Magnetic inductive flowmeter and method for operating a magnetic inductive flowmeter

Abstract

The invention relates to a magnetic-inductive flowmeter having a measuring tube for conducting a flowable medium, the measuring tube having a wall; at least three measuring electrodes which are arranged in the wall and which form an electrical contact with the flow medium; at least one magnetic-field generating device for generating a magnetic field through the medium; and a measuring circuit which is designed to ascertain at least one first measuring variable, wherein the measured value of the first measuring variable is ascertained at a first pair of measuring electrodes. The invention is characterized in that the evaluation circuit is designed to ascertain a Reynolds number and / or a kinematic viscosity value of the medium in the measuring tube using the measured value of the first measuring variable and the measured value of a second measuring variable which is different from the first measuring variable, the measured value of the second measuring variable being ascertained at a second pair of measuring electrodes.

Description

Background Technology

[0001] Magnetic induction flow meters are used to determine the velocity and volumetric flow rate of a medium flowing in a pipe. A magnetic induction flow meter has a magnet system that generates a magnetic field perpendicular to the direction of flow of the medium. One or more coils are typically used for this purpose. Furthermore, to achieve a predominantly uniform magnetic field, pole pieces are shaped and attached such that the magnetic lines of force extend across the entire cross-section of the pipe, thus being substantially perpendicular to the transverse axis of the measuring tube or parallel to its longitudinal axis. Measuring electrodes attached to the side surface of the measuring tube tap an electrical measuring voltage or potential difference applied perpendicular to the flow direction and the magnetic field, which occurs when the conductive medium flows in the flow direction when the magnetic field is applied. Because, according to Faraday's law of induction, the tapped measuring voltage depends on the velocity of the flowing medium, u, and with the aid of a known pipe cross-section, the volumetric flow rate of the medium can be determined from the induced measuring voltage U. For measuring voltage U, the following simplified equation applies:

[0002] U = f(Re)·u·S,

[0003] Here, S is the nominal signal strength, which depends on the sensor geometry and the magnetic field, and f(Re) is a correction factor that depends on the flow profile or Reynolds number. The correction factor f(Re) is usually assumed to be constant. However, this is not always the case. The nominal signal strength S is typically determined during instrument calibration and stored in the instrument.

[0004] The Reynolds number of the fluid flowing in the measuring tube is defined by the following formula.

[0005]

[0006] The diameter of the measuring tube is DN, the density of the medium is ρ, the dynamic viscosity of the medium is μ, and the kinematic viscosity of the medium is ν.

[0007] Magnetic induction flowmeters are highly sensitive to the Reynolds number of the medium in the measuring tube, as the Reynolds number determines the flow profile of the flowing medium. Depending on the pipe system, instrumentation, and installation scenario, the correction factor f(Re) can vary and differ from the assumed constant value by several percentage points. The arrangement of the measuring electrodes and the magnetic field generating device is typically optimized to make the flowmeter as linear as possible; that is, the induced measurement voltage is independent of the Reynolds number over the widest possible range, or, for a specific application, the Reynolds number range of interest. Therefore, flowmeters with a few percent deviation in the transitional flow region and approximately 0.2% deviation for flows with turbulent profiles are already industry standards.

[0008] In traditional magnetic induction flowmeters, the flow velocity and the Reynolds number-dependent correction factor f(Re) cannot be simultaneously determined by the induced flow velocity in the medium and by the measuring voltage tapped by the measuring electrodes. Therefore, f(Re) is assumed to be constant. Consequently, it is absolutely necessary to adapt the electrode system, magnet system, and pipe geometry of the magnetic induction flowmeter so that f(Re) remains constant over the maximum possible Reynolds number range. This adaptation always requires limitations, such as signal strength loss or dependence on the pole piece geometry.

[0009] EP 0 770 855 A1 teaches a magnetic induction flowmeter for measuring non-Newtonian liquids, the flowmeter having analytical electronics designed to determine the flow index and apparent viscosity of the flowing medium. Two measuring electrodes are arranged in a measuring tube such that two radii intersecting the respective measuring electrodes span an angle of 90° or 120°. A changeover switch is designed to connect two coils in series in the same or opposite directions. The potential difference between the two measuring electrodes is continuously determined for the setting of the two coils and is used to determine the flow index and apparent viscosity of the medium.

