Fluid measuring device

Abstract

Fluid measuring device for determining at least one characteristic property of a fluid, comprising a measuring tube having a fluid duct through which the fluid can flow and having a measuring section, the measuring tube being internally cylindrical and at least one region of the measuring tube wall being configured as a waveguide for surface acoustic waves, which waveguide forms an interface to the fluid, and a transmitter for exciting acoustic waves in the waveguide and a receiver for receiving acoustic waves from the waveguide, the transmitter and the receiver being arranged in direct contact with the outer surface of the waveguide, the acoustic waves excited by the transmitter being adapted to propagate at least partially as bulk waves through the fluid. The waveguide has at least one elongated waveguide path which extends at least partially at an acute angle to the longitudinal extension of the measuring tube relative to the center line of the waveguide and furthermore has a component in the peripheral direction, wherein the measuring tube wall has a smaller wall thickness in the region of the waveguide path than in the region of the measuring tube adjoining the waveguide path.

Description

Technical Field

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

[0002] This invention specifically 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, sound velocity, flow rate, flow volume, temperature, and / or its uniformity. Background Technology

[0003] Document DE102019110514A1 discloses a general 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 into the fluid in direct contact with the waveguide. A portion of the SAW in the waveguide is thus coupled into and passes through the fluid as a longitudinal volumetric acoustic wave.

[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] In fluid measurement devices known from the prior art, the transmitter and receiver are arranged on the outside of the measuring tube, thus positioned on a straight line parallel to the longitudinal axis of the measuring tube. This is primarily how the fluid flowing through the center of the measuring tube is measured. However, measurements at the center, especially at transitions from turbulent to laminar flow and from laminar to turbulent flow, or in the case of asymmetric flow profiles, lead to significant measurement errors. Since turbulent or unstable flow profiles often appear directly behind branches or similar locations, a large inflow path must be selected for the most accurate measurement, ensuring that the flow in the measurement region again primarily exhibits a stable flow profile. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide a fluid measuring device that avoids the aforementioned difficulties.

[0007] To this end, the present invention provides 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 the measuring tube having a measuring section in which the measuring tube is internally cylindrical and at least one region of the measuring tube wall is configured as a waveguide for surface acoustic waves, the waveguide forming an interface with respect to the fluid; and at least one transmitter for exciting acoustic waves in the waveguide and at least one receiver for receiving acoustic waves from the waveguide, the transmitter and receiver being arranged to directly contact the outer surface of the waveguide, wherein the acoustic waves excited by the transmitter are adapted to propagate through the fluid at least partially as volume waves. The waveguide has at least one elongated waveguide path extending at least partially at an acute angle to the longitudinal extension direction of the measuring tube relative to its centerline, and furthermore, the elongated waveguide path has a circumferential component, wherein the measuring tube wall has a smaller wall thickness in the region of the waveguide path compared to the region of the measuring tube adjacent to the waveguide path.

[0008] Preferably, at least in the measurement area, the measuring tube itself is constructed to be cylindrical.

[0009] Therefore, in the fluid measuring device according to the invention, the waveguide path extends at least partially obliquely around the measuring tube, wherein the angle need not be constant over the path length. This fluid measuring device also allows for high measurement accuracy, even for small inflow paths. Due to the smaller wall thickness, surface waves are guided through the waveguide path, which is particularly suitable for allowing surface waves to propagate particularly well along the waveguide path and to couple into the fluid equally well.

[0010] Preferably, the waveguide path extends substantially along a helix surrounding the fluid conduit and / or has an S-shape. In this configuration, surface waves couple from the waveguide path into the fluid within the measuring tube at arbitrary points, a fundamental helical waveform or an S-shaped helical waveform is also obtained for the volumetric waves in the measuring tube, which extends around the center of the measuring tube and avoids the center as far as possible. Because a larger portion of the flowing fluid (far from the center) is detected and measured due to the fundamental helical waveform, this results in higher measurement accuracy.

[0011] In the preferred configuration, a smaller wall thickness (d1) in the waveguide path region is generated by a groove in the outer part of the measuring tube. Therefore, the reduction of the wall thickness can be achieved particularly easily.

[0012] The groove is preferably produced by machining, particularly by milling, which results in a simple and cost-effective manufacture of the fluid measuring device.

[0013] Preferably, the groove has a substantially U-shaped cross-section. This results in a frame consisting of substantially vertical walls that define the waveguide path and serve as the directional guidance of surface waves and as a surface wave suppression element in the boundary region of the waveguide path.

