Fluid measuring device

Abstract

Fluid measuring device with a measuring tube (14) in which a circumferentially closed flow channel (16) for a fluid to be measured is formed and in which at least two regions of an outer wall (22) of the measuring tube (14) are designed as waveguide sections (24), each forming a waveguide for surface acoustic waves, wherein a first and / or a second signal converter (26, 28) is arranged on each waveguide section (24) and the signal converter(s) (26, 28) is designed to excite surface acoustic waves in the respective waveguide section (24) and / or to receive surface acoustic waves from the waveguide section (24), wherein the signal converter (26,28) emitted acoustic surface waves can be coupled out from the waveguide section (24) and propagate as acoustic volume waves (V) through the fluid in the flow channel (16) and / or acoustic volume waves (V) can be coupled into the waveguide section (24) and received by the signal converter (26, 28), wherein the waveguide sections (24) are arranged offset and spaced apart from each other along the circumference (U) of the flow channel (16) and 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 each other in the axial direction (A) of the flow channel (16), and the fluid measuring device (10) is designed such that a measuring section running through the flow channel (16) between two signal converters (26,28) with a greater length for fluids with higher sound velocities (cF2) and a measuring section running through the flow channel (16) between two signal converters (26, 28) with a shorter length for fluids with lower sound velocities (cF1), wherein each waveguide section (24) is opposite a region of the measuring tube (14) which is not designed as a waveguide section (24) and on which no signal converters (26, 28) are provided, wherein a wall thickness (W1) of the outer wall (22) of the measuring tube (14) in these regions is unchanged compared to the circumferentially adjacent regions of the outer wall (22), wherein the fluid measuring device (10) is designed such that the coupled volume sound wave (V) is reflected back at this region of the inner side (35) to the waveguide section (24) from which it was coupled, in particular only once,or an even number of waveguide sections (24), in particular at least four waveguide sections (24), is provided, wherein two waveguide sections (24) are arranged diametrically opposite each other and form a waveguide pair (38), wherein each waveguide pair (38) has 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 and / or the second signal converter (26, 28) on the measuring waveguide differs in at least two waveguide pairs (38).

Description

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

[0002] In many systems, it is necessary to determine the flow rate of a fluid. For this purpose, a fluid measuring device is installed in one of the system's fluid lines; that is, a device by means of which the flow rate of a fluid flowing through a measuring tube can be measured.

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

[0004] Naturally, the highest possible measurement accuracy is also desired in the case of uneven flow in the measuring tube, such as can occur when the fluid flow does not completely fill the cross-section of the measuring tube.

[0005] One measurement method suitable for such a task is the use of surface acoustic waves (SAWs). These waves are excited in an acoustic waveguide and partially coupled into the fluid, while the remaining portion is coupled back into another waveguide, where they continue to propagate as SAWs. The type and frequency of the SAWs are chosen such that partial coupling occurs as longitudinal volumetric sound waves into the fluid. The waves coupled into the fluid travel through it and are typically reflected once or multiple times along their measurement path by an inner surface of the measuring tube 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, which is arranged at a distance from the transmitter on a waveguide, the temporal intensity profile of which, including the time delay compared to the signal emitted by the transmitter, allows conclusions to be drawn about characteristic properties of the fluid such as speed of sound, temperature, homogeneity, flow velocity, flow rate, flow volume, density, composition of a multi-phase flow, concentration or viscosity.

[0006] This measurement method is particularly suitable for liquids, but also for highly viscous, dough-like, gel-like, or pasty fluids of homogeneous or inhomogeneous nature, including biological samples. Its use with gaseous fluids would also be conceivable, although in this case the significantly different sound velocities of gases and liquids would have to be taken into account. When the fluid flows through the measuring device, temporal changes in the fluid can also be detected.

[0007] The spatial propagation of volume sound waves in a fluid is achieved, for example, by coupling the volume sound waves into the fluid at an angle δ relative to a surface normal of the waveguide. For a stationary fluid, this relationship can be described by the following formula: δ = arcsin ( CMCS ) , where C MThe speed of sound of the volume sound waves within the fluid and the speed of sound of the acoustic surface waves propagating along the waveguide.

[0008] In the most common case, where the speed of sound in the fluid is lower than that of the surface waves in the waveguide, sound waves are coupled out at a non-zero angle, and the volumetric sound waves travel a spatial distance along the waveguide, possibly undergoing multiple reflections within the fluid. Since the coupling angle depends on the speed of sound in the fluid, the propagation of the volumetric waves through the fluid also depends on the fluid being measured.