[0010] Therefore, it is known in principle from the prior art that additional flow characteristics can be determined by modifying the magnetic field generating device and the arrangement of the measuring electrodes. However, a known drawback of the prior art is that, in order to determine the flow index, at least two measurement stages with different coil arrangements are always required, in which the magnetic field must be stabilized again in each case before the measurement can be performed. Summary of the Invention

[0011] Therefore, the present invention is based on the purpose of specifying a magnetic induction flow meter and a method for operating the magnetic induction flow meter, which is operated using a coil setup.

[0012] This objective is achieved by the magnetic induction flowmeter according to the present invention and the method for operating the magnetic induction flowmeter.

[0013] The magnetic induction flowmeter according to the invention comprises a measuring tube for conducting a flowable medium, wherein the measuring tube has a wall; at least three measuring electrodes arranged in the wall and in electrical contact with the flow medium; at least one magnetic field generating device for generating a magnetic field through the measuring tube; and a measuring circuit designed to determine at least one first measuring variable, wherein the measured value of the first measuring variable is determined at a first measuring electrode pair, particularly at the first and second measuring electrodes, and characterized in that an analysis circuit is designed to determine the Reynolds number and / or kinematic viscosity value of the medium in the measuring tube by means of the measured values ​​of the first and second measuring variables, wherein the measured value of the second measuring variable is determined at the second measuring electrode pair or at a third measuring electrode relative to a reference potential.

[0014] This is particularly advantageous if the flowmeter has at least three measuring electrodes. As a result, the flowmeter is designed such that the measured variable tapped at the first measuring electrode pair is independent of the Reynolds number, and the measured variable tapped at the second measuring electrode pair, or measured relative to a reference potential at the third measuring electrode, depends on the Reynolds number. If both measured variables are known, the Reynolds number can be determined. Without switching coil settings, the Reynolds number can be determined in a single measurement phase.

[0015] 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 measured voltage is determined either by directly measuring the potential difference between the two measuring electrodes or by measuring the dominant potentials relative to a reference potential at each measuring electrode and calculating the difference. Here, U1 = f1(Re)·S1·u and U2 = f2(Re)·S2·u, where f1(Re) and f2(Re) each describe a correction factor dependent on the Reynolds number. The determined measured values ​​are forwarded to an analysis circuit, which includes a storage unit where the reference value and the Reynolds number are stored, or a mathematical function assigning the Reynolds number to the reference value is stored.

[0016] Alternatively, the first potential difference U1 is measured at the first measuring electrode pair, and the potential relative to the reference potential is measured at the third measuring electrode.

[0017] It is particularly advantageous if the analysis circuit is designed to calculate the quotient of the measured values, compare them with a reference value in the data memory, and determine or read the Reynolds number assigned to the reference value. Alternatively, a mathematical function can be stored in the memory cell that assigns the measured values ​​of the first and second measured variables, or terms depending on the first and second measured variables, to the Reynolds number of the medium. In this case, the analysis circuit is designed to determine the Reynolds number using the measured values ​​of the two measured variables and the stored mathematical function. If the Reynolds number, flow rate, and pipe diameter are known, the kinematic viscosity can be calculated by applying v = u·DN / Re.

[0018] 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 various measured variables. Many different designs exist, each with its advantages and disadvantages. Firstly, a measurement circuit can be designed to be connected at one of the measuring electrodes to a potential relative to a reference potential. Even if one of the two measuring electrodes fails, the flow rate can still be determined based on the identified potential. The housing potential or ground potential is suitable as the reference potential. On the other hand, a measurement circuit can be designed to detect and receive the dominant potential difference between the two measuring electrodes. Therefore, a measurement circuit typically includes an analog-to-digital converter (ADC) that converts the input signal—in this case, the potential difference currently present in the corresponding measuring electrode pair—into digital data, which is then further processed or stored by analysis circuitry. However, other measurement converters or transducers in digital measurement technology are also known and suitable.

[0019] Analysis circuits are designed to process measurements taken by measurement circuits and to identify the sought-after measurement variable from noise. Therefore, analysis circuits typically include a microprocessor, amplifier, and noise filter. Measurement and analysis circuits can be modular designs and can communicate via wireless connections, or they can be part of a single measurement and analysis electronics housed within an instrument housing.

[0020] Advantageous embodiments of the present invention are as follows.

