Method for determining correction function

Abstract

The invention relates to a method for determining a correction function of a flow rate-dependent measurement variable of a flowable medium of a magnetic-inductive flow meter or a magnetic-inductive flow measuring probe, comprising the following method steps: modeling a magnetic field generating device, in particular by means of a preferably numerical simulation method, the modeling of the magnetic field generating device is influenced by the magnetic permeability of the magnetic field generating device,-determining a first reference state, in which the medium to be guided has a first magnetic permeability in the first reference state,-determining a second reference state, in which the medium to be guided has a second magnetic permeability different from the first magnetic permeability in the second reference state, -determining a deviation between the first reference state and the second reference state; and deriving a correction function as a function of the deviation. The invention further relates to a method for correcting a flow rate-dependent measurement variable, to a magnetic-inductive flow meter, and to a magnetic-inductive flow measuring probe.

Description

Technical Field

[0001] The invention relates to a method for determining a correction function, a method for correcting a flow rate-dependent measured variable, a magnetic-inductive flowmeter and a magnetic-inductive flow measuring probe. Background Art

[0002] Magnetic induction flowmeters are used to determine the flow rate and volume flow of a flowing medium in a pipeline. Here, a distinction is made between online magnetic induction flowmeters and magnetic induction flow measuring probes, which are inserted into the transverse openings of the pipeline. The magnetic induction flowmeter has a magnetic field generating device for generating a magnetic field. The main axis of the magnetic field extends substantially perpendicular to the flow direction of the flowing medium. Saddle-shaped or cylindrical coils are generally used for this purpose. In order to achieve a mainly uniform magnetic field, the pole shoes are additionally formed and attached relative to the flow direction so that the magnetic field lines extend substantially perpendicular to the transverse axis or parallel to the vertical axis of the measuring tube over the entire tube cross section. In addition, the magnetic induction flowmeter has a measuring tube, on the side surface of which the magnetic field generating device is arranged. The measuring electrode pairs attached to the side surface of the measuring tube tap an electrical measuring voltage or potential difference, which is applied perpendicular to the flow direction and the magnetic field, and occurs when the conductive medium flows in the flow direction when the magnetic field is applied. Since according to Faraday's law of induction, the tapped measuring voltage depends on the velocity, flow rate of the flowing medium, and in the case of a known pipeline cross section, the volume flow rate can be determined from the induced measuring voltage.

[0003] A magnetic-inductive flowmeter comprises a measuring tube for conducting the medium, which has an attachment device for generating a magnetic field penetrating the measuring tube and has measuring electrodes. In contrast to magnetic-inductive flowmeters, magnetic-inductive flow measuring probes are inserted into the transverse opening of the pipeline line with their usually circular cylindrical housing and fixed in a fluid-tight manner. A special measuring tube is no longer required. The arrangement of measuring electrodes and the coil arrangement on the side surface of the measuring tube mentioned in the introduction are omitted and replaced by a device for generating a magnetic field, which is arranged inside the housing and directly close to the measuring electrodes and is designed so that the axis of symmetry of the magnetic field lines of the generated magnetic field intersects perpendicularly with the front face or face between the measuring electrodes. In the prior art, there are already a number of different magnetic-inductive flow measuring probes.

[0004] Magnetic-inductive flow meters are commonly used in process and automation engineering for fluids starting from a conductivity of approximately 5 μS / cm. Corresponding flow measuring devices are marketed by the applicant in a wide variety of embodiments in various fields of application, for example under the names PROMAG or MAGPHANT.

[0005] It is known that magnetic solids in the medium may lead to increased errors in the determination of the flow velocity-related measured variable. One reason for this is that the magnetic flux density of the magnetic field generated during the measuring mode is usually not measured. Instead, a preset and expected magnetic flux density is assumed for the determination of the flow velocity-related measured variable. However, this is determined under ideal conditions at the plant and does not correspond to the magnetic flux density actually present if magnetic solids are present in the flowing medium.

[0006] DE 10 2006 026 772 A1 discloses a method for determining a flow rate-related measured variable by means of a magnetic-inductive flow meter, in which conclusions are drawn about the presence of magnetically conductive solid bodies in the medium based on the deviation of the current rise time from a predetermined rise time, which must be waited until the magnitude of the magnetic field, i.e. the magnetic flux density, assumes a predefined target value. Based on this deviation, a correction factor is then determined, with which the measurement error is compensated. Summary of the invention

[0007] The purpose of the present invention is to provide an alternative technical solution.

[0008] This object is achieved by a method for determining a correction function according to claim 1 , a method for correction according to claim 18 , a magnetic-inductive flowmeter according to claim 21 and a magnetic-inductive flow measuring probe according to claim 22 .

[0009] The method according to the invention for determining a correction function for a flow velocity-dependent measured variable of a flowable medium of a magnetic-inductive flowmeter or a magnetic-inductive flow measuring probe comprises the following method steps:

[0010] - modelling of the magnetic field generating device, in particular by means of preferably numerical simulation methods,

[0011] wherein the modeling of the magnetic field generating device is influenced by the magnetic permeability of the magnetic field generating device or of at least one individual component of the magnetic field generating device,

[0012] - determining a first reference state,

[0013] Wherein, in the first reference state, the medium to be guided has a first magnetic permeability,

[0014] - determining a second reference state,

[0015] wherein, in the second reference state, the medium to be guided has a second magnetic permeability different from the first magnetic permeability,

[0016] - determining a deviation between a first reference state and a second reference state; and

[0017] -Deriving a correction function based on the deviation.

[0018] The method according to the invention has the advantage that when determining the correction function, it not only takes into account the magnetic properties of the magnetic field generating device or the individual components of the magnetic field generating device, but also takes into account the influence of magnetic solids on the individual components and the interaction with the individual components of the magnetic field generating device. Therefore, the correction function of the method according to the invention is applicable to all magnetic-inductive flow meters and magnetic-inductive flow measuring probes with a known magnetic field generating device, regardless of the operating signal and the control method.

