MEASURING DEVICE FOR DETERMINING A FLUID VARIABLE

Abstract

A measuring device determines a fluid variable via a control device. A measuring tube serves to guide the fluid, and a first vibration transducer is arranged at the measuring tube. The first vibration transducer has a supporting device and two vibration elements spaced apart from one another. A spring element is clamped between a side face of the vibration elements averted from the measuring tube, which presses the respective vibration element against the measuring tube. The control device drives the vibration elements such that they excite a guided wave in a side wall of the measuring tube guided directly in the side wall or indirectly via the fluid to a second vibration transducer arranged at the measuring tube or back to the first vibration transducer, to be detected there by the control device resulting in measurement data. The control device determines the fluid variable depending on the measurement data.

Claims

1. A measuring device for determining a fluid variable relating to a fluid and/or a fluid flow of the fluid, the measuring device comprises: a controller; a measuring tube serving to accommodate and/or guide the fluid and having a side wall; vibration transducers including a first vibration transducer and a second vibration transducer, said first vibration transducer disposed at said measuring tube, said first vibration transducer having a supporting device in a location that is fixed with respect to said measuring tube, at least two vibration elements spaced apart from one another, and elastically deformed spring elements each clamped between a respective side face of one of said vibration elements averted from said measuring tube and said supporting device, said elastically deformed spring elements pressing said vibration elements against said measuring tube or a coupling element disposed between said measuring tube and said vibration elements; and said controller configured to drive said vibration elements in such a way that together said vibration elements excite a guided wave in said side wall of said measuring tube that can be guided directly in said side wall or indirectly via the fluid to said second vibration transducer disposed at said measuring tube or back to said first vibration transducer, in order to be detected there by said controller for a determination of measurement data, and said controller device configured to determine the fluid variable depending on the measurement data.

2. The measuring device according to claim 1, wherein: at least one of said vibration elements has a measuring tube side, a vibration body with a first side face and a second side face, a first electrode disposed on said first side face of said vibration body on said measuring tube side, and a second electrode averted from said measuring tube that is disposed at said second side face of said vibration body averted from said measuring tube on an opposite side to said measuring tube side, wherein said first electrode on said measuring tube side extends over a further side face of said vibration body that is angled with respect to said first and second side faces on said measuring tube side and averted from said measuring tube; and said controller is configured to vary a voltage between said first and second electrodes on said measuring tube side and averted from said measuring tube in order to excite said vibration body into vibration.

3. The measuring device according to claim 2, wherein said first electrode on said measuring tube side extends over said further side face as far as said second side face averted from said measuring tube.

4. The measuring device according to claim 2, wherein said first electrode or said second electrode is electrically contacted by one of said elastically deformed spring elements that is electrically conductive.

5. The measuring device according to claim 4, wherein at least one of said elastically deformed spring elements electrically contacts precisely one of said first or second electrodes of precisely one of said vibration elements.

6. The measuring device according to claim 2, wherein: said vibration body is rectangularly shaped vibration body; said first and second side faces on said measuring tube side and averted from said measuring tube are spanned by a longitudinal direction and a transverse direction of said rectangle; said vibration body has a first edge region at a first edge in the transverse direction and a second edge region at a second edge positioned opposite said first edge, in said first edge region only said first electrode on said measuring tube side is disposed both at said first side face on said measuring tube side and at said second side face averted from said measuring tube, and in said second edge region only said second electrode averted from said measuring tube is disposed both at said first side face on said measuring tube side and at said second side face averted from said measuring tube; and a respective one of said elastically deformed spring elements mechanically contacts said respective side face of said vibration elements averted from said measuring tube in said first and second edge region.

7. The measuring device according to claim 1, wherein: said vibration elements each have a plurality of spaced contact regions; and one of said elastically deformed spring elements contacts said respective side face of a respective one of said vibration elements averted from said measuring tube at said plurality of spaced contact regions, wherein said spaced contact regions are each disposed in a region of a vibration node of a natural vibration of said respective vibration element.