[0014] In a further development, in a top view of the groove, the groove has rounded longitudinal ends. Alternatively, the ends can also be configured to be angled or pointed. In either case, surface waves reaching the ends will be suppressed or reflected.

[0015] To achieve particularly good transmission of surface waves into the fluid, the measuring tube wall preferably has a substantially constant wall thickness along the waveguide path.

[0016] In a particularly preferred embodiment of the invention, two waveguide paths are provided. Specifically, both extend at least partially obliquely around the measuring tube. Of course, more than two waveguide paths are also conceivable. Combinations of paths extending along the measuring tube parallel to its longitudinal axis or extending circumferentially are also possible.

[0017] A particularly advantageous configuration is achieved when the two waveguide paths are staggered circumferentially along the measuring tube and, in particular, have the same shape and are preferably located at the same axial height of the measuring tube. Volume waves propagate in the fluid between the two waveguide paths.

[0018] Preferably, the two waveguide paths are circumferentially equidistant from each other along their lengths. Therefore, the two waveguide paths have identical winding, resulting in the propagation of volume waves in a fundamental helical shape within the fluid.

[0019] In a preferred embodiment, the two waveguide paths are arranged to be offset circumferentially by less than 180°, preferably about 120°. This results in the omission of the central region of the fluid conduit for volumetric waves, the diameter of which corresponds approximately half the diameter of the cylindrical fluid conduit.

[0020] Therefore, measurements are not performed at the center of the fluid conduit because simulations and measurements have shown that measurement errors occur particularly at the center of the fluid conduit during the transition from laminar to turbulent flow. In fluid measuring devices according to the prior art, these measurement errors are compensated for by large inflow paths, which are unnecessary in the construction according to the invention due to the higher measurement accuracy. Therefore, the fluid measuring device according to the invention can be arranged directly behind a T-shaped pipe section or an angled, bent, or curved pipe.

[0021] Preferably, each of the two waveguide paths is configured with a transmitter and a receiver. With a total of four transducer units, exceptionally precise measurements of the properties of the fluid flowing through the fluid conduit are achieved.

[0022] Viewed longitudinally from the measuring tube, each waveguide path preferably has a first end and a second end, wherein a transmitter is disposed at at least one first end and a receiver is disposed at at least one second end. In the case of two paths and two transmitter-receiver pairs, specifically, two transmitters are disposed at the first ends and two receivers are disposed at the second ends. If only one transmitter-receiver pair exists, the transmitter is disposed at the first end of the waveguide path, while the receiver may be disposed at the second end of the same waveguide path or another waveguide path.

[0023] In a further development of the invention, at least one end of the waveguide path where a transmitter or receiver is disposed is flat and forms a flat contact surface for the transmitter or receiver. The remaining waveguide paths (such as the outer surface of a cylindrical measuring tube) may protrude. The transducer unit is preferably coupled to the contact surface. Attached Figure Description

[0024] Further features and advantages will become clear and apparent from the following description of several preferred embodiments with reference to the accompanying drawings, wherein:

[0025] Figure 1 Partial transparent cross-sectional views of a first embodiment of the fluid measuring device according to the present invention are shown in two variations;

[0026] Figure 2 It shows Figure 1 The fluid measuring device along Figure 1 A partial sectional view of line AA in the diagram;

[0027] Figure 3 It shows Figure 1 The fluid measuring device along Figure 1 A partial sectional view of line BB in the middle;

[0028] Figure 4 It shows Figure 1 A partially transparent side view of a variant of the fluid measuring device;

[0029] Figure 5 It shows Figure 4 The fluid measuring device along Figure 4 The cross-section of line CC in the diagram;

[0030] Figure 6 It shows Figure 4 The fluid measuring device along Figure 4 The cross-section of line DD in the middle;

[0031] Figure 7 It shows Figure 4 The fluid measuring device along Figure 4 The cross-section of line EE in the middle;

[0032] Figure 8 It shows Figure 4 A top view of the front side of the fluid measuring device;

[0033] Figure 9 It shows Figure 4 A partially transparent perspective view of the fluid measuring device;

[0034] Figure 10 A partial transparent perspective view of a second embodiment of the fluid measuring device according to the present invention is shown;

[0035] Figure 11 A partial transparent perspective view of a third embodiment of the fluid measuring device according to the present invention is shown;

[0036] Figure 12 A partial transparent perspective view of a fourth embodiment of the fluid measuring device according to the present invention is shown. Detailed Implementation

[0037] Figure 1 A fluid measuring device 10 according to the invention is shown. The device includes a measuring tube 12 having a fluid inlet 14, a fluid outlet 16, and a fluid conduit 18 extending between the fluid inlet and outlet through which fluid F can flow. A middle 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, forming an interface with respect to the fluid F. The measuring tube 12 has a cylindrical, particularly circular, cross-section in the measuring section 20. Furthermore, the inner side of the measuring tube 12 is also configured as cylindrical.

