow measurement devices are used to determine the velocity and volumetric flow rate of a medium flowing in a pipe. These devices have a magnetic system that generates a magnetic field perpendicular to the flow direction of the medium. A single coil is typically used for this purpose. To achieve a substantially uniform magnetic field, pole pieces are additionally formed and attached such that the magnetic field lines extend substantially perpendicular to the transverse axis of the measuring tube or parallel to its longitudinal axis over the entire cross-section of the tube. Measuring electrodes attached to the side surface of the measuring tube tap an electrical measuring voltage or potential difference perpendicular to the flow direction and the magnetic field, and this voltage or potential difference is generated when the conductive medium flows in the flow direction while the magnetic field is applied. Because the tapped measuring voltage depends on the velocity u of the flowing medium according to Faraday's law of induction, and the volumetric flow rate V can be determined from the induced measuring voltage U by means of a known tube cross-section.

[0002] Unlike magnetic induction flow measurement devices, magnetic induction flow meters, whose housings are typically cylindrical, are inserted into a lateral opening in the pipe and secured with a fluid seal. A dedicated measuring tube is no longer required. Since the magnetic field exists only in the region of the flow meter's front end that extends into the fluid, or is generated in that region by a current flowing through its coil arrangement, the coil arrangement on the side surface of the measuring tube is eliminated. For this purpose, the magnet system is typically arranged within the housing and adjacent to the measuring electrodes, such that the axis of symmetry of the generated magnetic field lines intersects perpendicularly with the plane between the measuring electrodes. The measuring electrodes are located on the front or side of the housing.

[0003] For both measurement systems, the measurement voltage U applied to the measuring electrode consists of a simplified equation.

[0004] U = f(Re)·u·S

[0005] Here, S is the nominal signal strength, which depends on the sensor geometry and magnetic field, and f(Re) is a correction factor related to the flow profile or Reynolds number. It is typically assumed that the correction factor f(Re) is constant. However, this is not always the case. The nominal signal strength S is determined during flowmeter calibration, and its value is stored in the memory of the evaluation circuit.

[0006] The Reynolds number of the flowing medium in a pipe is defined by the following formula:

[0007]

[0008] Among them, the pipe diameter DN, the medium density ρ, the medium dynamic viscosity μ, and the medium kinematic viscosity ν.

[0009] Magnetic induction flow meters are particularly sensitive to the current Reynolds number of the medium in the pipe, as this determines the flow profile of the flowing medium. Depending on the pipe system, magnet system, and installation depth, the correction factor f(Re) can vary and deviate from its assumed constant value by several percentage points. Typically, the arrangement of the measuring electrodes and the magnetic field generating device is optimized so that the flow meter's characteristic curve is as linear as possible; that is, the induced measurement voltage is independent of the Reynolds number over the widest possible Reynolds number range or within the range of Reynolds number of interest for a specific application and predetermined installation depth. Therefore, flow meters with a few percent deviation in the transitional flow region and approximately 2% to 5% deviation for flows with turbulent profiles are already industry standards.

[0010] EP0892251 A1 discloses a magnetic induction flowmeter with a front end extending into the fluid in the form of a spherical cap, wherein first and second electrodes for forming current contact are symmetrically arranged on one of the meridians of the spherical cap with respect to the apex of the meridian. The spherical cap shape reduces the formation of flow eddies that occur when the medium flows against the flowmeter's front region, and increases measurement accuracy at low flow rates.

[0011] However, to date, the magnetic induction flow meter and the method for determining the Reynolds number of the medium and calibrating the flow value from it are unknown. Summary of the Invention

[0012] The purpose of this invention is to remedy this problem.

[0013] This objective is achieved by the magnetic induction flowmeter according to the invention, the method for operating the magnetic induction flowmeter according to the invention, and the flow measurement point according to the invention.

[0014] The magnetic induction flowmeter according to the present invention, which can be inserted into a pipe through which the medium flows, comprises:

[0015] -case,

[0016] The shell has a shell wall;

[0017] - At least a first measuring electrode and a second measuring electrode are arranged on the housing wall, each for forming an electric current contact with the flowing medium;

[0018] - At least one magnetic field generating device for generating a magnetic field that penetrates the shell wall.

[0019] The magnetic field generating device is housed within the casing; and

[0020] - A measurement circuit configured to determine at least a first measurement variable.

[0021] The measurement of the first measurement variable is performed between two measuring electrodes or at the measuring electrodes relative to a reference potential, especially ground potential.

[0022] And it is characterized by,

[0023] The evaluation circuit is configured to determine the Reynolds number and / or kinematic viscosity of the medium in the tube by means of a measured value of a first measured variable and a measured value of a second measured variable different from the first measured variable.

[0024] Specifically, the measured value of the second measurement variable is determined relative to a reference potential, especially ground potential, between two measuring electrodes or at one measuring electrode.

[0025] In this embodiment, at least one measuring electrode configured to determine the measured value of the second measuring variable is different from the measuring electrode configured to determine the measured value of the first measuring variable.

[0026] Of particular advantage, the magnetic induction flowmeter has an evaluation circuit configured to determine the Reynolds number and / or the Reynolds number-dependent kinematic viscosity of the medium in the pipe by means of measurements of two measured variables tapped at at least two measuring electrodes. The first and second measured variables are different. The difference between these two measured variables is that they are determined between different pairs of measuring electrodes or measured at different measuring electrodes.

[0027] Measurement circuits are well known in the field of flow measurement technology. The purpose of a measurement circuit is to detect very small absolute values ​​and changes in the corresponding measured variable. Several different embodiments exist, each with its own advantages and disadvantages.

[0028] On one hand, the measuring circuit can be configured to be connected to a potential at one of the measuring electrodes relative to a reference potential. Therefore, even if one of the two measuring electrodes fails, the flow rate can still be determined based on the determined potential. The housing potential or ground potential is suitable as the reference potential. The magnetic induction flowmeter can have a ground electrode connected to the reference potential. Thus, both measured variables can be potentials that prevail and are determined at each of the two measuring electrodes.

[0029] On the other hand, the measurement circuit can be designed to detect and record the prevailing potential difference between the two measurement electrodes.

[0030] Alternatively, the measurement circuit can be configured to measure the measurement voltage between the first and second measurement electrodes, and additionally, to measure the potential at one or the third measurement electrode relative to a reference potential.

