Magnetic inductive flow meter and method for designing a magnetic inductive flow meter
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- ENDRESS HAUSER FLOWTEC AG
- Filing Date
- 2024-07-29
- Publication Date
- 2026-06-10
Smart Images
Figure EP2024071487_06022025_PF_FP_ABST
Abstract
Description
[0001] Magnetic-inductive flowmeter and method for designing a magnetic-inductive flowmeter
[0002] The invention relates to a magnetic-inductive flowmeter for determining a flow velocity-dependent measured variable of a flowable medium and a method for designing the magnetic-inductive flowmeter according to the invention.
[0003] Magnetic-inductive flowmeters are used to determine the flow velocity and / or volume flow of a medium in a measuring tube. A magnetic-inductive flowmeter comprises a magnetic field-generating device that generates a magnetic field perpendicular to the transverse axis of the measuring tube. Single or multiple coils are typically used for this purpose. To create a predominantly homogeneous magnetic field, additional pole pieces are shaped and mounted so that the magnetic field lines run essentially perpendicular to the transverse axis across the entire measuring tube cross-section. A pair of electrodes attached to the outer surface of the measuring tube taps an inductively generated electrical measuring voltage, which arises when a conductive medium flows in the direction of the longitudinal axis when a magnetic field is applied.Since the measured 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 measuring tube cross-section, the volume flow of the medium can be determined from the measured voltage.
[0004] Magnetic-inductive flowmeters are sensitive to the flow profile of the medium. Depending on the pipe system and the 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 usually 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 pipe system is located in a very confined space. One solution is provided by the invention disclosed in DE 10 2014113408 A1, in which a narrowing of the pipe diameter leads to the conditioning of the flow, thereby minimizing the influence of the flow profile, so that a 0-DN inlet section can be used, i.e.This allows the magnetic-inductive flowmeter to be positioned directly behind the source of interference, eliminating the need to install a straight pipe between the source of interference and the face of the magnetic-inductive flowmeter. However, the disadvantage of this design is that, while it allows for lower sensitivity to rotationally asymmetric flow profiles, it results in a pressure loss. Furthermore, this design is limited to pipe systems with a DN < 600.
[0005] The sensitivity of flow measurement to a rotationally asymmetric flow profile depends on the geometry of the measuring tube and the measuring electrodes. Therefore, the influences of the measuring tube and measuring electrode geometry must be taken into account to correctly describe the velocity-dependent induced voltage. These two influences are mathematically described by a weighting function GF.
[0006] The influence of geometry on flow can best be illustrated by the following relationship: where to determine the voltage U(x), the flow velocity v(x') and the weighting function GF (x',x) are integrated over the volume of the measuring tube. The weighting function GF is described using GF(x',x) = B x FG(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 setup so that V x GF = 0 applies across the entire flow profile. However, this is not possible for a measuring tube with a single point-shaped electrode pair. One possible solution is to adapt the electrode shape. However, this is not practical and causes new difficulties. Another solution is to use multiple electrode pairs.
[0007] One solution is provided by the magnetic-inductive flowmeter known from CN 101294832 A. It features two pairs of measuring electrodes arranged axially symmetrically in a measuring tube cross-section to minimize the influence of the flow profile on the determination of the volume flow. The two measuring electrode axes defined by the respective pairs of measuring electrodes span a central angle of approximately 40° in the cross-section of the measuring tube.
[0008] A further embodiment is shown in DE 10 2015 113 390 A1, in which a second and third measuring electrode pair are arranged on defined electrode axes, which are arranged at an angle of less than or equal to ±45° with respect to a first measuring electrode axis oriented perpendicular to the magnetic field.
[0009] EP 0878694 A1 also discloses a magnetic-inductive flowmeter which, based on the prior art, achieves an improvement in measurement accuracy in the range of measurement errors below 1% by using two additional measuring electrode pairs, whose measuring electrode axes each form an angle of approximately 45° to the measuring electrode axis of the conventional measuring electrode pair and the measuring tube axis. This is achieved in particular by individually recording and weighting the electrical potential differences present at the measuring electrodes. DE 10 2018 108 197 A1 discloses a magnetic-inductive flowmeter which is robust against rotationally asymmetric flow profiles. For this purpose, the magnetic-inductive flowmeter has two or more measuring electrode pairs arranged on the measuring tube.
[0010] - and cylindrical coils, each with a pole piece. The geometry of the pole pieces is adapted to the center angle of the circular sector in which the measuring electrodes on one side of the measuring tube are located.
[0011] Such a solution has the disadvantage that solenoid coils have higher inductances, resulting in slower switching between the preferred magnetic field directions. Furthermore, solenoid coils also have a larger outer diameter than comparable saddle coils. Saddle coils have the advantage over solenoid coils in that they require less copper wire to achieve comparable magnetic field strengths. This allows for a more compact magnetic-inductive flowmeter.