8. The measuring device according to claim 1, wherein at least one of said elastically deformed spring elements and/or said supporting device contains at least one stop section that mechanically contacts one of said vibration elements on at least one side face of said one vibration element that is angled with respect to said respective side face of said one vibration element averted from said measuring tube, and/or that limits a movement of said one vibration element perpendicularly to said side face at least on one side.

9. The measuring device according to claim 8, wherein said one elastically deformed spring element has a recess formed therein and into said recess one of said vibration elements is inserted in such a way that a contact section of said elastically deformed spring element lies against said respective side face of said one vibration element averted from said measuring tube, and that at least one supporting section of said one elastically deformed spring element that extends in a direction of said measuring tube over and beyond said contact section forms said stop section.

10. The measuring device according to claim 1, wherein said elastically deformed spring elements are formed of a polymer, or an elastomer, or a metal, or comprises an adhesive layer or is an adhesive layer.

11. The measuring device according to claim 1, wherein: said first vibration transducer has a vibration membrane or a vibration plate as said coupling element that is fastened to said supporting device and coupled to said measuring tube directly or via a coupling layer; a respective one of said vibration elements is disposed at a surface of said vibration membrane or said vibration plate averted from said measuring tube at mutually spaced excitation regions; and said vibration elements are supported jointly by said elastically deformed spring elements and said vibration membrane or said vibration plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0047] Referring now to the figures of the drawings in detail and first, particularly to FIGS. 1 and 1A thereof, there is shown a measuring device 1 for determining a fluid variable relating to a fluid and/or a fluid flow. The fluid is guided here in a direction shown by arrow 7 through an interior space 4 of a measuring tube 3. In order to determine the fluid variable, in particular a volume flow rate, a transit time difference between transit times from a first vibration transducer 5 to a second vibration transducer 6 and vice versa can be determined by a control device 2. Use is made here of the fact that this transit time depends on a velocity component of the fluid parallel to a direction of propagation through the fluid of an ultrasonic beam 8. A fluid velocity in the direction of the respective ultrasonic beam 8 averaged over the path of the respective ultrasonic beam 8 can be determined from this transit time and thereby, approximately, an averaged flow velocity in the volume crossed by the ultrasonic beam 8.

[0048] In order first to enable an arrangement of the vibration transducers 5, 6 outside the measuring tube 3 and, secondly, to reduce sensitivity in respect of different flow velocities at different positions of the flow profile, the first vibration transducer 5 does not directly introduce an ultrasonic beam 8, i.e. a pressure wave, into the fluid. A guided wave is instead excited in a side wall 9 of the measuring tube 3 by the vibration transducer 5. The excitation takes place at a frequency that is selected such that a Lamb wave is excited in the side wall 9. Such waves can be excited if a thickness 10 of the side wall 9 is comparable to the wavelength of the transverse wave in the solid body, which is given from the ratio of the sound velocity of the transverse wave in the solid body to the excited frequency.

[0049] The guided wave excited in the side wall 9 by the vibration transducer 5 is shown schematically by arrow 11. Compression vibrations of the fluid, which are radiated into the fluid in the entire propagation path of the guided wave, are excited by the guided wave. This is illustrated schematically by the ultrasonic beams 8, offset with respect to one another in the flow direction. The radiated ultrasonic beams 8 are reflected at an opposite side wall 12 and guided through the fluid back to the side wall 9. The incoming ultrasonic beams 8 there again excite a guided wave in the side wall 9, illustrated schematically by arrow 13, which can be detected by the vibration transducer 6 in order to determine the transit time. Alternatively or in addition it is possible for the radiated ultrasonic waves to be detected by a vibration transducer 15 that is arranged at the side wall 12. In the illustrated example, the ultrasonic beams 8 are either not reflected or only reflected once at the side walls 9, 12 on their path to the vibration transducer 6, 15. It would, of course, be possible to use a longer measurement segment in which the ultrasonic beams 8 are reflected multiple times at the side walls 9, 12.