[0031] Therefore, the measurement circuit includes an analog-to-digital converter that converts the input signal (in this case, the potential difference currently present at the corresponding measurement electrode pair or the potential difference prevailing at the corresponding measurement electrode) into digital data, which is then further processed or stored by the evaluation circuit. However, other measurement converters or measurement transducers from the field of digital measurement technology are also known and suitable for detecting measurement voltages or potentials.

[0032] The evaluation circuit is configured to process the measured values ​​of the corresponding measurement variable measured by the measurement circuit and determine the desired measurement variable. Therefore, the evaluation circuit typically includes a microprocessor, amplifier, and noise filter. The measurement and evaluation circuit can be a modular design and can communicate wirelessly, or it can be part of a single electronic measurement and evaluation unit housed within the flowmeter's casing.

[0033] The method for operating a magnetic induction flow meter according to the present invention, and particularly the method for operating a magnetic induction flow meter according to the present invention,

[0034] The flow meter has a housing with walls.

[0035] The magnetic field generating device, used to generate a magnetic field that passes through the shell wall, is arranged inside the shell.

[0036] The measuring electrodes are arranged on the housing wall;

[0037] The following steps are included:

[0038] - Detect the measured value of the first measured variable and the measured value of the second measured variable, which is different from the first measured variable.

[0039] Among them, the measured value of the corresponding measurement variable is determined relative to the reference potential, especially the ground potential, between two measuring electrodes or at the measuring electrodes;

[0040] - Determine the Reynolds number, which depends on the first and second measured variables.

[0041] The measured value of a single variable is insufficient to determine the Reynolds number of the medium in the pipe because the two unknowns, namely the Reynolds number and the flow rate of the medium, cannot be determined by a single variable. For this reason, the entire measurement system is typically configured such that the induced measurement voltage is independent of the Reynolds number over the largest possible range. Thus, information about the current Reynolds number is lost. Therefore, it is particularly advantageous to configure the flow meter to determine a second measurement variable related to the Reynolds number in addition to the first measurement variable used to determine the flow measurement value, and to consider both measurement variables to determine the Reynolds number. In this case, the measurement system does not need to be adapted to make the measured voltage as independent of the Reynolds number as possible, which significantly limits the design of the magnet system and the measurement system.

[0042] The flow measurement points according to the present invention include

[0043] - Pipes with diameter DN and openings, and

[0044] -A magnetic induction flowmeter according to the present invention;

[0045] Its features

[0046] The magnetic induction flow meter is arranged in the opening and has an installation depth D, which in particular satisfies 0.05≤D / DN≤0.4 and preferably satisfies 0.1≤D / DN≤0.2.

[0047] One embodiment provides that measuring electrodes are arranged on the housing wall such that, during a test measurement, the quotient of the current measured value of a first measuring variable and the current measured value of a second measuring variable bijectively corresponds to the Reynolds number of the medium in the tube in a Reynolds number range of at least 10,000 ≤ Re ≤ 100,000, especially 5,000 ≤ Re ≤ 500,000, and preferably 1,000 ≤ Re ≤ 1,000,000.

[0048] The placement of measuring electrodes on the flowmeter housing is essential for determining the Reynolds number. In order to determine the Reynolds number based on two measured variables, the quotient of the measured values, or the mathematical function describing the quotient of the measured values ​​of the corresponding measured variables as the Reynolds number varies with the medium in the pipe, must be bijective. This is determined by the position of the measuring electrodes on the housing.

[0049] The position of the measuring electrodes is optimized in such a way that the quotient U1 / U2 of the first and second measuring variables, particularly the first and second measuring voltages, is bijectively expressed as a relation to the Reynolds number of the flowing medium in the tube. Optimization can be performed experimentally or by means of simulation methods—for example, by means of finite element simulation.

[0050] For the quotient U1 / U2, assuming the flow velocity is generated by the corresponding induced measured voltage of the common flow velocity u, the following results are obtained:

[0051]

[0052] In this case, g(Re) is invertible.

[0053]

[0054] Also applied, where g -1It is the inverse function of g. The bijectivity of the quotient can be most easily achieved by arranging the first and second measuring electrodes on the housing such that the first correction factor f1(Re) is independent of the Reynolds number within the Reynolds number range. In this case, the second correction factor f2 must correspond bijectively to the Reynolds number. Therefore, the position of one or the third measuring electrode is ideally chosen such that the change in the correction factor f2(Re) describing the Reynolds number correlation of the second measured variable, or the slope of the quotient U1 / U2, is as large as possible for different Reynolds numbers.

[0055] However, it is advantageous that at least three measuring electrodes can be used to determine the measured variable. The bijectivity of the quotient can then be achieved because the first and second measuring electrodes are arranged on the housing such that the first correction factor f1(Re), hidden behind the induced measuring voltage, is independent of the Reynolds number within the Reynolds number range. In this case, the second correction factor f2 must bijectively correspond to the Reynolds number. Therefore, the position of the third measuring electrode is ideally chosen such that the variation of the correction factor f2(Re), or the slope of the quotient, is as large as possible for different Reynolds numbers. Thus, the correction factor f2(Re) can be determined by the measuring voltage determined between the first and third measuring electrodes, by the measuring voltage determined between the second and third measuring electrodes, or by the potential determined at the third measuring electrode relative to a reference potential.

[0056] The positioning of a single measuring electrode on the housing is crucial for determining the Reynolds number or kinematic viscosity. The Reynolds number is determined by measurements of two variables. The first measured variable is determined using a measuring circuit at the electrode pair. The second measured variable is also preferably determined similarly. However, the position of the single measuring electrode cannot be arbitrarily chosen. The quotient of the measured values ​​of the first and second measured variables must bijectively correspond to the Reynolds number of the flowing medium in the pipe. This means that the quotient of the measured values ​​of the first and second measured variables within the Reynolds number range can be described by a mathematical function bijectively to the Reynolds number, or the set of quotients of the measured values ​​bijectively corresponds to a linked set of Reynolds numbers within the Reynolds number range.

[0057] This is achieved, for example, by arranging the first measuring electrode pair radially at the front, as is the case in conventional flow meters, and arranging the third measuring electrode, or the third and fourth measuring electrodes, at the front or side of the housing, offset from the first measuring electrode pair.

