Fluid measuring device

Abstract

This invention discloses a fluid measurement device for determining at least one characteristic property of a fluid, comprising a measuring tube having a fluid conduit through which the fluid can flow and a measuring section in which at least one region of the measuring tube wall is configured as a waveguide for surface acoustic waves, the waveguide forming an interface with the fluid. At least two piezoelectric transducers are provided, arranged in direct contact with the outer surface of the waveguide, one of which serves as a transmitter for exciting acoustic waves in the waveguide, and at least one as a receiver for receiving acoustic waves. The acoustic waves excited by the transmitter are capable of propagating through the fluid at least partially as volume waves, and the piezoelectric transducers are configured to be elastic and flexible while maintaining their function, wherein the piezoelectric transducers have a plurality of strip piezoelectric elements arranged parallel to each other, which are themselves rigid and have corresponding layers of elastic material disposed between them.

Description

Technical Field

[0001] The present invention relates to a fluid measuring device for determining at least one characteristic property of a fluid.

[0002] The present invention particularly relates to a fluid measuring device for determining one or more characteristic properties of a liquid flowing therethrough. Fluid properties include, for example, concentration, density, viscosity, velocity of sound, flow rate, flow rate, temperature, and / or its uniformity. Background Technology

[0003] Document DE102019110514A1 discloses a fluid measurement device for measuring certain properties of a fluid flowing in a fluid conduit using acoustic waves. For this purpose, surface acoustic waves (SAWs) are excited in a waveguide formed by a portion of the wall of the fluid conduit, the type and frequency of which are selected such that partial decoupling occurs in the fluid directly in contact with the waveguide. Therefore, a portion of the SAW in the waveguide is coupled into the fluid as a longitudinal volumetric acoustic wave and passes through it.

[0004] As the sound waves travel through the fluid, they are reflected at least once at the opposite walls of the fluid conduit, thus striking the waveguide again. Within the waveguide, a portion of these volumetric waves is coupled back as surface acoustic waves and continues its journey there. Consequently, a characteristic signal is generated at the receiver, whose temporal intensity progression (including the time delay relative to the signal emitted by the transmitter) allows for conclusions about the characteristic properties of the fluid. The receiver is positioned on the waveguide at a distance from the transmitter.

[0005] Piezoelectric transducers are used as both transmitters and receivers, and are typically attached to a measuring tube on a flat contact surface. However, under certain loads (such as high pressure or strong thermal stress), piezoelectric transducers may break, especially when they are large-area transducers that provide particularly high measurement accuracy. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide a fluid measuring device that avoids the above-mentioned problems.

[0007] According to the invention, this is achieved by a fluid measuring device for determining at least one characteristic property of a fluid, the device comprising a measuring tube and at least two piezoelectric transducers. The measuring tube has a fluid conduit through which the fluid can flow and a measuring section in which at least one region of the tube wall is configured as a waveguide for surface acoustic waves, the waveguide forming an interface with the fluid. The at least two piezoelectric transducers are arranged to be in direct contact with the outer surface of the waveguide. One of the piezoelectric transducers serves as a transmitter for exciting acoustic waves in the waveguide, and at least one serves as a receiver for receiving acoustic waves. The acoustic waves excited by the transmitter are able to propagate through the fluid at least partially as volume waves, and the piezoelectric transducers are configured to be elastic and flexible while maintaining their function, wherein the piezoelectric transducers have a plurality of strip piezoelectric elements arranged parallel to each other, the plurality of strip piezoelectric elements being rigid in themselves and having corresponding layers of elastic material arranged between them.

[0008] In the fluid measuring device according to the invention, the piezoelectric transducer is constructed to be elastic and flexible, eliminating the risk of breakage even under high loads and with some deformation of the measuring tube. For systems requiring particularly high measurement accuracy, large-area piezoelectric transducers are also feasible. Furthermore, due to their flexibility, the piezoelectric transducer can ideally adapt to the curvature of, for example, a cylindrical measuring tube, making the machining of the measuring tube (as done in the prior art, creating a flat contact surface for the transducer) unnecessary in the construction according to the invention. This simplifies manufacturing and consequently has a beneficial impact on manufacturing costs.

[0009] It should be noted here that, within the meaning of this invention, a strip piezoelectric element should be understood as a thin, plate-shaped piezoelectric element having a preferred elongated shape.

[0010] Preferably, the piezoelectric transducer is integrated into the measuring tube wall, thus enabling the fluid measuring device to be manufactured in a particularly simple and cost-effective manner.

[0011] Elastic materials may be elastomers or cast compounds.

