MAGNETIC-INDUCTIVE FLOW METER

Description

[0001] Magnetic-inductive flowmeters are used to determine the flow velocity and volume flow of a flowing medium in a pipeline. A magnetic-inductive flowmeter has a magnet system that generates a magnetic field perpendicular to the flow direction of the flowing medium. Individual coils are usually used for this purpose. To create a predominantly homogeneous magnetic field, additional pole pieces are shaped and attached 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. A pair of measuring electrodes attached to the outer surface of the measuring tube taps an electrical measuring voltage or potential difference applied perpendicular to the flow direction and the magnetic field. This potential difference arises when a conductive medium flows in the direction of flow when a magnetic field is applied.Since the tapped measuring voltage depends on the velocity of the flowing medium according to Faraday's law of induction, the flow velocity u and, with the addition of a known pipe cross-section, the volume flow V can be determined from the induced measuring voltage U.

[0002] Magnetic-inductive flowmeters are widely used in process and automation technology for fluids with an electrical conductivity of approximately 5µS / cm and above. The applicant markets corresponding flowmeters in a wide variety of designs for various applications, for example, under the name PROMAG.

[0003] DE 10 2014 113 409 A1 discloses a magnetic-inductive flowmeter comprising field feedback elements and pole pieces that are attached to the outer wall of the measuring tube and connected to each other via cylindrical coil cores. This arrangement is particularly suitable for magnetic-inductive flowmeters with large nominal diameters. Field feedback elements serve to guide the magnetic field lines from a first coil core to a second coil core. A disadvantage of the magnetic-inductive flowmeter described, however, is that the measured flow value is sensitive to the flow profile of the medium.

[0004] Conventional magnetic-inductive flowmeters are sensitive to the flow profile of the medium. Depending on the piping system and measuring device, measurement errors of several percent can occur. Therefore, a straight pipe, whose length corresponds to at least five to ten times the nominal diameter of the measuring pipe, is typically installed on the inlet-side face. However, there are known applications in which this minimum distance, the so-called inlet section, cannot be maintained. This is the case, for example, when a piping system is located in a very confined space. One solution is provided by the invention disclosed in DE 10 2014 113 408 A1, in which a narrowing of the pipe diameter leads to the conditioning of the flow, thereby minimizing the influence of the flow profile, allowing the use of a 0-DN inlet section.The disadvantage of this design, however, is that while it can achieve lower sensitivity to rotationally asymmetric flow profiles, it also results in a pressure loss. Furthermore, this design is limited to pipe systems with a diameter of less than 350 mm.

[0005] The sensitivity of the flow measurement to a rotationally asymmetric flow profile depends on the geometry of the measuring tube and the electrodes. Therefore, the influences of the tube and electrode geometry must be taken into account for the correct description of the velocity-dependent induced voltage. These two influences are mathematically represented by a weighting function. GF The influence of geometry on flow can best be illustrated by the following relationship: U x = ∫ V v x ′ GF x ′ , x dV where for the determination of the voltage U ( x ) , the flow velocity v (x' ) and the weight function GF ( x' , x ) are integrated over the volume of the measuring tube. The weight function GF based on GF ( x', x ) = B × ∇ G ( x' , x ), with the magnetic field B ( x ') and a Green's function G , which is given by the electrical boundary conditions. The goal of an optimization procedure is to optimize the geometry of the structure so that in the entire flow profile ∇ × GF = 0. However, this is not possible for a pipe with a single point-shaped measuring electrode pair. One possible solution is to adapt the electrode shape. However, this is impractical and creates new difficulties. Another solution is to use multiple measuring electrode pairs.

[0006] For example, CN 101294832 A discloses a magnetic-inductive flowmeter that features two pairs of measuring electrodes arranged axially symmetrically in a pipe cross-section to minimize the influence of the flow profile on the determination of the volume flow. The two electrode axes defined by the respective pairs of measuring electrodes span an angle of approximately 40° in the cross-section of the measuring tube.

[0007] WO2004 / 031699 A2 discloses an inductive flow meter for electrically conductive liquids, in which an improved insensitivity to influences of flow profile changes and flow profile asymmetries that distort the measured values ​​is achieved in that the magnetic field applied by the magnetic field generation system, which has an orientation transverse to the flow direction and transverse to the connecting line between the measuring electrodes on the flow channel inner wall, has a strongly concave distribution of the effective intensity of the magnetic field between a point located centrally between the measuring electrodes of the cross-sectional plane containing the measuring electrodes and the flow channel inner surface over the inner circumference of the flow channel up to a point close to the measuring electrodes.

