ULTRASONIC FLOWMETER AND METHOD FOR OPERATING AN ULTRASONIC FLOWMETER

Description

[0001] The invention is based on an ultrasonic flowmeter according to claim 1, comprising at least one first ultrasonic transducer and one second ultrasonic transducer and further comprising a control and evaluation unit, wherein the control and evaluation unit is connected to the first ultrasonic transducer and the second ultrasonic transducer, wherein the first ultrasonic transducer and / or the second ultrasonic transducer is / are designed as an ultrasonic transmitter and / or an ultrasonic receiver, wherein the first ultrasonic transducer and / or the second ultrasonic transducer is / are designed as a wedge transducer, wherein the first ultrasonic transducer and the second ultrasonic transducer are arranged on a measuring tube in such a way that a signal path is formed between the first and the second ultrasonic transducer, so that a measurement signal emitted by the ultrasonic transmitter runs via the signal path to the ultrasonic receiver.

[0002] Furthermore, the invention relates to a method according to claim 12 for operating an ultrasonic flowmeter, wherein the ultrasonic flowmeter comprises at least a first ultrasonic transducer and a second ultrasonic transducer and a control and evaluation unit, wherein the control and evaluation unit is connected to the first ultrasonic transducer and the second ultrasonic transducer, wherein the first ultrasonic transducer and / or the second ultrasonic transducer is / are designed as an ultrasonic transmitter and / or ultrasonic receiver, wherein the first ultrasonic transducer and / or the second ultrasonic transducer is / are designed as a wedge transducer, wherein the first ultrasonic transducer and the second ultrasonic transducer are arranged on a measuring tube in such a way that a signal path is formed between the first and the second ultrasonic transducer, such that a measurement signal emitted by the ultrasonic transmitter runs via the signal path to the ultrasonic receiver.

[0003] State-of-the-art ultrasonic flowmeters are often optimized for measuring specific media within expected flow velocity ranges. For this purpose, the ultrasonic transducers are arranged on the measuring tube in such a way that a signal path is formed between the ultrasonic transducers, the geometry of which is adapted to the expected measuring ranges and conditions.

[0004] However, when measuring under different conditions, specifically high flow velocities or other media or varying media properties, such measuring devices often have the disadvantage that the transmission of the measuring signal and thus the amplitude of the measuring signal detected at the receiver decreases due to the change in the geometry of the signal path between the ultrasonic transducers. For example, at particularly high flow velocities, the measuring signal is blown away by the drag effect, so that it no longer reaches the ultrasonic receiver optimally.

[0005] Particularly with clamp-on devices, as disclosed in US2015 / 160053-A1, DE102011005170-A1, and US2021 / 080303-A1, readjustment is required when the sound velocity of the medium changes. A change in the medium or the sound velocity of the medium due to changing process parameters results in a change in the coupling angle of the measuring signal into the measuring tube, which also influences the signal path. As a result, the amplitude detected by the ultrasonic receiver decreases; in the worst case, the ultrasonic receiver no longer detects the measuring signal.

[0006] Based on the prior art described, it is therefore an object of the invention to provide an ultrasonic flowmeter with a particularly wide range of applications. Furthermore, it is an object of the invention to provide an improved method for operating an ultrasonic flowmeter.

[0007] In principle, an ultrasonic flow meter within the scope of the present invention comprises the determination of the flow or the flow velocity based on the known conventional measuring methods, in particular based on the transit time principle or on the Doppler principle or on the drift principle.

[0008] Within the scope of the present invention, the measuring tube can be part of the ultrasonic flowmeter. Alternatively, the measuring tube can also be part of a system, with the flowmeter being arranged for operation on or at the measuring tube.

[0009] The first ultrasonic transducer has a first array of at least two active elements and / or the second ultrasonic transducer has a second array of at least two active elements, wherein at least one ultrasonic transducer having an array of at least two active elements is designed as a wedge transducer, wherein at least two active elements of the array arranged on the first ultrasonic transducer can be controlled separately by the control and evaluation unit and / or wherein at least two active elements of the array arranged on the second ultrasonic transducer can be controlled separately by the control and evaluation unit.

[0010] The control and evaluation unit controls the active elements with control parameters such as a phase, a frequency and an amplitude.

[0011] Particularly preferably, each ultrasonic transducer having an array of at least two active elements is designed as a wedge transducer.

[0012] According to the invention, it was recognized that the use of an ultrasonic transducer designed as a wedge transducer, wherein the ultrasonic transducer has an array of at least two active elements, is advantageous in that a measurement signal emitted by the array is composed of at least two components, namely at least a first ultrasonic signal and a second ultrasonic signal.

[0013] Because at least two active elements can be controlled separately, the shape and / or the radiation angle of the measurement signal can be influenced. To this end, the individual active elements can be operated at different times and / or with different amplitudes and / or phases. As a result, the shape of the measurement signal and / or the geometry of the signal path traversed by the measurement signal can be influenced and, in particular, adapted to changes in operation, so that the ultrasonic flowmeter can always operate under optimal conditions.

[0014] The measurement signal resulting from the superposition of the individual ultrasonic signals has at least one main lobe. During operation, the main lobe is directed toward the receiver to determine the flow rate. Depending on the design and / or control of the array, the measurement signal has at least two side lobes and / or at least two grating lobes.

[0015] The side lobes are essentially influenced by the control of the active elements, in particular by the amplitude with which the individual active elements are controlled.

[0016] The grating lobes are repetitions of the main lobe, including any side lobes. The appearance of grating lobes is influenced by the spacing d between the active elements. The spacing d between the active elements is defined as the distance between the centers of the active elements.

[0017] Particularly preferably, the array is designed and / or the array is controlled during operation in such a way that essentially no side lobes and / or grating lobes are formed.

[0018] Alternatively, the array can be designed and / or controlled in such a way that exactly two grating lobes are produced.

[0019] The present invention relates to influencing the measurement signal using a phased array. If the first ultrasonic signal and the second ultrasonic signal are transmitted with a time offset, this time offset is so minimal that the superposition of the signals results in a common measurement signal reaching the receiver, so that the first ultrasonic signal and the second ultrasonic signal are indistinguishable at the receiver. Thus, the invention does not relate to a time-division multiplexing method in which signals are transmitted and / or transmitted individually one after the other, i.e., without overlapping.

[0020] Alternatively or additionally, the at least one array, in the case in which it is designed as a receiving element, has a receiving characteristic which results from the signals measured at the individual active elements being superimposed with a time delay and / or phase shift and / or weighted with different amplitudes.

[0021] In this respect, the reception characteristics can also be adapted to a process-related change in the signal path during operation in such a way that the ultrasonic flow meter can always operate in an optimized manner.

