Magnetic-inductive flow meter

Abstract

The invention relates to a magnetic-inductive flow meter (1) in which the measuring electrodes (10) comprise at least a main body (11) and an electrode head (12), which is in contact with the medium and has a conical outer contour directed towards the medium. For hygienically reliable sealing of the measuring electrodes (10), it is proposed that the liner (20), with which the measuring tube (2) is lined, extends into the opening (3) in the wall of the measuring tube (2) such that the liner (20) functions as a sealing element acting between the electrode head (12) and the wall of the measuring tube (2), wherein, in the wall opening (3), the outer contour of the electrode head (12) and the inner contour of the liner (20) are at an angle to one another such that maximum compression of the liner (20) takes place exclusively in a quasi-linear sealing region facing the medium.

Description

[0001] Magnetic-inductive flow meter

[0002] The invention relates to a magnetic-inductive flow meter according to the preamble of claim 1.

[0003] Magnetic-inductive flowmeters, whose operation is based on the principle of electromagnetic induction (Faraday induction), have been known for many years and are widely used in industrial measurement technology. According to Faraday's law of induction, an electric field strength perpendicular to the flow direction and perpendicular to the magnetic field is generated in a flowing medium that carries charge carriers and flows through a magnetic field. In magnetic-inductive flowmeters, Faraday's law of induction is utilized by means of a magnetic field generation device, which typically comprises two energized magnetic coils. This magnetic field is guided at least partially through the measuring tube, and 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 to a measuring voltage that can be detected via the electrodes with the field strength generated in this volume element.

[0004] Since the induced voltage measured across the electrodes is proportional to the average flow velocity of the medium across the cross-section of the measuring tube, the volumetric flow rate can be directly determined from the measured voltage, provided the diameter of the measuring tube is known. The only requirement 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 to such an extent that the medium level is above the measuring electrodes.

[0005] Such measuring devices are well known, for example from German patents DE 10 2007 004 827 B4 and DE 10 2007 004 826 B4, and are essentially characterized by the fact that the magnetic coils and the electrodes are arranged directly on or in the wall of the measuring tube. The measuring electrodes usually consist of a cylindrical base body and an electrode head, which is in contact with the medium. The electrode head is typically mushroom-shaped, as is known, for example, from DE 102021 127 943 B3, but can also have a conical outer contour facing the medium, as is known from CN 2 09 197 811 U.

[0006] To prevent short circuits between the measuring electrodes themselves and between the measuring electrodes and the measuring tube, and to meet the requirements of applications in the pharmaceutical and food industries, it is known from the prior art that the measuring tube is lined or coated on the inside with a liner made of PFA or PTFE, for example. These materials are relatively soft, so that, as can be seen, for example, in Fig. 3 of DE 102021 127 943 B3, the measuring electrodes, i.e., the undersides of the electrode heads, are drawn into the soft material during assembly, thus achieving a hygienic seal between the measuring electrodes and the measuring tube.

[0007] A hygienic seal meets the requirements at least according to EHEDG or 3A and is characterized in particular by the absence of gaps and dead spaces in the area of ​​the transition between the electrode head and the measuring tube or liner.

[0008] Other measuring instruments in which the undersides of the electrode heads are drawn into the liner are known from CN 1 01 498 594 A or CN 1 02 252 717 A.

[0009] Further examples of state of the art include CN 2 01 037 779 Y and DE 10 2011 104 799 A1.

[0010] The object of the invention is to propose an alternative sealing method for the measuring electrodes of a magnetic-inductive flowmeter that is also suitable for hygienic applications.

[0011] The problem is solved according to the invention by a magnetic-inductive flow meter with the features of claim 1. Advantageous embodiments of the invention are specified in the dependent claims.

[0012] The invention focuses on measuring electrodes comprising a base body and an electrode head which is in contact with the medium and has a conical outer contour directed towards the medium. The electrode head of each measuring electrode is arranged in an opening in the wall of the measuring tube.

[0013] According to the invention, the liner extends from the inside of the measuring tube into the opening in the wall of the measuring tube where the measuring electrode is located. In addition to its primary function of preventing a short circuit between the two measuring electrodes and ensuring a hygienically sound lining of the inner surface of the measuring tube, the liner also acts as a sealing element between the electrode head and the wall of the measuring tube, eliminating the need for a separate sealing element. Within the wall opening, the outer contour of the electrode head and the inner contour of the liner are at an angle to each other – the wall opening must therefore be designed accordingly – so that maximum compression of the liner occurs exclusively in a quasi-linear sealing area facing the medium.The angle should be chosen such that the outer and inner contours of the opening in the wall become increasingly close to the medium, meaning that the inner and outer surfaces of the electrode head or liner taper to a point towards the medium. Regarding the conical contours, it should be noted that this term is not to be interpreted strictly in a mathematical-geometric sense, and therefore slight deviations from a conical shape, such as contours with a slight radius, are also included under this term.