[0012] Based on the prior art described, the present invention is based on the object of providing an alternative magnetic-inductive flowmeter which minimizes the influences of a rotationally asymmetric flow profile when determining the flow velocity and the volume flow.
[0013] The object is achieved by the magnetic-inductive flowmeter according to claim 1 and the method for designing the magnetic-inductive flowmeter according to claim 16.
[0014] The magnetic-inductive flowmeter according to the invention for determining a flow velocity-dependent measured variable of a flowable medium, comprising:
[0015] - a measuring tube for guiding the medium, wherein a longitudinal plane divides the measuring tube into a first side and a second side, wherein the measuring tube has an outer surface;
[0016] - a magnetic field generating device comprising:
[0017] - at least one saddle coil is arranged on the outer surface, wherein a coil wire of the saddle coil defines a saddle coil interior,
[0018] - a saddle coil core arrangement with at least one saddle coil core is arranged in the saddle coil interior, wherein a central angle a is arranged in a cross section through the magnetic-inductive flowmeter, wherein for the central angle a, 10 < a < 50, in particular 15 < a < 40 and preferably 20 < a < 30; and
[0019] - at least four measuring electrodes of the at least four measuring electrodes are arranged on the first side and at least two of the at least four measuring electrodes are also arranged on the second side, wherein a central angle ß spans a minimum circular sector in the cross section in which the at least two measuring electrodes of the first side are arranged, wherein for the central angle ß the following applies: 20 < ß < 70, in particular 30 < ß < 60 and preferably 40 < ß < 50.
[0020] Advantageous embodiments of the invention are the subject of the subclaims.
[0021] One embodiment provides that the center angle α and the center angle β are matched to one another in such a way that the magnetic-inductive flowmeter is insensitive to deviations caused by a rotationally symmetric flow to such an extent that the magnetic-inductive flowmeter detects a measurement error of the flow velocity-dependent measured variables, in particular a measurement error of a flow velocity A, during a test measurement. u = \ (u va - Us) / u va | and / or a measurement error of the volume flow 4'v = \ (y va - Vs) / Vva l> less than 1 ,0%, in particular less than 0.5% and preferably less than 0.2%, wherein a flow rate u va and / or a volume flow V va form a reference value, with a flow velocity u sand / or a volume flow 1 in the case of a rotationally asymmetric flow is determined, wherein for the test measurement a rotationally asymmetric flow is generated by a disturbance arranged on an inlet-side end face of the measuring tube and comprising at least one disturbance source.
[0022] One embodiment provides that the interference source comprises a diaphragm and / or a 90° pipe bend, wherein at least 10% of the cross-section of the measuring tube is covered by the diaphragm, wherein the diaphragm has a chord which limits the diaphragm to the measuring tube, wherein the diaphragm assumes a first diaphragm orientation or a second diaphragm orientation, wherein in the first diaphragm orientation the chord is oriented perpendicular to a main magnetic field axis and in the second diaphragm orientation the chord is oriented parallel to the main magnetic field axis, 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 main magnetic field axis and to the longitudinal axis of the measuring tube, and the second pipe bend orientation is characterized by a pipe axis running parallel to the main magnetic field axis and perpendicular to the longitudinal axis of the measuring tube.
[0023] One design provides that the interference source is set up at a distance of 0-DN from the inlet-side face.
[0024] One embodiment provides that the saddle coil interior in the cross section encompasses the measuring tube with a central angle y, wherein the central angle y is such that 60 < y < 120, in particular 70 < y < 110 and preferably 80 < y < 100.
[0025] One embodiment provides that the saddle coil interior in the cross section encompasses the measuring tube with a central angle y, wherein the measuring tube has a nominal width DN, where y = a • DN + b, with 0.05 < a < 0.09, in particular 0.06 < a < 0.08 and 45° < b < 95°, in particular 70° < b < 80°.
[0026] A further design includes:
[0027] - at least six measuring electrodes of the at least six measuring electrodes are arranged on the first side and at least three measuring electrodes of the at least six measuring electrodes are also arranged on the second side, wherein the at least three measuring electrodes of the first side are arranged in the minimum circular sector.
[0028] One embodiment provides that the saddle coil core arrangement comprises two saddle coil cores which are spaced apart from one another and do not directly touch one another.
[0029] One embodiment provides that the two saddle coil cores are spaced apart by a distance d, wherein the distance d is such that 5 mm < d < 30 mm, in particular 7.5 mm < d < 25 mm and preferably 10 mm < d < 20 mm.
[0030] A further design includes:
[0031] - two saddle coils arranged opposite one another on the measuring tube each have a saddle coil interior, wherein a saddle coil core arrangement is arranged in each of the two saddle coil interiors.
