Ultrasonic flowmeter and method for calibration

Abstract

The invention relates to a method for calibrating an ultrasonic flowmeter, which is coupled to a pipe (1), for measuring a flow velocity or a volumetric flow rate of a fluid by means of two ultrasonic transducers (2, 3) spaced apart from one another, wherein the main directions of the ultrasonic transducers (2, 3) are oriented at an angle to one another in a symmetrical V shape. The aim of the invention is to provide an improved method which allows the ultrasonic flowmeter to be installed on a pipe with minimal effort, even by untrained personnel, without the accuracy of the measurement being impaired. For this purpose, the invention proposes the following steps: - ascertaining the propagation speed of an ultrasonic signal propagating through the pipe wall as a surface wave; - ascertaining the wall thickness of the pipe by determining the propagation time of an ultrasonic signal through the pipe wall; - ascertaining the inner diameter of the pipe by deriving it from the value of the adjusted angle and the distance of the ultrasonic transducers, - adjusting the angle to the ascertained pipe geometry by means of at least one motorized actuating drive (5) which sets the angle and an electronic calibration device (6) which interacts with the actuating drive (5).

Description

[0001] Ultrasonic flow meter and calibration method

[0002] The invention relates to a method for calibrating an ultrasonic flow meter for measuring the flow velocity and / or volumetric flow rate of a fluid in a pipe, comprising two spaced-apart ultrasonic transducers, each having a transmission and reception characteristic oriented along a principal direction, wherein the principal directions of the ultrasonic transducers are aligned at an angle to each other in a symmetrical V-shape. The invention further relates to an ultrasonic flow meter configured to carry out such a method.

[0003] Such a flow measuring device is known, for example, from WO 88 / 08516 A1 or DE 10 2006 000 693 A1. The technology of measuring the flow of a fluid through a pipe using ultrasound is based on the principle of the transit-time difference of ultrasonic signals. The method is also known as transit-time ultrasonic flow measurement.

[0004] In one possible embodiment of such a flow measuring device, the ultrasonic transducers are mounted in pairs on the outside of the pipe at defined distances from each other in the direction of flow (so-called "clamp-on" mounting).

[0005] The ultrasonic transducers send and receive ultrasonic signals through the pipe and the fluid flowing within it. Two ultrasonic signals are used: one transmitted in the direction of flow and one transmitted against the flow. The ultrasonic signal transmitted in the direction of flow travels faster than the signal transmitted against the flow because the flowing fluid acts as the transmission medium for the sound wave of the ultrasonic signal. The time it takes for the ultrasonic signal to travel from one transducer to the other is measured as the transit time in both directions. From the difference in these transit times and the geometry of the arrangement, the flow velocity can be directly derived using established formulas. The flow velocity is proportional to the difference in transit times.

[0006] The described transit-time ultrasonic flow measurement with "clamp-on" mounting of the ultrasonic transducers is well-established and offers several advantages. A key advantage is that the measurement is non-contact. The measurement is performed without direct contact with the fluid. The ultrasonic transducers can be attached / clamped to the outside of the pipe. No modifications to the pipe system are necessary.

[0007] In many applications, the volumetric flow rate, i.e., the flow or throughput of the fluid (measured, for example, in liters per second) through the pipe, is of interest. This can be derived from the flow velocity determined by ultrasound, based on a calibration. The volumetric flow rate is the product of the flow velocity and the inner cross-section of the pipe. Therefore, the cross-section, or in the case of a circular cross-section, the inner diameter, must be determined as a calibration factor or known beforehand in order to calculate the volumetric flow rate.

[0008] Such ultrasonic flow measuring devices are used, among other things, to measure water flows in supply lines in building installations.

[0009] In building technology, monitoring and optimizing heating systems requires measuring the energy transport through the heating pipes, i.e., the amount of energy transported and consumed in the building. By comparing the amount of energy transported in the flow and return lines of the heating system, the energy consumed in the building can be precisely determined. Ultrasonic flow meters of the type described can be used for this purpose. By additionally measuring the temperature of the heat transfer fluid, typically the water flowing in the heating pipe, for example, using a temperature sensor attached to the heating pipe, the amount of energy transported can be directly derived from the measured flow rate. This calculation incorporates the (known) heat capacity of the heat transfer fluid.

