Method for determining a flow-rate-dependent measured variable

Abstract

The invention relates to a method for determining a flow-rate-dependent measured variable for a flowable medium in a process line (300) by means of a magnetically inductive flowmeter (1) or a magnetically inductive flow measurement probe (101), wherein the process line (300) has a process line section (301) that is in contact with the medium and that adjoins an end face of the magnetically inductive flowmeter (1), comprising the method steps of: - determining at least one process-line-specific criterion, wherein the process-line-specific criterion is related to an influence of a character of the process line (300), in particular of the process line section (301), on the electrical potential distribution in the process line section (301); and - determining the flow-rate-dependent measured variable, wherein the process-line-specific criterion, in particular a criterion-specific variable associated with the process-line-specific criterion, is used to determine the flow-rate-dependent measured variable. The invention also comprises a magnetically inductive flowmeter (1) and a magnetically inductive flow measurement probe (101).

Description

[0001] Method for determining a flow velocity-dependent measured variable

[0002] The invention relates to a method for determining 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] Efforts are underway to make magnetic-inductive flowmeters more compact and to reduce the longitudinal extension of the measuring tube to the smallest possible length. However, this is accompanied by a measurement error in the measured flow, which can vary from measuring point to measuring point (1 to 5 percent). This measurement point-dependent measurement error also occurs with magnetic-inductive flowmeters.

[0007] The invention is based on the object of remedying the problem.

[0008] The object is achieved by the method according to claim 1, the method according to claim 2, the magnetic-inductive flow measuring device according to claim 14 and the magnetic-inductive flow measuring probe according to claim 15.

[0009] The method according to the invention for determining a flow velocity-dependent measured variable of a flowable medium in a process line by means of a magnetic-inductive flowmeter, wherein the process line has a process line section in contact with the medium, which is adjacent to an end face of the magnetic-inductive flowmeter, wherein the magnetic-inductive flowmeter comprises a measuring tube for guiding the medium, a magnetic field generating device for generating a magnetic field penetrating the measuring tube and at least one measuring electrode for determining an induced measuring voltage in the medium, comprising the method steps:

[0010] - Determining at least one process line-specific criterion, wherein the process line-specific criterion is related to an influence of a condition of the process line, in particular of the process line section, on an electrical potential distribution, in particular in the flow direction of the medium, in the process line section; and - Determining the flow velocity-dependent measured variable, wherein the process line-specific criterion, in particular a criterion-specific variable associated with the process line-specific criterion, is included in the determination of the flow velocity-dependent measured variable.

[0011] The advantage of this design is that by taking the process line and its influence on the electrical potential distribution in the flowing medium into account when determining the flow velocity-dependent measured variable, the measuring point-dependent measurement error is reduced and magnetic-inductive flowmeters can thus be implemented more compactly without having to accept any loss of measuring accuracy. It has been found that by taking the process line-specific criterion into account, the measuring point-dependent measurement error can be corrected. The customer or the installer only has to specify the process line-specific criterion valid for the measuring point in question in the magnetic-inductive flowmeter (e.g. during commissioning) or select it from a predefined list in the control system of the magnetic-inductive flowmeter. The selected process line-specific criterion is assigned a correction variable, iea correction factor and / or a correction offset is assigned or the criterion-specific quantity is a correction factor and / or a correction offset, which takes into account the process line-related electrical potential distribution and its influence on the measurement.

[0012] The use of electrically conductive grounding plates is known from the state of the art. These are installed on the front side between the magnetic-inductive flowmeter and the process line. These serve to establish a controlled electrical potential in the flowing medium and prevent a shift in the zero point of the induced measuring voltage in the medium. However, this solution is very costly, especially for large nominal diameters and special applications where corrosion can occur. One advantage of this solution is that the magnetic-inductive flowmeter can be used without the need for grounding plates.

