Method for determining a correction function

Abstract

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

Description

[0001] Method for determining a correction function

[0002] The invention relates to a method for determining a correction function, a method for correcting a flow velocity-dependent measured variable, a magnetic-inductive flowmeter and a magnetic-inductive flowmeter probe.

[0003] Magnetic-inductive flow measuring devices are used to determine the flow velocity and volume flow of a flowing medium in a pipeline. In this case, a distinction is made between inline magnetic-inductive flow measuring devices and magnetic-inductive flow measuring probes, which are inserted into a lateral opening of a pipeline. A magnetic-inductive flow measuring device has a magnetic field-generating device for generating a magnetic field. A main axis of the magnetic field runs essentially perpendicular to the flow direction of the flowing medium. Saddle or cylindrical coils are typically used for this purpose. To create a predominantly homogeneous magnetic field, additional pole pieces are shaped and mounted relative to the flow direction so that the magnetic field lines run across the entire pipe cross-section essentially perpendicular to the transverse axis or parallel to the vertical axis of the measuring tube.In addition, a magnetic-inductive flowmeter has a measuring tube with a magnetic field-generating device located on its outer surface. A pair of measuring electrodes attached to the outer surface of the measuring tube taps an electrical measuring voltage or potential difference perpendicular to the flow direction and the magnetic field. This voltage or potential difference arises when a conductive medium flows in the direction of flow with a magnetic field applied. Since the tapped measuring voltage depends on the velocity of the flowing medium according to Faraday's law of induction, the flow velocity and—with the addition of a known pipe cross-section—the volumetric flow can be determined from the induced measuring voltage.

[0004] In contrast to a magnetic-inductive flowmeter, which comprises a measuring tube for conveying the medium with an attached device for generating a magnetic field penetrating the measuring tube and measuring electrodes, magnetic-inductive flow measuring probes with their usually circular-cylindrical housing are inserted into a lateral opening of a pipeline and fixed in a fluid-tight manner. A special measuring tube is no longer necessary. The measuring electrode arrangement and coil arrangement on the outer surface of the measuring tube mentioned above are omitted and replaced by a device for generating a magnetic field arranged inside the housing and in immediate proximity to the measuring electrodes. This device is designed such that an axis of symmetry of the magnetic field lines of the generated magnetic field intersects the front surface or the area between the measuring electrodes perpendicularly.There are already a variety of different magnetic-inductive flow measuring probes available in the state of the art.

[0005] Magnetic-inductive flow measuring devices are widely used in process and automation technology for fluids with an electrical conductivity of approximately 5 S / cm and above. The applicant markets corresponding flow measuring devices in a wide variety of designs for various applications, for example, under the names PROMAG or MAGPHANT.

[0006] It is known that magnetic solids in the medium can lead to increased errors in the determination of the flow velocity-dependent measured variable. One reason for this is that the magnetic flux density of the generated magnetic field during measurement is generally not measured. Instead, a preset and expected magnetic flux density is used to determine the flow velocity-dependent measured variable. However, this is determined at the factory under ideal conditions and, if magnetic solids are present in the flowing medium, does not correspond to the actual magnetic flux density.

[0007] DE 10 2006 026 772 A1 discloses a method for determining a flow velocity-dependent measured variable using a magnetic-inductive flowmeter. In this method, conclusions about the presence of magnetically conductive solids in the medium are drawn based on a deviation of the current rise time – which must be waited for until a magnitude of the magnetic field (i.e., the magnetic flux density) assumes a predetermined target value – from a predetermined rise time. Based on this deviation, a correction factor is then determined to compensate for the measurement error.

[0008] The invention is based on the object of providing an alternative solution.

[0009] The object is achieved by the method for determining a correction function according to claim 1, the method for correcting according to claim 18, the magnetic-inductive flow measuring device according to claim 21 and the magnetic-inductive flow measuring probe according to claim 22.

[0010] The method according to the invention for determining a correction function of a flow velocity-dependent measured variable of a flowable medium for a magnetic-inductive flowmeter or for a magnetic-inductive flowmeter probe comprises the following method steps:

[0011] - modelling a magnetic field generating device, in particular by means of a preferably numerical simulation method, wherein the modelling of the magnetic field generating device includes a magnetic permeability of the magnetic field generating device or at least one individual component of the magnetic field generating device,

[0012] - Determining a first reference state, wherein in the first reference state the medium to be guided has a first magnetic permeability,

[0013] - Determining a second reference state, wherein in the second reference state the medium to be fed has a second magnetic permeability that differs from the first permeability,

[0014] - Determining a deviation between the first reference state and the second reference state; and

[0015] - Deriving a correction function from the deviation.

[0016] The method according to the invention has the advantage that it not only considers the magnetic properties of the magnetic field-generating device or the individual components of the magnetic field-generating device when determining the correction function, but also the influence of the magnetic solids on the individual components and the interaction with the individual components of the magnetic field-generating device. Thus, the correction function of the method according to the invention is suitable for all magnetic-inductive flowmeters and magnetic-inductive flow measuring probes with known magnetic field-generating devices, regardless of the operating signal and control method.

[0017] Modeling, as defined in the present application, involves creating a model. The model is preferably created using a simulation process. Alternatively, modeling can also involve creating a prototype. In this case, a test setup with adjustable conditions corresponding to the first reference state and the second reference state is created and measured.

[0018] It is particularly advantageous to create the model using a suitable simulation method. A numerical simulation method such as the finite element method is particularly suitable.

