WO2016041725A1

WO2016041725A1 - Magnetoinductive flowmeter having a magnetic system with at least four coils

Info

Publication number: WO2016041725A1
Application number: PCT/EP2015/069054
Authority: WO
Inventors: Oliver Graf; Thomas Zingg
Original assignee: Endress+Hauser Flowtec Ag
Priority date: 2014-09-17
Filing date: 2015-08-19
Publication date: 2016-03-24
Also published as: DE102014113409A1

Abstract

Apparatus for measuring the flow rate of a fluid (2) flowing through a pipeline according to the magnetoinductive measurement principle, having a measuring tube (3), having at least two measuring electrodes (8, 8a) for tapping off an induced voltage, on or in which measuring tube (3) components are adjacently arranged in the circumferential direction for the purpose of generating a magnetic field (11) which permeates the measuring tube perpendicular to the direction of flow of the fluid (2) and perpendicular to a connecting line through the at least two measuring electrodes (8, 8a), comprising at least four coils (10, 10a, 10b, 10c) with coil cores (14, 14a, 14b, 14c), at least two pole shoes (12, 12a) which are spatially separate from one another and are arranged on opposite sides of the measuring tube (3) based on the centre thereof, wherein at least two coils (10, 10a, 10b, 10c) are arranged in each case, together with at least one of the at least two pole shoes (12, 12a), in such a manner that at least one coil (10, 10a, 10b, 10c) is arranged in each case in the region of each of the two ends of a pole shoe (12, 12a), at least four feedback plates (13, 13a, 13b, 13c) which are spatially separate from one another and from the at least two pole shoes (12, 12a), wherein two feedback plates (13, 13a, 13b, 13c) are arranged in each case on both sides of one of the at least two pole shoes (12, 12a) in a mirror-symmetrical manner with respect to one another such that each of the at least two feedback plates (13, 13a, 13b, 13c) magnetically couples a first coil (10, 10a, 10b, 10c), which is arranged in the region of a first of the at least two pole shoes (12, 12a), and a second coil (10, 10a, 10b, 10c), which is arranged in the region of a second of the at least two pole shoes (12, 12a), to one another.

Description

Magnetic-inductive flowmeter with a magnet system with at least four coils

The invention relates to a device for measuring the flow of a flowing fluid through a measuring tube after the magnetic-inductive

Measuring principle.

Magnetic-inductive flowmeters are widely used in process and automation technology for fluids with an electrical conductivity of about 5pS / cm. Corresponding flow measuring devices are sold by the applicant in various embodiments for various applications, for example, under the name PROMAG.

The measuring principle is based on Faraday ^'s law of magnetic induction and is known from various publications. By means of one at one

Measuring section fixed magnet system is generated substantially perpendicular to the flow direction of the conductive fluid, a magnetic field of constant time strength. As a result, the ions present in the flowing fluid in

deflected opposite directions. The electrical voltage generated by this charge separation is also by means of at least one in the

Tapping section attached measuring electrode pair tapped. The tapped voltage is proportional to the flow rate of the fluid and thus proportional to the volume flow. The measuring accuracy of a magnetic-inductive flowmeter depends on many different factors. Some of them concern the

Construction itself, such as the positioning accuracy and / or

Embodiment of the magnet system, or the reading of the measuring signal on the at least one measuring electrode pair and its geometry. Furthermore, the measurement performance and accuracy have a sensitive dependence on the prevailing flow profile of the fluid.

