Ultrasonic Flowmeter and Method for Operating an Ultrasonic Flowmeter

Abstract

An ultrasonic flowmeter includes first and second ultrasonic transducers and a control and evaluation unit connected thereto. The first and/or second ultrasonic transducer is/are an ultrasonic transmitter and/or an ultrasonic receiver. The first and second ultrasonic transducers are arranged on a measuring tube in such a way that a signal path is formed therebetween, and such that a measuring signal emitted by the ultrasonic transmitter runs via the signal path to the ultrasonic receiver. The first and/or second ultrasonic transducer has array to of at least two active elements. At least one ultrasonic transducer with an array of at least two active elements is formed as a wedge transducer. At least two active elements of the array arranged on the first ultrasonic transducer, and/or at least two active elements of the array arranged on the second ultrasonic transducer, are separately controllable by the control and evaluation unit.

Claims

1. An ultrasonic flowmeter, comprising: at least a first ultrasonic transducer; a second ultrasonic transducer; and a control and evaluation unit 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 or 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 measuring signal emitted by the ultrasonic transmitter runs via the signal path to the ultrasonic receiver; wherein 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, which has an array of at least two active elements is formed as a wedge transducer; and wherein at least two active elements of the array arranged on the first ultrasonic transducer are separately controllable by the control and evaluation unit and/or at least two active elements of the array arranged on the second ultrasonic transducer are separately controllable by the control and evaluation unit.

2. The ultrasonic flowmeter according to claim 1, 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, and the first array and the second array have the same number of active elements or a different number of active elements.

3. The ultrasonic flowmeter according to claim 1, wherein the first ultrasonic transducer comprises a first array of at least two active elements and the second ultrasonic transducer comprises a second array of at least two active elements and that the first array and the second array have an identical arrangement or a different arrangement of the active elements.

4. The ultrasonic flowmeter according to claim 3, wherein the first array and/or the second array is or are formed two-dimensionally at least in regions.

5. The ultrasonic flowmeter according to claim 3, wherein the first array and/or the second array is/are formed one-dimensionally at least in regions.

6. The ultrasonic flowmeter according to claim 3, wherein the first array and the second array are formed one-dimensionally and the second array is aligned at an angle to the first array, essentially perpendicular to the first array.

7. The ultrasonic flowmeter according to claim 3, wherein the first array and/or the second array is produced by introducing at least one 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 filled with an acoustically insulating or absorbing material.

8. The ultrasonic flowmeter according to claim 3, wherein the first array and/or the second array is produced by applying an electro-acoustic substrate to a carrier and by introducing at least one gap into the electro-acoustic substrate, wherein the gap completely cuts through the electro-acoustic substrate, wherein the at least one gap is filled with an acoustically insulating or absorbing material.

9. The ultrasonic flowmeter according to claim 3, wherein the number of active elements and the geometry of the first array and/or of the second array is determined depending on the expected pivot angle of the measuring signal, wherein at the same time the number of active elements is minimized.

10. The ultrasonic flowmeter according to claim 3, wherein the number of active elements and/or the geometry of the first array and of the second array are tuned 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. The ultrasonic flowmeter according to claim 3, wherein the first ultrasonic transducer and/or the second ultrasonic transducer an electro-acoustic substrate including 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 of active elements of this ultrasonic transducer is arranged in the first electro-acoustic disc and/or in the second electro-acoustic disc.

12. A method for operating an ultrasonic flowmeter, wherein the ultrasonic flowmeter includes 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 or 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 measuring signal emitted by the ultrasonic transmitter runs via the signal path to the ultrasonic receiver, wherein 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, the method comprising: the control and evaluation unit separately controlling at least two active elements of the array arranged on the first ultrasonic transducer and/or at least two active elements of the array arranged on the second ultrasonic transducer; the control and evaluation unit controlling the array 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 varying the reception characteristic of the array functioning as an ultrasonic receiver at least at times; in order to determine the flow rate during measurement, the measuring signal impinging on the ultrasonic receiver in an optimized manner and/or the ultrasonic receiver receiving the measuring signal in an optimized manner with respect to the radiation angle.

13. The method according to claim 12, wherein for installation of the ultrasonic transducers 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.

14. The method according to claim 12, wherein at least the ultrasonic transducer operating as an ultrasonic transmitter in an operating state has an array of at least two active elements, wherein the at least two active elements of the ultrasonic transmitter are separately controllable by the control and evaluation unit; wherein, in a first operating state, the first active element of the ultrasonic transmitter emits a first ultrasonic signal; wherein the second active element of the ultrasonic transmitter emits a second ultrasonic signal; and wherein the first ultrasonic signal and the second ultrasonic signal are superimposed to form the measuring signal.