[0019] The creation of correction functions or correction factors using simulation methods is already known in general. US Pat. No. 11,199,436 B2 discloses a magnetic-inductive flowmeter in which specific correction factors are stored using the finite element method and computational flow dynamics (CFD) to correct measurement errors caused by disturbances located on the inlet and / or outlet side (elbows, valves, etc.). These disturbances result in an asymmetric flow profile, and the assumption typically made when configuring the magnetic-inductive flowmeter that the flow profile is completely rotationally symmetrical is no longer valid.However, the present invention must be distinguished from the cited prior art, since the present solution does not take into account the influences of the process line on the flow profile in the measuring tube, but rather the influence of magnetic solids on the magnetic field generating device and the magnetic field generated by it.

[0020] The first reference state can, for example, reflect the state of the magnetic-inductive flowmeter or the magnetic-inductive flow probe during calibration. In this case, the medium can consist of water, which is free of magnetic solids.

[0021] In the second reference state, the medium can contain magnetic solids. For simplicity, the entire medium is assigned a second magnetic permeability. However, especially in simulations, it is also possible to provide a multiphase medium in which the individual phases have different magnetic permeabilities.

[0022] The flow velocity-dependent measured variable includes the electrical potential applied to a measuring electrode, the measuring voltage between two measuring electrodes, the determined flow velocity, the determined volume flow and / or the determined mass flow.

[0023] Advantageous embodiments of the invention are the subject of the subclaims.

[0024] One embodiment provides that the modeling of the magnetic field generating device comprises adapting it so that a magnetic characteristic of the magnetic field generating device resulting from the modeled magnetic field generating device, in particular a self-inductance of the magnetic field generating device, lies within a characteristic tolerance range, in particular a self-inductance tolerance range, which is determined in particular experimentally.

[0025] An advantage of this design is that the magnetic parameters of the magnetic field-generating device are incorporated into the model, thus enabling more precise correction. The magnetic parameter, in particular the self-inductance, can be determined using the magnetic-inductive flowmeter or the magnetic-inductive flowmeter probe. The determination of self-inductance is taught, for example, in WO 2021 / 121960 A9 and WO 2021 / 110442 A1, to which reference is made in its entirety. Thus, the self-inductance present during operation results, for example, from the temporal coil current curve and / or voltage curve. In the simulation, for example, the simulated self-inductance L results from the volume integral of the product of the magnetic field strength H and the magnetic flux density B divided by the square of the coil current I. 2The self-inductance L depends directly on the magnetic permeability of the medium, but not on the flow velocity-dependent size of the medium.

[0026] The self-inductance tolerance range can consist of a single self-inductance value determined for a single measuring instrument or of a range spanned by a large number of measured self-inductance values ​​from different measuring instruments.

[0027] One embodiment provides that the modeling of the magnetic field generating device comprises adapting it so that a calibration factor C resulting from the modeled magnetic field generating device lies within a calibration factor tolerance range, in particular determined experimentally.

[0028] For optimal model design, it is advantageous to check whether the calibration factor C resulting from the model lies within an experimentally determined calibration factor tolerance range. The experimentally determined calibration factor tolerance range results, for example, from the set of calibration factors for previously manufactured and calibrated magnetic-inductive flowmeters or magnetic-inductive flow probes. The calibration factor C resulting from the model can be determined, for example, by calculating the electrical potentials in the measuring cross-section at a set flow velocity.

[0029] The calibration factor tolerance range can consist of a single calibration value that is intended for a single measuring device or of a range that is spanned by a large number of measured calibration values ​​from different measuring devices.

[0030] One embodiment provides that the modeling of the magnetic field generating device comprises an adaptation of the device such that a linearity resulting from the modeled magnetic field generating device lies within a linearity tolerance range, in particular one determined experimentally.

[0031] The linearity is a measure of how the induced measuring voltage is independent of the Reynolds number over the largest possible Reynolds number range (usually 10 4 up to 10 6). If a magnetic-inductive flowmeter or a magnetic-inductive flow measuring probe is linear over a given Reynolds number range and thus Reynolds number independent, the correction factor C can be chosen to be constant and the simplification U = f S u can be assumed, where U is the induced measuring voltage, f is a Reynolds-dependent function (which is constant in this case), S is the nominal signal strength, and u is the flow velocity. The linearity of the model can be calculated for the fit. The calculated linearity is then compared with a linearity tolerance range.

[0032] The linearity tolerance range can consist of a single linearity value that is determined for a single measuring device or of a range that is spanned from a large number of measured linearity values ​​from different measuring devices.

[0033] One embodiment provides that when modeling the magnetic field generating device, a distance between at least two individual components of the magnetic field generating device or between a measuring tube of the magnetic inductive flowmeter and the magnetic field generating device or between a housing wall of the magnetic inductive flowmeter and the magnetic field generating device is assumed, wherein the modeling comprises adjusting the distance until the respective variables to be adjusted correspond to the corresponding tolerance range.

[0034] The advantage of this design is that it allows for a more precise match between the simulated magnetic-inductive flowmeter or the simulated magnetic-inductive flow measuring probe, in particular between the magnetic parameters resulting from the simulations and the magnetic parameters of a real magnetic-inductive flowmeter or magnetic-inductive flow measuring probe. By assuming a distance between two individual components of the magnetic field-generating device—for example, in the form of an air gap—influences from boundary areas between the generally ferromagnetic individual components can be taken into account in the modeling.

[0035] One embodiment provides that the magnetic field generating device comprises a coil and a coil core, wherein the magnetic permeability of the coil core is included in the modeling of the magnetic field generating device.

