DE102019123409A1 - Electromagnetic flow meter - Google Patents

Abstract

The invention relates to a magneto-inductive flow measuring device, which has a measuring tube for guiding a flowable medium in a longitudinal direction of the measuring tube, at least one metallic process connection, in particular a flange, at least two measuring electrodes placed opposite one another in the measuring tube for detecting a flow rate-dependent measuring voltage induced in the medium A magnetic field generating device for generating a magnetic field penetrating the measuring tube, the magnetic field generating device comprising at least one pole piece, the pole piece being attached to an outer wall of the measuring tube, the magnetic field generating device comprising at least four coil cores each with at least one coil and at least one field feedback arrangement, wherein the field return arrangement is attached to the outer wall of the measuring tube, wherein the coil cores connect the pole piece to the field return arrangement comprises and dadu It is characterized in that the field feedback arrangement is at least two-part, with a chord of a circle, the center of which is on a pipe axis of the measuring tube, describing the smallest distance between two opposing field feedback parts, with two end points lying on the chord and a center point of the measuring tube having a central angle α define, where for the central angle α it applies that 0.05 ° α 40 °, in particular 0.1 ° α 17 ° and preferably 0.1 ° α 6 °.

Description

Electromagnetic flowmeters are used to determine the flow rate and volume flow of a flowing medium in a pipeline. An electromagnetic flowmeter has a magnet system that generates a magnetic field perpendicular to the direction of flow of the flowing medium. Individual coils are usually used for this. In order to achieve a predominantly homogeneous magnetic field, pole pieces are additionally shaped and attached in such a way that the magnetic field lines run essentially perpendicular to the transverse axis or parallel to the vertical axis of the measuring tube over the entire pipe cross-section. A pair of measuring electrodes attached to the outer surface of the measuring tube picks up an electrical measuring voltage or potential difference that is applied perpendicular to the direction of flow and to the magnetic field, which occurs when a conductive medium flows in the direction of flow with an applied magnetic field. Since the measured voltage, according to Faraday's law of induction, depends on the speed of the flowing medium, the flow rate u and, with the addition of a known pipe cross-section, the volume flow V̇ can be determined from the induced measurement voltage U.

Magnetic-inductive flowmeters are widely used in process and automation technology for fluids with an electrical conductivity of around 5µS / cm. Corresponding flow measuring devices are sold by the applicant in a wide variety of embodiments for different areas of application, for example under the name PROMAG.

From the DE 10 2014 113 409 A1 a magneto-inductive flow measuring device is known which has field return parts and pole shoes which are attached to the outer wall of the measuring tube and are connected to one another via cylindrical coil cores. The field return parts are used to guide the magnetic field lines from a first coil core to a second coil core. The disadvantage of the taught magnet system, however, is that the time behavior of the magnetic field is disturbed due to eddy currents in the metallic process connection.

The invention is based on the object of providing a magneto-inductive flow measuring device whose time behavior of the magnetic field is less affected by interfering influences.

The object is achieved by the electromagnetic flowmeter according to claim 1.

• - ein Messrohr zum Führen eines fließfähigen Mediums in eine Längsrichtung des Messrohres;
• - mindestens einen metallischen Prozessanschluss gegenüberliegend angebrachte Messelektroden zum Erfassen einer strömungsgeschwindigkeitsabhängigen, in dem Medium induzierten Messspannung;
• - eine magnetfelderzeugende Vorrichtung zum Erzeugen eines das Messrohr durchsetzenden Magnetfeldes,
  • wobei die magnetfelderzeugende Vorrichtung mindestens einen Polschuh umfasst,
  • wobei der Polschuh an einer Außenwandung des Messrohres angebracht ist,
  • wobei die magnetfelderzeugende Vorrichtung mindestens vier Spulenkerne mit jeweils mindestens einer Spule umfasst; und
  • - mindestens eine Feldrückführungsanordnung an der Außenwandung des Messrohres angebracht ist,
  • wobei die Spulenkerne den Polschuh mit Feldrückführungsteilen der Feldrückführungsanordnung verbinden;
  • dadurch gekennzeichnet, dass die Feldrückführungsanordnung mindestens zwei Feldrückführungsteile umfasst,
  • wobei eine Kreissehne eines Kreises, dessen Mittelpunkt auf einer Rohrachse des Messrohres liegt, den geringsten Abstand zweier gegenüberliegender Feldrückführungsteile beschreibt,
  • wobei zwei auf der Kreissehne liegende Endpunkte und ein Mittelpunkt des Messrohres einen Mittelpunktswinkel α definieren,
  • wobei für den Mittelpunktswinkel α gilt, dass 0,05° ≤ α ≤ 40°, insbesonders 0,1° ≤ α ≤ 17° und bevorzugt 0,1° ≤ α ≤ 6° ist.