15. The method according to claim 14, wherein the measuring signal has at least one main lobe and at least two side lobes and/or at least two grid lobes due to the superposition of at least the first ultrasonic signal and the second ultrasonic signal.

16. The method according to claim 15, wherein 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 of the main lobe of the measuring signal is changed.

17. The method according to claim 12, wherein, 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 ultra sonic receiver is pivoted.

18. The method according to claim 12, wherein the control and evaluation unit monitors the amplitude of the measuring signal detected by the ultrasonic receiver, and that the radiation angle of the measuring signal and/or the reception characteristic of the ultrasonic receiver is changed if the amplitude falls below a threshold value.

19. The method according to claim 18, wherein the control and evaluation unit varies the radiation angle of the measuring signal and/or the reception characteristic of the ultrasonic receiver at regular or irregular intervals in order to maximize the measuring signal at the ultrasonic receiver; wherein, during the variation, the control and evaluation unit detects a maximum of the amplitude at the ultrasonic receiver as well as the corresponding control parameters of the active elements thereto; and wherein the control and evaluation unit subsequently controls the array of at least two active elements of the ultrasonic transmitter and/or of the ultrasonic receiver in accordance with the determined control parameters.

20. The method according to claim 19, wherein the control and evaluation unit adjusts the radiation angle of the measuring signal 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 is maximized at the ultrasonic receiver.

21. The method according to claim 12, wherein the control and evaluation unit 94 has a memory unit; and wherein a relationship between a radiation angle of the measuring signal or control parameters for the array of active elements 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 automatically adjusts the radiation angle of the measuring signal and/or the control parameters for the array of active elements and/or the reception characteristic of the ultrasonic receiver in accordance with the stored relationship.

22. The method according to claim 14, wherein the measuring signal has at least one main lobe and at least two side lobes and/or two grid lobes; wherein at least at times the at least one main lobe or at least one side lobe or at least one grid lobe is aligned with the measuring tube in such a way, that the main lobe or the side lobe or the grid lobe is reflected at the measuring tube and the reflection is received again by the array of active elements initially operating as an ultrasonic transmitter; and wherein the control and evaluation unit determines from the reflection of the main lobe or the side lobe or the grid lobe at least one item of information about an operating state and/or the measuring environment.

23. The method according to claim 22, wherein at least one main lobe or the at least one side lobe or the at least one grid lobe is aligned at least temporarily with the measuring tube in such a way that the at least one main lobe or the at least one side lobe or the at least one grid lobe excites a Lamb wave which propagates along the measuring tube wall 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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0095] There are now a multitude of possibilities for designing and further developing the ultrasonic flowmeter according to the invention and the method for operating the ultrasonic flowmeter. For this, reference is made to the following description of preferred embodiments in conjunction with the drawings.

[0096] FIG. 1 illustrates a first embodiment of an ultrasonic flowmeter according to the invention.

[0097] FIG. 2 illustrates a second embodiment of an ultrasonic flowmeter according to the invention.

[0098] FIG. 3 illustrates a one-dimensional arrangement of active elements.

[0099] FIG. 4 illustrates a one-dimensional arrangement of active elements as well as the resulting radiation characteristic.

[0100] FIG. 5 illustrates a comparison of the radiation characteristics of an antenna array and a single active element.

[0101] FIG. 6 illustrates an arrangement of a first one-dimensional array on a first ultrasonic transducer and a second one-dimensional array on a second ultrasonic transducer.

[0102] FIG. 7 illustrates 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.

[0103] FIG. 8 illustrates 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.

[0104] FIG. 9 illustrates a further arrangement of a first array on a first ultrasonic transducer and a second array on a second ultrasonic transducer.

[0105] FIG. 10 illustrates an embodiment of a one-dimensional array of radiating elements.

[0106] FIG. 11 illustrates another embodiment of a two-dimensional array of radiating elements.

[0107] FIG. 12 illustrates a further embodiment of a flowmeter according to the invention.

[0108] FIG. 13 illustrates a further embodiment of a flowmeter according to the invention.

[0109] FIG. 14 illustrates a further embodiment of a flowmeter according to the invention.

[0110] FIG. 15 illustrates a first embodiment of a method according to the invention.

[0111] FIG. 16 illustrates another embodiment of a method according to the invention.

[0112] FIG. 17 illustrates another embodiment of a method according to the invention.

[0113] FIG. 18 illustrates another embodiment of a method according to the invention.