[0050] It can be problematic in the procedure outlined that the dispersion relationship for Lamb waves in the side wall 9 has a plurality of branches. With excitation at a certain frequency determined by the control device 2, it would thus be possible for different vibration modes for the Lamb wave having different phase velocities to be excited. This has the result that the compression waves are radiated at different Rayleigh angles 14 depending on these phase velocities. From this, different paths, typically having different transit times, result for the guidance of the ultrasonic wave from the vibration transducer 5 to the vibration transducer 6 and vice versa. The received signals for these different propagation paths must thus be separated through a complex signal processing by the control device 2 in order to be able to determine the fluid variable. This requires, first, a complex control device and it cannot secondly be robust in all applications. The greatest possible modal purity of guided waves should therefore occur in the vibration transducer 5.

[0051] In order to achieve an excitation of a total guided wave in the side wall 9 that is largely modally pure, the vibration transducer 5 that contains a plurality of spaced vibration elements 17, 18, is used. These are driven by the control device 2 in such a way that together they excite a guided wave in the side wall 9 of the measuring tube 3. Centers 24, 25 of the excitation regions 21, 22 are here spaced apart at a fixed, predefined distance 23. Because the excitation frequency is chosen in such a way that only precisely two vibration modes of a Lamb wave can be excited in the side wall 9, and the spacing 23 and the phase relation or polarity with which the vibration elements 17, 18 vibrate is appropriately chosen, a destructive interference for an unwanted vibration mode can be ensured, so that a remaining vibration mode is excited in a substantially modally pure manner.

[0052] A correct arrangement of the vibration elements 17, 18 with respect to one another is crucial for the procedure described. The arrangement of the vibration elements 17, 18, is specified in the measuring device 1 by a supporting device 26 that is fastened to the measuring tube 3 by fastening means, not illustrated. This forms a type of housing for the vibration elements 17, 18. To ensure that side faces 19, 20 of the vibration elements 17, 18 that face the measuring tube are pressed with a defined contact pressure against the side wall 9 of the measuring tube 3, or onto the coupling element arranged between the vibration elements 17, 18 and the side wall 9, the vibration elements 17, 18, are not attached directly to the supporting device 26, for example being glued to it, but are instead supported via a respective spring element 30. The spring element 30 is clamped between side faces 31 of the respective vibration element 17, 18 that are averted from the measuring tube and the supporting device 26. When the measuring device is in the state in which it is used, in which the vibration transducer 5 is arranged at the side wall 9, it is already elastically deformed or prestressed, so that it exercises a force on the respective vibration element 17, 18.

[0053] In principle, a coupling element 16 illustrated in FIG. 1, could be omitted. The use of such a coupling element, for example a foil or a thin vibration plate, however offers first the advantage that the vibration elements 17, 18, are protected against environmental influences. Second, a supporting device 26, together with the coupling element 16, can support the vibration elements 17, 18, so that in the course of the manufacture of the measuring device, the vibration transducers 5, 6 can be assembled as separate components and arranged at the side wall 9.

[0054] The construction of the vibration transducer 5, along with details of the manufacture of the vibration transducer 5, is explained below with reference to FIGS. 2 and 3. FIG. 2 shows a view of the vibration transducer 5 before an application of the coupling element 16 to the supporting device 26. The supporting device 26 here has two recesses 27, 28, into which the vibration elements 17, 18 are inserted, in particular loosely. Because in this condition essentially no force yet acts on the side faces 19 of the vibration elements 17, 18 that face the measuring tube, the spring element 30, as illustrated in FIG. 3, is initially not yet elastically deformed or prestressed, so that the vibration elements 17, 18 initially protrude slightly above the edge of the supporting device 26. Only with the application of a sufficiently prestressed coupling element 16, or preferably only with the fastening of the supporting device to the side wall 9, is the spring element 30 compressed far enough that the vibration elements 17, 18 are pressed with a defined contact pressure against the side wall 9 or the coupling element 16, and typically are hereby substantially entirely accommodated in the respective recess 27, 28. The coupling element can, for example, be bonded to the supporting device 26 through gluing, through welding or through hot stamping. The bonding takes place in particular exclusively at the edge, as illustrated schematically through the connecting line 29. The vibration elements 17, 18 can thus be fully enclosed by the supporting device 26 and the coupling element 16 together, wherein they are in particular surrounded in a dust-proof and/or fluid-proof manner.