[0019] Modeling within the meaning of the present application includes the creation of a model. The model is preferably created using a simulation process. Alternatively, modeling may also include the creation of a prototype. In this case, a test setup with adjustable conditions corresponding to a first reference state and a second reference state is created and measured.

[0020] It is particularly advantageous to use suitable simulation methods to create the model. Numerical simulation methods such as the finite element method are particularly suitable for this purpose.

[0021] It is generally known to create correction functions or correction factors using simulation methods. From US 11,199,436 B2, a magnetic-inductive flowmeter is known in which certain correction factors are stored using the finite element method and computational fluid dynamics (CFD) to correct measurement errors caused by disturbances at the inlet side and / or outlet side (bends, valves, etc.). The disturbances lead to an asymmetric flow profile and the assumption that a completely rotationally symmetrical flow profile exists, which is usually made when configuring a magnetic-inductive flowmeter, no longer holds. However, the present invention differs from the cited prior art in that the present technical solution does not take into account the influence of the process line on the flow profile in the measuring tube, but rather the influence of the magnetic solid on the magnetic field generating device and the magnetic field generated thereby.

[0022] The first reference state can, for example, reflect the state of the magnetic-inductive flowmeter or the magnetic-inductive flow measuring probe during regulation. In this case, the medium can consist of water without magnetic solids.

[0023] In the second reference state, the medium may contain a magnetic solid. For simplicity, the second magnetic permeability is assigned to the entire medium. However, in particular in simulations, multiphase media may also be provided in which the individual phases have different magnetic permeabilities.

[0024] The flow rate-related measured variables include a potential applied to a measuring electrode, a measured voltage between two measuring electrodes, a determined flow rate, a determined volume flow and / or a determined mass flow.

[0025] Advantageous embodiments of the invention are subject matter of the dependent claims.

[0026] One embodiment provides that modeling the magnetic field generating device comprises adapting the magnetic field generating device such that a magnetic property of the magnetic field generating device generated by the modeled magnetic field generating device, in particular a self-inductance of the magnetic field generating device, lies within a property tolerance range, in particular a self-inductance tolerance range, in particular determined experimentally.

[0027] The advantage of this design is that the magnetic properties of the device generating the magnetic field are included in the model and a more accurate correction is thus achieved. The magnetic properties, in particular the self-inductance, can be determined using a magnetic-inductive flow meter or a magnetic-inductive flow measuring probe. The determination of the self-inductance is taught, for example, in WO 2021 / 121960 A9 and WO 2021 / 110442 A1 (which are fully referenced). For example, the self-inductance present during operation is generated by the time-varying coil current curve and / or voltage curve. In the simulation, for example, the self-inductance is simulated. By magnetic field strength and magnetic flux density divided by the square of the coil current The volume integral of the self-inductance is obtained. Depends directly on the magnetic permeability of the medium, but not on the flow rate-related variables of the medium.

[0028] The self-inductance tolerance range may consist of a single self-inductance value determined by a single measuring device, or may consist of a range spanned by multiple measured self-inductance values ​​from different measuring devices.

[0029] One embodiment provides that modeling the magnetic field generating device includes adapting the magnetic field generating device so that the calibration factor generated by the modeled magnetic field generating device is within a tolerance range of the calibration factor, in particular within an experimentally determined tolerance range of the calibration factor.

[0030] For the best design of the model, check the calibration factors generated by the model It is advantageous if the calibration factor tolerance range is determined experimentally. The calibration factor tolerance range determined experimentally is generated, for example, from a set of calibration factors of magnetic-inductive flow meters or magnetic-inductive flow measuring probes that have already been manufactured and adjusted. The calibration factors generated by the model It can be determined, for example, by calculating the potential in the measurement cross section at a set flow rate.

[0031] The calibration factor tolerance range may consist of a single calibration value intended for a single measurement device, or a range spanned by calibration values ​​from multiple measurements from different measurement devices.

[0032] An embodiment provides that modeling the magnetic field generating device comprises adapting the magnetic field generating device such that a linearity produced by the modeled magnetic field generating device lies within a linearity tolerance range, in particular an experimentally determined linearity tolerance range.

[0033] Linearity is the relationship between the Reynolds number and the induced measured voltage over the maximum possible Reynolds number range (typically 10 4 Up to 10 6 ) is a measure of the degree to which the correction factor is independent of the Reynolds number. If the magnetic inductive flow meter or magnetic inductive flow probe is linear over a given Reynolds number range and is therefore independent of the Reynolds number, then the correction factor can be chosen to be constant, and the simplification can be assumed ,in, is the induced measured voltage, is a Reynolds number-dependent function—however, in this case, it is constant—, is the nominal signal strength, and is the flow rate. The linearity of the model can be calculated for adjustment. The calculated linearity is then compared to the linearity tolerance range.

[0034] The linearity tolerance range may consist of a single linearity value determined for a single measurement device or a range spanned by multiple measured linearity values ​​from different measurement devices.

[0035] One embodiment provides that when modeling the magnetic field generating device, a distance is assumed between at least two individual components of the magnetic field generating device, or between a measuring tube of a magnetic-inductive flow meter and the magnetic field generating device, or between a housing wall of a magnetic-inductive flow measuring probe and the magnetic field generating device,

[0036] The modeling includes adjusting the distance until the variable to be adjusted matches the corresponding tolerance range.

[0037] An advantage of an embodiment is that a more precise match can thereby be achieved between a simulated magnetic-inductive flow meter or a simulated magnetic-inductive flow measuring probe, in particular between the magnetic properties generated by the simulation and the magnetic properties of an actual magnetic-inductive flow meter or a magnetic-inductive flow measuring probe. By assuming a distance between two individual components of the magnetic field generating device (e.g. in the form of an air gap), influences from boundary regions between the usually ferromagnetic individual components can be taken into account in the modeling.

