MAGNETIC-INDUCTIVE FLOW METER AND MEASURING POINT

Abstract

A magnetic-inductive flow meter for measuring flow velocity or volume flow rate of a medium includes: a measuring tube having a first cross-section and a middle segment, which has a second cross-section, between inlet side and outlet side end planes, wherein the first cross-sectional area is greater than the second cross-sectional area; a pole shoe or a saddle coil, which subtends the measuring tube with a maximum central angle; and an electrode system having two electrode pairs, wherein a central angle in the second cross-section defines a minimum circular sector in which the electrodes located on a side of the measuring tube are distributed, wherein the electrode pairs are arranged in the middle segment such that the central angle and the maximum central angle are adapted relative to one another such that the flow meter is insensitive to departures from a rotationally symmetric flow.

Claims

1-18. (canceled)

19. A magnetic-inductive flow meter for measuring flow velocity or volume flow rate of a medium, the flow meter comprising: a measuring tube having a first cross-sectional area and configured to convey the medium in a longitudinal direction defined by a measuring tube axis, wherein: the measuring tube has an inlet side end plane and an outlet side end plane, which bound the measuring tube in the longitudinal direction; the measuring tube includes between inlet side and outlet side end planes a middle segment, which has a second cross-sectional area, wherein the first cross-sectional area is greater than the second cross-sectional area; a vertical longitudinal plane divides the measuring tube into a first side and a second side; and the measuring tube includes a fluid conveying passageway, which includes a wall bounded by a liner; at least one magnetic field generator configured to generate a magnetic field in the medium extending essentially perpendicularly to the longitudinal direction, wherein the at least one magnetic field generator includes a pole shoe or a saddle coil, and wherein the pole shoe or the saddle coil in the second cross-sectional area of the measuring tube subtends the fluid conveying passageway with a maximum central angle; and an electrode system including at least two electrode pairs, which are adapted to register a voltage induced perpendicularly to the magnetic field and to the longitudinal direction between the electrode pairs, wherein: a first electrode of each electrode pair is disposed on the first side of the measuring tube; a second electrode of each electrode pair is disposed on the second side of the measuring tube; a central angle in the second cross-sectional area of the measuring tube defines a minimum circular sector in which electrodes of the at least two electrode pairs that are disposed on a same side of the measuring tube are distributed; and the at least two electrode pairs are arranged in the middle segment, wherein the central angle and the maximum central angle are configured relative to each other such that the flow meter is to a degree insensitive to departures from a rotationally symmetric flow such that the flow meter in a test measurement has a measurement error of flow velocity defined by ${\Delta }_u=.Math.\frac{u_{va}-u_S}{u_{va}}.Math.$  and/or a measurement error of volume flow rate defined by ${\Delta }_{\stackrel{.}{V}}=.Math.\frac{{\stackrel{.}{V}}_{va}-\stackrel{.}{V}s}{{\stackrel{.}{V}}_{va}}.Math.$  less than 1.0%, wherein: u.sub.va and u.sub.S are flow velocities, and {dot over (V)}.sub.va and {dot over (V)}.sub.S are volume flow rates of the medium; the flow velocity u.sub.va and the volume flow rate {dot over (V)}.sub.va form reference values; and the flow velocity u.sub.Sand/or the volume flow rate {dot over (V)}.sub.S are determined in the case of a rotationally unsymmetric flow.

20. The flow meter of claim 19, further comprising at least one disturbance source disposed at the inlet side end plane and configured to produce the rotationally unsymmetric flow for the test measurement.

21. The flow meter of claim 20, wherein the at least one disturbance source comprises a diaphragm or a 90° elbow, wherein: 50% of the cross-sectional area of the measuring tube is covered by the diaphragm; the diaphragm has a chord, which limits the diaphragm toward the tube; the diaphragm is disposed in a first diaphragm orientation or a second diaphragm orientation; in the first diaphragm orientation, the chord is oriented perpendicular to the magnetic field, and in the second diaphragm orientation, the chord is oriented parallel with the magnetic field; the 90° elbow assumes a first elbow orientation or a second elbow orientation; the first elbow orientation is defined by a pipe axis extending perpendicular to the magnetic field and to the longitudinal direction of the measuring tube, and the second elbow orientation is defined by the pipe axis extending parallel with the magnetic field and perpendicular to the longitudinal direction of the measuring tube.

