Magnetic-inductive flow meter

Abstract

The invention consists of a magnetic-inductive flowmeter (1) for determining a flow velocity-dependent measured quantity of a flowable medium, comprising: - a measuring tube (2) for guiding the medium; - two measuring electrodes (11, 12), - a coil system (3) for generating a magnetic field penetrating the measuring tube (2) at least section by section, wherein the coil system comprises at least one saddle coil (4a), wherein the at least one saddle coil (4a) has a saddle coil interior (5a), - a magnetic field guide (6) for guiding magnetic field lines outside the measuring tube (2), wherein the magnetic field guide (6) consists of a first field guide part (7a) and a second field guide part (7b) arranged opposite the first field guide part (7a), wherein the first field guidance part (7a) extends at least section by section into the saddle coil interior (5a), wherein the first field guidance part (7a) has an end section (EA) which is located in the saddle coil interior (5a) and which rests on the outer surface (MF) of the measuring tube (2), in particular directly, wherein in a cross-section (QS) through the at least one saddle coil (4a), the first field guidance part (7a) and the at least two measuring electrodes (11, 12) each point P located on a cross-sectional area (QS1) of the first field guidance part (7a) in the end section (EA) and each point Q located on a cross-sectional area (QS2) of the saddle coil (4a) spans a central angle δ which is greater than 12°, in particular greater than 17° and preferably greater than 22°, and less than 35°, in particular less than 32° and preferably less than 27°.

Description

[0001] The invention relates to a magnetic-inductive flow meter for determining a flow velocity-dependent measured quantity of a flowable medium.

[0002] Magnetic-inductive flowmeters are used to determine the flow velocity and / or volumetric flow rate of a free-flowing, electrically conductive medium in a pipeline. A magnetic-inductive flowmeter always includes a magnetic field-generating device designed to produce a magnetic field perpendicular to the horizontal axis of the measuring tube. This is typically achieved using a coil arrangement with a single coil or with several opposing coils. To ensure a largely homogeneous magnetic field, pole pieces can be shaped and attached so that the magnetic field lines run essentially perpendicular to the transverse axis across the entire cross-section of the pipe.A pair of measuring electrodes attached to the outer surface of the measuring tube detects an inductively generated electrical voltage. This voltage arises when a conductive medium flows along the longitudinal axis of the measuring tube under an applied magnetic field. Since the detected 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 cross-sectional area of ​​the measuring tube, the volumetric flow rate of the medium can be determined from the voltage.

[0003] German patent DE 10 2018 108 197 A1 discloses a magnetic-inductive flowmeter that is robust against rotationally asymmetrical flow profiles. For this purpose, the magnetic-inductive flowmeter has two or more pairs of measuring electrodes arranged on the measuring tube and cylindrical coils, each connected to a pole shoe. The geometry of the pole shoes is adapted to the central angle of the circular sector in which the measuring electrodes on one side of the measuring tube are located.

[0004] This type of solution has the disadvantage that cylindrical coils exhibit higher inductances, resulting in slower switching between the preferred magnetic field directions. Furthermore, cylindrical coils also have a larger outer diameter than comparable saddle coils. This allows for a more compact magnetic-inductive flowmeter.

[0005] A magnetic-inductive flowmeter is known from DE 10 2023 120 595.1, which has two opposing saddle coils. Each saddle coil has a saddle coil opening in which a coil core assembly consisting of a single coil core or two coil cores is positioned. The opposing coil cores are connected to each other via a field feedback in the form of a sheet metal part. By specifically designing the coil core geometry and the measuring electrode arrangement, the sensitivity to asymmetries in the flow profile can be reduced.

[0006] The invention is based on the objective of further simplifying the coil system without compromising measurement performance.

[0007] The problem is solved by the magnetic-inductive flow meter according to claim 1.