[0032] One embodiment provides that the two saddle coil core arrangements each comprise two saddle coil cores.
[0033] One embodiment provides that a saddle coil core of the first saddle coil core arrangement is connected to a saddle coil core of the second saddle coil core arrangement.
[0034] One embodiment provides that a first saddle coil core of the first saddle coil core arrangement is connected via a first field guide body to a first saddle coil core of the second saddle coil core arrangement, wherein a second saddle coil core of the first saddle coil core arrangement is connected via a second field guide body to a second saddle coil core of the second saddle coil core arrangement.
[0035] One embodiment provides that all measuring electrodes on one side are electrically connected to one another via an electrically conductive connecting element.
[0036] One embodiment provides that the saddle coil interior in cross section has an effective cross-sectional area A innen wherein the saddle coil core arrangement has an effective cross-sectional area A SK where A innen > A SK ■ k applies, with 2 < k < 8, in particular 3 < k < 7 and preferably 4 < k < 6.
[0037] The method according to the invention for designing a magnetic-inductive flowmeter according to one of the preceding claims, comprising the method steps:
[0038] - Adjusting the center angles a and ß and optionally y to each other in such a way that the magnetic inductive flowmeter is insensitive to deviations of a rotationally symmetric flow to such an extent that a measurement error of the flow velocity-dependent measured variable, in particular the flow velocity u = \ u va - and s )' / u va | and / or a measurement error of the volume flow less than 1.0%, in particular less than 0.5% and preferably less than 0.2%, wherein the adjustment of the center angles α and β comprises carrying out the test measurement, comprising the method steps:
[0039] - Determine the flow velocity u vaand / or the volume flow V va in the case of a flow with a fully developed flow profile; and
[0040] - Determine the flow velocity u s and / or the volume flow 1 in the case of a rotationally asymmetric flow, wherein the rotationally asymmetric flow is generated by a disturbance arranged on the inlet-side end face and comprising at least one disturbance source.
[0041] The invention is explained in more detail with reference to the following figures. They show:
[0042] Fig. 1 : a perspective view of a magnetic-inductive flow meter according to the prior art;
[0043] Fig. 2: a cross-section through a magnetic-inductive flowmeter according to the state of the art;
[0044] Fig. 3: a perspective view of a first embodiment of the magnetic-inductive flowmeter according to the invention;
[0045] Fig. 4: a cross section through the first embodiment of the magnetic inductive flow meter according to the invention;
[0046] Fig. 5: a perspective view of a second embodiment of the magnetic-inductive flowmeter according to the invention;
[0047] Fig. 6: a block diagram illustrating the method steps of the method according to the invention for designing the magnetic-inductive flowmeter;
[0048] Fig. 7: an embodiment of the electrically conductive connecting element; and
[0049] Fig. 8: multiple sources of interference.
[0050] Fig. 1 shows a perspective view of a magnetic-inductive flowmeter 1 with an open sensor system. Fig. 2 shows a cross-section through a magnetic-inductive flowmeter 1 which differs from the magnetic-inductive flowmeter 1 of Fig. 1 only in that the field guide bodies 60, 61 are not shown. The magnetic-inductive flowmeter 1 has a measuring tube 2 for guiding a flowable and electrically conductive medium. The measuring tube 2 shown in Fig. 1 is cylindrical. However, it can also have at least one section or several sections in which its own shape deviates from a cylindrical shape. Alternatively, the measuring tube 2 can also be completely non-cylindrical (e.g. as a square or rectangular tube).The measuring tube 2 can have a metallic support tube, on the inner surface of which an electrically insulating liner is arranged. The electrically insulating liner can be a plastic, a ceramic, and / or a glass. The electrically insulating liner is drawn into the support tube or applied to the inner surface of the support tube in the form of a generally flowable coating medium. Alternatively, the measuring tube 2 can have a support tube made of an electrically insulating material. The support tube can thus be designed as a plastic, ceramic, or glass tube. In this case, an additional liner is generally omitted.