22. The flow meter of claim 19, wherein the disturbance is provided with separation 0-DN at the inlet side end plane.

23. The flow meter of claim 19, wherein an insensitivity to a rotationally unsymmetric flow profile is enabled at a Reynolds number of the medium in the measuring tube greater than or equal to 100,000, especially greater than or equal to 50,000 and preferably greater than or equal to 10,000.

24. The flow meter of claim 19, wherein an insensitivity to a rotationally unsymmetric flow profile is enabled at a Reynolds number of the medium in the measuring tube greater than or equal to 10,000.

25. The flow meter of claim 19, wherein the at least two electrode pairs of the flow meter include two or three electrode pairs.

26. The flow meter of claim 19, wherein at least two electrodes of the at least two electrode pairs disposed, in each case, on one side of the measuring tube relative to the vertical measuring tube longitudinal plane are connected electrically.

27. The flow meter of claim 19, wherein the central angle is greater than or equal to 30° and less than or equal to 60°.

28. The flow meter of claim 19, wherein the maximum central angle is greater than or equal to 50° and less than or equal to 90°.

29. The flow meter of claim 19, wherein the electrodes of the at least two electrode pairs are arranged axisymmetrically to the vertical measuring tube longitudinal plane.

30. The flow meter of claim 19, wherein two neighboring electrodes of the at least two electrode pairs disposed on one side of the measuring tube are spaced by a near central angle defined by δ=α/(N−1) in the cross-sectional area of the measuring tube, wherein N is a natural number corresponds to the number of electrode pairs, and α is the central angle.

31. A measuring point for determining a flow profile independent flow velocity or volume flow rate of a medium, the measuring point comprising: a magnetic-inductive flow meter for measuring flow velocity or volume flow rate of the medium, the flow meter comprising: a measuring tube configured to convey the medium in a longitudinal direction defined by a measuring tube axis, wherein the measuring tube has an inlet side end plane and an outlet side end plane, which bound the measuring tube in the longitudinal direction, wherein the measuring tube includes a passageway, which includes a wall bounded by a liner; at least one magnetic field generator configured to generate a magnetic field in the medium extending essentially perpendicular to the longitudinal direction, wherein the magnetic field generator includes a pole shoe or a saddle coil, and wherein the pole shoe or the saddle coil in a cross-sectional area of the measuring tube subtends the measuring tube or the passageway with a maximum central angle; and an electrode system including at least two electrode pairs, each configured to detect a voltage induced in the medium perpendicular to the magnetic field and to the longitudinal direction, wherein: a vertical measuring tube longitudinal plane divides the measuring tube into a first side and a second side; in each case, a first electrode of an electrode pair of the at least two electrode pairs is disposed on the first side of the measuring tube; in each case, a second electrode of the electrode pair is disposed on the second side; and a central angle in the cross-sectional area of the measuring tube defines a minimum circular sector in which each electrode disposed on either the first or second side of the measuring tube are distributed, wherein the central angle and the maximum central angle are configured relative to each other such that the flow meter is insensitive to departures from a rotationally symmetric flow of the medium because of a disturbance source applied with a separation of 0-DN at the inlet side end plane, and wherein the flow meter has a measurement error of flow velocity defined by ${\Delta }_u=.Math.\frac{u_{va}-u_S}{u_{va}}.Math.$  and/or a measurement error of volume flow rate defined by ${\Delta }_{\stackrel{.}{V}}=.Math.\frac{{\stackrel{.}{V}}_{va}-\stackrel{.}{V}s}{{\stackrel{.}{V}}_{va}}.Math.$  less than 1.0%, wherein: u.sub.va and u.sub.S are flow velocities, and {dot over (V)}.sub.va and {dot over (V)}.sub.S are volume flow rates of the medium; the flow velocity u.sub.va and the volume flow rate {dot over (V)}.sub.va are determined in the case of a flow of the medium with fully developed flow profile; and the flow velocity u.sub.S and/or the volume flow rate V.sub.S are determined in the case of the applied disturbance source.

32. The measuring point of claim 31, wherein the wherein the central angle is greater than or equal to 30° and less than or equal to 60°, and wherein the maximum central angle is greater than or equal to 50° and less than or equal to 90°.

33. The measuring point of claim 31, wherein the at least two electrode pairs of the flow meter of the measuring point include two or three electrode pairs.

34. The measuring point of claim 31, wherein at least two electrodes of the at least two electrode pairs disposed on a side of the measuring tube relative to the vertical measuring tube longitudinal plane are connected electrically.