[0009] In known devices, the transmitter and receiver are attached to the side of the respective waveguide opposite the interface with the fluid. To couple surface sound waves excited on this side of the waveguide into the fluid, Lamb waves are preferably excited—waves whose wavelength is significantly longer than the thickness of the waveguide between the transmitter and the fluid. In this case, both the top and bottom surfaces of the waveguide move, and the oscillation also has a longitudinal component. Therefore, this type of excitation is suitable for coupling out volume sound waves. It is also possible to select the wavelength of the excited acoustic surface waves on the order of the thickness of the waveguide, thereby exciting surface waves in a transitional region between Lamb waves and Rayleigh waves. It would also be conceivable to use Rayleigh waves or leaky Rayleigh waves.

[0010] The devices described in the prior art so far, which operate according to the principle described above, are complex in design and costly in terms of manufacturing and maintenance.

[0011] The object of the invention is to create a compact and robust, yet flexibly applicable fluid measuring device based on the principle of acoustic surface waves with high measuring accuracy, which also achieves good measurement results when measuring different fluids.

[0012] This problem is solved with a fluid measuring device having the features of claim 1.

[0013] The fluid measuring device comprises a measuring tube in which a circumferentially closed flow channel for a fluid to be measured is formed, and in which at least two regions of an outer wall of the measuring tube are designed as waveguide sections, each forming a waveguide for surface acoustic waves. A first and / or a second signal converter is arranged on each waveguide section, wherein the signal converter(s) is / are designed to excite surface acoustic waves in the respective waveguide section and / or to receive surface acoustic waves from the waveguide section. Surface acoustic waves emitted by the signal converter can be coupled out from the waveguide section and propagate as volumetric acoustic waves through the fluid in the flow channel, and / or volumetric acoustic waves can be coupled into the waveguide and received by the signal converter.The waveguide sections are arranged offset from one another and spaced apart along the circumference of the flow channel. At least two first signal converters arranged on different waveguide sections, or two second signal converters arranged on different waveguide sections, are arranged offset from one another in the axial direction of the flow channel.

[0014] The waveguide sections are selected, particularly with regard to their wall thickness, such that incident volume sound waves are coupled into the respective waveguide section, and the resulting surface wave propagates along the waveguide section to one of the signal converters. It has proven advantageous to reduce the wall thickness of the measuring tube within 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 there is essentially only a reflection of the volume sound wave, but only a negligible coupling of surface waves.

[0015] Depending on the speed of sound of the fluid being measured, different measurement paths are formed between the individual signal converters through the flow channel, since the coupling angles and thus both the coupling points into the waveguide section and any reflection points on the inside of the flow channel shift on the waveguide sections or in the circumferential direction next to the waveguide sections.

[0016] It should be noted that this application only considers volume waves that are coupled into the fluid in the immediate vicinity of the signal converter acting as the transmitter. While it is conceivable that the volume waves propagate axially beyond the waveguide sections, resulting in reflection points and coupling points outside the waveguide sections and outside the axial area between the signal converters, such reflection points and coupling points are not considered in this application because they do not contribute to the measurement and are therefore negligible.

[0017] The different measurement paths (hereinafter also referred to as measurement sections), which are generally of different lengths, are accommodated by optimizing the arrangement of the signal converters for at least two different fluid sound velocities. For example, the signal intensity at the signal converter acting as a receiver depends on where the volume wave couples into the waveguide section where this signal converter is located. Particularly high signal intensities can be achieved if the coupling point is located immediately in front of or directly within the area of ​​this signal converter along the direction of propagation. Therefore, it is advantageous to consider the sound velocities of the fluids to be measured when selecting the distance between the signal converters acting as transmitters and receivers.

[0018] Since the position of the signal transducers in the completed fluid measuring device can no longer be changed, it is necessary to optimize the measuring paths and the position of the signal transducers specifically for selected sound velocities and fluids.

[0019] It has been found that good measurement results for different fluids can be achieved if the fluid measuring device is designed such that a measuring section running through the flow channel between two signal converters (one of which acts as a transmitter and one as a receiver; this is assumed below and not always explicitly stated) is of a longer length for fluids with higher sound velocities, and a measuring section running through the flow channel between two signal converters of a shorter length for fluids with lower sound velocities. The higher sound velocity can be selected to be greater than 1800 m / s and the lower sound velocity less than 1300 m / s. The coupling angles are, for example, in the range of approximately 20° to 40°. The terms "greater length" and "shorter length" refer to the other measuring section.

[0020] The fluid measuring device preferably comprises an evaluation unit that analyzes the intensity signals received by all signal transducers of the fluid measuring device that can be used as receivers during a measurement, and thus determines the desired parameter to be measured. During the evaluation, it is possible to disregard individual signals, for example, those that are too weak, or to combine several signals. It has been found that by selecting two measuring sections for relatively high and relatively low fluid sound velocities, fluids with intermediate sound velocities (as is the case, for example, with water and many aqueous solutions) can also be measured with very high accuracy.