[0008] The magnetic-inductive flow meter according to the invention for determining a flow velocity-dependent measured quantity of a flowable medium comprises: - a measuring tube for guiding the medium, wherein the measuring tube has an outer shell surface; - at least two measuring electrodes, - a measuring electronics, wherein the measuring electronics are connected to at least two measuring electrodes and are configured to determine a measuring voltage, - a coil system for generating a magnetic field that penetrates at least part of the measuring tube, wherein the coil system includes at least one saddle coil, wherein the at least one saddle coil is arranged on the outer surface of the measuring tube, wherein a coil wire of the at least one saddle coil defines a saddle coil interior, - a magnetic field guide for guiding magnetic field lines outside the measuring tube, wherein the magnetic field guidance consists of a first field guidance part and a second field guidance part arranged opposite the first field guidance part, wherein the first field guidance part extends at least partially into the interior of the saddle coil, wherein the first field guidance part has an end section which is located in the saddle coil interior and which rests on the outer surface of the measuring tube, in particular directly, wherein in a cross-section through the at least one saddle coil, the first field guidance part and the at least two measuring electrodes, each point P located on a cross-sectional area of ​​the first field guidance part in the end section and each point Q located on a cross-sectional area of ​​the saddle coil spans a central angle δ which is greater than 12°, in particular greater than 17° and preferably greater than 22°, and less than 35°, in particular less than 32° and preferably less than 27°.

[0009] It is known from the prior art to attach field guide elements to the saddle coil in such a way that, upon entering the interior of the saddle coil, the field guide element virtually hugs the surface of the saddle coil, so that no (air) gap is created between the outer surface of the saddle coil and the lower surface of the first field guide element. In this case, the field guide elements rest either directly or indirectly on the, usually insulated, coil wire of the saddle coil. Additional electrical insulation can also be arranged between the coil wire and the field guide element. However, if, as required by the invention, a minimum distance is maintained between the saddle coil winding and the end section of the first field guide element, the magnetic field generated by the at least one saddle coil is further centered.This reduces the sensitivity of the flow velocity-dependent measured quantity to asymmetries in the medium. Asymmetries in the medium typically occur after bends, elbows, orifices, valves, or tees.

[0010] Advantageous embodiments of the invention are the subject of the dependent claims.

[0011] One embodiment provides that the first and second field guidance parts are each a sectionally bent, magnetizable sheet metal part.

[0012] A sheet metal part is a flexible, thin rolled piece whose width and length are many times greater than its thickness. The sheet metal part can consist of a single electrical steel sheet or a large number of stacked electrical steel sheets.

[0013] One embodiment provides that the saddle coil interior spans a maximum central angle γ, for which 75° ≤ γ ≤ 105°, in particular 80° ≤ γ ≤ 100° and preferably 85°≤γ≤95°.

[0014] The maximum central angle γ determines not only the maximum diameter of the saddle coil's interior, but also the diameter of the saddle coil itself. Magnetic-inductive flowmeters with saddle coils that meet the above requirement for the maximum central angle are particularly insensitive to asymmetries in the medium.

[0015] One design includes: - at least four measuring electrodes, wherein a longitudinal plane divides the measuring tube into a first side and a second side, wherein at least two 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 β spans a circular sector in the cross-section in which the at least two measuring electrodes of the first side are arranged, where the central angle β is such that 20° ≤ β ≤ 70°, in particular 30° ≤ β ≤ 60° and preferably 40° ≤ β ≤ 50°.

[0016] The limits for the central angles β are adapted to the central angles y and / or δ in such a way that an extraordinary insensitivity of the flow velocity-dependent measured quantity to asymmetries in the medium is achieved.

[0017] One embodiment provides that a minimum distance d is ensured between the first and / or second field guidance part and the at least one saddle coil. where the measuring tube has a nominal diameter DN, where the minimum distance d is such that DN / 10 ≤ d ≤ DN / 2, in particular DN / 5 ≤ d ≤ DN / 3.

[0018] It is known from the prior art that the field guide elements rest directly on the saddle coil, so that no empty air space is created between them. The field guide elements conform almost perfectly to the outer contour.

[0019] One embodiment provides that the first field guidance section has a main section and a connecting section between the main section and the end section. wherein a first straight line running through point Q and a midpoint M of the measuring tube in the cross-section and a second straight line describing a course of the first field guidance part in the connecting section in the cross-section span an angle θ, where the angle θ is such that 5° ≤ θ ≤ 45°, in particular 7° ≤ θ ≤ 30° and preferably 10°≤θ≤20°.

