WO2004031700A1 - Inductive flow meter - Google Patents

Abstract

An inductive flow meter for electrically conductive liquids, comprising a flow channel section which is electrically insulated at least on the inside thereof and which has a substantially circular cross-section, a pair of diametrically opposite electrode arrangements which are electrically coupled to the electrically conductive liquid, a magnetic field generating system which generates a magnetic field which is oriented perpendicular to the longitudinal axis of the flow channel and perpendicular to the direct link between the electrode arrangement, penetrating the wall of the flow channel section and the inner area thereof, and measuring lines which are guided in an insulated manner from the outer side of the flow channel to the electrode arrangements, enabling the electrode arrangements to be connected to the measuring device. The line path concentration in the electrically conductive liquid to be analysed, which influences the measuring value, is reduced in the vicinity of the electrode surfaces of the electrode arrangements such that each of the electrode arrangements is configured in the form a web traversing a specific angle area of the inner periphery of the flow channel, whose radially inwardly directed web surface is essentially flush with the inner surface of the flow channel.

Description

 description

Inductive flow meter

The invention relates to inductive flow meters with the features of

Preamble of claim 1 or claim 2.

Flow meters of the type considered here serve to determine the flow of electrically conductive liquids through channels or pipes, in particular a circular cross section. In a channel section having an electrically insulating channel wall or tube wall, punctiform electrodes are provided at opposite points of a channel cross section, which electrodes are electrically coupled to the electrically conductive liquid, in particular are exposed to the channel interior and take up a conductive connection to the conductive liquid. The field lines of a magnetic field, which is generated by a permanent magnet arrangement or in particular by a coil arrangement, run perpendicular to the connecting line between the electrodes and perpendicular to the flow lines of the liquid flowing through the channel or the tube. Conductor paths which run from one point-shaped electrode to the other point-shaped electrode and on which the pipe section or channel section containing the electrodes penetrate the entire pipe cross section or channel cross section can, if the conductive liquid moves along the channel or pipe, as conductors moving in the magnetic field are understood, in which voltages are induced due to the liquid flow, which are taken from the punctiform electrodes via connections led through the insulating channel wall or tube wall and which are a measure of the flow of the conductive liquid through the tube or the channel. In more detail, the output signal of an inductive flow meter of the type described above, which can be taken from the electrodes, is to be given as follows

S ~ (B x W) v d (Vol)

(V „l) The integral over the volume is determined by the respective product value of

Vectors of three vector fields are formed, of which B is the magnetic induction in the flow channel section in the cylinder space delimited by the flow channel section with the inner channel cross section and with a certain length upstream and downstream of the radial plane containing the electrodes, and W denotes a valence vector field, including a field of vectors in the previously defined cylinder space is to be understood, which characterize the configuration of the conductor paths between the electrodes in the cylinder space. Finally, v denotes the vector field in the said cylinder space with vectors corresponding to the velocities of the particles of the conductive liquid

If the values of B were constant according to magnitude and direction (homogeneous magnetic field) and if the values of the valence vector field W were constant according to magnitude and direction according to current paths that run parallel to one another between parallel electrodes, the partial product B x W would be constant, such that non-uniform and / or asymmetrical velocity distributions of the flow of the electrically conductive liquid to be examined through the flow channel section do not lead to measurement value falsifications

It is true that the magnetic field of the magnetic field generation system can be designed with some effort so that it is essentially homogeneous in the area of the interior of the flow channel section, while the flow channel section is round in cross section and diametrically opposed to one another. the essentially vector-like electrodes, the value vector field is by no means homogeneous. The following consideration shows this without further ado:

If one draws these essentially completely covering conductor paths in pipe cross sections or channel cross sections, one recognizes that a conductor path concentration is present in the area near the punctiform electrodes, such that movements of the conductor paths due to the flow of the conductive liquid in these areas have a particularly strong influence on the have a detachable signal from the electrodes.

Characteristic flows in the flow channel section of an inductive flow meter, if they are laminar, have an undisturbed speed profile in the undisturbed state with respect to the central flow channel axis or, in the case of an asymmetrical disturbance, have a flow profile, the maximum of which is offset laterally in relation to the central flow channel axis. For high flow velocities, the flow can become turbulent in such a way that the flow profile has a plateau region with respect to the flow channel cross section and regions of lower flow velocity near the edge.

Both deformations of the flow profile as a function of the flow velocity and asymmetries of the flow profile have a falsifying influence on the measurement result obtained with an inductive flow meter of the type considered here.

In the technical teaching given by German Patent 1,295,223, the aim was to form the magnetic field in a flow channel section of an inductive flow meter in such a way that the influence of the inevitably present inhomogeneity of the valence vector Unfortunately, the measurement result is counteracted with a non-uniform flow distribution over the flow channel cross-section. For this purpose, German Patent 1,295,223 proposes that the magnet arrangement, that is to say the magnetic field generation system, be designed in such a way that the field component decreases in the radial plane containing the electrodes and in planes parallel to it in the direction of the connecting line between the electrodes from the inside to the outside.

In order to reduce the distortion of measured values due to non-uniform flow distribution, attempts have also already been made to compensate for the increased influence of the region of the flow cross section near the electrodes on the size of the measurement signal by, for example, according to German Offenlegungsschrift 26 22 943 when the magnetic field is generated by means of current flow Coils provided additional compensation coils, which generated magnetic fields in the cross-sectional plane of the flow channel section containing the electrodes or also upstream or downstream thereof, which penetrated the flow to generate the induced voltages in the conductor paths in those areas which are to be assigned to the areas located close to the electrodes are, the orientation of these magnetic fields was opposite to the main magnetic field.

The resulting structure of the entire device is comparatively complicated, the parts of the magnet system located in the vicinity of the electrodes, which act directly on the areas of very large conductor path densities, require very precise assembly and extremely fine adjustment.

A similar to the previously considered device acting inductive flow meter with a simplified structure of the magnetic field generation system is described in German Offenlegungsschrift 400 20 30. Finally, the European patent application, publication number 41 80 33, discloses an inductive flow meter of the type considered here with a main magnetic field generation system which is offset by 90 ° with respect to the pair of opposing measuring electrodes and which is equipped in each case with pole shoes which bear against its outer surface over a limited angular range of the flow channel wall and with auxiliary coils wrapping around these pole shoes, which nestle over a larger angular range on the outer surface of the flow channel section, in such a way that an approximately sinusoidal flow distribution of the magnetic field generation system between the measuring electrodes spans less than 180 ° in the circumferential direction is achieved.