[0012] Preferably, the rigid strip piezoelectric element and the elastic material layer disposed therebetween substantially form a cuboid in a non-bent state. In particular, the length of the cuboid is at most ten times its width, and the height is approximately one-tenth of its width. Alternatively, a transducer with a square base may also be used.

[0013] In a preferred variation, when viewed along the longitudinal direction of the cuboid, rigid strip piezoelectric elements and layers of elastic material disposed therebetween are arranged alternately, with each rigid strip piezoelectric element extending across the entire width of the cuboid. In this way, a piezoelectric transducer with the desired flexibility is obtained, and it has been demonstrated in tests to be particularly suitable for generating large-amplitude surface acoustic waves within the measuring tube wall.

[0014] In the alternative construction, when viewed in the longitudinal and transverse directions of the cuboid, rigid strip piezoelectric elements and layers of elastic material arranged between them are alternately arranged. This results in a structure in which multiple small rectangular piezoelectric elements are separated from each other by a mesh of elastic material, which improves the flexibility of the piezoelectric transducer.

[0015] If the piezoelectric transducer has a flexible printed circuit board or printed circuit board foil, a particularly simple and break-resistant construction is achieved, in which the strip piezoelectric elements are fastened to and electrically contacted with the flexible printed circuit board or printed circuit board foil. Preferably, when assembling the piezoelectric transducer, a cuboid composed of strip piezoelectric elements is first attached to the measuring tube wall, with an elastic material layer arranged therebetween, and then the flexible printed circuit board is attached to the other side of the cuboid.

[0016] The construction of piezoelectric transducers, each with two electrodes, has proven particularly advantageous in terms of manufacturing technology. These two electrodes are attached to a flexible printed circuit board or printed circuit board foil and are specifically arranged such that sound waves are coupled into or received from the measuring tube via the longest side of the piezoelectric transducer.

[0017] In a preferred embodiment, each piezoelectric transducer has at least one electrode pair, wherein a first electrode of the electrode pair is arranged on the side of the piezoelectric element facing away from the measuring tube, and a second electrode of the electrode pair is arranged on the side of the piezoelectric element facing the measuring tube and opposite to the first electrode, and wherein during operation of the piezoelectric transducer, a voltage is applied between the first and second electrodes of the electrode pair. In a top view of the transducer, the two electrodes of one electrode pair are thus positioned exactly one above the other. In this configuration, when an AC voltage is applied, the piezoelectric element oscillates primarily in a direction perpendicular to the measuring tube wall, which is particularly advantageous for exciting surface waves in the measuring tube wall below.

[0018] Preferably, each piezoelectric transducer has at least two electrode pairs, specifically wherein the electrodes of different electrode pairs arranged on the same side of the piezoelectric element are short-circuited. In this way, at least at the point where the electrode pairs are provided, the piezoelectric element oscillates in phase with a bending vibration type that has proven particularly suitable for generating SAW in the measuring tube wall. The distance between the electrode pairs specifically corresponds to the wavelength of the surface acoustic wave to be generated.

[0019] In a particularly preferred embodiment, all electrodes extend parallel to the longitudinal axis of the piezoelectric transducer, and at least two electrode pairs are positioned at different distances from the longitudinal axis; specifically, one electrode pair is located in the edge region of the piezoelectric transducer, and the other electrode pair is located in the central region. This configuration results in asymmetrical propagation of the surface acoustic waves emitted by the transducer; in particular, up to 50% greater amplitude is obtained on the side of the transducer where no electrode pair is located. Therefore, the acoustic waves coupled into the measuring tube via this side are advantageously used for measurement.

[0020] Preferably, the measuring tube wall has a substantially constant wall thickness throughout the measuring section, which further simplifies manufacturing. The wall thickness can even be less than that of known fluid measuring devices, as it eliminates the need for machining to create a flat contact surface for the piezoelectric transducer. This is particularly relevant to measuring tubes with a constant thin measuring tube wall, since removing material by milling is either impossible or nearly impossible in this case.

[0021] In a particularly preferred configuration, the measuring tube is constructed to be cylindrical internally and equipped with at least three piezoelectric transducers, one of which serves as a transmitter for exciting sound waves in the waveguide and at least two as receivers for receiving sound waves. The piezoelectric transducers are placed planarly against the wall of the measuring tube, and each piezoelectric transducer is arranged at an acute angle to the longitudinal extension direction of the measuring tube relative to the centerline of the measuring tube wall, and is also arranged to be staggered from each other in both the circumferential and longitudinal extension directions of the measuring tube.

[0022] This arrangement of the transducers allows for exceptionally long measurement paths for both measuring tubes with circular and angular cross-sections, thus enabling the consideration of a particularly large proportion of the fluid in the measurement.

