MAGNETIC-INDUCTIVE FLOW METER

Description

[0001] The invention relates to a method for operating a magnetic-inductive flowmeter according to the preamble of claim 1.

[0002] Magnetic-inductive flowmeters, whose operation is based on the principle of electromagnetic induction (= Faraday induction), have been known for many years and are used extensively in industrial measurement technology. According to the law of induction, an electric field strength perpendicular to the flow direction and perpendicular to the magnetic field is created in a flowing medium that carries charge carriers and flows through a magnetic field. This law of induction is exploited in magnetic-inductive flowmeters by using a magnetic field generating device, which usually has two energized magnetic coils, to generate a magnetic field that is guided at least partially through the measuring tube. The generated magnetic field has at least one component that is perpendicular to the flow direction.Within the magnetic field, each volume element of the flowing medium moving through the magnetic field and containing a certain number of charge carriers contributes, with the field strength generated in this volume element, to a measuring voltage that can be tapped off via the electrodes.

[0003] Since the induced voltage tapped across the electrodes is proportional to the flow velocity of the medium averaged over the cross-section of the measuring tube, the volume flow can be determined directly from the measured voltage, assuming the diameter of the measuring tube is known. The only prerequisite for using a magnetic-inductive flowmeter is a minimum conductivity of the medium. Furthermore, it must be ensured that the measuring tube is filled with the medium at least enough so that the level is above the measuring electrodes.

[0004] Such measuring devices are well known, for example from the German patent specifications DE 10 2007 004 827 B4 and DE 10 2007 004 826 B4, and are essentially characterized in that the magnetic coils and the electrodes are arranged directly on or in the wall of the measuring tube.

[0005] WO 2005 / 057140 A1 discloses a magnetic-inductive flow sensor in which the measuring tube comprises a support tube and a liner made of an insulating material housed in a lumen of the support tube. A support body is embedded in the liner for stabilization.

[0006] To prevent a short circuit between the two measuring electrodes, the measuring tube is made of a non-conductive material, typically PFA, PP, or PTFE. A challenge arose when installing the measuring electrodes in this plastic tube: securing them against rotation, as the frictional force between the plastic and the electrode head is usually insufficient to tighten a nut. Therefore, it was necessary to hold the electrode in place while screwing on the nut, usually with another tool.

[0007] Various mounting and arrangement options for the electrodes of a magnetic-inductive flowmeter are known in the prior art. DE 102013 103 970 A1 discloses a multi-part electrode anchor for attaching a measuring electrode to the measuring tube, even at high medium pressures above 50 bar. DE 10 2004 063 617 A1 discloses arranging the measuring electrodes such that the effective surface for tapping the induced voltage is not the end face of a pin-shaped electrode, for example, but rather its side surface, thus achieving a larger effective electrode surface for tapping the induced voltage.

[0008] The object of the invention is to facilitate the assembly of a magnetic-inductive flowmeter and in particular the installation of the measuring electrodes in the measuring tube.

[0009] The object is achieved according to the invention by a magnetic-inductive flowmeter having the features of claim 1. Advantageous embodiments of the invention are specified in the subclaims.

[0010] According to the invention, an insert part is arranged opposite one another on the outside of the measuring tube. The insert parts each have a through-bore through which the two measuring electrodes extend. The measuring electrodes have a non-circular cross-section, at least in sections, and the said through-bores in the two insert parts have a complementary contour. Finally, an external thread is provided at least partially on the measuring electrodes, and a nut is screwed onto each of these external threads, so that the measuring electrodes and the associated insert parts are firmly connected to the measuring tube.

[0011] An advantageous development of the invention provides that the measuring tube has a flat recess on its outer side, opposite each other. These recesses are positioned on the measuring tube so that the two measuring electrodes pass through them orthogonally. Furthermore, an insert part is arranged in each of the recesses.

[0012] A further advantageous development of the invention provides that the insert parts arranged in the recesses each have a base surface complementary to the contour of the recess. As a result, two stops are formed at least in the longitudinal direction of the measuring tube, by which the insert part arranged in the recess is fixed axially relative to the longitudinal direction of the measuring tube.

[0013] Advantageously, the flat recesses and, accordingly, the base surfaces of the inserts each have a rectangular contour, but preferably they have at least an angle of less than 90°. In this way, the circumference and thus the contacting stop surfaces can be increased without having to increase the base surfaces of the recesses or the inserts.