It turns out that even with this known inductive flow meter it is not possible to achieve a completely satisfactory insensitivity of the measurement result to changes in the flow profile depending on the flow speed and to asymmetrical distortions of the flow profile of the flow in the flow channel section. Significant improvements can be achieved here by special measures on the electrode arrangements and the measuring lines assigned to them. The following considerations should be made here.

According to a very expedient design of an inductive flow meter, as is known from the international patent application, publication number WO97 / 12208, one of the measuring lines, which is connected to one of the electrode arrangements, has a thin circular disk sector with an inside diameter larger than the inside diameter of the flow channel section, wherein this annular disk sector carries the associated electrode arrangement in the form of a short web having an approximately punctiform end face in the region of its circumferential center and in the region its interruption connects to a thin U-shaped shorting bar. The annular disk sector and the U-shaped shorting bar are located in a radial plane with respect to the longitudinal axis of the flow channel, the electrode arrangements also being located in this radial plane. The interruption of the circular washer sector and the shorting bar have such a clear width that they frame the other of the electrode arrangements and the other associated, strip-shaped measuring line with insulation spacing in the radial plane just mentioned. Substantial parts of the measuring lines and the associated electrode arrangements are embedded in the material of the flow channel section in an insulating manner and are held in a fixed mutual position.

In this known design of an inductive flow meter, the measuring electrodes have exposed, approximately punctiform electrode surfaces on the inner wall of the flow channel.

If currents are induced in the approximately cylindrical liquid volume when the electrically conductive liquid is moved in the flow channel section, the conduction paths passing through the flow channel interior between the electrodes are concentrated in the electrically conductive liquid near the exit point or entry point at the punctiform electrode surfaces, which is the case with certain flow profile distortions the flow channel cross section can lead to falsified measurements.

Attempts have already been made to mitigate the conduction path concentration close to the electrode arrangements diametrically opposite one another across the flow channel cross-section by designing each electrode arrangement to span a specific angular range of the flow channel inner circumference by, for example, on one side of the flow channel inner circumference. catch two circumferentially spaced electrodes and on the other side of the flow channel diametrically opposite also two electrodes were provided with the same circumferential distance.

The individual electrodes of an electrode arrangement were then interconnected via twisted lines outside the flow channel in such a way that the formation of conductor loops containing the individual electrodes and their leads was avoided, in which electromotive forces falsifying the measured values could be induced by certain stray components of the magnetic field of the magnetic field generation system.

The object of the present invention is to design an inductive flow meter of the type defined at the outset in such a way that the conduction path concentration influencing the measured value in the electrically conductive liquid to be examined is reduced near the electrode surfaces of the electrode arrangements, which is due to a particularly simple structure of the electrode arrangements and the associated measuring lines should be achieved with a construction that also enables simplification and cheaper manufacture.

This object is achieved by an inductive flow meter with the features of claim 1 or of claim 2. Advantageous refinements and developments are the subject of claims subordinate to claims 1 and 2, the content of which is hereby expressly made part of the description without repeating the wording here. Some of these claims include combinations of features of independent importance.

In the following, a few exemplary embodiments are explained in more detail with reference to the drawings, the principle of operation of which is primarily shown in the drawings clarifying schematic representation is selected and no importance is attached to scale. The drawings show:

Figure 1 is a partially sectioned perspective view of an inductive flow meter of the general type considered here for explaining terms and geometric relationships.

2 shows a perspective view of a part of an inductive flow meter for explaining the measurement-distorting influence of an asymmetrical distortion of the velocity vector field in the flow channel cross section relative to the flow channel center axis;

Fig. 3 is a perspective view of part of an inductive

Flow meter for explaining the measurement-distorting influence of a change in the flow velocity vector field symmetrical to the central flow channel axis during the transition from a laminar flow to a turbulent flow;

Fig .4 is a perspective view of a part of an inductive

Flow meter, through the flow channel cross section of which a laminar flow of the electrically conductive liquid occurs;

Fig. 5 is a perspective view of an inductive flow meter of the type specified here in a quarter of the wall the section containing the flow channel section with a definition of a coordinate system;

5a and 5b are diagrams in which values of a magnitude are plotted against the circumferential angle of the position of points of the flow channel inner surface between a point lying circumferentially in the middle between the electrodes and the position of an electrode, which are related to the flow values of the magnetic field generation system of the inductive flow meter stands;

FIG. 6 shows a diagram and a cross-sectional illustration of a development of the flow channel wall according to FIG. 5 to explain the extraction of diagrams according to FIGS. 5a and 5b;

7 to 12 show various advantageous forms of field coils of the magnetic field generation system attached to or in diametrically opposite wall regions of the flow channel section of the inductive flow meter, in which case the coil or coil arrangement located on one side is shown in a manner visible to the viewer;

Fi * ög. 13 shows a schematic sectional illustration of an inductive one

Flow meter in an embodiment in which the magnetic field generation system in a certain way formed pole pieces of a core system provided with an excitation winding;

FIG. 14 shows a perspective illustration of an embodiment of an inductive flow meter according to a modification compared to the embodiment according to FIG. 13;

Fig. 15 is a schematic perspective view of an inductive

Flow meter of the type considered here with the omission of the magnetic field generation system, but with a detailed representation of a particularly advantageous electrode system;

16 shows a radial section through the flow channel section of the inductive flow meter according to FIG. 15 in the plane containing the electrode arrangements;

17 and 18 representations similar to FIG. 16 of embodiments modified compared to the embodiment according to FIGS. 15 and 16;

Fi 'ög. 19 shows a schematic partial view of an inductive flow meter of the type specified here in the area of the outer connections of the measuring lines according to an advantageous embodiment

design; and

20 is a schematic side view of an inductive flow meter according to a further modification. The basic idea of the design of the electrode arrangement proposed here will first be explained with reference to the drawing figures 15 to 20. The inductive flow meter according to FIG. 15 contains the flow channel section 1, which is made of electrically insulating material and is round in cross section, through the cylindrical interior of which the electrically conductive liquid is guided parallel to the flow channel center axis Z, the flow of which is to be measured. 15 generates a magnetic field in the area of the flow channel section 1 with a direction transverse to the flow direction and transverse to the connecting line between the electrode arrangements 2 and 3. Via an approximately in the middle of the longitudinal extent of the flow channel section 1 cross-section of the flow channel interior diametrically opposed to each other are the electrode arrangements 2 and 3, each spanning a certain angular range α of the flow channel inside. The electrode arrangements have narrow, cylindrical-sector-shaped electrode surfaces which are flush with the inner surface of the flow channel section, as can be clearly seen from FIG. 16. The extension of the electrode surfaces over the angular range α causes the entry point or the exit point of the conduction paths, which penetrate the flow channel interior and in which electromotive forces are induced when the liquid is moved by means of the magnetic field B, to be lower in the area near the electrodes compared to arrangements with punctiform electrodes Have conduction path concentration, so that when the flow profile changes through the flow channel interior, less distortion of the measured value is achieved with the electrode arrangements shown here.

