Ultrasonic flow measurement machine

Abstract

The present invention provides an ultrasonic flowmeter capable of exciting and / or receiving induced ultrasound in an advantageous manner. It also provides a method for determining the advantageous vibration mode in which the induced ultrasound is excited. [Solution] In a measuring tube (2) through which a fluid (8) flows, an induced ultrasonic wave (9) is excited, and the induced ultrasonic wave (9) is guided and propagated in the fluid (8) within the measuring tube (2) in the direction extending in the axial direction of the measuring tube (2) in a combined waveguide including the measuring tube (2) and the fluid (8). Here, an ultrasonic sensor (7) receives the induced ultrasonic wave (9), and a control and evaluation unit (5) determines the flow velocity (v) of the fluid (8) by evaluating the received induced ultrasonic wave (9).

Description

Technical Field

[0001] The present invention relates to an ultrasonic flow measurement device including a measurement tube, a first ultrasonic transducer, a second ultrasonic transducer, and a control and evaluation unit. The first ultrasonic transducer and the second ultrasonic transducer are axially displaced and arranged on the measurement tube. The first ultrasonic transducer is configured at least as an ultrasonic actuator, and the second ultrasonic transducer is configured at least as an ultrasonic sensor. The control and evaluation unit drives and controls the ultrasonic actuator in the operating state of the ultrasonic flow measurement device, whereby induced ultrasonic waves are excited in the measurement tube through which the fluid flows. The induced ultrasonic waves are guided and propagated in the combined waveguide including the measurement tube and the fluid in the axial extension direction of the measurement tube in the measurement tube and the fluid. The ultrasonic sensor receives the induced ultrasonic waves, and the control and evaluation unit obtains the flow velocity of the fluid by evaluating the received induced ultrasonic waves. Furthermore, the present invention also relates to a method for determining at least one wave mode generated during the flow measurement in the above-described ultrasonic flow measurement device.

[0002] Flow measurement using ultrasonic waves has been known for decades. However, regardless of which measurement method (e.g., propagation time measurement, propagation time difference measurement (by the flow direction and its opposite direction), frequency measurement / Doppler effect) is used, the flow measurement is always based on the entrainment of ultrasonic waves in the fluid with the flow velocity to be captured flowing through the measurement tube.

[0003] In most ultrasonic flow measurement devices, the characteristic cross-sectional dimension of the measurement tube (diameter in the case of a circular measurement tube) is much larger than the wavelength of the ultrasonic waves generated by the ultrasonic actuator. In many cases, means for beam forming are taken. As a result, in this case, in any event, the ultrasonic waves propagating in the fluid inside the measurement tube can be regarded as free waves, and it can be explained that the measurement tube does not play a major role in its propagation except for reflections at the measurement tube wall.

[0004] This differs in the case of ultrasonic flow measuring instruments equipped with measuring tubes whose characteristic cross-sectional dimensions fall within the wavelength range of the ultrasound used. In this case, the measuring tube wall is a geometric boundary condition that must always be considered for the movement and propagation of ultrasound, and therefore the ultrasound propagates as induced ultrasound within a combined or hybrid waveguide including the measuring tube and the fluid; that is, these induced ultrasounds are induced and move through both the measuring tube and the fluid. An ultrasonic flow measuring instrument within the framework of this invention is intended to be an ultrasonic flow measuring instrument that operates according to this principle.

[0005] For clarification, it should be noted that the aforementioned functional principle on which the present invention is based differs from ultrasonic flow measuring devices that involve induced waves, where ultrasonic waves are induced and propagated only within the measuring tube. Ultrasound penetrates from the measuring tube into the fluid to varying degrees (depending on the type of ultrasound excited and induced within the measuring tube), but moves within the fluid as uninduced ultrasound, i.e., as free-space waves. This type of flow measuring device is also called a leaky Lamb wave flow measuring device, which operates with Lamb waves induced within the walls of the measuring tube, thereby involving free-space ultrasound generated within the medium. Within the framework of the present invention, ultrasonic flow measuring devices that operate according to such principles are not intended.

[0006] Depending on the geometric and physical boundary conditions of the measurement tube, the fluid parameters, and the frequency of the excited ultrasound, various vibration modes can propagate in the waveguide containing the measurement tube and fluid. In this case, these wave modes have different spatial and temporal propagation characteristics, and these wave modes can be selected to a greater or lesser advantage.

[0007] The problem on which the present invention is based is to provide an ultrasonic flowmeter of the above type that can excite and / or receive induced ultrasound in an advantageous manner, and similarly, to provide a method that can determine a favorable vibration mode in which induced ultrasound is excited.

[0008] This problem is solved by the ultrasonic flow measuring device described at the beginning, in which, firstly, the ultrasonic transducer configured as at least an ultrasonic actuator has multiple excitation structures in the direction extending in the axial direction of the measuring tube, and these excitation structures are spaced apart from each other in the direction extending in the axial direction of the measuring tube. Using these excitation structures, ultrasound is supplied to the measuring tube through which the fluid flows, and thereby, spatially dispersed in the direction extending in the axial direction of the measuring tube, the waveform pattern of at least one predetermined wave mode of induced ultrasound is excited in the measuring tube through which the fluid flows.

[0009] Given that ultrasonic waves are supplied to the fluid flowing through the measuring tube using excitation structures, these excitation structures have, in some form, contact surfaces with the measuring tube and / or with the fluid induced within the measuring tube. In this case, acoustic excitation of the measuring tube and / or fluid occurs through these contact surfaces, i.e., energy transfer takes place. In the free space between excitation structures due to separation, excitation of the measuring tube and / or fluid does not occur, and in any case, no active excitation occurs. Slight parasitic excitation may not be preventable in many cases, but this is not inconsistent with the teachings assumed herein.

[0010] Sound waves propagating through a medium and measuring tube along the axial path of the measuring tube in a particular vibration mode exhibit both spatial (direction of the measuring tube's extension) and temporal dependence. By observing a specific point in the measuring tube, the temporal amplitude change can be observed, and by observing the entire measuring tube at a specific point in time, the spatial path of the sound wave amplitude can be observed. Overall, ultrasound, at a specific frequency in a particular mode, has a characteristic spatial-temporal sine wave along the waveguide (from the ultrasonic actuator to the ultrasonic sensor) in the form of a measuring tube through which the fluid flows.

[0011] A major advantage of the ultrasonic flow measuring instrument according to the present invention is that, due to the multiple excitation structures spaced apart from each other, multiple acoustic excitations can be performed simultaneously or with a time staggeration at multiple locations in the direction of extension of the measuring tube. These excitations are selected so as to precisely correspond to characteristic spatial-temporal sine waves, that is, to precisely correspond to the waveform patterns of predetermined wave modes of ultrasound that are induced and propagated through the measuring tube through which the fluid flows.

[0012] Multiple spaced-apart excitation structures create an extended and structured excitation layer along the extension of the measurement tube, thereby enabling more specific excitation of desired (or multiple desired) and even predetermined wave modes than would be possible with only a single excitation site (viewed along the extension of the measurement tube). In practice, the waveform pattern of a desired and predetermined wave mode can be applied spatially and temporally to the flowing measurement tube. This automatically achieves higher selectivity in the excitation of wave modes than with only a single excitation source, thereby automatically and better suppressing undesirable wave modes. Moreover, it is possible to influence the intensity with which wave modes propagate from the excitation structure to the left and right. In other words, even in this way, selective suppression of undesirable wave modes in the direction toward the ultrasonic sensor can be achieved, and selective transport of desired, i.e., predetermined wave modes in the direction toward the ultrasonic sensor can be achieved.