[0021] This application generally assumes that each signal converter can function as both a transmitter and a receiver, even if this is not explicitly stated. The specific function can be defined by a suitable control unit for each measurement process and can also change during the course of a measurement. If multiple measurements are performed where the signal converter's function alternates between transmitter and receiver, for example, a measuring section running with the fluid flow and another running against the fluid flow can be implemented. The geometry of the measuring section typically remains unchanged, so the selected axial position of the signal converters is suitable for both measurement directions.

[0022] Furthermore, depending on the diameter of the flow channel, the measurement path for fluids with the described sound velocities will have more or fewer reflection points. With common measuring tube dimensions, for example, a diameter between 60 and 120 mm and a length between 60 and 130 mm, it is no longer possible to define a practical measurement path that includes a reflection point above a certain measuring tube diameter, since the reflected volume wave would only encounter the waveguide section from which it originates after passing through the signal converter. Even with lower fluid sound velocities and smaller measuring tube diameters, measurement paths are preferred in which at most one reflection of the volume wave occurs.

[0023] In general, it is possible to specify a basic course of the measuring section depending on the measuring tube diameter.

[0024] In one possible configuration, each waveguide section is opposite a portion of the measuring tube that is not designed as a waveguide section and on which no signal converters are provided. These portions of the outer wall of the measuring tube have a wall thickness that is unchanged compared to the circumferentially adjacent portions of the outer wall. The fluid measuring device is designed such that the coupled-out volume sound wave is reflected back at this portion of the inner wall to the waveguide section from which it was coupled. In particular, the volume wave is reflected only once.

[0025] In this configuration, the two waveguide sections are not diametrically opposed on the measuring tube, but rather the waveguide sections are offset along the circumference by an angle that deviates from 180°, where the angle is, for example, 45°, 60°, 90°, or 120°. Therefore, the volume wave coupled out from one waveguide section does not encounter another waveguide section, but is reflected back at the measuring tube wall to the waveguide section where the volume wave was generated, with no significant coupling occurring. There, the volume wave is partially coupled back into the waveguide section and travels within it to the signal converter, which serves as the receiver.

[0026] For such a fluid measuring device, a minimum of two waveguide sections and a total of four signal converters are required, with two signal converters arranged on each waveguide section.

[0027] This variant is suitable for smaller pipe diameters, for example, for measuring tube diameters between 4 mm and 50 mm, especially between 15 mm and 40 mm. This assumes a circular cross-section of the measuring tube.

[0028] The measuring sections for fluids with higher and lower speeds of sound differ primarily in the distance between the first and second signal converters on a waveguide section. Therefore, these distances should be different for at least two waveguide sections, with the two signal converters positioned further apart on the waveguide section assigned to the measuring section optimized for higher speeds of sound than on the other waveguide section.

[0029] Of course, it is possible to provide more than two waveguide sections, whereby the arrangement of the signal converters can be identical for several waveguide sections or different for all waveguides, in order to either increase the number of measurement paths for individual sound velocities or the number of measurement paths optimized for a specific sound velocity.

[0030] The direct path between the two signal converters on a waveguide section serves as a reference path on which the course of the uncoupled surface waves is recorded.

[0031] In another variant, the fluid measuring device has an even number of waveguide sections, with each pair of waveguide sections arranged diametrically opposite each other. Each waveguide pair comprises one waveguide section serving as a reference waveguide and one waveguide section serving as a measuring waveguide. The axial position of the first and / or the second signal transducer on the measuring waveguide differs in at least two waveguide pairs.

[0032] At least four waveguide sections are required to provide two measuring sections optimized for different sound velocities, with a minimum of three signal converters required per waveguide pair. Two signal converters are arranged on each reference waveguide. It is possible to use only a single signal converter on the measuring waveguides.

[0033] When using a total of four waveguide sections, these are preferably arranged at 90° intervals along the circumference.

[0034] The distance between the first and second signal converters is preferably the same on each of the reference waveguides.

[0035] This design is suitable for measuring tubes with a larger diameter, particularly between 10 mm and 400 mm and especially between 40 mm and 200 mm. Here too, a circular cross-section of the measuring tube is assumed.

[0036] Under these geometric conditions, there is normally no reflection point in the measuring section. The coupled-out volume waves traverse the flow channel only once and are coupled into the opposite waveguide section, where they encounter a signal converter that is currently acting as a receiver.

[0037] In different waveguide pairs, the first or second signal converters are located in different axial positions.

[0038] This makes it 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, whereby in particular the coupled-out acoustic volume waves are not reflected on an inside of the flow channel before they couple into the measuring waveguide.

[0039] Here, the length of the measuring section can be specified by the position of the signal converter on the measuring waveguide and optimized for different sound velocities.