35. The measuring point of claim 34, wherein the at least two electrodes are connected electrically by a stamped-bent part.

36. The measuring point of claim 31, wherein the measuring tube includes first and second cross-sectional areas, wherein the measuring tube includes, between the inlet side and outlet side end planes, a middle segment, which includes the second cross-sectional area, and wherein the at least two electrode pairs are disposed in the middle segment.

37. The measuring point of claim 31, wherein the disturbance source comprises a 90° elbow and/or a diaphragm and/or a valve and/or a pump and/or a T-piece and/or a double arch of two 90° elbows set one after the other.

Description

[0052] The invention will now be explained in greater detail based on the appended drawing, the figures of which show as follows:

[0053] FIG. 1 a schematic view of the cross-section of a magnetic-inductive flow meter according to the state of the art;

[0054] FIG. 2 a schematic view of the longitudinal section of a magnetic-inductive flow meter;

[0055] FIG. 3 a schematic view of the cross-section of a magnetic-inductive flow meter of the invention;

[0056] FIG. 4 a schematic view of the longitudinal section of a magnetic-inductive flow meter of the invention;

[0057] FIG. 5 a schematic view of different disturbance sources and measuring points with disturbance sources; and

[0058] FIG. 6 a graph of measurement error as a function of central angles α and β for a 50-DN measuring tube.

[0059] FIG. 1 shows a magnetic-inductive flowmeter known in the state of the art. The construction and the measuring principle of a magnetic-inductive flowmeter are basically known. An electrically conductive medium is led through the measuring tube (1). A magnetic field producing means (7) is arranged such that the magnetic field lines extend perpendicularly to a longitudinal direction defined by the measuring tube axis (13). Suited as magnetic field producing means (7) is preferably a saddle coil or a pole shoe (26) with superimposed coil and coil core. In the case of applied magnetic field, there arises in the measuring tube (1) a flow dependent potential distribution, which is sensed with two electrodes (3, 4) applied at the inner surface of the measuring tube (1). As a rule, these are arranged diametrically opposite one another and form an electrode axis, which extends perpendicularly to the magnetic field lines and to the longitudinal axis of the tube. Based on the measured voltage and taking into consideration the magnetic flux density, flow velocity can be determined and further taking into consideration the tube cross-sectional area, volume flow of the medium can be determined. In order to avoid the shorting of the measurement voltage on the electrodes (3, 4) through the tube (8), the inner surface is lined with an insulating material, for example, in the form of a plastic liner (2).

[0060] The magnetic field formed by a magnetic field producing means, for example, an electromagnet, is produced by a direct current of alternating polarity clocked by means of an operating unit. This assures a stable zero-point and makes the measuring insensitive to influences of electrochemical disturbances. A measuring unit reads out the voltage on the electrodes (3, 4) and outputs flow velocity and/or volume flow of the medium calculated by means of an evaluation unit. Usual magnetic-inductive flowmeters have supplementally to the electrodes (3, 4) two other electrodes (5, 6). On the one hand, a fill level monitoring electrode (5) mounted optimally at the highest point in the tube (8) serves to detect a partial filling of the measuring tube (1), to forward this information to the user and/or the fill level is taken into consideration for the ascertaining of volume flow. Furthermore, a reference electrode (6), which is usually mounted diametrically opposite the fill level monitoring electrode (5), serves to assure an effective grounding of the medium.

[0061] A magnetic-inductive flowmeter includes an inlet side end plane (10) and an outlet side end plane (11). The arrow in FIG. 2 indicates the flow direction of the medium. A 90° elbow (90° R) or a diaphragm (B) applied at the inlet side end plane (10) acts on the flow profile of the medium, such that a rotationally unsymmetric flow profile forms in the cross-section (12) of the measuring tube (1).