[0058] Therefore, the measured value of the first measured variable is essentially independent of the Reynolds number, while the measured value of the second measured variable is related to the Reynolds number. However, this is not the only possibility for realizing the flowmeter according to the invention. It is also conceivable that all measuring electrodes are arranged such that the measured value at the measuring electrode, within or a portion of the Reynolds number range, is related to the Reynolds number. However, in this case, the quotient of the measured value must correspond bijectively to the Reynolds number so that the Reynolds number can be determined.

[0059] The evaluation circuit typically has a memory cell containing a first dataset with reference values ​​associated with a first and a second measured variable and, in particular, proportional to the quotient of the first and second measured variables. The memory cell also contains a second dataset with Reynolds numbers. The first and second datasets correspond bijectively. The evaluation circuit is configured to determine the corresponding Reynolds number of the medium in the pipe based on the first and second measured variables.

[0060] Non-volatile memories such as flash memory or EPROM are suitable as memory cells. This can be integrated into the evaluation circuitry or provided separately. The memory cell preferably has at least first and second datasets. Reference values ​​are stored in the first dataset. These are derived from computer simulations or calibration measurements. The reference values ​​can, for example, be the quotient of the simulated or measured values ​​of the first and second measured variables. The second dataset has Reynolds numbers assigned to the quotients. Alternatively, pairs consisting of Reynolds numbers and reference values ​​can be stored in the memory cell. Alternatively, mathematical functions assigning Reynolds numbers to the two measured variables or terms depending on the two measured variables can also be stored in the memory cell.

[0061] One embodiment provides a measurement circuit configured to determine a measured value of a first measurement variable between a first measurement electrode and a second measurement electrode.

[0062] The measurement circuit is configured to determine the measured value of a second measurement variable between the first and third measurement electrodes or between the second and third measurement electrodes.

[0063] The measurement circuit is preferably designed to determine a first potential difference U1 between a first pair of measuring electrodes and a second potential difference U2 between a second pair of measuring electrodes. The measurement voltage is determined either by directly measuring the potential difference between the two measuring electrodes or by measuring the potential difference prevailing at each measuring electrode relative to a reference potential and forming a difference. In this case, U1 = f1(Re)·S1·u and U2 = f2(Re)·S2·u are applied, where f1(Re) and f2(Re) each describe a Reynolds number-related correction factor. The determined measurement value is forwarded to an evaluation circuit, which includes a memory cell storing the reference value and the Reynolds number, or storing a mathematical function that assigns the Reynolds number to the reference value.

[0064] Advantageously, the flow meter has exactly three measuring electrodes. This reduces the number of potential leak points to three. This embodiment can be most easily achieved by extending a conventional magnetic induction flow meter with two measuring electrodes with another measuring electrode. The latter can be arranged on the side or front of the housing, offset from the first and second measuring electrodes.

[0065] Of particular advantage is that the three measuring electrodes are arranged in a straight line extending along the diameter of the end face of the housing, especially the front face. In this embodiment, when held in the predetermined mounting position, a much larger measuring signal is present at the respective pairs of measuring electrodes than in other cases.

[0066] However, if the measured signal strength plays only a secondary role, the offset of the third measuring electrode relative to the straight line intersecting the first and second measuring electrodes results in additional degrees of freedom for optimizing the Reynolds number-related measurement variables or for the second measuring variable.

[0067] One embodiment provides a measurement circuit configured to determine a measured value of a first measurement variable between first and second measurement electrodes.

[0068] The measurement circuit is configured to determine the measured value of a second measurement variable between the third and fourth measurement electrodes.

[0069] The measurement circuit is preferably designed to determine a first potential difference U1 between a first pair of measuring electrodes and a second potential difference U2 between a second pair of measuring electrodes. The measurement voltage is determined either by directly measuring the potential difference between the two measuring electrodes or by measuring the potential prevailing at each measuring electrode relative to a reference potential and forming a difference. In this case, U1 = f1(Re)·S1·u and U2 = f2(Re)·S2·u are applied, where f1(Re) and f2(Re) are correction factors associated with each Reynolds number. The determined measurement values ​​are forwarded to an evaluation circuit, which includes memory cells storing the reference value and the Reynolds number, or storing a mathematical function that assigns the Reynolds number to the reference value.

[0070] To avoid common-mode interference and thus minimize noise in the signal, it is advantageous that the two measured variables are not potentials relative to a reference potential, but rather the measured potential difference.

[0071] In traditional magnetic induction flowmeters, the positions of the magnet system and measuring electrodes are optimized such that the prevailing potential at each measuring electrode is linearly related to the flow velocity. If a third measuring electrode is now added, and the potential difference between the third measuring electrode and one of the two measuring electrodes is measured, the effect of the linearized measuring system is always included in the second measured variable. However, the latter should be Reynolds number related over the largest possible range of Reynolds numbers.

[0072] Therefore, it is particularly advantageous that the measured value of the second measured variable is tapped at the third and fourth measuring electrodes, which are positioned offset from the first measuring electrode pair. Consequently, the potential difference present on the second measuring electrode pair is also decoupled from the two potentials of the first measured variable.

[0073] It is particularly advantageous that the first measuring electrode pair is arranged along the diametrical direction or is arranged on the front of the housing.

[0074] One embodiment provides a housing that is at least partially cylindrical and has a side surface, wherein a third measuring electrode is disposed on the side surface and forms current contact with a dielectric.

[0075] In this configuration, the third measuring electrode can be formed from a single needle electrode, extend across the entire side surface of the housing, or be formed from the conductive side surface of the housing. By fixing the third measuring electrode to the side surface, further optimization possibilities for the corresponding Reynolds number-related measuring variables are opened up, thereby expanding the range in which the quotient of the two measuring variables bijectively corresponds to the Reynolds number.

[0076] Furthermore, this specific arrangement allows for the creation of particularly narrow flow meters.

[0077] One embodiment provides that first, second, and third measuring electrodes are arranged on the end face of the housing.

[0078] This is particularly advantageous because it avoids the troublesome sealing of the measuring electrodes on the sides of the predominantly cylindrical housing. Furthermore, the production of this particular flowmeter is quite low-maintenance. For applications with small-diameter pipes, the installation depth is so small that only a minimal proportion of the sides are in contact with the medium.

[0079] One embodiment provides that the first and second measuring electrodes are located on a circumference extending on the end face and arranged coaxially with the housing.