[0040] Preferably, the length of a measuring section running through the flow channel between a first and a second signal converter of diametrically opposed waveguide sections is different for two waveguide pairs, so that at least two measuring sections optimized for different sound velocities are provided.

[0041] Of course, additional waveguide pairs can be provided, whereby either several measuring sections of equal length can be implemented or measuring sections of different lengths optimized for other sound velocities can be provided.

[0042] It is possible to use one of the signal converters on the reference waveguide or a signal converter on the measuring waveguide as a transmitter, so that measurement in and against the flow direction is possible in this variant as well.

[0043] The distance between the first and second signal converters can be the same on each waveguide section of two different waveguide pairs, preferably on the reference waveguide. Since only the surface wave propagating along the measuring tube wall is detected on the reference waveguide, which is independent of the speed of sound of the fluid being measured, it is not necessary to vary this distance.

[0044] In this variant, it is possible to use prefabricated sensor assemblies, each comprising two signal converters and a circuit board with the necessary electrical lines, on which the two signal converters are permanently mounted at a specified distance.

[0045] In each waveguide pair, two sensor assemblies are installed at different axial positions. This means that two signal converters are also provided on each measuring waveguide. It can then be advantageous to disable the signal converter located on the reference waveguide that is not axially aligned between the two signal converters.

[0046] Each waveguide section or waveguide pair can thus define a shorter measuring section running through the flow channel, and each waveguide section or waveguide pair can define a longer measuring section running through the flow channel, so that the fluid measuring device has different measuring sections, each designed for different fluid sound velocities.

[0047] It is conceivable to arrange all signal converters at different axial positions.

[0048] The measuring tube wall is normally formed in one piece in the area of ​​the flow channel. However, it could also be composed of several sections.

[0049] The flow channel preferably has a circular cross-section. However, in addition to a circular cross-sectional shape, the flow channel can also have any other suitable cross-sectional shape, such as square, rectangular, hexagonal, octagonal, or generally polygonal. The path of the measuring sections through the flow channel must be taken into account.

[0050] Materials with a high sound velocity, preferably >1800 m / s, are advantageous for the measuring tube. For example, metals such as stainless steel, brass, and copper, as well as high-strength plastics, possess this property.

[0051] If necessary, a velocity profile can be created across the cross-section of the flow channel using the fluid measuring device according to the invention.

[0052] It has proven advantageous to arrange all waveguide sections so that they each lie on a line parallel to the central axis of the flow channel. This ensures that the waveguide sections are parallel to the flow direction, which facilitates data analysis.

[0053] Preferably, the signal converters are arranged such that acoustic volume waves, immediately after being coupled from the respective waveguide section of each signal converter acting as a transmitter, pass through the central axis of the flow channel. This has the advantage that all measurement paths pass through the central axis and are thus geometrically defined in a simple manner. This also facilitates evaluation, especially when the flow channel is not completely filled with the fluid being measured.

[0054] The waveguide sections can form part of the inner surface of the flow channel that comes into direct contact with the fluid flowing through it. These waveguide sections are designed as flattened areas on a rounded outer wall of the measuring tube, where the wall thickness of the measuring tube is reduced. The first and second signal transducers are each placed directly on the flattened area of ​​a waveguide section.

[0055] The inner surface of the flow channel is not perforated, however, because the waveguides each form part of the flow channel wall. The flattening reduces the wall thickness to a non-zero value. The measuring tube can be designed, at least in the flow channel area, as a tube with a continuous, single-piece wall, with the waveguide sections formed by flattening of the outer wall of the measuring tube, where the wall thickness is reduced compared to the circumferentially adjacent areas.

[0056] The flattened sections can be inclined at their axial ends in side view, tapering towards the axial end. Such a shape results in a gradual increase of the reduced wall thickness to the full, undiminished wall thickness of the measuring tube, as seen in the axial direction, and has a beneficial effect on the propagation of surface waves and the decoupling of volume waves along the waveguide section.

[0057] The flattening can be produced, for example, by milling, which makes it easy to introduce areas with reduced wall thickness into the measuring tube.

[0058] If the signal converters are part of a sensor assembly as described above, a sensor assembly can be attached to each waveguide section in such a way that the two signal converters on the outer wall of the measuring tube are in direct contact with the waveguide section. Both the first and second signal converters on a waveguide section should rest on the flat surface.

[0059] Acoustic surface waves, generated by a signal converter acting as a transmitter, are then coupled directly into the waveguide section, from where they propagate partly along the waveguide as acoustic surface waves and partly are coupled out as volume waves into the flow channel. A signal converter acting as a receiver receives acoustic surface waves directly from the waveguide section.

[0060] The shape of the cross-section of the flow channel, in particular the curvature of an inside of the flow channel, should be the same in the area of ​​the waveguide sections and outside the waveguide sections in the case of a circular cross-section of the flow channel.

