Fluid measuring devices

Abstract

A fluid measuring device comprises a flow channel (16) for a fluid to be measured, the flow channel having at least two regions of an outer wall (22) forming waveguide sections (24) for surface acoustic waves. The waveguide sections (24) are arranged offset and spaced apart from one another along the circumference (U) of the flow channel (16). A first and / or second signal converter (26, 28) is arranged on each waveguide section (24), wherein at least two first signal converters (26) arranged on different waveguide sections (24) or two second signal converters (28) arranged on different waveguide sections (24) are arranged offset from one another in the axial direction (A) of the flow channel (16).

Description

Technical Field

[0001] The present invention relates to a fluid measuring device. Background Art

[0002] In many installations, it is necessary to determine the flow rate of a fluid. For this purpose, a fluid measuring device is inserted into one of the fluid lines of the installation, that is, the fluid measuring device is a device by which the flow rate flowing through a measuring tube can be measured.

[0003] The fluid measuring device used should be designed to be as compact and robust as possible, i.e., require as little installation space as possible and be as maintenance-free as possible. Furthermore, it is advantageous for the fluid measuring device to be as universally applicable as possible. In particular, the fluid measuring device should be usable for different fluids or for determining different properties.

[0004] Of course, even in the case of an inhomogeneous flow in the measuring tube, as occurs, for example, when the fluid flow does not completely fill the cross section of the measuring tube, the highest possible measurement accuracy is desired.

[0005] One measurement method suitable for this task uses surface acoustic waves. These are excited in an acoustic waveguide and partially coupled out into the fluid and partially coupled back from the fluid into the waveguide, where they propagate further as surface acoustic waves. The type and frequency of the surface waves are selected so that part of the coupled-out waves enter the fluid as longitudinal volume acoustic waves. The waves coupled out into the fluid pass through the fluid and are typically reflected one or more times on the inside of the measuring tube along their measurement path before being coupled back into the waveguide. For this measurement method, the fluid is in direct contact with the waveguide. In this way, a characteristic signal is obtained at an acoustic receiver, spaced apart from a transmitter, on the waveguide. The intensity-time curve of this characteristic signal includes a time delay relative to the signal emitted by the transmitter. This characteristic signal's intensity-time curve allows inferences to be drawn about characteristic properties of the fluid, such as sound velocity, temperature, homogeneity, flow velocity, flow rate, flow volume, density, composition of a multiphase flow, concentration, or viscosity.

[0006] This measurement method is particularly suitable for liquid fluids, but is also applicable to homogeneous or heterogeneous fluids with high viscosity, pastes, gels, or slurries, including biological samples. The use of gaseous fluids is also conceivable, in which case the sound velocity, which is significantly different from that of liquids, must be taken into account. Temporal changes in the fluid can also be detected as it flows through the measuring device.

[0007] The spatial propagation of volume acoustic waves in a fluid is achieved, for example, by coupling the volume acoustic waves out into the fluid at an angle δ relative to the surface normal of the waveguide. The interrelationship for a stationary fluid can be described by the following equation:

[0008]

[0009] where c M is the velocity of the volume sound wave in the fluid and c S is the speed of sound of surface acoustic waves propagating along the waveguide.

[0010] In the most common current situation, where the speed of sound in the fluid is lower than the speed of the surface wave in the waveguide, the sound wave is coupled out at a non-zero angle, and the volume wave can travel a spatial distance along the waveguide due to multiple reflections within the fluid. Since the coupling-out angle is dependent on the sound speed of the fluid, the course of the volume wave through the fluid is also dependent on the fluid to be measured.

[0011] In known devices, the transmitter and receiver are fixed to one of the boundary surfaces by means of the side of the respective waveguide facing the fluid. To couple the surface acoustic waves excited on this side of the waveguide into the fluid, Lamb waves are preferably excited—waves with a wavelength significantly greater than the thickness of the waveguide between the transmitter and the fluid. In this case, both the upper and lower sides of the waveguide are moved, with the oscillations also having a longitudinal component. This type of excitation is therefore suitable for coupling out volume acoustic waves. It is also possible to select the wavelength of the excited surface acoustic waves in the order of magnitude of the waveguide thickness, thereby exciting the surface waves in the transition region between Lamb waves and Rayleigh waves. It is also conceivable to use Rayleigh waves or leakage Rayleigh waves.

[0012] The devices described so far in the prior art which operate according to the above-mentioned principle are of complex construction and are complex to manufacture and maintain. Summary of the Invention

[0013] The object of the present invention is to create a compact and robust, yet still flexibly usable fluid measuring device which is based on the principle of surface acoustic waves and has a high measuring accuracy and which achieves good measuring results even when measuring different fluids.

[0014] This object is achieved by means of a fluid measuring device having the features of the invention.