[0080] The area in which the third measuring electrode is arranged, or preferably where the third and fourth measuring electrodes are arranged, is circumferentially arranged.

[0081] Of particular advantage is that three measuring electrodes are arranged on the end face. Simulations have shown that it is advantageous for a conventional magnet system consisting of a coil core, a coil, and a return body in which the coil core extends directly to the end face, if one or two additional measuring electrodes are attached to the front end in addition to the two conventional measuring electrodes, especially to the circular area defined by the two measuring electrodes.

[0082] Ideally, the positioning application of the first and second measuring electrodes satisfies R 12 / R f ≥0.8 and preferably R 12 / Rf ≥0.9, where R f It is the radius from the front to the center point, where the front is usually circular, and R is the radius from the front to the center point. 12 The distances between the first and second measuring electrodes and the center point are described.

[0083] One embodiment provides that the first and second measuring electrodes are arranged in a straight line extending from the end face.

[0084] The third and fourth measuring electrodes intersect the straight line.

[0085] The third and fourth measuring electrodes are arranged between the first and second measuring electrodes.

[0086] It has been surprisingly shown that, in order to satisfy the bijective relationship between two measurements, it is sufficient to place two additional measuring electrodes between the conventional two measuring electrodes, where all four measuring electrodes are essentially in a straight line.

[0087] By arranging all measuring electrodes in a straight line, maximum signal strength can be achieved for both measuring electrode pairs. Furthermore, this embodiment maintains bidirectional use of the flow meter within the pipeline.

[0088] One embodiment provides that the measuring electrodes are located on the circumference of concentric circles.

[0089] Wherein, the first measuring electrode and the second measuring electrode are located at a radius R 12 On one circumference of a circle,

[0090] The third and fourth measuring electrodes are located at a radius R 34 On one circumference of a circle,

[0091] The ratio of the two radii satisfies 0.2 ≤ R. 34 / R 12 ≤0.9, especially 0.3≤R 34 / R 12 ≤0.7 and preferably 0.4≤R 34 / R 12 Inequalities ≤ 0.6.

[0092] A particular advantage is that the ratio of the two radii mentioned above is maintained in the arrangement of the measuring electrodes. When the third and fourth measuring electrodes meet this condition, the induced measuring voltage is Reynolds number dependent, or the correction factor f(Re) has a particularly large Reynolds number dependence, making it possible to detect even very small changes in the Reynolds number of the medium.

[0093] One embodiment provides that, within the Reynolds number range of 10,000 ≤ Re ≤ 100,000, during test measurements, the current measured value of a first measurement variable is substantially proportional to the flow rate of the medium.

[0094] Within the Reynolds number range of 10,000 ≤ Re ≤ 100,000, during the test measurement period, the change in the current measured value of the second measurement variable is not constant as the Reynolds number increases.

[0095] At Reynolds numbers less than 1000, the flow rate lies in the transition region between turbulent and laminar flow, and f(Re) can no longer be described by a defined function. f(Re) exhibits hysteretic behavior or changes over time. At high Reynolds numbers, the flow profile is Reynolds number independent, and therefore f(Re) is constant for both measured variables. In this case, the Reynolds number cannot be determined.

[0096] One embodiment provides that, during test measurements, the flowing medium is a Newtonian fluid, particularly water.

[0097] During the test measurement, the flow meter is introduced into a pipe with a straight inlet cross-section of at least 20 DN and preferably at least 50 DN, such that a substantially symmetrical flow profile exists in the medium.

[0098] The pipe has a diameter of DN 80.

[0099] The distance between the end face and the opening of the pipe into which the flow meter is inserted describes the installation depth D.

[0100] The installation depth shall satisfy 0.05≤D / DN≤0.4 and preferably 0.1≤D / DN≤0.2.

[0101] This test measurement describes a measurement environment in which the condition for determining the Reynolds number, namely the bijectivity of the mapping from the quotient of two measured variables to the Reynolds number, is satisfied.

[0102] One embodiment provides the following method steps:

[0103] - A reference value is formed based on the measured values ​​of the first and second measured variables.

[0104] The reference value is proportional to the quotient of the measured value of the first measured variable and the measured value of the second measured variable; and

[0105] - Determine the Reynolds number as it varies with a reference value.

[0106] A particular advantage is that the Reynolds number is determined and output to the user. This makes it easy to check whether the measurement accuracy specified by the manufacturer is applied, or whether the current Reynolds number is outside the applicable range.

[0107] One embodiment provides the following method steps:

[0108] - Corrected flow rates and / or corrected volumetric flow rates are generated using a correction factor that depends on the Reynolds number; and / or

[0109] - The kinematic viscosity of the medium in the tube is determined by means of the measured value of the first or second measured variable and the determined Reynolds number.

[0110] Of particular advantage is that a correction factor, specifically one of two correction factors f1 and f2, for more accurate determination of flow rate and / or volumetric flow rate is stored in the storage unit. The correction factor can be determined in an analog method, or determined or measured in a calibration method.

[0111] By using a correction factor, the Reynolds number correlation deviation of flow measurement values ​​can be reduced, thereby improving the Reynolds number range that meets the specified measurement accuracy.

[0112] One embodiment provides that the function that assigns the Reynolds number to the quotient of the first and second measurement variables is bijective at least in the Reynolds number range of 10,000≤Re≤100,000, especially 5,000≤Re≤500,000 and preferably 1,000≤Re≤1,000,000.