[0021] According to one embodiment, the measuring electrodes are arranged in the measuring tube such that, in a test measurement, the quotient of the current measured values ​​of the first and second measuring variables corresponds bijectively to the Reynolds number of the flowing medium in the measuring tube, at least within the Reynolds number range of 10,000≤Re≤100,000, especially 5,000≤Re≤500,000, and preferably 1,000≤Re≤1,000,000.

[0022] The position of the third measuring electrode is optimized such that the quotient of the first and second potential differences, U1 / U2, exhibits a bijective relationship with the Reynolds number of the flowing medium in the measuring tube. Optimization can be performed using experimental or simulation methods, such as finite element simulation.

[0023] For the quotient U1 / U2, assuming the flow velocity in the measuring tube is constant, or the corresponding induced measurement voltage originates from the common flow velocity u, the results are as follows:

[0024]

[0025] If g(Re) is invertible, the following also applies:

[0026]

[0027] Where g -1It is the inverse function of g. The bijectivity of the quotient can be most easily achieved by attaching the first and second measuring electrodes to the measuring tube such that the first correction factor f1(Re) is independent of the Reynolds number over the Reynolds number range. In this case, the second correction factor f2 must correspond bijectively to the Reynolds number. Therefore, the position of the third measuring electrode is ideally chosen such that the slope of the correction factor f2(Re), or the quotient, varies as much as possible for different Reynolds numbers.

[0028] The positions of the measuring electrodes within the measuring tube are crucial for determining the Reynolds number or kinematic viscosity. The Reynolds number is determined by the measured values ​​of two variables. The first variable is determined by the measuring circuit at the electrode pair. This is preferably also applied to the second variable. However, the positions of the measuring electrodes cannot be arbitrarily chosen. The quotient of the measured values ​​of the first and second variables must bijectively correspond to the Reynolds number of the flowing medium in the measuring tube. This means that the quotient of the measured values ​​of the first and second variables, measured over the Reynolds number range, can be described by a function bijectively to the Reynolds number, or that the set of quotients of the measured values ​​over the Reynolds number range bijectively corresponds to the set of associated Reynolds numbers.

[0029] This is achieved, for example, by attaching the first measuring electrode pair to the measuring tube in a completely opposite manner, as is customary in conventional flow meters, and by arranging the third measuring electrode or the third and fourth measuring electrodes offset from the first measuring electrode pair.

[0030] 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 depends on the Reynolds number. However, this is not the only possibility for implementing the flowmeter according to the invention. It is also conceivable that all measuring electrodes are arranged such that the measured value tapped at the measuring electrode depends on the Reynolds number over or partially over the Reynolds number range. 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.

[0031] The analysis circuit typically has a storage unit containing a first dataset of reference values ​​associated with and particularly proportional to the quotient of the first and second measured variables, and a second dataset containing Reynolds numbers, wherein the first and second datasets are bijectively corresponding, and wherein the analysis circuit is designed to determine the corresponding Reynolds number of the medium in the measuring tube based on the first and second measured variables.

[0032] Non-volatile memories such as flash memory or EPROM are suitable as storage units. This can be integrated into the analysis circuitry or provided separately. The storage unit preferably has at least first and second data sets. Reference values ​​are stored in the first data set. These reference values ​​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 data set has Reynolds numbers assigned to the quotients. Alternatively, in each case, a pair consisting of Reynolds numbers and reference values ​​can be stored in the storage unit. Alternatively, a mathematical function assigning Reynolds numbers to the two measured variables or to terms depending on the two measured variables can also be stored in the storage unit.

[0033] Tests and measurements are performed using experimental or simulation procedures.

[0034] According to the first embodiment, the measuring electrodes are substantially located in the cross-sectional plane, wherein the first radius intersecting the second measuring electrode and the second radius intersecting the third measuring electrode span an angle α, wherein α ≥ 20°, especially α ≥ 30°, preferably 40° ≤ α ≤ 60°, wherein the measuring circuit is designed to determine the measured value of a first measuring variable between the first and second measuring electrodes, and wherein the measuring circuit is designed to determine the measured value of a second measuring variable between the first and third measuring electrodes or the measured value of a second measuring variable relative to a reference potential at the third measuring electrode.