[0014] A further advantageous development of the invention provides that a substantially cylindrical structure is arranged on the base surfaces of the insert parts, in the center of which structure the through-bore is located and whose circumference has at least one outwardly directed extension. This design is particularly advantageous if a disk is arranged between the insert part and the nut, which disk also has a through-bore complementary to the non-circular cross-section of the measuring electrodes, through which the two measuring electrodes each run, and which also has at least one outwardly directed extension complementary to the circumference of the cylindrical structure of the insert part. If a disk of a complementary design engages in the outwardly directed extension, this offers the advantage that even greater torques can then be transmitted.Further outward extensions would be advantageous to better transfer the torque from the cylindrical structure to the base of the insert.

[0015] The term "disk" is to be understood in the sense of the invention to also include a turning-milling part with a somewhat thicker or higher design than a typical disk.

[0016] As an alternative to the outwardly directed extension, the disc can also have an edge-shaped contour, in particular a square or hexagonal configuration. Accordingly, the insert parts also have a complementary edge-shaped contour, in particular a square or hexagonal one.

[0017] In order to electrically contact the electrodes, ie to tap the induced voltage, it is preferably provided to arrange a disc-shaped plug contact between the insert part and the nut.

[0018] A further advantageous development provides for a spring element to be arranged between the insert and the nut. The spring element, preferably designed as a disc spring, is preloaded when the nut is screwed on. This defined preload ensures that the surface pressure required for a tight seal between the electrode head and the plastic measuring tube is maintained on the inside of the measuring tube.

[0019] A further advantageous development provides that the external thread of the measuring electrodes is interrupted in the circumferential direction by at least one recessed facet. This easily achieves the non-circular cross-section of the measuring electrodes required for the invention.

[0020] The core of the invention is to transfer the torque generated when the nut is screwed on to the measuring tube in several intermediate steps. First, the torque is transferred from the nut to the measuring electrode, which, due to its non-circular cross-section, passes it on to the insert part with its through-bore complementary to the cross-section of the measuring electrode. The torque is finally transferred to the measuring tube via the insert part. If, advantageously, the insert parts arranged in the recesses each have a base area complementary to the contour of the recess and the insert part is axially fixed at least in the longitudinal direction of the measuring tube by the two stops, the torque is absorbed by the measuring tube via said stops without it spinning.Without these two stops, the insert would have to be manually held in place while tightening the nut. In both cases, the torque acting on the measuring tube is significantly reduced due to the insert's larger base area compared to the electrode cross-section, and the overall assembly effort is reduced.

[0021] This eliminates the need to hold the electrode above the nut during assembly, thus preventing it from twisting. The electrode pins can now be significantly shorter and, for example, be virtually flush with the nut.

[0022] The invention is explained in more detail below using exemplary embodiments with reference to the drawings.

[0023] They show schematically: Figure 1 shows a first embodiment of a magnetic-inductive flowmeter with the anti-twist device according to the invention in an exploded view; Figure 2 shows the magnetic-inductive flowmeter from Fig. 1 in side view without the anti-twist device according to the invention; Figure 3 the anti-twist device according to the invention from Fig. 1 in sectional view; Figure 4 shows a second embodiment of a magnetic-inductive flowmeter with the anti-twist device according to the invention in an exploded view; Figure 5 shows a third embodiment of a magnetic-inductive flowmeter with the anti-twist device according to the invention in an exploded view and Figure 6 shows the anti-twist device according to the invention from Fig. 5 in sectional view.

[0024] In the following description of the preferred embodiments, like reference numerals designate like or comparable components.

[0025] In Figure 1A magnetic-inductive flowmeter 1 is shown, with an unclad measuring tube 2, the two flanges 7 for connection to a pipeline, two threaded pins 8, onto which the magnetic field generating device required for flow measurement is mounted, and one of two pin-like measuring electrodes 3. The structure required for the anti-twist device according to the invention and for fixing the electrode 3 to the measuring tube 2 is shown in an exploded view. Even if in Fig. 1 only one measuring electrode 3 is shown with the anti-twist device, this of course also applies to the second measuring electrode hidden in the drawing on the opposite side of the measuring tube 2.

[0026] The basis of the anti-twist device is a flat recess 10 on the outside of the measuring tube 2, although a design without a recess 10 is also conceivable (see Fig. 4). This recess 10 is positioned on the measuring tube 2 such that it is penetrated orthogonally by the measuring electrode 3. An insert part 20 is inserted into the recess 10, the base area of ​​which has a contour that is complementary to the contour of the recess. The recess 10 creates two stops 11, at least in the longitudinal direction of the measuring tube 2, by means of which stops the insert part 20 arranged in the recess 10 is fixed axially to the longitudinal direction of the measuring tube 2. Depending on how deep the recess 10 is, stops can also form in the transverse direction. Advantageously, the contour of the recess 10 is not rectangular, but at least one angle is less than 90°. In this way, the circumference and thus the contacting stop surfaces can be enlarged without having to enlarge the base area of ​​the recess 10 and the insert part 20.