[0113] The measured values ​​are output, for example, via a display connected to the flow meter. Alternatively, the display could be part of a smartphone or laptop computer and receive the measured values ​​to be displayed from the evaluation circuitry via a wireless connection. Alternative output units known in process automation are systems for data transmission, such as fieldbus or real-time Ethernet. Attached Figure Description

[0114] The invention will be explained in more detail with reference to the following figures. The following are shown:

[0115] Figure 1 : Perspective view and partial cross-sectional view of a magnetic induction flowmeter based on existing technology;

[0116] Figure 2 A longitudinal cross-sectional view of a magnetic induction flow meter installed in a pipeline, based on existing technology;

[0117] Figure 3 Front view of a first embodiment of the magnetic induction flowmeter according to the present invention;

[0118] Figure 4 Front view of a second embodiment of the magnetic induction flowmeter according to the present invention;

[0119] Figure 5Longitudinal cross-sectional view of a first embodiment of a magnetic induction flowmeter with additional blades according to the present invention;

[0120] Figure 6 : A longitudinal cross-sectional view of a third embodiment of the magnetic induction flowmeter according to the present invention;

[0121] Figure 7 : A longitudinal cross-sectional view of a fourth embodiment of the magnetic induction flowmeter according to the present invention;

[0122] Figure 8 Two views, where the first view depicts the functions f1(Re) and f2(Re) as a function of Reynolds number, and the second view depicts the quotient g of the two functions f1(Re) and f2(Re) as a function of Reynolds number;

[0123] Figure 9 : A view showing the error for various electrode arrangements as the medium flow rate varies; and

[0124] Figure 10 : Flowchart of an embodiment of a method for operating a magnetic induction flowmeter. Detailed Implementation

[0125] First, based on Figure 1 The perspective and partial cross-sectional views are used to explain the measurement principle on which the invention is based. The flow meter 1 includes a generally cylindrical housing 3 with a predetermined outer diameter. The housing is adapted to the diameter of an orifice located in the wall of a pipe 13. Figure 1 Not shown in the text but Figure 2 As shown, the flow meter 1 is inserted into the pipe 13 in a fluid-tight manner. The medium to be measured flows in the pipe 13, and the flow meter 1 is immersed in the medium almost perpendicular to the flow direction of the medium, indicated by the wavy arrow 12. The front end 2 of the housing 3, which extends into the medium, is fluid-tightly sealed to the front portion 6 made of insulating material. A magnetic field 8 is generated by means of a coil arrangement 9 arranged in the housing 3, which extends through the front end into the medium. A coil core 7, at least partially made of soft magnetic material and arranged in the housing 3, terminates at or near the front end. A return element 10 surrounding the coil arrangement 9 and the coil core 7 is configured to return the magnetic field 8 extending through the front end into the housing 3. The coil core 7, the coil arrangement 9, and the return element 10 form a magnetic field generating device. First and second current measuring electrodes 4, 5 are arranged in the front portion 6 and contact the medium. The voltage induced based on Faraday's law of induction can be tapped on the measuring electrodes 4, 5 by means of a measuring and / or analyzing unit 11. This is maximized if the flow meter is installed in pipe 13 such that the plane spanned by the straight line intersecting the two measuring electrodes 4, 5 and the longitudinal axis of the flow meter extends perpendicular to the flow direction 12 or the longitudinal axis of pipe 21.

[0126] Figure 2 The longitudinal section of a flow meter 1 installed in a pipe is shown. The flow meter 1 is secured to the pipe 13 in a fluid-tight manner by, for example, a threaded connector 14 inserted into and welded to the wall of the pipe 13. This configuration of the measuring point is particularly suitable because the threaded connector 14 can be inserted into and welded into the pipe 13 first, and only then must the flow meter 1 be inserted into the threaded connector 14, screwed in, and sealed by means of a seal 15. This results in an unknown installation angle due to the installation. The first, second, third, and fourth measuring electrodes 4, 5, 19, and 20 are arranged symmetrically on the front end 2 with respect to the center point 23 of the front end 2. All four measuring electrodes 4, 5, 19, and 20 are in a straight line. The installation depth D indicates the depth to which the flow meter is inserted into the medium or extends into the pipe.

[0127] Figures 3 to 7 Different embodiments of the magnetic induction flowmeter according to the present invention are shown. The difference between the embodiments lies in the variation of the positioning of the measuring electrodes. For clarity of the drawings, illustrations of the magnetic field generating device are omitted. Figure 1 Alternatively, each of versions 2 discloses a magnet system comprising a coil, a coil core, and a return body. However, other magnetic field generating devices installed in magnetic induction flowmeters are also known. The precise arrangement of the measuring electrodes depends on the geometry and arrangement of the magnetic field generating device. Therefore, this must be considered when optimizing the ideal arrangement of the measuring electrodes.

[0128] Figure 3 A schematic front view of a first exemplary embodiment of the flowmeter according to the invention is shown. Arrows indicate the flow direction 12 of the flowing medium. The ideal installation orientation requires a straight reference line 21 intersecting the measuring electrode pair to extend perpendicular to the flow direction 12 of the medium. First and second measuring electrodes 3, 4 are arranged on the straight reference line, located on end face 22, and their positioning is adapted to a magnetic field generating device such that the induced measuring voltage applied to the two measuring electrodes 3, 4 is linear within a specified Reynolds number range. In addition to the first and second measuring electrodes 3, 4, third and fourth measuring electrodes 19, 20 are also arranged on end face 22. The third and fourth measuring electrodes 19, 20 are also located on the straight reference line 21 and are arranged between the first and second measuring electrodes 4, 5. The first and second measuring electrodes 4, 5 are located at a radius R. 12 On the circumference, and the third and fourth measuring electrodes are located on a circle with radius R. 34 On the circumference. According to this embodiment, R 34 <R 12 .

[0129] The measuring circuit is designed such that it taps a first potential difference U1 between the first and second measuring electrodes 4 and 5, and a second potential difference U2 between the third and fourth measuring electrodes 19 and 20, where U1 = f1(Re)·S1·u and U2 = f2(Re)·S2·u, where f1(Re) and f2(Re) each describe a Reynolds number-related correction factor. The positioning of the third and fourth measuring electrodes 19 and 20 is optimized such that the quotient U1 / U2 of the first and second potential differences is bijective with respect to the Reynolds number of the flowing medium in the tube, or a mathematical function that depends on the first and second potential differences and maps the Reynolds number to this quotient is bijective. This arrangement can be optimized experimentally or by means of simulation methods—e.g., by means of finite element simulation.

[0130] For the quotient U1 / U2, the following results are obtained:

[0131]

[0132] In this case, gRe is reversible.

[0133]

[0134] It is also used, where g -1 It is the inverse function of g. The bijectivity of the quotient can be achieved most easily because the first and second measuring electrodes are attached to the housing such that the first correction factor f1(Re) is independent of the Reynolds number in the Reynolds number range. In this case, the second correction factor f2 must correspond bijectively to the Reynolds number.