[0055] FIG. 3 shows, in addition, the detailed structure of a single vibration element 17. The vibration element consists of a vibration body 32, an electrode 33 on the measuring tube side, and an electrode 35 averted from the measuring tube 3. Both the electrode 33 on the measuring tube side and the electrode 35 averted from the measuring tube 3 are each taken to a further side face 34, 36 of the vibration element or of the vibration body, whereby an easier contacting, in particular of the electrode 33 on the measuring tube side is enabled while nevertheless, due to the symmetric electrode arrangement, symmetric natural vibrations of the vibration element 17 are not disturbed.

[0056] The electrical contacting of the electrodes 33, 35 is not illustrated in detail in FIG. 3. They can, for example, be made at the side faces 34, 36 by soldering or gluing them with conductive glue on appropriate lines. The electrode 35 can also be contacted by the spring element 30 if the spring element 30 is for example formed of a conductive elastomer, a conductive adhesive or the like. The manufacturing effort for manufacturing the measuring device 1 can be further reduced by contacting the electrode 35 in this sort of way.

[0057] FIG. 4 shows one possibility for mounting the vibration elements 17, 18 using a common spring element 37. A larger accommodation space of the supporting device, in which both vibration elements 17, 18 are arranged, is used here. For reasons of clarity, only the spring element 37 itself and, schematically, one of the vibration elements 17 are illustrated in FIG. 4. The spring element 37 is implemented as a stamped metal part. Stop sections 38 are formed here by bent-up straps which, after an insertion of the respective vibration element 17, 18, have a mean distance of, for example, less than 1 mm from the side faces 39 of the vibration element 17. In this way, the relative position and orientation of the vibration elements 17, 18 can be specified with little technical effort and with high precision, at least in the direction of the spacing between them.

[0058] The elastic effect of the spring element 37 is realized through elevations 40 that are produced through an appropriate bending of the stamped and bent part. These can be deformed elastically. The position of the elevations 40 is preferably selected such that they contact the respectively supported vibration element 17, 18 in a region in which vibration nodes of a natural mode of the respective vibration element 17, 18 are expected. When the measuring device is being operated for excitation of the guided wave, the vibration elements are preferably operated at an excitation frequency at which they vibrate in this natural mode. An influence of the bearing on the vibration of the vibration elements 17, 18, is hereby minimized.

[0059] Because a metallic spring element 37 is used, it is also possible to contact the electrode of the vibration elements 17, 18 averted from the measuring tube by means of the spring element 37. A predefined reference potential can, for example, be applied to the electrode 35 of both vibration elements 17, 18 that is averted from the measuring tube. The electrode 33 that faces the measuring tube can, as already explained, be contacted, for example, through the front faces 34. This for example enables an independent drive of the vibration elements 17, 18, for example in order to select a polarity of the drive, to specify a phase offset or to delay a drive signal by a certain time.

[0060] A particularly simple structure of the measuring device is possible if both electrodes 33, 35 of the vibration elements 17, 18 are contacted via a respective spring element 41, 42, as is illustrated in FIG. 5. In contrast to the exemplary embodiment illustrated in FIG. 3, the electrode 33 that faces the measuring tube is drawn onto the side face 31 averted from the measuring tube, and the electrode 35 averted from the measuring tube is drawn on to the side face 19 that faces the measuring tube. This makes it possible to contact both electrodes via the side face 31 averted from the measuring tube with a substantially symmetric electrode arrangement, and thus with only slight disturbance to the natural vibrations of the vibration body 32. In FIG. 5 the contacting takes place through conductive spring elements 41, 42 which can, for example, be formed of a conductive polymer or plastic. The spring elements 41, 42 here exclusively contact the side faces 31 in the edge regions 43, 44 in which respectively the same electrodes 33 or 35 is arranged on both side faces 19, 31. This has the effect that even when a voltage is applied between the electrodes 33, 35, the field strengths in the edge regions 43, 44 are very small, as a result of which also only very small vibration amplitudes occur there. This reduces, first, the influence of the bearing by way of the spring elements 41, 42 on the vibration behavior of the vibration element 17, and secondly coupling of vibration into the supporting device 26 can hereby be significantly reduced.