[0015] The fluid measuring device includes a measuring tube in which a flow channel is formed that is circumferentially closed for the fluid to be measured, and in which at least two areas of the outer wall of the measuring tube are configured as waveguide segments, each of which forms a waveguide for surface acoustic waves. A first and / or second signal converter is provided on each waveguide segment, wherein the signal converter or each signal converter is designed to excite surface acoustic waves in the corresponding waveguide segment and / or receive surface acoustic waves from the waveguide segment. The surface acoustic waves emitted by the signal converter can be coupled out of the waveguide segment and can propagate through the fluid in the flow channel as volume acoustic waves, and / or the volume acoustic waves can be coupled into the waveguide and can be received by the signal converter. The waveguide segments are arranged offset and spaced apart from each other along the circumference of the flow channel. At least two first signal converters arranged on different waveguide segments or two second signal converters arranged on different waveguide segments are arranged offset from each other in the axial direction of the flow channel.

[0016] The wall thickness of the waveguide sections is particularly selected such that incident sound waves are coupled out into the respective waveguide sections, and the resulting surface waves propagate along the waveguide sections to one of the signal converters. It has proven advantageous to reduce the wall thickness of the measuring tube in the waveguide sections compared to the wall thickness of the measuring tube outside the waveguide sections. The wall thickness of the measuring tube outside the waveguide sections is preferably selected to be large enough that reflection of bulk sound waves occurs predominantly there, while only negligible coupling out of surface waves occurs.

[0017] Between the individual signal converters, different measurement paths through the flow channel are formed depending on the sound velocity of the fluid to be measured, since the coupling-out angle and thus the coupling-in point in the waveguide section as well as possible reflection points on the inner side of the flow channel are all shifted on the waveguide section or near the waveguide section in the circumferential direction.

[0018] It should be noted that within the scope of this application, only volume waves are considered, which are coupled out into the fluid in the immediate vicinity of the signal converters, each operating as a transmitter. Although it is conceivable that the volume waves propagate beyond the waveguide section in the axial direction, so that reflection points and coupling-in locations also occur outside the waveguide section and outside the axial region between the signal converters, such reflection points and coupling-in locations are not considered within the scope of this application, as they do not contribute to the measurement and can therefore be ignored.

[0019] By optimizing the signal converter for at least two different fluid sound velocities, different measurement paths (hereinafter also referred to as measurement sections), which typically also have different lengths, are taken into account. For example, the signal strength at the signal converter operating as a receiver depends on where the volume waves are coupled into the waveguide section in which the signal converter is located. Particularly high signal strengths can be achieved if the coupling point is located directly before or in the region of the signal converter in the propagation direction. Therefore, it is advantageous to take the sound velocity of the fluid to be measured into account when selecting the spacing between the signal converter operating as a transmitter and the signal converter operating as a receiver.

[0020] Since the position of the signal converter in an already manufactured fluid measuring device cannot be changed, the measuring path and the position of the signal converter need to be optimized for the selected sound velocity and fluid.

[0021] It has been found that if the fluid measuring device is designed so that a measuring section with a greater length extending through the flow channel between two signal converters (of which one operates as a transmitter and the other as a receiver, which is a prerequisite below and not always mentioned separately) is provided for fluids with a greater sound velocity, and a measuring section with a smaller length extending through the flow channel between the two signal converters is provided for fluids with a lower sound velocity. The higher sound velocity can be selected in particular to be greater than 1800 m / s, while the lower sound velocity can be selected in particular to be less than 1300 m / s. The decoupling angle lies, for example, approximately in the range between 20° and 40°. The terms "greater length" and "shorter length" refer to the relative relationship with respect to the respective other measuring section.

[0022] The fluid measuring device preferably includes an evaluation unit that evaluates the intensity signals received from all signal converters of the fluid measuring device that are useful as receivers during the measurement and thereby determines the desired parameter to be determined. The evaluation can disregard individual signals that are, for example, too weak, or even combine multiple signals. It has been found that by selecting two measuring sections for relatively high and relatively low fluid sound velocities, it is possible to measure fluids with sound velocities that lie between these two measuring sections (for example, for water and many aqueous solutions) with very high accuracy.

[0023] In principle, within the scope of this application, it is provided that each signal converter can operate both as a transmitter and as a receiver, even if this is not otherwise stated. The corresponding function can be predetermined by a suitable control unit for the respective measurement process and can also be switched over during the time course of the measurement process. If multiple measurements are performed in which the function of the signal converter switches between transmitter and receiver, for example, a measuring section extending in the direction of fluid flow and a measuring section extending opposite to the direction of fluid flow can be implemented. The geometry of the measuring section generally remains unchanged, so that the selected position of the signal converter in the axial direction is suitable for both measuring directions.