[0135] The measurement circuit is configured to connect the potential difference between the first and second measuring electrodes 3 and 4 and the potential difference at the third and fourth measuring electrodes 19 and 20, or to measure the potential at the respective measuring electrodes relative to a reference potential. The measurement data is forwarded to an evaluation unit, which includes a storage unit storing the reference value and the Reynolds number. The evaluation circuit is configured to determine the Reynolds number of the medium in the pipe based on the measured data and the stored reference data. If the Reynolds number is known, the kinematic viscosity can be calculated using the measured value of a first or second measured variable, or a measured value of a known flow rate or volumetric flow rate. The measurement circuit, evaluation circuit, and storage unit may be arranged on the electronic unit in a manner different from that described in the schematic diagram.

[0136] According to the first embodiment, a measuring electrode with a measuring voltage least independent of the Reynolds number is located on a circumference surrounding a region in which two measuring electrodes with Reynolds number-related measuring voltages are arranged. However, by adapting the magnet system, the measuring voltage applied to the internal measuring electrode can also be linearly related to the flow velocity, and the measuring voltage applied to the external measuring electrode can be Reynolds number-related. According to the invention, it must be satisfied that the quotient of the two induced and measured measuring voltages must be bijective within a defined Reynolds number range.

[0137] Figure 4 A front view of a second embodiment of a magnetic induction flowmeter according to the present invention is shown. In this embodiment, four measuring electrodes 4, 5, 19, 20 are arranged on the front end 2 of the flowmeter. A first measuring electrode axis 24 intersects with a second measuring electrode pair 19, 20, and a second measuring electrode axis 25 intersects with a first measuring electrode pair 4, 5. The two measuring electrode axes 24, 25 extend substantially parallel to each other. A straight reference line 21, dividing the front end into two equal planes and extending parallel to the first or second measuring electrode axis 24, 25, passes through the center point 23 of the front end 2. One of the two measuring electrodes 19, 20 forming the second measuring electrode pair intersects the center point 23 with a second radius. One of the two measuring electrodes 4, 5 forming the first measuring electrode pair intersects the center point 23 of the front end 2 with a first straight line such that the straight reference line 21 and the first straight line cross an angle β. The first straight line intersecting the center point 23 and one of the two measuring electrodes 4, 5 forming the first measuring electrode pair, together with the straight reference line 21, crosses an angle α. If this angle is chosen so that α = β = 0°, the first embodiment is achieved. Starting with the magnet system, angles α and β can be optimized such that a measurement voltage independent of the Reynolds number is induced at one measuring electrode pair and a measurement voltage dependent on the Reynolds number is induced at the other measuring electrode pair, wherein the corresponding correlation applies to a finite Reynolds number range. Furthermore, the straight reference line 21 is also oriented perpendicular to the flow direction of the medium. The flow meter is mounted in the pipe such that the flow direction of the medium extends perpendicular to the straight reference line 21.

[0138] Figure 5 A modified longitudinal cross-sectional view of a first embodiment of the flow meter according to the present invention is shown. Figure 1 Conversely, the front end 2 has blades 26. Therefore, the front end 2 is not formed by a single front end, but by multiple front ends that extend partially perpendicularly or parallel to each other. This also means that the measuring electrodes can be arranged on the sides or front ends of the blades 26. However, according to the first embodiment, the measuring electrodes are not attached to the blades 26. The measuring electrodes 4, 5, 19, and 20 are located in the region between the blades 26 and the edge region of the front end 2. Each of the first and second measuring electrodes 4 and 5 has a distance R from the center point of the front end. 12The positions of the two measuring electrodes 4 and 5 are optimized so that the correction factor used to determine the flow rate is independent of the Reynolds number. The center point of the front end is located on the longitudinal plane of the flowmeter, which is also a mirror surface. The third and fourth measuring electrodes 19 and 20 are located at a distance of R from the center point. 34 On the perimeter of a circle with radius R. The positions of the two measuring electrodes 19 and 20 are optimized such that the correction factor used to determine the flow velocity depends on the Reynolds number. 34 <R 12 Applicable to Figure 5 The example shown.

[0139] Figure 6 A longitudinal cross-sectional view is shown of a second embodiment in which the third and fourth measuring electrodes 19, 20 are arranged on the side surface (28) of the housing and the first and second measuring electrodes 4, 5 are arranged on the front end 2. In this embodiment, the arrangement of the measuring electrodes 4, 5 on the front end is adapted to a magnetic field generating device such that the flow measurement value is linearly correlated with the determined measurement voltage over the largest possible Reynolds number range. The positioning of the measuring electrodes 19, 20, associated with the magnet system, arranged on the sheath is selected such that the measurement voltage induced on the two measuring electrodes is Reynolds number correlated over the largest possible Reynolds number range. The optimization of the two measuring electrodes 19, 20 occurs such that the slope of the correction factor f(Re) is as large as possible with respect to the Reynolds number.

[0140] Magnetic induction flowmeters are known in the art, which have measuring electrodes specifically attached to the side surface (28) of the housing. Therefore, the magnetic field generating device is also adapted to make the induced measuring voltage linearly related to the flow velocity. From such a flowmeter, the arrangement of the first and second measuring electrodes (4, 5) is selected according to the magnet system such that the induced measuring voltage is Reynolds number related over the largest possible Reynolds number range, or such that the gradient of the correction factor is as large as possible with increasing Reynolds number.

[0141] Figure 7 A longitudinal cross-section of the fourth embodiment is shown. In addition to the first and second measuring electrodes 4 and 5, both arranged on the front end 2, a third measuring electrode 19 is also positioned on the front end. The distance between the first and second measuring electrodes 4 and 5 defines the diameter of the circle. The third measuring electrode 19 is located outside the circular region. According to the fourth embodiment, the measuring circuit is configured such that it taps the measuring voltage at the first and second measuring electrodes 4 and 5 and the potential relative to ground at the third measuring electrode 19, or the measuring voltage between the third and the first or second measuring electrodes 19, 4 or 19, 5.

[0142] All embodiments apply, meaning the positioning of the measuring electrode relative to the magnetic field generating device must be chosen such that a first measuring variable unrelated to Reynolds numbers within the Reynolds number range and a second measuring variable related to Reynolds numbers within the same Reynolds number range can be determined. The quotient of the two measuring variables, describing the bijective mathematical function for different Reynolds numbers, must in particular be true.