[0014] If the measuring tube, or its inner surface, is lined with a liner made of a relatively hard material, the aforementioned quasi-linear sealing zone is created in the front area, which is in contact with the medium. Because the maximum compression of the liner occurs exclusively in this zone, relevant hygiene guidelines are met. The liner is preferably made of polyetheretherketone (PEEK), polypropylene (PP), or polyphenylene sulfide (PPS). However, various other materials are also conceivable for coating the measuring tube. Examples would be enamel, Rilsan, SOL-GEL, or other non-conductive coatings.

[0015] An advantageous embodiment provides that a sleeve is arranged in the opening in the wall of the measuring tube, the sleeve having at least a partially conical inner contour and a through-bore. The sleeve is bonded to the wall of the measuring tube, preferably by welding. The measuring electrode is arranged in the through-bore of the sleeve, and the liner extends at least partially within this through-bore. The measuring tube and sleeve are preferably made of metal.

[0016] The liner thus runs between the respective conical contours of the through-bore of the sleeve and the electrode head. The liner can therefore be made comparatively thin and preferably with a uniform thickness, and the second conical inner and outer contour, arranged in a quasi-coaxial manner, creates a stop during assembly that limits the screw-in depth of the measuring electrode or the electrode head.

[0017] To comply with the requirements of relevant hygiene guidelines, such as those of EHEDG or 3A, the transitions between the liner and the electrode head on the inside of the measuring tube are flush. If the previously described sleeve is present, the transitions between the measuring tube wall and the sleeve, as well as between the sleeve and the liner, are also flush.

[0018] For reliable and permanent mounting of the measuring electrodes on or in the measuring tube, a particularly advantageous embodiment of the invention provides that the base bodies of the measuring electrodes have an external thread at their ends opposite the electrode head, onto which a nut is screwed, thus firmly connecting the measuring electrodes to the measuring tube. A spring element is arranged coaxially to the longitudinal axis of the measuring electrodes between the measuring tube and the nut. A particularly advantageous feature of this embodiment is that the spring element is subjected to a defined preload by screwing on the nut, with a limiting element being arranged coaxially to the common longitudinal axis of the spring element and the measuring electrode, which is suitable for limiting the compression of the spring element.The preload of the spring element, preferably designed as a disc spring, generates a restoring force that guarantees the required surface pressure. The limiting element allows the spring force of the spring element to be adjusted, enabling the transmission of higher forces during insertion without exceeding the permissible stresses of the spring element. A further advantageous embodiment provides that the liner extends into the opening in the wall of the measuring tube in such a way that it forms a mounting sleeve extending through the wall of the measuring tube. This sleeve is suitable for gripping the measuring electrode, at least in the area of ​​the measuring tube wall. By forming a mounting sleeve, the liner simultaneously ensures a secure and stable fit for the measuring electrodes. Therefore, additional separate elements are unnecessary, further simplifying assembly.

[0019] Preferably, the liner extends through the measuring tube wall to such an extent that the resulting mounting sleeve projects radially from the outside of the measuring tube. This allows the area for receiving or gripping the measuring electrode to be lengthened, which provides the mounted measuring electrode with additional stability.

[0020] Preferably, the inside of the mounting sleeve has a shoulder. This shoulder can be used as a bearing surface for other parts of the electrode assembly, e.g., the aforementioned spring element, which is provided to generate a preload. The preload of the spring element, preferably designed as a disc spring, generates a restoring force that guarantees the required surface pressure.

[0021] The invention will now be explained in more detail using exemplary embodiments and with reference to the drawings.

[0022] They show schematically:

[0023] Figure 1 shows a cross-sectional view of a magnetic-inductive flow meter according to a first embodiment of the invention;

[0024] Figure 2 shows an enlarged section of a part of Fig. 1;

[0025] Figure 3 is an exploded view of Fig. 2;

[0026] Figure 4 shows a further embodiment of a magnetic-inductive flow meter according to the invention in perspective view;

[0027] Figure 5 shows a cross-section of the embodiment according to Figure 4 of a magnetic-inductive flowmeter according to the invention. In the following description of the preferred embodiments, the same reference numerals denote identical or comparable components.

[0028] Figure 1 shows a cross-sectional view of a magnetic-inductive flowmeter 1 according to a first embodiment of the invention, consisting of a measuring tube 2, on which a flange is arranged at each end face, and two measuring electrodes 10 with a corresponding structure. The magnetic field generation device necessary for the measurement is not shown.