[0024] Furthermore, depending on the diameter of the flow channel, even in fluids with the described sound velocities, the measurement path may have a greater or lesser extent of reflection points. With commonly used measuring tube dimensions, for example, diameters between 60 mm and 120 mm and lengths between 60 mm and 130 mm, a practical measuring path including reflection points cannot be defined upstream of a specific measuring tube diameter, because axially reflected bulk waves only strike the waveguide section that emitted them downstream of the signal converter. Even with low fluid sound velocities and small measuring tube diameters, a measuring path in which at most one bulk wave reflection occurs is preferred.

[0025] It is generally possible to predefine the basic extent of the measuring section as a function of the measuring tube diameter.

[0026] In a possible first variant, opposite each waveguide segment is a region of the measuring tube that is not designed as a waveguide segment and is not provided with a signal converter. The wall thickness of the outer wall of the measuring tube in these regions remains unchanged compared to the circumferentially adjacent regions of the outer wall. The fluid measuring device is designed to reflect the coupled-out volume sound waves back at these inner regions to the waveguide segment that coupled them out. In particular, the volume sound waves are reflected only once.

[0027] In this variant, the two waveguide sections are not diametrically opposed to one another on the measuring tube. Instead, the waveguide sections are circumferentially offset by an angle different from 180°, such as 45°, 60°, 90°, or 120°. Consequently, bulk waves coupled out of the waveguide sections do not impinge on the waveguide sections, but are reflected back onto the waveguide sections that excited them without significant coupling out into the measuring tube wall. There, they are partially coupled back into the waveguide sections and extend there to the signal converter serving as a receiver.

[0028] For such a fluid measuring device, a minimum of two waveguide sections and a total of four signal converters are required, two signal converters being provided on each waveguide section.

[0029] This variant is advantageous for smaller tube diameters, for example for tube diameters between 4 mm and 50 mm, in particular between 15 mm and 40 mm, based on a circular cross section of the measuring tube.

[0030] The difference between the measurement sections for fluids with a higher and lower sound velocity lies in the spacing between the first and second signal converters on the waveguide section. This spacing should therefore be different for at least two waveguide sections, with the two signal converters being located further apart from one another on the waveguide section associated with the measurement section optimized for the higher sound velocity than on the other waveguide sections.

[0031] It is of course possible to provide more than just two waveguide sections, wherein the arrangement of the signal converters can be identical for a plurality of waveguide sections or also different for all waveguides in order to either increase the number of measurement paths for individual sound velocities or to increase the number of measurement paths optimized for a specific sound velocity.

[0032] The direct measuring section between the two signal converters on the waveguide section serves in each case as a reference measuring section, on which the extension of the non-decoupled surface waves is detected.

[0033] In another embodiment, the fluid measuring device has an even number of waveguide segments, wherein two waveguide segments are arranged diametrically opposite each other and form a waveguide pair. Each waveguide pair includes a waveguide segment serving as a reference waveguide and a waveguide segment serving as a measuring waveguide. The axial position of the first signal converter and / or the second signal converter on the measuring waveguide differs in at least two of the waveguide pairs.

[0034] In total, at least four waveguide sections are required to provide two measuring sections optimized for different sound velocities. Each waveguide pair must be equipped with at least three signal converters. Two signal converters are provided on each reference waveguide. It is possible to provide only a single signal converter on the measuring waveguide.

[0035] When a total of four waveguide sections are used, these are preferably each arranged at 90° intervals along the circumference.

[0036] The distance between the first and second signal converters is preferably the same on each reference waveguide.

[0037] This embodiment is suitable for measuring tubes with larger diameters, wherein the measuring tube diameter is in particular between 10 mm and 400 mm, and in particular between 40 mm and 200 mm. Here, too, a circular cross section of the measuring tube is assumed.

[0038] Given these geometrical conditions, there are usually no reflection points in the measuring path. The outgoing bulk wave passes through the flow channel only once and is coupled back into the opposite waveguide section, where it impinges on the signal converter that is just operating as a receiver.

[0039] In different waveguide pairs, in particular the first or second signal converter is located in different axial positions.

[0040] It is therefore possible to form a measuring section between the first signal converter of the reference waveguide and the signal converter on the associated measuring waveguide of the waveguide pair, wherein in particular the outcoupled volume sound waves are not reflected on the inner side of the flow channel before they are coupled into the measuring waveguide.

[0041] In this case, the length of the measuring section can be predetermined by the position of the signal converter on the measuring waveguide and optimized for different sound speeds.

[0042] Preferably, the length of the measuring section extending through the flow channel between the first and second signal converters of diametrically opposed waveguide sections is different for the two waveguide pairs, so that at least two measuring sections optimized for different sound velocities are provided.

[0043] Of course, further waveguide pairs can be provided, in which case either a plurality of measuring sections of the same length can be realized or measuring sections of different lengths optimized for other sound velocities can be provided.

[0044] It is possible here to use one of the signal converters on the reference waveguide or the signal converter on the measuring waveguide as a transmitter, so that also in this variant, measurements in the flow direction and counter to the flow direction are possible.