[0036] One embodiment provides that the magnetic field generating device comprises a pole shoe, wherein the magnetic permeability of the pole shoe is included in the modeling of the magnetic field generating device.

[0037] One embodiment provides that the magnetic field generating device comprises two, in particular diametrically arranged, coils, each with a coil core and a field guide body connecting the two coil cores, wherein the magnetic permeability of the two coil cores and the field guide body is included in the modeling of the magnetic field generating device.

[0038] One embodiment provides that the magnetic field generating device comprises a coil, in particular a coil core-free coil, and a field guide body, wherein the magnetic permeability of the field guide body is included in the modeling of the magnetic field generating device.

[0039] One embodiment provides that in the first reference state, a first magnetic characteristic, in particular a first self-inductance or a variable dependent thereon, is determined, wherein in the second reference state, a second magnetic characteristic deviating from the first magnetic characteristic, in particular a second self-inductance deviating from the first self-inductance or a variable deviating therefrom, is determined.

[0040] The self-inductance of the magnetic field-generating device determined during operation includes not only the inductance resulting from the coil arrangement, but also its temperature dependence and its dependence on external magnetic fields. If the medium to be conveyed contains ferromagnetic solids, these influence the generated magnetic field, particularly the magnetic flux in the medium. As a first approximation, the medium and the ferromagnetic solid can be interpreted as part of the coil core. An approximate formula for the self-inductance of a long coil is L = n0 / i r N 2 A ■ l~ r , where A is the cross-sectional area of ​​the coil, N is the number of turns, and l is the length of the coil. To a first approximation, ferromagnetic solids therefore influence the n r, which can no longer be assumed to be constant. Thus, self-inductance is not only a variable, but also extremely sensitive to external magnetic fields—e.g., those generated by foreign magnetic bodies.

[0041] The determination of the self-inductance for the first reference state and the second

[0042] The reference state is advantageous because it allows a comparison with the real self-inductance of the magnetic-inductive flowmeter or the magnetic-inductive flowmeter probe during operation.

[0043] One 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 characteristic and the second magnetic characteristic, in particular the first self-inductance and the second self-inductance.

[0044] 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 velocity-dependent measured variable resulting from the first reference state and a second flow velocity-dependent measured variable resulting from the second reference state.

[0045] One embodiment provides that 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.

[0046] The correction function can be stored in the magnetic-inductive flowmeter or in the magnetic-inductive flow measuring probe and used in operation by a measuring circuit to determine a more accurate flow velocity-dependent measured variable.

[0047] One embodiment provides that the correction function can be described by means of a polynomial function with at least one linear component, wherein the linear component comprises a factor A.

[0048] One embodiment provides that the factor A is a magnet system geometry-specific value.

[0049] The factor A can vary with different magnet system geometries. This means that the factor A for a magnetic field generating device consisting of two diametrically arranged saddle coils differs from a factor A that occurs with a magnetic field generating device consisting of two diametrically arranged cylindrical coils. However, not only the individual components generating the magnetic field, but also the individual components conducting the magnetic field influence the factor A. Furthermore, magnetic-inductive flowmeters with more than two coils are known. These are usually arranged distributed across the measuring cross-section. This also influences the factor A. One embodiment provides that the factor A is selected from a first factor range with the limits 1 and 4, in particular 1.5 and 2.5, ortheir corresponding reciprocals in the case that the magnetic field generating device comprises a saddle coil, wherein the factor A is selected from a first factor range with the limits 4 and 8, in particular 5 and 7, or their corresponding reciprocals in the case that the magnetic field generating device comprises a cylindrical coil.

[0050] One embodiment provides that the factor A correlates with a measuring tube-specific variable or a pipeline-specific variable, in particular with a measuring tube inner diameter or pipeline inner diameter, via a second-order polynomial function.

[0051] Surprisingly, it has been found that the factor A increases with the measuring tube inner diameter or the diameter of the magnet system, while maintaining the same geometry.

[0052] Pipeline inner diameters correlate. Thus, although magnetic-inductive flowmeters with different nominal diameters have different A factors, they correlate with each other via a functional relationship. As the diameter increases, the A factor decreases. The correlation can be described using a second-order polynomial function.

[0053] For magnetic-inductive flowmeters, the factor correlates with the pipe diameter of the process line in which the magnetic-inductive flowmeter is installed. For this purpose, it can be advantageous if the polynomial function for describing the correlation is stored in the magnetic-inductive flowmeter and the pipe diameter of the process line can be specified by the user. The measuring circuit is configured to determine the applicable factor A, taking the specified pipe diameter into account, and to calculate the flow velocity-dependent measured variable based on the factor A.

[0054] The method according to the invention for correcting a flow velocity-dependent measured variable of a magnetic-inductive flowmeter or a magnetic-inductive flowmeter probe comprises the following method steps:

[0055] - Determining a current magnetic characteristic, in particular a current self-inductance or a current self-inductance-dependent quantity, of the magnetic-inductive flowmeter or the magnetic-inductive flowmeter probe; - Determining a flow velocity-dependent measured quantity;

[0056] - Applying a correction function, in particular a correction function determined by means of a method according to at least one of the preceding claims, for the determined current magnetic characteristic, in particular current self-inductance or the variable dependent on the current self-inductance for the correction of the flow velocity-dependent measured variable, wherein the correction function assigns the current magnetic characteristic, in particular the current self-inductance or the variable dependent on the current self-inductance, to a correction factor for the flow velocity-dependent measured variable.