[0062] FIG. 3 shows a cross-section of a middle segment of the magnetic-inductive flow meter of the invention. A magnetic field producing means (7) is placed such that the magnetic field lines extend perpendicularly to a longitudinal direction defined by the measuring tube axis (13). Suited as magnetic field producing means (7) is preferably a saddle coil or a pole shoe (14) with superimposed coil and coil core. In the presence of an applied magnetic field, there arises in the measuring tube (1) a flow dependent potential distribution, which is tapped with an electrode system (17). In FIG. 3, the electrode system (17) includes three electrodes placed on a first side (I) and three electrodes placed on a second side (II). A first electrode (18) of the first side (I) and a second electrode (19) of the second end (II) form an electrode pair. Based on the measured voltage and taking into consideration the magnetic flux density, flow velocity and, taking into consideration the tube cross-sectional area, volume flow rate of the medium can be determined. In order to avoid the shorting of the measurement voltage on the electrodes through the tube (8), the inner surface is lined with an insulating material, for example, in the form of a plastic liner (2). The magnetic field produced by a magnetic field producing means, for example, an electromagnet, is a direct current of alternating polarity clocked by means of an operating unit. This assures a stable zero-point and makes the measuring insensitive to influences of electrochemical disturbances. A measuring unit takes the voltage across the electrode system (17) and outputs on a display unit flow velocity and/or volume flow rate of the medium calculated by means of an evaluation unit.

[0063] The longitudinal section of a magnetic-inductive flow meter of the invention is shown in FIG. 4. The flow meter includes a fluid conveying passageway (22) of constricted diameter, wherein the fluid conveying passageway (22) has inlet and outlet regions (27, 28) having a first cross-section (37) and wherein the fluid conveying passageway (22) has a middle segment (29), which is located between the inlet and outlet regions (27, 28) and which has a second cross-section (38), wherein in the middle segment (29) of the fluid conveying passageway (22) an electrode system (26) is present, composed, in each case, of two electrodes arranged on opposing sides of the measuring tube. FIG. 4 shows a measurement system (24) of known form. It includes, among other things, two magnet coils (25) for producing a magnetic field.

[0064] These lie diametrically opposite one another on the passageway (22). Furthermore, the measurement system includes an electrode system (26) composed of four electrodes for the tapping the voltage induced by the magnet system. The passageway (22) is bounded by a wall (23). Special about the construction of FIG. 4 is that the wall (23) is simultaneously also the seating material for the measurement system (24), thus, for the magnetic field producing means and for the electrode system (26). The measurement system (24) and the magnetic field producing means can, however, also be arranged outside of the tube. Especially, the passageway forming wall (23) is formed of a cast material. The passageway forming wall (23) can supplementally to the liner (2) be introduced into, or applied against, the measuring tube (1) or comprise the liner (2).

[0065] In the first step, the central angles α and β are so adapted that the measurement error of flow velocity in test measurements with a single disturbance is minimum. In such case, the disturbance is generated by a diaphragm or a 90° elbow (90° R) (see FIG. 5). The diaphragm covers, in such case, 50% of the tube cross-section (12) and has a chord, which bounds the diaphragm toward the tube. The diaphragm assumes a first diaphragm orientation (B1) or a second diaphragm orientation (B2), which especially are rotated by 90° relative to one another. In such case, the chord in the case of the first diaphragm orientation (B1) is perpendicular to the magnetic field and to the vertical longitudinal plane and in the case of the second diaphragm orientation (B2) in parallel with the magnetic field and with the vertical longitudinal plane. The first diaphragm orientation (B1) and the second diaphragm orientation (B2) of a diaphragm are shown schematically in FIG. 5. The black filled circular segment represents, in such case, the area, which blocks a part of the cross-sectional area of the measuring tube. In the test measurement, the diaphragm (B) is placed at a distance of 0-DN from the inlet side end plane (10). Alternatively, a 90° elbow (90° R) is placed at the entrance to the inlet side end plane (10) at a distance of 0-DN, wherein the 90° elbow (90° R) assumes a first elbow orientation (R1) or a second elbow orientation (R2), which especially are rotated by 90° relative to one another. The first elbow orientation (R1) and the second elbow orientation (R2) of a 90° elbow (90° R) are schematically shown in FIG. 5. In the case of the first elbow orientation (R1), the tube axis (42) extends in parallel with the abscissa axis (41) of the flow meter. The selecting of the central angles α and β is preferably performed for both disturbances in both orientations.

[0066] In the second step, that central angle pair is determined, whose maximum measurement error for all performed test measurements is minimum.