[0022] Particularly preferably, the at least one wedge transducer comprising the array of active elements is arranged on the measuring tube in such a way that radiation of the measurement signal perpendicular to the inclination of the wedge defines a signal path that optimally reaches the ultrasonic receiver for the expected media and flow rate. Radiation of the measurement signal perpendicular to the inclination of the wedge corresponds to a non-swiveled measurement signal, i.e., a swivel angle of 0°. This has the advantage that any change in the radiation angle of the measurement signal when operating conditions change must be small in order to counteract the operational impact on the measurement signal.

[0023] In principle, an active element within the scope of the present invention is an electroacoustic transmitting and / or receiving element.

[0024] According to one embodiment, exactly one ultrasonic transducer is designed as a wedge transducer, which has an array of at least two active elements.

[0025] According to a further embodiment, the first ultrasonic transducer has a first array of at least two active elements, and the second ultrasonic transducer has a second array of at least two active elements. This embodiment is particularly advantageous because, during operation, both the measurement signal emitted in the flow direction and the measurement signal emitted against the flow direction can be influenced by controlling the individual active elements.

[0026] In addition, the array designed as a receiver can be adapted to receive the measurement signal both when measuring in the direction of flow and when measuring against the direction of flow.

[0027] According to a preferred embodiment, an array of at least two active elements has more than two active elements.

[0028] Particularly preferably, all active elements of an array can be controlled separately by the control and evaluation unit.

[0029] Alternatively, an array comprises at least two groups of active elements, wherein the active elements assigned to a group can be controlled together and wherein at least one group comprises at least two active elements.

[0030] According to a next advantageous embodiment, the first ultrasonic transducer has a first array of at least two active elements and the second ultrasonic transducer has a second array of at least two active elements, wherein the first array and the second array have the same number of active elements or a different number of active elements.

[0031] If the first array has the same number of active elements as the second array, the ultrasonic transducers can be manufactured particularly easily.

[0032] If the number of active elements in the first array differs from the number of active elements in the second array, the number of active elements required for operation can be advantageously minimized. This has the advantage of simplifying the overall manufacture and operation of the ultrasonic flowmeter.

[0033] According to a further preferred embodiment, the first ultrasonic transducer has a first array of at least two active elements and the second ultrasonic transducer has a second array of at least two active elements, wherein the first array and the second array have an identical arrangement or a different arrangement of the active elements.

[0034] If the first array and the second array have an identical arrangement of the active elements, the variation of the radiation angle of the measuring signal emitted in the flow direction can be identical to the variation of the radiation angle of the measuring signal emitted against the flow direction.

[0035] According to an alternative embodiment, the first array and the second array have a different arrangement of the active elements. Particularly preferably, the first array and the second array are coordinated with one another in such a way that unwanted components of the measurement signal emitted by the ultrasonic transmitter array can be suppressed by minima in the reception characteristics of the ultrasonic receiver array.

[0036] According to a further embodiment, the first array and / or the second array is / are two-dimensional, at least in some areas. This embodiment has the advantage that the measurement signal can be spatially pivoted during operation.

[0037] In principle, the wedge's slope can be either planar or curved. If the wedge's slope is curved according to one design, the maximum pivot angle in the edge area of ​​the measuring tube can be increased.

[0038] According to a further embodiment, the first array and / or the second array is / are one-dimensional, at least in some regions. This embodiment is particularly advantageous if the first array and the second array are aligned at an angle to one another.

[0039] For example, the second array is aligned essentially perpendicular to the first array.

[0040] This design has the advantage that the radiation angle of the measurement signal can be changed in two planes, while at the same time the number of necessary active elements can be minimized.

[0041] A next embodiment is characterized in that the first array and / or the second array is / are produced by introducing at least one gap into an electroacoustic substrate, so that the substrate has at least two separately contactable regions on the upper side and a common ground connection on the lower side, wherein the at least one gap is preferably filled with an acoustically insulating material.

[0042] The gap can be introduced into the substrate, for example, by sawing or etching or by another suitable method.

[0043] The electroacoustic substrate is preferably a piezoelectric substrate.

[0044] Alternatively, the first array and / or the second array can be produced by applying an electroacoustic substrate to a carrier and by introducing at least one gap into the electroacoustic substrate, wherein the gap completely separates the electroacoustic substrate, wherein the at least one gap is preferably filled with an acoustically insulating material.

[0045] By filling the gap, crosstalk between the individual active elements can be avoided or at least minimized. For example, at least one gap is filled with silicone, epoxy resin, or rubber.

[0046] According to a next embodiment of the ultrasonic flowmeter, the number of active elements and the geometry of the first array and / or the second array are determined as a function of the expected maximum swivel angle, wherein preferably the number of active elements is minimized at the same time.

[0047] In detail, the total length L of the array determines the width of the main lobe of the measurement signal. The spacing d between the active elements determines the angular separation between the main lobe and the grating lobes. By appropriately adjusting the width of the active elements, the amplitude of the grating lobes can be attenuated.

[0048] A construction of an array of active elements can advantageously comprise the following steps: First, the total length L of the array is determined to define the width of the main lobe.

[0049] Subsequently, the required maximum sweep angle ρ 0 , under which the main lobe is to be radiated, is determined.

[0050] Based on this, the minimum tolerable angular separation of the grating lobes from the main lobe is determined. This should be such that the grating lobes do not influence the measurement. The grating lobes can also be attenuated by adjusting the width w of the active elements.

[0051] Finally, the maximum distance between the active elements and the minimum required number of active elements are determined.

[0052] By minimizing the number of active elements, the electronics of the control and evaluation unit can also be simplified, since fewer channels are required to control the individual active elements.

[0053] Particularly preferably, the number of active elements and / or the geometry of the first array and the second array are matched to one another in such a way that undesired signal components, for example side lobes and / or grating lobes, of the measurement signal emitted by the ultrasonic transmitter are suppressed by minima in the reception characteristic of the ultrasonic receiver.

[0054] According to a next advantageous embodiment, the first ultrasonic transducer and / or the second ultrasonic transducer has an electroacoustic substrate comprising at least a first and a second electroacoustic disc, wherein the first and the second electroacoustic disc are arranged on top of one another and wherein the array of active elements of this ultrasonic transducer is arranged in the first electroacoustic disc and / or in the second electroacoustic disc.

[0055] If at least one active element is arranged on both the first and second electroacoustic discs, the frequency of the measurement signal can be influenced in addition to varying the radiation angle of the measurement signal. If the active elements can be controlled separately, the electroacoustic discs can also be excited to oscillate separately. Thus, for example, one electroacoustic disc can be excited, while the other disc also oscillates. Alternatively, both discs can be excited to oscillate. By varying the oscillating body, the frequency of the measurement signal can also be varied.

[0056] The ultrasonic flow meter can therefore be adapted particularly flexibly to different measuring situations.

[0057] Particularly preferably, the ultrasonic flowmeter is designed to carry out one of the methods described below.