For the magnet system various arrangements have become known in the prior art. Often are on opposite sides of the measuring tube arranged two coils and optionally pole pieces and / or return plates, such as for example from DE10201 1079351 A1 become known modular construction of a magnet system. The manufacturing costs for a

Due to the growing quantity of required materials for the coils, pole shoes and return plates, the corresponding measuring device increases significantly as the nominal diameter of the measuring tube increases. A construction for one

Magnetic system, which has the minimization of the required material and, accordingly, a minimization of the production costs has the goal, is disclosed in EP0649005A1. In this arrangement, the pole shoes and return plates are realized as bent plates, which are arranged along the lateral surfaces of the measuring tube. In this case, either two flat coils or two pairs of divided partial coils are provided. The use of flat coils reduces the need for copper compared to saddle coils. In addition to this example, other magnet systems which make a division of the coil arrangement have become known. US4726236B discloses a magnet system having a common circumferential cylindrical core and wound around it a coil assembly of a total of four coils. In the

DE1648143 describes a magnet system in which pin-like formations for attaching the coils are provided on a coil core in the form of a circumferential ring. Finally, DE202012104036U1 discloses a modular magnet system with at least four coils, which are arranged circumferentially distributed to the measuring tube on pole shoes. The division of the coil arrangement serves to reduce stray fields.

For all mentioned magnet systems with a distribution of the coils, however, the production costs increase significantly with increasing nominal width of the measuring tube. On the one hand, this concerns the material costs for the individual components. On the other hand, but also the particular construction for fixing the

Magnetic system on the measuring tube more complicated and expensive, and the

Ensuring a stable attachment more difficult. The present invention has for its object to provide a device for

To provide flow measurement according to the magnetic-inductive measuring principle with high accuracy at low production costs. This object is achieved by a device for measuring the flow of a flowing fluid through a pipeline according to the magnetic-inductive measuring principle with a measuring tube,

- With at least two measuring electrodes for tapping an induced

Tension,

- Are arranged on or in which measuring tube in the circumferential direction components for generating a measuring tube passing through the magnetic field perpendicular to the flow direction of the fluid and perpendicular to a connecting line through the at least two measuring electrodes comprising

at least four coils with coil cores,

at least two mutually spatially separated pole shoes, which are arranged with respect to their center on opposite sides of the measuring tube,

wherein in each case at least two coils are arranged together with at least one of the at least two pole pieces such that in the region of each of the two ends of a pole piece in each case at least one coil is arranged, at least four from each other and at least two pole shoes spatially separated return plates, wherein each two return plates on either side of one of the at least two pole pieces are arranged mirror-symmetrically to each other such that each of the at least two return plates a first coil, which is arranged in the region of a first of the at least two pole pieces, and a second coil, which is arranged in the region of a second of the at least two pole pieces , magnetically coupled with each other. Depending on the arrangement and construction, either each of the at least four coils can have at least one coil core. However, two or more coils may share a common coil core. The direct arrangement of the coils, pole pieces and return plates on the measuring tube significantly reduces the material requirements for these components. Furthermore, the

Attachment to the measuring tube particularly simple and at the same time very stable. Despite the reduction of manufacturing costs, a high accuracy of measurement can be achieved because disturbing 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 to the measuring tube.

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

In a further preferred embodiment, the measuring tube consists of a metal, which is lined in the fluid-contacting region with an electrically insulating liner. Alternatively, the measuring tube can also consist of a ceramic or a plastic, wherein the at least two pole pieces and / or the at least two return plates are arranged on the outer surface of the measuring tube, or 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 disturbances 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 in terms of cost.

Furthermore, it is advantageous if each of the at least four coils is of the same type. This simplifies the construction and assembly. In a preferred embodiment, the return plates and pole shoes in the form of rectangular curved plates, wherein the curvature of the

Measuring tube is adapted. It is advantageous if in each case a pole piece and two return plates are made of a rectangular sheet such that the return plates in the form of rectangular strips whose length is smaller than that of the sheet, cut on both sides along the longitudinal axis of the sheet starting from the center become. This further reduces the material requirements and, correspondingly, the production costs, since both components can be manufactured from the same metal sheet.

In a particularly preferred embodiment, exactly four coils, exactly two pole shoes and exactly four return plates are provided. This choice is particularly suitable for smaller sizes. It is advantageous if the coils have coil cores with an H-shape. This simplifies the production of a magnetic coupling by means of

Feedback sheets.

In a further particularly preferred embodiment, at least eight coils, exactly two pole shoes and exactly four return plates are provided.