[0008] A further embodiment is shown in DE 102015113390 A1, in which a second and third pair of measuring electrodes are arranged on defined electrode axes, which are arranged at an angle of less than or equal to ±45° with respect to a first electrode axis oriented perpendicular to the magnetic field.

[0009] EP 0878694 A1 also discloses a magnetic-inductive flowmeter that, based on the prior art, achieves an improvement in measurement accuracy with errors of less than 1% by using two additional measuring electrode pairs, whose electrode axes each form an angle of approximately 45° to the electrode axis of the conventional measuring electrode pair and the measuring tube axis. This is achieved in particular by individually detecting and weighting the potential differences present at the electrodes.

[0010] However, these designs have the disadvantage that, while the measurement accuracy is optimized for small diameters, they do not achieve the desired reduction in measurement errors for commercially available measuring tubes with large nominal diameters. Another disadvantage is that a weighting factor must be considered for each measuring electrode pair, and it is not immediately clear how this should be selected depending on the pipe system or the rotationally asymmetric flow profile.

[0011] Based on the prior art described, the present invention is based on the object of providing a magnetic-inductive flow meter which minimizes the influences of a rotationally asymmetric flow profile when determining the flow measurement value.

[0012] The problem is solved by the magnetic-inductive flowmeter according to claim 1.

[0013] The magnetic-inductive flowmeter according to the invention comprises: a measuring tube for guiding a flowable medium in a longitudinal direction; a measuring electrode arrangement for detecting a flow velocity-dependent measuring voltage induced in the medium, wherein the measuring electrode arrangement has two measuring electrode groups which are mounted opposite one another on the measuring tube, wherein two radii, each intersecting a measuring electrode of a measuring electrode group which is located outside in a cross-sectional plane of the measuring tube, form a central angle α where 20° ≤ α ≤ 40° is met; and a magnetic field generating device for generating a magnetic field passing through the measuring tube, wherein the magnetic field generating device has at least two coil core groups, each with at least two coil cores, wherein a reference plane which is spanned by a longitudinal axis of the measuring tube and a transverse axis of the measuring tube intersecting measuring electrodes of the measuring electrode arrangement, divides the measuring tube into a first and a second part, wherein the first and the second part of the measuring tube each have at least one coil core group, wherein two radii intersecting the coil cores of a coil core group lying outside in a cross-sectional plane of the measuring tube form a central angle β where the central angle β it applies that 60° ≤ β ≤ 80°.

[0014] Advantageously, at least two coil cores, each with at least one coil, are arranged in the respective parts of the measuring tube. This configuration provides a further optimization option for the resulting magnetic field in the measuring tube. Optimization options include the position of the respective coil cores, the number of coils, the diameter of the coil core, the number of turns, and the cross-section of the turns.

[0015] To create a flow-profile-independent magnetic-inductive flowmeter, the arrangement of the coil cores must be adapted to the number of measuring electrodes. The preferred center angles for both cases are mutually exclusive.

[0016] In a further preferred embodiment, the measuring tube is made of a metal lined with an electrically insulating liner in the fluid-contacting area. Alternatively, the measuring tube can also be made of a ceramic or a plastic, with the at least two pole pieces and / or the at least two return plates being arranged on the outer surface of the measuring tube or embedded in the measuring tube.

[0017] According to the invention, all measuring electrodes of a measuring electrode group are electrically connected to one another, in particular short-circuited.

[0018] The short-circuiting can be realized by conventional cables or by means of specially shaped contact bodies, which simplify the connection of the measuring electrodes during the manufacture of the magnetic-inductive flowmeter.

[0019] The technical success of this embodiment of the invention is that it was found that by adjusting the angles α and β Sampling the individual potential differences with the addition of empirically determined weighting factors is no longer necessary, and the applied voltage across all electrodes deviates by less than 0.5% from a measured value determined based on a fully developed flow profile in the event of a fault. Weighting of the individual voltage values ​​is therefore unnecessary, which significantly simplifies the evaluation unit for determining the applied voltage and the resulting flow velocity. It is now sufficient to convert the measured voltage value into a flow velocity or volume flow rate using calibration.