[0051] The magnetic field generating device 3 is arranged on the outer surface of the measuring tube, in particular the support tube. The magnetic field generating device 3 is designed to generate a magnetic field penetrating the measuring tube 2 and is positioned and oriented on the measuring tube 2 such that a main magnetic field axis of the generated magnetic field perpendicularly intersects the longitudinal axis of the measuring tube 2. The magnetic field generating device 3 has at least one saddle coil 4, which plays an active role in generating the magnetic field. In the illustrated embodiment, the magnetic field generating device 3 has two saddle coils 4, 9 arranged opposite one another. The shape of each saddle coil 4, 9 adapts to the shape of the outer surface of the measuring tube 2. The saddle coil 4, 9 comprises a wound coil wire that defines a saddle coil interior 5 for receiving a saddle coil core 6, 18.A saddle coil core 6 is arranged inside the at least one saddle coil 4. In the illustrated embodiment, saddle coil cores 6, 18 are arranged in each of the two saddle coils 4, 9. A saddle coil core 6, 18 is usually made of a soft magnetic material and has the task of increasing the inductance of the overall saddle coil system. The saddle coil cores 6, 18 are designed such that they fill the respective saddle coil interior 5 as completely as possible. However, there can also be a narrow gap between the saddle coil 4, 9 and the saddle coil core 6, 18. This results in an approximately Gaussian distribution for the magnetic field strength in the measuring tube cross-section and along an imaginary measuring electrode axis. The vertex of the Gaussian distribution is intersected by the main magnetic field axis.The maximum magnitude of the magnetic field strength is significantly higher compared to a solution without a saddle coil core and decreases radially comparatively more slowly than is the case with a magnet system without a saddle coil core.
[0052] The two saddle coil cores 6, 18 are connected to each other via two field guide bodies 60, 61. Two field guide bodies 60, 61 are shown, but alternatively, the magnetic coupling of the two saddle coil cores 6, 18 can also be achieved by exactly one field guide body 60. The field guide bodies 60, 61 shown are made of a material suitable for guiding the magnetic field lines from the saddle coil core 6 to the saddle coil core 18, thus achieving a magnetic coupling of the two saddle coil cores 6, 18. A soft magnetic material is suitable for this purpose. The field guide bodies 60, 61 can be formed from stamped-packet electrical steel sheets.
[0053] Alternatively, the saddle coil interior 5, 10 can be free of a saddle coil core (not shown). In this case, the saddle coils 4, 9 are air-core coils. Furthermore, the magnetic field-generating device 3 is free of a cylindrical coil and a pole piece, as taught, for example, in DE 10 2018 108 197 A1.
[0054] The saddle coils 4, 9 are electrically connected to operating electronics (not shown), which are configured to operate the saddle coils 4, 9 with an operating signal. The operating signal can be a time-varying electrical voltage or current. The saddle coils 4, 9 can be connected in series or parallel.
[0055] The magnetic-inductive flowmeter 1 shown further comprises two oppositely positioned, in particular diametrically opposed, measuring electrodes 11, 12, each arranged in an opening in the measuring tube 2. The measuring electrodes 11, 12 are each connected to the operating electronics (not shown), which is configured to measure the measuring voltage applied to the measuring electrodes 11, 12 or the electrical potential present at the measuring electrodes 11, 12. The measured measuring voltage is proportional to the flow velocity of the electrically conductive medium flowing through the measuring tube. The measuring electrodes 11, 12 can take any form already known from the prior art (e.g., DE 10 2012 109 308 A1). The illustrated magnetic-inductive flowmeter 1 also has a level monitoring electrode 30, which is arranged opposite a reference electrode 31 on the measuring tube.Both electrodes are located in the saddle coil interior 5 and are also connected to . The level monitoring electrode 30 is designed to monitor whether the container is full. The reference electrode 31 is connected to an electrical reference potential and is frequently used in measuring tubes 2 that are completely electrically insulating. However, the level monitoring electrode 30 and the reference electrode 31 are not essential to the invention.
[0056] Fig. 3 shows a first embodiment of the magnetic-inductive flowmeter 1 according to the invention for determining a flow velocity-dependent measured variable of a flowable medium. Fig. 4 shows a cross-section through the magnetic-inductive flowmeter 1 of Fig. 3, with the field guide bodies 60, 61 not shown for clarity.
[0057] The magnetic-inductive flowmeter 1 has a measuring tube 2 for guiding the medium, which is divided by a longitudinal plane LE into a first side I and a second side II. The longitudinal axis of the measuring tube and the main axis of the magnetic field generated by the magnetic field generating device 3 lie in the longitudinal plane LE.
[0058] The magnetic field generating device 3 comprises at least one saddle coil 4, or in the illustrated case, two oppositely arranged saddle coils 4, 9. In each of the saddle coils 4, 9, in particular in the saddle coil interiors 5, 10, a saddle coil core arrangement 6, 17 with at least one saddle coil core 7, 18 is arranged. In the illustrated embodiment, the saddle coil core arrangements 6, 17 each comprise exactly one saddle coil core 7, 18. The inventive embodiment of Fig. 3 differs from that in Fig.1 and 2 in that a central angle α in a cross section through the magnetic-inductive flowmeter 1, in particular through a measuring section - in which the magnetic field generating device and the measuring electrodes are arranged - of the magnetic-inductive flowmeter 1, spans a minimal circular sector (see dot-dashed circular sector) in which the saddle coil core arrangement 6, 17 is arranged. This means that the central angle α specifies or restricts the dimensioning of the saddle coil core arrangement 6, 17. For the central angle α, 10 < α < 50, in particular 15 < α < 40 and preferably 20 < α < 30 applies. The specified limit values for the angle α are given in degrees. The saddle coil core 7 of the first saddle coil core arrangement 6 is connected, in particular exclusively, via a field guide body 60, 61 to the saddle coil core 18 of the second saddle coil core arrangement.