[0020] This not only has the advantage that the field guide elements are easier to manufacture, but the angle range according to the invention also prevents the magnetic properties of the field guide element from being degraded in the bent area. The angle range according to the invention is ideally suited, especially in applications with large nominal diameters, where thicker field guide elements (e.g., in the form of several layers of electrical steel sheets) are required.

[0021] The invention is explained in more detail with reference to the following figures. They show: Fig. 1: a sectional view through an embodiment of the magnetic-inductive flowmeter according to the invention; Fig. 2: a perspective view of a measuring tube with attached coil system and magnetic field guide; and Fig. 3: a partial section from a sectional view through a further embodiment of the magnetic-inductive flowmeter according to the invention.

[0022] Fig. Figure 1 shows a sectional view through part of an embodiment of the magnetic-inductive flowmeter 1 according to the invention. Fig. Figure 2 shows a perspective view of the measuring tube of the Fig. 1. The operating signal cables, housing, and any potting compound have been omitted from the illustration. The magnetic-inductive flowmeter 1 is designed to determine a flow velocity-dependent measured quantity of a flowable medium. This flow velocity-dependent measured quantity is typically the current flow velocity of the flowable and electrically conductive medium being monitored. Alternatively, the flow velocity-dependent measured quantity can be a volumetric flow rate or—if the medium density is known—a mass flow rate.

[0023] To guide the medium, the magnetic-inductive flowmeter typically has a measuring tube 2. The measuring tube 2 comprises a support tube. This support tube can be made of metal or an electrically insulating plastic. If the support tube is metallic, its inner surface is usually lined with an electrically insulating material. The measuring tube 2 typically has a hollow cylindrical shape, at least in some sections; however, magnetic-inductive flowmeters with a rectangular cross-section, at least in some sections, are also known. The measuring tube 2 has an inner surface that comes into contact with the medium during operation and an outer surface MF that faces away from the medium. The measuring tube 2 itself has a characteristic nominal diameter DN, which for magnetic-inductive flowmeters is typically between 10 and 3000 millimeters.

[0024] To determine the measured values ​​of the flow velocity-dependent quantity, the magnetic-inductive flowmeter typically has at least two measuring electrodes 11, 12. These at least two measuring electrodes 11, 12 are arranged opposite each other and are intersected by an imaginary measuring electrode axis MEA. The measuring electrode axis MEA runs perpendicular to a longitudinal axis ML of the measuring tube and to a principal axis Y of the generated magnetic field, or to an axis of symmetry. The measuring electrode axis MEA does not necessarily have to pass through a center point of the measuring tube 2. Magnetic-inductive flowmeters with more than two measuring electrodes 11, 12 are also known. The two measuring electrodes 11, 12 shown are in contact with the medium; that is, when a medium flows through the measuring tube, the at least two measuring electrodes 11, 12 are in contact with the medium.However, capacitive measuring electrodes are also known that measure through the wall of the support tube and / or the liner and therefore do not need to be in contact with the medium. Furthermore, magnetic-inductive flowmeters are also known that have two, three, or more measuring electrodes on each side. The [document / section] in the... Fig. The at least two measuring electrodes 11, 12 shown in Figure 1 are electrically connected to an electronic measuring unit 100 (shown schematically here) via signal cables. This unit is configured to determine a measuring voltage induced at the (at least) two measuring electrodes 11, 12. Based on the determined voltage value, a measured value of the flow velocity-dependent quantity can be determined by the measuring unit 100. The measuring unit 100 includes electronic components such as amplifiers, converters, microcontrollers, and / or microprocessors for this purpose.