[0020] The electrodes are connected to a measuring circuit that uses the voltage induced in the electrodes to provide information about the flow rate of the medium in the measuring tube. The flow rate includes the flow velocity, volume flow, and mass flow of the flowing medium.

[0021] According to the invention, two radii, each intersecting a measuring electrode of a measuring electrode group located outside in a cross-sectional plane of the measuring tube, form a central angle α where 20° ≤ α ≤ 40° is met.

[0022] Advantageously, the measuring tube comprises at least two measuring electrodes instead of large-area measuring electrodes in order to measure the potential distribution in the medium at multiple positions or to obtain an average of the potential distribution in the medium over a larger area. The claimed arrangement has proven particularly advantageous because the measuring voltage applied to the measuring electrodes is particularly insensitive to asymmetries in the flow profile.

[0023] However, this arrangement correlates with the arrangement of the coil cores. It is only the combination of these two features that results in insensitivity to asymmetries in the flow profile.

[0024] The radii that run through the outer measuring electrodes span a circular section in which all measuring electrodes of a measuring electrode group are arranged.

[0025] According to the invention, a coil core group comprises at least four coil cores which are mounted in a cross-sectional plane of the measuring tube, wherein the radii intersecting the inner coil cores of a coil core group each define a central angle γ for which 1° ≤ c ≤ 80° applies.

[0026] It is particularly advantageous if the coil core groups have at least two additional coil cores arranged between the two outer coil cores, in addition to the two outer coil cores. This can increase the magnetic flux density in the measuring tube. This also provides a further optimization option for controlling the magnetic field inside the measuring tube.

[0027] The above-claimed arrangement of the inner coil cores of a coil core group in combination with the arrangement claimed for the measuring electrodes and the outer coil cores has proven to be advantageous in that, in addition to the increasing compactness of the components attached to the outer wall of the measuring tube, a reduction in the sensitivity to asymmetries in the flow profile is achieved.

[0028] Preferably, the coil cores each have a slot through which a clamping band is passed, which secures the coil cores to the measuring tube. The claimed arrangement is further advantageous with regard to the fastening of the coil cores and the field feedback arrangement, since, particularly with the claimed arrangement of the inner coil cores, the clamping band not only presses the coil cores against the outer wall of the measuring tube or against parts of the pole piece and the field feedback, but also the ends of the field feedbacks. This leads to a minimization of overshoot and to better control of the overshoot behavior of the magnetic field during changes of direction.

[0029] According to the invention, it is provided that a coil core runs through at least two and preferably exactly two coils, wherein a longitudinal axis of the coil core runs parallel to the longitudinal axis of the measuring tube.

[0030] To increase the magnetic flux density in the measuring tube, the number of windings or the coil current must be increased. Increasing the diameter of the windings and arranging additional coils on the measuring tube has proven advantageous. This ensures a compact design for the magnetic-inductive flowmeter and allows magnetic-inductive flowmeters, especially with large nominal diameters, to be realized from many identical components or identical components.

[0031] According to the invention, the two parts of the measuring tube each have exactly two coil core groups, wherein a first coil core group and a second coil core group are arranged in the first part of the measuring tube, wherein the first coil core group is arranged in a first cross-sectional plane and a second coil core group is arranged in a second cross-sectional plane, wherein the first and second cross-sectional planes are spaced apart in the longitudinal direction.

[0032] This ensures a symmetrical distribution of the magnetic field in the measuring tube.

[0033] According to the invention, it is provided that the measuring electrode arrangement is arranged in a third cross-sectional plane, wherein the third cross-sectional plane is arranged between the first and the second cross-sectional plane and preferably forms a plane of symmetry of the coil core groups and preferably of the magnetic field generating device.

[0034] This creates a symmetrical distribution of the magnetic field in the measuring tube, allowing the measuring tube to be operated in either longitudinal direction. This arrangement is particularly suitable for measuring tubes with nominal diameters ≥ DN1000.

[0035] It is advantageous if each of the at least four coils has the same geometry, in particular a non-saddle-shaped, flat geometry. The use of flat coils advantageously reduces the copper requirement in terms of cost.

[0036] Furthermore, it is advantageous if each of the at least four coils is of the same design. This simplifies construction and assembly.