[0038] One embodiment provides that the magnetic field generating device comprises a coil and a coil core,

[0039] In this case, the magnetic permeability of the coil core is taken into account in the modeling of the magnetic field generating device.

[0040] An embodiment provides that the magnetic field generating device comprises a pole shoe,

[0041] In this case, the magnetic permeability of the pole piece is taken into account in the modeling of the magnetic field generating device.

[0042] One embodiment provides that the magnetic field generating device comprises two—in particular diametrically arranged—coils, each coil having a coil core and a field guide connecting the two coil cores,

[0043] In this case, the magnetic permeabilities of the two coil cores and the field guide are taken into account in the modeling of the magnetic field generating device.

[0044] One embodiment provides that the magnetic field generating device comprises a coil, in particular without a coil core and a field guide,

[0045] In this case, the magnetic permeability of the field guide is taken into account in the modeling of the magnetic field generating device.

[0046] One embodiment provides that in a first reference state, a first magnetic property, in particular a first self-inductance or a variable depending thereon, is determined.

[0047] Therein, in the second reference state, a second magnetic property deviating from the first magnetic property is determined, in particular a second self-inductance deviating from the first self-inductance or a variation deviating from the first self-inductance.

[0048] The self-inductance of the magnetic field generating device determined during operation includes not only the inductance generated by the coil arrangement, but also its temperature dependence and its dependence on the external magnetic field. If the medium to be transported contains ferromagnetic solids, these influence the generated magnetic field and in particular the magnetic flux in the medium. As a first approximation, the medium and the ferromagnetic solids can be interpreted as part of the coil core of the coil. The approximate formula for the self-inductance of a long coil is ,in, is the cross-sectional area of ​​the coil, is the number of turns, and is the length of the coil. In a first approximation, the ferromagnetic solid thus affects , which can no longer be assumed to be constant. Therefore, the self-inductance is not only a variable that can change, but also a variable that is extremely sensitive to external magnetic fields, for example generated by magnetic foreign objects.

[0049] The determination of the self-inductance of the first reference state and the second reference state is advantageous because it enables a comparison with the actual self-inductance of the magnetic-inductive flow meter or of the magnetic-inductive flow measuring probe during operation.

[0050] An embodiment provides that determining a deviation between the first reference state and the second reference state comprises determining a first deviation between the first magnetic property and the second magnetic property, in particular a first deviation between the first self-inductance and the second self-inductance.

[0051] One embodiment provides that determining a deviation between the first reference state and the second reference state comprises determining a second deviation between a first flow rate-related measured variable resulting from the first reference state and a second flow rate-related measured variable resulting from the second reference state.

[0052] One embodiment provides that the correction function is generated from a functional relationship between a first deviation or a variable derivable from the first deviation and a second deviation or a variable derivable from the second deviation.

[0053] The correction function may be stored in the magnetic-inductive flow meter or in the magnetic-inductive flow measuring probe and may be used by the measuring circuit during operation to determine a more accurate flow rate-related measured variable.

[0054] One embodiment provides that the correction function can be described by means of a polynomial function having at least one linear part,

[0055] The linear part includes the factors .

[0056] One embodiment provides for the factor is a variable specific to the geometry of the magnetic system.

[0057] factor can vary with different magnetic system geometries. This means that the factor in the magnetic field generating device consisting of two diametrically arranged saddle coils is Deviation factor occurs in a magnetic field generating device consisting of two cylindrical coils arranged along the diameter However, not only the individual components that generate the magnetic field, but also the individual components that conduct the magnetic field, influence the factor In addition, magnetic-inductive flow meters with more than two coils are known. These are usually arranged in the measuring cross section. This also affects the factor .

[0058] One embodiment provides that in the case where the magnetic field generating device comprises a saddle coil, the factor is selected from a first factor range having limits 1 and 4, in particular 1.5 and 2.5, or their corresponding reciprocals,

[0059] Where the magnetic field generating device comprises a cylindrical coil, the factor A first factor range is selected having limits 4 and 8, in particular 5 and 7, or their corresponding reciprocals.

[0060] One embodiment provides for the factor The correlation is carried out via a second-order polynomial function with a measuring tube-specific variable or a pipeline-specific variable, in particular with the measuring tube inner diameter or the pipeline inner diameter.

[0061] Surprisingly, when the magnet system geometry remains unchanged, the factor Related to the inner diameter of the measuring tube or pipeline. Therefore, magnetic inductive flow meters with different nominal widths have different factors. , but these are related to each other via a functional relationship. As the diameter increases, the factor The correlation can be described by a second-order polynomial function.

[0062] For magnetic inductive flow measurement probes, the factor is correlated with the line diameter of the process line in which the magnetic-inductive flow measuring probe is arranged. For this purpose, it can be advantageous if the polynomial function describing the correlation is stored in the magnetic-inductive flow measuring probe and the line diameter of the process line can be specified by the user. The measuring circuit is arranged to take into account the specified line diameter in determining the factor to be applied , and according to the factor Calculation of flow rate dependent measured variables.

[0063] The method according to the invention for correcting a flow rate-related measured variable of a magnetic-inductive flow meter or a magnetic-inductive flow meter probe comprises the following method steps:

[0064] - determining the current magnetic properties of the magnetic-inductive flowmeter or of the magnetic-inductive flow measuring probe, in particular the current self-inductance or a current variable dependent on the self-inductance;

[0065] - Determine the flow rate related measurement variables;

[0066] - applying a correction function to the determined current magnetic property, in particular the current self-inductance or a variable dependent on the current self-inductance, in order to correct the flow velocity-dependent measured variable, the correction function being in particular a correction function determined by means of the method of at least one of the preceding claims,

[0067] Therein, the correction function assigns a current magnetic property, in particular the current self-inductance or a variable which depends on the current self-inductance, to a correction factor for the flow rate-dependent measured variable.

[0068] One embodiment provides that the correction function is independent of the flow rate.

