The invention relates to a magnetically inductive flowmeter for measuring volume flow or flow velocity of a medium flowing through a measuring tube.
Magnetically inductive flowmeters are based on measuring an electrical voltage induced in an electrically conductive medium by a magnetic field, which electrical voltage is linearly dependent on the applied magnetic field and on the volume flow of the medium through the measuring tube.
The magnetic field is usually produced by means of a magnet system having at least one coil. Thus, for example, DE102015122664A1 discloses a magnetically inductive flowmeter, in the case of which a magnetic field perpendicular to a measuring tube axis is produced by means of two coils, wherein the coil axes are perpendicular to the measuring tube axis. The magnetic field outside of the measuring tube and outside of the coils is led between the two coils by means of a field guide, wherein a magnetic connecting between coil core of a coil and field guide as well as between measuring tube and coil core is produced, in each case, by means of a pole shoe. Since each connection represents an interruption of the magnetic flux, such degrades performance of the flowmeter. Moreover, the concentration of the production of the magnetic field in the region of the coils means that many turns of a coil wire must be applied in a narrow spatial region. This leads to a lessened heat emission and to a waste of costly raw materials, since many turns in a narrow spatial region can only be accomplished by using a large number of winding layers.
An object of the invention is, consequently, a magnetically inductive flowmeter, which at least lessens at least one of the aforementioned disadvantages.
The object is achieved by a magnetically inductive flowmeter as defined in independent claim 1.
A magnetically inductive flowmeter of the invention for measuring volume flow or flow velocity of a medium flowing through a measuring tube comprises:
the measuring tube having a measuring tube axis and a measuring tube wall;
a magnet system for producing a magnetic field, which extends perpendicularly to the measuring tube axis, wherein the magnet system is placed on an outside of the measuring tube;
at least one pair of measuring electrodes, which are coupled capacitively or galvanically with the medium located in the measuring tube, wherein the measuring electrodes are adapted to sense an electrical voltage induced in the medium by the magnetic field, wherein a first measuring electrode of the pair of measuring electrodes is arranged on a first side of the measuring tube and a second measuring electrode of the pair of measuring electrodes is arranged on a second side of the measuring tube;
an electronic measuring/operating circuit for operating the magnet system and the measuring electrodes as well as for providing measured values of flow,
wherein the magnet system comprises:
a coil system having at least one coil having a coil core;
two pole shoes, which are arranged on opposite sides of the measuring tube, wherein the pole shoes are adapted to transfer the magnetic field produced by the coil system into the measuring tube as well as to receive the magnetic field, which has passed through the measuring tube, and to lead the magnetic field back to the coil system;
wherein the coil system has a means for field guide-back, which is adapted to lead the magnetic field outside of the measuring tube between the pole shoes,
characterized in that
a tangential fraction of the magnetic field in the coil relative to the measuring tube axis amounts to at least 80% and especially at least 90% of the total magnetic field,
wherein the means for field guide-back has at least one guide-back part, which extends through at least one coil and forms the coil core of the at least one coil.
A measuring tube can be described by means of a cylindrically symmetrical coordinate system comprising a radial coordinate, an axial coordinate and a tangential coordinate. The tangential fraction of the magnetic field concerns, thus, the part of the magnetic field, which is oriented along the tangential coordinate. Tangential orientation of the at least one coil on the measuring tube and extension of the field guide-back through the coil eliminates a transition at each pole shoe between a field guide and a coil core by combining the field guide-back and at least one coil core into one unit, in order to eliminate a connecting of two components. In this way, a magnetic resistance of the magnet system is reduced. A minimum fraction of 80% of the tangential fraction to the total magnetic field can leave room for an easy axial or radial orientation of the coil along the associated guide-back part.
The pole shoes are, in each case, produced preferably of at least one non-grain oriented sheet metal piece and lie against the measuring tube.
In an embodiment, the guide-back part comprises at least one ply of electrical sheet metal, which meets the requirements of the standard, DIN EN 10106 edition 2007-11, or wherein the electrical sheet metal is especially grain oriented and meets the requirements of the standard, DIN EN 10107 edition 2005-10, wherein the grain orientation is in parallel with the magnetic flux in the guide-back part.
A grain orientation of a magnetically conductive material provides a non-isotropic magnetic conductivity, wherein a magnetic resistance of the material along the grain orientation is minimum. By orienting the grain orientation along the magnetic flux of the magnetic field in the guide-back, thus, the magnetic resistance of the magnet system is lessened.
In an embodiment, the coil has at most 15 winding plies and especially at most 10 winding plies and preferably at most 5 winding plies.
In this way, use of raw materials applied for winding the coil, such as, for example, copper or silver, can be minimized. Moreover, this lessens the danger of an overheating of the coils, which results from high current flow in the coil and many winding layers.