[0023] If each piezoelectric transducer is arranged at different acute angles relative to its corresponding centerline and the longitudinal extension direction of the measuring tube, a volume wave process in the fluid can be realized, which is particularly advantageous for measurement.

[0024] According to a preferred embodiment, a first receiver is disposed on the wall of the measuring tube to receive an acoustic wave signal that is directly transmitted through the measuring tube wall, which serves as a waveguide, and a second receiver is disposed on the wall of the measuring tube to receive an acoustic wave signal that has partially propagated through the fluid as a volume wave without being reflected at the measuring tube wall. The first receiver serves as a reference, while the second receiver measures a first wave group or a first wave order.

[0025] In further development, at least one additional receiver was provided, and said additional receiver was arranged on the wall of the measuring tube to receive the signal of an acoustic wave that propagates through the fluid partly as a volume wave and has already been reflected at least once at the wall of the measuring tube. Thus, the receiver or these receivers(s) detect a second wave group or higher wave order, each receiver specifically receiving exactly one wave group through a suitable arrangement on the measuring tube.

[0026] In a preferred embodiment of the invention, at least five piezoelectric transducers are provided. In this way, three (or more) wave groups or wave orders are measured.

[0027] The signal characteristics of volume waves (which have been found to be particularly advantageous in testing) stem from the fact that the piezoelectric transducer is arranged along the measuring tube such that the two consecutive reflection zones of the volume wave in the axial direction of the measuring tube are arranged to be offset from each other by less than 180° in the circumferential direction, preferably about 125° to 130°.

[0028] In a preferred configuration, a piezoelectric transducer is arranged along a cylindrical measuring tube within the measuring section, such that the volumetric waves in the fluid travel substantially along a helix. For this purpose, the sensor is also arranged along a helix surrounding the wall of the measuring tube. With this helical waveform, a significant portion of the fluid is included in the measurement.

[0029] Advantageously, the volumetric wave omits the central region of the fluid conduit. Specifically, the diameter of the central region corresponds to half the diameter of the fluid conduit. Especially during transitions from turbulent / unsteady flow to laminar / steady flow (and vice versa) or in the case of asymmetric flow profiles, measuring the center can lead to significant measurement errors. Since unsteady flow profiles often appear directly behind branches or the like, a large inflow path must be selected in known fluid measurement devices to achieve the most accurate measurement possible, ensuring that the flow in the measurement region again primarily exhibits a steady flow profile. Therefore, measurements outside the center can achieve high measurement accuracy with a smaller inflow path. Thus, the system according to the invention can be arranged, for example, directly behind a T-section or an angled, curved, or bent pipe.

[0030] According to another preferred embodiment, the measuring tube in the measuring section is substantially rectangular in cross-section and has a flat side to which a piezoelectric transducer is attached. This refers both to the internal cross-section (i.e., the cross-section of the fluid conduit) and the external cross-section of the measuring tube, where the actual "corners" can be rounded. A substantially square cross-section is also possible, and rounded corners may be used if desired.

[0031] Exceptionally high measurement accuracy can be achieved if the piezoelectric transducer extends to at least 90% of the width of the fluid conduit. Due to the flexible design of the piezoelectric transducer, transducer lengths of 80 mm or longer are also possible.

[0032] If at least two piezoelectric transducers can operate as both transmitters and receivers, a fluid measurement device that can be used in a particularly variable manner is obtained. This design enables measurements to be taken both in the direction of and against the flow. Attached Figure Description

[0033] Further features and advantages will become apparent from the following description of several preferred embodiments with reference to the accompanying drawings, in which:

[0034] Figure 1 A partial transparent perspective view of a first embodiment of the fluid measuring device according to the present invention is shown;

[0035] Figure 2 It shows Figure 1 A partially transparent schematic side view of a fluid measurement device, illustrating the process of surface acoustic waves;

[0036] Figure 3 A to 3D shows Figure 2 Different cross-sectional views of the fluid measuring device, i.e. Figure 3 A is along line BB. Figure 3 B is along line CC. Figure 3 C is along line DD and Figure 3 D is along line EE;

[0037] Figure 4 A and Figure 4 B shows Figure 1 The front part of the fluid measurement device is partially transparent, showing the process of surface acoustic waves used as a reference.

[0038] Figure 5 A through 5C show Figure 1 The fluid measurement device is partially transparent from the side, front top, and bottom top views, thus illustrating the process of the first wave group of volume waves.

[0039] Figure 6 A through 6C show Figure 1 The fluid measurement device is partially transparent from the side, front top, and bottom top views, thus illustrating the process of the first and second wave groups of volume waves.