[0114] FIG. 19 illustrates another embodiment of a method according to the invention.

DETAILED DESCRIPTION

[0115] FIG. 1 shows a first embodiment of an ultrasonic flowmeter 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.

[0116] The first ultrasonic transducer 2 has a first array 5 of active elements 6, wherein the array 5 is arranged such that the measuring 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.

[0117] 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 measuring signal 8 emitted in the first operating state 25 and also emits a measuring signal 8 in the direction of the first ultrasonic transducer 2 in a second operating state 26.

[0118] Both arrays 5 and 7 are formed in two dimensions, i.e. the active elements 6 are arranged in a two-dimensional plane. Moreover, the slope of the wedges 10 of the ultrasonic transducers is planar in each case.

[0119] In addition, a control and evaluation unit 9 is provided which separately controls the active elements 6 with control parameters.

[0120] If, during operation, the active elements 6 of the ultrasonic transmitter are operated at least at times with a time delay and/or with different amplitude and/or different phase, i.e. with varying control parameters, the radiation angle of the measuring signal 8 and, in this respect, the angle at which the measuring signal 8 couples into the measuring tube 4 can be varied.

[0121] The flowmeter 1 shown is configured such that in a first operating state 25 the first array 5 emits 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 emits a measuring signal 8 which the first array 5 receives.

[0122] The measuring signal 8 emitted by the array 5, 7 first passes through the wedge, is then refracted in the measuring tube wall 11, and is finally refracted from the measuring tube wall 11 into the interior of the measuring tube 4.

[0123] The angle of coupling into the inside of the measuring tube depends on the sound velocity of the medium and thus also on the medium arranged in the measuring tube 4.

[0124] During operation, it can therefore occur that the intensity captured at the ultrasonic receiver decreases when the sound velocity of the medium changes due to deflection of the measuring signal 8. Similarly, the intensity of the measuring signal 8 at the ultrasonic receiver can decrease if the measuring signal 8 no longer fully impinges on the ultrasonic receiver at high flow velocities due to the drift effect.

[0125] Both effects can be counteracted by the possibility of varying the radiation angle of the measuring signal at the ultrasonic transmitter and/or by changing the reception characteristics at the ultrasonic receiver. In particular, the measuring signal 8 that is emitted in the direction of flow can be oriented differently than the measuring signal 8 that is emitted against the direction of flow.

[0126] The embodiment shown thus ensures optimized settings even if the process condition is outside the process condition initially specified for optimal operation.

[0127] FIG. 2 shows that the measuring signal 8 emitted by a two-dimensional array 5, 7 can also be emitted in the edge region 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 region.

[0128] FIG. 3 shows a one-dimensional array 5, 7 of active elements 6. In the embodiment shown, the one-dimensional array 5, 7 has five active elements 6 arranged next to each other at a distance d. Each active element 6 has a height h and a width w. In this case, the active elements 6 are arranged at a sufficient distance d from each other so that crosstalk between the individual active elements 6 is prevented or at least minimized.

[0129] FIG. 4 shows the beam characteristics of the array 5,7 shown in FIG. 3 in the far field. The signals emitted by the individual active elements 6 are superimposed in the embodiment shown to form a measuring signal 8, which has a main lobe 12, two side lobes 13 and two grid lobes 14 in the far field. The main lobe 12 is radiated at an angle ρ.sub.0.

[0130] Usually, the occurrence of side lobes 13 or grid lobes 14 is undesirable, since a part of the radiated power is also included in these side lobes. However, the side lobes 13 or grid lobes 14 can also be used to obtain information about tube properties and/or tube geometries or process conditions.

[0131] If the individual active elements 6 are operated separately and with a time delay and/or with different amplitude and/or different phase, 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.

[0132] 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, where the zero point corresponds to perpendicular radiation. The amplitude of the measuring signal is plotted on the ordinate. Due to the discrete arrangement of individual active elements, the measuring signal 8 results in a combination of maxima and minima by interference. In contrast, the radiation pattern 15 of a single active element 6 exhibits a continuous distribution over the angular range under consideration.

[0133] At a beam angle ρ.sub.0, the main lobe 12 is emitted by the array 5, 7. Side lobes 13 are formed next to the main lobe 12. In addition, two grid lobes 14 are present. The width of the main lobe is proportional to λ/L, where λ, is the wavelength of the measuring signal 8 and L is the total length of the array 5, 7. The angular distance of the grid lobes 14 from the main lobe 12 is proportional to λ/d, where λ, is the wavelength of the measuring signal 8 and d is the distance between the individual active elements 6. The angular extent of the radiation pattern 15 of a single active element 6 is proportional to λ/w, where λ, is the wavelength of the measuring signal 8 and w is the width of the active element 6.