[0045] The distance between the first and second signal converters can be identical on each waveguide section of two different waveguide pairs, preferably on each reference waveguide. Since only surface waves running along the measuring tube wall are detected on the reference waveguide, which are independent of the sound velocity of the respective fluid to be measured, this distance does not need to be changed.

[0046] In this variant, it is possible to use prefabricated sensor assemblies which each comprise two signal converters and a printed circuit board with the necessary electrical lines, on which the two signal converters are fixedly mounted at a predetermined distance.

[0047] Then, in each waveguide pair, two sensor assemblies are mounted at different axial positions. Thus, two signal converters are also provided on each measuring waveguide. It can then be advantageous to disable the signal converter that is not located axially between the two signal converters on the reference waveguide.

[0048] Therefore, each waveguide segment or waveguide pair can define a shorter measuring section extending through the flow channel, and each waveguide segment or waveguide pair can define a longer measuring section extending through the flow channel, so that the fluid measuring device has different measuring sections, which are respectively designed for different fluid sound velocities.

[0049] It is conceivable to arrange all signal converters at different axial positions.

[0050] Typically, the measuring tube wall is formed in one piece in the region of the flow channel, but it can also be composed of a plurality of sections.

[0051] The flow channel preferably has a circular cross-section. However, in addition to a circular cross-section, the flow channel can also have any other suitable cross-sectional shape, such as a square, rectangular, hexagonal, octagonal, or generally polygonal cross-sectional shape. However, the extent of the measuring path through the flow channel must be carefully considered.

[0052] Materials with a high sound velocity of preferably >1800 m / s are advantageous as materials for the measuring tube. For example, metals such as stainless steel, brass and copper, but also high-strength plastics have this property.

[0053] If necessary, a velocity distribution over the cross section of the flow channel can be generated using the flow measuring device according to the invention.

[0054] It has proven advantageous to arrange all waveguide sections so that they lie on parallel lines with respect to the center axis of the flow channel. The waveguide sections are therefore parallel to the flow direction. This makes the evaluation easier.

[0055] The signal converters are preferably arranged such that the volume sound waves extend from each signal converter serving as a transmitter directly through the central axis of the flow channel after being coupled out of the corresponding waveguide section. This has the advantage that all measurement paths extend through the central axis and are therefore geometrically fixed in a simple manner. This also makes evaluation easier, particularly when the flow channel is not completely filled with the fluid to be measured.

[0056] The waveguide section can form a portion of the inner side of the flow channel that is in direct contact with the fluid flowing therethrough, wherein the waveguide section is designed as a flattened portion on the rounded outer wall of the measuring tube, in which the wall thickness of the measuring tube is reduced. The first and second signal converters are each placed directly on the flattened portion of the waveguide section.

[0057] However, the inner side of the through-flow channel has no perforations, since the waveguides each form part of the through-flow channel wall. The flattened portion reduces the wall thickness to a value different from zero. The measuring tube can be designed as a tube with an uninterrupted, one-piece wall, at least in the region of the through-flow channel, wherein the waveguide section is formed by a flattened portion of the outer wall of the measuring tube, in which the wall thickness of the measuring tube is reduced compared to the circumferentially adjacent regions.

[0058] The flattened portion can be designed at its axial ends to be inclined in a side view and to taper toward the axial ends. This shape results in a continuous increase in the reduced wall thickness to the entire wall thickness of the measuring tube viewed in the axial direction, i.e., the unreduced wall thickness, and has a favorable effect on the propagation of surface waves and the coupling-out of volume waves along the waveguide section.

[0059] The flattened portion can be produced, for example, by milling, which makes it possible in a simple manner to introduce a region with reduced wall thickness into the measuring tube.

[0060] If the signal converter is a component of the sensor assembly as described above, the sensor assembly can be fixed to each waveguide segment so that the two signal converters on the outer wall of the measuring tube are in direct contact with the waveguide segment. The first and second signal converters on the waveguide segment should both be located on the flat portion.

[0061] The surface acoustic waves generated by the signal converter operating as a transmitter are then coupled directly into the waveguide section, from which they partially continue along the waveguide section as surface acoustic waves and partially couple out into the flow channel as volume waves. The signal converter operating as a receiver receives the surface acoustic waves directly from the waveguide section.

[0062] In the case of a circular cross section of the through-flow channel, the cross-sectional shape of the through-flow channel, in particular the curvature of the inner side of the through-flow channel, should be identical in the region of the waveguide section and outside the waveguide section. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The present invention will be described in detail below with reference to a number of exemplary embodiments and with reference to the accompanying drawings.