The electrode arrangement 2 projects radially inward as an arcuate web from an annular disk sector 40, which connects to a thin U-shaped shorting bar 50 in the region of its interruption. The circle- washer sector 40 and the U-shaped shorting bar 50 lie in a radial plane with respect to the longitudinal axis Z of the flow channel, in which the center planes of the electrode arrangements 2 and 3 are also located.

The interruption of the annular disk sector 40 and the short-circuiting bracket 50 have such a clear width that they frame the other electrode arrangement 3 and a strip-shaped measuring line 60 leading to it with insulation spacing in the radial plane. The electrode arrangement 3 can either widen from the measuring line 60 in the direction of the inner surface of the flow channel section, as indicated in FIG. 15, or can be formed by a front part of the measuring line 60, which then has such a width over its entire length has that the measuring electrode arrangement 3 finally spans the same circumferential angle α on the inside of the flow channel as the electrode arrangement 2.

17 shows an embodiment in which each electrode arrangement has two individual electrodes 2a and 2b or 3a and 3b, which are spaced apart on the inner circumference of the flow channel section 1 over the angular range α. With this arrangement, too, the concentration of the conduction paths in the region near the electrodes is reduced, which leads to an improvement in the independence of the measurement result from flow profile distortions in the electrically conductive liquid.

In the embodiment according to FIG. 18, four web-shaped individual electrodes 2a to 2d or 3a to 3d are distributed over the angular range of α. The individual electrodes according to FIG. 3 and the individual electrodes according to FIG. 18 do not need to be placed on separate measuring line sections, which, if necessary, would have to be twisted out of the flow channel section, in order to influence measurement-induced influences of induction voltages in the measuring lines excluded. Rather, the individual electrodes of the electrode arrangements are each short-circuited directly via measuring line sections, namely the individual electrodes 2a and 2b via the arc section of the annular disk sector 40 connecting them and the individual electrodes 3a and 3b through the end face of the strip-shaped part 60 connecting them. The same applies to the embodiment according to Fig. 17.

15 to 18 that the annular disk sector 40 and parts of the shorting bar 50 as well as the strip-shaped conductor 60 carrying the electrode arrangement 3 are partially embedded in the wall of the flow channel section 1 in a radial central plane. The aforementioned conductor parts can be cast into the flow section 1, which is designed as a plastic injection-molded part, such that the electrode surfaces are exposed on the inside of the flow channel and the shorting bar 50 and the strip-shaped conductor 60 protrude laterally from the wall of the flow channel section 1, in such a way that a measuring device is connected here can be designated 70 in the drawing.

It is particularly expedient if the shorting bar 50 and the strip-shaped measuring line 60 protrude laterally sufficiently far from the flow channel wall surrounding them and are initially connected in one piece in this area by conductor webs, such that the electrode arrangements become one during the embedding of the electrode arrangements and the measuring lines maintain a fixed relative position to each other. After the embedding, the connecting conductor webs are removed by punched-out separating regions spaced apart from the outer flow channel wall, the mutual position of the electrode arrangements no longer changing. Such punching-out separation areas are indicated at 80 in FIG. 19. The two measuring lines with their electrode arrangements can thus be provided as a uniform sheet metal stamped part and are embedded in the flow channel section 1, which is designed as an injection molded part, and only then are they electrically separated from one another by the punched-out separation regions.

The annular disk sector 40 and the strip-shaped measuring line 60 have a considerable width in the radial plane with respect to the longitudinal axis Z of the flow channel in order to provide sufficient conductor cross sections for a safe short circuit of the individual electrodes of each electrode arrangement. If the electrode arrangements and measuring lines are embedded in the wall of the flow channel section 1, the flow channel section can assume a considerable wall thickness, such that in some embodiments it is difficult to establish a sufficiently intense magnetic field in the interior of the flow channel section 1.

To avoid this problem, according to the embodiment of

20, the electrode arrangements and the measuring lines are embedded in a flange body 90 of larger diameter of the flow channel section 1, to which thin-walled channel parts 100 and 110 of the flow channel section 1 connect. The interiors of these channel parts are aligned with the central opening of the flange body 90 of larger diameter. The outer walls of the thin-walled channel parts 100 and 110 are turned over by pairs of field coils or pole pieces 120 of the magnetic field generation system, which face each other across the flow channel interior, in such a way that the magnetic field emanating from the coils of the type specified here passes through the channel walls in a comparatively short way the liquid volume in the flow channel section 1 is reached. The angular range defined here is at least 125 °, preferably more than 140 °. It has been shown that a special interaction of a special design of the course of the effective intensity of the magnetic field of the magnetic field generation system with the shape of the electrode surfaces of electrodes 2 and 3 indicated here leads to a surprising additional improvement in the sensitivity of the inductive flow meter to flow profile changes and Flow profile asymmetries can be achieved, the manufacture of the electrode arrangement also being simplified and cheaper.

The inductive flow meter of the general type considered here, shown in its basic components in FIG. 1, in turn contains a flow channel section 1 in the form of a tube made of electrically insulating material. The central longitudinal axis of the flow channel section 1 is designated Z. In the middle of the longitudinal extent of the flow channel section 1 there are electrode arrangements of the type previously discussed, diametrically opposite one another across the relevant flow channel cross-section, wherein in FIGS. 1 to 14 these electrode arrangements each extend over the angular range α by punctiform electrodes 2 and 3 are symbolized in the middle of the respective angular range in order to simplify the illustration. The measuring electrodes 2 and 3 are connected to a voltage measuring device 6 via measuring lines 4 and 5, which extend through the wall of the electrically insulating flow channel section 1. The measuring electrodes 2 and 3 can directly connect on the inside of the flow channel section 1 to the electrically conductive liquid flowing through the flow channel section 1 or, in the case of alternating current excitation of a magnetic field product system of the inductive flow meter known to the person skilled in the art, be capacitively coupled to the electrically conductive liquid, so that the measuring electrodes do not need to be exposed on the inside of the flow channel section 1 in this case. The distance between the cross-sectional plane containing the measuring electrodes 2 and 3 of the flow channel section 1 from its upstream end and its downstream end is denoted in each case by z.