The electromagnetic flowmeter according to the invention comprises:

• - A measuring tube for guiding a flowable medium in a longitudinal direction of the measuring tube;
• - At least one metallic process connection oppositely attached measuring electrodes for detecting a flow rate-dependent measuring voltage induced in the medium;
• - a magnetic field generating device for generating a magnetic field penetrating the measuring tube,
  • wherein the magnetic field generating device comprises at least one pole piece,
  • wherein the pole piece is attached to an outer wall of the measuring tube,
  • wherein the magnetic field generating device comprises at least four coil cores, each with at least one coil; and
  • - at least one field feedback arrangement is attached to the outer wall of the measuring tube,
  • wherein the coil cores connect the pole piece to field return parts of the field return arrangement;
  • characterized in that the field return arrangement comprises at least two field return parts,
  • where a chord of a circle, the center of which lies on a pipe axis of the measuring pipe, describes the smallest distance between two opposing field return parts,
  • where two end points lying on the circular chord and a center point of the measuring tube define a center angle α,
  • where for the central angle α it applies that 0.05 ° α 40 °, in particular 0.1 ° α 17 ° and preferably 0.1 ° α 6 °.

In a preferred embodiment, the field return parts and pole shoes have the shape of rectangular curved metal sheets, the curvature being adapted to the measuring tube. The field return parts and the pole shoes are attached to the outer wall of the measuring tube. It is advantageous here if the pole shoes are designed in two parts, since this enables simple assembly, particularly in the case of measuring tubes with large nominal widths (≥ DN 1000). The same also applies to the field return parts.

The inventive magnet system with the at least four coils is characterized in that for a large area for the Nominal width of the measuring tube, the same coil with the same dimensions can be used in each case. Accordingly, only the coil cores, the width of the pole shoes and field return parts have to be adapted. In addition to a reduction in the number of components that have to be specially manufactured for each nominal size, this also results in savings in terms of copper requirements. Because the components are attached directly to the measuring tube, in particular to the outer jacket surface, the entire construction is particularly simple and easy to assemble in terms of its structure.

In a preferred variant of this embodiment, a coil and a coil core are arranged on each of the two ends of each of the two pole shoes, the longitudinal axis of the two coil cores running essentially parallel to the axis of the measuring tube.

The direct arrangement of the coils, pole shoes and field return parts 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, a high level of measurement accuracy can be achieved, since disruptive stray fields can be minimized. A direct arrangement means that the components are arranged directly on the measuring tube. For example, they can be glued directly onto the measuring tube.

In a preferred embodiment, the at least two pole shoes and / or the at least four return plates are made from a soft magnetic material.

In a further preferred embodiment, the measuring tube consists of a metal which is lined with an electrically insulating liner in the area in contact with the fluid. Alternatively, the measuring tube can also consist of a ceramic or a plastic, the at least two pole shoes and / or the at least two return plates being arranged on the outer casing surface of the measuring tube or being embedded in the measuring tube.

In a particularly preferred embodiment, a housing made of a metal, preferably with a magnetic shielding effect, is provided. In this way, further interferences can be eliminated.

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

It is also advantageous if each of the at least four coils is of the same type. This simplifies construction and assembly.

The above-mentioned arrangement of two opposing field return parts is particularly advantageous because it shields magnetic field lines which, starting from the pole piece, penetrate the metallic process connection and cause eddy currents there. In addition, the advantage of an assembly-friendly attachment of the field return parts is not negated.

The time behavior of the magnetic field describes the development of the magnetic field over time. With conventional electromagnetic flowmeters, the direction of the magnetic field changes over time. When changing direction, the magnetic field may not directly reach the intended target value, but rather an overshoot of the magnetic field occurs beforehand and the magnetic field only reaches the temporally constant target value after a settling time. Only when the target value has been reached is the measurement voltage recorded on the measurement electrodes and taken into account for determining the flow measurement value. It is therefore important to reduce this settling time so that measurements can be taken earlier. Eddy currents in metallic bodies attached to the measuring tube are a factor in the overshoot of the magnetic field.

It is particularly advantageous if the distance between the two field return parts is particularly small, in particular fulfills the above requirements, since the overshoot behavior of the magnetic field decreases significantly compared to the geometry mentioned in the prior art.

Advantageous refinements of the invention are the subject matter of the subclaims.

One embodiment provides that a field return part has a field return body which is formed from at least one sheet metal part, in particular electrical sheet metal part.