[0013] The process line-specific criterion is a characteristic of the process line that influences the electrical potential distribution in the longitudinal direction of the flowing medium. The electrical potential distribution results from the local distribution of the electrical potential in a longitudinal section through the process line and the magnetic-inductive flowmeter.The method according to the invention for determining a flow velocity-dependent measured variable of a flowable medium in a process line by means of a magnetic-inductive flow measuring probe, wherein the process line has a process line section in contact with the medium, in which an opening is arranged, wherein the magnetic-inductive flow measuring probe is arranged in the opening, wherein the magnetic-inductive flow measuring probe comprises a medium-contacting housing, a magnetic field generating device for generating a magnetic field penetrating the housing and at least one measuring electrode for determining an induced measuring voltage in the medium, comprising the method steps:.

[0014] - Determining at least one process line-specific criterion, wherein the process line-specific criterion is related to an influence of a condition of the process line, in particular of the process line section, on an electrical potential distribution, in particular in the flow direction of the medium, in the process line section; and

[0015] - Determining the flow velocity-dependent measured variable, wherein the process line-specific criterion, in particular a criterion-specific variable assigned to the process line-specific criterion, is included in the determination of the flow velocity-dependent measured variable.

[0016] The advantage of this design is that by taking the process line and its influence on the electrical potential distribution in the flowing medium into account when determining the flow velocity-dependent measured variable, the application possibilities for magnetic-inductive flow measuring probes are significantly increased. This allows magnetic-inductive flow measuring probes to be used simultaneously in both metal and plastic process lines without the need for recalibration. Another advantage is that a single calibration is sufficient, for example, in a metal process line, even if the magnetic-inductive flow measuring probe is subsequently used in a plastic process line.

[0017] Advantageous embodiments of the invention are the subject of the dependent claims. One embodiment provides that the criterion-specific variable is determined by means of a simulation method, in particular a numerical one, wherein the process line-specific criterion is incorporated into the simulation method.

[0018] The use of numerical simulation methods to create flow simulations is already known and is already being used for the design of magnetic-inductive flowmeters and magnetic-inductive flow probes. The Navier-Stokes equations, Euler equations, Stokes equations, or potential equations are typically used for this purpose. Numerical simulation methods eliminate the need for experiments with flowing media and the experimental testing of a large number of potential measuring points. 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 (bends, valves, etc.).The aforementioned disturbances result in an asymmetric flow profile, and the assumption typically made when configuring the magnetic-inductive flowmeter that a completely rotationally symmetrical flow profile is present is no longer valid. However, the present invention differs from the cited prior art because the present solution does not consider the influence of the process line on the flow profile in the measuring tube, but rather the influence on the electrical potential distribution present in the medium, and in particular, its local distribution in the flow direction.

[0019] The numerical simulation method is not only suitable for simulating the electrical potential distribution in the medium for a given process line-specific criterion, but also for determining the criterion-specific quantity with which the measurement error can be corrected by the user.

[0020] The criterion-specific quantity can be stored in a memory of the magnetic-inductive flowmeter or the magnetic-inductive flowmeter probe or can be provided via a wired or wireless connection to an external computing system - where it is determined.

[0021] One embodiment provides that the simulation procedure includes a calculation using the finite element method.

[0022] One embodiment provides that no flow simulation is included in the determination of the criterion-specific variable. The finite element method is a numerical simulation method commonly used in strength and deformation studies of solids. According to the invention, the finite element method is not used to simulate the flow profile of the flowing medium, but rather the process line, the individual components of the magnetic-inductive flowmeter or the magnetic-inductive flow probe, or the magnetic field distribution generated thereby, the medium itself, and the distribution of the electrical potential in the medium.

[0023] One embodiment provides that the, in particular numerical, simulation method comprises determining the electrical potential distribution, in particular in the flow direction of the medium, in the process line, in particular in the process line section, and / or in the magnetic-inductive flowmeter, wherein a deviation of the determined potential distribution from a predetermined potential distribution is included in the determination of the criterion-specific variable.