[0069] One embodiment includes the following method steps:

[0070] - Determining the effective magnetic permeability of the medium as a function of the current magnetic properties, in particular the current self-inductance or a variable which depends on the current self-inductance, and / or a correction factor.

[0071] The magnetic-inductive flowmeter according to the invention for determining a flow velocity-dependent measured variable of a flowable medium comprises:

[0072] - measuring tube for conducting the medium;

[0073] - a magnetic field generating device for generating a magnetic field penetrating the measuring tube;

[0074] at least one measuring electrode for determining a measuring voltage induced in the flowable medium; and

[0075] - a measuring circuit for determining a flow rate-related measured variable;

[0076] And is characterized in that the measuring circuit is arranged to carry out the correction method according to the invention.

[0077] The magnetic-inductive flow measuring probe according to the invention for determining a flow velocity-dependent measured variable of a flowable medium,

[0078] The magnetic induction flow measurement probe can be arranged in the opening of the pipeline, including:

[0079] - housing in contact with the medium,

[0080] - a magnetic field generating device for generating a magnetic field penetrating the housing,

[0081] wherein the magnetic field generating device is arranged in the housing;

[0082] - at least one measuring electrode for determining a measuring voltage induced in the medium; and

[0083] - a measuring circuit for determining a flow rate-related measured variable;

[0084] And is characterized in that the measuring circuit is arranged to carry out the correction method according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] The present invention is explained in more detail with reference to the following drawings. In the drawings:

[0086] Figure 1 : shows an embodiment of a magnetic induction flow meter according to the present invention;

[0087] Figure 2 : A perspective view showing a partially cutaway embodiment of a magnetic-inductive flow measurement probe according to the present invention;

[0088] Figure 3 : shows another embodiment of the magnetic induction flowmeter according to the present invention;

[0089] Figure 4 : shows an embodiment of the method for correcting a flow rate-related measured variable according to the present invention;

[0090] Figure 5 : shows an embodiment of a method for determining a correction function according to the present invention;

[0091] Figure 6 : shows the functional relationship between the measurement error caused by magnetic solids in the medium and the change of the determined magnetic properties of the magnetic field generating device; and

[0092] Figure 7 : shows the factor Functional relationship between the inner diameter of the measuring tube or pipeline. DETAILED DESCRIPTION

[0093] Figure 1 A cross section of an embodiment of a magnetic-inductive flowmeter 1 according to the invention, which is in particular a measuring sensor, is shown. The structure and measuring principle of the magnetic-inductive flowmeter 1 are known in principle. A flowable medium is conducted through a measuring tube 2, which must have a minimum electrical conductivity so that a flow rate-related measured variable can be determined. The measuring tube 2 comprises a carrier tube 3, which is usually formed of or at least comprises steel, ceramic, plastic or glass. A magnetic field generating device 5 for generating a magnetic field is arranged on the carrier tube 3 so that the magnetic field lines are oriented substantially perpendicular to the longitudinal direction defined by the measuring tube axis. The magnetic field generating device 5 usually comprises at least one saddle coil or at least one (cylindrical) coil 6i. The coil core 14i usually extends through the socket 15 of the coil 6i. The socket 15 should be understood as a volume limited by the coil wire forming the coil 6i. Therefore, the socket 15 of the coil 6i can be formed by a coil holder or by an imaginary closed volume. The latter occurs when the coil wire of the coil 6i is directly wound around the coil core 14i. The coil core 14i is formed of a magnetically conductive, in particular soft magnetic material. The magnetic field generating device 5 further comprises at least one pole shoe 21i arranged at one end of the coil core 14i. The pole shoe 21i may be a separate component or may be monolithically connected to the coil core 14i. Figure 1In the embodiment shown in, two diametrically arranged coils 6a, 6b each have a coil core 14a, 14b and a pole shoe 21a, 21b. The coils 6a, 6b can be electrically connected in series. The two coil cores 14a, 14b are connected to each other via a field guide 22. The field guide 22 connects the mutually opposite sides of the coil cores 14a, 14b and is arranged to guide the generated magnetic field. However, a magnetic induction flowmeter having exactly one coil core 14 and exactly one coil 6 without a field guide 22 is also known. The coils 6a, 6b are connected to an operating circuit 7 that drives the coils 6a, 6b with an operating signal. The operating signal can be a voltage with a time-varying curve and is characterized by operating signal parameters, wherein at least one of the operating signal parameters is controllable. The magnetic field generated by the device 5 for generating a magnetic field is generated using a pulsed direct current of alternating polarity provided by the operating circuit 7. This ensures a stable zero point and makes the measurement insensitive to influences due to electrochemical perturbations. The two coils 6a, 6b may be connected individually to the operating circuit 7 or connected in series or in parallel with each other.

[0094] When a magnetic field is applied, a flow-related potential distribution appears in the measuring tube 2 or in the flowing medium, which potential distribution can be detected, for example, in the form of an induced measurement voltage. A device 8 for tapping the induced measurement voltage is arranged on the measuring tube 2. In the embodiment shown, the device 8 for tapping the induced measurement voltage is formed by two oppositely arranged measurement electrodes 17, 18 to form a current contact with the medium. However, magnetic induction flowmeters are also known, which include measurement electrodes arranged on the outer wall of the carrier tube 3 that is not in contact with the medium. The measurement electrodes 17, 18 are usually arranged along the diameter and form an electrode axis, or intersect with a transverse axis extending perpendicular to the magnetic field lines and the longitudinal axis of the measuring tube 2. However, the device 8 is also known for tapping the induced measurement voltage, which has more than two measurement electrodes. Flow rate-related measurement variables can be determined based on the measured measurement voltage. Flow rate-related measurement variables include flow rate, volume flow rate and / or mass flow rate of the medium. The measuring circuit 23 is arranged to detect the induced measurement voltage applied to the measuring electrodes 17 , 18 and the evaluation circuit 24 is arranged to determine the flow rate-related measured variable and further arranged to carry out the method according to the invention for correcting a flow rate-related measured variable.