In this case, each of the at least eight coils advantageously has an L-shaped coil core. Such an arrangement is particularly suitable for larger sizes.

In a preferred variant of this embodiment, each of the two pole shoes has a coil arranged on both sides at each of the two ends, wherein the axis through the two coils runs essentially parallel to the axis of the measuring tube.

The magnet system according to the invention with the at least four coils is characterized in that for a large range for the nominal diameter of the measuring tube in each case the same coil can be used with the same dimensions.

Accordingly, in each case only the coil cores, the width of the pole shoes and return plates must be varied. This brings next to a reduction in the number of components that need to be custom-made for each nominal size, also savings in relation to the need for copper. The fact that the components are attached directly to the measuring tube, in particular at the

Outer shell surface, the entire construction is particularly simple in construction and easy to assemble. In particular, in relation to other arrangements of such magnet systems, a large part of the units and / or components used for fastening the magnet system are eliminated, which causes a further reduction of the manufacturing costs.

In addition, the direct arrangement of the components of the magnet system directly on the measuring tube offers the advantage that compared to extra arranged

Mounting units less design-related natural vibrations occur.

Despite the considerable simplification in the assembly, the reduction of the

Material expenditure and the production costs can be achieved with the magnet system according to the invention a high accuracy of measurement, because by the

extensive arrangement of the individual coils stray fields are minimized.

The invention as well as its advantageous embodiments are described below with reference to FIGS. 1 to 3. It shows

Fig. 1: a magnetic-inductive flowmeter according to the prior art, Fig. 2: an embodiment of a magnet system with four coils

a) in a 2D view

b) in a 3D view

3 shows an embodiment of a magnet system with eight coils

a) in a 2D view

b) in a 3D view

Fig. 4 is a pole piece and two return plates, which are made of a single sheet. FIG. 1 shows a magnetic-inductive flow meter 1 for measuring the flow of a flowing fluid 2 through a measuring tube 3. The

Measuring tube 3 is made of either a metal, in particular stainless steel, and in the fluid-facing region, d. H. on the inside over the entire length, provided with an electrically insulating liner 4. It goes without saying, however, that the measuring tube can also be made of a suitable ceramic, in particular aluminum oxide, or of a plastic, for example hard rubber. For the sensor unit are at least two measuring electrodes 8,8a for

Tapping the induced voltage and the magnet system 9 shown, which is shown for simplicity by two cuboids. The magnet system 9 comprises at least two coils 10, 10a [not shown here] for generating the magnetic field 11 and possibly also pole shoes 12, 12a [not shown here] for realizing an advantageous spatial distribution and / or return plates 13, 13a, 13b, 13c [also not shown here]. The

Connecting axes of the measuring electrodes 8,8a and the coils 10,10a each perpendicular to each other, wherein the two coils 10,10a and the two

Measuring electrodes 8,8a are each positioned on opposite sides of the measuring tube 3. The sensor unit is usually at least partially surrounded by a housing 5. In the housing 5 or in the present case outside the housing 5, an electronics unit 6 is further provided which is electrically connected via a connecting cable 7 to the field device 1. The electronics unit serves the

Signal acquisition and / or evaluation and the supply of the coils, and as an interface to the environment, eg. B. the measured value output or setting the device.

In Fig. 2 is a first embodiment of an inventive

Magnetic system 9 'shown with four coils 10,10a, 10b, 10c, once in a two-dimensional a) and once in a three-dimensional b) view. The measuring tube 3 is also drawn, since the magnet system 9 'is attached directly thereto. The four coils 10, 10a10b, 10c are arranged circumferentially distributed on the measuring tube 3, wherein each two of the four coils 10,10b and 10a, 10c are opposite. The angle α between the virtual connecting lines through each Coils arranged on opposite sides can vary from application to application.

The coils 10, 10 a, 10 b, 10 c are preferably planar non-saddle-shaped coils with coil cores 14, 14 a, 14 b, 14 c. Each of the four coils 10, 10a, 10b, 10c has its own coil core 14, 14a, 14b, 14c.