[0029] The inside of the measuring tube 2 is lined with a liner 20 made of a non-conductive material. Due to its good chemical resistance and suitability for hygienic applications, PEEK is particularly suitable, or alternatively PP or PPS. However, various other materials are also conceivable for the measuring tube lining. Examples would be enamel / Rilsan / SOL-GEL or other non-conductive coatings. In the area of ​​the measuring electrodes 10, the measuring tube 2 is shaped to create a flat surface. An opening 3 is located in the center of this surface, in which the measuring electrodes 10 are arranged. The liner 20 extends from the inside of the measuring tube 2 into the openings 3 containing the measuring electrodes 10.

[0030] Figure 2 shows an enlarged view of the area marked “A” in Fig. 1, and Figure 3 shows an exploded view of it.

[0031] A sleeve 4 with a through-opening 4a is welded into the opening 3, its medium-side surface also coated with the liner 20. The measuring electrode 10 is inserted into this sleeve 4, and the liner 20 extends seamlessly from the inside of the measuring tube 2 into the through-opening 4a of the sleeve 4. The measuring electrode consists of a cylindrical base body 11 and an electrode head 12. Within the through-opening 4a, the liner 20 surrounds the measuring electrode 10 essentially only in the area of ​​the electrode head 12.

[0032] A key aspect of the invention is that the electrode head 12 has a conical outer contour and the liner 20 is applied to a conical inner contour, with both positioned at an angle to each other. This ensures that, after assembly, maximum compression of the liner 20 occurs exclusively in a quasi-linear sealing area facing the medium, thus achieving a hygienic seal. This high stress in this quasi-linear area must be considered when selecting the material for the liner 20, which is why, for example, PEEK is a suitable material.

[0033] Assembly is essentially achieved by screwing a nut 13 onto the end of the electrode base body 11 opposite the electrode head 12. Prior to this, a spring element 14, advantageously consisting of disc springs, together with a corresponding assembly comprising a limiting element 15, is slid onto the electrode base body 11. By screwing on and tightening the nut 13, the spring element 14 is subjected to a defined preload. The limiting element 15, arranged coaxially to the common longitudinal axis of the spring element 14 and the measuring electrode 10, limits the compression of the spring element 14.The preload of the spring element 14 generates a restoring force that guarantees the required surface pressure, and the limiting element 15 allows the spring force of the spring element 14 to be adjusted, while still allowing higher forces to be transmitted during insertion without exceeding the permissible stresses of the spring element 14.

[0034] The embodiment of the invention shown in Figures 2 and 3 is characterized in that the liner 20 runs between the respective conical contours of the through-bore 4a of the sleeve 4 and the electrode head 12. The liner 20 can thus be made comparatively thin and with a uniform thickness. The liner 20 and the inner contour of the sleeve 4 are at an angle to each other, ensuring that maximum compression of the liner 20 occurs exclusively in the quasi-linear sealing area facing the medium. Due to the quasi-coaxial arrangement of the conical inner and outer contours, a stop is formed during assembly, limiting the screw-in depth of the measuring electrode 10 or the electrode head 12.

[0035] In this embodiment, it is ensured that at least the transitions between liner 20 and electrode head 12 are flush. If the sleeve 4 is present, the transitions between the measuring tube wall 2 and sleeve 4, as well as between sleeve 4 and liner 20, are also flush. Thus, the assembly is easily cleanable and gap-free, thereby meeting the requirements of relevant hygiene guidelines. Figure 4 shows a second embodiment of a magnetic-inductive flowmeter 1 according to the invention, initially consisting, as in Figure 1, of a measuring tube 2 with a flange arranged at each end face, and a lateral opening 3 in the measuring tube 2 for a measuring electrode. A second opening 3 for the second measuring electrode is located on the concealed rear side of the measuring tube 2. As in Figure 1, the illustration of the magnetic field generation device necessary for the measurement has been omitted.Only the two pins projecting upwards and downwards for mounting the coils are shown. The upper opening 3 can, for example, be used to mount a temperature sensor. Both openings 3 show the liner's exit to the outside of the measuring tube 2. In this area, the liner forms a mounting sleeve 21, which is suitable for enclosing the measuring electrodes inserted into the openings 3, or preferably also a temperature sensor, at least in the area of ​​the measuring tube wall.

[0036] Figure 5 shows a cross-section of this second embodiment. The inside of the measuring tube 2 is lined with a liner 20 made of a non-conductive material. As in the first embodiment, PEEK is particularly suitable for this purpose, due in part to its good chemical resistance and suitability for hygienic applications, or alternatively PP or PPS.