Electrical sheet metal parts in accordance with the standards EN 10106 and EN 10107 are particularly suitable as field feedback parts, as eddy currents that arise under the influence of variable magnetic fields are minimized.

One embodiment provides that the field return body is formed from N stacked, in particular punch-packaged sheet metal parts,
where N is a natural number,
where 2 N 30, in particular 6 N 15, applies.

For sufficient shielding of the process connection, the field return body of the field return parts must have a certain thickness. It has been found to be advantageous to stack between 2 and 30, in particular between 6 and 15 sheet metal parts in order to ensure adequate shielding and improved time behavior of the magnetic field. As the number increases, the sensitivity of the magnet system increases and the magnetic resistance is reduced. It has been found, however, that a cost-optimized solution and, at the same time, optimal shielding are implemented for the required number of field feedback bodies.

One embodiment provides that the field return body has a thickness d _FK of a maximum of 15 millimeters and the thickness d _{FK is} preferably in the range from 1.8 to 5 millimeters.

A sheet metal part preferably has a thickness of 0.3 ± 0.1 millimeters.

One embodiment provides that the pole piece has a thickness d _P ,
wherein the thicknesses d _P and d _FK are chosen such that a longitudinal axis of the coil core runs essentially parallel to the longitudinal axis of the measuring tube, in particular that d _FK = d _P applies.

In order for the magnetic field lines to be optimally coupled into the pole piece and the field return parts, it is essential that a sufficient contact area is guaranteed in each case. In order for this to be achieved, it is advantageous if the thickness of the pole _{piece d P} and the thickness of the field feedback body d _FK are essentially the same. This ensures that the longitudinal axis of the coil cores run parallel to the longitudinal axis of the measuring tube and that there is no air gap between the two contact surfaces of the pole piece and the field return part.

One embodiment provides that the process connection and the field return part are spaced apart,
wherein the smallest distance between the process connection and the field return part is between 50 and 1000 millimeters and preferably between 80 and 200 millimeters.

In addition to shielding the process connection from the magnetic field, it is advantageous if a distance is maintained between the process connection and the field return part. Due to the design of the field return arrangement, it is sufficient to space the process connection between 50 and 1000 millimeters and preferably between 80 and 200 millimeters from the field return arrangement. Without the field feedback arrangement according to the invention, a significantly greater spacing would be necessary.

One embodiment provides that the field return part has a width which is between 50 and 500 millimeters, in particular between 60 and 300 millimeters and preferably between 80 and 200 millimeters.

One embodiment provides that the measuring tube has a diameter which is in the range from DN 1000 to DN 3000.

One embodiment provides that exactly four field return parts are provided,
where exactly eight, twelve or sixteen coil cores are provided.

In a particularly preferred embodiment, at least eight coils, each with a coil core, exactly two or four pole shoes and exactly four return plates are provided. Each of the at least eight coils advantageously has a U-shaped or L-shaped coil core. Such an arrangement is particularly suitable for larger nominal sizes.

In a further particularly preferred embodiment, exactly twelve coil cores, each with at least one coil, exactly two pole shoes and four field return parts are provided. The four additional coil cores provided in comparison to the previous embodiments are not attached to the ends of the respective pole shoes but in the area where the ends of the opposing field return parts come closest to one another. The four additional coil cores can be arranged, for example, in such a way that they each touch two opposing field return parts.

In a further particularly preferred embodiment, exactly sixteen coil cores, each with at least one coil, exactly two pole shoes and four field return parts are provided. The eight additional coil cores provided in comparison to the first embodiment are arranged at the ends of the respective opposing field return parts. According to this embodiment, coil cores are provided at the ends of the pole shoes and at the ends of the field return parts.

It applies to all configurations that a pole piece can be designed in one, two or four parts.

One embodiment provides that the field return arrangement, in addition to the function of returning the magnetic field, is set up to shield the metallic process connection from the magnetic field generated by the coils.

A field return arrangement is usually provided to capture magnetic field lines which emerge from the coil core and do not or only partially cut the measuring tube and to conduct them from one coil core to another coil core. Therefore, the field return parts usually connect the side of the coil cores facing away from the pole piece or the respective ends of the coil cores which do not touch the pole piece with one another. The field return arrangement according to the invention is, however, characterized in that it not only returns the magnetic field lines, but also serves as a shield for the metallic process connection.

• 1: eine perspektivische Darstellung einer Ausgestaltung des erfindungsgemäßen magnetisch-induktiven Durchflussmessgerätes;
• 2: einen Querschnitt entlang des Messrohres des erfindungsgemäßen magnetisch-induktiven Durchflussmessgerätes; und
• 3: ein Diagramm, welches das Zeitverhalten des Magnetfeldes für unterschiedliche Feldrückführungsanordnungen zeigt.