[0010] The ultrasonic transducers in flow measuring devices typically exhibit a directional transmission and reception characteristic. The main direction of the directional characteristic is the direction of the transducer's highest ultrasonic intensity. This main direction is crucial for effective sound coupling and dissipation, as well as for the accuracy of the ultrasonic flow measurement. It is known to align the main directions of the ultrasonic transducers at an oblique angle to the pipe axis and to each other in a symmetrical V-shape. The ultrasonic transducers are arranged on the same side of the pipe, and the emitted ultrasonic signal is reflected along a corresponding V-shaped path on the opposite pipe wall. The ultrasonic signal traverses the pipe cross-section with a component of the ultrasonic propagation that runs parallel (or antiparallel) to the flow direction. This is taken into account when determining the transit-time difference, or...The flow velocity is utilized according to the principle described above. The V-shape is therefore symmetrical with respect to a plane oriented perpendicular to the pipe axis. This arrangement allows for easy installation and is also suitable for smaller pipe diameters. Correct alignment of the ultrasonic transducers relative to each other, adapted to the pipe geometry (especially the inner pipe diameter), is crucial for precise and reliable measurement. Only in this way can it be ensured that the ultrasonic signal is transmitted and received in the main direction of the ultrasonic transducers.

[0011] Although installing ultrasonic flow meters on pipes is generally straightforward thanks to existing clamp-on solutions, the problem is that the exact pipe geometry (especially the inner diameter) is often unknown and, in closed pipe systems, cannot be easily determined from the outside. When retrofitting heating systems with flow meters, installation is frequently carried out by untrained personnel for cost reasons, who are unable to perform the complex calibration and adjustment procedure. Consequently, the measuring devices are often not calibrated correctly. Without correct calibration, however, flow measurement is unreliable. The measurement of the flow velocity is inaccurate. The energy quantities derived from the measured flow velocities exhibit systematic errors.

[0012] Bailleu (“Ultrasonic Transducer Positioning System for Clamp-on Flowmeter Applications”, 2016 IEEE Sensors Applications Symposium (SAS), 2016, ieeexplore.ieee.org) describes a non-standard flowmeter in which the spacing of the ultrasonic transducers can be adjusted by sliding them along the pipe using a motorized spindle to automatically adapt to the pipe geometry. Two additional sensors are also provided: one to measure the pipe's outer diameter and the other to determine its wall thickness. The known device has the disadvantage that, in practice, it is almost impossible to ensure that the ultrasonic transducers remain acoustically coupled to the pipe during movement, as the pipe surface is often rough and uneven, and any existing coupling medium is scraped off during this process.Another disadvantage is that, in addition to the two ultrasonic transducers, further sensor systems are required, namely at least a precise displacement measuring device and an acoustic thickness gauge to determine the wall thickness of the pipe. This makes the known device unsuitable as a mass-produced product due to the manufacturing effort and costs.

[0013] DE 10 2006 000 693 A1 discloses a clamp-on flow meter with motor-adjustable ultrasonic transducers, in which the beam angle can be automatically adjusted depending on the received signal strength. Calibration is thus purely empirical: the angle is varied until a signal maximum is reached or determined. However, this approach has technical weaknesses. Signal strength alone does not provide reliable information about the actual geometry of the pipe. In particular, with unknown wall thickness, varying material properties, or unknown diameter, the setting determined in this way can be erroneous or unstable. Precise and reproducible calibration is not guaranteed on this basis.Against this background, the object of the invention is to provide an improved method for calibrating an ultrasonic flow meter, by which the ultrasonic flow meter can be installed on a pipe with minimal effort and at low cost, even by untrained personnel, without impairing the accuracy of the measurement.

[0014] The invention solves this problem by means of a method for calibrating an ultrasonic flow measuring device of the type mentioned above, by carrying out the following steps:

[0015] Determination of the propagation speed of an ultrasonic signal propagating as a surface wave through the pipe wall;

[0016] Determining the wall thickness of the pipe by measuring the transit time of an ultrasonic signal through the pipe wall;

[0017] Determination of the pipe inner diameter by derivation from the value of the adjusted angle and the distance of the ultrasonic transducers, adjustment of the angle to the determined pipe geometry by means of at least one motorized actuator setting the angle and an electronic calibration device cooperating with the actuator.

[0018] The propagation of the ultrasonic signal in the pipe wall affects the transit-time measurement, as part of the ultrasonic signal's propagation path passes through the pipe wall. The parameters of propagation speed through the pipe material, pipe wall thickness, and pipe inner diameter are therefore relevant for correctly deriving the flow velocity and volumetric flow rate from the measured ultrasonic signals and transit times. These parameters can be automatically determined using the ultrasonic flow meter described above and below. This allows the device to be fully self-calibrating. The propagation speed and the wall thickness of the ultrasonic signal (speed of sound) in the pipe wall depend on the pipe material. This is often unknown when installing the measuring device.To determine the propagation speed of the ultrasound signal, the angle can be adjusted so that an ultrasound signal emitted by one of the transducers propagates as a surface wave along the pipe wall and is received by the other transducer. The propagation speed is then derived from the travel time of the ultrasound signal from one transducer to the other and from the distance between the transducers. The material of the pipe can then be deduced from the propagation speed.