Finally, a magnetic field generation system 7 is indicated in FIG. 1 by a block symbol. This generates an induction vector field B represented by vectors of magnetic induction, the magnetic field lines penetrating the wall of the flow channel section 1 and its interior and being oriented essentially perpendicular to the central axis Z and perpendicular to the diameter line of the flow channel cross section connecting the measuring electrodes 2 and 3 ,

The length of the interior of the

Flow channel section 1 of 2z is chosen to be approximately equal to the diameter of the flow channel cross section. A magnetic field generated by the magnetic field generation system 7 is initially assumed to be homogeneous in the entire interior of the flow channel section 1 for the purposes of explanation in connection with FIG. 1. If an electrically conductive liquid is now passed through the interior of the flow channel section 1, the flow particles of the liquid have speeds corresponding to the individual speed vectors of a vector field v parallel to the central longitudinal axis Z.

A multiplicity of the conductor paths passing through the entire interior of the flow channel section 1 both over the channel cross section and over the length of the flow channel section 1 are indicated by dashed lines w in FIG. 1. If the electrically conductive liquid moves through the flow channel section 1 in accordance with the speed vector field v, the conductor paths in accordance with the lines w are to be understood as conductors moved in the magnetic field, in each of which electromotive forces are due to the movement of the conductor paths are induced in such a way that a resulting induced measuring voltage is finally present between the measuring electrodes 2 and 3, which is measured by the measuring device 6 and is related to the flow rate per unit time of the electrically conductive liquid.

Because of the orientation and the course of the conductor paths assumed in the electrically conductive liquid according to the lines w, the electromotive forces induced in the individual conductor paths contribute to the measurement signal S which can finally be read off on the measuring device 6 in different degrees. This results from the fact that the conductor paths, at least in certain sections of their course between the measuring electrodes 2 and 3, have a different orientation from the course perpendicular to the central longitudinal axis Z and perpendicular to the field lines of the magnetic field and also have different lengths.

For this reason, considering the conductor path configuration as a conductor path configuration value vector field W is justified, this vector system, hereinafter abbreviated as a value vector field, taking into account the orientation components responsible for the induction of electromotive forces, the conductor path.

The signal S readable on the voltage measuring device 6 can be expressed as follows:

S ~ (B x W) - v d (Vol)

(Vι, l)

If all of the vectors of the flow velocity vector field v parallel to the central longitudinal axis Z have the same length, ie if the flow velocity is constant over the flow channel cross section, this results in a linear dependence of the measurement signal S on the flow velocity, since the product (B x W) is essentially a device constant determined by the geometrical arrangement in the flow meter.

In practice, however, the velocity vector field v suffers for certain

Operating cases of the inductive flow meter certain distortions, which are briefly treated qualitatively with reference to FIGS. 2 to 4.

2 shows a vector field v of the velocity distribution over the flow channel cross section, in which there is no rotational symmetry of the flow profile with respect to the central longitudinal axis Z of the flow channel section 1. The range of maximum speed vectors of the vector field v is asymmetrically offset downwards with respect to the central longitudinal axis Z. This speed distribution can result, for example, from the fact that there are flow obstacles, for example valve spools, pipe elbows and the like, in channel sections which are upstream of the flow channel section 1, which have the effect that, for example, the maximum flow vectors of the flow distribution are located in the lower quadrant of the pipe cross section. However, the range of the maximum can also lie in other quadrants, for example in a cross-sectional quadrant to which the measuring electrode 2 is adjacent, or in a cross-sectional quadrant that is adjacent to the apex of the flow channel section 1, or also in the cross-sectional quadrant to which the measuring electrode 3 is adjacent ,

FIG. 3 shows a situation in which a transition from the laminar flow (see FIG. 4) to a turbulent flow has occurred due to the high flow velocity in the flow channel section 1. The flow profile is approximated to a trapezoidal shape in an axial longitudinal section, with boundary layers of low flow velocity being relatively low radial Have strength. In the area of a laminar flow according to FIG. 4, the flow profile of the vector field has the shape of a paraboloid of revolution symmetrical to the central longitudinal axis Z.

Both the position and the size of the asymmetry of the flow profile with respect to the central longitudinal axis Z according to FIG. 2 as well as the basic shape of a flow profile symmetrical to the central longitudinal axis Z according to FIGS. 3 and 4 and finally also the shape of a paraboloidal flow profile in the laminar flow area have an influence 1 in the sense of a measurement value falsification if a homogeneous magnetic field B is assumed, since deviations in the practical velocity vector fields v from a uniform distribution over the flow channel cross section each result in different movements of the line field w in Fig. 1 symbolized conductor paths of the value vector field W and thus mean different contributions to the signal S.

It has now been found that the compensation of the measurement value falsifying

Influence of the distortion of the flow velocity distribution across the flow channel cross-section through special design of the vector field of magnetic induction B is particularly successful when a magnetic field generation system effective in the flow channel section 1 penetrates the interior of the flow channel section with an effective intensity i, which is plotted over a development of the flow channel inner wall , between a circumferential point halfway between the measuring electrodes and one of the measuring electrodes in each case has a concave shape which is pronounced in a very specific way. The effective intensity i of the magnetic field generated by the magnetic field generation system in relation to the cylinder surface in which the magnetic lines enter and interact with the electrically conductive liquid, that is to say in relation to the inner wall surface of the flow channel section 1, is defined here as follows:

Herein, φ means the circumferential angle measured in the channel cross-sectional plane of the electrodes 2, 3 between a point of the flow channel inner surface located centrally between the electrodes and a point of the flow channel inner surface and the channel cross-sectional area closer to it, the significance of the angle φ also referring to the meaning of the angle Fig. 5 should be noted.