[0061] The invention is described in more detail below with reference to several exemplary embodiments and the accompanying drawings. The drawings show: - Fig. 1 a schematic sectional view of a fluid measuring device according to the invention with a measuring tube and a housing surrounding the measuring tube; - Fig. 2 the measuring tube of the fluid measuring device Fig. 1; - Fig. 3 a schematic perspective representation of the measuring tube made of Fig. 2, showing waveguide sections and signal converters arranged on them; - Fig. 4 a schematic perspective representation of the measuring tube made of Fig. 2, in which sensor assemblies are mounted on the individual waveguide sections; - Fig. 5 and Fig. 6 possibilities for arranging the waveguide sections on the measuring tube of a fluid measuring device according to the invention for different measuring tube diameters, in an axial top view; - Fig. 7 a possible course of the volume waves in the measuring tube of the Fig. 6, in an axial top view; - Fig. 8 and Fig. 9 a course of a measuring section through the flow channel for a first embodiment of the invention; and - Fig. 10 and Fig. 11 a course of a measuring section through the flow channel for a second embodiment of the invention.

[0062] Fig. Figure 1 shows a fluid measuring device 10, which is designed to measure different fluids flowing through it (not shown) in order to determine a flow rate and / or other properties of the respective fluid.

[0063] In a case 12 is an elongated measuring tube 14 arranged to form a flow channel 16 for the respective fluid to be measured. The flow channel 16 is a tube that is closed along its entire axial extent along a flow direction D and has a fluid inlet at one end. 18 and at the other end into a fluid outlet 20 transitions. In the area of ​​the fluid inlet. 18 and the fluid outlet 20 Each is a flange 21 on the measuring tube 14 trained, which serves to operate the fluid measuring device 10 to be installed in a fluid-carrying system. Fluid inlet is normally 18 and fluid outlet20 Interchangeable in their function.

[0064] The flow channel 16 This forms a straight path along the flow direction D through which the fluid to be measured flows, where the cross-sectional area of ​​the flow channel 16 In this example, the length is constant.

[0065] The flow direction D coincides here with the axial direction A of the measuring tube. 14 together.

[0066] The case 12 is outside the measuring tube 14 It is not designed to carry fluids. For example, it contains electrical and electronic connections, as well as a control unit for operating the fluid measuring device. 10 arranged. A display may also be provided.

[0067] On one outside 23 an exterior wall 22 of the measuring tube 14 Several waveguide sections are distributed around the circumference. 24designed for acoustic surface waves (see also Fig. 9 and Fig. 11).

[0068] On each of the waveguide sections 24 is in direct contact with the outer wall 22 of the measuring tube 14 a first and / or a second signal converter 26 , 28 arranged.

[0069] In the Fig. 1 and Fig. 2 is the arrangement of the signal converters 26 , 28 Only shown schematically. In particular, possible axial positions of the signal converters. 26 . 28 result from the Fig. 9 and Fig. 11.

[0070] In this example, the two signal converters 26 , 28 on a waveguide section 24 each part of a sensor assembly 30 be, which are next to the two signal converters 26 , 28 also a circuit board 32 includes the two signal converters26 , 28 at a predetermined distance as are mounted from each other (see Fig. 2 and Fig. 4).

[0071] Optionally, the sensor assembly can be 30 also have a (not shown) temperature sensor.

[0072] All signal converters 26 , 28 are identically constructed and are piezo transducers in the form of an interdigital converter that covers the waveguide section 24 contacted directly. The signal converters 26 , 28 They can each be used as both transmitters and receivers. In transmitter mode, an alternating voltage is applied to the signal converter. 26 , 28 acoustic surface waves in the waveguide section 24 stimulated. In receiver mode, the signal converter can 26 , 28 Surface waves from the waveguide section 24 receive and convert into electrical signals.

[0073] All signal converters 26 , 28 and all waveguide sections 24 are at the flow channel 16 arranged. It is only a single flow channel. 16 in the fluid measuring device 10 planned.

[0074] The measuring tube 14 In this example, it has a circular cross-section and therefore also an essentially round outer wall. 22 (see for example) Fig. 3 and Fig. 4).

[0075] The waveguide sections 24 are flattenings extending in the axial direction A 34 in the outer wall 22 of the measuring tube 14 trained.

[0076] The width of the flattening 34 In the circumferential direction, U is only slightly larger than the width of the signal converter. 26 , 28 , which are entirely on the respective flattening 34 are arranged.