[0057] One embodiment provides that the correction function is independent of the flow velocity.

[0058] One embodiment includes the following procedural step:

[0059] - Determination of an effective magnetic permeability of the medium as a function of the current magnetic characteristic, in particular the current self-inductance or a value dependent on the current self-inductance and / or the correction factor.

[0060] The magnetic-inductive flowmeter according to the invention for determining a flow velocity-dependent measured variable of a flowable medium comprises:

[0061] - a measuring tube for guiding the medium;

[0062] - a magnetic field generating device for generating a magnetic field penetrating the measuring tube;

[0063] - at least one measuring electrode for determining a measuring voltage induced in the flowable medium; and

[0064] - a measuring circuit for determining the flow velocity-dependent measured variable; and is characterized in that the measuring circuit is configured to carry out the correction method according to the invention.

[0065] The magnetic-inductive flow measuring probe according to the invention for determining a flow velocity-dependent measured variable of a flowable medium, wherein the magnetic-inductive flow measuring probe can be arranged in an opening of a pipeline, comprises:

[0066] - a housing in contact with the medium,

[0067] - a magnetic field generating device for generating a magnetic field penetrating the housing, wherein the magnetic field generating device is arranged in the housing;

[0068] - at least one measuring electrode for determining a measuring voltage induced in the medium; and

[0069] - a measuring circuit for determining the flow velocity-dependent measured variable; and is characterized in that the measuring circuit is configured to carry out the correction method according to the invention.

[0070] The invention is explained in more detail with reference to the following figures. They show:

[0071] Fig. 1: an embodiment of a magnetic-inductive flow meter according to the invention;

[0072] Fig. 2: a perspective view of a partially sectioned embodiment of a magnetic-inductive flow measuring probe according to the invention;

[0073] Fig. 3: a further embodiment of the magnetic-inductive flow meter according to the invention;

[0074] Fig. 4: an embodiment of the method according to the invention for correcting the flow velocity-dependent measured variable;

[0075] Fig. 5: an embodiment of the method according to the invention for determining the correction function;

[0076] Fig. 6: the functional relationship between the measurement errors caused by magnetic solids in the medium and the change in the determined magnetic characteristic of the magnetic field generating device; and

[0077] Fig. 7: the functional relationship between factor ,4 and measuring tube inner diameter or pipeline inner diameter.

[0078] Fig. 1 shows a cross-section of an embodiment of the magnetic-inductive flowmeter 1 according to the invention, in particular of the measuring sensor. The structure and measuring principle of a magnetic-inductive flowmeter 1 are basically known. A flowable medium is passed through a measuring tube 2, which medium must have a minimum electrical conductivity so that the flow velocity-dependent measured variable can be determined. The measuring tube 2 comprises a support tube 3, which is usually made of steel, ceramic, plastic or glass or at least comprises these. A magnetic field generating device 5 for generating a magnetic field is arranged on the support tube 3 such that the magnetic field lines are oriented essentially perpendicular to a longitudinal direction defined by a measuring tube axis. The magnetic field generating device 5 usually comprises at least one saddle coil or at least one (cylindrical) coil 6i.A coil core 14i typically extends through a receptacle 15 of the coil 6i. Receptacle 15 is understood to be the volume defined by the coil wire forming the coil 6i. The receptacle 15 of the coil 6i can thus be formed by a coil holder or by the imaginary enclosed volume. The latter occurs when the coil wire of the coil 6i is wound directly around the coil core 14i. The coil core 14i is formed from a magnetically conductive, in particular soft-magnetic, material. The magnetic field-generating device 5 further comprises a pole shoe 21i arranged at one end of the coil core 14i. The pole shoe 21i can be a separate component or monolithically connected to the coil core 14i. In the embodiment shown in Fig. 1, two diametrically arranged coils 6a, 6b each have a coil core 14a, 14b and a pole piece 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 body 22. The field guide body 22 connects the opposite sides of the coil cores 14a, 14b and is designed to guide the generated magnetic field. However, magnetic-inductive flowmeters with exactly one coil 6, with exactly one coil core 14, and without a field guide body 22 are also known. The coils 6a, 6b are connected to an operating circuit 7, which operates the coils 6a, 6b with an operating signal. The operating signal can be a voltage with a time-varying profile and is characterized by operating signal parameters, wherein at least one of the operating signal parameters is controllable. The magnetic field generated by the magnetic field-generating device 5 is generated by a direct current of alternating polarity, clocked by an operating circuit 7.This ensures a stable zero point and makes the measurement insensitive to the influence of electrochemical interference. The two coils 6a, 6b can be connected separately to the operating circuit 7 or connected in series or parallel to each other.

[0079] When a magnetic field is applied, a flow-dependent potential distribution is created in the measuring tube 2 or in the flowing medium, which can be detected, for example, in the form of an induced measuring voltage. A device 8 for tapping the induced measuring voltage is arranged on the measuring tube 2. In the embodiment shown, the device 8 for tapping the induced measuring voltage is formed by two oppositely arranged measuring electrodes 17, 18 for forming a galvanic contact with the medium. However, magnetic-inductive flowmeters are known which have measuring electrodes arranged on the outer wall of the support tube 3 that are not in contact with the medium. As a rule, the measuring electrodes 17, 18 are arranged diametrically and form an electrode axis or are intersected by a transverse axis that runs perpendicular to the magnetic field lines and the longitudinal axis of the measuring tube 2.However, devices 8 for tapping the induced measuring voltage are also known, which have more than two measuring electrodes. The flow velocity-dependent measured variable can be determined based on the measured measuring voltage. The flow velocity-dependent measured variable includes the flow velocity, the volume flow rate, and / or the mass flow rate of the medium. A measuring circuit 23 is configured to detect the induced measuring voltage applied to the measuring electrodes 17, 18, and an evaluation circuit 24 is configured to determine the flow velocity-dependent measured variable and is further configured to carry out the inventive method for correcting the flow velocity-dependent measured variable.