[0038] The waveguide includes two slender waveguide paths 24a and 24b, which are respectively positioned relative to their respective centerlines L. a or L b (Continuing along the longitudinal direction of this path) at least partially in the longitudinal extension direction L of the measuring tube 12 M The waveguide paths 24a and 24b extend at an acute angle θ and have a component in the circumferential direction U. They also extend obliquely along the wall 22 of the measuring tube 12. The longitudinal extension direction L of the measuring tube 12... M It should be understood as a straight line extending parallel to the central axis of the measuring tube 12 within the measuring tube wall 22.

[0039] The angle θ along waveguide paths 24a and 24b can be constant, which results in a precise helix for the route of the corresponding path, but it is not necessary.

[0040] For example, in this configuration, waveguide paths 24a and 24b are slightly deviated from the precise helix and configured to be slightly S-shaped, wherein the corresponding waveguide path 24a or 24b extends from the first end 26a or 26b of the path to the center 28a or 28b of the path, thus curving slightly to the left or right. At the center 28a or 28b, the direction of curvature to the second end 30a or 30b of the corresponding waveguide path 24a or 24b changes. In the top view of the measuring tube 12, the two waveguide paths 24a and 24b may have a relative centerline L a or L b Converse or identical curvature.

[0041] In the illustrated configuration, the two waveguide paths 24a and 24b are essentially right-handed, meaning they each wind around the measuring tube 12 in a clockwise direction. Figure 1 and 4 In the side view, the first waveguide path 24a extends obliquely from top to bottom along the outer side of the measuring tube 12, while in the same side view, the second waveguide path 24b extends obliquely from bottom to top along a portion of the measuring tube wall 2 arranged in the rear part of the figure.

[0042] Two waveguide paths 24a and 24b are staggered along the circumferential direction U of the measuring tube 12. These two waveguide paths are located at the same axial height of the measuring tube 12 and have the same shape. In addition, the two waveguide paths 24a and 24b have the same winding, that is, they are equidistant from each other along the circumferential direction in their length.

[0043] For example, you can find Figure 2 and 3 As seen in the cross-sectional view, compared to the regions adjacent to waveguide paths 24a and 24b of the measuring tube 12, the measuring tube wall 22 has a smaller wall thickness d1 in the regions of waveguide paths 24a and 24b. The wall thickness d1 is constant along the entire waveguide path 24a or 24b and is the same for both waveguide paths 24a and 24b. The larger wall thickness in the adjacent regions (which also corresponds to the thickness of the rest of the measuring tube 12) is represented by d2 in the figure.

[0044] The reduced wall thickness d1 along waveguide paths 24a, 24b is achieved by creating corresponding grooves 32a or 32b in the outer portion of the measuring tube 12, more specifically in the measuring tube wall 22. The grooves 32a, 32b are manufactured by machining, for example by milling, and these grooves have a generally U-shaped cross-section. This results in an edge or a frame 34a or 34b made of a practically vertical wall, which defines the corresponding waveguide path 24a or 24b (see details). Figure 2 and 6 ).

[0045] Furthermore, the grooves 32a, 32b (as seen in the top view of the respective grooves 32a, 32b) have rounded longitudinal ends 36a or 36b. Alternatively, they may also be configured to be angular or pointed.

[0046] A transmitter 38 for exciting acoustic waves in the waveguide, particularly in the first waveguide path 24a, is disposed at a first end 26a of the first waveguide path 24a. Furthermore, a receiver 40 is disposed at a second end 30b of the second waveguide path 24b for receiving acoustic waves from the waveguide, particularly from the second waveguide path 24. Both the transmitter 38 and the receiver 40 are arranged to be in direct contact with the outer surface of the waveguide or the corresponding waveguide paths 24a, 24b.