[0095] For this purpose, the evaluation circuit 24 is designed to determine the current magnetic property, in particular the self-inductance or a current variable dependent on the self-inductance. Furthermore, the evaluation circuit 24 is designed to apply a correction factor of a correction function to the determined flow rate-related measured variable in order to correct the variable, the correction function being stored or determined as a function of the magnetic property variable, in particular the self-inductance or a variable dependent on the self-inductance, and being determined using the method according to the invention for determining a correction function.

[0096] The evaluation circuit 24 can be arranged in the measuring sensor or in the measuring transmitter.

[0097] The carrier tube 3 is typically formed from an electrically conductive material such as steel. In order to prevent the measuring voltage applied to the first and second measuring electrodes 2 , 3 from being conducted away via the carrier tube 3 , the inner wall is lined with an insulating material, such as a (plastic) liner 4 .

[0098] In addition to the measuring electrodes 17, 18, commercially available magnetic-inductive flow meters also have two further electrodes 19, 20. In the first case, the fill level monitoring electrode 19, which is optimally attached at the highest point in the measuring tube 2, serves to detect partial filling of the measuring tube 1 and is arranged to convey this information to the user and / or to take the fill level into account when determining the volume flow. In addition, a reference electrode 20, which is usually attached diametrically to the fill level monitoring electrode 19 or at the lowest point of the measuring tube cross section, serves to establish a controlled potential in the medium. Typically, the reference electrode 20 serves to connect the flowing medium to ground potential.

[0099] The operating circuit 7, the controller circuit 10, the measuring circuit 23 and the evaluation circuit 24 can be part of a single electronic circuit or can form individual circuits. The evaluation circuit 24 comprises electronic components for carrying out the method according to the invention. For this purpose, it can have a microcontroller, a logic electronic component and / or an electronic component.

[0100] However, magnetic-inductive flow meters are also known which have a magnetic field generating device 5 which is different from the one shown in the illustration. For example, the magnetic field generating device 5 can comprise only exactly one coil in the form of a cylindrical coil or a saddle coil, or can also have more than two coils which are distributed over the side surface in the circumferential direction or also in the longitudinal direction. For an optimal design of the coil, a coil core is usually provided, which extends through the coil holder. For a more uniform magnetic field distribution in the measuring tube, in particular when using cylindrical coils, a pole shoe is provided, which is usually arranged between the coil and the side surface of the measuring tube and covers a larger surface area of ​​the side surface than the coil. The pole shoe 21 does not necessarily have to have a Figure 1 , but can also be rounded and take the shape of an arc, as disclosed, for example, in WO 2021 / 043586 A1. The field return 22 also does not have to be angular as shown, but can also take the form of an arc. The field guide 22 magnetically connects the two coil cores 6a, 6b to each other in order to achieve a more effective and faster reversal of the polarity of the magnetic field.

[0101] First, based on Figure 2The perspective and partially cross-sectional illustration of the flow measurement probe 101 is used to explain the measurement principle on which the invention is based. The flow measurement probe 101 comprises a substantially circular cylindrical housing 102 having a predetermined outer diameter. The housing is adapted to the diameter of a hole located in the pipeline ( Figure 1 116 ) and the flow measurement probe 101 is inserted therein in a fluid-tight manner. The medium to be measured flows in the pipeline and the flow measurement probe 101 is immersed in the medium in fact perpendicularly to the flow direction of the medium (which is indicated by the wavy arrow 118). The front end 116 of the housing 102 protruding into the medium is sealed in a fluid-tight manner with a front body 115 made of insulating material. With the help of a magnetic field generating device 105 arranged in the housing 102 and comprising a coil arrangement 106, a magnetic field 109 extending through the end to the medium can be generated. The coil core 111, which is at least partially composed of a soft magnetic material and arranged in the housing 102, ends at or near the end 116. The field return body 114 surrounding the coil arrangement 106 and the coil core 111 is configured to return the magnetic field 109 extending through the end to the housing 102. The coil core 111, the pole shoe 112 and the field return body 114 are each a field conductor 110, which together form a field conduction arrangement 105. The first measuring electrode 103 and the second measuring electrode 104, which form a current contact with the medium to be conducted, form a device for detecting the measuring voltage induced in the medium and are arranged in the front body 115 and, similar to the outer wall of the housing, touch the medium. The voltage induced due to Faraday's law of induction can be tapped at the measuring electrodes 103, 104 by means of a measuring circuit. If the flow measurement probe 101 is installed in the pipeline line so that the plane spanned by the straight line intersecting the two measuring electrodes 103, 104 and by the longitudinal axis of the flow measurement probe extends perpendicular to the flow direction 118 or the longitudinal axis of the pipeline line, the voltage is at a maximum. The operating circuit 107 is electrically connected to the coil arrangement 106, in particular to the coil 113, and is configured to apply a clocked operating signal to the coil 113 so as to generate a clocked magnetic field 109.

[0102] The evaluation circuit 119 of the magneto-inductive flow measuring probe 101 is arranged to carry out the correction method according to the invention. For this purpose, the evaluation circuit 119 is arranged to determine the current magnetic property, in particular the self-inductance or a current variable dependent on the self-inductance. Furthermore, the evaluation circuit 119 is arranged to apply a correction factor of a correction function to the determined flow rate-related measured variable in order to correct the determined flow rate-related measured variable, the correction function being stored or determined as a function of the magnetic property, in particular the self-inductance or a property dependent on the self-inductance, and being determined using the method according to the invention for determining a correction function.

[0103] Figure 3A further embodiment of a magnetic-inductive flowmeter 301 according to the invention is shown. The magnetic field generating device 305 of the illustrated embodiment comprises two diametrically arranged saddle coils 306, the shape of which is adapted in each case to the outer contour of the side surface of the measuring tube 302. Furthermore, the magnetic-inductive flowmeter 301 may also comprise a field guide (not shown) which is arranged to guide the magnetic field from one saddle coil 306 to the opposite saddle coil 306. Alternatively, the magnetic-inductive flowmeter 301 may comprise only exactly one saddle coil 306.