[0037] One embodiment provides that all coils connected in series have an electrical resistance which is between 2 and 300 Ω, in particular between 100 and 280 Ω and preferably between 150 and 260 Ω.

[0038] One embodiment provides that the magnetic field generating device has two pole shoes, wherein the pole shoes are mounted opposite one another, in particular adjacent to an outer wall of the measuring tube, wherein the pole shoes are each formed by at least two and preferably exactly two or exactly four pole shoe bodies, wherein the pole shoe bodies are formed from stacked sheet metal parts, in particular electrical sheets.

[0039] This allows for simplified mounting of the pole shoes on the outer wall of the measuring tube.

[0040] One embodiment provides that two adjacent pole shoe bodies have a minimum distance C in the longitudinal direction of the measuring tube which is less than 500 millimeters, in particular less than 50 millimeters and preferably between 2 and 5 millimeters.

[0041] By spacing two pole pieces apart, a guide is formed for guiding the wiring of the measuring electrodes. However, the claimed pole piece arrangement ensures that the magnetic field lines in the measuring area run essentially perpendicular to the electrode axis and the longitudinal axis of the measuring tube.

[0042] One embodiment provides that at least one field feedback arrangement is mounted on the outer wall of the measuring tube, in particular adjacent to it, wherein the field return arrangement comprises at least two field returns, wherein the coil cores connect the pole pieces to the field returns.

[0043] In a preferred embodiment, the field return elements and pole pieces are shaped like rectangular, curved sheets, with the curvature adapted to the measuring tube. The field return elements and pole pieces are mounted adjacent to the outer wall of the measuring tube. It is advantageous if the pole pieces are constructed in two parts, as this allows for easy installation, especially in measuring tubes with large nominal diameters (≥ DN 1000). The same applies to the field return elements.

[0044] The direct arrangement of the coils, pole pieces, and field feedback elements on the measuring tube significantly reduces the material requirements for these components. Furthermore, the attachment to the measuring tube is particularly simple and at the same time particularly stable. Despite the reduction in manufacturing costs, high measurement accuracy can be achieved because disruptive stray fields can be minimized. A direct arrangement means that the components are located directly on the measuring tube. For example, they can be glued directly onto the measuring tube.

[0045] A field feedback arrangement is typically designed to capture magnetic field lines emerging from the coil core and not intersecting the measuring tube, or only partially intersecting them, and to guide them from one coil core to another. Therefore, the field feedbacks typically connect the side of the coil cores facing away from the pole piece or the respective ends of the coil cores that do not touch the pole piece.

[0046] The angles α, β and in particular c are matched to each other in such a way that the flowmeter is insensitive to deviations of a rotationally symmetric flow to such an extent that the magnetic-inductive flowmeter detects a measurement error of the flow velocity during a test measurement Δ u = u va − u S u va and / or a measurement error of the volume flow Δ V ˙ = V ˙ va − V ˙ S V ˙ va less than 1.0%, in particular less than 0.5% and preferably less than 0.2%, wherein a flow rate you are and / or a volume flow V̇ va in the case of a flow with a fully developed flow profile, where a flow velocity u S and / or a volume flow V̇ S in the case of rotationally asymmetric flow.

[0047] After disturbances, measurement errors occur due to a non-ideal flow profile, depending on the distance and type of disturbance. A magnetic flowmeter normally assumes and has been optimized for a fully developed, rotationally symmetric flow profile. A fully developed, rotationally symmetric flow profile is defined as a flow profile that no longer changes in the direction of flow. Such a flow profile is formed, for example, in a measuring tube with an inlet section corresponding to 30 times the nominal diameter of the measuring tube and a medium velocity of 2 m / s.

[0048] The test measurement can also be used to adjust the optimal angle α and β and is then carried out in advance so that, taking into account the angle pair ( α - β ) a flow profile-independent magnetic-inductive flowmeter is realized.

[0049] The test measurement can include many different interference sources, all of which can assume any installation angle. By using sufficiently different interferences, the angle α and β be optimized so that the measurement error of a specific disturbance is less than 0.05% and the maximum measurement error of any disturbance is less than 0.5%.

[0050] It has been found that by using two sufficiently different sources of interference, in particular an orifice plate and a 90° pipe bend, a sufficiently good angle pair ( α- β ) is determined for a magnetic-inductive flowmeter that exhibits a maximum measurement error of 0.5% for any other type of disturbance. By including additional sources of disturbance in the test measurement, the optimized parameters change only marginally, resulting in only a minor change in the resulting measurement error.