[0047] like Figure 1 As shown by the dashed lines, in a second variation of the invention, additional transmitter-receiver pairs 38', 40' can also be provided, with the second transmitter 38' positioned at the first end 26b of the second waveguide path 24b, and the second receiver 40' positioned at the second end 30a of the first waveguide path 24a. In this configuration with a total of four transducer units (which has proven particularly advantageous in testing), transmitters 38 or 38' and receivers 40' or 40 are thus assigned to each waveguide path 24a, 24b.

[0048] The waveguide paths 24a, 24b, with their transmitter 38, 38' or receiver 40' ends 26a, 26b and 30a, 30b being flat, form flat contact surfaces for the transmitter 38, 38' or receiver 40, 40'. Transducer units are preferably bonded to these contact surfaces. The remaining waveguide paths 24a, 24b and the measuring tube 12 are curved (see also details). Figure 3 and 6 ).

[0049] The measuring tube 12 is also provided with a first pair of flanges 42 and a second pair of flanges 44. The first pair of flanges is used to attach the sensor housing and evaluation electronics (not shown in the figure), and the second pair of flanges is used to integrate the fluid measuring device 10 into the piping network (see in particular). Figure 1 ).

[0050] from Figure 4 , Figures 5 to 7 Related sectional views and Figure 8 and Figure 9 (In the first variant of the fluid measuring device 10, which has only one transmitter-receiver pair 38, 40, it can be clearly seen that the two waveguide paths 24a, 24b are arranged to be offset by approximately 120° along the circumference of the measuring tube 12.)

[0051] To measure certain properties of the fluid F within the fluid conduit 18, the transmitter 38 excites surface acoustic waves OW in the region of the waveguide path 24a directly below the transmitter 38. These surface waves OW travel substantially along the centerline L along the waveguide path 24a in the measuring tube wall 22. a Propagation occurs in the longitudinal direction. Due to the frame 34a surrounding the waveguide path 24a, the signal is purposefully guided from the transmitter 38 to the second end 30a, while surface waves OW in all other propagation directions are suppressed (see...). Figure 9 The smaller wall thickness d1 in the region of waveguide path 24a allows for good coupling and propagation of the surface wave OW along the guide path in the measuring tube wall 22. However, in the region with a larger wall thickness d2, the surface wave OW is suppressed and cannot propagate or can only propagate slightly.

[0052] Due to the direct interface between the fluid F and the waveguide or waveguide path 24a, a portion of the energy of the surface acoustic wave OW is coupled into the fluid F as a volume wave V passing through the fluid F at any point on the inner surface of the measuring tube 12 along the waveguide path 24a, and propagates from there at a specific propagation angle α (relative to the normal to the surface of the waveguide). At the opposite measuring tube wall 22, this volume wave V is coupled into the waveguide path 24b at each point and continues there as the surface wave OW to the receiver 40 that detects the corresponding signal.

[0053] This also applies to the second transmitter-receiver pair for signals at 38' and 40' (if present).

[0054] Due to the geometric design of the ends 36a and 36b of the grooves 32a and 32b, the surface waves OW reaching there are suppressed and / or reflected away from the receiver 40 or 40'.

[0055] If the fluid F does not move within the measuring tube 12, the incident angle α of the volume wave V into the fluid F is determined by the speed of sound c in the fluid F. f The sound velocity c of the surface wave OW in the measuring tube wall 22 (or waveguide path 24a or 24b) w The ratio gives us "α = arcsin(c)". f / c w )".

[0056] Therefore, angle α is derived from "material pairing," where the sound velocity c in the measuring tube wall 22 (or waveguide paths 24a, 24b) is measured. w It must be higher than the speed of sound c in fluid F. fIn order to obtain a value other than zero, the surface wave OW couples into the fluid F at a speed lower than the sound velocity in the measuring tube wall and covers a certain spatial distance as a volume wave V along the waveguide. Surface waves include, in particular, Lamb waves, Rayleigh waves, or Leaky Rayleigh waves, all of which are used in surface waves.

[0057] Preferably, the smaller wall thickness d1 of the measuring tube wall 22 in the regions of waveguide paths 24a, 24b is less than or equal to the wavelength of the surface acoustic wave OW, and in particular equal to about 50% of the wavelength of the surface acoustic wave. At this optimal wall thickness, the surface wave can propagate particularly well.