[0077] The measuring tube points along the circumferential direction U. 14 in the area of ​​the flow channel 16 outside the flattened areas 34 the waveguide sections 24 a first, thicker wall thickness W1 on, which is also referred to here as undiminished wall thickness. In the flattened areas 34 , i.e., the waveguide sections 24 , is the wall thickness W1 to a smaller value W2 reduced. However, the wall thickness always remains different from zero, the outer wall 22 of the measuring tube 14 is therefore in the area of ​​the flow channel 16 not penetrated at any point.

[0078] In the flow channel 16 The fluid flowing through comes into direct contact with the inside. 35 of the measuring tube 14 , also on the sections of the inside 35 , where the flattenings are radially outside 34and thus the waveguide sections 24 are provided for. The signal converters 26 , 28 The generated acoustic surface waves are therefore partially converted into acoustic volume waves upon contact with the fluid. V from the waveguide sections 24 coupled out into the fluid and conversely partially back into the waveguide sections 24 coupled. This is schematically shown in the Fig. 1 and Fig. Figure 2 shows the reflection points of the acoustic volume waves only schematically, and also those in the waveguide sections. 24 The propagating acoustic surface waves are not shown. It is also possible, depending on the coupling angle, the diameter, and the length of the measuring tube. 14 that the volume wave within the flow channel 16 after a reflection, it no longer appears on the inside at all. 35 hits.

[0079] In the Fig. 2 to Fig. 4 are also the flattened areas. 34 It is easy to see which are the respective waveguide sections. 24 form. Each of the flattenings 34 runs in axial direction A at both axial ends 36 in side view oblique to the respective axial end 36 to such an extent that the flattening occurs in the axial direction A 34 The reduced wall thickness decreases steadily and without an abrupt step. W2 to the undiminished wall thickness W1 the surrounding outer wall 22 transitions.

[0080] In the Fig. 6 to Fig. In the embodiment shown in 9, the waveguide sections are 24 each pair diametrically opposite each other on the outer wall 22 of the measuring tube 14 arranged so that an imaginary straight line runs between opposing waveguide sections 24 through a central axis M of the flow channel 16It runs through four waveguide sections. 24 provided for, with two opposing waveguide sections each 24 to a waveguide pair 38 are summarized. In each waveguide pair 38 One of the waveguide sections serves as a reference waveguide. 40 and the other waveguide section 24 a measuring waveguide 42 (see Fig. 9).

[0081] The measuring tube 14 In this embodiment, it has a relatively large diameter. d2 , which can be, for example, between 10 mm and 400 mm and, in particular, between 40 mm and 200 mm.

[0082] This leads to the following, as in Fig. 9 shows that the volume waves V after disconnecting the flow channel 16 only traverse the measuring path once and only those in the opposite waveguide section 24coupled components of the volume waves V Contributing to the measurement signal. Reflected components of the volume waves V They only meet (if at all) after the second signal converter. 28 , which receives the signal, back onto the wall of the measuring tube.

[0083] The two waveguide pairs 38 are designed differently in that the position of the second signal converter 28 on the respective measuring waveguides 42 The choice is different.

[0084] In both waveguide pairs 38 The second signal converters are located 28 on the measuring waveguides 42 in axial direction A between the first and second signal converters 26 , 28 on the reference waveguides 40 , however in different axial positions.

[0085] The exact axial positions of the second signal converter 28on the measuring waveguides 42 is each tied to a fixed, predetermined fluid sound velocity C F1 , C F2 adjusted.

[0086] In the examples shown here, the speed of sound C F1 For example, equal to or less than 1300 m / s and the speed of sound C F2 For example, a speed of 1800 m / s or greater was chosen.

[0087] At each waveguide section 24 is a sensor assembly 30 mounted so that on all four waveguide sections 24 two signal converters each 26 , 28 at the same distance a s are arranged. This is done for manufacturing reasons. Of course, the signal converters could also be 26 , 28 They can be mounted separately. The first signal converters 26 on the measuring waveguides 42 However, they are non-functional here and may also be deactivated by the evaluation unit.

[0088] On the two reference waveguides 40 The first and second signal converters are located there 26 , 28 here in the same axial position.

[0089] In the Fig. 9 upper waveguide pair 38 is the second signal converter 28 on the measuring waveguide 42 mounted in an axial position that provides maximum received signal intensity for the fluid speed of sound C F1 is adapted.

[0090] In the Fig. 9 lower waveguide pair 38 is the second signal converter 28 however, on the measuring waveguide 42 mounted in an axial position that provides maximum received signal intensity for the fluid speed of sound C F2 is adapted.

[0091] The two waveguide pairs 38are mounted offset from each other by 90° in the circumferential direction U, as shown in Fig. 8 is shown.

[0092] To measure a fluid, a fluid flow is observed through the flow channel. 16 generated, which along the flow direction D either from the fluid inlet 18 to the fluid outlet 20 or vice versa.