[0025] To generate a magnetic field, the magnetic-inductive flowmeter 1 has a coil system 3. The magnetic field generated by the coil system 3 penetrates the measuring tube 2 and, during operation, thus also the medium, at least partially. According to the invention, the coil system 3 comprises at least one saddle coil 4a. In contrast to a cylindrical coil, a saddle coil is a wound coil wire that typically does not require a coil former and is arranged directly or indirectly on the outer surface of the measuring tube via an electrically insulating mat. Saddle coils with a coil former are also known. In this case, the former is either integrally formed with the outer surface of the measuring tube, at least partially, or is designed to be flexible so that it can be deformed and adapted to the shape of the measuring tube when the saddle coil is attached.By eliminating the need for a solid plastic coil former, the shape of the saddle coil 4a can be easily adapted to the shape of the measuring tube. A saddle coil also offers the advantage of achieving a larger measurement signal compared to a cylindrical coil with comparable power. The at least one saddle coil 4a is arranged on the outer surface MF of the measuring tube 2 and is fixed in place, for example, by means of field guides or a provided fastening device (e.g., clamps, bolts, screws, etc.). A coil wire of the saddle coil 4a at least partially defines the interior space 5a of the saddle coil. This interior space 5a is defined not only by the wound coil wire but also by the outer surface MF of the measuring tube. An outer saddle coil surface SFO forms an imaginary curved area that also defines the interior space 5a of the saddle coil.

[0026] In addition to the coil system 3, the magnetic-inductive flowmeter 1 has a magnetic field guide 6. The magnetic field guide 6 is designed to guide magnetic field lines outside the measuring tube 2. In the illustrated embodiment, the magnetic field guide 6 consists of a first field guide part 7a and a second field guide part 7b, arranged opposite the first field guide part 7a and of an identical design. According to the invention, further separate coil cores or separate pole shoes are not required.

[0027] The first field guidance section 7a extends at least partially into the interior of the saddle coil 5a. In this specific case, the first field guidance section 7a has an end section EA, which is located in the interior of the saddle coil 5a. In addition to the end section EA, a connecting section VA of the first field guidance section 7a, which connects the end section EA to a main section HA, is also located, at least partially, in the interior of the saddle coil 5a. The main section HA can also project, at least partially, into the interior of the saddle coil 5a, contrary to the illustration. The end section EA of the first field guidance section 7a rests on the outer surface MF of the measuring tube 2, in particular directly.

[0028] In a cross-section QS through the at least one saddle coil 4a, the first field guide element 7a, and the at least two measuring electrodes 11, 12, each point P located on a cross-sectional area QS1 of the first field guide element 7a in the end section (EA) and each point Q located on a cross-sectional area QS2 of the saddle coil 4a defines a central angle δ that is greater than 12°, in particular greater than 17° and preferably greater than 22°, and less than 35°, in particular less than 32° and preferably less than 27°. The central angle δ is defined with respect to a center point M lying on a longitudinal axis ML of the measuring tube. The center point M is also determined by the intersection of the principal axis Y and the measuring electrode axis MEA.

[0029] The first and second field guide parts 7a and 7b can each be a sheet metal part bent in sections. The sheet metal part can comprise a large number of stacked electrical steel sheets. Alternatively, the sheet metal part can also comprise a single electrical steel sheet.

[0030] Furthermore, the saddle coil interior 5a can span a maximum central angle γ such that 75° ≤ γ ≤ 105°, in particular 80° ≤ γ ≤ 100° and preferably 85° ≤ γ ≤ 95°.

[0031] Furthermore, the magnetic-inductive flowmeter can comprise at least four measuring electrodes 11, 12, 13, 14, wherein the two measuring electrodes 11, 13 of the at least four measuring electrodes 11, 12, 13, 14 are arranged on a first side I of the measuring tube 2, and likewise the two measuring electrodes 12, 14 of the at least four measuring electrodes 11, 12, 13, 14 are arranged on the second side II. The first side I and the second side II of the measuring tube 2 are uniquely characterized by a longitudinal plane LE dividing the measuring tube 2. The principal axis Y and the longitudinal axis ML of the measuring tube span the longitudinal plane LE. Furthermore, the longitudinal plane LE is intersected perpendicularly by the measuring electrode axis MEA.