[0013] A preferred configuration of an ultrasonic flow measuring device is characterized in that a second ultrasonic transducer, configured as an ultrasonic sensor, is configured in essentially the same way as a first ultrasonic transducer, configured as an ultrasonic actuator, that is, it is equipped with multiple excitation structures, thereby allowing the excitation structures to act as capture structures. In particular, the second ultrasonic transducer is configured identically to the first ultrasonic transducer, configured as an ultrasonic actuator.

[0014] The realization of an ultrasonic sensor equipped with multiple excitation structures acting as capture structures essentially provides a means for selectively capturing and identifying specific wave modes of induced ultrasound, allowing for spatial and temporal filtering of undesirable wave modes. This filtering can be performed independently, by the geometric arrangement of the multiple excitation / capture structures, or by temporal windowing or summation of the received signals appropriately delayed by the individual excitation / capture structures.

[0015] In a more advantageous configuration, the first ultrasonic transducer is also configured as an ultrasonic sensor, and the second ultrasonic transducer is also configured as an ultrasonic actuator. Here, for example, the realization of an excitation structure using a piezoelectric element that can be used as an actuator or a sensor as needed is considered. Given that many ultrasonic flow measuring instruments achieve propagation time difference measurement, that is, propagation time measurement in the direction of fluid flow and the opposite direction, the identical configuration of the first and second ultrasonic transducers is also significant. Preferably, the control and evaluation unit operates the first and second ultrasonic transducers so that the flow velocity of the fluid in the measuring tube can be determined via propagation time difference measurement.

[0016] In one advanced form of ultrasonic flowmetering equipment, the measuring tube is configured as an acoustic coupling member to improve (impedance matching) acoustic transmission from the excited structure to the fluid within the measuring tube in the region of the excited structure. In an alternative advanced form of ultrasonic flowmetering equipment, the measuring tube is configured by the excited structure itself for direct acoustic transmission from the excited structure to the fluid within the measuring tube in the region of the excited structure.

[0017] There are very different means of constructing an ultrasonic flow measuring instrument equipped with multiple excitation structures, as described above. Two different concepts of this configuration are described below.

[0018] A first concept of the configuration of the ultrasonic flow measuring device according to the present invention is characterized in that the excitation structure is formed by at least two rings that are spaced apart from each other in the axial direction of the measuring tube and surround the measuring tube in the circumferential direction. A particularly simple arrangement is when there are at least three rings that are equally spaced apart from each other.

[0019] In a preferred development of ultrasonic flow measuring instruments, the ring is a separate ultrasonic exciter, and in this particular case, the ultrasonic exciter can be driven and controlled independently of the control and evaluation unit. In this configuration, multiple excitation structures that are spaced apart from each other can be driven and controlled at multiple locations in the direction of extension of the measuring tube with a time staggered. This excitation is carried out so as to precisely produce a waveform pattern of ultrasonic waves of a predetermined wave mode that is induced and propagated through the measuring tube through which the fluid flows. The advantage of the time-variable and independently driveable capability of the ring-type ultrasonic exciter is its ability to adapt to changing ambient conditions, for example, when the fluid changes in its composition or when there are also temperature changes.

[0020] In an alternative configuration, multiple excitation structures, configured as rings, are simultaneously driven and controlled by a control and evaluation unit, which simplifies the configuration of the control and evaluation unit. In this case, the spacing between the separate rings must be selected so that a predetermined wave-mode ultrasonic waveform pattern is precisely elicited, which is induced and propagated through a fluid-flowing measurement tube.

[0021] What can be seen from these examples is that, when a predetermined wave mode is excited in a measuring tube through which a fluid flows, there are basically two degrees of freedom to excite the spatial-temporal sine of the desired wave mode (at a specific frequency): in detail, the spatial spacing between excited structures and the temporal excitation time of each excited structure (as long as it can be excited separately).

[0022] A special configuration of an ultrasonic flow measuring instrument operating with an excitation structure implemented as a ring is characterized in that the ring is brought into contact with a control and evaluation unit via its inner and outer covering surfaces, respectively (radial operation mode), or that the ring is driven and controlled by the control and evaluation unit via contact with two opposing bottom surfaces, respectively (axial operation mode). This is particularly significant when the excitation structure configured as a ring is a piezoelectric element, or in any case when it has a piezoelectric element.

[0023] In a further preferred configuration of the ultrasonic flowmeter, the rings are supported by a common ring holder, and in particular, the rings are connected to the common ring holder via their own outer covering surfaces, in which case the common ring holder has a material that at least partially attenuates ultrasonic crosstalk between the multiple rings. The advantage of this procedure is that multiple rings can be configured within the ring holder, that is, for example, the holding can be brought to a desired interval where it is secure, and thus can be initially attached to the measuring tube. This is advantageous in terms of ease of handling, especially in the case of a so-called clamp-on configuration.

[0024] In a preferred configuration of the control and evaluation unit for an ultrasonic flow metering device, the ring of the ultrasonic actuator is driven with a time delay in the direction toward the ultrasonic sensor, thereby amplifying ultrasonic waves of a predetermined wave mode toward the ultrasonic sensor. This procedure also achieves a degree of directional selectivity, i.e., amplification of ultrasonic waves toward the ultrasonic sensor from the ultrasonic actuator.

[0025] In an advantageous configuration of an ultrasonic flow measuring instrument, where the ultrasonic sensor is also configured like an ultrasonic actuator having multiple excitation structures, the selectivity for capturing a predetermined wave mode waveform pattern is obtained by evaluating the received signals supplied from the multiple capture structures by temporally windowing or temporally delaying them according to the propagation characteristics of the predetermined wave mode. In the case of temporal windowing, for example, the propagation speed of the desired wave mode and the spatial interval of the maximum amplitude at a particular frequency can be used. If no received signal matching the propagation characteristics of the wave mode is received in the temporal evaluation window, this is an indication of the absence of the desired wave mode. In the temporal delay of signals captured by various capture structures and their lower-level summation, an upward signal level may indicate the presence of a captured predetermined wave mode, and a downward signal level may indicate the absence of a predetermined wave mode.

[0026] Based on the replacement of ultrasonic flowmeters with multiple annular excitation and capture structures, it is well recognized that multiple vibration modes can also be excited simultaneously. In the case of two rings, there are two degrees of freedom in the design of the excitation structure, specifically the spatial separation of the rings and their temporally delayed excitation. Multiple excitation structures automatically provide more degrees of freedom in their design, thereby making it possible to selectively excite multiple modes and selectively capture multiple modes.

[0027] The second concept of the configuration of the ultrasonic flow measurement device according to the present invention is that the ultrasonic actuator includes a conical base body having a central hollow portion for receiving the measurement tube. In this case, the inner wall portion of the base body formed by the hollow portion is structured in the axial extension direction of the measurement tube by at least one recess extending in the circumferential direction of the measurement tube, and at least two protrusions formed by the at least one recess form excitation structure portions on the inner wall portion of the base body. An ultrasonic oscillator for supplying ultrasonic waves to the conical base body is arranged on the bottom surface of the conical base body. In this case, the ultrasonic waves are at least partially reflected on the covering surface of the conical base body, and guided ultrasonic waves are excited in the measurement tube through which the fluid flows via the protrusions on the inner wall portion of the base body. In this configuration, the protrusions on the wall portion of the base body form contact surfaces for energy transfer to the measurement tube / fluid.