[0040] Figure 7 A through 7C show Figure 1The fluid measurement device is partially transparent from the side, front top, and bottom top views, thus illustrating the process of the first, second, and third wave groups of volume waves.

[0041] Figure 8 It shows Figure 1 A partially transparent perspective view of a variant of the fluid measuring device;

[0042] Figure 9 A perspective view of a piezoelectric transducer for a second embodiment of a fluid measuring device according to the present invention is shown;

[0043] Figure 10 A perspective view of a second embodiment of the fluid measuring device according to the invention is shown during the assembly of a piezoelectric transducer;

[0044] Figure 11 This shows the result after the piezoelectric transducer has been installed. Figure 10 A perspective view of the fluid measuring device;

[0045] Figure 12 A perspective view of a third embodiment of the fluid measuring device according to the invention is shown during the assembly of a piezoelectric transducer;

[0046] Figure 13 It shows Figure 12 A partially transparent perspective view of the fluid measuring device;

[0047] Figure 14 A partial longitudinal sectional view of a measuring tube with two piezoelectric transducers specifically designed for use with... Figures 1 to 8 In fluid measuring devices; and

[0048] Figure 15 A top view shows an alternative construction of a piezoelectric transducer for a fluid measuring device according to the present invention. Detailed Implementation

[0049] Figures 1 to 7 A fluid measuring device 10 according to the present invention is shown. The fluid measuring device includes a measuring tube 12 having a fluid inlet 14, a fluid outlet 16, and a fluid conduit 18 extending between the fluid inlets, through which fluid F can flow. The central section of the measuring tube 12 serves as a measuring section 20, in which a region of the measuring tube wall 22 is configured as a waveguide for surface acoustic waves OW, forming an interface with the fluid F.

[0050] For example, and not in a limiting sense, the measuring tube 12 has a cylindrical, particularly circular, cross-section in the measuring section 20, and is also internally constructed to be cylindrical.

[0051] On the outside of the measuring tube 12, a total of five piezoelectric transducers 24a, 24b, 24c, 24d, and 24e are arranged at intervals and in direct contact with the outer surface of the measuring tube wall 22 (and with the waveguide). The piezoelectric transducers 24a to 24e are integrated into the measuring tube wall 22.

[0052] To adapt the curvature of the measuring tube 12 in a planar manner without requiring milling to flatten it, the piezoelectric transducers 24a to 24e are constructed to be elastically flexible while maintaining their function. Each piezoelectric transducer has multiple strip-shaped piezoelectric elements 26 arranged parallel to each other. These strip-shaped piezoelectric elements are themselves rigid, and corresponding elastic material layers 28 are arranged between them (see, in particular). Figure 2 (Magnified details).

[0053] For example, the strip piezoelectric element 26 is approximately four to five times wider than the elastic material layer 28 (in Figure 2 (Measured in the longitudinal direction of the length l drawn in the figure), the elastic material layer is an elastomer or a cast compound.

[0054] In the non-bending state of the piezoelectric transducers 24a to 24e, the rigid strip piezoelectric element 26 and the elastic material layer 28 disposed therebetween essentially form a cuboid 30, the length l of which is approximately three times its width b, and the height h of the cuboid 30 is approximately one-tenth of its width b (see also...). Figure 9 In the construction shown, the length l of the cuboid 30 is between 5 mm and 15 mm.

[0055] When viewed in the longitudinal direction of the cuboid 30, rigid strip piezoelectric elements 26 and elastic material layers 28 arranged therebetween are alternately arranged, and each rigid strip piezoelectric element 26 extends over the entire width b of the cuboid 30.

[0056] In addition, each piezoelectric transducer 24a to 24e has a flexible printed circuit board 32 or a printed circuit board foil, for clarity, Figure 1 and 2 The illustration of the flexible printed circuit board or printed circuit board foil has been omitted. In this regard, refer to... Figure 9 The illustration shows a piezoelectric transducer 24a used in another embodiment of the fluid measuring device 10 according to the invention. Figure 1 and 2 The transducers 24a to 24e also provide corresponding flexible printed circuit boards 32 or printed circuit board foils.

[0057] A strip piezoelectric element 26 is attached to and electrically contacts a printed circuit board 32 or a printed circuit board foil. For this purpose, two electrodes 34a and 34b are provided, which are mounted on the flexible printed circuit board 32 or the printed circuit board foil.

[0058] Two electrodes 34a and 34b are arranged such that acoustic waves emitted or received by the corresponding transducers 24a to 24e are decoupled or coupled to the measuring tube 12 via the longest side S of the piezoelectric transducers 24a to 24e.