[0024] Using the simulation method, the electrical potential present in the medium is determined in at least one longitudinal section through the process line and / or the magnetic inductive flowmeter. This results in an electrical potential distribution which takes into account the electrical properties of the process line and / or the magnetic inductive flowmeter. The determination is carried out for a reference system and for different measuring points, each of which differs in terms of the process line-specific criteria. If the measuring point has an electrically conductive process line, for example, the electrical potential in the section of the process line adjacent to the magnetic inductive flowmeter is set to zero. If the process line is electrically insulating or has an electrically insulating coating, the contact surface between the process line and the medium has an infinitely high resistance.a very high resistance relative to the electrical resistance of a metallic pipe (several orders of magnitude greater). The reference system can be the calibration measuring point used during calibration of the magnetic-inductive flowmeter or magnetic-inductive flow probe. The deviation between the potential distributions of the reference system and the measuring point is incorporated into the final criterion-specific value.

[0025] One embodiment provides that the simulation method comprises determining a weight function at least in one measuring electrode cross-section, wherein a deviation of the determined weight function from a predetermined weight function is included in the determination of the criterion-specific variable, wherein the measuring electrode cross-section intersects the at least one measuring electrode.

[0026] Alternatively or additionally, the simulation procedure can determine the weight function in the measuring electrode cross-section, which provides information about the measurable induced voltage present at the measuring electrodes. When determining the weight function, the local potential distribution in the measuring electrode cross-section is summed or integrated. The individual electrical potentials depend on the potential distribution in the direction of flow. The weight function is also determined for a reference system and for the corresponding measuring points. Any deviation between the two weight functions is incorporated into the criterion-specific value.

[0027] One design provides that the process management-specific criterion corresponds to at least one criterion from the following list:

[0028] - the process line is electrically conductive;

[0029] - the process line is electrically insulating;

[0030] - the process line is electrically insulating and an earthing ring is arranged between the process line and the magnetic-inductive flowmeter;

[0031] - the process line is electrically insulating and no earthing ring is arranged between the process line and the magnetic-inductive flowmeter;

[0032] - an electrically insulating coating is present in the process line, in particular in the process line section;

[0033] - Carrying a medium containing deposit-forming substances;

[0034] - the process line has an electrically insulating process line liner;

[0035] - the process line has an internal diameter that differs from the internal diameter of the measuring tube.

[0036] The specified criteria are not necessarily stored in the measuring device as formulated above, but are stored analogously. From the list, it is clear that the electrical properties of the part of the process line in contact with the medium play a key role. As shown in the list, a criterion can also encompass two or more characteristics of the process line. One embodiment provides that the process line-specific criterion includes the material of the process line section of the process line, in particular a process line body of the process line.

[0037] The material of the process pipe walls typically includes metal, glass, cement, plastic, ceramic, enamel and / or GRP.

[0038] One embodiment provides that the process line-specific criterion includes an inner diameter of the process line.

[0039] Even though there are standards for pipes and process lines regarding their nominal diameters, deviations from the standard can still occur. For example, the inner diameter of the process line often does not match the inner diameter of the magnetic-inductive flowmeter, resulting in an offset at the transition between the process line and the magnetic-inductive flowmeter. This offset can cause a shift in the electrical potential distribution, which results in a shift in the calibration factor or an offset in the measured values ​​(zero point shift). If the offset is known, a criterion-specific variable assigned to the offset can be used to correct the zero point shift.

[0040] One embodiment provides that the magnetic-inductive flowmeter has an electrical device potential, wherein the process line-specific criterion comprises whether the magnetic-inductive flowmeter or the magnetic-inductive flow measuring probe is operated in a ground-free mode, wherein the ground-free mode comprises the operation of the magnetic-inductive flowmeter or the magnetic-inductive flow measuring probe with galvanic isolation of the medium from the device potential.

[0041] Correct potential equalization is a prerequisite for stable, reliable flow measurement. Insufficient or faulty potential equalization can lead to device failure and pose a safety risk. To ensure proper measurement, it is essential that the medium, the sensor, and the transmitter are at the same electrical potential. The required potential equalization connection can be achieved by a grounding cable with a minimum cross-section of 6 mm. 2 be manufactured.

[0042] In a metallic, grounded process line without a lining, potential equalization is achieved via the measuring tube of the magnetic-inductive flowmeter. If the process line is properly grounded on both sides, the medium is at the same electrical potential as the process line, since the process line wall in contact with the medium is electrically conductive. The medium is thus set to earth potential.