[0058] According to a second teaching of the present invention, the object mentioned at the outset is achieved by a method described at the outset for operating an ultrasonic flowmeter in that that the first ultrasonic transducer has a first array of at least two active elements and / or that the second ultrasonic transducer has a second array of at least two active elements, wherein at least two active elements of the array arranged on the first ultrasonic transducer are controlled separately by the control and evaluation unit and / or that at least two active elements of the array arranged on the second ultrasonic transducer are controlled separately by the control and evaluation unit, and that the control and evaluation unit controls the array functioning as an ultrasonic transmitter in such a way that the radiation angle of the measurement signal is varied at least temporarily and / or that the control and evaluation unit varies the reception characteristic of the array functioning as an ultrasonic receiver at least temporarily,so that in order to determine the flow rate during the measurement, the measuring signal is optimally directed at the ultrasonic receiver and / or the ultrasonic receiver receives the measuring signal in an optimized manner based on the beam angle.

[0059] The method according to the invention is used to position and align the ultrasonic transducers on the measuring tube in such a way that the ultrasonic transmitter array transmits the measurement signal without being pivoted and that the ultrasonic receiver array receives the measurement signal without being pivoted. To this end, the ultrasonic transducers are first placed on the measuring tube in such a way that a measurement signal transmitted by the ultrasonic transmitter reaches the ultrasonic receiver via the signal path. By pivoting the reception characteristic, the pivot angle at which the receiver optimally receives the measurement signal is determined. Based on the pivot angle, the control and evaluation unit determines a position for the ultrasonic transmitter and / or the ultrasonic receiver, taking into account the geometry of the signal path, at which the ultrasonic transmitter array transmits the measurement signal without being pivoted and at which the ultrasonic receiver array receives the measurement signal without being pivoted.In this way, the ultrasonic transducers on the measuring tube can be adjusted to each other before commissioning or at regular or irregular intervals.

[0060] According to one embodiment, at least the ultrasonic transducer operating as an ultrasonic transmitter in one operating state has an array of at least two active elements, wherein the at least two active elements of the ultrasonic transmitter can be controlled separately by the control and evaluation unit, wherein in the first operating state the first active element of the ultrasonic transmitter emits a first ultrasonic signal and wherein the second active element of the ultrasonic transmitter emits a second ultrasonic signal, so that the first ultrasonic signal and the second ultrasonic signal are superimposed to form the measurement signal.

[0061] The ultrasonic receiver receives the measuring signal and forwards it to the control and evaluation unit, which determines the flow rate taking into account the received measuring signal.

[0062] According to a particularly preferred embodiment of the method, the measurement signal has at least one main lobe due to the superposition of at least the first ultrasonic signal and the second ultrasonic signal. In addition, the measurement signal can also have at least two side lobes and / or at least two grating lobes.

[0063] According to another particularly preferred embodiment, the first ultrasonic signal and the second ultrasonic signal are transmitted at least temporarily with a time offset and / or with different amplitudes and / or with different phases, thereby changing the radiation angle of the measurement signal, in particular the main lobe of the measurement signal. In this way, the signal path traversed by the measurement signal can be modified so that the maximum of the measurement signal, in particular the maximum of the main lobe, is optimally directed onto the ultrasonic receiver.

[0064] Alternatively or additionally, the signals measured at the individual active elements of the array functioning as an ultrasonic receiver can be superimposed, at least temporarily, with a time delay and / or a phase shift and / or weighted with different amplitudes. In this way, the reception characteristic can be pivoted, which also ensures that the maximum of the measurement signal, in particular the maximum of the main lobe, is optimally incident on the ultrasonic receiver. According to a further embodiment of the method, at least one array is designed to be two-dimensional, at least in some regions, so that the radiation angle of the measurement signal, in particular of the main lobe, and / or the reception characteristic of the array can be varied within a solid angle.This has the advantage that, in the event that the measurement signal does not reach the ultrasonic receiver or does not reach it optimally due to a speed deviating from the expected speed, the coupling of the measurement signal can be readjusted so that the measurement signal reaches the ultrasonic receiver in an optimized manner. In addition, the measurement signal can also be pivoted towards the edge region of the measuring tube in such a way that it is also possible to measure edge regions of the flow profile. Furthermore, the reception characteristics of the array can also be adapted to a change in the signal path of the measurement signal. According to a further embodiment of the method, the control and evaluation unit monitors the amplitude of the measurement signal detected by the ultrasonic receiver, whereby the radiation angle of the measurement signal and / or the reception characteristics are changed by the control and evaluation unit if the amplitude falls below a threshold value.

[0065] According to a particularly preferred embodiment of the method, the control and evaluation unit varies the radiation angle of the measurement signal and / or the reception characteristic of the ultrasonic receiver at regular or irregular intervals in order to maximize the measurement signal at the ultrasonic receiver, wherein the control and evaluation unit detects a maximum of the amplitude at the ultrasonic receiver and the corresponding control parameters of the active elements therefor during the variation, and that the control and evaluation unit subsequently controls the array of the at least two active elements of the ultrasonic transmitter and / or the ultrasonic receiver according to the determined control parameters.

[0066] The variation of the beam angle is preferably carried out by a preset angle, for example of approximately 5° or of approximately 10° or of approximately 20°, around the current position of the main lobe.

[0067] For example, the control and evaluation unit varies the radiation angle of the measuring signal with a frequency of 1 Hz or 0.1 Hz or 0.01 Hz.

[0068] This regular slight swiveling of the measuring signal or the reception characteristic ensures that the flow meter recognizes and uses optimized control parameters for the ultrasonic transmitter and / or the ultrasonic receiver during operation.

[0069] As a result, the measurement signal always reaches the ultrasonic receiver in an optimized manner during the measurement operation.

[0070] At the beginning of the measurement operation, the swivel angles of the ultrasonic transmitter and the ultrasonic receiver are preferably aligned identically. Subsequently, the orientation of the ultrasonic transmitter and / or the orientation of the ultrasonic receiver is varied so that the ultrasonic receiver optimally receives the measurement signal.

[0071] Alternatively or additionally, the control and evaluation unit adjusts the radiation angle of the measurement signal emitted by the ultrasonic transmitter and / or the reception characteristics of the ultrasonic receiver depending on the measured flow velocity of the medium and / or depending on the speed of sound of the medium, such that the measurement signal at the ultrasonic receiver is maximum.

[0072] For this purpose, the control and evaluation unit particularly preferably has a memory unit, wherein a relationship between a radiation angle of the measurement signal or control parameters for the array of active elements and different media and / or different flow velocities and / or different sound velocities is stored in the memory unit, so that when the flow velocity and / or the medium changes and / or the sound speed of the medium changes due to changing process parameters, the control and evaluation unit automatically adapts the radiation angle of the measurement signal or the control parameters for the array of active elements and / or the reception characteristics of the ultrasonic receiver according to the stored relationship.