[0032] Furthermore, a central angle β can define a circular sector in the cross-section QS in which the at least two measuring electrodes 11, 13 of the first side I are arranged, wherein the central angle β is such that 20° ≤ β ≤ 70°, in particular 30° ≤ β ≤ 60°, and preferably 40° ≤ β ≤ 50°. The same can also apply to the two measuring electrodes 12, 14 arranged on side II. If a third measuring electrode 15 is provided on side I in addition to the two measuring electrodes 11, 13, it also lies within the circular sector defined by the central angle β.

[0033] If the magnetic-inductive flowmeter, as shown, has more than two measuring electrodes, the measuring electrodes arranged on each side of the measuring tube 2 can be electrically short-circuited before they are connected to the measuring electronics 100. The short-circuiting can be done via an electrically conductive connecting element (e.g., a cable).

[0034] Alternatively, each measuring electrode 11, 12, 13, 14, 15, 16 can be connected separately to the measuring electronics 100.

[0035] Furthermore, it may be required that a minimum distance d be ensured between the first and / or second field guide section 7a, 7b and the at least one saddle coil 4a. This creates an air space, particularly an empty one, between the first and / or second field guide section 7a, 7b. The minimum distance d depends on the nominal diameter of the measuring tube and is preferably selected such that DN / 10 ≤ d ≤ DN / 2, and in particular DN / 5 ≤ d ≤ DN / 3. It has been found that the described spacing of the field guide sections 7a, 7b, in conjunction with more than two measuring electrodes, improves the insensitivity of the measurement signal to flow asymmetries in the medium.

[0036] According to one embodiment, the magnetic field guide 6 consists of a first field guide part 7a and a second field guide part 7b arranged opposite the first field guide part 7a. The first and second field guide parts 7a, 7b are completely separated by a gap 20, meaning that there are no points of contact between the two field guide parts 7a, 7b. The gap 20, designed as an air gap, is spanned in a cross-section QS by the magnetic-inductive flowmeter 1 at a central angle α, for which 1° ≤ α ≤ 60°, in particular 5° ≤ α ≤ 40°, and preferably less than 15°. The gap 20 is considered an air gap if no magnetic or magnetizable component bridges or covers it. The gap 20 is located, as shown, in the interior of the saddle coil 5.Furthermore, the gap 20 is characterized by a circular arc, which itself depends on the surface curvature of the measuring tube 2 and the central angle α.

[0037] Fig. Figure 3 shows a partial section from a sectional view through a further embodiment of the magnetic-inductive flowmeter according to the invention.

[0038] The first field guide section 7a can be divided into a main section HA, a connecting section VA, and an end section EA. The connecting section VA lies between the end section EA and the main section HA. The main section HA describes the more elongated part of the first field guide section 7a, which is located outside the interior of the saddle coil. The end section EA is the one-sided part of the first field guide section 7a, which rests on the outer surface of the measuring tube 2 and functions as a pole piece. The connecting section VA extends partly inside and partly outside the interior of the saddle coil.

[0039] In the cross-section QS, an imaginary first line G1, passing through the end point R and a midpoint M of the measuring tube 2, and a second line G2, describing the course of the first field guide element 7a in the connecting section VA, span an angle θ such that 5° ≤ θ ≤ 45°, in particular 7° ≤ θ ≤ 30°, and preferably 10° ≤ θ ≤ 20°. The end point R is located at a boundary between the end section EA and the connecting section VA. In the embodiment of the Fig. 1 and Fig. In case 2, the angle θ is 0°±2°.

[0040] The first and second field guide elements 7a, 7b shown in the embodiments can be identical parts, so that the requirements for the first field guide element 7a are also applicable to the second field guide element 7b. Generally, a mirror-symmetrical arrangement is usually required for magnetic-inductive flowmeters. This also follows from the Fig. 1 and Fig. 2. Thus, requirements that relate only to one side of the measuring tube, to one half of the coil system, or to one half of the magnetic field guidance also apply to the other unaddressed half or side. REFERENCE MARK LIST 1 magnetic-inductive flow meter 2 measuring tubes 3 coil system 4a, 4b saddle spool 5a, 5b Saddle coil interior 6 Magnetic field guidance 7a, 7b Field Command Section 11, 12, 13, 14, 15, 16 Measuring electrode 100 measuring electronics QS cross-section QS1, QS2 cross-sectional area MF surface area MEA measuring electrode axis Y main axis ML measuring tube longitudinal axis M Center LE Longitudinal plane d minimum distance P, Q point EA End Section VA connecting section HA Main Section G1, G2 Straight β,γ,δ Central angles θ angle QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2018 108 197 A1