[0043] If the process line includes a plastic pipe or an electrically insulating lining that comes into contact with the medium, the potential equalization is carried out via earthing terminals and earthing disks.

[0044] In floating mode, the medium potential may differ from the potential of the measuring device. Floating mode enables galvanic isolation of the measuring system from the device potential. This minimizes harmful compensating currents caused by potential differences between the medium and the device. The voltage differences between the medium potential and the device potential should be as small as possible and typically lie in the mV range. If a plastic pipeline is used and the sensor and transmitter are properly grounded, a potential difference may occur between the medium and the protective earth, meaning compensating currents through the medium cannot be ruled out. Potential equalization between the medium potential and the protective earth via the reference electrode is minimized in floating mode.

[0045] One embodiment provides that a calibration factor K is included in the determination of the flow velocity-dependent measured variable, wherein the calibration factor K is determined by means of an adjustment method.

[0046] One embodiment provides that the criterion-specific variable is determined by a distance of the magnetic field generating device from the process line, in particular from the process line section, or a length of the measuring tube.

[0047] One embodiment provides that the criterion-specific quantity is determined by a distribution-specific quantity, in particular a half-width, of the magnetic field.

[0048] As the measuring tube length decreases, the magnetic field generated by the magnetic field-generating device increasingly overlaps with the process line section adjacent to the magnetic-inductive flowmeter. This leads to the separation of charges in the flowing medium already within the process line. The disadvantage of this is that the electrical properties present in the process line are unknown, thus leading to an erroneous offset in the flow velocity-dependent measured variable.

[0049] The distribution-specific magnitude of the magnetic field generated by the magnetic field-generating device can be determined using a simulation method or measured at the factory during calibration of the magnetic-inductive flowmeter or magnetic-inductive flow probe. Measurement can be performed using commercially available magnetic field sensors. The finite element method is also suitable as a simulation method.

[0050] One embodiment provides that the criterion-specific quantity is independent of a maximum magnetic field strength of the generated magnetic field.

[0051] Surprisingly, it has been found that the criterion-specific size does not correlate with the maximum magnetic field strength of the generated magnetic field, but depends strongly on the distribution, in particular the half-width of the magnetic field.

[0052] One embodiment provides that the method according to the invention comprises the method steps:

[0053] - User-specific specification of the process line-specific criterion;

[0054] - Manufacturer-side calculation of the criterion-specific size depending on the specified process line-specific criterion;

[0055] - Provision of the criterion-specific size to the user by the manufacturer;

[0056] - Optional: Selection of the process line-specific criterion on the magnetic inductive flowmeter or on the magnetic inductive flow measuring probe by the user.

[0057] As an alternative to the conventional storage of pre-defined lists of criteria and correspondingly assigned criterion-specific variables or correction variables, it is advantageous if the user independently describes his or her process line-specific criterion and sends it to the manufacturer to determine the criterion-specific variable. This can be done informally as a voice message, text, or with the help of a software program that is set up to guide the user so that all necessary information is provided. Once all information has been received, the manufacturer then calculates the criterion-specific variable and makes it available to the user. The criterion-specific variable can be transferred directly from the manufacturer to the magnetic-inductive flowmeter or the flowmeter.The magnetic-inductive flowmeter probe or transmitted to the user, who then enters the criterion-specific value into the corresponding measuring device. This has the advantage that not all possible measuring points have to be simulated, but rather this is done on a needs-based basis. Furthermore, this has the advantage that the measuring point or the specific process line can be included in the simulation in more detail, and the criterion-specific value can be determined more precisely. The magnetic-inductive flowmeter according to the invention is characterized in that the magnetic-inductive flowmeter is configured to carry out the method according to the invention.

[0058] The magnetic-inductive flow measuring probe according to the invention is characterized in that the magnetic-inductive flow measuring probe is designed to carry out the method according to the invention.