[0027] The insert part 20 has a through hole 22 which is Fig. 1 can only be partially seen. The measuring electrode 3 runs through this through-hole 22 when mounted. The measuring electrode 3 must have a non-circular cross-section in the area of ​​the through-hole 22, which Fig. 1 was realized in that an external thread of the measuring electrode 3 is interrupted in the circumferential direction by a recessed facet 6. Corresponding to the non-circular cross-section of the measuring electrode 3, the through-bore 22 in the insert part 20 has a complementary contour.

[0028] The insert part 20 is further characterized in that a substantially cylindrical structure 23 is mounted on the base surface 21. The through-bore 22 is located at the center of this structure 23. The periphery of the structure 23 is characterized by three outwardly directed extensions 24, one of which is slightly larger than the other two.

[0029] A disc 40 is arranged in this special contour with the three extensions 24. This disc also has a through-bore 41 complementary to the non-circular cross-section of the measuring electrode 3 and also has three outwardly directed extensions complementary to the contour of the cylindrical structure 23 of the insert part 20. This allows even greater torques to be transmitted.

[0030] A spring element 5 is placed on the disc 40 on the measuring electrode 3. The spring element 5, in this case designed as a disc spring, ensures, by means of a certain preload, that the surface pressure required for the tightness between the electrode head and the plastic measuring tube is guaranteed inside the measuring tube 2.

[0031] In order to electrically contact the measuring electrode 3, ie to tap the induced voltage, a disc-shaped plug contact 4 is placed on the measuring electrode 3.

[0032] Finally, a nut 30 is screwed onto the external thread of the measuring electrode 3 so that the measuring electrodes 3 and the intermediate elements insert part 20, disc 40, spring element 5 and plug contact 4 are firmly connected to the measuring tube 3.

[0033] As the nut 30 is screwed on, the resulting torque is transferred to the measuring tube 3 in several intermediate steps. First, the torque is transferred from the nut 30 to the measuring electrode 3, which, due to its non-circular cross-section, passes it on to the insert part 20 with its through-bore 22 complementary to the cross-section of the measuring electrode 3. Due to the disk 40 and the engagement of the three outwardly directed extensions in the corresponding counterparts of the cylindrical structure 23 of the insert part 20, the torque is transmitted not only via the through-bore 22, but also via these outwardly directed extensions 24. Since the insert part 20 is fixed at least in the longitudinal direction of the measuring tube 3 by the two stops 11, the torque is finally transferred to the measuring tube 3.Due to the base area 21 of the insert part 20 being now larger than the electrode cross-section, the torque acting on the measuring tube 3 is significantly reduced and can be absorbed by the measuring tube 3 by the stops 11 without it spinning.

[0034] In Figure 2 the magnetic-inductive flowmeter 1 according to the invention, with measuring tube 2, the two flanges 7, the electrode 3 in the center in the flat recess 10 and the two radially projecting threaded pins 8 for the magnetic field generating device, is shown in side view without the anti-twist device according to the invention.

[0035] In Figure 3 The anti-twist device according to the invention is shown in a sectional view, so that it is clear how the Fig. 1The exploded view shows the assembled structure. It shows how the measuring electrode 3 extends through the measuring tube 2, how the insert part 20, acting as a foundation for the entire structure, is inserted into the flat recess 10 on the top side of the measuring tube 2, and how the individual elements, disc 40, spring element 5, plug contact 4, and nut 40, are arranged relative to one another within the cylindrical structure 23 of the insert part 20.

[0036] The Figure 4 shows an embodiment without recess 10 in the measuring tube 2. Everything else is identical, so that to avoid repetition, the description of the Fig. 1 is referred to.

[0037] The Figures 5 and 6show a further embodiment of the invention. The essential structure corresponds to that of the previous figures, so that reference is made to these to avoid repetition. The difference is that the recess 10 and the base surface of the insert part 20 do not have complementary contours. As a result, as can be seen from Fig. 6 As can be seen, no stops 11 are formed in the longitudinal direction of the measuring tube 2. While tightening the nut 30, the insert part 20 would then have to be secured manually if necessary. For this purpose, the insert part 20 advantageously has a circumferential edge through which the manual fixation can be performed.