[0080] For this purpose, the evaluation circuit 24 is configured to determine a current magnetic characteristic, in particular a self-inductance or a current variable dependent on the self-inductance. Furthermore, the evaluation circuit 24 is configured to apply a correction factor of a correction function, which is stored or determined as a function of the magnetic characteristic, in particular the self-inductance or the variable dependent on the self-inductance and is determined using the method according to the invention for determining a correction function, to the determined flow velocity-dependent measured variable in order to correct it.

[0081] The evaluation circuit 24 can be arranged in the sensor or in the transmitter.

[0082] The support tube 3 is often made of an electrically conductive material, such as steel. To prevent the measuring voltage applied to the first and second measuring electrodes 2, 3 from being dissipated via the support tube 3, the inner wall is lined with an insulating material, for example, a (plastic) liner 4.

[0083] Commercially available magnetic-inductive flowmeters have, in addition to the

[0084] Measuring electrodes 17, 18 have two further electrodes 19, 20. Firstly, a level monitoring electrode 19, ideally mounted at the highest point in the measuring tube 2, serves to detect partial filling of the measuring tube 1 and is configured to forward this information to the user and / or to take the level into account when determining the volume flow. Furthermore, a reference electrode 20, which is usually mounted diametrically opposite the level monitoring electrode 19 or at the lowest point of the measuring tube cross-section, serves to set a controlled electrical potential in the medium. The reference electrode 20 is generally used to connect the flowing medium to a ground potential.

[0085] The operating circuit 7, regulator circuit 10, measuring circuit 23, and evaluation circuit 24 can be part of a single electronic circuit or form separate circuits. The evaluation circuit 24 comprises electronic components for implementing the method according to the invention. For this purpose, it can comprise a microcontroller, logic electronic components, and / or electrical components.

[0086] However, magnetic-inductive flowmeters are also known with a magnetic field generating device 5 that differs from the one shown. For example, the magnetic field generating device 5 can comprise just one coil - in the form of a cylindrical coil or a saddle coil - or it can have more than two coils that are distributed over the casing surface in the circumferential direction or longitudinal direction. For optimal coil design, coil cores are generally provided that extend through a coil receptacle. For a more homogeneous magnetic field distribution in the measuring tube, especially when cylindrical coils are used, pole shoes are provided that are generally arranged between the coil and the casing surface of the measuring tube and cover a larger proportion of the casing surface than the coil. The pole shoe 21 does not necessarily have to have bevelled areas as shown in Fig. 1, but can also - as for exampleThe field guide body 22 can be rounded and take the shape of a circular arc, as disclosed in WO 2021 / 043586 A1. The field return body 22 does not have to be angular as shown, but can also take the shape of a circular arc. The field guide body 22 magnetically connects the two coil cores 6a, 6b to achieve a more effective and faster reversal of the magnetic fields.

[0087] The measuring principle underlying the invention is first explained using the perspective and partially sectioned illustration in Fig. 2. A flow measuring probe 101 comprises a generally circular-cylindrical housing 102 having a predetermined outer diameter. This housing is adapted to the diameter of a bore located in a wall of a pipeline (not shown in Fig. 1) and into which the flow measuring probe 101 is inserted in a fluid-tight manner. A medium to be measured flows in the pipeline, into which the flow measuring probe 101 is immersed practically perpendicular to the flow direction of the medium, which is indicated by the wavy arrows 118. A front end 116 of the housing 102 projecting into the medium is fluid-tightly sealed by a front body 115 made of insulating material.By means of a magnetic field-generating device 105 arranged in the housing 102, comprising a coil arrangement 106, a magnetic field 109 can be generated that extends through the end section into the medium. A coil core 111, which is made at least partially of a soft magnetic material and is arranged in the housing 102, ends at or near the end section 116. A field return body 114, which encloses the coil arrangement 106 and the coil core 111, is configured to return the magnetic field 109 extending from the end section into the housing 102. The coil core 111, the pole piece 112, and the field return body 114 are each field guide bodies 110, which together form a field guide arrangement 105.A first and a second measuring electrode 103, 104, which forms a galvanic contact with the medium to be conveyed, form the device for detecting a measuring voltage induced in the medium. They are arranged in the front body 115 and, like the outer walls of the housing, contact the medium. An electrical voltage induced at the measuring electrodes 103, 104 based on Faraday's law of induction can be tapped using a measuring circuit. This voltage is maximum when the flow measuring probe 101 is installed in the pipeline in such a way that a plane spanned by a straight line intersecting the two measuring electrodes 103, 104 and a longitudinal axis of the flow measuring probe runs perpendicular to the flow direction 118 or the longitudinal axis of the pipeline.An 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 in order to thereby generate a clocked magnetic field 109.

[0088] The evaluation circuit 119 of the magnetic-inductive flow measuring probe 101 is configured to carry out the correction method according to the invention. For this purpose, the evaluation circuit 119 is configured to determine a current magnetic characteristic, in particular a self-inductance or a current variable dependent on the self-inductance. Furthermore, the evaluation circuit 119 is configured to apply a correction factor of a correction function, which is stored or determined as a function of the magnetic characteristic, in particular the self-inductance or the variable dependent on the self-inductance and which is determined using the method according to the invention for determining a correction function, to the determined flow velocity-dependent measured variable in order to correct it.