In an embodiment, a length of the coil along its longitudinal axis subtends an angle α of at least 2 degree, and especially at least 5 degree and preferably at least 10 degree about the measuring tube axis. A greater length contributes to reducing the number of winding plies.
In an embodiment, there is arranged on the first side and the second side of the measuring tube, in each case, at least one coil with an associated guide-back part.
A two-sided arrangement of coils and associated guide-back parts contributes to an equally formed magnetic flux in the pole shoes, this leading to a spatially homogeneous distribution of the magnetic field in the region of the measuring electrodes.
In an embodiment, the measuring tube has extending along the measuring tube axis two far regions, a central region and two intermediate regions, wherein, in each case, an intermediate region is arranged between a far region and the central region,
wherein the measuring tube has in its far regions, in each case, a flange and a collar, which flanges are adapted to be connected to a pipeline,
wherein the at least one measuring electrode pair is arranged in the central region.
In an embodiment, the pole shoes and/or guide-back parts and/or coils are, in each case, arranged symmetrically relative to a cross- and/or longitudinal section of the measuring tube.
By increasing a degree of symmetry of the magnet system, a spatial distribution of the magnetic field in the region of the measuring electrodes can be formed homogeneously.
In an embodiment, the pole shoes subtend in the central region an angle βM of at least 40 degree and especially at least 80 degree and preferably at least 120 degree about the measuring tube axis, wherein the pole shoes are separated from one another by two gaps, wherein each gap subtends an angle γ of at least 5 degree and especially at least 10 degree and preferably at least 15 degree about the measuring tube axis.
In this way, the distribution of the magnetic field in the measuring tube can be adapted. The minimum extension of the gap between the pole shoes contributes to preventing a magnetic short circuit, in the case of which a magnetic flux in the measuring tube would be disturbed.
In an embodiment, the guide-back part is arranged in the central region and includes especially at least one feedthrough for contacting a measuring electrode and/or for grouting,
wherein the guide-back part extends through at least one coil, and preferably through two coils, wherein the at least two coils are arranged on opposite sides relative to the corresponding measuring electrode.
In an embodiment, the pole shoes subtend in the intermediate regions about the measuring tube axis, in each case, an angle βZ, which is less than the angle βM by at least 30 degree and especially at least 40 degree and preferably at least 50 degree,
wherein the field guide-back has on the first side and/or second side at least two guide-back parts, which magnetically connect the pole shoes, in each case, in an intermediate region.
In an embodiment, the magnet system includes a shielding apparatus, which is adapted to minimize magnetic disturbing influences of the flanges and collars,
wherein the shielding apparatus has at least one shielding band, which at least partially surrounds the measuring tube, wherein the shielding band is arranged between a flange and the central region or on a side of the collar facing the central region,
wherein the shielding band is made of a magnetically conductive material,
wherein the shielding band is, for example, one piece or composed of a plurality of band portions.
This contributes to an increasing of a possible switching frequency of the magnet system as well as to longer measuring times, since magnetic disturbing influences caused by currents induced in the flanges and collars in the measuring electrode region fall faster under a critical limit.
In an embodiment, the shielding apparatus has two shielding bands, each of which is associated with a flange.
In an embodiment, the guide-back part has at least 5 and especially at least 10 and preferably at least 15 plies of electrical sheet metal. In this way, the magnetic conductivity of the guide-back part can be improved.
In an embodiment, the measuring tube has an inner diameter of at least 0.35 meters and especially at least 1 meters and preferably at least 1.5 meters.
Especially in the case of measuring tubes with large tube diameters, the invention provides great advantages as regards the performance of the flowmeter.
The invention will now be described based on examples of embodiments presented in the appended drawing, the figures of which show as follows:
For an advantageous spatial formation of the magnetic field in the region of the measuring electrodes 20, the pole shoes subtend in the central region 10.1 relative to the measuring tube axis 10.6 an angle βM of at least 40 degree and especially at least 80 degree and preferably at least 120 degree, wherein the pole shoes are separated from one another by two gaps, wherein each gap has an angle γ of at least 5 degree and especially at least 10 degree and preferably at least 15 degree. The gaps are adapted to prevent a magnetic short circuit between the pole shoes.
The guide-back parts can have a feedthrough (not shown) for measuring electrode contacting.
A magnetically inductive flowmeter of the invention is not limited to four coils and two guide-back parts. A flowmeter of the invention can have n1 coils and n2 guide-back parts, wherein n1 and n2 are natural numbers and n2<n1+1.
Common to the embodiments of the magnet systems shown in
The magnet system includes on the side of the measuring tube opposite the shown side preferably at least one other coil and at least one other guide-back part, which advantageously are arranged symmetrically to the shown coils as well as to the guide-back parts relative to a longitudinal section of the measuring tube.
Number | Date | Country | Kind |
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10 2017 131 202.1 | Dec 2017 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2018/084182 | 12/10/2018 | WO | 00 |