[0064] Figure 1 A schematic sectional view of a fluid measuring device according to the present invention is shown, which comprises a measuring tube and a housing surrounding the measuring tube;

[0065] Figure 2 Show Figure 1 Measuring tube of a fluid measuring device;

[0066] Figure 3 Show Figure 2 Schematic perspective view of a measuring tube in FIG, showing a waveguide section and a signal converter arranged thereon;

[0067] Figure 4 Show Figure 2 Schematic perspective view of a measuring tube in FIG, wherein sensor assemblies are mounted on the individual waveguide sections;

[0068] Figure 5 and 6 An axial top view shows the possibilities for arranging the waveguide section on the measuring tube of the fluid measuring device according to the invention for different measuring tube diameters;

[0069] Figure 7 The axial top view shows the volume wave Figure 6 Possible stretching in the measuring tube;

[0070] Figure 8 and 9 shows the course of the measuring section through the fluid passage for a first embodiment of the present invention; and

[0071] Figure 10 and 11 The course of the measuring section through the flow channel is shown for a second embodiment of the present invention. DETAILED DESCRIPTION

[0072] Figure 1 A flow measuring device 10 is shown, which is designed to measure different fluids (not shown) flowing through it in order to determine the flow velocity and / or other properties of the respective fluid.

[0073] An elongated measuring tube 14 is disposed in the housing 12 and forms a flow channel 16 for the respective fluid to be measured. The flow channel 16 is a tube that is circumferentially closed along its entire axial extension in the flow direction D. At one end, it transitions into a fluid inlet 18 and at the other end into a fluid outlet 20. A flange 21 is formed on the measuring tube 14 in the region of the fluid inlet 18 and the fluid outlet 20, respectively, and serves to mount the fluid measuring device 10 in a fluid-carrying installation. The fluid inlet 18 and the fluid outlet 20 are generally interchangeable in terms of their function.

[0074] The through-flow channel 16 forms a rectilinear section along the through-flow direction D, through which the fluid to be measured flows, wherein in the present example the cross section of the through-flow channel 16 is constant over its length.

[0075] In this case, the throughflow direction D coincides with the axial direction A of the measuring tube 14 .

[0076] The housing 12 is not designed to conduct fluid outside the measuring tube 14. Here, for example, electrical and electronic interfaces are provided, as well as a control unit, for example, for operating the fluid measuring device 10. A display is also provided if necessary.

[0077] On the outer side 23 of the outer wall 22 of the measuring tube 14, a plurality of waveguide sections 24 for surface acoustic waves are formed distributed over the circumference (see also Figure 9 and 11 ).

[0078] On each of the waveguide sections 24 , a first and / or second signal converter 26 , 28 is arranged in direct contact with the outer wall 22 of the measuring tube 14 .

[0079] exist Figure 1 and 2 The arrangement of the signal converters 26, 28 is shown only schematically. Figure 9 and 11 In particular, the possible axial positions of the signal converters 26 , 28 are shown in FIG.

[0080] In this example, the two signal converters 26, 28 on the waveguide section 24 can each be part of a sensor assembly 30 which, in addition to the two signal converters 26, 28, also includes a circuit board 32. S Mounted on the circuit board 32 (see Figure 2 and 4 ).

[0081] Optionally, the sensor arrangement 30 can also include a temperature sensor (not shown).

[0082] All signal converters 26, 28 are identically designed and are piezoelectric converters in the form of interdigital converters, which are in direct contact with the waveguide section 24. Each of these signal converters 26, 28 can function as a transmitter and a receiver. In transmitter mode, surface acoustic waves are excited in the waveguide section 24 by applying an AC voltage to the signal converters 26, 28. In receiver mode, the signal converters 26, 28 can receive the surface waves from the waveguide section 24 and convert them into electrical signals.

[0083] All signal converters 26, 28 and all waveguide sections 24 are arranged on the through-flow channel 16. In the fluid measuring device 10, only a single through-flow channel 16 is provided.

[0084] In this example, the measuring tube 14 has a circular cross section and, accordingly, also a substantially circular outer wall 22 (see, for example, Figure 3 and 4 ).

[0085] The waveguide section 24 is designed as a flattened portion 34 extending in the axial direction A in the outer wall 22 of the measuring tube 14 .

[0086] The width of the flattened portion 34 in the circumferential direction U is only slightly greater than the width of the signal converter 26 , 28 arranged completely on the respective flattened portion 34 .

[0087] Along the circumferential direction U, the measuring tube 14 has a first, thicker wall thickness W1, also referred to herein as the unreduced wall thickness, in the region of the through-flow channel 16, outside the flat portion 34 of the waveguide section 24. In the flat portion 34, i.e., in the waveguide section 24, the wall thickness W1 is reduced to a smaller value W2. However, the wall thickness always remains different from zero, so that the outer wall 22 of the measuring tube 14 does not break at any point in the region of the through-flow channel 16.