[0089] Fig. 3 shows a further embodiment of the magnetic-inductive

[0090] Flowmeter 301. The magnetic field-generating device 305 of the illustrated embodiment comprises two diametrically arranged saddle coils 306, the shape of which each adapts to the outer contour of the outer surface of the measuring tube 302. Additionally, the magnetic-inductive flowmeter 301 can also comprise field guide bodies (not shown) configured to guide the magnetic field from one saddle coil 306 to the opposite saddle coil 306. Alternatively, the magnetic-inductive flowmeter 301 can comprise only one saddle coil 306.

[0091] Fig. 4 shows an embodiment of the method according to the invention for correcting the flow velocity-dependent variable with the method steps 401 to 404.

[0092] In a first method step 401, the current magnetic characteristic, in particular a self-inductance or a current variable dependent on the self-inductance, of the magnetic-inductive flowmeter or the magnetic-inductive flowmeter probe is determined. Magnetic-inductive flowmeters are already known that are designed to determine, in addition to the flow velocity-dependent measured variable, also the self-inductance resulting from the temporal coil current and / or voltage curve. The self-inductance results, for example, from the rise behavior of the coil current when rectangular voltage curves are applied. The self-inductance determined in this way is a measure of the presence of magnetic solids in the medium. The self-inductance is a variable and can depend on the temperature and aging state of the magnetic field-generating device.

[0093] Subsequently, a flow velocity-dependent measured variable is determined in a second method step 402. The flow velocity-dependent measured variable can be an electrical potential measured at a measuring electrode, a potential difference or measuring voltage present between two measuring electrodes, a determined flow velocity, a determined volume flow, or a determined mass flow.

[0094] The third method step 403 comprises applying a correction function stored in the magnetic-inductive flowmeter or in the magnetic-inductive flow measuring probe, or a correction factor of the correction function, to correct the flow velocity-dependent measured variable. This is determined at the factory using the method according to the invention and stored in the magnetic-inductive flowmeter or the magnetic-inductive flow measuring probe. The correction function corresponds to the correction function assigned to the determined current magnetic characteristic variable, in particular the current self-inductance or the variable dependent on the current self-inductance, which assigns the current magnetic characteristic variable, in particular the current self-inductance or the variable dependent on the current self-inductance, to a correction factor for the flow velocity-dependent measured variable.

[0095] The correction function is determined in such a way that it is independent of the flow velocity.

[0096] The correction function can be a polynomial function with a linear component, where in the linear component the polynomial function has a gradient corresponding to the factor A.

[0097] An optional fourth method step 404 comprises determining an effective magnetic permeability of the medium as a function of the current magnetic characteristic, in particular the current self-inductance or a value dependent on the current self-inductance and / or the correction factor.

[0098] Fig. 5 shows an embodiment of the method according to the invention for determining the correction function for the flow velocity-dependent measured variable of a flowable medium for a magnetic-inductive flowmeter or for a magnetic-inductive flowmeter probe, comprising the method steps 501 to 505:

[0099] The 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 of an individual component of the magnetic field-generating device. The magnetic field-generating device generally consists of several individual components, such as one or more cylindrical or saddle coils, one or more coil cores, one or more pole pieces, and / or one or more field guide bodies. The finite element method, for example, is suitable as a simulation method.

[0100] Depending on the design of the magnetic field generating device and the presence of the individual components, the magnetic permeability of the individual component or the magnetic permeabilities of all individual components are taken into account for the modeling, i.e. in the model, the individual component or all individual components are each assigned a magnetic permeability which essentially corresponds to the actual magnetic permeability of the individual component installed in the measuring device. If at least one coil core is present, the magnetic permeability of at least one coil core is used in the modeling of the magnetic field generating device, i.e. in the model, the coil core is assigned the magnetic permeability of the coil core actually used in the measuring device. If at least one pole shoe is present, the magnetic permeability of the pole shoe is used in the modeling of the magnetic field generating device.If the magnetic field generating device has two coils, each with a coil core, which are connected to each other via a field guide body, then in addition to the magnetic permeability of the two coil cores, the magnetic permeability of the field guide body is also taken into account in the modeling of the magnetic field generating device.

[0101] Once all magnetic permeabilities have been assigned to the individual components of the magnetic field-generating device, the magnetic characteristic of the magnetic field-generating device resulting from the model, in particular a self-inductance of the magnetic field-generating device, is determined. The model is sufficiently suitable if the determined magnetic characteristic, in particular the self-inductance, lies within a characteristic tolerance range, in particular a self-inductance tolerance range, determined experimentally. Furthermore, a calibration factor C resulting from the modeled magnetic field-generating device must lie within a calibration factor tolerance range, determined experimentally.The calibration factor C is applied to the measured electrical potential, the measured and / or determined potential difference, or the measured voltage to determine the flow velocity or process variables derived therefrom. Furthermore, for a suitable model, the linearity resulting from the modeled magnetic field-generating device must lie within a linearity tolerance range, particularly one determined experimentally.