[0038] In both embodiments, the torque acting on the measuring tube 2 is significantly reduced due to the base area of ​​the insert part 20 being now larger than the electrode cross-section, and the measuring electrodes 3 can be easily mounted in the measuring tube 2 despite their compact design. List of reference symbols

[0039] 1 Electromagnetic flowmeter 2 Measuring tube 3 Measuring electrode 4 Plug-in contact 5 Spring element 6 Facet 7 Flange 8 Threaded pin 10 Flat recess 11 Stop 20 Insert part 21 Base 22 Through hole 23 Cylindrical structure 24 Outward-facing extension 30 Nut 40 Washer 41 Through hole

Claims

1. Magnetic-inductive flowmeter for measuring the flow of a flowing, conductive medium, comprising a measuring tube (2) made of a non-conductive material, with a magnetic field generating device for generating a magnetic field passing through the measuring tube (2) perpendicularly to the longitudinal axis of the measuring tube (2) and with two pin-shaped measuring electrodes (3) for tapping a measuring voltage induced in the flowing medium, the measuring electrodes (3) being arranged along a connecting line running perpendicularly to the longitudinal axis of the measuring tube (2) and perpendicularly to the magnetic field direction, characterized in that an insert part (20) is arranged on each side of the measuring tube (2) on the outer face, the insert parts being opposite each other, the insert parts (20) each having a through-hole (22) through which the two measuring electrodes (3) run, the measuring electrodes (3) having a non-circular cross-section at least in portions and the through-holes (12) of the two insert parts (20) having a contour complementary thereto and the pin-shaped measuring electrodes (3) at least partially having an external thread and a nut (30) being screwed onto each of them, by means of which the measuring electrodes (3) and the associated insert parts (20) are firmly connected to the measuring tube (2).

2. Magnetic-inductive flowmeter according to claim 1, characterized in that the measuring tube (2) has a flat recess (10) on each side on its outer face, which recesses are opposite each other and are penetrated orthogonally by the two measuring electrodes (3), and in that an insert part (20) is arranged in each of the recesses (10).

3. Magnetic-inductive flowmeter according to claim 2, characterized in that an insert part (20) with a base surface (21) complementary to the contour of the particular recess (10) is arranged in each of the recesses (10), so that two stops (11) are formed at least in the longitudinal direction of the measuring tube (2), by means of which the insert parts (20) are fixed axially to the longitudinal direction of the measuring tube (2).

4. Magnetic-inductive flowmeter according to claim 3, characterized in that the flat recesses (10) and correspondingly the base surfaces (21) of the insert parts (20) each have a rectangular contour.

5. Magnetic-inductive flowmeter according to claim 3, characterized in that the flat recesses (10) and correspondingly the base surfaces (21) of the insert parts (20) each have a contour with at least one angle of less than 90°.

6. Magnetic-inductive flowmeter according to any of the preceding claims, characterized in that a substantially cylindrical structure (23) is arranged on the base surfaces (21) of the insert parts (20), in the center of which the through-hole (22) is located and the circumference of which has at least one outwardly directed extension (24) or an edge-shaped, in particular a square or hexagonal, contour.

7. Magnetic-inductive flowmeter according to claim 6, characterized in that a disk (40) is arranged between the insert part (20) and the nut (30), which disk also has a through-hole (41) complementary to the non-circular cross-section of the measuring electrodes (3), through which the two measuring electrodes (3) each run, and which also has at least one outwardly directed extension complementary to the circumference of the cylindrical structure (23) of the insert part (20).

8. Magnetic-inductive flowmeter according to claim 6, characterized in that a disk (40) is arranged between the insert part (20) and the nut (30), which disk also has a through-hole (41) complementary to the non-circular cross-section of the measuring electrodes (3), through which the two measuring electrodes (3) each run, and which also has an edge-shaped, in particular a square or hexagonal, contour complementary to the circumference of the cylindrical structure (23) of the insert part (20).

9. Magnetic-inductive flowmeter according to any of the preceding claims, characterized in that a disk-shaped plug contact (4) for electrically contacting the measuring electrode (3) is arranged between the insert part (20) and the nut (30).

10. Magnetic-inductive flowmeter according to any of the preceding claims, characterized in that a spring element (5) is arranged between the insert part (20) and the nut (30).

11. Magnetic-inductive flowmeter according to any of the preceding claims, characterized in that the external thread of the measuring electrodes (3) is interrupted in the circumferential direction by at least one recessed facet (6).