In addition to the four coils 10, 10a, 10b, 10c, the magnet system 9 'also has two pole shoes 12, 12a and four return plates 13, 13a, 13b, 13c, which are each manufactured from bent metal sheets of rectangular basic shape, and the like

Curvature is adapted to that of the measuring tube 3. The pole pieces 12, 12a are arranged relative to their center on opposite sides of the measuring tube. The exact positioning of the pole pieces 12, 12a and return plates

13, 13a, 13b, 13c on the measuring tube will be apparent from Fig. 2b. Two coils 10, 10a each are arranged in the end regions of one of the pole shoes 12. Similarly, although not shown, the coils 10b, 10c are disposed in the end portions of the pole piece 12a. Thus, the coils 10 and 10b and 10a and 10c are opposite.

In the section around the measuring tube 3 between the two pole shoes 12, 12a, two return plates 13, 13a are arranged on both sides with respect to the coils 10, 10c. By means of the return plates 13,13a, the two coils 10,10c are magnetically coupled together. Analog are on the invisible

two return plates 13b, 13c arranged on the opposite side of the measuring tube 3, which couple the two coils 10a, 10b magnetically with each other.

A second embodiment is the subject of Fig. 3, again in a two-dimensional a) and three-dimensional b) view. In this example, the magnet system 9 "has eight coils 10, 10.1, 10a, 10a.1, 10b, 10b.1, 10c, 10c.1, two coils each forming one unit, each of the eight coils 10, 10.1, 10a , 10a.1, 10b, 10b.1, 10c, 10c.1 has a separate coil core

14,14.1, 14a, 14a.1, 14b, 14b.1, 14c, 14c.1. The arrangement of the pole shoes 12, 12a and the return plates 13, 13a, 13b, 13c is substantially analogous to that shown in FIG. Therefore, the following description focuses only on the differences with respect to the coils, which can be seen from the three-dimensional view in Fig. 3b. There is a unit of two coils 10 and 10.1, each with a coil core 14 and 14.1 visible, the coils are arranged on the two opposite sides of an end portion of the pole piece 12. In this case, the return plate 13 magnetically couples the coils 10 and 10c with each other, and the return plate 13a, the two coils 10.1 and 10c.1. Likewise, the two coils 10a and 10a.1 are magnetically coupled to the coils 10b and 10b.1 by means of the return plates 13b, 13c, which are not visible here.

In principle, either the return plates 13, 13a, 13b, 13c and pole shoes 12, 12a can each be manufactured from separate metal sheets. However, a pole piece 12 and two return plates 13, 13 a can also be produced from a single metal sheet, as shown in FIG. 4. The latter variant is particularly material-and accordingly also cost-saving.

reference numeral

1 magnetic inductive flow meter according to the prior art

2 flowing fluid

3 pipeline

4 electrically insulating lining, liner

5 housing unit or housing

6 electronics unit

7 connection cable

8.8a measuring electrodes

9 magnet system

10, 10, 1, 10a, 10a.1, 10b, 10b.1, 10c, 10c.1 coils

1 1 magnetic field perpendicular to the flow direction of the fluid and to the

measuring electrodes

12,12a pole shoes

13, 13a, 13b, 13c return plates

14,14.1, 14a, 14a.1, 14b, 14b.1, 14c, 14c.1 spool cores

Claims

claims

Vornchtung for measuring the flow of a flowing fluid (2) through a pipe according to the magnetic-inductive measuring principle with a measuring tube (3),