[0058] Conversely, the larger wall thickness d2 of the enclosure region is 20% to 95%, and especially 50%, greater than the wall thickness d1 of waveguide paths 24a and 24b. This prevents surface waves from coupling into the wall region surrounding waveguide paths 24a and 24b.

[0059] In the configuration shown, waveguide paths 24a and 24b are arranged to be offset by approximately 120° circumferentially along the measuring tube 12, for the fluid F generated and in Figures 5 to 8 The volume wave V shown is bypassed from the central region 46 of the fluid conduit 18, thus preventing the measurement of fluid F within this central region 46. The diameter of the omitted central region 46 is approximately half the total diameter D of the fluid conduit 18. Conversely, the region surrounding the central region 46 is fully detected. Measurements and simulations demonstrate that this method yields the best measurement results.

[0060] Figure 5 , 6 The superposition of 7 and produced Figure 8 The spiral waveform of the volume wave V in the fluid F (except for a slight S-shaped bend) and the avoidance from the central region 46 can be seen.

[0061] Figure 10 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.

[0062] according to Figure 10A fluid measuring device 10 is shown, comprising only a measuring tube 12 without any flanges, having only a single waveguide path 24a with two transducer units 39 arranged at the two ends 26a and 30a of the waveguide path 24a. In this configuration, volume waves V coupled to the fluid F are reflected, for example, in the region of the measuring tube wall 22 opposite to the waveguide path 24a. As shown by surface waves OW extending from the two ends 26a, 30a of the waveguide path 24a toward the center 28a, the two transducer units 39 can operate alternately as a transmitter and a receiver. However, a (fixed) transmitter 38 and a (fixed) receiver 40 may also be provided.

[0063] Besides those shown in the figures, other variations are of course possible. While a configuration including two transmitter-receiver pairs 38, 40, or 38', 40' is preferred, it is also sufficient to provide one transmitter 38 and one receiver 40, with the transmitter 38 arranged at a first end of one waveguide path and the receiver 40 arranged at a second end of another waveguide path. However, it is also possible to have two transducer units at each corresponding end of one waveguide path, while having no transducer units on the other waveguide path.

[0064] Furthermore, in the case of multiple waveguide paths 24a, 24b, it is also conceivable that the transducer unit can operate alternately as a transmitter and receiver.

[0065] Of course, more than two waveguide paths can be arranged on the measuring tube 12. Combinations of waveguide paths extending along the measuring tube 12 or along its circumferential direction U are also possible.

[0066] Figure 11 and 12 Two corresponding embodiments are shown, with the same parts again bearing the same reference numerals, and only the differences from the embodiments described so far are discussed.

[0067] according to Figure 11 The fluid measuring device 10 has a fluid measuring device 10 with a fluid measuring device 10 according to Figures 4 to 9 The fluid measuring device 10 has a similar design, except that it extends in the longitudinal direction L relative to the measuring tube 12. M In addition to the two inclined waveguide paths 24a and 24b, a further extension along the measuring tube 12 (i.e., parallel to the longitudinal extension direction L) is provided. M Another waveguide path 48.

[0068] Compared to the region adjacent to the waveguide path 48 of the measuring tube 12, the measuring tube wall 22 also has a smaller wall thickness in the region of the waveguide path 48. The smaller wall thickness in the region of the waveguide path 48 is also achieved by a groove 50 in the outer portion of the measuring tube 12, which is specifically manufactured by milling.

[0069] The transmitter 38” and receiver 40” are arranged on the waveguide path 48, and it is also conceivable here that the transducer unit operates alternately as a transmitter and receiver.

[0070] However, according to Figure 12 The fluid measuring device 10 has only one waveguide path 24a, which is relative to the longitudinal extension direction L of the measuring tube 12. M It extends obliquely and between two waveguide paths 48a and 48b, each of which extends along the measuring tube 12 and is arranged to be offset from each other by approximately 180° in the circumferential direction U.

[0071] Waveguide path 24a is directly connected to waveguide paths 48a and 48b, so that the wave generated by transmitter 38 can propagate along waveguide path 24a to receiver 40, and along waveguide path 48a to the other end where a second receiver 40” is arranged. In addition, receiver 40 can also receive surface acoustic waves from another transmitter 38” arranged on waveguide path 48b.

[0072] Waveguide paths 48a and 48b also have a smaller wall thickness, which is also produced by milling grooves 50a and 50b into the outer part of the measuring tube 12.