[0028] Compared with the first concept of the configuration of the ultrasonic actuator, the second concept has fewer degrees of freedom. This is because the protrusions are fixedly installed on the base body. Also, the ultrasonic waves are generated only by the ultrasonic oscillator that supplies ultrasonic waves to the conical base body. In this case, the ultrasonic waves are dispersed into the base body by reflection on the covering surface there, and finally supplied to the waveguide (measurement tube / fluid) via the protrusions in the wall portion of the base body.

[0029] In the advantageous configuration of the ultrasonic flow measurement device described above, the ultrasonic oscillator is configured as a ring, particularly as an annular piezoelectric element. In this case, preferably, the annular piezoelectric element is brought into contact by the control and evaluation unit via the inner and outer covering surfaces of the ring (radial excitation mode). Alternatively, the annular piezoelectric element is driven and controlled by the control and evaluation unit via two opposing bottom surfaces (axial excitation mode).

[0030] Regardless of whether the ultrasonic actuator is configured according to the first concept or the second concept, in any case it is advantageous that the ultrasonic actuator is composed of a plurality of parts, whereby it is radially insertable into the measuring tube, especially in this case when the plurality of parts are pivotably supported relative to each other via one or more hinges. Thereby, the ultrasonic actuator (and, as a matter of course, also the correspondingly configured ultrasonic sensor in some cases) can be subsequently attached to the measuring tube (clamp-on), and the free end of the pipe for moving the ultrasonic transducer from there to the measuring tube is unnecessary.

[0031] The problem stated at the beginning is also solved by a method for determining at least one oscillation mode that is generated during the flow measurement in the ultrasonic flow measurement device, i.e., used as a predefined oscillation mode during the operation of the ultrasonic flow measurement device. Here too, starting from an ultrasonic flow measurement device comprising a measuring tube, a first ultrasonic transducer, a second ultrasonic transducer, and a control and evaluation unit. The first ultrasonic transducer and the second ultrasonic transducer are axially offset and arranged on the measuring tube, where the first ultrasonic transducer is configured at least as an ultrasonic actuator, and where the second ultrasonic transducer is formed at least as an ultrasonic sensor, and where the control and evaluation unit drives and controls the ultrasonic actuator in the operating state of the ultrasonic flow measurement device, whereby, in the measuring tube through which the fluid flows, an induced ultrasonic wave is excited. The ultrasonic sensor receives the induced ultrasonic wave. The control and evaluation unit determines the flow velocity of the fluid by evaluating the received induced ultrasonic wave. At least the ultrasonic transducer configured as an ultrasonic actuator has a plurality of excitation structures in the axial extension direction of the measuring tube, where the excitation structures are spaced apart from each other in the axial extension direction of the measuring tube. Using the excitation structures, ultrasonic waves are supplied to the measuring tube through which the fluid flows, whereby they are spatially dispersed in the axial extension direction of the measuring tube, and a waveform pattern of a predefined oscillation mode of the induced ultrasonic wave is excited in the measuring tube through which the fluid flows.

[0032] To enable the estimation of favorable predetermined wave modes as intended, the phase velocity and group velocity of sound waves in a frequency range are determined for multiple wave modes, based on the geometric and physical boundary conditions of the measuring tube through which the fluid flows. Then, at a specific frequency within the frequency range, the wave mode that receives the highest evaluation in at least one of the following criteria is selected as the predetermined wave mode.

[0033] The smaller the difference between the phase velocity and the group velocity, the better this is evaluated. This is particularly advantageous in conjunction with the additional criterion that the evaluation improves as the phase velocity and / or group velocity approach the speed of sound in the fluid. This criterion ensures that the induced wave is as flat as possible across the cross-section of the measurement tube.

[0034] This is better evaluated when the frequency dependence of the phase velocity and group velocity is low. As a result, the dependence of the excitation frequency change is kept low.

[0035] This is better evaluated when the minimum interval in phase velocity between different modes is large. This ensures that the desired, and therefore predetermined, vibration modes and other, i.e., undesired, vibration modes have significantly different waveform patterns, thus enabling good selective excitation and reception.

[0036] This is better evaluated when the minimum spacing in the group velocity between different modes is large. This achieves that the desired mode has propagation time characteristics as different as possible from other vibration modes, thereby increasing the discriminability of the modes as much as possible.

[0037] This is better evaluated the more axially symmetric the mode is. This ensures that flow measurement has as little dependence as possible on flow non-uniformity with respect to the axis of the measuring tube.

[0038] This is better evaluated the more the relative changes in phase velocity and / or group velocity are similar to the relative changes in the velocity of sound in the fluid. This allows the phase velocity and / or group velocity in the fluid to remain as similar as possible to the velocity of sound, even when the velocity of sound in the fluid changes. This is advantageous with respect to maintaining a flat waveform, because a flat waveform is essentially averaged over the velocity profile (in propagation time difference measurements), thereby allowing the fluid velocity to be determined independently of the velocity profile.

[0039] This is better evaluated when the attenuation of mode amplitude during propagation in a fluid is small. This ensures good signal intensity for predetermined wave modes.

[0040] This is better evaluated when the mode amplitude is uniform across the inner cross-section of the measuring tube. This criterion makes the measurement less dependent on non-uniformity of fluid flow across the cross-section of the measuring tube.

[0041] In one advanced form of this method, the design of the excitation structure is selected based on the acquired predetermined wave mode and the acquired specific frequency, and in particular, the spatial spacing between the excitation structures along the measurement tube axis and / or the temporal interval of excitation of the excitation structures are appropriately selected.

[0042] One advanced form of this method relates to the examination of the usefulness of the design of a selected excitation structure (including the temporal drive control of the structure). It is examined whether the amplitude achieved for a given, and therefore desired, mode is sufficiently large, and, if possible, larger than the amplitude of an undesirable mode at a specific frequency. That is, one advanced form of this method is characterized in that, considering the geometric and physical boundary conditions of the measuring tube through which the fluid flows, and taking into account the design of the excitation structure, the amplitude of the sound wave generated at the excitation frequency is determined for at least one predetermined wave mode within a frequency range dependent on the phase velocity of the generated sound wave. If the amplitude of a particular wave mode does not reach the minimum amount, in particular, if the amplitude of a particular wave mode at a specific frequency is smaller than the amplitude of an undesirable wave mode, the design of the excitation structure is discarded and modified. In particular, this process is repeated until a design of the excitation structure that should no longer be rejected is found.

[0043] In a preferred embodiment of this method, the evaluation of the criteria is assumed to be performed by scoring the observed and examined wave modes based on the criteria in an evaluation order, and determining the best mode as a predetermined mode based on the achieved total score. What has proven practical here is to employ a relative evaluation scale rather than an absolute evaluation scale for each criterion. For example, when examining four wave modes, these criteria are calculated under the observed frequencies (e.g., near the phase velocity relative to the acoustic velocity in the fluid), and the wave mode that best satisfies the criteria receives a score of 4, the second-best wave mode receives a score of 3, and so on.

[0044] When certain criteria are particularly important, it has been found to be advantageous to incorporate various criteria with different weightings into the evaluation. In the evaluation example above, important criteria in the relative evaluation scale can, for example, be weighted twice.