φ ₀ is the value of φ for the point closest to the electrode of a coil arrangement or pole shoe surface which wraps around the flow channel section 1, such that φ ₀ is equal to half the wrap angle of this coil arrangement or the relevant pole shoe surface.

Θ is the magnetic flux in ampere turns of a coil or a pole piece of the magnetic field generating system with the wrap angle 2φ, such that if, for example, a coil arrangement of a pair of coil arrangements of the magnetic field generating system consists of individual coils of different wrap angles, the respective magnetic flux of these individual coils for calculating the summands the above equation is to be considered. b (φ) is the respective local coil width or the respective local pole shoe width (measured in the direction of the longitudinal axis of the flow channel).

R, is the inner radius of the flow channel section.

R _Φ is the local distance of a magnetic pole compartment facing the flow channel from the longitudinal axis Z of the flow channel.

effektiven Intensität des Magnetfeldes an der Innenwandfläche des Strömungskanalabschnittes 1 durch solche Teile des Magentfelderzeugungssystems, also Spulenteile oder Polschuhflächenteile, welche vergleichsweise größeren Abstand von der Strömungskanalmittellägsachse haben.The correction factor ² takes into account the generation of a smaller one

effective intensity of the magnetic field on the inner wall surface of the flow channel section 1 through those parts of the magnetic field generation system, that is to say coil parts or pole shoe surface parts, which have a comparatively greater distance from the longitudinal axis of the flow channel.

If one were to measure a flow channel section 1 with a series of rectangular coils of the same width provided on the jacket of the flow channel wall in the direction of the channel axis, the wrap angle increasing linearly from coil to coil with the same position of the coil center, this would result in accordance with the relationships shown above a linear course of the effective intensity. Such a dimensioning of the magnetic field generation system does not meet the technical teaching specified here.

Even a single field coil, which is diamond-shaped in view of the development of the flow channel inner surface, on each side of the flow channel section does not lead to the above-mentioned, particularly concave shape of the characteristic curve of the effective intensity, because with the diamond shape mentioned, the local coil width decreases linearly and again not a "concave" course 2 ^

the characteristic of the effective intensity of the magnetic field within the flow channel section is given.

Then, if according to the teaching of the European patent application briefly discussed at the beginning, publication number 04 180 33, coils of the magnetic field generation system wrapping around the outer wall of the flow channel are provided in such a circumferential distribution that an approximately sinusoidal flow distribution over the circumference on a less than 180 ° arc is reached between the electrodes, as comparatively simple considerations show, using the above definition equation for the effective intensity gives a sine characteristic that has a concave shape.

It has been found that in many cases it is not sufficient to merely require a concave course of the effective intensity of the magnetic field of the gastric generation system over the inner circumference of the flow channel towards the electrodes, but that a special quality of this concave course leads to surprising results and sudden improvements in terms of change sensitivity to measurement falsifications due to changes in the flow profile depending on the flow speed or due to asymmetries in the flow profile.

This means that according to the invention the characteristic curve i (φ) or, insofar as this

Has discontinuity areas, a concave envelope curve i '(φ) of this characteristic, that is, for example, stepped or kinked, on the one hand has to meet the condition that it starts from a maximum value at or near φ = 0 for

φ = φ _n drops to 0 in such a way that - or - at least in the predominant part dφ dφ of the range is negative, which means that the characteristic curve is essentially above the entire specified range is falling. In addition, however, the condition must be met that the characteristic curve in this area at least in sections

has smaller values than the characteristic i = i _max (l -), with at least one sin φ _{Q of} these smaller values being 10% smaller than the corresponding value of the characteristic i =

This particularly pronounced concavity of the course of the characteristic curve proposed here for the effective intensity of the magnetic field of the magnetic field generation system is to be observed in all of the embodiments specified here and is the reason for the significant and, in some cases, order of magnitude improvements in insensitivity to measurement distortion influences.

5a and 5b show the course of the effective intensity of the magnetic field, plotted against the angle φ, which is the circumferential angle measured in the channel cross-sectional plane of the electrodes between a point of the flow channel inner surface located centrally between the electrodes, that is to say between the apex 5 and a point closer to one of the electrodes. The characteristic curve i = f (φ) drops according to FIG. 5a from a maximum value at φ = 0 with an essentially continuously decreasing gradient in the direction of the circumferential position of the electrode 2 and reaches at φ ₀ sufficiently before the abscissa value of φ = 90 ° a zero crossing according to the position of the electrode. In the example of FIG. 5b, the characteristic curve i = f (φ) rises from a certain value for φ = 0 to a maximum at a still relatively small value for φ, and then with an initially increasing gradient, but then similarly as with the characteristic curve according to FIG. 5a with a steadily decreasing To strive towards a zero point at φ ₀ , which is close to the electrode position at φ = 90 °.

It goes without saying that the characteristic curves i = f (φ) repeat themselves symmetrically as they progress in the circumferential direction towards the other measuring electrode 3 in the circumferential regions of the flow channel inner surface lying to the left of FIGS. 5a and 5b with respect to the axis of the ordinate.

In practical cases, in which discrete coils wrap around the outer circumference of the flow channel section 1, the characteristic curve i = f (φ) has a staircase shape, as is made clear in the illustration in FIG. 6. The one specified here

In these cases, teaching relates to a concave envelope curve i '(φ), which in

6 is shown by a dash-dotted line 10.

The invention also encompasses characteristic curve forms in which i = f (φ) drops from a certain maximum value for abscissa values of φ close to zero to a zero point, in order then to increase again above zero for a larger value of φ, but to a new maximum, that is very substantially below the first-mentioned maximum, after which the i-value finally drops to zero for a value φ = φ ₀ before the circumferential position of the measuring electrode is reached. The angular position of this final drop from f (φ) to zero in the vicinity of the measuring electrode 2 or 3 can be referred to as half the wrap angle φ of the magnetic field generation system. With reference to the representations according to FIGS. 5, 5a, 5b and 6, it is in any case less than 90 ° and, based on the representation of two quadrants between the measuring electrodes 2 and 3, in any case less than 180 °.