[0073] In the fluid measuring device 10 according to the invention, in principle, a single transmitter-receiver pair is sufficient to realize the basic helical waveform of the volume wave V in the fluid F. The surface wave OW is guided or directed by (multiple) waveguide paths and is transmitted particularly well into the fluid F due to the small, constant wall thickness d1 along the (multiple) waveguide paths. In contrast to known prior art structures, the center of the measuring tube 12 through which the fluid F flows is omitted during measurement, resulting in the avoidance of significant measurement errors, particularly at transitions from turbulent to laminar (or vice versa) flow or in the case of asymmetric flow profiles. Since turbulent or unstable flow profiles often appear directly behind branches or similar locations, a shorter inflow path can be selected for the fluid measuring device 10 according to the invention than in the prior art, while still achieving high measurement accuracy of the flow profile.

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 (F) can flow, and a measuring section (20) in which the measuring tube (12) is internally cylindrical, and 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 respect to the fluid (F), and At least one transmitter (38, 38') for exciting acoustic waves in the waveguide and at least one receiver (40, 40') for receiving acoustic waves from the waveguide, the transmitter and receiver being arranged to be in direct contact with the outer surface of the waveguide. The sound waves excited by the transmitter (38, 38') are adapted to propagate through the fluid (F) at least partially as volume waves (V). The waveguide is characterized in that it has at least two elongated waveguide paths (24a, 24b) arranged to be offset by less than 180° along the circumferential (U) direction of the measuring tube (12), and the volume wave (V) propagates in the fluid between the two waveguide paths (24a, 24b). The central region (46) of the fluid conduit (18) is avoided by the volume wave (V). Wherein, at least one of the waveguide paths (24a, 24b) is relative to its centerline (L) a L b At least partially aligned with the longitudinal extension direction (L) of the measuring tube (12). M The waveguide extends at an acute angle (θ), and furthermore, the waveguide path also has a component in the circumferential direction (U), and In the region of the waveguide path (24a, 24b) adjacent to the waveguide path (24a, 24b) of the measuring tube (12), the measuring tube wall (22) has a smaller wall thickness (d1).

2. The fluid measuring device according to claim 1, characterized in that, The at least one waveguide path (24a, 24b) extends along a helix around the fluid conduit (18) and / or has an S-shape.

3. The fluid measuring device according to claim 1 or 2, characterized in that, The smaller wall thickness (d1) in the region of the waveguide path (24a, 24b) is generated by the groove (32a, 32b) in the outer part of the measuring tube (12).

4. The fluid measuring device according to claim 3, characterized in that, The grooves (32a, 32b) are produced by machining.

5. The fluid measuring device according to claim 3, characterized in that, The grooves (32a, 32b) have a U-shaped cross-section.

6. The fluid measuring device according to claim 3, characterized in that, In the top view of the grooves (32a, 32b), the grooves (32a, 32b) have rounded longitudinal ends (36a, 36b).

7. The fluid measuring device according to claim 1 or 2, characterized in that, The measuring tube wall (22) has a constant wall thickness (d1) along the waveguide path (24a, 24b).

8. The fluid measuring device according to claim 1 or 2, characterized in that, The two waveguide paths (24a, 24b) have the same shape.

9. The fluid measuring device according to claim 1 or 2, characterized in that, The two waveguide paths (24a, 24b) are arranged at the same axial height of the measuring tube (12).

10. The fluid measuring device according to claim 1 or 2, characterized in that, The two waveguide paths (24a, 24b) have the same distance in the circumferential direction along their lengths.

11. The fluid measuring device according to claim 1 or 2, characterized in that, The two waveguide paths are arranged to be staggered by 120°.

12. The fluid measuring device according to claim 1 or 2, characterized in that, Each path is configured with a transmitter (38, 38') and a receiver (40, 40').

13. The fluid measuring device according to claim 1 or 2, characterized in that, From the longitudinal extension direction (L) of the measuring tube (12) M Looking at the waveguide path (24a, 24b), each waveguide path has a first end (26a, 26b) and a second end (30a, 30b), a transmitter (38, 38') disposed at at least one first end (26a, 26b) and a receiver (40, 40') disposed at at least one second end (30a, 30b).

14. The fluid measuring device according to claim 13, characterized in that, The first end (26a, 26b) and the second end (30a, 30b) of the waveguide path (24a, 24b), where at least a transmitter (38, 38') or a receiver (40, 40') is arranged, are flat and form a flat contact surface for the transmitter (38, 38') or the receiver (40, 40').

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