[0104] Figure 4 An embodiment of a method according to the invention for correcting a flow rate-dependent variable with method steps 401 to 404 is shown.

[0105] In a first method step 401, a current magnetic characteristic variable of a magnetic-inductive flowmeter or a magnetic-inductive flow measuring probe is determined, in particular the self-inductance or a current variable dependent on the self-inductance. Magnetic-inductive flowmeters are known which are designed to determine the self-inductance resulting from the time-varying coil current curve and / or voltage curve in addition to the flow velocity-related measured variable. For example, the self-inductance is generated by the rising behavior of the coil current when a rectangular voltage curve is applied. The self-inductance determined in this way is a measure for the presence of magnetic solids in the medium. The self-inductance is a variable that can vary and can depend on the temperature and the aging state of the magnetic field generating device.

[0106] Subsequently, in a second method step 402, a flow rate-related measured variable is determined. The flow rate-related measured variable may be a potential measured at a measuring electrode, a potential difference between two measuring electrodes or a measured voltage, a determined flow rate, a determined volume flow or a determined mass flow.

[0107] The third method step 403 comprises applying a correction function or a correction factor of a correction function stored in the magnetic-inductive flowmeter or in the magnetic-inductive flow measuring probe to correct the flow rate-related measured variable. This is determined at the factory using the method according to the invention and stored in the magnetic-inductive flowmeter or in the magnetic-inductive flow measuring probe. The correction function corresponds to a correction function assigned to the determined current magnetic property, in particular the current self-inductance or a variable depending on the current self-inductance, which assigns the current magnetic property, in particular the current self-inductance or a variable depending on the current self-inductance, to a correction factor of the flow rate-related measured variable.

[0108] The correction function is determined in such a way that it is independent of the flow rate.

[0109] The correction function may be a polynomial function having a linear portion, wherein in the linear portion the polynomial function has a linear relationship corresponding to the factor The slope of .

[0110] An optional fourth method step 404 comprises determining the effective magnetic permeability of the medium as a function of the current magnetic properties, in particular the current self-inductance or a variable which depends on the current self-inductance, and / or a correction factor.

[0111] Figure 5 An embodiment of a method according to the invention for determining a correction function for a flow velocity-dependent measured variable of a flowable medium for a magnetic-inductive flowmeter or a magnetic-inductive flow measuring probe is shown, comprising method steps 501 to 505:

[0112] A first method step 501 comprises modeling a magnetic field generating device, in particular by means of a preferably numerical simulation method. The modeling of the magnetic field generating device takes into account the magnetic permeability of the magnetic field generating device or at least individual components of the magnetic field generating device. The magnetic field generating device usually consists of a plurality of individual components, such as one or more cylindrical or saddle-shaped coils, one or more coil cores, one or more pole shoes and / or one or more field guides. The finite element method is an example of a suitable simulation method.

[0113] Depending on the embodiment of the magnetic field generating device and the presence of individual components, the magnetic permeability of the individual components or the magnetic permeability of all individual components is taken into account for modeling; i.e., in the model, the individual components or all individual components are each assigned a magnetic permeability which substantially corresponds to the actual magnetic permeability of the individual components installed in the measuring device. Thus, if at least one coil core is present, the magnetic permeability of at least one coil core is taken into account in the modeling of the magnetic field generating device; i.e., in the model, the magnetic permeability of the coil core actually used in the measuring device is assigned to the coil core. If at least one pole shoe is present, the magnetic permeability of the pole shoe is taken into account in the modeling of the magnetic field generating device. If the magnetic field generating device has two coils, each coil having a coil core which is connected to one another via a field guide, the magnetic permeability of the field guide is taken into account in the modeling of the magnetic field generating device in addition to the magnetic permeability of the two coil cores.

[0114] Once all magnetic permeabilities have been correspondingly assigned to the individual components of the magnetic field generating device, the magnetic properties of the magnetic field generating device generated by the model, in particular the self-inductance of the magnetic field generating device, are determined. If the determined magnetic properties, in particular the self-inductance, are within a tolerance range for the properties, in particular a tolerance range for the self-inductance determined experimentally, the model is sufficiently appropriate. Furthermore, the calibration factor generated by the modeled magnetic field generating device must be within the calibration factor tolerance, especially the calibration factor tolerance determined experimentally. A measured potential, a measured and / or determined potential difference or a measured voltage is applied to determine the flow rate or a process variable derived therefrom. Furthermore, for a suitable model to be suitable, the linearity produced by the modeled magnetic field generating device must lie within a linearity tolerance range, in particular an experimentally determined linearity tolerance range.

[0115] If the magnetic properties, in particular the self-inductance, are not within the tolerance range of the properties, in particular not within the tolerance range of the self-inductance, an adjustment of the modeled magnetic field generating device is necessary. This adjustment is preferably performed by providing a distance between at least two individual components of the magnetic field generating device or between the measuring tube of a magnetic-inductive flowmeter and the magnetic field generating device or between the housing wall of a magnetic-inductive flow measuring probe and the magnetic field generating device in the model. The volume bounded by the individual components has the magnetic properties of air or vacuum. This distance is a variable that can be varied in the model and is changed until the variable to be adjusted ( , self-inductance and / or linearity) to match the corresponding tolerance range.

[0116] Method step 502 comprises determining a first reference state in which the medium to be guided has a first magnetic permeability. Water without magnetic foreign matter is a suitable medium for this purpose. For the first reference state, a first magnetic property is determined, in particular a first self-inductance or a variable dependent thereon.