[0059] The saddle coil core arrangement 5, 10 or the saddle coil cores fill only a small portion of the saddle coil interior 5, 10. The saddle coil interior 5, 10 has an effective cross-sectional area A innen and the saddle coil core arrangement 6, 17 in cross section an effective cross-sectional area A SK The following applies: A innen > A SK ■ k is, with 2 < k < 8, in particular 3 < k < 7 and preferably 4 < k < 6.
[0060] Furthermore, the magnetic field generating device 3 according to the invention is free of a cylindrical coil and a pole piece, as taught, for example, in DE 10 2018 108 197 A1, CN 204 694 303 U or EP 0 418 033 A1.
[0061] The saddle coil interior 5, 10 encompasses, in particular encompasses its boundaries, in the cross-section of the magnetic-inductive flowmeter 1, the measuring tube 2 with a central angle y (see dotted circular sector). The central angle y is a measure of the length of the saddle coil 4, 9 and also indirectly of the portion of the outer surface of the measuring tube that is covered by the saddle coil 4, 9. The following applies to the central angle y: 60 < y < 120, in particular 70 < y < 110 and preferably 80 < y < 100. The specified limit values for the angle y are given in degrees. The saddle coil interior 5, 10 encompasses a significantly larger area of the outer surface of the measuring tube 2 in the circumferential direction than the saddle coil core arrangement 6, 17. Alternatively, the advantageous central angle y can be described by the equation y = a • DN + b.Where DN stands for the nominal diameter of the measuring tube 2 and it applies that 0.05 < a < 0.09, in particular 0.06 < a < 0.08 and 45° < b < 95°, in particular 70° < b < 80°.
[0062] The magnetic-inductive flowmeter 1 according to the invention has at least four measuring electrodes 11, 12, 13, 14, wherein at least two measuring electrodes 11, 13 of the at least four measuring electrodes 11, 12, 13, 14 are arranged on the first side I and likewise at least two measuring electrodes (concealed by the measuring tube in Fig. 3) of the at least four measuring electrodes 11, 12, 13, 14 are arranged on the second side. A central angle β spans a minimal circular sector (see dashed circular sector) in the cross-section through the magnetic-inductive flowmeter 1, in which the at least two measuring electrodes 11, 13 of the first side I are arranged. For the central angle β, 20 < β < 70, in particular 30 < β < 60 and preferably 40 < β < 50. The specified limit values for the angle ß are given in degrees.The minimum circular sector is limited by the openings for the measuring electrodes in the measuring tube or by the shafts of the outer measuring electrodes, or by the longitudinal and / or symmetry axes of the outer measuring electrodes. It is therefore possible that the measuring electrode heads lie at least partially outside the defined minimum circular sector.
[0063] In the illustrated embodiment, the magnetic-inductive flowmeter 1 has six measuring electrodes 11, 12, 13, 14, 15, 16, of which three measuring electrodes 11, 13, 15 are arranged on the first side I and the three measuring electrodes 12, 14, 16 are arranged on the second side II of the measuring tube 2. All measuring electrodes on one side are arranged in the minimum circular sector. The positioning of the measuring electrodes on the respective sides is limited by the circular sector spanned by the central angle ß.
[0064] The center angles α and β are not arbitrarily chosen. The center angle α and the center angle β are matched to one another in such a way that the magnetic-inductive flowmeter 1 is insensitive to a deviation caused by a rotationally symmetric flow to such an extent that the magnetic-inductive flowmeter 1, during a test measurement, detects a measurement error of the flow velocity-dependent measured variables, in particular a measurement error of a flow velocity A u = |(u va - and s ) / u va | and / or a measurement error of the volume flow v = \(V va - V s ) / V va |, less than 1 ,0%, in particular less than 0.5% and preferably less than 0.2%. The flow velocity u va and / or the volume flow V va a reference value and the flow rate u sand / or the volume flow 1 is determined in the case of a rotationally asymmetric flow. The rotationally asymmetric flow is generated in the test measurement by a disturbance arranged on an inlet-side end face of the measuring tube 2 and comprising at least one disturbance source (see Fig. 8). The center angle y is also not chosen arbitrarily, but rather a free parameter that is adapted / optimized according to the center angles α and β such that the magnetic-inductive flowmeter 1 is insensitive to a deviation caused by a rotationally symmetric flow to such an extent that the magnetic-inductive flowmeter 1, during a test measurement, detects a measurement error of the flow velocity-dependent measured variables, in particular a measurement error of a flow velocity A u = |(u va - and s ) / u va I and / or a measurement error of the volume flow v = | (V va - Vs ) / V va | , less than 1 ,0%, in particular less than 0.5% and preferably less than 0.2%.