[0035] It is advantageous if the flow meter has exactly three measuring electrodes. This reduces the number of potential leakage points to three. This embodiment can be most easily achieved by adding another measuring electrode to a conventional magnetic induction flow meter that has two measuring electrodes. While maintaining the required angle, a magnetic induction flow meter that satisfies the prerequisite for determining the Reynolds number of the medium can thus be realized.

[0036] According to the second embodiment, the first measuring electrode axis intersecting with the first and second measuring electrodes and the second measuring electrode axis intersecting with the third and fourth measuring electrodes extend substantially parallel to each other, wherein the measuring circuit is designed to determine the measured value of a first measuring variable between the first and second measuring electrodes, and wherein the measuring circuit is designed to determine the measured value of a second measuring variable between the third and fourth measuring electrodes.

[0037] In traditional magnetic induction flowmeters, the positions of the magnet system and measuring electrodes are optimized such that the dominant potentials at the measuring electrodes are 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 linearization system is always included in the second measured variable. However, this depends on the Reynolds number within the maximum possible Reynolds number range.

[0038] Therefore, it is particularly advantageous if the measured value of the second measured variable is tapped at the third and fourth measuring electrodes, which are arranged off-center from the first measuring electrode pair. As a result, the potential difference present in the second measuring electrode pair is also decoupled from the two potentials of the first measured variable.

[0039] This is particularly advantageous if the first measuring electrode pair is arranged in a diametrically opposed manner or located on the transverse axis of the measuring tube.

[0040] According to one embodiment, the first measurement variable and the second measurement variable are respectively the potential difference between a pair of measuring electrodes.

[0041] To avoid common-mode interference and thus minimize noise in the signal, it is advantageous if the two measured variables are not potentials relative to a reference potential, but rather the potential difference being measured.

[0042] According to one embodiment, the Reynolds number of the medium in the measuring tube is greater than 1,000, especially greater than 5,000 and preferably greater than 10,000, wherein the Reynolds number of the medium in the measuring tube is less than 1,000,000, especially less than 500,000 and preferably less than 100,000.

[0043] According to one embodiment, in the test measurement, a first measurement variable is substantially proportional to the flow rate of the medium within the Reynolds number range of 10,000≤Re≤1,000,000, wherein, in the test measurement, a second measurement variable does not change constantly with increasing Reynolds number within the Reynolds number range of 10,000≤Re≤1,000,000.

[0044] At Reynolds numbers less than 1,000, the flow exists 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 varies with time. At high Reynolds numbers, the flow profile is independent of the Reynolds number, and therefore f(Re) is constant for both measured variables. In this case, the Reynolds number cannot be determined.

[0045] According to one embodiment, in the test measurement, the medium is a Newtonian fluid, particularly water, wherein, in the test measurement, the flow meter is introduced into a pipe having a straight inlet section of at least 20 DN, preferably at least 50 DN, such that there is a substantially symmetrical flow profile in the measurement area, wherein the measuring pipe has a diameter of DN 80.

[0046] According to one embodiment, the magnetic field generating device includes two coils, specifically coils connected in series in the same direction and attached opposite to each other.

[0047] Two opposing coils connected in series in the same direction each generate a magnetic field, which points primarily in the same direction as the magnetic field generated by the other coil in each case. In this case, the magnetic field lines formed between the two coils extend substantially parallel to the axis of symmetry connecting the two coils. When the coils are connected in series in the same direction, current also flows through the coils in the same direction. EP 0 770 855 A1 teaches the magnetic field distribution of coils connected in series in the same and opposite directions.

[0048] The method for operating a magnetic induction flowmeter according to the present invention includes the following steps:

[0049] - Detect the measured value of the first measured variable and the measured value of the second measured variable, wherein the corresponding measured values ​​of the two measured variables are determined at different measuring electrode pairs;

[0050] - The Reynolds number is determined based on the measured values ​​of the first and second measurement variables.

[0051] The measured values ​​of the first and second measured variables are detected using a measurement circuit. The detected measured values ​​are evaluated in an analysis circuit, and the current Reynolds number of the medium is determined.

[0052] It is particularly advantageous to calculate the quotient of the first and second measurements and compare it with a reference value stored in the storage unit. In this case, the reference value can be the quotient of the measurement data previously tapped at the measurement electrode pair during calibration. Alternatively, a mathematical function describing the relationship between the Reynolds number and the two measured variables or terms dependent on the two measured variables can also be stored in the storage unit. For example, the mathematical function can be a polynomial, especially a higher-order polynomial, derived from the measurement data determined during calibration. If the measured variables satisfy the aforementioned bijectivity condition, the Reynolds number can be determined.