[0045] If, using the indicated method for determining a favorable predetermined wave mode, such a favorable predetermined wave mode is found at a specific frequency, this predetermined wave mode is excited at that specific frequency during the operation of the ultrasonic flowmeter.

[0046] In detail, there are numerous means of configuring and further developing the ultrasonic flow measuring apparatus and method according to the present invention. These are referred to, on the one hand, to the claims dependent on the independent claims, and on the other hand to the following description of embodiments related to the drawings. [Brief explanation of the drawing]

[0047] [Figure 1] This is a schematic diagram showing an ultrasonic flow metering device known from the conventional technology that operates using guided ultrasound. [Figure 2] This is a schematic diagram showing one embodiment of an ultrasonic flow measuring device equipped with an ultrasonic actuator having multiple excitation structures. [Figure 3] This is a schematic diagram showing an ultrasonic actuator having multiple excitation structures and acoustic coupling members, and in direct contact with a fluid. [Figure 4] This is a schematic diagram showing an ultrasonic actuator having equally spaced excitation structures. [Figure 5] This is a schematic diagram showing an excitation element formed in a ring shape as a piezoelectric element having different contact points. [Figure 6] This is a schematic diagram showing an ultrasonic actuator composed of multiple parts, each having a component that is supported in a manner that allows for rotation between them. [Figure 7] This is a schematic diagram showing an ultrasonic flow measurement device equipped with an ultrasonic actuator and an ultrasonic sensor, which have a conical base having multiple excitation structures. [Figure 8] This is a schematic diagram showing a more enlarged and detailed view of the ultrasonic actuator shown in Figure 7. [Figure 9]This is a schematic diagram illustrating a method for determining the appropriate wave mode to be used as a predetermined wave mode when operating one of the ultrasonic flow measuring devices described above. [Figure 10] This is a schematic diagram showing the phase velocities and group velocities of various wave modes for a specific configuration of an ultrasonic flowmeter. [Figure 11] This schematic diagram shows the amplitude of the excited ultrasound, depending on the excitation frequency and effective phase velocity, with one amplitude in the positive propagation direction and the other in the negative propagation direction.

[0048] Multiple drawings show various embodiments of the ultrasonic flow measuring device 1, in which case the ultrasonic flow measuring device 1 comprises a measuring tube 2, a first ultrasonic transducer 3, a second ultrasonic transducer 4, and a control and evaluation unit 5. The first ultrasonic transducer 3 and the second ultrasonic transducer 4 are arranged in the measuring tube 2 offset in the axial direction, the first ultrasonic transducer 3 is configured as at least an ultrasonic actuator 6, and the second ultrasonic transducer 4 is configured as at least an ultrasonic sensor 7. The control and evaluation unit 5 drives and controls the ultrasonic actuator 6 in the operating state of the ultrasonic flow measuring device 1, thereby exciting induced ultrasonic waves 9 in the measuring tube 2 through which the fluid 8 flows. The ultrasonic sensor 7 receives the induced ultrasonic waves 9, and the control and evaluation unit 5 determines the flow velocity v of the fluid 8 by evaluating the received induced ultrasonic waves 9.

[0049] Figure 1 shows a conventional ultrasonic flow measuring device 1 that operates with induced ultrasonic waves 9. The measuring tube 2 and the fluid 8 induced within the measuring tube 2 form a single waveguide, through which the induced ultrasonic waves 9 propagate. The propagation of the induced ultrasonic waves 9 along the waveguide is represented by a wave equation, and the solution to such an equation must consider the geometric boundary conditions of the waveguide and, naturally, other physical parameters of the arrangement, such as the physical parameters of the medium. It is known that only specific waveforms, also called wave modes, can propagate stably along the waveguide. In the embodiment shown here, the flow velocity v of the fluid 8 is determined by the propagation time difference method; that is, the signal propagation time of the induced ultrasonic waves 9 is determined by the direction of flow of the fluid 8 and the direction opposite to that direction. This has the advantage that, when calculating the fluid velocity v, identical components of the velocity of the ultrasonic waves 9 in the fluid 8 are automatically canceled out, regardless of the direction of flow of the fluid 8.

[0050] As shown in Figure 1, in the conventional ultrasonic flow measuring device 1, there is only one ultrasonic actuator 6 that acts as a single point and one ultrasonic sensor 7 that receives signals as a single point. Due to the principle, the ultrasonic actuator 6 can only excite extremely nonspecific ultrasound, and due to the principle, the ultrasonic sensor 7 can only capture extremely nonspecific ultrasound.

[0051] In contrast, the ultrasonic flow measuring device 1 shown in another drawing operates with significant modifications. The ultrasonic flow measuring device 1, separately illustrated, which includes an ultrasonic actuator 6 or an ultrasonic sensor 7, is characterized in that at least the ultrasonic transducer 3, configured as the ultrasonic actuator 6, has a plurality of excitation structures 10 extending in the axial direction of the measuring tube 2, and in this case, these excitation structures 10 are spaced apart from each other in the axial direction of the measuring tube 2. Using these excitation structures 10, ultrasound 9 is supplied to the measuring tube 2 through which the fluid 8 flows, thereby exciting the waveform pattern of at least one predetermined wave mode of the induced ultrasound 9 within the measuring tube 2 through which the fluid 8 flows, by spatially dispersing it in the axial direction of the measuring tube 2. The excitation structures 10 have contact surfaces 11 with respect to the measuring tube 2 and / or with respect to the fluid 8 induced within the measuring tube 2, and in this case, acoustic excitation of the measuring tube 2 and / or the fluid 8 occurs via these contact surfaces 11.

[0052] Multiple spaced excitation structures 10 at multiple locations along the extension direction of the measuring tube 2 allow for multiple acoustic excitations to be performed simultaneously or with a time staggeration. These excitations are selected so as to precisely correspond to characteristic spatial-temporal sine waves, that is, precisely to the waveform patterns of predetermined wave modes of ultrasonic waves 9 induced and propagated through the measuring tube 2 through which the fluid 8 flows. The spaced-apart excitation structures 10 create an expanded and structured excitation layer along the extension direction of the measuring tube 2, thereby enabling the specific excitation of desired (or multiple desired) and ultimately predetermined wave modes. This is an advantage over the embodiment shown in Figure 1, which has only one excitation location. As a result, the waveform pattern of a desired predetermined wave mode can be applied spatially and temporally into the measuring tube 2 through an excitation layer via spatially dispersed excitation structures 10 along the measuring tube 2.

[0053] The embodiments shown in Figures 2 and 7 share the common feature that the second ultrasonic transducer 4, configured as an ultrasonic sensor 7, is basically configured in the same way as the first ultrasonic transducer 2, configured as an ultrasonic actuator 6. In other words, the ultrasonic sensor 7 also has multiple excitation structures 10, and in this case, the excitation structures 10 act as trapping structures. In the embodiment shown in Figure 7, the second ultrasonic transducer 4 is configured identically to the first ultrasonic transducer 3, configured as an ultrasonic actuator 6.

[0054] In all ultrasonic flow measuring devices 1 shown in the drawings, the first ultrasonic transducer 3 is also configured as an ultrasonic sensor 7, and the second ultrasonic transducer 4 is also configured as an ultrasonic actuator 6. This is significant because (as explained above) the control and evaluation unit 5 drives the first ultrasonic transducer 3 and the second ultrasonic transducer 4 so that the flow velocity v of the fluid 8 in the measuring tube 2 can be determined by measuring the propagation time difference.