[0065] Fig. 5 shows a second embodiment of the magnetic-inductive flowmeter 1 according to the invention for determining a flow velocity-dependent measured variable of a flowable medium. The embodiment of Fig. 5 differs from Fig. 3 in that the saddle coil core assemblies 6, 17 each comprise two saddle coil cores 7, 8, 18, 19 that are spaced apart from one another and do not directly touch one another, and not just one saddle coil core 7, 18 per saddle coil. The respective saddle coil cores 7, 8, 18, 19 forming a saddle coil core pair are spaced apart by a distance d for which 5 mm < d < 30 mm, in particular 7.5 mm < d < 25 mm and preferably 10 mm < d < 20 mm applies. The distance d should be kept as small as possible. By splitting the saddle coil core into two separate, spaced-apart saddle coil cores, a free space is created in which a level monitoring electrode or a reference electrode (not shown) can be arranged.A first saddle coil core 7 of the first saddle coil core arrangement 6 is connected via a first field guide body 60 to a first saddle coil core 18 of the second saddle coil core arrangement 17 and a second saddle coil core 8 of the first saddle coil core arrangement 6 is connected via a second field guide body 61 to a second saddle coil core 19 of the second saddle coil core arrangement 17.
[0066] Fig. 6 shows a block diagram illustrating the method steps of the method according to the invention for designing the magnetic-inductive flowmeter (see Figs. 3 to 5).
[0067] Process step I includes:
[0068] - Adjusting the center angles a and ß and optionally y to each other in such a way that the magnetic inductive flowmeter is insensitive to deviations of a rotationally symmetric flow to such an extent that a measurement error of the flow velocity-dependent measured variable, in particular the flow velocity Au = l(u va - and s ) / u va | and / or a measurement error of the volume flow
[0069] AV = l( a > ^ ) / ^va\ is less than 1 ,0%, in particular less than 0.5% and preferably less than 0.2%.
[0070] The center angles α and β, and optionally γ, are adjusted by performing a test measurement. This involves performing steps II and III. Step II includes:
[0071] - Determine the flow velocity u va and / or the volume flow V vain the case of a flow in the measuring tube with a fully developed flow profile.
[0072] After disturbances, measurement errors in the magnetic-inductive flowmeter due to a non-ideal flow profile can occur depending on the distance and type of disturbance source, as the 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.
[0073] Process step III includes:
[0074] - Determine the flow velocity u sand / or the volume flow 1 in case of a rotationally asymmetric flow in the measuring tube.
[0075] The rotationally asymmetric flow is generated by a disturbance arranged on the inlet-side end face and comprising at least one disturbance source. The disturbance source is arranged at a distance of 0-DN from the inlet-side end face 22. The potential disturbance sources are shown in Fig. 8. However, other disturbance sources are also suitable. However, it is justified to point out that by optimizing the magnetic-inductive flowmeter with an orifice plate or a 90° pipe bend or a combination of the two disturbance sources (with appropriate orientations) to create a magnetic-inductive flowmeter that meets the requirements (measurement error less than 1%, in particular less than 0.5% and preferably less than 0.2% after a disturbance) even for other types of disturbance sources.
[0076] Process steps II and III are not necessarily performed consecutively. Furthermore, process steps II and III can be performed using a computer simulation program (e.g., finite element method (FEM) or computational fluid dynamics (CFD) simulations using ANSYS, COMSOL, and / or STARCCM+) or experimentally.
[0077] Process steps II and III are carried out for a large number of center angle pairs or triplets.
[0078] In a final method step IV, the pair(s) or triple(s) of center angles that satisfy(s) the measurement error condition are then selected. Fig. 7 shows an embodiment of the electrically conductive connecting element 40, which is designed as a bent sheet metal part. Reference is made in full to DE 10 2018 116 400 A1, which discloses a multitude of variants for suitable bent sheet metal parts. The bent sheet metal part has three openings that simplify its arrangement and fixing to the measuring electrodes 11, 13, 15. Alternatively, the connecting element 40 can also be one or more electrical cables that electrically connect(s) or short-circuit(s) the measuring electrodes to one another.