[0059] The basic idea is to consider the electrical charge distribution in the medium resulting from the process line when determining the flow velocity-dependent measured variable. The necessary correction variable (i.e., the criterion-specific variable) is preferably determined using a simulation method. Simulation methods in which the geometry of the process line and the resulting flow profile of the flowing medium are simulated are state of the art. In the present invention, the electrical properties of the process line are essentially used to determine the correction variable. Using the correction variable determined using the simulation method, measuring point-dependent measurement errors can be minimized.

[0060] The invention is explained in more detail with reference to the following figures. They show:

[0061] Fig. 1: an embodiment of the magnetic-inductive flow meter according to the invention;

[0062] Fig. 2: a perspective view of a partially sectioned embodiment of a magnetic-inductive flow measuring probe according to the invention;

[0063] Fig. 3: a perspective view of a magnetic-inductive flowmeter installed in a process line;

[0064] Fig. 4: the relationship between the measurement error and the measuring tube length for different magnetic field distributions; and

[0065] Fig. 5: an embodiment of the method according to the invention; and

[0066] Fig. 6: a menu structure for operating the magnetic-inductive flowmeter or the magnetic-inductive flow measuring probe.

[0067] 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 which has electrical conductivity is passed through a measuring tube 2. 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 substantially perpendicular to a longitudinal direction defined by a measuring tube axis. The magnetic field generating device 5 usually comprises a saddle coil or at least one (cylindrical) coil 6i. A coil core 14i usually extends through a receptacle 15 of the coil 6i.The receptacle 15 is understood to be the volume delimited 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 device 5 for generating the magnetic field comprises a pole piece 21i arranged at one end of the coil core 14i. The pole piece 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 two coil cores 14a, 14b are connected to each other via a field return 22.The field feedback 22 connects the opposite sides of the coil cores 14a, 14b to one another. However, magnetic-inductive flowmeters with exactly one coil 6 with exactly one coil core 14 and without field feedback are also known. The coil 6 is connected to an operating circuit 7, which operates the coil 6 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 built up 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 in series orbe connected in parallel to each other.

[0068] When a magnetic field is applied, a flow-dependent potential distribution is created in the measuring tube 2, 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 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 designed to determine the flow velocity-dependent measured variable. The evaluation circuit 24 can be part of the measuring transducer.

[0069] 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.

[0070] Commercially available magnetic-inductive flowmeters have two additional electrodes 19, 20 in addition to the measuring electrodes 17, 18. Firstly, a level monitoring electrode 19, ideally located at the highest point in the measuring tube 2, serves to detect partial filling of the measuring tube 1 and is configured to transmit 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 typically located diametrically opposite the level monitoring electrode 19 or at the lowest point of the measuring tube cross-section, serves to establish a controlled electrical potential in the medium. The reference electrode 20 is typically used to connect the flowing medium to a ground potential.

[0071] The operating circuit 7, control circuit 10, measuring circuit 23 and evaluation circuit 24 can be part of a single electronic circuit or form individual circuits.

[0072] The magnetic-inductive flowmeter 1 is configured to carry out the method according to the invention. For this purpose, the evaluation circuit 24 is configured to incorporate a criterion-specific variable selected directly or indirectly by the operator from a list into the determination of the flow velocity-dependent measured variable. Thus, the measured induced measuring voltage or the measured electrical potentials can be corrected using the criterion-specific variable. The evaluation circuit 24 comprises a microprocessor, logic switching components, and / or electronic components to carry out the method according to the invention.

[0073] Based on the perspective and partially cut representation of the

[0074] Fig. 2 first explains the measuring principle underlying the invention. 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) into which the flow measuring probe 101 is inserted in a fluid-tight manner. A medium to be measured flows through 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 coil arrangement 106 arranged in the housing 102, a magnetic field 109 can be generated that extends through the end section into the medium.A coil core 111, which is at least partially made 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 designed 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 form a galvanic contact with the medium to be guided, form the device for detecting a measuring voltage induced in the medium and 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 by a measuring and / or evaluation unit. This voltage is maximum when the flow measuring probe 101 is installed in the pipeline such 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 impress a clocked operating signal onto the coil 113 in order to thus generate a clocked magnetic field 109.