[0093] For example, during a measurement, both first signal converters are used. 26 the reference waveguide 40 the two waveguide pairs 38 excited and generate surface waves 44 These surface waves 44 They run, firstly, along the reference waveguide 40 to the respective second signal converter 28 on the respective reference waveguide 40 and are detected there. A portion of the excited surface waves 44 is described as volume waves V into the fluid inside the flow channel 16They are coupled out at an angle determined by the fluid's speed of sound and pass through the fluid until they reach the opposite measuring waveguide. 42 They meet and are partially re-coupled there. The surface waves thus generated then travel to the second signal converter. 28 on the measuring waveguide 42 and are detected there as an intensity signal with a temporal profile and passed on to the evaluation unit.

[0094] The evaluation unit uses the received data to determine the desired fluid parameter. It is possible to analyze measurement signals from individual signal converters. 28 to ignore or the measurement signals of several or all signal converters 28 to combine.

[0095] Due to the non-zero coupling angle, the measuring section, which measures the volume wave V through the flow channel 16travels and the first signal converter acting as a transmitter 26 of the reference waveguide 40 through the flow channel 16 to the measuring waveguide 42 and from there to the second signal converter 28 on the measuring waveguide 42 runs, an axial component that either in or against the flow direction of the fluid in the flow channel 16 The process runs. If measurement is to be taken in the other direction, the second signal converter can be used in each case. 28 on the measuring waveguide 42 be used as a transmitter, while the first signal converter 26 on the reference waveguides 40 It serves as a receiver. The measuring path is traversed in reverse. The reference signal can be obtained either by using the second signal converter. 28 on the reference waveguides 40 generated as transmitters or by temporarily using the first signal converters 26on the reference waveguides 40 as a sender.

[0096] Fig. Figure 7 shows that all measuring distances pass through the center point. M of the flow channel 16 get lost.

[0097] The Fig. 5, Fig. 10 and Fig. Figure 11 shows a second embodiment, which is particularly suitable for measuring tubes 14 with a smaller diameter d1 between, for example, 4 mm and 50 mm, especially 15 mm and 40 mm.

[0098] In this case, there are only two waveguide sections in total. 24 provided that they are offset from each other at an acute angle, for example about 60° in the circumferential direction U on the measuring tube 14 are arranged (see Fig. 5 and Fig. 10) Opposite the respective waveguide sections 24 The normal wall of the measuring tube is located there 14 with the undiminished wall thickness W1 and without a signal converter26 , 28 , so no waveguide section 24 .

[0099] On the two waveguide sections 24 Each is a first and a second signal converter. 26 , 28 arranged, wherein the distances between the signal converters 26 , 28 a waveguide section 24 for both waveguide sections 24 are chosen differently. In Fig. 11 is the one with the lengths as and as + av illustrates this. It is possible for one of the two waveguide sections. 24 a sensor assembly described above 30 to be used with the specified signal converter spacing as and only for the second waveguide section 24 the two signal converters 26 , 28 with an additional offset av to be arranged along the axial direction A. Here, the distance between the two signal converters could be 26 , 28also smaller than the distance between the two signal converters 26 , 28 on the other waveguide section 24 to be elected.

[0100] In this embodiment, in contrast to the embodiment described above, the decoupled volume waves V for both fluid sound velocities C F1 , C F2 exactly once at the respective waveguide section 24 diametrically opposite inner side 35 of the flow channel 16 reflected and thus hits the waveguide section again 24 , from which it was coupled, and is operated by the second signal converter 28 on this waveguide section 24 detected.

[0101] Otherwise, the measurement procedure is the same as described for the first embodiment.

[0102] Here too, it is possible to reverse the course of the measuring section by using the second signal converter. 28 as a transmitter and the first signal converter 26 a waveguide section 24 works as a recipient.

[0103] The reference signal is also applied to the respective waveguide section. 24 generated by the first signal converter 26 to the second signal converter 28 surface wave 44 is detected. All waveguide sections 24 are identically shaped here. In the variants shown here, all waveguide sections are identical. 24 arranged in the same position with respect to the axial direction A.

[0104] By evaluating the temporal intensity profile, e.g., during a transit time difference measurement between different measurement paths, the evaluation unit, which is either in the fluid measuring device, generates 10or can be designed as an external unit, which determines the desired properties of the fluid. This allows conclusions to be drawn about properties of the fluid in the flow channel, such as flow velocity, flow rate, concentration, viscosity, speed of sound, temperature, and homogeneity.