[0073] Conversely, by storing the relationship between a radiation angle of the measurement signal or control parameters for the array of active elements and various media and / or various flow velocities in the storage unit, a flow velocity and / or a medium can be determined from an optimal radiation angle found by the control and evaluation unit. In this respect, the control and evaluation unit can determine the flow velocity in two ways, which serve as a mutual control instance. In detail, the flow velocity can be determined based on the principle underlying the measuring device or by evaluating the swivel angle in combination with the stored relationship. In addition, conclusions can be drawn about the acoustic properties of the medium based on the set radiation angle.

[0074] In addition to the possibility of maximizing the signal at the ultrasonic receiver by adjusting the measurement signal, the orientation of the measurement signal or a part of the measurement signal can also be used to obtain information about an operating state and / or the measurement environment.

[0075] For this purpose, the measurement signal has, for example, at least one main lobe and at least two side lobes and / or two grating lobes, wherein the at least one main lobe or at least one side lobe or at least one grating lobe is at least temporarily aligned with the measuring tube in such a way that the side lobe or the grating lobe is reflected on the measuring tube and the reflection is received again by the array of active elements previously acting as an ultrasonic transmitter, wherein the control and evaluation unit determines at least one item of information about an operating state and / or the measuring environment from the reflection of the at least one main lobe or the one side lobe or the grating lobe. For example, the control and evaluation unit determines the thickness of the measuring tube wall and / or the inner measuring tube diameter. By repeatedly determining the thickness of the measuring tube wall, deposits on the measuring tube wall, for example, can be detected.In particular, the resulting reduction in the measuring tube diameter can be taken into account when determining the mass flow rate.

[0076] Alternatively or additionally, the main lobe, a side lobe, or a grating lobe can be aligned with the measuring tube in such a way that it excites a Lamb wave in the measuring tube wall, which propagates along the measuring tube wall in the direction of the ultrasonic receiver and is detected by the ultrasonic receiver, with the amplitude and / or the propagation time and / or the spectrum of the Lamb wave being evaluated. This configuration allows the propagation velocity of the measurement signal within the measuring tube wall to be determined, which improves knowledge of the coupling into the measuring tube and thus the knowledge of the signal path traversed by the measurement signal. Furthermore, deposits on the measuring tube wall can also be detected from the propagation characteristics of the Lamb wave. This also works if the ultrasonic transmitter does not have an array of active elements.

[0077] Particularly preferably, the flow meter is designed to carry out one of the previously described methods according to one of the embodiments described above.

[0078] There are now numerous possibilities for designing and developing the ultrasonic flowmeter according to the invention and the method for operating the ultrasonic flowmeter. Reference is made to the claims subordinate to the independent claims and to the following description of preferred embodiments in conjunction with the drawings. The drawings show: Fig. 1 shows a first embodiment of an ultrasonic flow meter according to the invention, Fig. 2 shows a second embodiment of an ultrasonic flow meter according to the invention, Fig. 3 shows a one-dimensional arrangement of active elements, Fig. 4 shows a one-dimensional arrangement of active elements and the resulting radiation characteristics, Fig. 5 shows a comparison of the radiation characteristics of an antenna array and a single active element, Fig. 6 shows the arrangement of a first one-dimensional array on a first ultrasonic transducer and a second one-dimensional array on a second ultrasonic transducer, Fig. 7 shows a further arrangement of a first one-dimensional array on a first ultrasonic transducer and a second one-dimensional array on a second ultrasonic transducer, Fig.8 shows a further arrangement of a first one-dimensional array on a first ultrasonic transducer and a second one-dimensional array on a second ultrasonic transducer, Fig. 9 shows a further arrangement of a first array on a first ultrasonic transducer and a second array on a second ultrasonic transducer, Fig. 10 shows an embodiment of a one-dimensional array of radiating elements, Fig. 11 shows a further embodiment of a two-dimensional array of radiating elements, Fig. 12 shows a further embodiment of a flow meter according to the invention, Fig. 13 shows a further embodiment of a flow meter according to the invention, Fig. 14 shows a further embodiment of a flow meter according to the invention, Fig. 15 shows a first embodiment of a method according to the invention, Fig. 16 shows a next embodiment of a method according to the invention, Fig. 17 shows a next embodiment of a method according to the invention, Fig.18a next embodiment of a method according to the invention Fig. 19a next embodiment of a method according to the invention. .

[0079] Fig. 1 shows a first embodiment of an ultrasonic flow meter 1, with a first ultrasonic transducer 2 and a second ultrasonic transducer 3, wherein the first ultrasonic transducer 2 is designed as a wedge transducer and wherein the second ultrasonic transducer 3 is also designed as a wedge transducer and wherein the ultrasonic transducers 2, 3 are arranged on a measuring tube 4.

[0080] The first ultrasonic transducer 2 has a first array 5 of active elements 6, wherein the array 5 is arranged such that the measurement signal 8 emitted by the array 5 in a first operating state 25 is emitted into the measuring tube 4 in the direction of the second ultrasonic transducer 3.

[0081] The second ultrasonic transducer 3 has a second array 7 of active elements 6, wherein the second array 7 is arranged such that it receives the measurement signal 8 emitted in the first operating state 25 and, in a second operating state 26, also emits a measurement signal 8 in the direction of the first ultrasonic transducer 2.

[0082] Both arrays 5 and 7 are two-dimensional, meaning the active elements 6 are arranged in a two-dimensional plane. Furthermore, the slope of the wedges 10 of the ultrasonic transducers is planar.

[0083] In addition, there is a control and evaluation unit 9 which controls the active elements 6 separately with control parameters.

[0084] If, during operation, the active elements 6 of the ultrasonic transmitter are operated at least temporarily with a time delay and / or with different amplitudes and / or different phases, i.e. with varying control parameters, the radiation angle of the measuring signal 8 and, to that extent, the angle at which the measuring signal 8 is coupled into the measuring tube 4 can be varied.

[0085] The flow meter 1 shown is designed such that in a first operating state 25 the first array 5 transmits a measuring signal 8 and the second array 7 receives the measuring signal 8, and that in a second operating state 26 the second array 7 transmits a measuring signal 8 which the first array 5 receives.

[0086] The measuring signal 8 emitted by the array 5, 7 first passes through the wedge, is then refracted into the measuring tube wall 11 and finally refracted by the measuring tube wall 11 into the interior of the measuring tube 4.

[0087] The coupling angle into the interior of the measuring tube depends on the speed of sound of the medium and thus also on the medium arranged in the measuring tube 4.

[0088] During operation, it may therefore happen that the intensity detected at the ultrasonic receiver decreases when the sound velocity of the medium changes due to deflection of the measuring signal 8. Likewise, the intensity of the measuring signal 8 at the ultrasonic receiver may decrease if the measuring signal 8 no longer fully impinges on the ultrasonic receiver at high flow velocities due to the drift effect.