[0053] Advantageous embodiments of the present invention are as follows.

[0054] According to one embodiment, the method according to the present invention includes the following method steps:

[0055] - The corrected flow rate and / or corrected volumetric flow rate are calculated using a correction factor, where the correction factor depends on the determined Reynolds number.

[0056] It is particularly advantageous if the correction factor used to more accurately determine flow rate and / or volumetric flow rate, especially one of the two correction factors f1 and f2, is stored in the storage unit. The correction factor can be determined in the simulation method or identified or measured during the calibration process.

[0057] According to one embodiment, the method according to the present invention includes the following method steps:

[0058] - Determine the kinematic viscosity value, which is determined by means of a measurement of a first or second measurement variable and a determined Reynolds number.

[0059] According to one embodiment, the mapping of the Reynolds number to the quotients of the first and second measurement variables is bijective, at least within the Reynolds number range of 10,000≤Re≤100,000, especially 5,000≤Re≤500,000 and preferably 1,000≤Re≤1,000,000.

[0060] The measured values ​​are output, for example, by means of a display attached to or connected to the flow meter. Alternatively, the display can also be part of a smartphone or laptop and receive the measured values ​​to be displayed from the analysis circuitry via a wireless connection. Alternative output units known in process automation are for data transmission systems such as fieldbus or real-time Ethernet. Attached Figure Description

[0061] The invention will be explained in more detail with reference to the following figures. As shown below:

[0062] Figure 1 Cross-sectional view of a magnetic induction flowmeter based on existing technology;

[0063] Figure 2 Cross-sectional view of a first exemplary embodiment of the magnetic induction flowmeter according to the present invention;

[0064] Figure 3 Cross-sectional view of a second exemplary embodiment of the magnetic induction flowmeter according to the present invention;

[0065] Figure 4 Two graphs: the first graph shows the functions f1 and f2 according to the Reynolds number, and the second graph shows the quotient g of the two functions f1 and f2 according to the Reynolds number; and

[0066] Figure 5 : A flowchart of an exemplary embodiment of a method for operating a magnetic induction flowmeter. Detailed Implementation

[0067] Figure 1A known magnetic induction flowmeter in the prior art is shown. In principle, the structure and measurement principle of a magnetic induction flowmeter are known. A conductive medium is conducted through a measuring tube (1). A magnetic field generating device (7) is attached such that the magnetic lines of force are oriented substantially perpendicular to the longitudinal direction defined by the axis of the measuring tube. A saddle-shaped coil or pole shoe (10) with a mounted coil and coil core is preferably suitable as the magnetic field generating device (7). When a magnetic field is applied, a flow-dependent potential distribution is generated in the measuring tube (1), which is tapped by two opposing measuring electrodes (3, 4) attached to the inner wall of the measuring tube (1). Typically, they are arranged opposite each other and form an electrode axis, or intersect a transverse axis extending perpendicular to the magnetic field lines and the longitudinal axis of the tube. Based on the measured voltage U, the flow velocity can be determined, taking into account the magnetic flux density, and additionally, the volumetric flow rate of the medium can be determined, taking into account the tube cross-sectional area. To prevent the measuring voltage present at the first and second measuring electrodes (3, 4) from discharging via the pipe (8), the inner wall is lined with an insulating material—for example, a plastic liner (2). The magnetic field generated by the magnetic field generating device (7), for example, an electromagnet, is generated by an alternating polarity direct current timed by means of an operating circuit. This ensures a stable zero point and makes the measurement insensitive to the effects of electrochemical interference. The measuring circuit is designed to read the measuring voltage present at the first and second measuring electrodes (3, 4), and the analytical circuit is designed to determine the flow velocity and / or volumetric flow rate of the medium. In addition to the measuring electrodes (3, 4), commercially available magnetic induction flow meters also have two other electrodes (5, 6). First, a fill level monitoring electrode (5), which is optimally attached to the highest point in the pipe (8), is used to detect the partial fill of the measuring tube (1) and is designed to forward this information to the user and / or take the fill level into account when determining the volumetric flow rate. In addition, a reference electrode (6), which is typically attached diametrically to the fill level monitoring electrode (5) or the lowest point of the pipe cross-section, is used to ensure that the medium is adequately grounded.