[0059] Figure 14 An exemplary arrangement of two piezoelectric transducers 24a and 24b on the measuring tube wall 22 is shown, wherein, for clarity, the longitudinal extension direction L parallel to the measuring tube 12 is shown here. M The arrangement of the two transducers 24a and 24b. Transducer 24a serves as the transmitter of surface acoustic waves (SAW) and transducer 24b serves as the receiver of SAW, and the illustration of the flexible printed circuit board 32 or printed circuit board foil has been omitted. The two piezoelectric transducers 24a and 24b are attached to the measuring tube wall 22 via an adhesive layer 35.

[0060] As can be seen from the figure, the additional electrodes 34a' and 34b' arranged on the side of the piezoelectric element 26 facing the measuring tube 12 are respectively arranged opposite to each of electrodes 34a and 34b, and electrodes 34a and 34b are respectively arranged on the side of the piezoelectric element 26 of transducers 24a and 24b away from the measuring tube 12. Electrodes 34a and 34a' or electrodes 34b and 34b' of each transducer 24a or 24b form an electrode pair.

[0061] During operation of the piezoelectric transducers 24a and 24b, an alternating voltage is applied between the first electrode 34a or 34b of the corresponding electrode pair and the associated second electrode 34a' or 34b. Furthermore, the two first electrodes 34a and 34b of different electrode pairs are short-circuited with the two second electrodes 34a' and 34b', causing the piezoelectric element 26 to oscillate in phase at the point where the electrode pair is located during operation, thereby generating surface acoustic waves OW that propagate in the measuring tube wall 22.

[0062] from Figure 2 It can also be seen that all electrodes 34a, 34a', 34b, and 34b' are parallel to the longitudinal axis L of the corresponding piezoelectric transducers 24a to 24e. W Extending, the two electrode pairs are spaced L from the longitudinal axis W The distances are different. One electrode pair 34a, 34a' is arranged in the edge region, while the other electrode pair 34b, 34b' is arranged in the central region of the corresponding piezoelectric transducers 24a to 24e.

[0063] In this way, asymmetric propagation of surface wave OW emitted by piezoelectric transducer 24a is obtained, wherein the amplitude is up to 50% larger than that on the (longest) side S of transducer 24a where no electrode pair is directly arranged (i.e., in the desired propagation direction of surface acoustic wave OW) than on the opposite (longest) side.

[0064] Especially from Figure 1 and 7 As can be seen in section B, the piezoelectric transducers 24a to 24e are each placed in a planar manner against the curved section of the measuring tube wall 22, and are positioned relative to its centerline M and the longitudinal extension direction L of the measuring tube 12. M Forming an acute angle θ a θ b θ c θ d θ e Arrangement. The centerline M is perpendicular to the longest side l of the cuboid 30, and therefore parallel to the propagation direction of the surface wave OW.

[0065] It should be noted that each piezoelectric transducer 24a to 24e is aligned with the longitudinal extension direction L of the measuring tube 12. M Closed into different acute angles θ a θ b θ c θ d θ e ( Figure 1 ).

[0066] Due to the structure of the rigid strip piezoelectric element 26, with a flexible layer 28 arranged therebetween, the piezoelectric transducers 24a to 24e themselves can also be twisted to a certain extent, relative to the longitudinal extension direction L of the measuring tube 12. M When arranged at an angle, this can ideally accommodate the curvature of the measuring tube wall 22.

[0067] Furthermore, piezoelectric transducers 24a to 24e are arranged in the circumferential direction U and the longitudinal extension direction L of the measuring tube 12. M They are staggered from each other.

[0068] If the measurement of the characteristic properties of the fluid F in the fluid conduit 18 is performed in the flow direction, then transducer 24a is used as a transmitter for exciting sound waves in the waveguide, while the remaining transducers 24b, 24c, 24d, and 24e are used as receivers for receiving sound waves.

[0069] To measure certain properties of the fluid F within the fluid conduit 18, transmitter 24a excites surface acoustic waves OW in a region of the measuring tube wall 22 directly below transmitter 24a. Due to the orientation of transducers 24a and 24b relative to each other, these surface waves OW travel along the measuring tube wall 22, which serves as a waveguide, and propagate relative to the measuring tube 12, primarily in the direction toward the first receiver 24b, where they are detected. Therefore, the first receiver 24b receives a reference signal transmitted directly through the measuring tube wall 22 (see in particular...). Figure 4 A).

[0070] Since the fluid F is in direct contact with the measuring tube wall 22, part of the energy of the surface acoustic wave OW (from the transmitter 24a) is decoupled at the interface with the fluid F on the inner surface of the measuring tube 12, and from there travels through the fluid F as a volume wave V with a specific propagation angle α (relative to the normal of the surface of the measuring tube wall 22).