[0055] The embodiment of the ultrasonic flowmeter 1 shown in the drawings operates using a measuring tube 2 having an inner diameter significantly less than 1 centimeter. The measuring tube 2 is tubular and flexible, and in detail, is made of a perfluoroalkoxy polymer, i.e., elastic plastic. In other configurations not shown herein, the measuring tube 2 is mechanically rigid and is made of metal, plastic, ceramic, or glass, in particular.

[0056] In the ultrasonic flow measurement device 1 shown in Figure 3a, the measuring tube 2 is configured as an acoustic coupling member 12 in the region of the excitation structure 10 to improve acoustic transmission from the excitation structure 10 to the fluid 8 within the measuring tube 2.

[0057] In the ultrasonic flow measurement device 1 shown in Figure 3b, the measuring tube 2 is composed of the excitation structure 10 itself in the region of the excitation structure 10, for direct acoustic transmission from the excitation structure 10 to the fluid 8 within the measuring tube 2. In other words, the contact surface 11 is in direct contact with the fluid 8.

[0058] In the ultrasonic flow measuring device 1 shown in Figures 2 to 4, the excitation structure 10 is formed by at least two rings that are spaced apart from each other in the axial direction of the measuring tube 2 and surround the measuring tube 2 in the circumferential direction. In the embodiments shown in Figures 2 and 3, the rings of the ultrasonic actuator 6 have varying spacings from each other, and the spacing of the rings of the ultrasonic sensor 7 is different from the spacing of the rings of the ultrasonic actuator 6 (Figure 2). In the embodiment shown in Figure 4, it is carried out differently, where the distances between the excitation structure 10 formed as rings are equal, which offers advantages in manufacturing.

[0059] In the ultrasonic flow measuring device 1 shown in Figures 2 and 3, the ring is a separate ultrasonic exciter 22, and in particular a separate piezoelectric element 13. In this case, the ultrasonic exciter 22 can be driven and controlled independently of the control and evaluation unit 5, thus achieving particularly great flexibility with respect to changing operating conditions and boundary conditions. Furthermore, the ultrasonic sensor 7 is also composed of piezoelectric elements 13, and the sensor signals of each capture structure 10, which is configured as a piezoelectric element ring, can be read independently.

[0060] Figure 5 shows individual excitation structures or trapping structures 10 realized as an annular piezoelectric element 13. In the piezoelectric element 13 shown in Figure 5a, the ring is brought into contact by the control and evaluation unit 5 via two opposing bottom surfaces 15 (axial mode). In the piezoelectric element 13 shown in Figure 5b, the ring is brought into contact by the control and evaluation unit 5 via the inner and outer coating surfaces 14 of the ring (radial mode). Figure 5c shows an annular piezoelectric element 13 having a layer 25 configured as an adaptation layer for better transmission of ultrasonic waves (for example, for applications shown in Figures 2 and 4), or an annular piezoelectric element 13 having a layer 25 configured as an attenuation layer to avoid transmission of ultrasonic waves (for example, for applications shown in Figures 7 and 8, where a support portion not shown would also be directly provided on the measuring tube 2).

[0061] The ability of the control and evaluation unit 5 to independently drive and control multiple interconnected excitation structures 10, as shown in Figure 2, allows for the excitation of multiple interconnected excitation structures 10 at multiple locations (viewed in the direction of extension of the measuring tube 2) with a time staggered. Such excitation is performed in such a way that it precisely produces a waveform pattern of ultrasonic waves 9 of a predetermined wave mode, which are induced and propagated through the measuring tube 2 through which the fluid 8 flows. The advantage of the time-variable and independently drive-controllable ring lies in its ability to adapt to changing operating conditions, for example, when the fluid 8 changes, or even when only temperature changes are present.

[0062] In the ultrasonic flow measurement device 1 shown in Figure 4, multiple excitation structures 10, configured as rings, are simultaneously driven and controlled by a control and evaluation unit 5, which simplifies the configuration of the control and evaluation unit 5. In this case, the spacing between the separate rings must be selected so as to precisely produce a waveform pattern of ultrasonic waves 9 of a predetermined wave mode that is induced and propagated through the measuring tube 2 through which the fluid 8 flows.

[0063] In the ultrasonic flow measuring device 1 shown in Figure 2, the ring of the ultrasonic actuator 6 is driven with a time delay in the direction toward the ultrasonic sensor 7, thereby amplifying the ultrasonic waves 9 of a predetermined wave mode toward the ultrasonic sensor 7. In contrast, the generated wave amplitude is smaller in the direction opposite to the ultrasonic sensor 7. This is because such amplitudes do not overlap in that propagation direction based on the time-delayed drive control. This achieves remarkable directional selectivity.

[0064] In the ultrasonic transducer 4 configured as the ultrasonic sensor 7 shown in Figure 2, the selectivity for capturing the waveform pattern of a predetermined wave mode is obtained by evaluating the received signals supplied from multiple capture structures 10 by temporally windowing or temporally delaying them according to the propagation characteristics and waveform pattern of the predetermined wave mode. The signals captured by the two capture structures 10 of the ultrasonic sensor 7 can, for example, be added together. In this case, the first signal to arrive is delayed by the amount of time required for one ultrasonic signal 9 of a predetermined wave mode to reach the right side of the two capture structures 10 from the left side of the two capture structures 10. These signals can be added together based on the phase velocity dependent on the wave mode, but only for the corresponding wave modes. This allows the signal input side to verify based on additive signal intensity in the expected predetermined wave mode.

[0065] Similarly, temporal windowing can also be implemented, in which case the signal input side on the left of the two capture structures 10 triggers a capture window on the right of the two capture structures 10. If no signal enters this triggered window, it is not the ultrasonic wave 9 of a predetermined wave mode. This assumes that the predetermined wave mode and the excitation frequency of the predetermined wave mode are cleverly selected to allow the predetermined wave mode to be well distinguished from other wave modes.

[0066] The ultrasonic flow measuring device 1 shown in Figures 7 and 8 does not operate using a separate ring, but rather has a conical base 16 with a central hollow portion 17 for housing the measuring tube 2. In this case, the inner wall portion 18 of the base 16 formed by the hollow portion 17 is structured in the axial direction of the measuring tube 2 by a recessed portion 19 that extends circumferentially along the measuring tube 2. A projection 20 formed by the recessed portion 19 on the inner wall portion 18 of the base 16 forms an excitation structure 10. An ultrasonic exciter 22 is positioned on the bottom surface 21 of the conical base 16, which supplies ultrasonic waves (indicated by arrows) to the conical base 16. In this case, the ultrasonic waves are at least partially reflected by the covering surface 23 of the conical base 16, and induced ultrasonic waves 9 are excited in the measuring tube 2 through which the fluid 8 flows via the projection 20 of the inner wall portion 18 of the base 16.

[0067] This replacement of the ultrasonic actuator 6 is somewhat more restrictive than a configuration with a separate ring, because the projection 20 is structurally fixed and mounted on the conical base 16. Also, the ultrasound is generated only by the ultrasonic exciter 22 that supplies ultrasound to the conical base 16, in which case the ultrasound is dispersed within the base 16 by reflection at the covering surface 23 and finally supplied to the waveguide (measuring tube / fluid) via the projection 20 in the wall of the base 16.