Claims

[1] Fluid measuring device with a measuring tube (14) in which a circumferentially closed flow channel (16) for a fluid to be measured is formed and in which at least two regions of an outer wall (22) of the measuring tube (14) are formed as waveguide sections (24), each forming a waveguide for surface acoustic waves, wherein a first and / or a second signal converter (26, 28) is arranged on each waveguide section (24) and the signal converter(s) (26, 28) is designed to excite surface acoustic waves in the respective waveguide section (24) and / or to receive surface acoustic waves from the waveguide section (24), wherein the signal converter (26,28) emitted acoustic surface waves can be coupled out from the waveguide section (24) and propagate as acoustic volume waves (V) through the fluid in the flow channel (16) and / or acoustic volume waves (V) can be coupled into the waveguide section (24) and received by the signal converter (26, 28), wherein the waveguide sections (24) are arranged offset and spaced apart from each other along the circumference (U) of the flow channel (16) and 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 each other in the axial direction (A) of the flow channel (16). [2] Fluid measuring device according to claim 1, characterized by, that the fluid measuring device (10) is designed such that a measuring section running through the flow channel (16) between two signal transducers (26, 28) of a greater length is available for fluids with higher sound velocities (C F2 ) is provided, in particular for sound velocities > 1800 m / s, and a measuring section running through the flow channel (16) between two signal converters (26, 28) with a shorter length for fluids with lower sound velocities (C F1 ), especially for sound speeds < 1300 m / s. [3] Fluid measuring device according to one of the preceding claims, characterized by, that each waveguide section (24) is opposite a region of the measuring tube (14) which is not designed as a waveguide section (24) and on which no signal converters (26, 28) are provided, wherein a wall thickness (W1) of the outer wall (22) of the measuring tube (14) in these regions is unchanged compared to the circumferentially adjacent regions of the outer wall (22), wherein the fluid measuring device (10) is designed such that the coupled volume sound wave (V) is reflected back at this region of the inner side (35) to the waveguide section (24) from which it was coupled, in particular only once. [4] Fluid measuring device according to claim 3, characterized by that the fluid measuring device has a measuring tube with a diameter between 4 and 50 mm, in particular between 15 and 40 mm. [5] Fluid measuring device according to one of claims 3 and 4, characterized by, that the distance between the first and second signal converters (26, 28) of a waveguide section (24) is different for at least two waveguide sections (24). [6] Fluid measuring device according to any of the preceding claims, characterized by , that an even number of waveguide sections (24), in particular at least four waveguide sections (24), is provided, wherein two waveguide sections (24) are arranged diametrically opposite each other and form a waveguide pair (38), wherein each waveguide pair (38) has 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 and / or the second signal converter (26, 28) on the measuring waveguide differs in at least two waveguide pairs (38). [7] Fluid measuring device according to claim 6, characterized bythat the fluid measuring device has a measuring tube with a diameter between 10 and 400 mm, in particular between 40 and 200 mm. [8] Fluid measuring device according to claim 6 or 7, characterized by , that the length of a measuring section running through the flow channel (16) between a first and a second signal converter (26, 28) of diametrically opposite waveguide sections (24) is different for two waveguide pairs (38). [9] Fluid measuring device according to any one of claims 6 to 8, characterized by , that in different waveguide pairs (38) the first or the second signal converters (26, 28) are located at different axial positions. [10] Fluid measuring device according to claim 9, characterized by, that a measuring section is formed between the first signal converter (26) of the reference waveguide (40) and the signal converter (26, 28) on the associated measuring waveguide (42) of the waveguide pair (38), wherein in particular the coupled-out acoustic volume waves (V) are not reflected on an inside (35) of the flow channel (16) before they couple into the measuring waveguide (42). [11] Fluid measuring device according to any one of claims 6 to 10, characterized by , that the distance (as) between the first and the second signal converter (26, 28) on each waveguide section (24) of two different waveguide pairs is the same. [12] Fluid measuring device according to any one of claims 3 to 11, characterized by, that each waveguide section (24) or waveguide pair (38) defines a shorter measuring section through the flow channel (16) and each waveguide section (24) or waveguide pair (38) defines a longer measuring section through the flow channel (16). [13] Fluid measuring device according to any of the preceding claims, characterized by , that all waveguide sections (24) are arranged such that they each lie on a parallel to the central axis (M) of the flow channel (16). [14] Fluid measuring device according to one of the preceding claims, characterized by , that the signal converters (26, 28) are arranged such that acoustic volume waves pass through the central axis (M) of the flow channel (16) directly after coupling from the respective waveguide section (24) of each signal converter (26, 28) acting as a transmitter. [15] Fluid measuring device according to any of the preceding claims, characterized by, that the waveguide sections (24) form a part of the inside (35) of the flow channel (16) which comes into direct contact with the fluid flowing through it, wherein the waveguide sections (24) are designed as flattenings (34) on a round outer wall (22) of the measuring tube (14) in which the wall thickness of the measuring tube (14) is reduced, wherein in particular the flattenings (34) are designed at their axial ends (36) in side view each beveled and tapering towards the axial end (36).

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