[0089] Both effects can be counteracted by varying the radiation angle of the measurement signal at the ultrasonic transmitter and / or by changing the reception characteristics of the ultrasonic receiver. In particular, the measurement signal 8 transmitted in the direction of flow can be oriented differently than the measurement signal 8 transmitted against the direction of flow.

[0090] The illustrated embodiment thus ensures optimized settings even if the process conditions lie outside the process conditions initially specified for optimal operation.

[0091] Fig. 2 shows that the measurement signal 8, which is emitted by a two-dimensional array 5, 7, can also be transmitted to the edge area of ​​the measuring tube. This has the advantage that the flow profile can also be measured outside the center of the measuring tube in the edge area.

[0092] In Fig. 3 A one-dimensional array 5, 7 of active elements 6 is shown. In the illustrated embodiment, the one-dimensional array 5, 7 has five active elements 6 arranged next to one another at a distance d. Each active element 6 has a height h and a width w. The active elements 6 are arranged at a sufficient distance d from one another so that crosstalk between the individual active elements 6 is prevented or at least minimized.

[0093] Fig. 4 shows the beam characteristics of the Fig. 3 shown arrays 5, 7 in the far field. In the illustrated embodiment, the signals emitted by the individual active elements 6 are superimposed to form a measurement signal 8, which has a main lobe 12, two side lobes 13, and two grating lobes 14 in the far field. The main lobe 12 is radiated at an angle ρ 0. The occurrence of side lobes 13 or grating lobes 14 is usually undesirable, since a portion of the radiated power also flows into these secondary maxima. However, the side lobes 13 or grating lobes 14 can also be used to obtain information about pipe properties and / or geometries or process conditions.

[0094] If the individual active elements 6 are operated separately and with a time offset and / or with different amplitudes and / or different phases, the direction of the main lobe 12 can be varied. During operation, the main lobe 12 can be aligned with the ultrasonic receiver by appropriately controlling the active elements 6 in such a way that the intensity of the received signal is maximized.

[0095] Fig. 5 shows a comparison of the beam characteristics of a one-dimensional array 5, 7 of active elements 6 and a single active element 6. The radiation angle ρ is plotted on the abscissa, with the zero point corresponding to a perpendicular radiation. The amplitude of the measurement signal is plotted on the ordinate. Due to the discrete arrangement of individual active elements, the measurement signal 8 results from interference into a combination of maxima and minima. In contrast, the beam characteristic 15 of a single active element 6 exhibits a continuous distribution over the observed angular range.

[0096] The main lobe 12 is emitted from the array 5, 7 at a radiation angle φ 0. Side lobes 13 are formed next to the main lobe 12. In addition, there are two grating lobes 14. The width of the main lobe is proportional to λ / L, where λ is the wavelength of the measurement signal 8 and L is the total length of the array 5, 7. The angular distance of the grating lobes 14 to the main lobe 12 is proportional to λ / d, where λ is the wavelength of the measurement signal 8 and d is the distance between the individual active elements 6. The angular extent of the radiation characteristic 15 of an individual active element 6 is proportional to λ / w, where λ is the wavelength of the measurement signal 8 and w is the width of the active element 6.

[0097] In this respect, the shape of the measurement signal 8 can be adapted to the expected measurement situation by appropriate geometric design of the array 5, 7.

[0098] Fig. 6 shows the arrangement of a first one-dimensional array 5 on a first ultrasonic transducer 2 and a second one-dimensional array 7 on a second ultrasonic transducer 3. The first array 5 has four active elements 6, the second array 7 has three active elements 6, which are oriented perpendicular to the first array 5.

[0099] If the first array 5 is the transmitting array in a first operating state 25, the measurement signal 8 spreads out in a fan-like pattern inside the measuring tube. The orientation of the measurement signal 8 in the plane of the array 5 can be varied. In this first operating state 25, the second array 7 is the ultrasonic receiver. The second array 7 is aligned such that it captures the measurement signal in a fan-like pattern. The orientation of the fan-shaped reception area along the measuring tube axis can be varied. This has the advantage that the number of active elements 6 can be minimized overall.

[0100] If this second array 7 is in a next operating state 26 ultrasonic transmitter, it can emit a measuring signal 8, the orientation of which can be varied along the measuring tube axis.

[0101] Overall, the measurement signal 8 can be varied in two planes during operation. However, compared to ultrasonic transducers with two-dimensional arrays, the number of active elements 6 is minimized, resulting in a less complex ultrasonic flowmeter 1.

[0102] In Fig. 7 A further arrangement of a first one-dimensional array 5 on a first ultrasonic transducer 2 and a second one-dimensional array 7 on a second ultrasonic transducer 3 is shown. In the illustrated embodiment, both arrays 5, 7 have three active elements 6.

[0103] The arrays 5, 7 are rotated in opposite directions by an angle α, starting from a line parallel to the measuring tube axis. In the illustrated embodiment, the angle α is approximately 45°, so that the arrays 5, 7 have a largely identical input impedance, thus ensuring the best possible reciprocal operation with identical measurement signals 8 in and against the flow direction.

[0104] Fig. 8 shows a further arrangement of a first two-dimensional array 5 on a first ultrasonic transducer 2 and a second two-dimensional array 7 on a second ultrasonic transducer 3. Both arrays 5 and 7 have a cross-shaped arrangement of the active elements 6 and are thus identically designed. During operation, both the measurement signal 8 emitted by the first array 5 and the measurement signal 8 emitted by the second array 7 can be varied in at least two planes. Due to the identical design and arrangement of the arrays 5 and 7, this exemplary embodiment also has the previously mentioned advantages that the arrays have a largely identical input impedance and thus the best possible reciprocal operation with identical measurement signals 8 in and against the flow direction can be ensured.

[0105] In Fig. 9 1 shows a further arrangement of a first two-dimensional array 5 on a first ultrasonic transducer 2 and a second two-dimensional array 7 on a second ultrasonic transducer 3. In both arrays 5 and 7, the active elements 6 are arranged irregularly on a regular grid and at least partially with a large spacing. If, in a first operating state 25, the first array 5 is designed as an ultrasonic transmitter, a narrow, conical measurement signal 8 is emitted. Due to the sometimes large spacing between the active elements 6, equally significant side lobes 13 and grating lobes 14 are simultaneously realized in addition to the main lobe 12. The second array 7 is constructed and controlled during operation in such a way that local minima of the radiation characteristic of the receiver overlap with the interfering grating lobes and / or side lobes of the measurement signal emitted by the ultrasonic transmitter 2.