[0088] In the flow channel 16, the fluid flowing through is also in direct contact with the inner side 35 of the measuring tube 14, also in the section of the inner side 35 where the flattened portion 34 and thus the waveguide section 24 are provided radially on the outside. Therefore, the surface acoustic waves generated by the signal converters 26, 28 are partially coupled out of the waveguide section 24 into the fluid as volume acoustic waves V when in contact with the fluid, and conversely, are partially coupled back into the waveguide section 24. This is in Figure 1 and 2, wherein only the reflection points of the volume acoustic waves are schematically shown, and the surface acoustic waves running in the waveguide section 24 are not shown. It is also possible, more precisely depending on the outcoupling angle, the diameter and the length of the measuring tube 14, that the volume acoustic waves within the flow channel 16 no longer strike the inner side 35 at all after reflection.

[0089] exist Figures 2 to 4 2 and 3. The flat portions 34 forming the respective waveguide sections 24 can also be clearly seen in FIG. Each of the flat portions 34 tapers in the axial direction A at both axial ends 36, in a side view, obliquely to the respective axial end 36, so that in the axial direction A the flat portions 34 are continuous and transition without abrupt changes from the reduced wall thickness W2 to the non-reduced wall thickness W1 of the surrounding outer wall 22.

[0090] exist Figures 6 to 9 In the embodiment shown in FIG, the waveguide sections 24 are each arranged in pairs diametrically opposite one another on the outer wall 22 of the measuring tube 14, so that an imaginary straight line between the opposing waveguide sections 24 runs through the center axis M of the throughflow channel 16. A total of four waveguide sections 24 are provided, of which two opposing waveguide sections 24 are combined to form a waveguide pair 38. In each waveguide pair 38, one of the waveguide sections is a reference waveguide 40, and the other waveguide section 24 is a measuring waveguide 42 (see FIG. Figure 9 ).

[0091] In this embodiment, the measuring tube 14 has a relatively large diameter d2 , which can lie, for example, between 10 mm and 400 mm, and in particular between 40 mm and 200 mm.

[0092] As in Figure 9 As shown in , this has the effect that, after being coupled out, the bulk wave V passes through the flow channel 16 only once during the course of the measuring section, and only the portion of the bulk wave V coupled into the opposite waveguide section 24 contributes to the measuring signal. The reflected portion of the bulk wave V strikes the measuring tube wall again only downstream (if any) of the second signal converter 28 that receives the signal.

[0093] The two waveguide pairs 38 are designed differently, so that the positions of the second signal converters 28 on the respective measuring waveguides 42 are selected differently.

[0094] In both waveguide pairs 38 , second signal converter 28 on measuring waveguide 42 is located in each case in axial direction A between first and second signal converter 26 , 28 on reference waveguide 40 , but at different axial positions.

[0095] The exact axial position of the second signal converter 28 on the measuring waveguide 42 is adapted to the fixed predetermined fluid sound velocity c F1 、c F2 .

[0096] In the example shown here, the speed of sound c F1 Exemplarily selected to be equal to or less than 1300 m / s, and the speed of sound c F2 Select a speed equal to or greater than 1800 m / s.

[0097] A sensor assembly 30 is mounted on each waveguide section 24 so that the sensor assembly 30 is mounted on all four waveguide sections 24 at the same distance a. S Two signal converters 26, 28 are provided in each case. This is done for manufacturing reasons. Of course, the signal converters 26, 28 can also be installed separately. However, in this case, the first signal converter 26 on the measuring waveguide 42 is inactive and can also be switched out of operation by the evaluation unit.

[0098] On the two reference waveguides 40 , the first and second signal converters 26 , 28 are each located at the same axial position.

[0099] exist Figure 9 In the upper waveguide pair 38 in FIG. 1 , the second signal converter 28 is arranged on the measuring waveguide 42 in an axial position adapted to the fluid sound velocity c F1 The maximum received signal strength.

[0100] And in Figure 9 In the lower waveguide pair 38 in FIG. 1 , the second signal converter 28 is arranged on the measuring waveguide 42 in an axial position which is adapted to the fluid sound velocity c F2 The maximum received signal strength.

[0101] The two waveguide pairs 38 are installed offset from each other by 90° along the circumferential direction U, as shown in FIG. Figure 8 As shown in .

[0102] To measure a fluid, a fluid flow is generated through the flow channel 16 , which fluid flow extends along a flow direction D from the fluid inlet 18 to the fluid outlet 20 , or vice versa.

[0103] During a measurement, for example, the two first signal converters 26 of the reference waveguides 40 of two waveguide pairs 38 are excited and generate surface waves 44. These surface waves 44 extend along the reference waveguides 40 to the corresponding second signal converters 28 on the respective reference waveguides 40 and are detected there. A portion of the excited surface waves 44 is coupled out as volume waves V into the fluid within the flow channel 16 at an angle determined by the fluid's sound velocity and passes through the fluid until a portion of the surface waves impinges on the opposite measuring waveguide 42 and is partially coupled back in there. There, the surface waves generated in this way extend to the second signal converter 28 on the measuring waveguide 42, where they are detected as intensity signals with a time profile and forwarded to the evaluation unit.