[0075] The magnetic-inductive flow measuring probe 101 is configured to carry out the method according to the invention. For this purpose, the measuring and / or evaluation unit is configured to incorporate a criterion-specific variable selected directly or indirectly by the operator from a list into the determination of the flow velocity-dependent measured variable. For example, the measured induced measuring voltage or the measured electrical potentials can be corrected using the criterion-specific variable.

[0076] Fig. 3 shows a perspective view of a magnetic-inductive flowmeter 302 installed in a process line 300. The process line section 301 comprises the area of ​​the process line 300 in the immediate vicinity of the connection devices (e.g., flange) of the magnetic-inductive flowmeter 302. The process line section 301 in contact with the medium generally also comprises a process line connection device (e.g., flange). Especially in compact magnetic-inductive flowmeters 302, the generated magnetic field extends into the process line section 301. The process line section 301 thus ends where the magnetic-inductive flowmeter 302 begins, and the overlapping magnetic field is so small that a separation of the electrical charges in the medium does not occur.

[0077] Fig. 4 shows the relationship between the measurement error (Y-axis) and the length of the measuring tube (X-axis) for magnetic field distributions with different half-widths. Fig. 4 shows how the increase in the measurement error is related to a reduction in the length of the measuring tube. Very short measuring tubes (length less than 2 DN) in particular have extreme measurement errors. If the magnetic field distribution of the electromagnetic flowmeter has a half-width of 1.18 times the length of the measuring tube - i.e. the magnetic field strength in the process line section is greater than half the maximum magnetic field strength in some places - the measurement error increases sharply with decreasing length of the measuring tube, so that for a length of 1 DN it is 7% (see A). If the half-width of the generated magnetic field is reduced by approximately half, the measurement error is also reduced by approximately half (see B).If, when designing the magnetic-inductive flowmeter, the magnet system is dimensioned and constructed such that the magnetic field distribution in the longitudinal direction has a half-width of only approximately 1% of the length of the measuring tube, then even with a measuring tube length of 1 DN, a measurement error of 1 to 2% will still occur. Consequently, it is not sufficient to design the magnetic field-generating device so that the magnetic field distribution of the generated magnetic field is as narrow as possible.

[0078] Fig. 5 shows an embodiment of the method according to the invention for determining a flow velocity-dependent measured variable of a flowable medium in a process line using a magnetic-inductive flowmeter or a magnetic-inductive flowmeter probe. The method comprises method steps 501 and 502. In a first method step 501, at least one process line-specific criterion is determined or selected. This is performed by the operator on-site at the corresponding measuring device or remotely by the manufacturer.The process line-specific criterion describes the influence of a condition of the process line, in particular of the process line section which is in the immediate vicinity of the magnetic-inductive flow meter or the magnetic-inductive flow measuring probe, on the electrical potential distribution, in particular in the flow direction of the medium in a longitudinal section, in the process line section.

[0079] If at least one process line-specific criterion is selected, a criterion-specific variable associated with the process line-specific criterion is determined or specified. The criterion-specific variable can be stored in the measuring device's memory, for example, in the form of a list, or transmitted remotely by the manufacturer. The determined criterion-specific variable is then used in a second process step to determine the flow velocity-dependent measured variable. The criterion-specific variable corrects the measured, error-prone measuring voltage or potential at the measuring electrodes.

[0080] The criterion-specific variable (correction variable) is or will be determined using a simulation method, particularly a numerical one. The simulation method recreates the process line-specific criterion as accurately as possible for the measuring point. The finite element method is suitable for this purpose, with which the process line, the magnetic-inductive flowmeter or the magnetic-inductive flowmeter probe, and the medium are simulated. The defined framework conditions then result in an electrical potential distribution, particularly in the flow direction of the medium, in the process line, particularly in the process line section, and / or in the magnetic-inductive flowmeter. If the potential distribution for a reference system and a measuring point is known, a deviation of the determined potential distribution from a specified potential distribution can be determined.The deviation is used to determine the criterion-specific value, which is used to correct the measured values.