[0106] A realization of a one-dimensional array 5 of active elements 6 is shown in Fig 10 For this purpose, gaps 17 of a predetermined depth are sawn into a bar 16 of piezoelectric material. The upper electrodes are individually contacted and can therefore be controlled separately; the lower electrode is designed as a common ground electrode. The gaps 17 are filled with a filler material that, in particular, has high acoustic damping to prevent crosstalk between the individual active elements 6.

[0107] Fig. 11 shows a further embodiment of an array 5, 7 of active elements, which is produced by sawing gaps 17 into a piezoelectric disc 18, which gaps are filled with an acoustically insulating material. In contrast to the Fig. 9 In the embodiment shown, the array 5, 7 of active elements 6 is formed two-dimensionally. The lower electrode is, as in Fig. 9 shown, designed as a common ground electrode.

[0108] During operation, all active elements 6 can be controlled separately, but only some active elements 6 can also be controlled.

[0109] According to an alternative embodiment, the piezoelectric substrate can be applied, for example, glued, to a solid support, and the piezoelectric substrate can be sawn through completely to produce the separate active elements 6, for example, such that the solid support also has a gap of a certain depth beneath the piezoelectric substrate. The solid support can, for example, be formed as a printed circuit board or be a plastic or metal support.

[0110] Fig. 12 shows an embodiment of a flow measuring device 1, wherein only the first ultrasonic transducer 2, which in a first operating state 25 is designed as an ultrasonic transmitter, is shown. The first ultrasonic transducer 2 has an array 5 of active elements 6, which during operation emits a measurement signal 8 consisting of a main lobe and at least two side lobes 13 and two grating lobes 14. In the illustrated embodiment, the measurement signal 8 is directed onto the measuring tube in such a way that at least one grating lobe 14 impinges essentially perpendicularly on the measuring tube wall, wherein the reflection of the grating lobe 14 on the measuring tube is detected and evaluated. Information about the measuring tube wall thickness can be obtained from the reflection. According to this embodiment, deposits on the inner measuring tube wall, for example, can be detected and taken into account in the further flow determination.

[0111] Fig. 13 shows a next embodiment of a flowmeter 1 with a first ultrasonic transducer 2 and a second ultrasonic transducer 3, wherein both ultrasonic transducers 2, 3 have an array 5, 7 of active elements 6 and wherein a portion of the measurement signal 8 is aligned by appropriate control of the array 5 operating as an ultrasonic transmitter such that it excites a Lamb wave in the measuring tube wall, which propagates in the direction of the ultrasonic receiver and is detected by it. In the illustrated embodiment, the main lobe 12 is emitted such that it excites a Lamb wave in the measuring tube wall.

[0112] Alternatively, the array 5 can also be controlled in such a way that a side lobe 13 or a grating lobe 14 excites a Lamb wave in the measuring tube wall.

[0113] Fig. 14 shows a further embodiment of a flowmeter 1, wherein an array 5, 7 of active elements 6 couples a portion of the measurement signal 8 into the measuring tube wall in such a way that the measurement signal 8 propagates along the circumference of the measuring tube. Another portion of the measurement signal 8 propagates within the measuring tube and, after a plurality of reflections, hits the ultrasonic receiver.

[0114] In principle, the signal path between the first and second ultrasonic transducers can be V-shaped or W-shaped, or even have no reflection at all on the inner wall of the measuring tube. Likewise, the signal path can be designed as a polygon, in particular a triangle, square, or pentagon, when viewed from above.

[0115] In Fig 15 a first embodiment of a method 19 for operating an ultrasonic flowmeter is shown, wherein the ultrasonic flowmeter 1 is operated according to the method shown in Fig. 1 illustrated embodiment.

[0116] In a first operating state 25, the first ultrasonic transducer 2 operates as an ultrasonic transmitter and the second ultrasonic transducer 3 operates as an ultrasonic receiver.

[0117] In a first method step 20, the first active element 6 of the ultrasonic transmitter emits a first ultrasonic signal.

[0118] Simultaneously or with a time delay, the second active element 6 of the ultrasonic transmitter transmits a second ultrasonic signal 21, so that the first ultrasonic signal and the second ultrasonic signal are superimposed 22 to form the measurement signal 8.

[0119] The measurement signal 8 has a main lobe 12, two side lobes 13 and two grating lobes 14.

[0120] The main lobe 12 is radiated in such a way that it hits the ultrasonic receiver in an optimized manner.

[0121] In a next step 23, the ultrasonic receiver receives the measurement signal 8 and forwards it to the control and evaluation unit.

[0122] In a second operating state 26, the second ultrasonic transducer 3 now operates as an ultrasonic transmitter and the first ultrasonic transducer 2 operates as an ultrasonic receiver.

[0123] Since in the illustrated embodiment the second ultrasonic transducer also has an array 7 of at least two active elements 6, steps 20 to 23 are repeated.

[0124] The control and evaluation unit 9 then determines the flow rate from the transit time difference between the measuring signals 8 transmitted in and against the flow direction.

[0125] In the Fig. 16 In the embodiment of the method 19 shown, the ultrasonic flowmeter 1, after the first operating state 25, is in an adjustment state 27 in which the control and evaluation unit 9 controls the active elements 6 of the ultrasonic transmitter such that the measurement signal 8, in detail the main lobe 12, is pivoted by an angle of approximately 10° around the current position of the main lobe. During the adjustment state, the control and evaluation unit 9 detects and stores the control parameters for the position in which the signal at the ultrasonic receiver is at its maximum.

[0126] The control and evaluation unit then operates the active elements 6 of the first ultrasonic transducer 2 with the control parameters found.

[0127] Subsequently, the control of the array 7 of active elements of the second ultrasonic transducer 3 is also readjusted as previously described.

[0128] Such readjustment of the control of arrays 5, 7 can be carried out at regular intervals during operation in order to always ensure optimal control.

[0129] Alternatively or additionally, such a readjustment 27 can also be carried out depending on the determined flow rate.

[0130] Fig. 17 shows that after the determination of the flow velocity 24, if it is determined that the velocity exceeds an upper limit or falls below a lower limit, a readjustment of the control of the arrays 5, 7 is carried out.

[0131] The optimal control of the arrays can be determined either as previously described by slightly pivoting the main lobe 12 around the current position 27.

[0132] Alternatively or additionally, a relationship between different flow velocities and the control parameters of the arrays 5, 7 can be stored in the control and evaluation unit 9, so that the control of the arrays is directly determined by determining the flow velocity 28.

[0133] Accordingly, readjustment can be performed when the speed of sound changes. For this purpose, the control and evaluation unit 9 continuously or regularly monitors the amplitude of the measurement signal 8 at the ultrasonic receiver, with readjustment being performed according to method steps 27 or 28 if the amplitude falls below a lower limit.