[0051] According to one embodiment, the interference source comprises an aperture or a 90° pipe bend, wherein 10% of the cross-section of the measuring tube is covered by the aperture, wherein the aperture has a circular chord which delimits the aperture towards the pipe, wherein the aperture assumes a first aperture orientation or a second aperture orientation, wherein in the first aperture orientation the circular chord is oriented perpendicular to the magnetic field and in the second aperture orientation the circular chord is oriented parallel to the magnetic field, wherein the 90° pipe bend assumes a first pipe bend orientation or a second pipe bend orientation, wherein the first pipe bend orientation is characterized by a pipe axis running perpendicular to the magnetic field and to the longitudinal direction of the measuring tube and the second pipe bend orientation is characterized by a pipe axis running parallel to the magnetic field and perpendicular to the longitudinal direction of the measuring tube.

[0052] Until now, users of magnetic-inductive flowmeters have been given a prescribed inlet length. This prescribed inlet length is necessary to maintain the measurement error specified for the device. The measurement errors that occur must be determined once for each disturbance type, distance, mounting angle, and possibly Reynolds number. This is done either through complex series of measurements or by simulating the flow conditions under different disturbances and evaluating the calculated flow profiles. The result of this step is data that indicates the magnitude of the measurement error that would arise if a magnetic-inductive flowmeter were installed in the corresponding position, and the magnitude of the measurement error if the setup were supplemented with additional measuring electrodes or the magnetic field-generating device was adapted.

[0053] According to a further embodiment, the disturbance is arranged at a distance of 0-DN from the inlet-side front face.

[0054] According to a further development, insensitivity to a rotationally asymmetric flow profile is given at a Reynolds number of the medium in the measuring tube greater than or equal to 10,000, in particular greater than or equal to 50,000 and preferably greater than or equal to 100,000.

[0055] According to a further embodiment, a measuring electrode group has exactly three measuring electrodes.

[0056] The measuring electrode groups do not necessarily have to be arranged diametrically. The measuring electrodes are galvanically or capacitively coupled to the measuring medium. The invention is explained in more detail with reference to the following figures. They show: Fig. 1 : a non-inventive example of a magnetic-inductive flowmeter; and Fig. 2: a parallel projection of the first and third cross-sectional planes A, B through a second embodiment of the magnetic-inductive flowmeter.

[0057] The design and measuring principle of a magnetic-inductive flowmeter are generally known. Fig. 1 shows a non-inventive example of a magnetic-inductive flowmeter. A medium having electrical conductivity is passed through a measuring tube 1. A magnetic field generating device 4 is arranged on the measuring tube such that the magnetic field lines are oriented substantially perpendicular to a longitudinal direction defined by the measuring tube axis. A saddle coil or a pole piece 5 with a coil core 7 and coil 8 mounted thereon is preferably suitable as the magnetic field generating device 4. Fig. 1 depicts two pole shoes 5, each of which is designed in two parts.