- With at least two measuring electrodes (8,8a) for tapping a

induced voltage,

- At or in which measuring tube (3) in the circumferential direction fitting

Components are arranged for generating a magnetic field passing through the measuring tube (1 1) perpendicular to the flow direction of the fluid (2) and perpendicular to a connecting line through the at least two measuring electrodes (8,8a) comprising

at least four coils (10, 10a, 10b, 10c) with coil cores (14, 14a, 14b, 14c)

at least two mutually spatially separated pole pieces (12, 12a) which are arranged with respect to their center on opposite sides of the measuring tube (3), wherein in each case at least two coils (10, 10a, 10b, 10c) together with at least one of the at least two pole pieces (12, 12a) are arranged such that in each case at least one coil (10, 10a, 10b, 10c) is arranged in the region of each of the two ends of a pole piece (12.12a),

at least four spaced from each other and from the at least two pole pieces (12,12a) spatially separate return plates (13,13a, 13b, 13c), wherein each two return plates (13, 13a, 13b, 13c) on both sides of one of the at least two pole pieces (12,12a ) are arranged mirror-symmetrically to one another such that each of the at least two return plates (13, 13a, 13b, 13c) has a first coil (10, 10a, 10b, 10b) arranged in the region of a first of the at least two pole shoes (12, 12a) is, and a second coil (10,10, a, 10b, 10c), which in the region of a second of the at least two pole pieces (12,12a) is arranged, magnetically coupled to each other.

2. Apparatus according to claim 1,

wherein the at least two pole shoes (12, 12a) and / or the at least four return plates (13, 13a, 13b, 13c) are made of a soft magnetic material.

3. Apparatus according to claim 1,

wherein the measuring tube (3) consists of a metal, which in

fluid contacting area is lined with an electrically insulating liner.

4. Apparatus according to claim 1,

wherein the measuring tube (3) consists of a ceramic or a plastic, and wherein the at least two pole pieces (12, 12a) and / or the at least two return plates (13, 13a, 13b, 13c) are arranged on the outer surface of the shell

Measuring tube (3) arranged, or are embedded in the measuring tube (3).

5. Device according to at least one of the preceding claims,

wherein a housing (5) made of a metal, preferably with a magnetic shielding effect, is provided.

6. Device according to at least one of the preceding claims,

wherein each of the at least four coils (10, 10a, 10b, 10c) have the same geometry, in particular a non-saddle-shaped planar geometry.

7. Device according to at least one of the preceding claims,

wherein each of the at least four coils (10, 10a, 10b, 10c) is of the same type.

8. Device according to at least one of the preceding claims,

wherein the return plates (13, 13a, 13b, 13c) and pole pieces (12, 12a) are in the form of rectangular curved plates, the curve being adapted to the measuring tube (3).

9. Device according to at least one of the preceding claims, wherein in each case one pole shoe (12, 12a) and two return plates

(13,13a, 13b, 13c) are made of a rectangular sheet metal such that the return plates (13,13a, 13b, 13c) in the form of rectangular strips whose length is smaller than that of the sheet, on both sides along the longitudinal axis of the sheet be cut from its center.

10.Vorrichtung according to at least one of the preceding claims,

wherein exactly four coils (10, 10a, 10b, 10c), exactly two pole shoes (12, 12a) and exactly four return plates (13, 13a, 13b, 13c) are provided.

1 1 .Vorrichtung according to claim 10,

wherein the coil cores (14,14a, 14b, 14c) have an H-shape.

12. Device according to at least one of claims 1 to 10,

exactly eight coils (10, 10.1, 10a, 10a.1, 10b, 10b.1, 10c, 10c.1), exactly two pole shoes (12, 12a) and exactly four return plates (13, 13a, 13b, 13c) are provided are.

13. Device according to at least one of the preceding claims,

wherein each of the at least eight coils

(10,10.1, 10a, 10a.1, 10b, 10b.1, 10c, 10c.1), having an L-shaped coil core.

14. Device according to claim 13,

wherein at each of the two ends of each of the two pole pieces (12,12a) on both sides in each case a coil (10,10.1, 10a, 10a.1, 10b, 10b.1, 10c, 10c.1) is arranged, wherein the axis through the two coils

(10,10.1, 10a, 10a.1, 10b, 10b.1, 10c, 10c.1), substantially parallel to the axis of the measuring tube (3).