[0134] In a next embodiment of the method 19, in the first operating state 25 and / or the second operating state, a measurement signal is emitted according to steps 20 to 22 of an array 5, 7, wherein the main lobe 12 is emitted in the direction of the ultrasonic receiver and wherein a grating lobe 14 is emitted in the direction of the measuring tube 4 such that further information about the operating state of the ultrasonic flowmeter 1 or about the measuring environment can be obtained by receiving the grating lobe.

[0135] In the Fig. 18 In the embodiment shown, the grating lobe 14 emitted by the first array 5 is emitted perpendicularly onto the measuring tube 4, with the reflections on the inner and outer measuring tube walls being received again by the first array 5. The thickness of the measuring tube wall can be determined from the reflection. According to this embodiment, the presence of deposits on the measuring tube wall can be detected and taken into account when determining the flow rate.

[0136] In the Fig. 19 In the embodiment shown, the grating lobe 14 is coupled into the measuring tube wall in such a way that it excites a Lamb wave, which propagates in the direction of the ultrasonic receiver and is detected by the ultrasonic receiver. The Lamb wave can either strike the ultrasonic receiver with a time delay from the main lobe 12 or be detected by another active element 6, so that the Lamb wave is detected separately from the main lobe. The amplitude and / or the propagation time and / or the spectrum of the Lamb wave are then evaluated. Bezugszeichen

[0137] 1Ultrasonic flowmeter 2First ultrasonic transducer 3Second ultrasonic transducer 4Measuring tube 5First array 6Active element 7Second array 8Measurement signal 9Control and evaluation unit 10Wedge 11Measuring tube wall 12Main lobe 13Side lobe 14Grid lobe 15Emission characteristic of a single active element 16Bar 17Gap 18Disc 19Method for operating an ultrasonic flowmeter 20Emission of a first ultrasonic signal 21Emission of a second ultrasonic signal 22Superposition to form a measurement signal 23Reception and transmission of the measurement signal 24Determination of the flow 25First operating state 26Second operating state 27Adjustment state 28Adjustment state 29Emission and reception of a grating lobe

Claims

1. Ultrasonic flowmeter (1) comprising at least a first ultrasonic transducer (2) and a second ultrasonic transducer (3) and further comprising a control and evaluation unit (9), wherein the control and evaluation unit (9) is connected to the first ultrasonic transducer (2) and the second ultrasonic transducer (3), wherein the first ultrasonic transducer (2) and / or the second ultrasonic transducer (3) is / are designed as an ultrasonic transmitter and / or ultrasonic receiver, wherein the first ultrasonic transducer (2) and / or the second ultrasonic transducer (3) is or are designed as a wedge transducer, wherein the first ultrasonic transducer (2) and the second ultrasonic transducer (3) are arranged on a measuring tube (4) in such a way that a signal path is formed between the first (2) and the second ultrasonic transducer (4), so that a measuring signal (8) emitted by the ultrasonic transmitter runs via the signal path to the ultrasonic receiver, wherein the first ultrasonic transducer (2) has a first array (5) of at least two active elements (6) and / or that the second ultrasonic transducer (3) has a second array (7) of at least two active elements (6), wherein at least one ultrasonic transducer (2, 3) which has an array (5, 7) of at least two active elements (6) is formed as a wedge transducer wherein at least two active elements (6) of the array (5) arranged on the first ultrasonic transducer (2) are separately controllable by the control and evaluation unit (9) and / or that at least two active elements of the array (7) arranged on the second ultrasonic transducer (3) are separately controllable by the control and evaluation unit (9) characterized in that the ultrasonic flowmeter is designed for carrying out a method according to any one of claims 12 to 22.

2. Ultrasonic flowmeter (1) according to claim 1, characterized in that the first ultrasonic transducer (2) has a first array (5) of at least two active elements (6) and the second ultrasonic transducer (3) has a second array (7) of at least two active elements (6), and that the first array (5) and the second array (7) have the same number of active elements (6) or a different number of active elements (6).

3. Ultrasonic flowmeter (1) according to claim 1 or 2, characterized in that the first ultrasonic transducer (2) comprises a first array (5) of at least two active elements (6) and the second ultrasonic transducer (3) comprises a second array (7) of at least two active elements (6), and that the first array (5) and the second array (7) have an identical arrangement or a different arrangement of the active elements (6).

4. Ultrasonic flowmeter (1) according to any one of claims 1 to 3, characterized in that the first array (5) and / or the second array is or are formed two-dimensionally at least in regions.

5. Ultrasonic flowmeter (1) according to one of claims 1 to 4, characterized in that the first array (5) and / or the second array (7) is / are formed one-dimensionally at least in regions.

6. Ultrasonic flowmeter (1) according to one of claims 1 to 5, characterized in that first array (5) and the second array (7) are formed one-dimensionally and that the second array (7) is aligned at an angle to the first array (5), essentially perpendicular to the first array (5).

7. Ultrasonic flowmeter (1) according to any one of claims 1 to 6, characterized in that the first array (5) and / or the second array (7) is produced by introducing at least one gap (17) into an electro-acoustic substrate so that the substrate has at least two separately contactable regions on the upper side and a common ground connection on the lower side, wherein the at least one gap (17) is preferably filled with an acoustically insulating or absorbing material.

8. Ultrasonic flowmeter (1) according to one of claims 1 to 6, characterized in that the first array (5) and / or the second array (7) is produced by applying an electro-acoustic substrate to a carrier and by introducing at least one gap (17) into the electro-acoustic substrate, wherein the gap (17) completely cuts through the electro-acoustic substrate, wherein the at least one gap (17) is preferably filled with an acoustically insulating or absorbing material.

9. Ultrasonic flowmeter (1) according to any one of claims 1 to 8, characterized in that the number of active elements (6) and the geometry of the first array (5) and / or of the second array (7) is determined depending on the expected pivot angle of the measuring signal, wherein preferably at the same time the number of active elements (6) is minimized.

10. Ultrasonic flowmeter (1) according to one of claims 1 to 9, characterized in that the number of active elements (6) and / or the geometry of the first array (5) and of the second array (7) are matched to one another in such a way that undesired signal components of the measuring signal emitted by the ultrasonic transmitter are suppressed by minima in the reception characteristic of the ultrasonic receiver.

11. Ultrasonic flowmeter (1) according to any one of claims 1 to 10, characterized in that the first ultrasonic transducer (2) and / or the second ultrasonic transducer (3) comprise an electro-acoustic substrate comprising at least a first and a second electro-acoustic disc, wherein the first and the second electro-acoustic disc are arranged on top of each other and wherein the array (5, 7) of active elements (6) of this ultrasonic transducer (2, 3) is arranged in the first electro-acoustic disc and / or in the second electro-acoustic disc.