The invention is explained in more detail with reference to the following figures. It shows:

• 1 : a perspective view of an embodiment of the magnetic-inductive flow measuring device according to the invention;
• 2 : a cross section along the measuring tube of the magnetic-inductive flow measuring device according to the invention; and
• 3rd : a diagram showing the time behavior of the magnetic field for different field feedback arrangements.

The structure and the measuring principle of a magnetic-inductive flow measuring device are basically known. The 1 shows an embodiment of the magnetic-inductive flow measuring device according to the invention. Through a measuring tube 1 a medium is passed that has an electrical conductivity. A magnetic field generating device 4th is arranged on the measuring tube in such a way that the magnetic field lines are oriented essentially perpendicular to a longitudinal direction defined by the measuring tube axis. As a magnetic field generating device 4th a saddle coil or a pole piece is preferably suitable 5 with attached coil 8th and coil core 7th . The pole piece is designed in two parts. In the 1 are only six out of eight cylindrical coil cores 7th and coils 8th pictured. The longitudinal axis of the coil cores 7th runs essentially parallel to the longitudinal axis 15th of the measuring tube. The coil cores 7th connect the pole piece to the field feedback bodies 10 . Between the field feedback bodies 10 and one of the pole pieces is the coil 8th arranged. Furthermore, the electromagnetic flowmeter has a field feedback arrangement 9 consisting of four field return parts 10 , with only two field return parts 10 are shown. These are adjacent to the outer wall 6th of the measuring tube 1 appropriate. Each field feedback part 10 includes a field feedback body 11 , which is formed from several punch packaged electrical sheet metal parts. Where is the thickness of the pole piece 5 and the thickness of the field return part 10 essentially the same size. The field return parts 10 each connect two different coil cores 7th with each other, whereby a magnetic coupling is realized. The individual components of the magnet system are attached to the measuring tube body by means of screws. When a magnetic field is applied, it arises in the measuring tube 1 a flow-dependent potential distribution, with two on the inner wall of the measuring tube 1 opposite, attached measuring electrodes 3rd is tapped. As a rule, these are arranged diametrically and form an electrode axis or are cut through a transverse axis that runs perpendicular to the magnetic field lines and the longitudinal axis of the measuring tube. Based on the measured voltage U, taking into account the magnetic flux density, the flow rate u and, with additional consideration of the pipe cross-sectional area, the volume flow V̇ of the medium can be determined. If the density of the medium is also known, the mass flow auch can also be monitored. To derive the at the first and second measuring electrode 3rd To prevent the measuring voltage being applied via the measuring tube, the inner wall is lined with an insulating material, for example a plastic liner. A measuring circuit is set up for this purpose on the measuring electrodes 3rd to detect applied measuring voltage. An evaluation circuit is designed to determine the measured flow values of the medium from the detected measurement voltage. The magnetic field generating device 4th is controlled via an operating circuit. Commercially available magnetic-inductive flowmeters have, in addition to the measuring electrodes 3rd two more electrodes. On the one hand there is one, ideally at the highest point in the measuring tube 1 attached level monitoring electrode 12th in addition, a partial filling of the measuring tube 1 to detect, and is set up to forward this information to the user and / or to take the fill level into account when determining the volume flow. Furthermore, a grounding electrode is used to ensure adequate grounding of the medium. There are metallic process connections at the ends of the measuring tube 2 appropriate. In this case, it is a question of flanges that are designed to integrate the measuring tube into a pipeline. There are also two collars on the measuring tube between the field return arrangement and the process connection 2 attached to form the lateral outer walls of a housing.

The 2 shows a cross section through the measuring tube of the magnetic-inductive flow measuring device according to the invention through part of the field feedback arrangement 9 . In the cross section are two opposite and on the outer wall of the measuring tube 1 attached field return parts 10 pictured. The shape of both field return parts 10 can begin to get through describe an arc. On a field return part 10 are at least two coil cores according to this embodiment 7th arranged, each having a coil and the field return parts 10 connect with the pole pieces. The ends of the respective field return parts 10 and the center of the measuring tube 1 in cross section form a central angle α and an arc of a circle 16 . The smallest distance between the respective ends is made by the circular tendon 13th described. For the central angle α, it applies that 0.05 ° α 40 °, in particular 0.1 ° α 17 ° and preferably 0.1 ° α 6 °. In the embodiment shown, the central angle α is approximately 40 °.

The 3rd shows a diagram which shows the time behavior of the resulting magnetic field of a magneto-inductive flowmeter for different field feedback arrangements. The x-axis describes the time t and the y-axis describes the magnetic field B in the center of the sensor.