[0037] There is an opening 3 on each side of the measuring tube 2, in which the measuring electrodes 10 are arranged. The measuring electrodes 10 consist of a base body 11 and an electrode head 12. The liner 20 extends from the inside of the measuring tube 2 into the openings 3 containing the measuring electrodes 10 and forms a mounting sleeve 21 around them. This means that the measuring electrodes 10 are enclosed in a sleeve-like manner, at least in the area of ​​the measuring tube wall, and are thus firmly and stably mounted in the measuring tube 2.

[0038] A key feature of the invention is that the electrode head 12 has a conical outer contour and the liner 20 is applied to a conical inner contour, with both positioned at an angle to each other. This ensures that, after assembly, maximum compression of the liner 20 occurs exclusively in a quasi-linear sealing area facing the medium, thus achieving a hygienic seal. The coaxial arrangement of the conical inner and outer contours creates a stop during assembly that limits the screw-in depth of the measuring electrode 10 and the electrode head 12, respectively.

[0039] Reference symbol list

[0040] 1 magnetic-inductive flow meter

[0041] 2 measuring tubes

[0042] 3 Opening

[0043] 4 Sleeve

[0044] 4a Through hole

[0045] 10 measuring electrodes

[0046] 11 Basic shapes

[0047] 12 Electrode head

[0048] 13 Mother

[0049] 14 spring element

[0050] 15 Boundary element

[0051] 20 liners

[0052] 21 Mounting sleeve

Claims

Patent claims 1. Magnetic-inductive flowmeter for measuring the flow rate of a flowing, conductive medium, comprising a measuring tube (2) lined internally with a liner (20) made of a non-conductive material, a magnetic field generation device for generating a magnetic field passing through the measuring tube (2) perpendicular to the longitudinal axis of the measuring tube (2), and two pin-shaped measuring electrodes (10) for detecting a measuring voltage induced in the flowing medium, wherein the measuring electrodes (10) are arranged along a connecting line perpendicular to the longitudinal axis of the measuring tube (2) and perpendicular to the direction of the magnetic field, wherein the measuring electrodes (10) comprise at least a base body (11) and an electrode head (12) which is in contact with the medium and has a conical outer contour directed towards the medium.and wherein the electrode head (12) of each measuring electrode (10) is arranged in an opening (3) in the wall of the measuring tube (2), the liner (20) extending into the opening (3) in the wall of the measuring tube (2) so that the liner (20) acts as a sealing element between the electrode head (12) and the wall of the measuring tube (2), wherein in the wall opening (3) the outer contour of the electrode head (12) and the inner contour of the liner (20) are at an angle to each other, so that maximum compression of the liner (20) occurs exclusively in a quasi-linear sealing area facing the medium.

2. Magnetic-inductive flowmeter according to claim 1, characterized in that a sleeve (4) with a through-bore (4a) is arranged in the opening (3) in the wall of the measuring tube (2), which has at least partially a conical inner contour, is materially connected to the wall of the measuring tube (2) and in whose through-bore (4a) the liner (20) runs at least partially and the measuring electrode (10) is arranged.

3. Magnetic-inductive flowmeter according to claim 1 or 2, characterized in that the liner (20) is designed with a uniform thickness.

4. Magnetic-inductive flowmeter according to one of the preceding claims, characterized in that the transitions between liner (20) and electrode head (12) are flush on the inside of the measuring tube (2).

5. Magnetic-inductive flowmeter according to one of the preceding claims, characterized in that the base bodies (11 ) of the measuring electrodes (10) have an external thread at their ends opposite the electrode head (12), onto which a nut (13) is screwed, such that the measuring electrodes (10) are firmly connected to the measuring tube (2), and a spring element (14) is arranged between the measuring tube (2) and the nut (13) coaxially to the longitudinal axis of the measuring electrodes (10).

6. Magnetic-inductive flow meter according to claim 5, characterized in that the spring element (14) is subjected to a defined preload by screwing on the nut (13), wherein a limiting element (15) is arranged coaxially to the common longitudinal axis of spring element (14) and measuring electrode (10), which is suitable for limiting the compression of the spring element (14).

7. Magnetic-inductive flowmeter according to one of the preceding claims, characterized in that the liner (20) consists of polyetheretherketone (PEEK), polypropylene (PP) or polyphenylene sulfide (PPS).

8. Magnetic-inductive flowmeter according to one of the preceding claims, characterized in that a mounting sleeve (21) extending through the wall of the measuring tube (2) is formed which is suitable to The measuring electrode (10) is to be enclosed in a sleeve-like manner, at least in the area of ​​the measuring tube wall.

9. Magnetic-inductive flowmeter according to claim 8, characterized in that the liner (20) extends through the measuring tube wall to such an extent that the resulting mounting sleeve (21) protrudes radially from the outside of the measuring tube (2).

10. Magnetic-inductive flow meter according to one of claims 8 or 9, characterized in that the inside of the mounting sleeve (21) has a shoulder.

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