12. Method (19) for operating an ultrasonic flowmeter (1), wherein the ultrasonic flowmeter (1) comprises at least a first ultrasonic transducer (2) and a second ultrasonic transducer (3) and a control and evaluation unit (9), wherein the control and evaluation unit (9) is connected to the first ultrasonic transducer (2) and the second ultrasonic transducer (3), wherein the first ultrasonic transducer (2) and / or the second ultrasonic transducer (3) is / are designed as an ultrasonic transmitter and / or ultrasonic receiver, wherein the first ultrasonic transducer (2) and / or the second ultrasonic transducer (3) is or are designed as a wedge transducer, wherein the first ultrasonic transducer (2) and the second ultrasonic transducer (3) are arranged on a measuring tube (4) in such a way that a signal path is formed between the first (2) and the second ultrasonic transducer (3), so that a measuring signal (8) emitted by the ultrasonic transmitter runs via the signal path to the ultrasonic receiver, wherein the first ultrasonic transducer (2) has a first array (5) of at least two active elements (6) and / or that the second ultrasonic transducer (3) has a second array (7) of at least two active elements (6) wherein at least two active elements (6) of the array (5) arranged on the first ultrasonic transducer (2) are separately controlled by the control and evaluation unit (9) and / or that at least two active elements (6) of the array (7) arranged on the second ultrasonic transducer (3) are separately controlled by the control and evaluation unit (9), and that the control and evaluation unit drives the array (5, 7) functioning as an ultrasonic transmitter in such a way that the radiation angle of the measuring signal is varied at least at times and / or that the control and evaluation unit (9) varies the reception characteristic of the array functioning as an ultrasonic receiver at least at times, so that, in order to determine the flow rate during measurement, the measuring signal impinges on the ultrasonic receiver in an optimized manner and / or the ultrasonic receiver receives the measuring signal in an optimized manner with respect to the radiation angle, characterized in that for installation of the ultrasonic transducers (2, 3) on the measuring tube, the ultrasonic transmitter emits a measuring signal, wherein by pivoting the reception characteristic of the ultrasonic receiver, the pivoting angle at which the ultrasonic receiver optimally receives the measuring signal, is determined and wherein the control and evaluation unit, starting from the pivoting angle and taking into account the geometry of the signal path, determines a position for the ultrasonic transmitter and / or the ultrasonic receiver at which the ultrasonic transmitter array transmits the measuring signal in a non-pivoted manner and at which the ultrasonic receiver array receives the measuring signal in a non-pivoted manner.

13. Method according to claim 12, characterized in that at least the ultrasonic transducer (2, 3) operating as an ultrasonic transmitter in an operating state (25, 26) has an array (5, 7) of at least two active elements (6), wherein the at least two active elements (6) of the ultrasonic transmitter are separately controllable by the control and evaluation unit (9), that, in a first operating state (25), the first active element (6) of the ultrasonic transmitter emits (20) a first ultrasonic signal, and that the second active element (6) of the ultrasonic transmitter emits a second ultrasonic signal (21), so that the first ultrasonic signal and the second ultrasonic signal are superimposed (22) to form the measuring signal (8).

14. Method (19) according to any one of claims 12 to 13, characterized in that the measuring signal (8) has at least one main lobe (12) and optionally at least two side lobes (13) and / or at least two grid lobes (14) due to the superposition of at least the first ultrasonic signal and the second ultrasonic signal.

15. Method (19) according to any one of claims 12 to 14, characterized in that the first ultrasonic signal and the second ultrasonic signal are emitted at least at times with a time delay and / or with different amplitude and / or with different phase, whereby the radiation angle of the measuring signal (8), in particular of the main lobe (12) of the measuring signal (8), is changed.

16. Method according to any one of claims 12 to 15, characterized in that, at least at times, the signals measured at the individual active elements of the array functioning as an ultrasonic receiver are superimposed on one another in a time-delayed and / or phase-shifted manner and / or weighted with different amplitude, whereby the reception characteristic of the ultrasonic receiver is pivoted.

17. Method (19) according to any one of claims 12 to 16, characterized in that the control and evaluation unit (9) monitors the amplitude of the measuring signal (8) detected by the ultrasonic receiver, and that the radiation angle of the measuring signal (8) and / or the reception characteristic of the ultrasonic receiver is changed if the amplitude falls below a threshold value.

18. Method (19) according to claim 17, characterized in that the control and evaluation unit (9) varies the radiation angle of the measuring signal (8) and / or the reception characteristic of the ultrasonic receiver at regular or irregular intervals in order to maximize the measuring signal (8) at the ultrasonic receiver, wherein, during the variation, the control and evaluation unit (9) detects a maximum of the amplitude at the ultrasonic receiver as well as the corresponding drive parameters of the active elements (6) thereto, and that the control and evaluation unit (9) subsequently drives the array (5, 7) of at least two active elements (6) of the ultrasonic transmitter and / or of the ultrasonic receiver in accordance with the determined drive parameters.

19. Method (19) according to claim 17 to 18, characterized in that the control and evaluation unit (9) adjusts the radiation angle of the measuring signal (8) emitted by the ultrasonic transmitter and / or the reception characteristic of the ultrasonic receiver depending on the measured flow velocity of the medium and / or depending on the sonic velocity of the medium, in such a way that the measuring signal (8) is maximized at the ultrasonic receiver.

20. Method (19) according to any one of the claims 12 to 19, characterized in that the control and evaluation unit (9) has a memory unit, wherein a relationship between a radiation angle of the measuring signal (8) or control parameters for the array of active elements (6) of the ultrasonic transmitter and / or the ultrasonic receiver and different media and / or different flow rates and / or different sound velocities is stored in the memory unit, so that when the flow rate changes and / or when the medium changes, the control and evaluation unit (9) automatically adjusts the radiation angle of the measuring signal and / or the drive parameters for the array (5, 7) of active elements and / or the reception characteristic of the ultrasonic receiver (6) in accordance with the stored relationship.

21. Method (19) according to any one of claims 12 to 20, characterized in that the measuring signal (8) has at least one main lobe (12) and at least two side lobes (13) and / or two grid lobes (14), that at least at times the at least one main lobe or at least one side lobe (13) or at least one grid lobe (14) is aligned with the measuring tube (4) in such a way, that the main lobe (12) or the side lobe (13) or the grid lobe (14) is reflected at the measuring tube (4) and the reflection is received again by the array (5, 7) of active elements (6) initially operating as an ultrasonic transmitter, and that the control and evaluation unit (9) determines from the reflection of the main lobe (12) or the side lobe (13) or the grid lobe (14) at least one item of information about an operating state and / or the measuring environment.

22. Method (19) according to any one of claims 12 to 21, characterized in that the at least one main lobe (12) or the at least one side lobe (13) or the at least one grid lobe (14) is aligned at least temporarily with the measuring tube (4) in such a way that it excites a Lamb wave which propagates along the measuring tube wall (11) in the direction of the ultrasonic receiver and which is detected by the ultrasonic receiver, wherein the amplitude and / or the propagation time and / or the spectrum of the Lamb wave is evaluated.