The dashed line (B) describes the course of a resulting magnetic field of a magnetic-inductive flowmeter with short feedbacks. If a voltage is applied to the coil arrangement, the resulting magnetic field increases over time. The resulting magnetic field increases, exceeds the nominal value of the magnetic field, which it assumes in the steady state and then decreases steadily. A time range is shown in the course in which the induced measurement voltage is tapped and the measured flow value is determined. Due to the overshoot behavior, the magnetic field is not constant over time in the measuring phase and the nominal value of the magnetic field is not yet reached in the measuring phase.

The solid line (A) describes the development over time of the magnetic field of a magneto-inductive flowmeter with elongated field return parts that meet the claimed geometry. By shielding the process connection by means of the field feedback arrangement, influences from the eddy currents are reduced and the overshoot of the magnetic field is dampened. The course of the magnetic field reaches the nominal value earlier and has already settled during the measurement phase, i.e. constant over time.

List of reference symbols

1

Measuring tube

2

metallic process connection / flange

3

Measuring electrode

4th

Magnetic field generating device

5

Pole piece

6th

Outer wall

7th

Coil core

8th

Kitchen sink

9

Field return arrangement

10

Field return parts

11

Field feedback body

12th

Level monitoring electrode

13th

Circular tendon

14th

Focus

15th

Pipe axis

16

Circular arc

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102014113409 A1 [0003]

Claims (10)

Magnetic-inductive flow measuring device, comprising: - a measuring tube (1) for guiding a flowable medium in a longitudinal direction of the measuring tube (1); - At least one metallic process connection (2), in particular a flange; - At least two measuring electrodes (3) mounted opposite one another in the measuring tube (1) for detecting a flow rate-dependent measuring voltage induced in the medium; - A magnetic field generating device (4) for generating a magnetic field penetrating the measuring tube (1), the magnetic field generating device (4) comprising at least one pole piece (5), the pole piece (5) on an outer wall (6) of the measuring tube (1) is attached, wherein the magnetic field generating device (4) comprises at least four coil cores (7) each with at least one coil (8); and - at least one field return arrangement (9), the field return arrangement (9) being attached to the outer wall (6) of the measuring tube (1), the coil cores (7) connecting the pole piece (5) with field return parts (10) of the field return arrangement (9) connect; characterized in that the field return arrangement (9) comprises at least two field return parts (10), a circular chord (13) of a circle, the center of which lies on a pipe axis (15) of the measuring tube (1), the smallest distance between two opposing field return parts (10) describes, whereby two end points lying on the circular chord (13) and a center point (14) of the measuring tube (1) define a center point angle α, whereby for the center point angle α it applies that 0.05 ° ≤ α ≤ 40 °, in particular 0.1 ° α 17 ° and preferably 0.1 ° α 6 °. Flow meter according to Claim 1 , wherein a field return part (10) has a field return body (11) which is formed from at least one sheet metal part, in particular electrical sheet metal part. Flow meter according to Claim 2 , the field return body (11) being formed from N stacked sheet metal parts, in particular stamped and stacked, where N is a natural number, where 2 N 30, in particular 6 N 15 applies. Flow meter according to Claim 2 and / or 3, wherein the field return body (11) has a thickness d _FK of a maximum of 15 millimeters and the thickness d _{FK is} preferably in the range from 1.8 to 5 millimeters. Flow measuring device according to one of the preceding claims, wherein the pole piece (5) has a thickness d _P , the thicknesses d _P and d _FK being selected so that a longitudinal axis of the coil core (7) runs essentially parallel to the longitudinal axis of the measuring tube (1) , in particular that d _FK = d _P applies. Flow measuring device according to one of the preceding claims, wherein the process connection (2) and the field return part (10) are spaced apart, wherein the smallest distance between the process connection (2) and the field return part (10) is between 50 and 1000 millimeters and preferably between 80 and 200 millimeters. Flow measuring device according to one of the preceding claims, wherein the field return part (10) has a width which is between 50 and 500 millimeters, in particular between 60 and 300 millimeters and preferably between 80 and 200 millimeters. Flow measuring device according to one of the preceding claims, wherein the measuring tube (1) has a diameter which is in the range from DN 1000 to DN 3000. Flow measuring device according to one of the preceding claims, exactly four field return parts (10) being provided, exactly eight, twelve or sixteen coil cores (7) being provided. Flow measuring device according to one of the preceding claims, wherein the field return arrangement (9), in addition to the function of returning the magnetic field, is set up to shield the metallic process connection (2) from the magnetic field generated by the coils (8).

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