[0102] If the magnetic parameter, in particular the self-inductance, is not within the parameter tolerance range, in particular the self-inductance tolerance range, an adjustment of the modeled magnetic field-generating device is necessary. This adjustment is preferably achieved by providing a distance between at least two individual components of the magnetic field-generating device, or between a measuring tube of the magnetic-inductive flowmeter and the magnetic field-generating device, or between a housing wall of the magnetic-inductive flowmeter probe and the magnetic field-generating device in the model. The volume delimited by the individual components exhibits the magnetic properties of air or a vacuum.The distance is a variable in the model and is varied until the respective variables to be adjusted (CALF, self-inductance and / or linearity) match the corresponding tolerance range.

[0103] Method step 502 comprises determining a first reference state in which the medium to be conveyed has a first magnetic permeability. Water, which is free of magnetic foreign bodies, is suitable for this purpose. A first magnetic characteristic, in particular a first self-inductance or a variable dependent thereon, is determined for the first reference state.

[0104] Method step 503 comprises determining a second reference state in which the medium to be conveyed has a second magnetic permeability that differs from the first permeability. The second magnetic permeability results from the presence of magnetic solids in the medium (e.g., water). During modeling, the second magnetic permeability is assigned to the entire volume of water. For the second reference state, a second magnetic characteristic that differs from the first magnetic characteristic, in particular a second self-inductance that differs from the first self-inductance or a value that differs therefrom, is determined.

[0105] Method step 504 comprises determining a deviation between the first reference state and the second reference state. A first deviation between the first magnetic characteristic and the second magnetic characteristic, in particular the first self-inductance and the second self-inductance, is determined. In addition, a second deviation between a first flow velocity-dependent measured variable resulting from the first reference state and a second flow velocity-dependent measured variable resulting from the second reference state is determined.

[0106] Method step 505 comprises deriving a correction function from the deviation. 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. The correction function can be described by means of a polynomial function with at least one linear component and has a linear component with a factor A. The factor A is a magnet system geometry-specific variable and is selected from a first factor range with the limits 1 and 4, in particular 1.5 and 2.5, or their corresponding reciprocals in the case that the magnetic field generating device comprises a saddle coil, and selected from a first factor range with the limits 4 and 8, in particular 5 and 7, or their corresponding reciprocals in the case that the magnetic field generating device comprises a cylindrical coil.

[0107] Furthermore, factor A correlates with a measuring tube-specific variable or a pipeline-specific variable, in particular with a measuring tube inner diameter in the case of a magnetic-inductive flowmeter or a pipeline inner diameter in the case of a magnetic-inductive flowmeter, via a second-order polynomial function. Fig. 6 shows the functional relationship between the measurement errors caused by magnetic solids in the medium and the change in the determined magnetic characteristic of the magnetic field-generating device. The plotted measurement points were recorded in a test line using a magnetic-inductive flowmeter. Magnetic foreign bodies with known magnetic properties were mixed with water and pumped through the test line.The error of the flow velocity-dependent measured variable (Y-axis) was determined using a reference flowmeter that is insensitive to magnetic foreign bodies. A Coriolis flowmeter was used for this purpose. At the same time, the flowmeter's own self-inductance was continuously determined. The determined self-inductance is the self-inductance of the magnetic field-generating device, derived from the coil current and / or coil voltage over time. If the measurement error of the flow velocity-dependent measured variable is plotted against the change in the determined self-inductance (X-axis), a linear relationship is obtained. This relationship can be well described by the simulated function obtained from the inventive model. The determined straight line has a gradient that corresponds to the inventive factor ^.If the correction function or the factor ^4 is stored in the measuring device and the deviation of the self-inductance from the reference value can be determined, the error in the flow velocity-dependent measured value caused by magnetic foreign bodies can be determined or corrected.

[0108] Fig. 7 shows the functional relationship between factor ^ and the measuring tube inner diameter or pipeline inner diameter. The factor I (Y-axis), which results from the inventive method for determining a correction function, is determined for magnetic-inductive flowmeters with the same magnetic field-generating devices but different inner diameters and is plotted as a function of this (X-axis).

[0109] LIST OF REFERENCE SYMBOLS magnetic-inductive flowmeter 1

[0110] Measuring tube 2

[0111] Support tube 3

[0112] Liner 4 magnetic field generating device 5

[0113] Coil 6

[0114] Operating circuit 7

[0115] Device for tapping an induced measuring voltage 8

[0116] Regulator circuit 10

[0117] Coil core 14i

[0118] Recording of the coil 15

[0119] Measuring electrode 17

[0120] Measuring electrode 18

[0121] Level monitoring electrode 19

[0122] Reference electrode 20

[0123] Pole piece 21

[0124] Field guide body 22

[0125] Measuring circuit 23

[0126] Evaluation circuit 24

[0127] Coil arrangement 25 magnetic-inductive flow measuring probe 101

[0128] Housing 102

[0129] Measuring electrode 103

[0130] Measuring electrode 104 magnetic field generating device 105

[0131] Coil arrangement 106

[0132] Operating circuit 107

[0133] Field guidance arrangement 108

[0134] Magnetic field 109

[0135] Field guide body 110

[0136] Coil core 1 11

[0137] Pole piece 1 12

[0138] Coil 113

[0139] Field feedback body 1 14

[0140] Front body 115

[0141] End section 116

[0142] Housing wall 117 Flow direction of the medium 1 18

[0143] Evaluation circuit 1 19

Claims

PATENT CLAIMS 1 . A method for determining a correction function of a flow velocity-dependent measured variable of a flowable medium for a magnetic-inductive flowmeter (1) or for a magnetic-inductive flowmeter probe (101), comprising the method steps: - modelling a magnetic field generating device (5, 105), in particular by means of a preferably numerical simulation method, wherein the modelling of the magnetic field generating device (5, 105) includes a magnetic permeability of the magnetic field generating device (5, 105) or of at least one individual component 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 fed has a second magnetic permeability that differs from the first permeability, - Determining a deviation between the first reference state and the second reference state; and - Deriving a correction function from the deviation.