[0068] Figure 6 shows an ultrasonic flow measuring device 1 comprising an ultrasonic actuator 6 and / or ultrasonic sensor 7, which is radially insertable into the measuring tube 2, and in this particular case, the multiple components are supported to pivot relative to each other via one or more hinges 24. The fitting layer 25 provides optimal transmission of ultrasound from the ultrasonic exciter 22 to the measuring tube 2 and the fluid 8 within the measuring tube 2.

[0069] Figures 9 to 11 show a method 26 for identifying at least one wave mode generated during flow measurement in an ultrasonic flow measuring device 1. This ultrasonic flow measuring device 1 is of the type described above, namely comprising a measuring tube 2, a first ultrasonic transducer 3, a second ultrasonic transducer 4, and a control and evaluation unit 5. The first ultrasonic transducer 3 and the second ultrasonic transducer 4 are positioned in the measuring tube 2 offset in the axial direction, where the first ultrasonic transducer 3 is configured as at least an ultrasonic actuator 6, and the second ultrasonic transducer 4 is configured as at least an ultrasonic sensor 7. The control and evaluation unit 5 drives and controls the ultrasonic actuator 6 in the operating state of the ultrasonic flow measuring device 1, thereby exciting induced ultrasonic waves 9 in the measuring tube 2 through which the fluid 8 flows.

[0070] The ultrasonic sensor 7 receives the induced ultrasonic waves 9, and the control and evaluation unit 5 determines the flow velocity of the fluid 8 by evaluating the received induced ultrasonic waves 9. The ultrasonic transducer 3, configured as an ultrasonic actuator 6, has a plurality of excitation structures 10 extending in the axial direction of the measuring tube 2, and in this case, these excitation structures 10 are spaced apart from each other in the axial direction of the measuring tube 2. Using these excitation structures 10, ultrasonic waves are supplied to the measuring tube 2 through which the fluid 8 flows, and thereafter, the waveform pattern of a predetermined wave mode m_det of the induced ultrasonic waves 9 is excited in the measuring tube 2 through which the fluid flows, by spatially dispersing it in the axial direction of the measuring tube 2.

[0071] As shown in Figure 9, method 26 determines the phase velocity c_ph and group velocity c_gr of sound waves in a frequency range for multiple wave modes m, given the geometric and physical boundary conditions bound of the measuring tube 2 through which the fluid 8 flows, func(bound, f). Here, at a specific frequency f_det within the frequency range, the following criterion krit: a) The smaller the difference between the phase velocity c_ph and the group velocity c_gr, the better the result. b) The closer the phase velocity c_ph and / or group velocity c_gr are to the speed of sound of the fluid, the better. c) The lower the frequency dependence of the phase velocity c_ph and group velocity c_gr, the better the result. d) The larger the minimum spacing in the phase velocity c_ph between various modes m, the better. e) The larger the minimum interval in the group velocity c_gr between various modes m, the better the result. f) The more axisymmetric mode m is, the better. g) The better the relative change in phase velocity c_ph and / or group velocity c_gr is, the more similar it is to the relative change in the speed of sound of the fluid 8. h) The smaller the attenuation of the mode amplitude during propagation in the fluid, the better the result. i) The more uniform the mode m amplitude is across the inner cross-section of the measuring tube 2, the better the result. The wave mode that receives the highest evaluation eval_max during at least one of the evaluations eval is selected as the predetermined wave mode m_det.

[0072] In other words, the results of this method include not only the identification of a desired, and therefore predetermined, wave mode m_det, but also the specific frequency f_det at which the predetermined wave mode m_det is excited.

[0073] The importance of the criteria is explained in the general explanation section. Some of the criteria are explained in detail based on Figures 10 and 11.

[0074] Figure 10a shows the calculated phase velocity c_ph of the ultrasound in the frequency range of 0 to approximately 1 MHz, and Figure 10b shows the calculated group velocity c_gr. As boundary conditions, a straight measurement tube 2 made of elastic perfluoroalkoxy polymer tubing with an outer diameter of 6.35 mm and an inner diameter of 4.35 mm was selected. Furthermore, the speed of sound in water was assumed to be 1480 m / s, and the fluid density was assumed to be 1000 kg / m³. The space outside the measurement tube 2 was also assumed to be air at atmospheric pressure and temperature. This calculation does not depend on the specific configuration of the excitation structures 10, i.e., the spatial spacing between the excitation structures 10, or, in some cases, the time interval related to the driving control of the excitation structures 10. This concerns only the problem of wave modes that can propagate under selected geometric and physical boundary conditions of the measurement tube and fluid at a specific frequency of the excitation wave.

[0075] As can be seen from Figure 10, the phase velocity c_ph and group velocity c_gr of wave mode m1 are close to the fluid sound velocity of 1480 m / s at a frequency of 480 kHz, which leads to a good evaluation in criteria a) and b) (flat wave). Furthermore, at this frequency, mode m1 has little dispersion in phase velocity c_ph and group velocity c_gr, which means that the phase velocity c_ph and group velocity c_gr have little dependence on the frequency of the transmitted wave, which leads to a good evaluation in criterion c).

[0076] Furthermore, at a frequency of 480 kHz, there is a significant difference between the phase velocity c_ph and the group velocity c_gr between wave mode m1 and adjacent modes m2 and m3, which leads to a favorable evaluation of criteria d) and g).

[0077] Although not shown here, the calculations show that the relative changes in phase velocity c_ph and / or group velocity c_gr are remarkably similar to the relative changes in the speed of sound of fluid 8 (changes in the medium), which leads to a favorable evaluation at criterion g).

[0078] Overall, this consideration leads to the conclusion that wave mode m1 is the preferred result and is therefore selected as the predetermined wave mode m_det at a specific frequency f_det480kHz, in which case wave mode m2 exhibits interference based on the nearest velocity. Given the knowledge that vibration mode m1 should be excited at a specific frequency f_det480kHz, the excitation structure 10 can be designed with spatial arrangement along the measurement tube axis and / or temporal excitation, depending on the existing degrees of freedom. In this case, two excitation structures 10 are selected with an excitation delay of 2.74μs and a distance of 4.15mm between them.

[0079] Here, it is useful to answer the question of how the amplitudes of various modes m1 and m2 behave relative to each other during the same excitation, but this cannot be seen from Figure 10. In particular, it is desirable that the amplitudes of predetermined modes be large enough to achieve, for example, a good signal-to-noise ratio. For this purpose, the absolute value of the two-dimensional Fourier transform of the wave function is calculated as the amplitude A, and this calculation also takes into account the characteristics of the excitation structure, namely, the two excitation structures having the above-mentioned spacing and excitation delay.

[0080] Considering the design of the excitation structure 10, the amplitude A in the form of the absolute value of the two-dimensional Fourier transform of the generated ultrasound is represented in gray tones in Figure 11 (assuming the same excitation is always used) and normalized to intervals from 0 to 1.

[0081] Figure 11a shows the resulting ultrasonic amplitude A for the direction of wave movement from the ultrasonic actuator 6 to the ultrasonic sensor 7. In contrast, Figure 11b shows the solution to the wave equation for the resulting ultrasonic amplitude A for the direction of wave movement from the ultrasonic actuator 6 away from the ultrasonic sensor 7, that is, the direction of wave movement in the opposite direction away from the actual measurement distance.

[0082] In both Figures 11a and 11b, wave modes m1 and m2 are transcribed from the corresponding depictions in Figure 10a. Based on Figure 11a, it is clearly evident that wave mode m1 has a significantly higher amplitude in the direction toward the ultrasonic sensor 7 than the next faster wave mode m2. This greatly enhances the temporal discriminability of the two wave modes. Furthermore, the amplitude of wave mode m1 in the opposite direction toward the ultrasonic sensor 7 is significantly suppressed with respect to wave mode m2 (Figure 11b). This supports the good support of wave mode m1 for the measurement task.