[0117] Method step 503 comprises determining a second reference state in which the medium to be guided has a second magnetic permeability that deviates from the first magnetic permeability. The second magnetic permeability is caused by the presence of magnetic solids in the medium, for example water. During modeling, the second magnetic permeability is assigned to the total volume of the water. For the second reference state, a second magnetic property that deviates from the first magnetic property is determined, in particular a second self-inductance that deviates from the first self-inductance or a variable that deviates from the first self-inductance.

[0118] Method step 504 comprises determining a deviation between a first reference state and a second reference state. In this case, a first deviation between the first magnetic property and the second magnetic property, in particular a first deviation between the first self-inductance and the second self-inductance, is determined. In addition, a second deviation is determined between a first flow rate-related measurement variable generated by the first reference state and a second flow rate-related measurement variable generated by the second reference state.

[0119] Method step 505 comprises deriving a correction function from the deviations. The correction function is generated by a functional relationship between a first deviation or a variable that can be derived from the first deviation and a second deviation or a variable that can be derived from the second deviation. The correction function can be described by a polynomial function having at least one linear part and having a factor The linear part of . is a magnetic system geometry specific variable and is selected from a first factor range having limits 1 and 4, in particular 1.5 and 2.5, or their corresponding reciprocals, in the case where the magnetic field generating device comprises a saddle coil, and is selected from a first factor range having limits 4 and 8, in particular 5 and 7, or their corresponding reciprocals, in the case where the magnetic field generating device comprises a cylindrical coil.

[0120] In addition, the factor The correlation is carried out via a second-order polynomial function with a measuring tube-specific variable or a pipeline-specific variable, in particular with the measuring tube inner diameter in the case of a magnetic-inductive flow meter or with the pipeline inner diameter in the case of a magnetic-inductive flow measuring probe.

[0121] Figure 6 The functional relationship between the measurement error caused by magnetic solids in the medium and the change in the determined magnetic properties of the magnetic field generating device is shown. The plotted measurement points are measured in a test line using a magnetic-inductive flowmeter. Magnetic foreign bodies with known magnetic properties are mixed in water and pumped through the test line. A reference flowmeter that is insensitive to the magnetic foreign bodies is used to determine the error of the flow rate-related measured variable (y-axis). A Coriolis flowmeter is used for this purpose. At the same time, the magnetic-inductive flowmeter is used to continuously determine the inherent self-inductance. The determined self-inductance is the self-inductance of the magnetic field generating device derived from the time-varying coil current and / or coil voltage. If the measurement error of the flow rate-related measured variable is plotted as a function of the change in the determined self-inductance (x-axis), a linear relationship is obtained. This relationship can be well described by a simulation function obtained from the model according to the invention. According to the invention, the determined straight line has a value corresponding to the factor If the correction function or factor If the self-inductance is stored in the measuring device and the deviation of the self-inductance from a reference value can be determined, errors in the flow rate-related measured variables caused by magnetic foreign matter can be determined or corrected.

[0122] Figure 7 The factor The factor generated by the method for determining the correction function according to the invention is (Y-axis) is determined for magnetic-inductive flow meters having the same magnetic field generating device but different inner diameters and is plotted as a function thereof (X-axis).

[0123] Reference numerals list

[0124] Magnetic induction flowmeter 1

[0125] Measuring tube 2

[0126] Loading tube 3

[0127] Pad 4

[0128] Magnetic field generating device 5

[0129] Coil 6

[0130] Operation circuit 7

[0131] Device for measuring voltage of tapping induction 8

[0132] Controller circuit 10

[0133] Coil core 14i

[0134] Coil socket 15

[0135] Measuring electrode 17

[0136] Measuring electrode 18

[0137] Fill level monitoring electrode 19

[0138] Reference electrode 20

[0139] Pole shoe 21

[0140] Field guide 22

[0141] Measurement circuit 23

[0142] Evaluation circuit 24

[0143] Coil device 25

[0144] Magnetic induction flow measurement probe 101

[0145] Housing 102

[0146] Measuring electrode 103

[0147] Measuring electrode 104

[0148] Magnetic field generating device 105

[0149] Coil device 106

[0150] Operation circuit 107

[0151] Field conduction device 108

[0152] Magnetic Field 109

[0153] Field conductor 110

[0154] Coil core 111

[0155] Pole shoe 112

[0156] Coil 113

[0157] Field return body 114

[0158] Precursor 115

[0159] End 116

[0160] Housing wall 117

[0161] Flow direction of the medium 118

[0162] Evaluation circuit 119

Claims

1. A method for determining a correction function for a flow velocity-dependent measured variable of a flowable medium of a magnetic-inductive flowmeter (1) or a magnetic-inductive flow measuring probe (101), comprising the following method steps: - modeling the magnetic field generating device (5, 105), in particular by means of simulation methods, preferably numerical simulation methods, in, The modeling of the magnetic field generating device (5, 105) is influenced by the magnetic permeability of the magnetic field generating device (5, 105) or at least individual components of the magnetic field generating device (5, 105), - determining a first reference state, Wherein, in the first reference state, the medium to be guided has a first magnetic permeability, - determining a second reference state, wherein, in the second reference state, the medium to be guided has a second magnetic permeability that deviates from the first magnetic permeability, - determining a deviation between said first reference state and said second reference state; and - deriving a correction function based on said deviation.

2. The method according to claim 1, in, Modeling the magnetic field generating device (5, 105) comprises adapting the magnetic field generating device so that the magnetic properties of the magnetic field generating device (5, 105) generated by the modeled magnetic field generating device (5, 105), in particular the self-inductance of the magnetic field generating device (5, 105), are within a characteristic tolerance range, in particular a self-inductance tolerance range, in particular determined experimentally.

3. The method according to claim 1 or 2, in, Modeling the magnetic field generating device (5, 105) comprises adapting the magnetic field generating device so that the calibration factor generated by the modeled magnetic field generating device (5, 105) is within a tolerance range of the calibration factor, in particular within an experimentally determined tolerance range of the calibration factor.