[0058] Furthermore, the magnetic-inductive flowmeter has a field feedback arrangement 9, consisting of four field feedback parts 10, whereby only two field feedback parts 10 are shown. These are attached to the outer wall 6 of the measuring tube 1. In the Fig. 1Only six of eight cylindrical coil cores 7 and coils 8 are shown. The longitudinal axis of the coil cores 7 runs essentially parallel to the longitudinal axis 15 of the measuring tube. The coil cores 7 connect the pole piece 5 to the field feedback bodies 10. A coil 8 is arranged between the field feedback bodies 10 and one of the pole pieces 5. However, according to the invention, more coils can also be arranged. Each field feedback part 10 comprises a field feedback body 11, which is formed from several stamped-packet electrical sheet metal parts. The thickness of the pole piece body 19 and the thickness of the field feedback part 10 are essentially the same. The pole piece bodies 19 are preferably formed from stamped-packet electrical sheet metal parts. The field feedback parts 10 each connect at least two different coil cores 7 to one another, thereby realizing a magnetic coupling.The individual components of the magnet system are attached to the measuring tube body by means of screws. When a magnetic field is applied, a flow-dependent potential distribution is created in the measuring tube 1, which is tapped by two measuring electrode groups 16 attached opposite one another on the inner wall of the measuring tube 1. These are generally 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. The measuring electrodes 3 are all located in a third cross-section C. In this design, a measuring electrode group 16 has exactly three measuring electrodes 3. On the basis of the tapped measuring voltage U, the flow velocity u can be determined, taking into account the magnetic flux density, and the volume flow V of the medium can be determined, also taking into account the pipe cross-sectional area. If the medium density is also known, the mass flow can also be determined. ṁbe monitored. In order to prevent the measuring voltage applied to measuring electrode groups 16 from being diverted via the measuring tube 1, the inner wall is lined with an insulating material, for example a plastic liner. A measuring circuit is configured to detect the measuring voltage applied to the measuring electrode groups 16. The respective measuring electrodes 3 of a measuring electrode group 16 are electrically connected to one another. An evaluation circuit is designed to determine the flow measured values ​​of the medium from the detected measuring voltage. The magnetic field generating device 4 is controlled via an operating circuit. Commercially available magnetic-inductive flowmeters have two further electrodes in addition to the measuring electrodes 3.Firstly, a level monitoring electrode 12, optimally mounted at the highest point in the measuring tube 1, 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 grounding electrode serves to ensure sufficient grounding of the medium. Metallic process connections 2 are attached to the ends of the measuring tube. In this case, these are flanges designed to integrate the measuring tube into a pipeline. Furthermore, two collars are attached to the measuring tube between the field feedback arrangement and the process connection 2, which form the lateral outer walls of a housing. A first coil core group 17.1 has coil cores 7 arranged in a first cross-sectional plane A. A second coil core group 17.2 has coil cores 7 which are arranged in a second cross-sectional plane B. The positions of the coil cores 7 of the individual coil core groups 17 meet the claimed requirements, namely that 60° ≤ . β ≤ 80°. The positions of the individual measuring electrodes 3 meet the claimed requirements, namely that 20° ≤ α ≤ 40° applies.

[0059] The Fig. 2shows a parallel projection representation of a second embodiment of the magnetic-inductive flowmeter according to the invention to illustrate the arrangement of the coil cores 7 and the measuring electrodes 3. The measuring tube 1 is divided into two parts I, II by means of a reference plane. In the first part I, a first coil core group 17.1 is arranged and in the second part II, a second coil core group 17.2 is arranged. In comparison to the first embodiment, each coil core group 17 comprises two further coil cores 7, which are arranged between the outer coil cores 7 and whose position is determined by the center angle cdescribed. In the cross-section, two opposing pole pieces 5 are shown, which are attached to the outer wall of the measuring tube 1. The shape of both pole pieces 5 can be roughly described by a circular arc. According to this embodiment, four coil cores 7 are arranged on a pole piece 5, each of which has at least one coil (not shown) and connects the field feedbacks to the pole pieces 5. The outer coil cores 7, in particular a point lying on the longitudinal axis of the respective coil core 7, and the center point 14 of the measuring tube 1 in the cross-section form circular arcs with a center angle β. For the center angle β it applies that 60° ≤ β ≤ 80°. The illustrated design has a central angle β of approximately 110°. The outer measuring electrodes 3 of the measuring electrode group 16 and the center point 14 form a circular section with a center angle α.For the central angle α it applies that 10° ≤ α ≤ 60°, especially 15° ≤ α ≤ 50° and preferably 20° ≤ α ≤ 40° is met. In the illustrated design, the central angle α at approximately 30°. The arrangement of the internally mounted coil cores can be determined by a central angle c For this, 1° ≤ c ≤ 80°, especially 2° ≤ c ≤ 50° and preferably 10° ≤ c ≤ 40°. Reference symbol list

[0060] 1Measuring tube 2Metallic process connection / flange 3Measuring electrode 4Magnetic field generating device 5Pole shoe 6Outer wall 7Coil core 8Coil 9Field feedback arrangement 10Field feedback 11Field feedback body 12Level monitoring electrode 13Measuring electrode arrangement 14Center point 15Longitudinal axis of the measuring tube 16Measuring electrode groups 17Coil core group 17.1First coil core group 17.2Second coil core group 18Reference plane 19Pole shoe body IFirst part IISecond part AFirst cross-sectional plane BSecond cross-sectional plane CThird cross-sectional plane

