MEASURING DEVICE FOR DETERMINING A FLUID VARIABLE

Abstract

A measuring device determines a fluid variable with a control device, a measuring tube and a first vibration transducer arranged at the measuring tube. The first vibration transducer contains a vibration element. The vibration element has a vibration body, a first electrode on the measuring tube side and a second electrode averted from the measuring tube. The first electrode extends over a first end face of the vibration body. The second electrode extends to a second end face that lies opposite the first end face. A respective conductive contact element contacts the first electrode at a first end face and the second electrode at a second end face electrically and mechanically such that the vibration element is supported by the contact elements. A voltage between the first and second electrodes can be varied through the vibration element to excite a guided wave in a side wall of the measuring tube.

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 comprising: a controller; a measuring tube serving to accommodate and/or guide the fluid and having a side wall; and 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 at least one vibration element, said at least one vibration element having a vibration body with a first end face and a second end face, a first electrode on a measuring tube side and disposed on a first side face of said vibration body on a side of said measuring tube, and a second electrode averted from said measuring tube and is disposed at a second side face of said vibration body averted from said measuring tube on an opposite side to said first side face on said measuring tube side, wherein said first electrode on said measuring tube side extending over a first end 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, wherein said second electrode averted from said measuring tube extends to said second end face that lies opposite said first end face, said first vibration transducer further having contact elements contacting said first electrode on said measuring tube side at said first end face and said second electrode averted from said measuring tube at said second end face electrically and mechanically in such a way that said vibration element is supported by said contact elements, wherein through this electrical contacting by means of said controller a voltage between said first and second electrodes on said measuring tube side and averted from said measuring tube can be varied in order through said vibration element to excite, in said side wall of said measuring tube, a guided wave that can be guided directly via 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, and which can be detected there by said controller for a determination of measured data, wherein the fluid variable can be determined by said controller depending on the measured data.

2. The measuring device according to claim 1, wherein said vibration element is supported with friction locking by said contact elements.

3. The measuring device according to claim 1, wherein at least one of said contact elements is elastically deformed by mechanical contact with said vibration element.

4. The measuring device according to claim 1, wherein at least one of said contact elements can be or comprises a plate that extends substantially parallel to said first or second end face contacted by said one contact element, wherein said plate is bent elastically through the contact with said vibration element.

5. The measuring device according to claim 1, wherein: said at least one vibration element of said first vibration transducer is one of a plurality of vibration elements which are vibrationally coupled directly or via a coupling element to a respective excitation region of said side wall; and said controller is configured to drive said vibration elements in such a way that in each said respective excitation region a partial wave guided in said side wall is excited, wherein partial waves overlay to form the guided wave, wherein a vibration mode that is to be attenuated is at least partially eliminated through a destructive interference of the partial waves.

6. The measuring device according to claim 5, wherein at least one of said contact elements electrically and mechanically contacts precisely one of said first and second electrodes of precisely one of said vibration elements.

7. The measuring device according to claim 5, further comprising at least one common contact element electrically and mechanically contacting a respective one of said first and second electrodes of at least two of said vibration elements.

8. The measuring device according to claim 7, wherein said common contact element contains two separate contact sections that are exclusively connected by a plate-shaped connecting section that is disposed separately from said vibration elements.

9. The measuring device according to claim 5, wherein said coupling element is a vibration membrane or a vibration plate which extends over and beyond said excitation regions of said vibration elements of said first vibration transducer.

10. The measuring device according to claim 5, wherein: said first vibration transducer contains a housing that has a housing wall that extends over and beyond said second side faces of said vibration elements that are averted from said measuring tube; and said contact elements extend through said housing wall.

11. The measuring device according to claim 1, wherein at least one of said contact elements is formed of a metal plate or a conductive elastomer.

12. The measuring device according to claim 1, wherein said first electrode on said measuring tube side is disposed exclusively at said first side face that faces said measuring tube and precisely one of said first and second end faces, and said second electrode averted from said measuring tube exclusively at said second side face averted from said measuring tube and said other end face, or said first and second electrodes on said measuring tube side and averted from said measuring tube are disposed at said respective ones of said first and second end faces and said first side face that faces said measuring tube and said second side face averted from said measuring tube.

13. The measuring device according to claim 8, wherein said two separate contact sections are plate-shaped.

14. The measuring device according to claim 11, wherein said metal plate or said conductive elastomer is sprayed onto said housing of said first vibration transducer.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0033] FIGS. 1 and 2 are diagrammatic, sectional views of an exemplary embodiment of a measuring device according to the invention; and

[0034] FIGS. 3 and 4 are sectional views of further exemplary embodiments of a measuring device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0035] Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a measuring device 1 for determining a fluid variable related to a fluid and/or a fluid flow. The fluid is guided here in a direction shown by the 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 the 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 thus be determined from this transit time and thereby, approximately, an averaged flow velocity in the volume crossed by the ultrasonic beam 8.