A preferred degree of wrap in the above sense is φ> 70 °. based on the representation of two quadrants, 2φ> 140 °. In principle, two approaches which have the same effectiveness are suitable for reducing the influence of a distortion of the flow velocity vector field on the measured value in the manner specified here, the total magnetic flux used being divided up in such a way that the previously defined shape of the characteristic curve i = f (φ) results. On the one hand, a pole surface or flow channel inner wall surface of a constant width in the circumferential direction in the longitudinal direction of the flow channel can be occupied with locally different electrical fluxes, which means that, for example, a first coil with a lower wrap in the circumferential direction has an ampoule number of 1,000, while a second coil with a larger wrap, for example, has one Ampere-turn number of about 0.1. The measurement inaccuracies due to an asymmetry of the flow velocity vector field fluctuate between the circumferential position of a measuring electrode and the circumferential position of the circumferential center between the two measuring electrodes when the flow maximum moves. Compared to an optimized rectangular coil, the maximum amount of measurement inaccuracy is reduced to one tenth. A dependence of the measurement accuracy on the flow velocity, that is, the shape of a symmetrical flow profile according to FIGS. 3 and 4, is essentially no longer given in this embodiment of the magnetic field generation system of the type specified here.

Another way of designing the magnetic field generation system in such a way that the desired shape of the characteristic curve results is to design the outer contour of a coil provided with a uniform electrical flow. This training is shown in Fig. 7. The coils opposite each other across the flow channel interior are each cross-shaped and give the desired characteristic curve i = f (φ). 5b with the result of a largely independence of the knife Result of the asymmetry of the flow velocity V field of Fig. 2 within limits of about 0.5% to -0.1% and largely independence of the measurement result from rotationally symmetrical flow profiles.

One based on the effective intensity of the magnetic field generation system

7 corresponding effective intensity can also be achieved according to FIG. 8 by means of a narrow coil of larger wrap and a wide coil of lower wrap on each flow channel side.

Another way of training is shown in Fig. 9, in each

Flow channel side a narrow coil of large wrap and two further coils of smaller wrap located on the flow channel jacket downstream and upstream of the narrow coil are provided. Of course, all the coils according to FIGS. 8 and 9, as well as also according to FIGS. 10, 11 and 12 to be considered briefly below, have current flowing through them in the same direction of rotation.

10 shows in its upper part an embodiment in which a coil with a smaller wrap in the direction of the central longitudinal axis of the flow channel section is arranged symmetrically with respect to the circumferential center between the measuring electrodes 2 and 3 and narrow on the coil sides parallel to the central longitudinal axis of the flow channel section Connect the coils, the coil sides of which lie away from the center of the wide coil mentioned, each being close to the measuring electrodes 2 and 3. The embodiment indicated in the lower part of Fig. 10 still provides a space between the central, wide coil and the narrow coils closer to the measuring electrodes, which has the effect that when recording the characteristic curve i = f (φ) according to the context with the rules given in FIG. 6, a section of the characteristic curve in the area between the coils comes together, which together with the abscissa falls. As already stated above, such embodiments also fulfill the technical teaching given here of an indented or “concave” profile of the characteristic i = f (φ), for example according to FIGS. The narrower coils adjoining a central, wide coil can also have a triangular or round shape instead of the rectangular shape seen from above.

The narrow coil of large wrap angle according to FIG. 9, which is located between the upstream and downstream coils with a lower wrap angle, can also be divided into two narrow individual coils.

The coil parts of smaller width in the direction of the central longitudinal axis of the flow channel 1 according to FIG. 7 need not have a rectangular shape when viewed from above, but can also taper to a point in the direction of the measuring electrodes 2 and 3.

Fig. 11 shows an embodiment in a corresponding representation as in Figs. 7 to 10, wherein the diametrically opposed coil arrangements each have a division into two coils of different wrap with the same coil width in the direction of the flow channel longitudinal axis Z in the upper part of the drawing and a division into three Have coils of different wrap but the same coil width in the direction of the flow channel longitudinal axis Z in the lower part of the drawing. The coils can have different numbers of turns and / or can be supplied with different excitation currents.

12 shows an embodiment in which the mutually opposite coil arrangements each have a coil of specific wrap and interact with auxiliary pole shoe parts h, which are located symmetrically to the channel cross-sectional planes of the electrodes and are shown in the present embodiment. lance-shaped example. They extend over a region between the flow channel section 1 and the coil arrangement in the direction of the electrodes and are formed by strip-like soft magnetic components. The auxiliary pole shoe parts h can also each have a narrow strip-shaped or leaf-shaped or diamond-shaped design and, together with the associated coils of the magnetic field generation system, result in the particular shape of the course of the effective intensity of the magnetic field specified here.

It should be expressly mentioned here that in no embodiment is a curve of the characteristic curve i = f (φ) approximated, as is achieved by a diamond-shaped coil in supervision, by means of which a curve which deviates from the shape according to FIGS. 5a and 5b, is approximately rectilinear The characteristic curve i = f (φ) is achieved, while, according to the teaching given here, the characteristic curve i = f (φ) is characterized by a concave course which is qualified in a certain way in at least one substantial area.

The equation given here for the effective intensity of the magnetic field, namely i = f (φ), has a gradually decreasing coil only when using coils that are finely distributed over the wrap in the circumferential area between the measuring electrodes or in the case of coils with a direction towards the measuring electrodes In turn, a constant course, while in most embodiments, as indicated in FIG. 6, a stepped characteristic curve i = f (φ) is obtained. The design rule given here for the characteristic curve i = f (φ) is such that the characteristic curve has a concave course over a substantial area between the circumferential center of the flow channel inner wall between the measuring electrodes and an angular position of the flow channel inner wall near the measuring electrodes. in the case of a stepped characteristic curve, such as already said, on the concave envelope i '(φ), which is shown at 10 in FIG.

The previously discussed embodiments of an inductive flow meter of the type considered here have, on opposite sides of the flow channel section 1 in circumferential areas between the measuring electrodes 2 and 3 on the outside of the wall or embedded in the wall of the flow channel section 1, current-carrying field coils which generate the magnetic field of the desired effective intensity ,

Instead of the field coils, however, an arrangement of pole shoes of a magnetic closing circuit opposite one another via the flow channel section 1 can also be provided, as is shown in FIGS. 13 and 14. This magnetic closing circuit is designated by 20 in FIGS. 13 and 14 and carries a concentrated excitation winding 21 which is supplied with clocked direct current or alternating current, depending on whether the inductive flow meter is to deliver a direct current measuring signal or alternating current measuring signal.