Claims

1. A magneto-inductive flowmeter, comprising: - A measuring tube (1) for conducting a flowable medium in a longitudinal direction; - a measuring electrode arrangement (13) for detecting a measuring voltage induced in the medium dependent on the flow velocity, wherein the measuring electrode arrangement (13) has two measuring electrode groups (16) which are attached opposite each other on the measuring tube (1), wherein each measuring electrode group (16) has at least two measuring electrodes (3), wherein two radii, each intersecting an external measuring electrode (3) of a measuring electrode group (16) in a cross-sectional plane of the measuring tube (1), form a central angle α such that 20° ≤ α ≤ 40°, wherein all measuring electrodes (3) of a measuring electrode group (13) are electrically connected to each other; and - a magnetic-field-generating device (4) for generating a magnetic field which passes through the measuring tube (1), wherein the magnetic-field-generating device (4) has at least two coil core groups (17) each with at least two coil cores (7), wherein a reference plane (18), which is formed by a longitudinal axis (15) of the measuring tube (1) and a lateral axis of the measuring tube (1) intersecting measuring electrodes (3) of the measuring electrode arrangement (16), divides the measuring tube (1) into a first part and a second part (I, II), wherein both the first and the second parts (I, II) of the measuring tube (1) have at least one coil core group (17), wherein two radii intersecting the external coil cores (7) of a coil core group (17) in a cross-sectional plane of the measuring tube (1) form a central angle β, wherein for the central angle β, 60° ≤ β ≤ 80°, characterized in that a coil core group (17) has at least four coil cores (7) which are attached in a cross-sectional plane of the measuring tube (1), wherein the radii intersecting each internal coil core (7) of a coil core group (17) form a central angle γ, for which 1° ≤ γ ≤ 80°, wherein one coil core (7) extends through at least two coils (8), wherein a longitudinal axis of the coil core runs parallel to the longitudinal axis (15) of the measuring tube (1), wherein the two parts (I, II) of the measuring tube (1) each have exactly two coil core groups (17), wherein a first coil core group (17.1) and a second coil core group (17.2) are arranged in the first part (I) of the measuring tube (1), wherein the first coil core group (17.1) is arranged in a first cross-sectional plane (A) and a second coil core group (17.2) is arranged in a second cross-sectional plane (B), wherein the first and the second cross-sectional planes (A, B) are spaced apart in the longitudinal direction of the measuring tube (1), wherein the measuring electrode arrangement (13) is arranged in a third cross-sectional plane (C), wherein the third cross-sectional plane (C) is arranged between the first and the second cross-sectional planes (A, B) and preferably forms a plane of symmetry for the coil core groups (17), and preferably for the magnetic-field-generating device (4).

2. The flowmeter as claimed in claim 1, wherein the coil core group (17) has exactly four coil cores (7) which are attached in the cross-sectional plane of the measuring tube (1), wherein for the central angle γ, 2° ≤ γ ≤ 50° and preferably 10° ≤ γ ≤ 40°.

3. The flowmeter as claimed in one of the preceding claims, wherein a coil core (7) runs through exactly two coils (8).

4. The flowmeter as claimed in one of the preceding claims, wherein all coils (8) which are connected in series have an electrical resistance between 2 and 300 Ω, in particular between 100 and 280 Ω, and preferably between 150 and 260 Ω.

5. The flowmeter as claimed in one of the preceding claims, wherein the magnetic-field-generating device (4) has two pole shoes (5), wherein the pole shoes (5) are attached opposite each other, in particular in contact with an outer wall of the measuring tube (1), wherein each pole shoe (5) is formed by at least two and preferably exactly two or exactly four pole shoe bodies (19), wherein the pole shoe bodies (19) are formed by stacked sheet metal parts, in particular electrical steel.

6. The flowmeter as claimed in claim 5, wherein two adjacent pole shoe bodies (19) are spaced a minimum distance C apart in the longitudinal direction of the measuring tube (1), said distance being less than 500 mm, in particular less than 50 mm, and preferably between 2 and 5 mm.

7. The flowmeter as claimed in one of the preceding claims, wherein at least one field return arrangement (9) is attached to the outer wall of the measuring tube (1), in particular is adjacent, wherein the field return arrangement (9) comprises at least two field returns (10), wherein the coil cores (7) connect the pole shoes (5) to the field returns (10).