[0068] According to existing technology, magnetic induction flowmeters are optimized based on the positioning of their measuring electrodes and the configuration of their magnetic field generating devices to make the flowmeter linear, i.e., the correction factor f(Re) is essentially constant for a given measurement range. Therefore, the following simplification is applied to the first approximation:

[0069] U = f·S·u,

[0070] Here, f is assumed to be constant over the Reynolds number range, and S is determined via calibration, i.e., measured in a known measurement environment and then stored in the flow meter to determine the flow rate and / or volumetric flow rate.

[0071] Figure 2A schematic cross-section of a first exemplary embodiment of the flowmeter according to the invention is shown. First and second measuring electrodes (3, 4) are arranged in diametrical opposition and adapted to a magnetic field generating device such that the flowmeter is linear over a specified Reynolds number range. In addition to the first and second measuring electrodes (3, 4), a third measuring electrode (11) is arranged in the measuring tube (1). A second radius (14) intersecting the third measuring electrode (11) and the transverse axis of the measuring tube (15) spans the central angle α. The measuring circuit (16) is designed such that it taps a first potential difference U1 between the first and second measuring electrodes (3, 4) and a second potential difference U2 between the first and third measuring electrodes (3, 11), where U1 = f1(Re)·S1·u and U2 = f2(Re)·S2·u, where f1(Re) and f2(Re) each depend on a correction factor for the Reynolds number. The position or central angle α of the third measuring electrode (11) is optimized such that the quotient U1 / U2 of the first and second potential differences is bijective to the Reynolds number of the flowing medium in the measuring tube, or such that the mathematical function mapping the Reynolds number to the quotient is bijective. This arrangement can be optimized by means of experimental or simulation methods—for example, by means of finite element simulation.

[0072] For the quotients U1 / U2, the results are as follows:

[0073]

[0074] If g(Re) is invertible, the following equations also apply:

[0075]

[0076] Where g -1 It is the inverse function of g. The bijectivity of the quotient can be most easily achieved by attaching the first and second measuring electrodes to the measuring tube, such that the first correction factor f1(Re) is independent of the Reynolds number over the Reynolds number range. In this case, the second correction factor f2 must correspond bijectively to the Reynolds number.

[0077] The measurement circuit (16) is designed to connect the potential difference between the first and second measuring electrodes (3, 4) and the potential difference between the first and third measuring electrodes (3, 11), or to measure the potential at the third measuring electrode relative to a reference potential. The measurement data is forwarded to an analysis unit, which includes a storage unit for storing reference values ​​and Reynolds numbers. The analysis circuit is designed to determine the Reynolds number of the medium in the measuring tube 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 values ​​of the first or second measuring variables or a known flow rate or volumetric flow rate. The measurement circuit, analysis circuit, and storage unit can be arranged on the electronic unit in a manner different from that shown in the schematic diagram.

[0078] Figure 3 A schematic cross-section of a second embodiment of the flowmeter according to the invention is shown. First and second measuring electrodes (3, 4) forming a first electrode pair intersect a first measuring electrode axis (17), which extends parallel to a second measuring electrode axis (18) and a transverse axis (15). This second measuring electrode axis (18) intersects a third measuring electrode (11) and another fourth measuring electrode (12). The third and fourth measuring electrodes (11, 12) form the second measuring electrode pair. A first radius (13) intersecting the second measuring electrode (4) and the transverse axis (15) spans a central angle β. A second radius (14) intersecting the third measuring electrode (11) and the transverse axis (15) spans a central angle γ. The measuring circuit (16) is designed to intersect a first potential difference at the first measuring electrode pair and a second potential difference at the second measuring electrode pair. Both central angles β and γ are selected or optimized such that, in test measurements, the quotient U1 / U2 of the first and second potential differences, or the measured value, bijectively corresponds to the quotient of the Reynolds number of the flowing medium. In the simplest case, the central angle β is set to zero, and the central angle γ is adjusted until the above conditions are met, in particular the condition that the Reynolds number range 10,000≤Re≤1,000,000 is met.