[0143] Figure 8 Two views are shown. The first view illustrates the relationship between the various correction factors f1, f2 and the Reynolds number of the flowing medium in the pipe, and the second view illustrates the relationship between the quotient g of the correction factors and the Reynolds number of the flowing medium in the pipe. These two views are limited to approximately 10... 3 Up to 10 7 Within the Reynolds number range. Correction factors f1 and f2 are linked to one of the two potential differences tapped by different measuring electrode pairs, respectively. The curves of functions f1 and f2 have three ranges I, II, and III. In the first range I and the third range III, the curve of f1 is not constant. In this example, the curve has a negative slope in the first range I and a positive slope in the third range III. Conversely, the curve of f1 is constant in the second range II. The flowmeter is linear for this Reynolds number range. The second function f2 is bijective, at least in the second range. In the example shown, the curve of f2 is also bijective in the first range I and the third range III. This results in the quotient g being bijective in the first to the three ranges I, II, and III. Therefore, the Reynolds number can be explicitly assigned to each quotient of the measurement data for the two measured variables. This means that if the value of g can be determined, the corresponding Reynolds number can be derived. For the range where the flow rate is sensitive to changes in the Reynolds number, see ranges I and III, a Reynolds number-related correction function can be considered to correct for measurement bias.

[0144] Figure 9A view illustrating the effect of the position of the measuring electrode at the front end on the Reynolds number correlation of the induced measuring voltage is shown. This view maps the Reynolds number-dependent measurement error to the flow velocity. The Reynolds number depends on the flow velocity. Measurements were taken at five different measuring electrode positions (distances of 5, 7, 9, 9.5, and 11 mm from the center point), and the deviations from the actual flow values ​​were determined (curve AE). The value following the symbol “e” indicates the radius of the imaginary circle in millimeters where the measuring electrode is located. The measurement data show that at a distance of 9.5 mm, the deviation of the flow measurement values ​​over the entire depicted Reynolds number range is substantially independent of the Reynolds number, or the error is always less than 2.5% (see dashed line B). However, if the measuring electrode is arranged on a circle with a radius of 5 mm, it is no longer possible to assume a correction factor independent of the Reynolds number. Measurement deviations of up to 20% exist (see curve E). With the aid of a flowmeter having a pair of measuring electrodes on a circumference of 9.5 mm and an additional pair of measuring electrodes on a circumference of 5 mm radius, the Reynolds number can now be determined, or a Reynolds number-related correction for the measuring voltage can now be performed, taking into account one of the two measuring voltages applied to each measuring electrode pair.

[0145] Figure 10 A flowchart illustrating an embodiment of a method for operating a magnetic induction flowmeter is shown. In a first step, a first potential difference U1 is measured at a first measuring electrode pair. In a second step, a second potential difference U2 is measured at a second measuring electrode pair. Alternatively, the potential of the corresponding measuring electrode relative to a reference potential can be measured in both steps, and this difference can be generated, for example, in an evaluation circuit. The two first steps do not necessarily have to be performed consecutively, but can also be performed simultaneously. Alternatively, the second potential difference U2 can be measured first, followed by the first potential difference U1. However, to determine the flow rate or volumetric flow rate, it is generally considered that different, especially opposite, DC voltages are applied to each coil and the magnetic field is adjusted in two measurement phases. Thus, zero-point offset can be compensated. The measurement of the potential difference or potential is performed via a measuring circuit. The evaluation circuit generates a quotient of the two measured values, especially the potential difference, and compares this quotient with a Reynolds number assigned to the determined quotient. The Reynolds number is stored in a memory. Alternatively, a mathematical equation or mathematical function assigning the Reynolds number or a range of Reynolds numbers to the quotient can also be stored in memory. Alternatively, data already determined in the calibration method can also be stored in memory. The data can be reference values ​​measured in the calibration method, but it can also be interpolated or extrapolated values, or, for example, values ​​of a smoothed characteristic curve or fitted function of the measured data. Reference values ​​can be determined in the calibration method through experimentation and / or by means of simulation procedures.

[0146] List of reference numerals

[0147] 1. Flow meter

[0148] 2. Frontend

[0149] 3. Shell

[0150] 4 First measuring electrode

[0151] 5 Second measuring electrode

[0152] 6. Front

[0153] 7. Coil core

[0154] 8. Magnetic field lines

[0155] 9. Coil Arrangement

[0156] 10 returned items

[0157] 11 Measurement, operation and / or evaluation unit

[0158] 12. Flow direction

[0159] 13 Pipelines

[0160] 14 Threaded fasteners

[0161] 15. Seals

[0162] 16 Measuring electrodes

[0163] 17. Radius R 12

[0164] 18. Radius R 34

[0165] 19 Third measuring electrode

[0166] 20 Fourth measuring electrode

[0167] 21 straight reference line

[0168] 22 End face

[0169] 23. Center point

[0170] 24 First measuring electrode axis

[0171] 25 Second measuring electrode axis

[0172] 26 blades

[0173] 27 Vertical axis

[0174] 28 side surfaces

Claims

1. A magnetic-inductive flowmeter (1) which can be inserted into a pipe through which a medium flows, the magnetic-inductive flowmeter (1) comprising: - a housing (3), wherein the housing (3) has a housing wall; - at least a first measuring electrode (4) and a second measuring electrode (5), which are arranged on the housing wall so as to each form galvanic contact with the flowing medium; - at least one magnetic-field generating device for generating a magnetic field through the housing wall, wherein the magnetic-field generating device is arranged in the housing (3); and - a measuring circuit which is configured to determine at least a first measuring variable, wherein a measured value of the first measuring variable is measured between two measuring electrodes or at a measuring electrode with respect to a reference potential, characterized in that the evaluation circuit is configured to determine a Reynolds number and / or a kinematic viscosity value of the medium in the pipe by means of a measured value of the first measuring variable and a measured value of a second measuring variable which is different from the first measuring variable, wherein the measured value of the second measuring variable is determined between two measuring electrodes or at one measuring electrode with respect to a reference potential, wherein at least one measuring electrode which is configured to determine the measured value of the second measuring variable is different from a measuring electrode which is configured to determine the measured value of the first measuring variable, wherein the measuring electrodes are arranged on the housing wall such that, during a test measurement, a quotient of a current measured value of the first measuring variable and a current measured value of the second measuring variable bijectively corresponds to a Reynolds number of the medium in the pipe at least in a Reynolds number range of 10,000 < Re < 100,000.