[0083] Given this background, Method 26 considers the design of the excitation structure 10 in relation to the geometric and physical boundary conditions of the measuring tube 2 through which the fluid 8 flows, and determines that the amplitude A of the sound wave generated at the excitation frequency is within a frequency range that depends on the phase velocity c_ph of the generated sound wave, at least for a predetermined wave mode m_det. If the amplitude A of the determined wave mode m_det does not reach a minimum, the design of the excitation structure 10 is rejected and modified. The criterion for such a minimum is that the amplitude A of the determined wave mode m_det (wave mode m1) must not be smaller than the amplitude A of an undesirable wave mode m2. Since this is not the case here, the design of the excitation structure 10 is maintained. If the results are unsatisfactory, the inspection process described above will be repeated until a design of the excitation structure 10 that should no longer be rejected is found.

[0084] A particularly simple method for implementing this method 26 is that the evaluation of the criterion krit, eval, brings the observed and examined modes m based on the criterion krit into an evaluation order rang and scores them, and the best mode is determined as a specific mode m_det based on the achieved total scoring state sum_rang.

[0085] If different values ​​are assigned to the criterion krit, these various criterion krits are considered with different weights in the evaluation, and this is quite easy to implement.

[0086] After performing Method 26, the ultrasonic flowmeter 1 will operate so that a specific frequency f_det is used within the frequency range to excite a predetermined wave mode m_det. For this purpose, it is necessary to consider not only the excitation frequency but also the phase velocity of the predetermined wave mode, i.e., wave mode m1 at a specific frequency f_det of 480 kHz in this case. [Explanation of Symbols]

[0087] 1 Ultrasonic flow measurement equipment 2 Measuring tube 3. First ultrasonic transducer 4. Second ultrasonic transducer 5. Control and Evaluation Unit 6. Ultrasonic Actuator 7. Ultrasonic Sensor 8 fluid 9. Guided Ultrasound 10 Excited structure, trapping structure 11 Contact surface 12 Acoustic coupling member 13 Piezoelectric element 14 Ring coating surface 15. Bottom of the ring 16 Conical base 17 Central Hollow 18 Inner wall portion of the base 19 Recessed portion of the inner wall 20 Protrusion 21 Base of the cone base 22. Ultrasonic Excitator 23 Covering surface of the conical substrate 24 Hinge 25 layers, adaptation layer or damping layer 26 methods m_det Pre-defined wave mode m wave mode c_ph Phase velocity c_gr group velocity Geometric and physical boundary conditions of a measuring tube through which a fluid flows f_det specific frequency Krit standards Evaluation based on eval criteria evalmax Top rating A. Amplitude as the absolute value of the two-dimensional Fourier transform of the wave function, taking into account the characteristics of the excited structure. rang (rank) Evaluation order Sum_rang Total score status

Claims

1. An ultrasonic flow measuring device (1) comprising a measuring tube (2), a first ultrasonic transducer (3), a second ultrasonic transducer (4), and a control and evaluation unit (5), The first ultrasonic transducer (3) and the second ultrasonic transducer (4) are positioned in the measuring tube (2) with an axial offset, The first ultrasonic transducer (3) is configured as at least an ultrasonic actuator (6), The second ultrasonic transducer (4) is configured as at least an ultrasonic sensor (7), The control and evaluation unit (5) drives and controls the ultrasonic actuator (6) in the operating state of the ultrasonic flow measuring device (1), thereby exciting induced ultrasonic waves (9) in the measuring tube (2) through which the fluid (8) flows, and the induced ultrasonic waves (9) are guided and propagated in the measuring tube (2) in the direction extending in the axial direction of the measuring tube (2) through the fluid (8) in a combined waveguide including the measuring tube (2) and the fluid (8). In an ultrasonic flow rate measuring device (1), the ultrasonic sensor (7) receives the induced ultrasonic waves (9), and the control and evaluation unit (5) determines the flow velocity (v) of the fluid (8) by evaluating the received induced ultrasonic waves (9). The ultrasonic transducer (3), which is configured as at least an ultrasonic actuator (6), has a plurality of excitation structures (10) in the direction extending in the axial direction of the measuring tube (2), The excitation structure (10) is spaced apart from each other in the direction of extension in the axial direction of the measuring tube (2). An ultrasonic flow rate measuring device (1) is characterized in that ultrasonic waves are supplied to the measuring tube (2) through which the fluid flows using the excitation structure (10), thereby exciting the waveform pattern of at least one predetermined wave mode (m_det) of the induced ultrasonic waves (9) within the measuring tube (2) through which the fluid (8) flows, by spatially dispersing it in the axial direction of the measuring tube (2).

2. The ultrasonic flow measuring device (1) according to claim 1, wherein the second ultrasonic transducer (4), configured as an ultrasonic sensor (7), is configured in basically the same way as the first ultrasonic transducer (2), configured as an ultrasonic actuator (6), and thereby the excitation structure (10) acts as a capture structure, and in particular the second ultrasonic transducer (4) is configured identically to the first ultrasonic transducer (3), configured as an ultrasonic actuator (6).

3. The ultrasonic flow rate measuring device (1) according to claim 1 or 2, wherein the first ultrasonic transducer (3) is also configured as an ultrasonic sensor (7), and the second ultrasonic transducer (4) is also configured as an ultrasonic actuator (6), and in particular, the control and evaluation unit (5) operates the first ultrasonic transducer (3) and the second ultrasonic transducer (4) such that the flow velocity (v) of the fluid (8) in the measuring tube (2) can be determined by measuring the propagation time difference.

4. The ultrasonic flow measuring instrument (1) according to any one of claims 1 to 3, wherein the measuring tube (2) is mechanically rigid and is made of metal, plastic, ceramic, or glass, or the measuring tube is flexibly constructed in a tubular shape and is made of elastic plastic, particularly perfluoroalkoxy polymer.

5. The ultrasonic flow measuring device (1) according to any one of claims 1 to 4, wherein the measuring tube (2) is configured as an acoustic coupling member (12) in the region of the excitation structure (10) to improve acoustic transmission from the excitation structure (12) within the measuring tube (2) to the fluid (8).

6. The ultrasonic flow measuring instrument (1) according to any one of claims 1 to 4, wherein the measuring tube (2) is composed of the excitation structure (10) itself in the region of the excitation structure (10) for direct acoustic transmission from the excitation structure (10) to the fluid (8) within the measuring tube (2).

7. The ultrasonic flow measuring device (1) according to any one of claims 1 to 6, wherein the excitation structure (10) is formed by at least two rings that are spaced apart from each other in the axial direction of the measuring tube (2) and surround the measuring tube (2) in the circumferential direction, and in particular, at least three rings in which these rings are spaced equally apart from each other.

8. The ultrasonic flow measuring device (1) according to claim 7, wherein the ring is a separate ultrasonic exciter, in particular a separate piezoelectric element (13), and in particular the ultrasonic exciter is drive-controllable separately from the control and evaluation unit (5).

9. The ring is brought into contact by the control and evaluation unit (5) via its inner and outer covering surfaces (14), respectively, or the ring is driven and controlled by the control and evaluation unit (5) via two opposing bottom surfaces (15), respectively, the ultrasonic flow measuring device (1) according to claim 7 or 8.