[0134] In this respect, the shape of the measuring signal 8 can be adapted to the expected measurement situation by appropriate geometric design of the array 5, 7.

[0135] 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 oriented perpendicularly to the first array 5.

[0136] When the first array 5 is in a first operating state 25 of the transmitting array, the measuring signal 8 propagates fan-like inside the measuring tube. Thereby, the orientation of the measuring 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 oriented such that it captures the measuring signal in a fan-like manner. In this case, the orientation of the fan-like reception area can be varied along the measuring tube axis. This has the advantage that the total number of active elements 6 can be minimized.

[0137] If this second array 7 is in a next operating state 26 of the ultrasonic transmitter, it can emit a measuring signal 8 whose orientation can be varied along the measuring tube axis.

[0138] Overall, the measuring signal 8 can be varied in two planes during operation. However, compared to ultrasonic transducers that have two-dimensional arrays, the number of active elements 6 is minimized, so that as a result the ultrasonic flowmeter 1 has a less complex design.

[0139] 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. Both arrays 5, 7 have three active elements 6 in the illustrated embodiment. The arrays 5, 7 are rotated in opposite directions to each other by an angle α starting from a 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 and thus the best possible reciprocal operation with identical measuring signals 8 in and against the flow direction can be ensured.

[0140] 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 measuring signal 8 emitted by the first array 5 and the measuring signal 8 emitted by the second array 7 can be varied at least in two planes. Due to the identical design and arrangement of the arrays 5 and 7, this 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 measuring signals 8 in and against the flow direction can be ensured.

[0141] FIG. 9 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 measuring signal 8 is emitted. Due to the partially large distances of the active elements 6 to each other, in addition to the main lobe 12, equally significant side lobes 13 and grid lobes 14 are simultaneously implemented. The second array 7 is constructed and controlled during operation in such a way that local minima of the radiation characteristic of the receiver are superimposed on the interfering grid lobes and/or side lobes of the measuring signal emitted by the ultrasonic transmitter 2.

[0142] An implementation of a one-dimensional array 5 of active elements 6 is shown in FIG. 10. For this, gaps 17 with a predetermined depth are sawn into a bar 16 of piezo-electric material. The upper electrodes are contacted individually and can therefore be controlled separately, while the lower electrode is designed as a common ground electrode. The gaps 17 are filled with a filler material, which, in particular, has a large acoustic attenuation in order to avoid crosstalk between the individual active elements 6.

[0143] FIG. 11 shows a further embodiment of an array 5, 7 of active elements made by sawing gaps 17 in a piezo-electric disc 18 which are filled with an acoustically insulating material. In contrast to the embodiment shown in FIG. 9, the array 5, 7 of active elements 6 is formed in two dimensions. The lower electrode is also designed as a common ground electrode, as shown in FIG. 9.

[0144] During operation, all active elements 6 can be controlled separately, but it is also possible to only control some of the active elements 6.

[0145] According to an alternative embodiment, the piezo-electric substrate can be applied to a solid support, for example glued, and the piezo-electric substrate can be completely sawed through to produce the separate active elements 6, for example in such a way that the solid support also has a gap of a certain depth under the piezo-electric substrate. The solid support can, for example, be formed as a printed circuit board or be a plastic support or a metal support.

[0146] FIG. 12 shows an embodiment of a flowmeter 1, wherein only the first ultrasonic transducer 2, which is formed as an ultrasonic transmitter in a first operating state, is shown. The first ultrasonic transducer 2 has an array 5 of active elements 6, which, during operation, emits a measuring signal 8 consisting of a main lobe and at least two side lobes 13 and two grid lobes 14. In the embodiment shown, the measuring signal 8 is aligned with the measuring tube in such a way that at least one grid lobe 14 impinges essentially perpendicularly on the measuring tube wall, and the reflection of the grid lobe 14 from the measuring tube is captured and evaluated. From the reflection, information about the measuring tube wall thickness can be obtained. According to this embodiment, for example, deposits on the inner measuring tube wall can be detected and taken into account in further flow determination.

[0147] 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 part of the measuring signal 8 is aligned by appropriate control of the array 5 operating as an ultrasonic transmitter in such a way that it excites a Lamb wave in the measuring tube wall, which propagates in the direction of the ultrasonic receiver and is captured by the latter. In the illustrated embodiment, the main lobe 12 is emitted such that it excites a Lamb wave in the measuring tube wall.