[0104] From the data received in this way, the evaluation unit determines the expected parameters of the fluid. It is possible here to ignore the measurement signals of individual signal converters 28 or to combine the measurement signals of several or all signal converters 28.

[0105] Since the coupling-out angle is different from zero, the measuring section through which the volume wave V passes through the flow channel 16, as well as the measuring section extending from the first signal converter 26 of the reference waveguide 40 acting as a transmitter through the flow channel 16 to the measuring waveguide 42 and from there to the second signal converter 28 on the measuring waveguide 42, has an axial component that extends in the direction of flow of the fluid in the flow channel 16 or in the opposite direction to the flow direction. If measurement is to be carried out in the other direction, the second signal converter 28 on the measuring waveguide 42 can be used as a transmitter and the first signal converter 26 on the reference waveguide 40 as a receiver. The measuring section is traversed in this case in the opposite direction. The reference signal can be generated by using the second signal converter 28 on the reference waveguide 40 as a transmitter or by temporarily using the first signal converter 26 on the reference waveguide 40 as a transmitter.

[0106] Figure 7 All measuring sections are shown which each pass through a center point M of the through-flow channel 16 .

[0107] Figure 5 、 10 1 and 11 show a second embodiment, which is used in particular for a measuring tube 14 having a smaller diameter d1 , for example between 4 mm and 50 mm, in particular between 15 mm and 40 mm.

[0108] In this case, a total of only two waveguide sections 24 are provided, which are arranged offset relative to one another at an acute angle, for example, approximately 60°, in the circumferential direction U on the measuring tube 14 (see Figure 5and 10 ). With respect to the corresponding waveguide section 24 , there is a normal wall of the measuring tube 14 with an unreduced wall thickness W1 and no signal converters 26 , 28 , ie no waveguide section 24 .

[0109] A first and a second signal converter 26, 28 are respectively arranged on the two waveguide sections 24, wherein the distance between the signal converters 26, 28 of the waveguide section 24 is selected to be different for the two waveguide sections 24. Figure 11 In this case, the length a S and a S +a V It is possible to use a signal converter having a predetermined distance a for one of the two waveguide sections 24. S The sensor assembly 30 is described above and only for the second waveguide section 24 the two signal converters 26, 28 are shifted by an additional V Arranged along the axial direction A. Here, the distance between the two signal converters 26 , 28 can also be selected to be smaller than the distance a between the two signal converters 26 , 28 on the other waveguide section 24 . S .

[0110] In this embodiment, in contrast to the above embodiment, the sound velocity c for the two fluids is F1 、c F2 The coupled-out volume wave V is reflected just once on the inner side 35 of the flow channel 16 diametrically opposite the corresponding waveguide section 24 and then strikes the waveguide section 24 that couples out the volume wave again and is detected by the second signal converter 28 on this waveguide section 24.

[0111] Otherwise, the measuring method is carried out as described for the first embodiment.

[0112] It is also possible here to reverse the extent of the measuring section by operating the second signal converter 28 of the waveguide section 24 as a transmitter and the first signal converter 26 as a receiver.

[0113] Here, the reference signal is also generated on the corresponding waveguide section 24, in which the surface wave 44 extending from the first signal converter 26 to the second signal converter 28 is detected. All waveguide sections 24 are identically shaped. In the variant shown here, all waveguide sections 24 are arranged at the same position with respect to the axial direction A.

[0114] By evaluating the temporal profile of the intensity, for example, when measuring the run time difference between different measuring sections, the desired properties of the fluid are determined in the evaluation unit, which can be formed in the fluid measuring device 10 or also as an external unit. Thus, it is possible to draw conclusions about the properties of the fluid in the flow channel, such as flow velocity, flow rate, concentration, viscosity, sound velocity, temperature, and homogeneity.

Claims

1. A fluid measuring device comprising a measuring tube (14), in which a flow channel (16) is formed which is circumferentially closed for the fluid to be measured, and in which at least two regions of an outer wall (22) of the measuring tube (14) are formed as waveguide sections (24), each of which forms a waveguide for surface acoustic waves. A first signal converter (26) and / or a second signal converter (28) is provided on each waveguide section (24), and the first signal converter (26) or the second signal converter (28) or each signal converter is designed to excite surface acoustic waves in the corresponding waveguide section (24) and / or to receive surface acoustic waves from the waveguide section (24), wherein the surface acoustic waves emitted by the first signal converter and / or the second signal converter can be coupled out from the waveguide section (24) and can propagate as volume acoustic waves (V) through the fluid in the through-flow channel (16), and / or the volume acoustic waves (V) can be coupled into the waveguide section (24) and can be received by the first signal converter and / or the second signal converter, wherein the waveguide sections (24) are arranged offset and spaced apart from each other along the circumference (U) of the through-flow channel (16), At least two first signal converters (26) arranged on different waveguide sections (24) or two second signal converters (28) arranged on different waveguide sections (24) are arranged offset from each other along the axial direction (A) of the through-flow channel (16), and The fluid measuring device (10) is designed so that a measuring section with a greater length extending between two signal converters through the flow channel (16) is provided for a flow with a greater sound velocity (c F2 ) of the fluid, and a measuring section having a short length extending through the flow channel (16) between the two signal converters is provided for a fluid having a low sound velocity (c F1 ) of fluid.