[0079] Fig. 8 shows two interference sources 50, each of which can have different orientations relative to the magnetic inductive flowmeter. The interference source 50 to be used for the test measurement comprises an orifice plate B and / or a 90° pipe bend 90°R. The orifice plate B covers at least 10% or, for example, exactly 12.5% of the cross-section of the measuring tube 2, in particular of the measuring channel delimited by the liner or the support tube. During the test measurement, the orifice plate B can assume a first orifice plate orientation B1 or a second orifice plate orientation B2. In the first orifice plate orientation B1, the chord is oriented perpendicular to a main magnetic field axis, and in the second orifice plate orientation B2, the chord is oriented parallel to the main magnetic field axis. The 90° pipe bend 90°R can also assume two orientations for the test measurement: a first pipe bend orientation R1 or a second pipe bend orientation R2.The first pipe bend orientation R1 is characterized by a longitudinal axis of the pipe bend 90°R oriented perpendicular to the main magnetic field axis MA (shifted in the diagram) and perpendicular to the longitudinal axis LA of the measuring tube 2, and the second pipe bend orientation R2 is characterized by a longitudinal axis of the pipe bend 90°R oriented parallel to the main magnetic field axis MA and perpendicular to the longitudinal axis LA of the measuring tube 2.
Claims
PATENT CLAIMS 1. A 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, wherein a longitudinal plane (LE) divides the measuring tube (2) into a first side (I) and a second side (II), wherein the measuring tube (2) has an outer lateral surface; - a magnetic field generating device (3), which magnetic field generating device (3) comprises: - at least one saddle coil (4), wherein the saddle coil (4) is arranged on the outer surface, wherein a coil wire of the saddle coil (4) delimits a saddle coil interior (5), - a saddle coil core arrangement (6) with at least one saddle coil core (7), wherein the saddle coil core arrangement (6) is arranged in the saddle coil interior (5), wherein a central angle α in a cross section through the magnetic-inductive flowmeter (1), in particular through a measuring section of the magnetic-inductive flowmeter (1), spans a minimum circular sector in which the saddle coil core arrangement (6) is arranged, wherein for the central angle α, 10 < α < 50, in particular 15 < α < 40 and preferably 20 < α < 30 applies; and - at least four measuring electrodes (11, 12, 13, 14), wherein at least two (11, 13) of the at least four measuring electrodes (11, 12, 13, 14) are arranged on the first side (I) and also at least two (12, 14) of the at least four measuring electrodes (11, 12, 13, 14) are arranged on the second side (II), wherein a central angle ß spans a minimum circular sector in the cross section in which the at least two measuring electrodes (11, 13) of the first side (I) are arranged, where for the central angle ß it applies that 20 < ß < 70, in particular 30 < ß < 60 and preferably 40 < ß < 50.
2. Magnetic-inductive flowmeter (1) according to claim 1, wherein the center angle α and the center angle β are matched to one another in such a way that the magnetic-inductive flowmeter (1) is insensitive to deviations caused by a rotationally symmetric flow to such an extent that the magnetic-inductive flowmeter (1) in a test measurement has a measurement error of the flow velocity-dependent measured variables, in particular a measurement error of a flow velocity A u = \ (u va - Us) / u va | and / or a measurement error of the volume flow v = \ (Vva ~ Vs) / va l> less than 1 ,0%, in particular less than 0.5% and preferably less than 0.2%, wherein a flow velocity u va and / or a volume flow V va form a reference value, with a flow velocity u sand / or a volume flow 1 in the case of a rotationally asymmetric flow is determined, wherein for the test measurement a rotationally asymmetric flow is generated by a disturbance arranged on an inlet-side end face (22) of the measuring tube (2) and comprising at least one disturbance source (50).
3. Magnetic-inductive flowmeter (1) according to claim 2, wherein the interference source (50) comprises an orifice plate (B) and / or a 90° pipe bend (90°R), wherein at least 10% of the cross-section of the measuring tube (2) is covered by the orifice plate (B), wherein the orifice plate (B) has a chord of a circle which delimits the orifice plate (B) towards the measuring tube (2), wherein the orifice plate (B) assumes a first orifice plate orientation (B1) or a second orifice plate orientation (B2), wherein in the first aperture orientation (B1) the chord is oriented perpendicular to a main magnetic field axis and in the second aperture orientation (B2) the chord is oriented parallel to the main magnetic field axis, wherein the 90° pipe bend (90°R) assumes a first pipe bend orientation (R1) or a second pipe bend orientation (R2), wherein the first pipe bend orientation (R1) is characterized by a pipe axis (101) running perpendicular to the main magnetic field axis and to the longitudinal axis (LA) of the measuring tube (2) and the second pipe bend orientation (R2) is characterized by a pipe axis (101) running parallel to the main magnetic field axis and perpendicular to the longitudinal axis (LA) of the measuring tube (2).
4. Magnetic-inductive flowmeter (1) according to claim 2 or 3, wherein the interference source (50) is arranged at a distance of 0-DN from the inlet-side end face (22).