[0071] If the fluid F does not move within the measuring tube 12, the incident angle α of the volume wave V entering the fluid F is derived from the ratio of the sound velocity cf in the fluid F to the sound velocity cw of the surface wave OW in the measuring tube wall 22.

[0072] α = arcsin(cf / cw)

[0073] Therefore, angle α is generated by “material pairing”, where the sound velocity cw in the measuring tube wall must be higher than the sound velocity cf in the fluid F, thus obtaining a value other than zero. Below this value, the surface wave OW couples into the fluid F and covers the spatial distance as a volume wave V. Surface waves include, in particular, Lamb waves, Rayleigh waves, or leaky Rayleigh waves used therein.

[0074] Then, the volume wave V strikes the measuring tube wall 22 in the region of the transducer 24c, which serves as the second receiver. A portion of its energy is coupled into the measuring tube 12 as a surface acoustic wave and detected by the second receiver 24c. Therefore, the second receiver 24c is arranged on the measuring tube wall 22 to detect the signal of the first wave group or first wave order of the volume wave V, which propagates directly from the transmitter 24a through the fluid F without being reflected at the measuring tube wall 22 (see, in particular). Figure 5 AC).

[0075] A portion of the energy of the volume wave V is also reflected at the measuring tube wall 22 and subsequently strikes the measuring tube wall 22 again in the region of the transducer 24d. Similarly, a portion of the energy of the volume wave V is coupled into the measuring tube 12 as a surface acoustic wave and detected by the third receiver 24d, which thus receives the signal of the second wave group or wave order of the volume wave V, which is reflected once at the measuring tube wall 22. In this way, the volume wave V propagates through the fluid F (see...). Figure 6 AC).

[0076] The remainder of the volume wave V is reflected again and eventually strikes the measuring tube wall 22 in the region of the transducer 24e, which serves as the fourth receiver, where a portion of the energy is again coupled into the measuring tube 12 as a surface acoustic wave. This is recorded by the fourth receiver 24e as the third group or wave order of the volume wave V, which propagates through the fluid F and has already been reflected twice at the measuring tube wall 22, particularly effective from... Figure 7 This can be seen from AC.

[0077] From the propagation delay between the wave pulse emitted by transmitter 24a and the signal arriving at receivers 24b to 24e, as well as from its intensity and time course, conclusions can be drawn about the properties of fluid F, such as its concentration, viscosity, speed of sound, flow rate, flow rate, temperature, and uniformity.

[0078] in particular Figure 7 As can be seen in B, piezoelectric transducers 24a, 24c, 24d, and 24e are arranged along the measuring tube 12, such that the volume wave V extends along the axial direction or longitudinal direction L of the measuring tube 12. M The two consecutive reflective regions on the surface are arranged to be offset from each other by approximately 125° to 130° in the circumferential direction U.

[0079] It is also possible to provide more piezoelectric transducers, thereby enabling the measurement of more wave groups or wave orders. However, it should be noted that the signal becomes weaker with each additional receiver.

[0080] exist Figures 1 to 7 In the construction of C, piezoelectric transducers 24a to 24e are arranged along the cylindrical measuring tube 12, such that the volume wave V in the fluid F travels substantially along a helix.

[0081] from Figure 3 As can be seen from AD, it shows various cross sections passing through the measuring tube 12 in the region of the first wave group of the volume wave V, for those generated in the fluid F and... Figure 3The volumetric wave V shown in AC achieves avoidance of the central region 36 of the fluid conduit 18, thus preventing measurement of the fluid F within this central region 36. The diameter of the omitted central region 36 is approximately half the total diameter D of the fluid conduit 18. Conversely, the region surrounding the central region 36 is fully detected. Measurements and simulations show that optimal measurement results are obtained in this manner.

[0082] Figure 3 The superposition of AC caused Figure 3 D, in which the spiral waveform of the volume wave V in the fluid F and the avoidance of the central region 36 can be seen.

[0083] exist Figure 3 It can also be seen from AC that the measuring tube wall 22 has a constant wall thickness d throughout the entire measuring section 20.

[0084] At least transducers 24a and 24e can operate as both transmitters and receivers, enabling measurements in the reverse flow direction as described above, in addition to measurements in the flow direction. If the measurement is performed in the reverse flow direction, then transducer 24e is the transmitter, transducer 24d is the first receiver, transducer 24c is the second receiver, transducer 24a is the third receiver, and transducer 24b continues to be used as a reference receiver for surface wave overcurrent (OW).