[0003] DE 10 2023 120 595.1

[0005]

Claims

A magnetic-inductive flowmeter (1) for determining a flow velocity-dependent measured quantity of a flowable medium, comprising: - a measuring tube (2) for guiding the medium, wherein the measuring tube (2) has an outer surface (MF); - at least two measuring electrodes (11, 12); - measuring electronics (100), wherein the measuring electronics (100) is connected to the at least two measuring electrodes (11, 12) and is configured to determine a measuring voltage; - a coil system (3) for generating a magnetic field penetrating at least sectionally the measuring tube (2), wherein the coil system (3) comprises at least one saddle coil (4a), wherein the at least one saddle coil (4a) is arranged on the outer surface (MF) of the measuring tube (2), wherein a coil wire of the at least one saddle coil (4a) at least partially delimits a saddle coil interior (5a); - a magnetic field guide (6) for guiding magnetic field lines outside the measuring tube (2),wherein the magnetic field guide (6) consists of a first field guide part (7a) and a second field guide part (7b) arranged opposite the first field guide part (7a), wherein the first field guide part (7a) extends at least section by section into the saddle coil interior (5a), wherein the first field guide part (7a) has an end section (EA) which is located in the saddle coil interior (5a) and which rests on the outer surface (MF) of the measuring tube (2), in particular directly, wherein in a cross-section (QS) through the at least one saddle coil (4a), the first field guide part (7a) and the at least two measuring electrodes (11, 12) each point P located on a cross-sectional area (QS1) of the first field guide part (7a) in the end section (EA) and each point Q located on a cross-sectional area (QS2) of the saddle coil (4a) span a central angle δ which is greater than as 12°,in particular greater than 17° and preferably greater than 22°, and less than 35°, in particular less than 32° and preferably less than 27°. Magnetic-inductive flowmeter according to claim 1, wherein the first and second field guide part (7a) are each a sectionally bent sheet metal part. Magnetic-inductive flowmeter according to claim 1 or 2, wherein the saddle coil interior (5a) spans a maximum central angle y such that 75° ≤ γ ≤ 105°, in particular 80° ≤ γ ≤ 100° and preferably 85° ≤ γ ≤ 95°. A magnetic-inductive flowmeter according to one of the preceding claims, comprising: - at least four measuring electrodes (11, 12, 13, 14), wherein a longitudinal plane (LE) divides the measuring tube (2) into a first side (I) and a second side (II), 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 β spans a circular sector in the cross-section (QS) in which the at least two measuring electrodes (11, 13) of the first side (I) are arranged, wherein for the central angle β, 20° ≤ β ≤ 70°, in particular 30° ≤ β ≤ 60° and preferably 40° ≤ β ≤ 50°. Magnetic-inductive flowmeter according to one of the preceding claims, wherein a minimum distance d is ensured between the first and / or second field guide part (7a, 7b) and the at least one saddle coil (4a), wherein the measuring tube has a nominal diameter DN, wherein the minimum distance d is such that DN / 10 ≤ d ≤ DN / 2, in particular DN / 5 ≤ d ≤ DN / 3. Magnetic-inductive flowmeter according to one of the preceding claims, wherein the first field guidance part (7a) has a main section (HA) and a connecting section (VA) between the main section and the end section (EA), wherein a first straight line (G1) extending in the cross-section (QS) through the end point R and a midpoint M of the measuring tube and a second straight line (G2) describing a course of the first field guidance part (7a) in the connecting section in the cross-section (QS) span an angle θ, wherein the end point R lies in a boundary between the end section (EA) and the connecting section (VA), wherein the angle θ is such that 5° ≤ θ ≤ 45°, in particular 7° ≤ θ ≤ 30° and preferably 10° ≤ θ ≤ 20°.

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