5. Magnetic-inductive flowmeter (1) according to one of the preceding claims, wherein the saddle coil interior (5) in the cross section encompasses the measuring tube (2) with a central angle y, wherein for the central angle y it applies that 60 < y < 120, in particular 70 < y < 110 and preferably 80 < y < 100.
6. Magnetic-inductive flowmeter (1) according to one of claims 1 to 4, wherein the saddle coil interior (5) in the cross section encompasses the measuring tube (2) with a central angle y, wherein the measuring tube (2) has a nominal diameter DN, where y = a • DN + b, with 0.05 < a < 0.09, in particular 0.06 < a < 0.08 and 45° < b < 95°, in particular 70° < b < 80°.
7. Magnetic-inductive flowmeter (1) according to one of the preceding claims, comprising: - at least six measuring electrodes (11, 12, 13, 14, 15, 16), wherein at least three measuring electrodes (11, 13, 15) of the at least six measuring electrodes (11, 12, 13, 14, 15, 16) are arranged on the first side (I) and at least three measuring electrodes (12, 14, 16) of the at least six measuring electrodes (11, 12, 13, 14, 15, 16) are also arranged on the second side (II), wherein the at least three measuring electrodes (11, 13, 15) of the first side (I) are arranged in the minimum circular sector.
8. Magnetic-inductive flowmeter (1) according to the preceding claim, wherein the saddle coil core arrangement (6) comprises two saddle coil cores (7, 8) which are spaced apart from one another and do not directly touch one another.
9. Magnetic-inductive flowmeter (1) according to claim 8, wherein the two saddle coil cores (7, 8) are spaced apart by a distance d, wherein the distance d is such that 5 mm < d < 30 mm, in particular 7.5 mm < d < 25 mm and preferably 10 mm < d < 20 mm.
10. Magnetic-inductive flowmeter (1) according to the preceding claim, wherein the magnetic field generating device (3) comprises: - two saddle coils (4, 9) arranged opposite one another on the measuring tube (2), wherein the two saddle coils (4, 9) each have a saddle coil interior (5, 10), wherein a saddle coil core arrangement (6, 17) is arranged in each of the two saddle coil interiors (5).
11. Magnetic-inductive flowmeter (1) according to claim 10, wherein the two saddle coil core assemblies (6, 17) each comprise two saddle coil cores (4, 9, 18, 19).
12. Magnetic-inductive flowmeter (1) according to claim 11, wherein a saddle coil core (7, 8) of the first saddle coil core arrangement (6) is connected, in particular exclusively, via a field guide body (60, 61) to a saddle coil core (18, 19) of the second saddle coil core arrangement (17).
13. Magnetic-inductive flowmeter (1) according to claim 11 or 12, wherein a first saddle coil core (7) of the first saddle coil core arrangement (6) is connected via a first field guide body (60) to a first saddle coil core (18) of the second saddle coil core arrangement (17), wherein a second saddle coil core (8) of the first saddle coil core arrangement (6) is connected via a second field guide body (19) to a second saddle coil core (19) of the second saddle coil core arrangement (17).
14. Magnetic-inductive flowmeter (1) according to one of the preceding claims, wherein all measuring electrodes (11, 13, 15 or 12, 14, 16) of one side (I or II) are electrically connected to one another via an electrically conductive connecting element (40).
15. Magnetic-inductive flowmeter (1) according to one of the preceding claims, wherein the saddle coil interior (5, 10) in cross section has an effective cross-sectional area within SUfweiSt, wherein the saddle coil core arrangement (6, 17) in cross section has an effective cross-sectional area A SK where A innen > A SK ■ k applies, with 2 < k < 8, in particular 3 < k < 7 and preferably 4 < k < 6.
16. Method for designing a magnetic-inductive flowmeter (1) according to one of the preceding claims, comprising the method steps: - Adjusting the center angles a and ß and optionally y to each other in such a way that the magnetic inductive flowmeter (1) is insensitive to deviations of a rotationally symmetric flow to such an extent that a measurement error of the flow velocity dependent measured variable, in particular the flow velocity Au = l(u va - and s ) / u va | and / or a measurement error of the volume flow AV = l( V va ~ 7 S ) / V va \ is less than 1.0%, in particular less than 0.5% and preferably less than 0.2%, wherein the adjustment of the central angles a and ß comprises carrying out the test measurement, comprising the method steps: - Determine the flow velocity u va and / or the volume flow V va in the case of a flow with a fully developed flow profile; and - Determine the flow velocity u sand / or the volume flow 1 in the case of a rotationally asymmetric flow, wherein the rotationally asymmetric flow is generated by a disturbance arranged on the inlet-side end face and comprising at least one disturbance source (50).