10. The ultrasonic flow measuring device (1) according to any one of claims 7 to 9, wherein the ring is supported by a common ring holder, and in particular is connected to the common ring holder via its outer covering surface (15), and the common ring holder has, at least partially, a material that attenuates ultrasonic crosstalk between the plurality of rings.

11. The ultrasonic flow measuring device (1) according to any one of claims 7 to 10, wherein the ring of the ultrasonic actuator (6) is driven with a time delay in the direction toward the ultrasonic sensor (7), thereby amplifying the ultrasonic waves (9) of the predetermined wave mode toward the ultrasonic sensor (7).

12. The selectivity for capturing the waveform pattern of the predetermined wave mode is obtained by evaluating the received signals supplied from the plurality of capture structures (10) by temporally windowing or temporally delaying them according to the propagation characteristics and waveform pattern of the predetermined wave mode, as described in any one of claims 7 to 11, relating to claim 2.

13. The ultrasonic actuator (6) includes a conical base (16) having a central hollow portion (17) for receiving the measuring tube (2), the inner wall portion (18) of the base (16) formed by the hollow portion (17) is structured in the axial direction of the measuring tube (2) by at least one recessed portion (19) extending in the circumferential direction of the measuring tube (2), and at least two protrusions (20) formed by the at least one recessed portion (19) are located on the inner wall portion of the base (16) The ultrasonic flow rate measuring device (1) according to any one of claims 1 to 6, wherein the excitation structure (10) is formed, and an ultrasonic exciter (22) for supplying ultrasonic waves to the conical base (16) is arranged on the bottom surface (21) of the conical base (16), the ultrasonic waves are at least partially reflected by the covering surface (23) of the conical base (16), and the induced ultrasonic waves (9) are excited in the measuring tube (2) through which the fluid (8) flows via the protruding portion (20) of the inner wall portion (18) of the base (16).

14. The ultrasonic exciter (22) is configured as a ring, particularly as an annular piezoelectric element (13), preferably the annular piezoelectric element (13) is brought into contact with the control and evaluation unit (5) via the inner and outer covering surfaces (14) of the ring, or the annular piezoelectric element (13) is driven and controlled by the control and evaluation unit (5) via two opposing bottom surfaces (15), as described in claim 13.

15. The ultrasonic actuator (6) is composed of a plurality of parts, thereby allowing the ultrasonic actuator (6) to be inserted radially into the measuring tube (2), and in particular the plurality of parts are supported so as to be rotatable relative to each other via one or more hinges (24), as described in any one of claims 1 to 14.

16. An ultrasonic flow measuring instrument (1) according to any one of claims 1 to 15, wherein a predetermined wave mode is identified according to the method (26) according to any one of claims 17 to 21.

17. A method (26) for determining at least one wave mode generated during flow measurement in an ultrasonic flow measuring device (1), The ultrasonic flow measuring device (1) includes a measuring tube (2), a first ultrasonic transducer (3), a second ultrasonic transducer (4), and a control and evaluation unit (5). The first ultrasonic transducer (3) and the second ultrasonic transducer (4) are positioned in the measuring tube (2) with an axial offset, The first ultrasonic transducer (3) is configured as at least an ultrasonic actuator (6), The second ultrasonic transducer (4) is configured as at least an ultrasonic sensor (7), The control and evaluation unit (5) drives and controls the ultrasonic actuator (6) in the operating state of the ultrasonic flow measuring device (1), thereby exciting induced ultrasonic waves (9) in the measuring tube (2) through which the fluid (8) flows, and the induced ultrasonic waves (9) are guided and propagated in the measuring tube (2) in the direction extending in the axial direction of the measuring tube (2) through the fluid (8) in a combined waveguide including the measuring tube (2) and the fluid (8). The ultrasonic sensor (7) receives the induced ultrasonic waves (9), and the control and evaluation unit (5) determines the flow velocity of the fluid (8) by evaluating the received induced ultrasonic waves (9). At least the ultrasonic transducers (3, 4) configured as ultrasonic actuators (6) have a plurality of excitation structures (10) in the direction extending in the axial direction of the measuring tube (2), The excitation structure (10) is spaced apart from each other in the direction of extension in the axial direction of the measuring tube (2). Using the excitation structure (10), ultrasonic waves are supplied to the measuring tube (2) through which the fluid (8) flows, thereby spatially dispersing in the axial direction of the measuring tube (2) and exciting the waveform pattern of a predetermined wave mode (m_det) of the induced ultrasonic waves (9) within the measuring tube (2) through which the fluid flows. Regarding the geometric and physical boundary conditions of the measuring tube (2) through which the fluid (8) flows, the phase velocity (c_ph) and group velocity (c_gr) of the sound waves in the frequency range are determined for multiple wave modes (m), and at a specific frequency (f_det) within the frequency range, the following criteria (krit): a) The smaller the difference between the phase velocity (c_ph) and the group velocity (c_gr), the better the result. b) The closer the phase velocity (c_ph) and / or group velocity (c_gr) are to the speed of sound of the fluid, the better. c) The lower the frequency dependence of the phase velocity (c_ph) and group velocity (c_gr), the better. d) The larger the minimum spacing in the phase velocity (c_ph) between different modes (m), the better. e) The larger the minimum interval in the group velocity (c_gr) between different modes (m), the better. f) The more axisymmetric the mode (m), the better. g) The better the relative change in phase velocity (c_ph) and / or group velocity (c_gr) is, the more similar it is to the relative change in the speed of sound of the fluid (8). h) The smaller the attenuation of the mode amplitude during propagation in the fluid, the better. i) The more uniform the mode (m) amplitude is across the inner cross-section of the measuring tube (2), the better. A method (26) in which, during at least one of the evaluations (eval), the wave mode that receives the highest evaluation (eval_max) is selected as a predetermined wave mode (m_det).

18. The method (26) of claim 17, wherein the design of the excitation structure (10) is selected based on the acquired predetermined wave mode (m_det) and the specific frequency (f_det), and in particular the spatial spacing between the excitation structures (10) along the measurement tube axis and / or the temporal interval of the excitation of the excitation structures (10) is selected.

19. With regard to the geometric and physical boundary conditions of the measuring tube (2) through which the fluid (8) flows, taking into consideration the design of the excitation structure (10), the amplitude (A) of the sound wave generated at the excitation frequency is determined in a frequency range that depends on the phase velocity (c_ph) of the generated sound wave for at least a predetermined wave mode (m_det). The method (26) of claim 18, wherein if the amplitude (A) of the particular wave mode (m_det) does not reach a minimum amount, in particular if the amplitude (A) of the particular wave mode (m_det) is smaller than the amplitude (A) of an undesirable wave mode, the design of the excitation structure (10) is discarded and modified, in particular, the process is repeated until a design of the excitation structure that should no longer be rejected is found.

20. The method (26) according to any one of claims 17 to 19, wherein the evaluation (eval) of the criterion (krit) is performed by bringing the observed modes (m) that have been inspected based on the criterion (krit) into an evaluation order (rang) and scoring them, and the best mode is determined as a specific mode (m_det) based on the achieved total scoring state (sum_rang).

21. The method (26) of claim 20, wherein various criteria (krit) having different weights are incorporated into the evaluation.

22. The method (26) according to any one of claims 17 to 21, wherein the specific frequency (f_det) within the frequency range is the frequency at which the specific mode (m_det) is excited.

Images