[0079] Figure 4 Two graphs are shown. The first graph illustrates the relationship between the various correction factors f1, f2 and the Reynolds number of the flowing medium in the measuring tube, and the second graph illustrates the relationship between the quotient g of the correction factor and the Reynolds number of the flowing medium in the measuring tube. Both graphs are limited to approximately 10. 3 Up to 10 7 The Reynolds number range. Correction factors f1 and f2 are each associated with one of the two potential differences tapped by different measuring electrode pairs. The curves of functions f1 and f2 have three ranges (I, II, III). In the first and third ranges (I, 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). In contrast, the curve of f1 is constant in the second range (II). In this Reynolds number range, the flowmeter is linear. 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 and third ranges (I, III). For the quotient g, this means it is bijective in ranges one through three (I, II, III). Therefore, the Reynolds number can be explicitly assigned to each quotient of the measurement data for the two measurement variables. For the ranges where flow velocity is sensitive to changes in the Reynolds number (see ranges I and III), measurement bias can be corrected for by the correction function.

[0080] Figure 5A 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, in the above two steps, the potential at each measuring electrode can also be measured relative to a reference potential, and the potential difference in the analysis circuit can be calculated, for example. The first two steps do not necessarily have to be performed sequentially and can be performed simultaneously. It is also possible to measure the second potential difference U2 first and then the first potential difference U1. However, to determine the flow rate or volumetric flow rate, it is generally necessary to consider the measuring voltages of the two measurement stages, where different, especially opposite, DC voltages are applied to the coils respectively, and a magnetic field has been incorporated therein. This allows for compensation for deviations in the measuring voltage. The measurement of the potential difference or potential is performed via a measuring circuit. The analysis circuit calculates the quotient of the two measured values, especially the quotient of the potential difference, and compares the quotient with a Reynolds number assigned to the determined quotient. This Reynolds number is stored in a memory. Alternatively, the mathematical equation or function that assigns the Reynolds number or range of Reynolds numbers to the quotient can also be stored in memory. Alternatively, data identified during the calibration process can also be stored in memory. For example, the data could be a reference value measured during calibration, an extrapolated value, the value of a smoothed characteristic curve, or a fitted function of the measured data. During calibration, the reference value can be determined through experimental or simulation procedures.

[0081] List of reference numerals

[0082] 1 measuring tube

[0083] 2 Linings

[0084] 3 First measuring electrode

[0085] 4 Second measuring electrode

[0086] 5 Filling level monitoring electrode

[0087] 6 reference electrodes

[0088] 7. Magnetic field generating equipment

[0089] 8 pipes

[0090] 9. Measurement, operation, and / or analysis circuits

[0091] 10 Extreme Boots

[0092] 11 Third measuring electrode

[0093] 12 Fourth measuring electrode

[0094] 13 First radius

[0095] 14 Second Radius

[0096] 15 horizontal axes

[0097] 16 Measurement Circuit

[0098] 17 First straight line

[0099] 18 Second straight line

[0100] 19 Analysis Circuits

[0101] 20 storage units

[0102] 21 coils

[0103] I First Range

[0104] II Second Range

[0105] III. Third Range

Claims

1. A magnetic induction flow meter, comprising: - A measuring tube (1) for guiding flowable media, The measuring tube (1) has a wall; - At least three measuring electrodes (3, 4, 11, 12) are arranged in the wall to form electrical contact with the flowing medium in each case; - At least one magnetic field generating device (7), said at least one magnetic field generating device (7) for generating a magnetic field passing through the measuring tube; and - Measurement circuit (16), said measurement circuit (16) is designed to determine at least one first measurement variable, The measured value of the first measured variable is determined at the first measuring electrode pair. Its features are, The analysis circuit (19) is designed to determine the Reynolds number and / or kinematic viscosity of the medium in the measuring tube (1) by means of the measured value of the first measured variable, the measured value of the second measured variable different from the first measured variable, and a stored mathematical function, wherein the stored mathematical function assigns the measured values ​​of the first and second measured variables, or terms depending on the first and second measured variables, to the Reynolds number of the medium. The measured value of the second measured variable is determined at the second measuring electrode pair or at the third measuring electrode (11) relative to the reference potential.

2. The flow meter according to claim 1, in, The measured value of the first measured variable is determined at the first measuring electrode (3) and the second measuring electrode (4).