[0061] The spring elements 41, 42 can already be arranged at the vibration element 17 in a preparatory working step before the latter is inserted into the supporting device 26. The vibration element 17 can, for example, be given an elastomer or a layer of adhesive in the illustrated regions. This, first, simplifies the assembly of the measuring device. Second, an intended alignment of the vibration element 17 during installation into the supporting device 26 is hereby made clearly recognizable, whereby an installation with incorrect polarity can, for example, be avoided.

[0062] The arrangement of the electrodes 33, 35 and spring elements 41, 42 shown in FIG. 5 can also be advantageous when the electrodes 33, 35, are not contacted by way of the spring elements 41, 42 since the previously described advantages of the arrangement of the spring elements 41, 42 in the edge regions 43, 44 continue to apply.

[0063] The mounting of the vibration element 17 by means of the spring elements 45, 46 illustrated in FIG. 6 largely corresponds to the mounting illustrated in FIG. 5, but instead of blocks of elastic material, metal sheet springs are used as spring elements 45, 46. These can, for example, be cast into the supporting device 26 or inserted into this in a preceding working step. The use of such spring elements 45, 46 enables a particularly simple contacting, since simple contacting is possible at, for example, an end 49 of the metal sheet brought out from the supporting device 26. The spring elements 45, 46 each have a recess 47 which can, for example, be stamped into the corresponding metal sheet. This has the result that supporting sections 48 that extend over and beyond a contact section of the spring elements 45, 46 that lies against the side face 31 averted from the measuring tube form stop sections, as was already explained with reference to FIG. 4. In this way, the position of the vibration element 17 perpendicular to the plane of the drawing is also specified by the spring elements 45, 46.

[0064] FIG. 7 shows a further possibility for the elastic mounting of the vibration element 17. Spring elements 50, 51 can here again for example be formed of blocks of an elastic material, for example rubber or another elastomer, and optionally also be conductive, in order to contact the electrode 35. The spring elements 50, 51 contact the side faces 31 averted from the measuring tube of the vibration element 17 in two separated contact regions 52, 53 which, as was already explained in respect of FIG. 4, are each arranged in regions of a vibration node of a natural vibration of the vibration element 17.

LIST OF REFERENCE SIGNS

[0065] 1 Measuring device [0066] 2 Control device [0067] 3 Measuring tube [0068] 4 Interior space [0069] 5 Vibration transducer [0070] 6 Vibration transducer [0071] 7 Arrow [0072] 8 Ultrasonic beam [0073] 9 Side wall [0074] 10 Thickness [0075] 11 Arrow [0076] 12 Side wall [0077] 13 Arrow [0078] 14 Rayleigh angle [0079] 15 Vibration transducer [0080] 16 Coupling element [0081] 17 Vibration element [0082] 18 Vibration element [0083] 19 Side face [0084] 20 Side face [0085] 21 Excitation region [0086] 22 Excitation region [0087] 23 Distance [0088] 24 Center [0089] 25 Center [0090] 26 Supporting device [0091] 27 Recess [0092] 28 Recess [0093] 29 Connecting line [0094] 30 Spring element [0095] 31 Side face averted from the measuring tube [0096] 32 Vibration body [0097] 33 Electrode [0098] 34 Side face [0099] 35 Electrode [0100] 36 Side face [0101] 37 Spring element [0102] 38 Stop section [0103] 39 Side face [0104] 40 Elevation [0105] 41 Spring element [0106] 42 Spring element [0107] 43 Edge region [0108] 44 Edge region [0109] 45 Spring element [0110] 46 Spring element [0111] 47 Recess [0112] 48 Supporting section [0113] 49 End [0114] 50 Spring element [0115] 51 Spring element [0116] 52 Contact region [0117] 53 Contact region