4. The method according to at least one of the preceding claims, in, Modeling the magnetic field generating device (5, 105) comprises adapting the magnetic field generating device such that a linearity generated by the modeled magnetic field generating device (5, 105) lies within a linearity tolerance range, in particular within an experimentally determined linearity tolerance range.

5. The method according to at least one of claims 2 to 4, in, When modeling the magnetic field generating device (5, 105), a distance is assumed between at least two individual components of the magnetic field generating device (5, 105), or between the measuring tube (2) of the magnetic-inductive flowmeter (1) and the magnetic field generating device (5), or between the housing wall (117) of the magnetic-inductive flow measuring probe (101) and the magnetic field generating device (105), The modeling includes adjusting the distance until the variable to be adjusted matches the corresponding tolerance range.

6. The method according to at least one of the preceding claims, in, The magnetic field generating device (5, 105) comprises a coil (6, 113) and a coil core (14, 111), Therein, the magnetic permeability of the coil core (14, 111) is included in the modeling of the magnetic field generating device (5, 105).

7. The method according to claim 6, in, The magnetic field generating device (5, 105) comprises a pole shoe (21, 112), Therein, the magnetic permeability of the pole shoe (21, 112) is included in the modeling of the magnetic field generating device (5, 105).

8. The method according to at least one of claims 1 to 5, in, The magnetic field generating device (5, 105) comprises two, in particular diametrically arranged, coils (6i), each coil having a coil core (14i) and a field guide (22) connecting the two coil cores (14i). Therein, the magnetic permeabilities of the two coil cores (14i) and the field guide (22) are included in the modeling of the magnetic field generating device (5, 105).

9. The method according to at least one of claims 1 to 5, in, The magnetic field generating device (5, 105) comprises a coil (6), which in particular has no coil core and no field guide (22). Therein, the magnetic permeability of the field guide (22) is included in the modeling of the magnetic field generating device (5, 105).

10. The method according to at least one of the preceding claims, in, In said first reference state, a first magnetic property is determined, in particular a first self-inductance or a variable which depends on said first self-inductance, Therein, in the second reference state, a second magnetic property deviating from the first magnetic property is determined, in particular a second self-inductance deviating from the first self-inductance or a variation deviating from the first self-inductance.

11. The method according to claim 10, in, Determining a deviation between the first reference state and the second reference state comprises determining a first deviation between the first magnetic property and the second magnetic property, in particular a first deviation between the first self-inductance and the second self-inductance.

12. The method according to at least one of the preceding claims, in, Determining a deviation between the first reference state and the second reference state includes determining a second deviation between a first flow rate related measurement variable resulting from the first reference state and a second flow rate related measurement variable resulting from the second reference state.

13. The method according to claims 11 and 12, in, The correction function results from a functional relationship between the first deviation or a variable derivable from the first deviation and the second deviation or a variable derivable from the second deviation.

14. The method according to at least one of the preceding claims, in, The correction function can be described by means of a polynomial function having at least one linear part, The linear part includes the factor .

15. The method according to claim 14, in, The factor is a variable specific to the geometry of the magnetic system.

16. The method according to claim 14 or 15, in, In the case where the magnetic field generating device (5, 105) comprises a saddle coil, the factor is selected from a first factor range having limits 1 and 4, in particular 1.5 and 2.5, or their corresponding reciprocals, Wherein, in the case where the magnetic field generating device (5, 105) comprises a cylindrical coil, the factor A first factor range is selected having limits 4 and 8, in particular 5 and 7, or their corresponding reciprocals.

17. The method according to any one of claims 14 to 16, in, The factor The correlation is carried out via a second-order polynomial function with a measuring tube-specific variable or a pipeline-specific variable, in particular with the measuring tube inner diameter or the pipeline inner diameter.

18. A method for calibrating a flow rate-related measured variable of a magnetic induction flow meter (1) or a magnetic induction flow meter probe (101), comprising the following method steps: - determining the current magnetic properties of the magnetic-inductive flowmeter (1) or of the magnetic-inductive flow measuring probe (101), in particular the self-inductance or a current variable dependent on the self-inductance; - Determine the flow rate related measurement variables; - applying a correction factor of a correction function, in particular a correction function determined by means of a method according to at least one of the preceding claims, to the determined current magnetic property, in particular the current self-inductance or a variable depending on the current self-inductance, for correcting the flow rate-related measured variable, in, The correction function assigns the current magnetic property, in particular the current self-inductance or a variable which depends on the current self-inductance, to a correction factor for the flow rate-dependent measured variable.

19. The method according to claim 18, in, The correction function is independent of the flow rate.

20. The method according to claim 18 or 19, comprising the following method steps: - determining the effective magnetic permeability of the medium as a function of the current magnetic property, in particular the current self-inductance or a variable which depends on the current self-inductance, and / or the correction factor.

21. A magnetic induction flowmeter (1) for detecting a flow velocity-related measurement variable of a flowable medium, comprising: A measuring tube (2), the measuring tube being used for conducting a medium; A magnetic field generating device (5), the magnetic field generating device being used to generate a magnetic field penetrating the measuring tube (2); at least one measuring electrode (17, 18) for determining a measuring voltage induced in the flowable medium; and an evaluation circuit (24) for determining the flow rate-related measurement variable; Characterized in that the evaluation circuit (24) is configured to carry out the method according to at least one of claims 18 to 20.

22. A magnetic induction flow measurement probe (101) for detecting a flow velocity-related measurement variable of a flowable medium, in, The magnetic induction flow measurement probe (101) can be arranged in an opening of a pipeline, comprising: - a housing (102) in contact with the medium, - a magnetic field generating device (105) for generating a magnetic field penetrating the housing (102), Wherein, the magnetic field generating device (105) is arranged in the housing (102); - at least one measuring electrode (103, 104) for determining a measuring voltage induced in the medium; and - an evaluation circuit (119) for determining the flow rate-related measured variable; The method is characterized in that the evaluation circuit (119) is configured to carry out the method according to at least one of claims 18 to 20.

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