[0036] In order on the one hand to enable an arrangement of the vibration transducers 5, 6 outside the measuring tube 3 and, on the other hand, 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 and the transverse wave in the solid body to the excited frequency.

[0037] The guided wave excited in the side wall 9 by the vibration transducer 5 is shown schematically by the 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 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.

[0038] 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, on the one hand, a complex control device and it cannot on the other hand be robust in all applications. The guided waves should therefore be excited with the greatest possible modal purity in the vibration transducer 5.

[0039] 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 arranged in spaced excitation regions 21, 22 is used. The arrangement should be done in such a way that a center 24, 25 of the excitation regions 21, 22 have a defined spacing 23 which, as will be explained later in yet more detail, is important for the modally pure excitation. In order to enable an accurate positioning and the contacting of the vibration elements 17, 18 at the same time with low effort, these are not arranged individually at the side wall 9, but are supported by the respective contact elements 28, 29, as is shown in detail in FIG. 2, in a recess 27 of a housing 26, so that the housing 26 with the vibration elements 17, 18 held to it by the contact elements 28, 29, can subsequently be arranged on the side wall 9 as a module.

[0040] As is illustrated in FIG. 1, it can be advantageous here to use in addition a coupling element 16, for example a thin foil or a vibration plate, which is arranged between the vibration elements 17, 18 and the respective excitation regions 21, 22 of the side wall 9. By mounting such a coupling element 16 on the housing 26, the vibration transducer 5 is provided as a compact module. This, on the one hand, makes the handling of the vibration elements 17, 18 easier in the context of the assembly of the measuring device 1, and on the other hand serves to encapsulate the vibration elements 17, 18 against environmental influences.

[0041] As shown in detail in FIG. 2, the vibration elements 17, 18 each consist of a vibration body 30, an electrode 31 on the measuring tube side, and an electrode 32 averted from the measuring tube. The electrode 31 on the measuring tube side here is arranged on a side face 33 that faces the measuring tube, and extends as far as the first end face 34 at which it is electrically contacted by the contact element 28. The electrode 32 that faces the measuring tube correspondingly extends on the one hand over the side face 35 averted from the measuring tube and on the other hand as far as the second end face 36, where it is electrically contacted by the contact element 29. The contact elements 28, 29 are fastened to the housing 26, and together clamp the respective contact element 17, 18, so that these are each mechanically supported.

[0042] The contact elements 28, 29 are each manufactured from metal sheet, for example cut or stamped, and have a certain elasticity, so that when the respective vibration element 17, 18 is inserted between the respective contact elements 28, 29 they are elastically deformed, and thus apply a certain compression force to the vibration element 17, 18, and thus support it with friction locking. The vibration elements 17, 18 are here each contacted by separate contact elements 28, 29. This makes it possible to provide different control signals, or control signals of different polarity, to the vibration elements 17, 18, whereby, for example, a modally selective excitation of different vibration modes depending on the drive by the control device 2 is made possible. The end 37 of the contact elements 28, 29 that does not lie on the vibration element 17, 18 is in each case brought through a housing wall 38 of the housing 26 that borders the recess 27 at the side averted from the measuring tube. A simple contacting of the vibration elements 17, 18, from the rear side of the housing is thus made possible, wherein at the same time the vibration elements 17, 18 can be encapsulated in the housing in order to protect them from environmental influences and to improve their handleability.

[0043] It is not required in all applications that it must be possible for different signals to be supplied to the electrodes 31 on the measuring tube side and the electrodes 32 averted from the measuring tube of the two vibration elements 17, 18. It can, for example, be possible that both electrodes 31 on the measuring tube side, or both electrodes 32 that are averted from the measuring tube, or one of these electrodes in each case, should be placed at a specific reference potential, and it should only be possible for the electrode of the vibration elements 17, 18 remaining in each case to be separately driven. In this case the structure of the measuring device 1 can be further simplified, for example in that the common contact element 39 shown in FIG. 3 is used instead of the contact element 28 or 29. This comprises two separate, plate-shaped contact sections 40, 41, each of which serves to contact or to support the vibration elements 17, 18 only suggested schematically in FIG. 3. The two contact sections 40, 41 are exclusively joined by a plate-shaped connecting section 42 in that the contact element 39 can be fastened to the housing 26 or which can serve to bring the contact element 39 through the housing wall 38 in order to enable contacting on the rear side.