[0081] Alternatively, a weighting function is determined at least in one measuring electrode cross-section which intersects the at least two measuring electrodes, which is a measure of the sum or the integral of all electrical potentials in the measuring electrode cross-section. The weighting function is determined for a reference system and a measuring point at which the process line-specific criterion is present. A deviation of the determined weighting function of the measuring point from a predetermined weighting function of the reference system is included in the determination of the criterion-specific variable. Furthermore, the inner diameter of the process line of the measuring point, the shortest distance of the magnetic field generating device to the process line, the length of the measuring tube or a distribution-specific variable of the generated magnetic field (e.g. the half-width) can be included in the criterion-specific variable. These are usually determined by the manufacturer.but they can also be entered by the operator.

[0082] Fig. 6 shows an example of a menu structure through which the operator selects the process line-specific criterion. Under a menu item (I), the operator accesses a list of process line-specific criteria (II to VII), from which they can select one or more process line-specific criteria.

[0083] The list includes, for example:

[0084] - the process line is electrically conductive (II);

[0085] - the process line is electrically insulating (III);

[0086] - the process line is electrically insulating and an earthing ring is arranged between the process line and the magnetic-inductive flowmeter (IV);

[0087] - the process line is electrically insulating and no earthing ring is arranged between the process line and the magnetic-inductive flowmeter (V);

[0088] - an electrically insulating coating is located in the process line (VI);

[0089] - Carrying a medium containing deposit-forming substances (VII);

[0090] - the process line has an electrically insulating process line liner (VIII);

[0091] - the process line has an internal diameter that differs from the internal diameter of the measuring tube (IX).

[0092] Alternatively, the operator can specify a process line material or select one from a predefined list. The aforementioned entries can also be made by the manufacturer. LIST OF REFERENCE SYMBOLS electromagnetic flowmeter 1

[0093] Measuring tube 2

[0094] Support tube 3

[0095] Liner 4 magnetic field generating device 5

[0096] Coil 6

[0097] Operating circuit 7

[0098] Device for tapping an induced measuring voltage 8

[0099] Regulator circuit 10

[0100] Coil core 14

[0101] Recording of the coil 15

[0102] Measuring electrode 17

[0103] Measuring electrode 18

[0104] Level monitoring electrode 19

[0105] Reference electrode 20

[0106] Pole piece 21

[0107] Field feedback 22

[0108] Measuring circuit 23

[0109] Evaluation circuit 24

[0110] Coil arrangement 25 magnetic-inductive flow measuring probe 101

[0111] Housing 102

[0112] Measuring electrode 103

[0113] Measuring electrode 104 magnetic field generating device 105

[0114] Coil arrangement 106

[0115] Operating circuit 107

[0116] Field guidance arrangement 108

[0117] Magnetic field 109

[0118] Field guide body 110

[0119] Coil core 1 11

[0120] Pole piece 1 12

[0121] Coil 113

[0122] Field feedback body 1 14

[0123] Front body 115

[0124] End section 116

[0125] Flow direction of the medium 1 18

[0126] Regulator circuit 120

Claims

PATENT CLAIMS 1. A method for determining a flow velocity-dependent measured variable of a flowable medium in a process line (300) by means of a magnetic-inductive flowmeter (1), wherein the process line (300) has a process line section (301) in contact with the medium, which is adjacent to an end face of the magnetic-inductive flowmeter (1), wherein the magnetic-inductive flowmeter (1) comprises a measuring tube (2) for guiding the medium, a magnetic field generating device (5) for generating a magnetic field penetrating the measuring tube (2), and at least one measuring electrode (17, 104) for determining an induced measuring voltage in the medium, comprising the method steps: - determining at least one process line-specific criterion, wherein the process line-specific criterion is related to an influence of a condition of the process line (300), in particular of the process line section (301), on the electrical potential distribution, in particular in the flow direction of the medium, in the process line section (301); and - Determining the flow velocity-dependent measured variable, wherein the process line-specific criterion, in particular a criterion-specific variable assigned to the process line-specific criterion, is included in the determination of the flow velocity-dependent measured variable.