[0085] Figure 8 A slightly modified fluid measuring device 10 is shown, which is consistent with... Figures 1 to 7 The only difference is that the sensor housing is used for attaching to the sensor housing and Figure 8 The first pair of flanges 38 (not shown) for evaluating electronic equipment and the second pair of flanges 44 for integrating the fluid measuring device 10 into the piping network are disposed on the measuring tube 12, adjacent to the measuring section 20.

[0086] Figure 10 and Figure 11 A second embodiment of the fluid measuring device 10 according to the present invention is shown, with the same parts bearing the same reference numerals, and only the differences from the embodiments described so far are discussed below.

[0087] According to Figure 10 and Figure 11 In the fluid measuring device 10, the measuring tube 12 in the measuring section 20 is substantially rectangular in cross-section with slightly rounded corners. Therefore, the measuring tube 12 has a total of four flat sides 42 that are attached to the piezoelectric transducer.

[0088] In this configuration, two transducers 24a and 24b are arranged... Figure 10 and Figure 11A transducer 24c is provided on the top flat side 42 shown, and a transducer 24c is provided on the lower flat side 42 which is not visible in the figure.

[0089] All transducers 24a to 24c are arranged such that their centerline M is parallel to the longitudinal extension direction L of the measuring tube 12. M And it extends over at least 90% of the width of the fluid channel 18, and here it even extends over the entire width.

[0090] In this embodiment, the length l of transducers 24a to 24c is approximately six times their width b (see...). Figure 9 The transducers 24a to 24c are approximately 80 mm long and do not bend in the installed state because they are placed against the flat side 42 of the measuring tube 12.

[0091] When installing transducers 24a to 24c, a cuboid 30 consisting of a rigid strip piezoelectric element 26 and an elastic material layer 28 arranged therebetween is first attached to the measuring tube wall 22. Figure 10 Then, the printed circuit board 32 or printed circuit board foil, along with electrodes 34a and 34b, are attached to it. Figure 11 This also applies, incidentally, to the previously described embodiments.

[0092] Figure 12 and Figure 13 A third embodiment of the fluid measuring device 10 according to the present invention is shown, which is consistent with... Figure 10 and Figure 11 The only difference in the embodiments is the number and arrangement of the piezoelectric transducers.

[0093] Here, three piezoelectric transducers 24a to 24c are combined with two transducers 24d and 24e, and the three piezoelectric transducers are arranged such that their centerline M is parallel to the longitudinal extension direction L of the measuring tube 12. M The two transducers extend in the longitudinal direction L relative to the measuring tube 12. M The tube is inclined and arranged on the wall 22 of the measuring tube, thus enabling the helical propagation of volume waves in the fluid F.

[0094] at last, Figure 15 An alternative configuration of the piezoelectric transducer 24a is shown, which can be used to replace the other transducers 24a to 24e shown in the figures.

[0095] exist Figure 15In the piezoelectric transducer 24a, when viewed in the longitudinal and transverse directions of the cuboid 30, rigid strip-shaped piezoelectric elements 26 and layers of elastic material 28 disposed therebetween are arranged alternately. This results in the structure of the thin-plate piezoelectric elements 26 having an elongated shape and being separated from each other by a mesh of elastic material, thereby achieving improved flexibility.

[0096] Other arrangements of the piezoelectric transducer shown in the figure are of course possible; in particular, combinations of tilted flexible transducers with arrangements known in the prior art are conceivable.

Claims

1. A fluid measuring device for determining at least one characteristic property of a fluid, comprising: A measuring tube (12) having a fluid conduit (18) through which fluid can flow, and a measuring section (20) in which at least one region of the measuring tube wall (22) is configured as a waveguide for surface acoustic waves, the waveguide forming an interface with the fluid, and the measuring tube (12) being configured to be cylindrical internally. At least three piezoelectric transducers are arranged to be in direct contact with the outer surface of the waveguide, and one of the at least three piezoelectric transducers serves as a transmitter for exciting sound waves in the waveguide, and at least two piezoelectric transducers serve as receivers for receiving sound waves. in, The sound waves excited by the transmitter can propagate through the fluid, at least partially, as volume waves. The piezoelectric transducers are constructed to be elastic and flexible while maintaining their function, wherein the piezoelectric transducers have a plurality of strip piezoelectric elements (26) arranged in parallel with each other, the strip piezoelectric elements themselves being rigid, and corresponding elastic material layers (28) arranged between the strip piezoelectric elements. The piezoelectric transducer is placed against the wall of the measuring tube (22) in a planar manner. The piezoelectric transducers are arranged at an acute angle to the longitudinal extension direction of the measuring tube (12) relative to their center lines. Furthermore, the piezoelectric transducers are also arranged to be offset from each other in both the circumferential and longitudinal extension directions of the measuring tube (12). The piezoelectric transducer is arranged along the measuring tube (12), which is cylindrical in the measuring section (20), such that the volume wave in the fluid travels along a spiral, and the volume wave omits the central region (36) of the fluid conduit (18).