[0044] Through the Y-like structure shown in FIG. 3 it is possible for the two vibration elements 17, 18, to be contacted with very little effort, while at the same time a vibration coupling between the vibration elements 17, 18 is largely avoided through the use of separate contact sections 40, 41. The contact element 39 can, for example, be made of metal sheet, for example stamped or cut from a metal sheet.

[0045] FIG. 4 shows a further possibility for configuring contact elements 43, 44 which on the one hand contact the electrodes 31, 32 at the end faces 34, 36 and, on the other hand, clamp the vibration elements 17, 18 by means of the mechanical force applied in this way and thus support them in a fixed position. In the exemplary embodiment shown in FIG. 4 the contact elements 43, 44 are formed of a conductive polymer that is, for example, foamed or sprayed onto the housing 26. The contact elements 43, 44 are dimensioned here in such a way that they are pushed together in the transverse direction in FIG. 4 when the respective vibration element 17, 18 is inserted, as a result of which they exert a clamping force on the end faces 34, 36 after the insertion of the vibration elements 17, 18, and thus support the vibration elements 17, 18 with friction locking. In the exemplary embodiment shown, the housing 26 also has openings 19 that are also filled with the conductive polymer, so that in this exemplary embodiment too the contact elements 43, 44 are brought through the housing wall 38 to the rear side 20 of the housing 26, where they can be contacted without difficulty by way of the rear side 20 even after the application of the housing 26 and thereby of the vibration elements 17, 18 to the measuring tube 3.

[0046] Even with the use of a conductive polymer it would, in principle, as explained above, be possible for the contact elements 43, 44 to mechanically and electrically contact the vibration elements 17, 18 exclusively at the end faces 34, 36. It can, however, be advantageous if the contact elements 43, 44 additionally support the vibration element 17, 18 at the side face 35 that faces away from the measuring tube, as illustrated in FIG. 4.

[0047] In order in addition here to improve the contacting of the electrode 31 on the measuring tube side, it is drawn in the edge region 45 as far as the side face 35 of the vibration body 30 that faces away from the measuring tube. Since an asymmetric arrangement of the electrodes 31, 32 can lead to anti-symmetric vibration modes, which can potentially conflict with a modally pure excitation of guided waves, the electrode 32 averted from the measuring tube is in addition drawn in the edge region 46 up to the side face 33 of the vibration body 30 that faces the measuring tube. This sort of arrangement of the electrodes 31, 32 can also be advantageous, since in the edge regions 45, 46, due to the same respective electrode 31, 32 being arranged on both side faces 33, 35, even when voltage is applied to the vibration elements 17, 18, only very low field strengths result, and thus the vibration amplitudes in the edge regions 45, 46 are also small. This on the one hand removes stress from the mechanical contacts that serve to support the vibration elements 17, 18, and on the other hand reduces the coupling of vibration into the housing 26. A disturbance of the natural modes of the vibration elements 17, 18 resulting from a coupling with the housing can also be reduced by such a procedure. It can therefore also be advantageous to use such an electrode arrangement when the electrodes 31, 32 are exclusively contacted by way of the end faces 36, 37, as was explained above in relation to FIGS. 2 and 3.

LIST OF REFERENCE SIGNS

[0048] 1 Measurement device [0049] 2 Control device [0050] 3 Measurement tube [0051] 4 Interior [0052] 5 First vibration transducer [0053] 6 Second vibration transducer [0054] 7 Arrow [0055] 8 Ultrasonic beam [0056] 9 Side wall [0057] 10 Thickness [0058] 11 Arrow [0059] 12 Side wall [0060] 13 Arrow [0061] 14 Angle [0062] 15 Vibration transducer [0063] 16 Coupling element [0064] 17 Vibration element [0065] 18 Vibration element [0066] 19 Opening [0067] 20 Rear face [0068] 21 Excitation region [0069] 22 Excitation region [0070] 23 Distance [0071] 24 Centre [0072] 25 Centre [0073] 26 Housing [0074] 27 Recess [0075] 28 Conductive contact element [0076] 29 Conductive contact element [0077] 30 Vibration body [0078] 31 Electrode on the measuring tube side [0079] 32 Electrode averted from the measuring tube [0080] 33 Side face on the measuring tube [0081] 34 First end face [0082] 35 Side face averted from the measuring tube [0083] 36 Second end face [0084] 37 End face [0085] 38 Housing wall [0086] 39 Conductive contact element [0087] 40 Contact section [0088] 41 Contact section [0089] 42 Connecting section [0090] 43 Conductive contact element [0091] 44 Conductive contact element [0092] 45 Edge region [0093] 46 Edge region