2. Method for determining a flow velocity-dependent measured variable of a flowable medium in a process line (300) by means of a magnetic-inductive flow measuring probe (101), wherein the process line (300) has a medium-contacting process line section (301) with an opening, wherein the magnetic-inductive flow measuring probe (101) is arranged in the opening, wherein the magnetic-inductive flow measuring probe (101) has a medium-contacting housing (102), a magnetic field generating device (5, 105) for Generating a magnetic field penetrating the housing and at least one measuring electrode (17, 104) for determining an induced measuring voltage in the medium, comprising the method steps: - determining at least one process line-specific criterion, wherein the process line-specific criterion is related to an influence of a condition of the process line (300), in particular of the process line section (301), on the electrical potential distribution, in particular in the flow direction of the medium, in the process line section (301); and - Determining the flow velocity-dependent measured variable, wherein the process line-specific criterion, in particular a criterion-specific variable assigned to the process line-specific criterion, is included in the determination of the flow velocity-dependent measured variable.

3. Method according to claim 1 or 2, wherein the criterion-specific variable is or is determined by means of a, in particular numerical, simulation method, wherein the process line-specific criterion is included in the simulation method.

4. The method according to claim 3, wherein the simulation method comprises a calculation using the finite element method.

5. The method according to claim 3 or 4, wherein the simulation method comprises determining an electrical potential distribution, in particular in the flow direction of the medium, in the process line (300), in particular in the process line section (301), and / or in the magnetic inductive flowmeter, whereby a deviation of the determined potential distribution from a given potential distribution is included in the determination of the criterion-specific quantity.

6. Method according to at least one of claims 3 to 5, wherein the simulation method comprises determining a weight function at least in one measuring electrode cross-section, wherein a deviation of the determined weight function from a predetermined weight function is included in the determination of the criterion-specific variable, wherein the measuring electrode cross-section intersects the at least one measuring electrode (17, 104).

7. Method according to at least one of the preceding claims, wherein the process line-specific criterion corresponds to a criterion from the following list: - the process line (300) is electrically conductive; - the process line (300) is electrically insulating; - the process line (300) is electrically insulating and an earthing ring is arranged between the process line (300) and the magnetic-inductive flowmeter; - the process line (300) is electrically insulating and no grounding ring is arranged between the process line (300) and the magnetic-inductive flowmeter; - an electrically insulating coating is located in the process line (300), in particular in the process line section; - Carrying a medium containing deposit-forming substances; - the process line (300) has an electrically insulating process line liner; - the process line (300) has a process line inner diameter that differs from a measuring tube inner diameter.

8. Method according to at least one of the preceding claims, wherein the process line-specific criterion comprises which material the process line section (301) of the process line (300), in particular a process line body of the process line (300), comprises.

9. Method according to at least one of the preceding claims, wherein the process line-specific criterion comprises an inner diameter of the process line (300).

10. Method according to at least one of the preceding claims, wherein the magnetic-inductive flowmeter (1) has an electrical device potential, wherein the process line-specific criterion comprises whether the magnetic-inductive flowmeter (1) or the magnetic-inductive flow measuring probe (101) is operated in a floating mode, wherein the floating mode comprises operating the magnetic-inductive flowmeter or the magnetic-inductive flow measuring probe (101) with galvanic isolation of the medium from the device potential. 1 1. Method according to at least one of the preceding claims, wherein the criterion-specific variable is determined by a distance of the magnetic field generating device (5) to the process line (300), in particular to the process line section (301), or a length of the measuring tube (2).

12. Method according to at least one of the preceding claims, wherein the criterion-specific variable is determined by a distribution-specific variable, in particular a half-width, of the generated magnetic field.

13. Method according to at least one of the preceding claims, where the criterion-specific quantity is independent of a maximum magnetic field strength of the generated magnetic field.

14. Magnetic-inductive flowmeter (1), characterized in that the magnetic-inductive flowmeter (1) is designed to carry out the method according to at least one of claims 1 to 13.

15. Magnetic-inductive flow measuring probe (101), characterized in that the magnetic-inductive flow measuring probe (101) is designed to carry out the method according to at least one of claims 2 to 13.

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