[0148] Alternatively, the array 5 can also be controlled in such a way that a side lobe 13 or a grid lobe 14 excites a Lamb wave in the measuring tube wall.

[0149] FIG. 14 shows another embodiment of a flowmeter 1, wherein an array 5, 7 of active elements 6 couples a part of the measuring signal 8 into the measuring tube wall in such a way that the measuring signal 8 propagates along the measuring tube circumference. Another part of the measuring signal 8 propagates inside the measuring tube and hits the ultrasonic receiver after a plurality of reflections.

[0150] In principle, the signal path between the first and second ultrasonic transducers can be v-shaped or w-shaped, or it can have no reflection at all on the inner wall of the measuring tube. Likewise, the signal path can be formed as a polygon, in particular as a triangle, quadrilateral or pentagon, when viewed from above the measuring tube.

[0151] FIG. 15 shows a first embodiment of a method 19 for operating an ultrasonic flowmeter, wherein the ultrasonic flowmeter 1 is designed according to the embodiment shown in FIG. 1.

[0152] 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.

[0153] In a first method step 20, the first active element 6 of the ultrasonic transmitter transmits a first ultrasonic signal.

[0154] Simultaneously or with a time delay, 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.

[0155] The measuring signal 8 has a main lobe 12, two side lobes 13, and two grid lobes 14.

[0156] The main lobe 12 is emitted in such a way that it is optimized to hit the ultrasonic receiver.

[0157] In a next step 23, the ultrasonic receiver receives the measuring signal 8 and forwards it to the control and evaluation unit.

[0158] 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.

[0159] 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.

[0160] Subsequently, the control and evaluation unit 9 determines 24 the flow rate from the difference in transit time between the measuring signals 8 emitted in and against the direction of flow.

[0161] In the embodiment of the method 19 shown in FIG. 16, the ultrasonic flowmeter 1 is in an adjustment state 27 after the first operating state 25, in which the control and evaluation unit 9 controls the active elements 6 of the ultrasonic transmitter in such a way that the measuring signal 8, in detail the main lobe 12 is pivoted by an angle of approximately 10° to 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 maximum.

[0162] Subsequently, the control and evaluation unit operates the active elements 6 of the first ultrasonic transducer 2 with the control parameters found.

[0163] Subsequently, the control of the array 7 of active elements of the second ultrasonic transducer 3 is also readjusted as described above.

[0164] Such a readjustment of the control of the arrays 5, 7 can be carried out during operation at regular intervals in order to always ensure an optimal control.

[0165] Alternatively or additionally, such readjustment 27 can also be carried out in dependence on the determined flow rate.

[0166] FIG. 17 shows that after determining the flow velocity 24, if it is determined that the velocity exceeds an upper limit value or falls below a lower limit value, a readjustment of the control of the arrays 5, 7 is carried out.

[0167] Optimal control of the arrays can be determined 27 as previously described by slightly pivoting the main lobe 12 around the current position.

[0168] Alternatively or also additionally, a relationship between different flow rates and the control parameters of the arrays 5, 7 can be stored in the control and evaluation unit 9, so that, with the determination of the flow rate, the control of the arrays is directly determined 28.

[0169] Accordingly, readjustment can be carried out when the sound velocity changes. For this, the control and evaluation unit 9 constantly or regularly monitors the amplitude of the measuring signal 8 at the ultrasonic receiver, wherein readjustment is carried out in accordance with process steps 27 or 28 if the amplitude falls below a lower limit value.

[0170] In a next embodiment of the method 19, in the first operating state 25 and/or the second operating state, a measuring 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 grid lobe 14 is emitted in the direction of the measuring tube 4 in such a way that further information about the operating state of the ultrasonic flowmeter 1 or about the measurement environment can be obtained by receiving the grid lobe.

[0171] In the embodiment shown in FIG. 18, the grid lobe 14 emitted from the first array 5 is emitted perpendicularly to the measuring tube 4, and the reflections from the inner and outer measuring tube walls are again received by the first array 5. From the reflection, the thickness of the measuring tube wall can be determined. According to this embodiment, in this respect the presence of deposits on the measuring tube wall can be detected and taken into account when determining the flow rate.

[0172] In the embodiment shown in FIG. 19, the grid 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 captured by the ultrasonic receiver. In this process, the Lamb wave can either strike the ultrasonic receiver with a time delay with respect to the main lobe 12 or can also be captured by another active element 6, so that the Lamb wave is captured separately from the main lobe. The amplitude and/or the propagation time and/or the spectrum of the Lamb wave is then evaluated.