[0067] FIG. 6 shows, by way of example, simulated measurement error (Z axis) for a 50-DN middle segment as a function of the central angle α (Y axis) and the central angle β (X axis). Based on this, the minimum measurement error for a specific disturbance, in this case, an elbow (90° R) optimized as regards first and second elbow orientations (R1, R2), is ascertained. In such case, the first elbow orientation (R1) is distinguished by a measuring tube axis (13) extending perpendicularly to the magnetic field and to the longitudinal direction and the second elbow orientation (R2) by a measuring tube axis (13) extending in parallel with the magnetic field and perpendicularly to the longitudinal direction (see FIG. 5). This procedure is repeated for all above mentioned disturbances, wherein, in the last step, that central angle pair is ascertained, which has the smallest measurement error with reference to all test measurements. The desired accuracy can only be achieved for certain combinations of the central angles α and β. The mere optimizing of the electrode distribution or the mere adapting of the pole shoes leads, thus, not to reducing the flow profile dependence, or the measurement error. The values for the central angles α and β are varied until the resulting measurement error for all test measurements is less than 0.5%, preferably less than 0.2%.

[0068] Based on the above described optimizing method, a magnetic-inductive flow meter with three electrode pairs, a 50-DN middle segment and a medium having a flow velocity of 1 m/s has a measurement error of 0.05% in the case of an installed diaphragm (B) with diaphragm orientation (B1) and a measurement error of 0.05% in the case of an installed diaphragm (B) with diaphragm orientation (B2).

[0069] Based on the above described optimizing method, a magnetic-inductive flow meter with three electrode pairs, a 50-DN middle segment and a medium having a flow velocity of 1 m/s has a measurement error of 0.05% in the case of a 90° elbow (90° R) installed with elbow orientation (R1) and a measurement error of 0.5% in the case of a 90° elbow (90° E) installed with elbow orientation (R2).

[0070] Based on the above described optimizing method, a magnetic-inductive flow meter with three electrode pairs, a 300-DN middle segment and a medium having a flow velocity of 1 m/s has a measurement error of 0.1% in the case of a diaphragm (B) installed with diaphragm orientation (B1) and a measurement error of 0.1% in the case of a diaphragm (B) installed with diaphragm orientation (B2).

[0071] Based on the above described optimizing method, a magnetic-inductive flow meter with three electrode pairs, a 300-DN middle segment and a medium having a flow velocity of 1 m/s has a measurement error of 0.1% in the case of a 90° elbow (90° R) installed with elbow orientation (R1) and a measurement error of 0.1% in the case of a 90° elbow (90° R) installed with elbow orientation (R2).

[0072] Based on the above described optimizing method, a magnetic-inductive flow meter with three electrode pairs, a 500-DN middle segment and a medium having a flow velocity of 1 m/s has a measurement error of 0.1% in the case of a diaphragm (B) installed with diaphragm orientation (B1) and a measurement error of 0.1% in the case of a diaphragm (B) installed with diaphragm orientation (B2).

[0073] Based on the above described optimizing method, a magnetic-inductive flow meter with three electrode pairs, a 500-DN middle segment and a medium having a flow velocity of 1 m/s has a measurement error of 0.1% in the case of a 90° elbow (90° R) installed with elbow orientation (R1) and a measurement error of 0.1% in the case of a 90° elbow (90° R) installed with elbow orientation (R2).

[0074] In all of the above simulations, the DN data is for the nominal diameter, or the inner diameter, of the fluid conveying passageway in the region of the middle segment.

List of Reference Characters

[0075] 1 measuring tube

[0076] 2 liner

[0077] 3 first electrode

[0078] 4 second electrode

[0079] 5 fill level monitoring electrode

[0080] 6 reference electrode

[0081] 7 magnetic field producing means

[0082] 8 tube

[0083] 9 measuring, operating and/or evaluation unit

[0084] 10 inlet side end plane

[0085] 11 outlet side end plane

[0086] 12 cross-section

[0087] 13 measuring tube axis in the longitudinal direction

[0088] 14 pole shoe

[0089] 15 abscissa

[0090] 16 vertical measuring tube longitudinal plane

[0091] 17 electrode system

[0092] 18 first electrode of an electrode pair

[0093] 19 second electrode of an electrode pair

[0094] 20 center

[0095] 21 wall

[0096] 22 passageway

[0097] 23 wall

[0098] 24 measurement system

[0099] 25 magnet coil

[0100] 26 electrode system

[0101] 27 inlet region

[0102] 28 outlet region

[0103] 29 middle segment

[0104] 30 flange

[0105] 31 pole shoe

[0106] 32 field return piece of sheet metal

[0107] 33 pipe

[0108] 34 measuring and/or evaluation unit

[0109] 35 magnetic field producing means

[0110] 37 first cross-section

[0111] 38 second cross-section

[0112] 40 vertical measuring tube longitudinal plane

[0113] 41 abscissa

[0114] 42 tube axis

[0115] 43 magnetic-inductive flow meter