2. The flowmeter (1) according to claim 1, wherein the reference potential is a ground potential.

3. The flowmeter (1) according to claim 1, wherein, the Reynolds number of the medium in the pipe is at least in a Reynolds number range of 5,000 < Re < 500,000.

4. The flowmeter (1) according to claim 1, wherein the Reynolds number of the medium in the pipe is at least in a Reynolds number range of 1,000 < Re < 1,000,000.

5. The flowmeter (1) according to claim 1, wherein the measuring circuit is configured to determine the measured value of the first measuring variable between the first measuring electrode (4) and the second measuring electrode (5), wherein the measuring circuit is configured to determine a measured value of a second measuring variable between the first measuring electrode (4) and a third measuring electrode (19) or between the second measuring electrode (5) and the third measuring electrode (19).

6. The flowmeter (1) according to claim 1, wherein the measuring circuit is configured to determine the measured value of the first measuring variable between the first measuring electrode (4) and the second measuring electrode (5), wherein the measuring circuit is configured to determine a measured value of the second measuring variable between a third measuring electrode (19) and a fourth measuring electrode (20).

7. The flow meter (1) according to claim 5 or 6, wherein, the housing (3) is at least partially cylindrical and has a lateral surface (28), wherein the third measuring electrode (19) is arranged on the lateral surface (28) and forms galvanic contact with the medium.

8. The flow meter (1) according to claim 5 or 6, wherein the first measuring electrode (4), the second measuring electrode (5) and the third measuring electrode (19) are arranged on an end face of the housing (3).

9. The flow meter (1) according to claim 8, wherein the first measuring electrode (4) and the second measuring electrode (5) are located on a circumference extending on the end face (22) and are arranged coaxially to the housing (3), wherein the circumference surrounds an area in which the third measuring electrode (19) is arranged.

10. The flow meter (1) according to claim 9, wherein the circumference surrounds an area in which the third measuring electrode (19) and the fourth measuring electrode (20) are arranged.

11. The flow meter (1) according to claim 8, wherein the first measuring electrode (4) and the second measuring electrode (5) are arranged on a straight line extending on an end face (22), wherein the third measuring electrode (19) and the fourth measuring electrode (20) are intersected by the straight line, wherein the third measuring electrode (19) and the fourth measuring electrode (20) are arranged between the first measuring electrode (4) and the second measuring electrode (5).

12. The flow meter (1) according to any one of claims 9 to 11, wherein the measuring electrodes (4, 5, 19, 20) are located on a circumference of a concentric circle, wherein the first measuring electrode (4) and the second measuring electrode (5) are located on one circumference of circumferences having a radius R 12 , wherein the third measuring electrode (19) and the fourth measuring electrode (20) are located on one circumference of circumferences having a radius R 34 , wherein the ratio of the two radii satisfies the inequality 0.2 34 / R 12 ≤ 0.

9.

13. The flow meter (1) according to claim 12, wherein The ratio of the two radii satisfies the inequality 0.3 ≤ R 34 / R 12 ≤ 0.

7.

14. The flow meter (1) according to claim 12, wherein, The ratio of the two radii satisfies the inequality 0.4 ≤ R 34 / R 12 ≤ 0.

6.

15. The flow meter (1) according to any one of claims 1 to 6, wherein, during the test measurement in a Reynolds number range of 10,000 < Re < 100,000, the current measurement value of the first measurement variable is substantially proportional to the flow velocity of the medium, wherein, during the test measurement in a Reynolds number range of 10,000 < Re < 100,000, the change of the current measurement value of the second measurement variable is not constant as the Reynolds number increases.

16. The flow meter (1) according to claim 8, wherein, during the test measurement, the flow medium is a Newtonian fluid, wherein, during the test measurement, the flow meter (1) is introduced into a pipe having a straight inlet cross section of at least 20 DN, so that there is a substantially symmetrical flow profile in the medium, wherein the diameter DN of the pipe is DN 80, wherein the distance between the end face (22) and the opening of the pipe into which the flow meter (1) is inserted describes a mounting depth D, wherein the mounting depth D fulfills 0.05 < D / DN < 0.

4.

17. The flow meter (1) according to claim 16, wherein the flow medium is water.

18. The flow meter (1) according to claim 16, wherein During the test measurement, the flowmeter (1) is introduced into a pipe having a straight inlet cross section of at least 50 DN, such that there is a substantially symmetrical flow profile in the medium.

19. The flowmeter (1) according to claim 16, wherein the installation depth D fulfils 0.1 < D / DN < 0.

2.

20. A method for operating a magnetic-inductive flowmeter (1) according to any one of claims 1 to 19, wherein the flowmeter (1) has a housing (3) with a housing wall, wherein a magnetic field generating device for generating a magnetic field through the housing wall is arranged in the housing, wherein the measuring electrodes are arranged on the housing wall; the method comprises the following method steps: - detecting a measurement value of a first measurement variable and a measurement value of a second measurement variable different from the first measurement variable, wherein the measurement values of the respective measurement variables are determined between two measuring electrodes or at a measuring electrode with respect to a reference potential; - determining a Reynolds number which depends on the first measurement variable and the second measurement variable, - forming a reference value from the measurement value of the first measurement variable and the measurement value of the second measurement variable, wherein the reference value is proportional to the quotient of the measurement value of the first measurement variable and the measurement value of the second measurement variable; and - determining a Reynolds number which varies with the reference value.

21. The method according to claim 20, wherein, the reference potential is a ground potential.

22. The method according to claim 20, comprising the method steps: - forming a corrected flow rate and / or a corrected volume flow by means of a correction factor which depends on the Reynolds number; and / or - determining a kinematic viscosity value of the medium in the pipe by means of the measurement value of the first measurement variable or the measurement value of the second measurement variable and the determined Reynolds number.

23. A flow measurement point, comprising: - a pipe (13) having a diameter DN and an opening, and - a magnetic-inductive flowmeter (1) according to any one of claims 1 to 19; characterized in that the magnetic-inductive flowmeter (1) is arranged in the opening and has an installation depth D.

24. The flow measurement point according to claim 23, wherein the installation depth D fulfils 0.05 < D / DN < 0.

4.

25. The flow measurement point according to claim 23, wherein, the installation depth D fulfils 0.1 < D / DN < 0.2.

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