3. The flow meter according to claim 1, in, The measuring electrodes (3, 4, 11, 12) are arranged in the measuring tube (1) such that, in the test measurement, at least within the Reynolds number range of 10,000 ≤ Re ≤ 100,000, the quotient of the current measured values ​​of the first and second measuring variables corresponds bijectively to the Reynolds number of the flowing medium in the measuring tube (1).

4. The flow meter according to claim 3, in, In the test measurement, within the Reynolds number range of 5,000≤Re≤500,000, the quotient of the current measured values ​​of the first and second measured variables corresponds bijectively to the Reynolds number of the flowing medium in the measuring tube (1).

5. The flow meter according to claim 4, in, In the test measurement, within the Reynolds number range of 1,000≤Re≤1,000,000, the quotient of the current measured values ​​of the first and second measured variables corresponds bijectively to the Reynolds number of the flowing medium in the measuring tube (1).

6. The flow meter according to claim 1, in, The measuring electrodes (3, 4, 11, 12) are essentially located in one cross-section. The first radius (13) intersecting the second measuring electrode (4) and the second radius (14) intersecting the third measuring electrode (11) span an angle α, where α ≥ 20°. The measurement circuit (16) is designed to determine the measured value of a first measurement variable between the first measurement electrode (3) and the second measurement electrode (4). The measurement circuit (16) is designed to determine the measured value of the second measurement variable between the first measurement electrode (3) and the third measurement electrode (11) or the measured value of the second measurement variable relative to a reference potential at the third measurement electrode (11).

7. The flow meter according to claim 6, in, α≥30°。 8. The flow meter according to claim 7, in, 40°≤α≤60°。 9. The flow meter according to claim 1, in, The first measuring electrode axis (17) intersecting the first measuring electrode (3) and the second measuring electrode (4) and the second measuring electrode axis (18) intersecting the third measuring electrode (11) and the fourth measuring electrode (12) are substantially parallel. The measurement circuit (16) is designed to determine the measured value of the first measurement variable between the first measurement electrode (3) and the second measurement electrode (4). The measurement circuit (16) is designed to determine the measured value of the second measurement variable between the third measurement electrode (11) and the fourth measurement electrode (12).

10. The flow meter according to any one of claims 1-9, in, In the test measurement, the first measurement variable is substantially proportional to the flow rate of the medium within the Reynolds number range of 10,000 ≤ Re ≤ 1,000,000. In the test measurement, within the Reynolds number range of 10,000 ≤ Re ≤ 1,000,000, the change of the second measurement variable is not constant as the Reynolds number increases.

11. The flow meter according to any one of claims 1-9, in, In the aforementioned test and measurement, the medium is a Newtonian fluid. In the aforementioned test measurement, the flow meter is introduced into a pipe with a straight inlet section of at least 20 DN, resulting in a substantially symmetrical flow profile in the measurement region. The measuring tube (1) has a diameter of DN 80.

12. The flow meter according to claim 11, in, The medium is water.

13. The flow meter according to claim 11, in, In the test measurement, the flow meter is introduced into a pipe with a straight inlet section of at least 50 DN.

14. The flow meter according to any one of claims 1-9, in, The magnetic field generating device (7) includes two coils (21) attached opposite to each other, which are connected in series in the same direction.

15. A method for operating a magnetic induction flowmeter according to any one of claims 1-14, comprising the following method steps: - Detect the measured values ​​of the first and second measured variables. in, The corresponding measured values ​​of the two measured variables were determined at different measuring electrode pairs; - Determine the Reynolds number based on the measured values ​​of the first and second measured variables.

16. The method of claim 15, comprising the following steps: - Calculate the corrected flow rate and / or corrected volumetric flow rate using a correction factor. in, The correction factor depends on the determined Reynolds number.

17. The method according to claim 15, comprising the following steps: - Determine the kinematic viscosity value in, The kinematic viscosity value is determined by means of the measured value of the first or second measured variable and the determined Reynolds number.

18. The method according to any one of claims 15-17, in, At least within the Reynolds number range of 10,000 ≤ Re ≤ 100,000, the mapping of the Reynolds number to the quotient of the first and second measured variables is bijective.

19. The method according to claim 18, in, The mapping is bijective within the Reynolds number range of 5,000 ≤ Re ≤ 500,000.

20. The method according to claim 19, in, The mapping is bijective within the Reynolds number range of 1,000 ≤ Re ≤ 1,000,000.

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