The pole shoes 22 and 23 which face each other across the flow channel section 1 in the embodiment according to FIG. 13 have side-mounted pole shoe parts 24, the pole shoe surfaces of which lie against the flow channel section outer wall at a smaller distance from the respective measuring electrodes 2 and 3, the pole shoe parts 24 through constrictions or punchings, not shown in the drawing, so that they have an increased magnetic resistance, such that the flux density to be measured on the pole shoe surfaces of the pole shoe parts 24 is less than the flux density resulting from the pole shoe surfaces of the main parts of the pole shoes 22 and 23 emerges, which means that the effective intensity of the magnetic field is designed according to an equivalent number of ampere turns of a field coil arrangement replaced by the pole shoes 22 and 23.

In the embodiment according to FIG. 14, the pole shoes 22 and 23 have lugs 25 of smaller width on the side in relation to the dimension in the direction of the central longitudinal axis Z of the flow channel section 1, the side lugs 25 having a near pole faces facing the flow channel interior Apply the looping area to the measuring electrodes 2 and 3. Those skilled in the art will recognize that the embodiment shown in FIG. 14 with pole pieces 22 and 23 forming part of a magnetic circuit corresponds to an embodiment with field coils of the magnetic field generation system according to FIG. 7. An embodiment according to FIG. 13 with the side of the main pole pieces 22 and 23 and branches off from these pole piece parts 24, if these pole piece parts 24 have a smaller width than the main pole piece parts in the direction of the central longitudinal axis of the flow channel section 1, is equivalent to a field coil Magnetic field generating device can be viewed according to the lower part of FIG. 10.

In a modification of the embodiments according to FIGS. 13 and 14, to form the magnetic field generation system of the inductive flow meter of the type specified here, a plurality of magnetic closing circuits with excitation windings with different currents can also be provided, as a result of which further magnetic field generation systems with pole shoe arrangements equivalent to magnetic field generation systems with field coils can be constructed, which of the rules given here for the course of the effective intensity of the magnetic field over the circumferential angle of the inner wall of the flow channel between the measuring electrodes An additional variable for influencing the vector field B of the magnetic induction in the interior of the flow channel section 1 to produce the desired distribution of the effective intensity of the magnetic field on the inner surface of the flow channel is the distance between coils or coil sets or between the pole shoe surfaces of the poles of the magnetic field generation system the outer lateral surface of the flow channel section 1 as a function of the angular position between the circumferential center between the measuring electrodes and the respective measuring electrode. In some cases, it may be expedient if the coils or coil sets have a stepped or continuously increasing distance with increasing proximity to the measuring electrodes, so that the corresponding distance to the inner surface of the flow channel increases in the circumferential direction towards the measuring electrodes. The same applies correspondingly to the distances of the pole shoe surface areas from the outer surface or from the inner surface of the wall of the flow channel section 1. When calculating the magnetic field generation system of the type proposed here, the respective local distance of the coil surfaces or the pole shoe surfaces from the

R ²

Flow channel longitudinal axis Z anyway by the correction factor - '-, which here

^R <? given equation for i (φ) in the calculation.