2. The method according to claim 1, wherein the modeling of the magnetic field generating device (5, 105) comprises adapting it so that a magnetic characteristic of the magnetic field generating device (5, 105) resulting from the modeled magnetic field generating device (5, 105), in particular a self-inductance of the magnetic field generating device (5, 105), lies within a characteristic tolerance range, in particular a self-inductance tolerance range, in particular an experimentally determined one.

3. The method according to claim 1 or 2, wherein the modeling of the magnetic field generating device (5, 105) comprises adapting it so that a calibration factor C resulting from the modeled magnetic field generating device (5, 105) lies within a calibration factor tolerance range, in particular an experimentally determined one.

4. Method according to at least one of the preceding claims, wherein the modeling of the magnetic field generating device (5, 105) comprises adapting it so that a linearity resulting from the modeled magnetic field generating device (5, 105) lies within a linearity tolerance range, in particular one determined experimentally.

5. Method according to at least one of claims 2 to 4, wherein the modeling of the magnetic field generating device (5, 105) is based on a distance between at least two individual components of the magnetic field generating device (5, 105) or between a measuring tube (2) of the magnetic inductive flow measuring device (1) and the magnetic field generating device (5) or between a housing wall (117) of the magnetic inductive flow measuring probe (101) and the magnetic field generating device (105), wherein the modeling comprises adjusting the distance until the respective variables to be adjusted agree with the corresponding tolerance range.

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

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

8. Method according to at least one of claims 1 to 5, wherein the magnetic field generating device (5, 105) comprises two, in particular diametrically arranged, coils (6i), each with a coil core (14i) and a field guide body (22) connecting the two coil cores (14i), wherein the magnetic permeability of the two coil cores (14i) and of the field guide body (22) is included in the modeling of the magnetic field generating device (5, 105).

9. Method according to at least one of claims 1 to 5, wherein the magnetic field generating device (5, 105) comprises a coil (6), in particular a coil core-free coil, and a field guide body (22), wherein the magnetic permeability of the field guide body (22) is included in the modeling of the magnetic field generating device (5, 105).

10. Method according to at least one of the preceding claims, wherein in the first reference state a first magnetic characteristic, in particular a first self-inductance or a variable dependent thereon, is determined, wherein in the second reference state a second magnetic characteristic deviating from the first magnetic characteristic, in particular a second self-inductance deviating from the first self-inductance or a variable deviating therefrom, is determined.

11. Method according to claim 10, wherein determining a deviation between the first reference state and the second reference state comprises determining a first deviation between the first magnetic characteristic and the second magnetic characteristic, in particular the first self-inductance and the second self-inductance.

12. The method according to at least one of the preceding claims, wherein determining a deviation between the first reference state and the second reference state comprises determining a second deviation between a first flow velocity-dependent measured variable resulting from the first reference state and a second flow velocity-dependent measured variable resulting from the second reference state.

13. The method according to claim 11 and 12, wherein 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. Method according to at least one of the preceding claims, wherein the correction function can be described by means of a polynomial function with at least one linear component, wherein the linear component comprises a factor A.

15. The method according to claim 14, wherein the factor A is a magnet system geometry-specific quantity.

16. Method according to claim 14 or 15, wherein the factor / is selected from a first factor range with the limits 1 and 4, in particular 1.5 and 2.5, or their corresponding reciprocals in the case that the magnetic field generating device (5, 105) comprises a saddle coil, wherein the factor / is selected from a first factor range with the limits 4 and 8, in particular 5 and 7, or their corresponding reciprocals in the case that the magnetic field generating device (5, 105) comprises a cylindrical coil.

17. Method according to at least one of claims 14 to 16, wherein the factor / correlates with a measuring tube-specific variable or a pipeline-specific variable, in particular with a measuring tube inner diameter or pipeline inner diameter, via a second-order polynomial function.

18. Method for correcting a flow velocity-dependent measured variable of a magnetic-inductive flowmeter (1) or a magnetic-inductive flowmeter probe (101), comprising the method steps: - determining a current magnetic characteristic, in particular a self-inductance or a current variable dependent on the self-inductance, of the magnetic-inductive flowmeter (1) or the magnetic-inductive flowmeter probe (101); - Determination of a flow velocity-dependent measured variable; - 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, for the determined current magnetic characteristic, in particular current self-inductance or the variable dependent on the current self-inductance for the correction of the flow velocity-dependent measured variable, wherein the correction function assigns the current magnetic characteristic, in particular the current self-inductance or the variable dependent on the current self-inductance, to a correction factor for the flow velocity-dependent measured variable.

19. Method according to claim 18, where the correction function is independent of flow velocity.

20. The method according to claim 18 or 19, comprising the step of: - Determination of an effective magnetic permeability of the medium as a function of the current magnetic characteristic, in particular the current self-inductance or a value dependent on the current self-inductance and / or the correction factor.

21. Magnetic-inductive flowmeter (1) for determining a flow velocity-dependent measured variable of a flowable medium, comprising: - a measuring tube (2) for guiding the medium; - a magnetic field generating device (5) for generating 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 velocity-dependent measured 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-inductive flow measuring probe (101) for determining a flow velocity-dependent measured variable of a flowable medium, wherein the magnetic-inductive flow measuring 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 velocity-dependent measured variable; 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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