2. The fluid measuring device according to claim 1, characterized in that, The piezoelectric transducer is integrated into the measuring tube wall (22).

3. The fluid measuring device according to claim 1 or 2, characterized in that, The elastic material is an elastomer or a cast compound.

4. The fluid measuring device according to claim 1 or 2, characterized in that, A rigid strip piezoelectric element (26) and an elastic material layer (28) disposed between the rigid strip piezoelectric element form a cuboid (30) in a non-bending state, the length of the cuboid (30) being up to ten times its width and the height being one-tenth of its width.

5. The fluid measuring device according to claim 4, characterized in that, When viewed in the longitudinal direction of the cuboid (30), the rigid strip piezoelectric elements (26) and the elastic material layers (28) arranged between the rigid strip piezoelectric elements are alternately arranged, and each of the rigid strip piezoelectric elements (26) extends over the entire width of the cuboid (30).

6. The fluid measuring device according to claim 4, characterized in that, When viewed in the longitudinal and transverse directions of the cuboid (30), the rigid strip piezoelectric element (26) and the elastic material layer (28) arranged between the rigid strip piezoelectric element are alternately arranged.

7. The fluid measuring device according to claim 1 or 2, characterized in that, The piezoelectric transducer has a flexible printed circuit board (32) or a printed circuit board foil, and the strip piezoelectric element (26) is fastened to the flexible printed circuit board or the printed circuit board foil and is in electrical contact with the flexible printed circuit board or the printed circuit board foil.

8. The fluid measuring device according to claim 7, characterized in that, Each of the piezoelectric transducers has two electrodes mounted on the elastic printed circuit board (32) or printed circuit board foil and arranged such that sound waves are coupled into or received from the measuring tube (12) via the longest side of the piezoelectric transducer.

9. The fluid measuring device according to claim 1 or 2, characterized in that, Each piezoelectric transducer has at least one electrode pair, with the first electrode of the electrode pair disposed on the side of the piezoelectric element (26) facing away from the measuring tube (12) and the second electrode of the electrode pair disposed on the side of the piezoelectric element (26) facing the measuring tube (12) and opposite to the first electrode, and during operation of the piezoelectric transducer, a voltage is applied between the first and second electrodes of the electrode pair.

10. The fluid measuring device according to claim 9, characterized in that, Each piezoelectric transducer has at least two electrode pairs.

11. The fluid measuring device according to claim 10, characterized in that, All electrodes extend parallel to the longitudinal axis of the piezoelectric transducer, and the at least two electrode pairs are at different distances from the longitudinal axis.

12. The fluid measuring device according to claim 1 or 2, characterized in that, The measuring tube wall (22) has a constant wall thickness throughout the measuring section (20).

13. The fluid measuring device according to claim 1 or 2, characterized in that, Each piezoelectric transducer is arranged at an acute angle relative to its corresponding centerline to a different direction from the longitudinal extension of the measuring tube (12).

14. The fluid measuring device according to claim 1 or 2, characterized in that, A first receiver is arranged on the measuring tube wall (22) to receive the signal of the acoustic wave transmitted directly through the measuring tube wall (22) which serves as a waveguide, and a second receiver is arranged on the measuring tube wall (22) to receive the signal of the acoustic wave that has been partially propagated through the fluid as a volume wave and has not been reflected at the measuring tube wall (22).

15. The fluid measuring device according to claim 14, characterized in that, At least one additional receiver is provided, and the at least one additional receiver is arranged on the measuring tube wall (22) to receive the signal of the sound wave that has been partially propagated through the fluid as a volume wave and has been reflected at least once on the measuring tube wall (22).

16. The fluid measuring device according to claim 1 or 2, characterized in that, It is equipped with at least five piezoelectric transducers.

17. The fluid measuring device according to claim 1 or 2, characterized in that, The piezoelectric transducer is arranged along the measuring tube (12) such that the two consecutive reflection regions of the volume wave in the longitudinal extension direction of the measuring tube (12) are arranged to be offset from each other by less than 180° in the circumferential direction.

18. The fluid measuring device according to claim 1 or 2, characterized in that, The diameter of the central region (36) corresponds to half the diameter of the fluid conduit (18).

19. The fluid measuring device according to claim 1 or 2, characterized in that, At least two of the piezoelectric transducers can operate as both transmitters and receivers.

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