Claims

Expectations 1. Inductive flow meter for electrically conductive liquids, - With a flow channel section (1) which is electrically insulating at least on its inside and has a substantially circular cross section; with a pair of diametrically opposed electrode arrangements (2, 3) electrically coupled to the electrically conductive liquid; with a magnetic field generation system (7; 20, 21, 22, 23) which generates a magnetic field which is oriented essentially transversely to the longitudinal axis of the flow channel (Z) and transversely to the direct connecting line between the electrode arrangements (2, 3) and penetrates the wall of the flow channel section and its interior ; and with measuring lines (40, 50, 60), which are guided from the outside of the flow channel to the electrode arrangements (2, 3) and via which the electrode arrangements are connected to a measuring device (70), characterized, that each of the electrode arrangements (2, 3) is designed as a web spanning a specific angular range (α) of the flow channel inner circumference, the radially inwardly directed web surface of which is essentially flush with the flow channel inner surface. Inductive flow meter for electrically conductive liquids, - With a flow channel section (1) which is electrically insulating at least on its inside and has a substantially circular cross section; with a pair of diametrically opposed electrode arrangements (2, 3) electrically coupled to the electrically conductive liquid; with a magnetic field generation system (7; 20, 21, 22, 23) which generates a magnetic field which is oriented essentially transversely to the longitudinal axis of the flow channel (Z) and transversely to the direct connecting line between the electrode arrangements (2, 3) and penetrates the wall of the flow channel section and its interior ; and with measuring lines (40, 50, 60), which are guided from the outside of the flow channel to the electrode arrangements (2, 3) and via which the electrode arrangements are connected to a measuring device (70), characterized, that each of the electrode arrangements (2, 3) is formed by a plurality of short-circuited electrode webs (2a, 2b, 3a, 3b; 2a - 2d, 3a - 3d) distributed circumferentially over a certain angular range (α), the web surfaces of which are directed radially inwards with the Flow channel inner surface substantially aligned. 3. Inductive flow meter according to claim 1 or 2, characterized in that one of the measuring lines has a thin annular disk sector (40) with an inner diameter larger than the inner diameter of the flow channel section (1), which in the region of its circumferential center with one of the electrode arrangements (2, 3rd ) is connected and in the region of its interruption to a thin U-shaped short-circuiting bracket (50), the annular ring sector (40) and the U-shaped shorting bracket also being located in a radial plane with respect to the longitudinal flow channel axis (Z), in which also the electrode arrangements (2, 3) are located, and the interruption of the annular disk sector and the shorting bar have such a clear width that they frame the other of the electrode arrangements and the other strip-shaped measuring line (60) connected therewith with insulation spacing in the radial plane mentioned. 4. Inductive flowmeter according to claim 3, characterized in that the electrode arrangements (2, 3) from an arcuate portion of the Annular disk sector (40) or the strip-shaped measuring line (60) project radially inwards to the flow channel interior. 5. Inductive flow meter according to claim 3 or 4 and / or claim 2, characterized in that each of the electrode arrangements contains two electrode webs (2a, 2b, 3a, 3b) which are arranged at the beginning and at the end of the specific angular range (α). 6. Inductive flow meter according to claim 3 or 4 and / or claim 2, characterized in that the electrode webs have different lengths in the circumferential direction. 7. Inductive flow meter according to one of claims 3 to 6, characterized in that the strip-shaped measuring line (60) and the short-circuiting bracket (50) adjoining the annular disk sector protrude from the flow duct wall surrounding it in regions and have at least one punched-out separation region (80) spaced from the outer flow duct wall, such that both measuring lines with their electrode arrangements as a uniform sheet metal A stamped part can be provided, can be embedded in the flow channel (1) designed as an injection molded part and can then be electrically separated from one another by producing the punched-out separation regions (80). 8. Inductive flow meter according to one of claims 3 to 7, characterized in that the electrode arrangements (2, 3) and the measuring lines are embedded in a flange body (90) of larger diameter of the flow channel section (1), to which thin-walled channel parts (100, 110) of the flow channel section (1) connect, the inner wall of which is connected to the central one The opening of the flange body is aligned and its outer walls on both sides of the flange body of field coils (120) of the magnetic field, which face each other in pairs across the flow channel interior. generation system are wrapped in certain circumferential angular ranges. Inductive flow meter according to one of claims 1 to 8, in which the magnetic field generated by the magnetic field generation system (7; 20, 21, 22, 23) has an effective intensity i on the inner surface of the flow channel, which is defined by the following equation: Coil or l'olschu N f „ R. i (φ) = ∑ D (φ) ^• b (φ) Coil or pukchuh Ni IK ^R 9 J wherein φ denotes the circumferential angle measured in the channel cross-sectional plane of the electrodes (2, 3) between a point of the flow channel inner surface located centrally between the electrode arrangements and a point of the flow channel inner surface and the channel cross-sectional plane closer to one of the electrode arrangements, φ ₀ denotes the value of φ for the point closest to the electrode of a coil arrangement or pole shoe surface of the magnetic field generating system that wraps around the flow channel section (1), such that φ ₀ is equal to half the wrap angle, Θ is the magnetic flux in ampere turns of a coil or a pole piece of the magnetic field generation system with the wrap angle 2φ. b (φ) is the local coil width or the local pole shoe width in the direction of the longitudinal flow channel axis (Z), R, the inner radius of the flow channel section, and R _φ the local distance of a main coil surface facing the flow channel or a pole shoe surface from the Is the flow channel longitudinal central axis; characterized in that the characteristic curve i = f (φ) or, as far as this has discontinuities, a concave envelope curve i '= f (φ) of this characteristic curve, starting from a maximum value i _max at or near φ = 0, for φ = φ ₀ to zero drops that - or - at least in the major part of the range is negative dφ dφ and in this area at least in sections has smaller values than that Characteristic curve i = i, _ra (l -— - -), with at least one of these smaller values sin φ Is 10% smaller than the corresponding value of the characteristic curve i = i _max (1 -). sin φ _o 10. Inductive flow meter according to claim 9, characterized in that the magnetic field generation system is a pair opposite one another across the flow channel section (1), essentially nestling against the flow channel section (1) Has individual coils whose width in the direction parallel to Flow channel longitudinal axis (Z) is stepped with increasing proximity to the electrodes (2, 3) and / or decreases continuously (Fig. 7). 11. Inductive flow meter according to claim 9, characterized in that the magnetic field generation system comprises a pair of coils or coil groups which are diametrically opposed to one another across the flow channel section (1) and which wrap around a smaller area of the flow channel circumference between the measuring electrodes (2, 3) and have a larger width in the direction of the longitudinal flow channel axis (Z), and contains a further pair of coils or coil groups, which wrap around a larger area of the circumference of the flow channel section (1) between the measuring electrodes (2, 3), but have a smaller width measured in the direction of the longitudinal axis (Z) of the flow channel (FIG. 8, 9). 12. Inductive flow meter according to claim 9, characterized in that the magnetic field generation system comprises a pair of coils or coil groups which are diametrically opposed to one another over the flow channel section (1) and which wrap around a smaller area of the flow channel circumference between the measuring electrodes and have a larger width in the direction of the longitudinal axis (Z) of the flow channel, and two pairs of coils each Contains a smaller width in the direction of the longitudinal flow channel axis (Z), each of which is closer to the electrodes (2, 3) and separate from the coils or coil groups of the former Pair lie at the ends of an area that further wraps around the flow channel section (Fig. 10). 13. Inductive flow meter according to claim 9, characterized in that the magnetic field generation system comprises a pair of coils or coil groups, which are diametrically opposed to one another via the flow channel section (1) and loop around a smaller area of the circumference of the flow channel section (1) between the measuring electrodes (2, 3), and a further pair of coils or coil groups, which loop around a larger area of the circumference of the flow channel section (1) between the measuring electrodes (2, 3) (Fig. 11). 14. Inductive flow meter according to one of claims 10 to 13, characterized in that the pair of coils or coil groups which cover the circumferential area of the Loop the flow channel section (1) between the measuring electrodes (2, 3) with a smaller circumferential angle, is acted upon by a different excitation current than the pair of coils or coil groups which cover the circumference of the flow channel section (1) between the measuring electrodes (2, 3 ) wrap around with a larger wrap angle or whose area wraps around the flow channel section with a larger wrap angle. 15. Inductive flow meter according to one of claims 9 to 14, characterized in that the magnetic field generation system has at least one pair of coils or coil groups opposite one another across the flow channel section (1), the distance from the inner surface of the flow channel increasing with increasing proximity to the measuring electrodes (2, 3) steadily or gradually. 16. Inductive flow meter according to one of claims 9 to 15, characterized in that the coil arrangements of the magnetic field generation system interact with auxiliary pole shoe parts (h) which form the channel cross-sectional plane of the Electrodes (2, 3) are located symmetrically, in particular are strip-shaped or lance-shaped or leaf-shaped and extend over a region between the flow channel section (1) and the coil arrangements in the direction of the electrodes (2, 3) (Fig. 12). 17. Inductive flow meter according to claim 9, characterized in that the magnetic field generation system contains pole shoes (22, 23) diametrically opposed to one another across the flow channel section (1) and has at least one magnetic closing circuit (20) which is acted upon by one or respectively one excitation winding (21), the pole shoes each containing pole shoe parts measured in the direction of the flow channel longitudinal axis (Z) of greater width and in the direction of the peripheral region between the measuring electrodes (2, 3) smaller wrap angle and in the circumferential direction in the measuring electrodes (2, 3) closer areas lateral pole piece parts (24; 25), from which magnetic fields with less effective intensity than those of the former pole shoes emanate and / or in Direction of the flow channel longitudinal axis (Z) have a smaller width.