2. The fluid measuring device according to claim 1, wherein: The measuring section with the greater length is provided for a sound speed of >1800 m / s, and the measuring section with the smaller length is provided for a sound speed of <1300 m / s.

3. The fluid measuring device according to claim 1, wherein: All waveguide sections (24) are opposite a respective region of the measuring tube (14), which is not formed as a waveguide section (24) and at which no signal converter is provided, wherein the wall thickness (W1) of the outer wall (22) of the measuring tube (14) in this region does not change compared to adjacent regions of the outer wall (22) in the circumferential direction, wherein the fluid measuring device (10) is designed to reflect the outcoupled volume sound waves (V) back at this region of the inner side (35) of the through-flow channel (16) to the outcoupled waveguide section (24).

4. The fluid measuring device according to claim 3, characterized in that: The volume sound wave is reflected only once.

5. The fluid measuring device according to claim 3, wherein: The fluid measuring device has a measuring tube with a diameter between 4 mm and 50 mm.

6. The fluid measuring device according to claim 5, characterized in that: The measuring tube has a diameter between 15 mm and 40 mm.

7. The fluid measuring device according to claim 3, characterized in that: The distance between a first signal converter (26) and a second signal converter (28) of a waveguide section (24) is different for at least two waveguide sections (24).

8. The fluid measuring device according to claim 1, wherein: An even number of waveguide sections (24) are provided, wherein two waveguide sections (24) are arranged diametrically opposite each other and form a waveguide pair (38), wherein each waveguide pair (38) comprises a waveguide section (24) serving as a reference waveguide (40) and a waveguide section (24) serving as a measuring waveguide (42), wherein the axial position of the first signal converter (26) and / or the second signal converter (28) on the measuring waveguide differs in at least two waveguide pairs (38).

9. The fluid measuring device according to claim 8, characterized in that: At least four waveguide sections (24) are provided.

10. The fluid measuring device according to claim 8, wherein The fluid measuring device has a measuring tube whose diameter lies between 10 mm and 400 mm.

11. The fluid measuring device according to claim 10, wherein: The diameter of the measuring tube lies between 40 mm and 200 mm.

12. The fluid measuring device according to claim 8, wherein The length of a measuring section extending through the flow channel (16) between a first signal converter (26) and a second signal converter (28) of diametrically opposed waveguide sections (24) is different for the two waveguide pairs (38).

13. The fluid measuring device according to claim 8, wherein: In different waveguide pairs (38), the first signal converter (26) and the second signal converter (28) are located at different axial positions.

14. The fluid measuring device according to claim 13, wherein: A measuring path is formed between a first signal converter (26) of the reference waveguide (40) of the waveguide pair (38) and a signal converter on the associated measuring waveguide (42).

15. The fluid measuring device according to claim 14, wherein: The outgoing volume sound waves (V) are not reflected on the inner side (35) of the flow channel (16) before they are coupled back into the measuring waveguide (42).

16. The fluid measuring device according to claim 8, wherein The distance (a) between the first signal converter (26) and the second signal converter (28) S ) are identical on each waveguide section (24) of two different waveguide pairs.

17. The fluid measuring device according to any one of claims 3 to 16, characterized in that: A respective waveguide section (24) or waveguide pair (38) defines a shorter measuring section extending through the through-flow channel (16), and a respective waveguide section (24) or waveguide pair (38) defines a longer measuring section extending through the through-flow channel (16).

18. The fluid measuring device according to any one of claims 1 to 16, characterized in that: All waveguide sections (24) are arranged such that they are each located on parallel lines with respect to a center axis (M) of the through-flow channel (16).

19. The fluid measuring device according to any one of claims 1 to 16, characterized in that: The signal converters are arranged such that the volume sound waves extend from each signal converter serving as a transmitter directly after being coupled out of the corresponding waveguide section (24) through the center axis (M) of the through-flow channel (16).

20. The fluid measuring device according to any one of claims 1 to 16, characterized in that: The waveguide section (24) forms a portion of the inner side (35) of the flow channel (16) that is in direct contact with the fluid flowing through, wherein the waveguide section (24) is designed as a flattened portion (34) on the rounded outer wall (22) of the measuring tube (14), in which the wall thickness of the measuring tube (14) is reduced.

21. The fluid measuring device according to claim 20, wherein: The flattened portions (34) are each formed obliquely at their axial ends (36) in a side view and taper toward the axial ends (36).

Images