[0019] To determine the pipe wall thickness, an ultrasonic signal can be emitted from one of the two ultrasonic transducers in a direction perpendicular to the pipe axis, and the ultrasonic signal reflected from the inner surface of the pipe can be detected. The pipe wall thickness is then derived from the transit time of the ultrasonic signal, i.e., the measured duration of the time interval between emission and detection, and from the propagation speed of the ultrasonic signal in the pipe material. This corresponds to the standard method for determining wall thickness using ultrasound.

[0020] Alternatively, to determine the wall thickness of the pipe using an ultrasonic transducer, an ultrasonic signal can be emitted at an angle such that the ultrasonic signal propagates under total internal reflection between the outer and inner surfaces of the pipe wall, whereby the wall thickness of the pipe is derived from the transit time of the ultrasonic signal, i.e., from the measured duration of the time interval between emission by one ultrasonic transducer and detection by the other ultrasonic transducer, from the value of the angle, and from the propagation speed of the ultrasonic signal in the material of the pipe.

[0021] The invention further proposes an ultrasonic flow measuring device configured to carry out the methods according to the invention. For this purpose, the calibration device of the ultrasonic flow measuring device according to the invention is designed to execute the methods according to the invention, e.g., by appropriate programming.

[0022] The actuator adjusts the angle at which the main directions of the ultrasonic transducers are aligned relative to each other. The actuator is controlled by the electronic, preferably program-controlled, calibration unit to automatically set the angle appropriate for the determined pipe geometry and the specific measurement task. During installation, only the measuring device needs to be attached / clamped to the pipe and the calibration process started. The calibration unit then automatically sets the correct angle for the respective pipe. This ensures that the measured transit times, flow velocities, and energy quantities are determined accurately. The personnel involved in the installation do not need to worry about the correct setting, i.e., calibration.

[0023] In the simplest case, the calibration device then adjusts the angle until an ultrasonic signal emitted by one transducer is received by the other transducer at maximum signal strength. Due to the directional characteristics of the transducers, the correct adaptation of the V-shape to the pipe geometry is achieved when the ultrasonic signal is received at maximum signal strength. The calibration device thus achieves the correct setting through a simple control mechanism, where the received signal strength is the controlled variable and the angle is the manipulated variable.

[0024] In one possible embodiment, each ultrasonic transducer is associated with a coupling body designed for ultrasound coupling into the pipe. The respective transducer is connected to this coupling body via a swivel joint, with the actuator adjusting the angle by synchronously rotating the ultrasonic transducers in opposite directions around the swivel joint's axes of rotation. The coupling body, ideally made of a material that attenuates the ultrasound signal as little as possible, provides a mechanically simple and reliable solution for variable angle adjustment via the swivel joint. The swivel joints can, for example, each have a cylindrical sliding bearing whose joint gap is filled with an ultrasound-transmitting coupling medium, in particular a coupling fluid. A coupling body with a cylindrical sliding bearing can consist of only two parts, which are positively locked together by the cylindrical sliding bearing.For ultrasound transmission between the parts, a coupling fluid can very easily be introduced into the joint space of the swivel joint.

[0025] In one possible configuration, the actuator is a rotary drive, e.g. a stepper motor with gearbox, which rotates the ultrasonic transducers synchronously around the axes of rotation of the rotary joints in opposite directions.

[0026] Alternatively, the actuator comprises a motor and a spindle driven by the motor to convert the spindle's rotation into a linear motion, which in turn, via leverage, causes the ultrasonic transducers to rotate in the opposite direction (synchronously) around their axes. To achieve this synchronous, counter-rotating motion, the spindle can have two threaded sections with different pitches and / or numbers of threads. One ultrasonic transducer is coupled to the motor, and the other to a nut running on one of the threaded sections. The nut running on the other threaded section is stationary, i.e., coupled to a housing connected to the pipe or to a support of the measuring device.It is also conceivable that the spindle has a first section with a right-hand thread, associated with one ultrasonic transducer, and a second section with a left-hand thread, associated with the other ultrasonic transducer, in order to achieve an equal, opposite adjustment of the angle. It is essential that the actuator is designed so that a symmetrical V-shape is always maintained when the angle is adjusted.

[0027] In another possible embodiment, the ultrasonic flow meter incorporates a temperature sensor that detects the temperature at the outer surface of the pipe. This allows, as explained above, the determination of the amount of energy transported by the heat transfer fluid flowing through the pipe. In another possible embodiment, an electronic control and evaluation unit, connected to the ultrasonic transducers and, if applicable, the temperature sensor, is integrated into the ultrasonic flow meter. This unit controls the ultrasonic transducers, receives measurement signals from them, and derives flow meter readings. The control and evaluation unit includes an interface for the transmission of these flow meter readings, particularly wirelessly. This integrates all components required for flow measurement. The device simply needs to be clamped onto a pipe.It then automatically calibrates itself and transmits the flow rate measurements (and / or temperature and / or energy values) derived from the ultrasonic signals for further processing and analysis of the data, e.g., via a data network, preferably wirelessly (via radio), according to a common transmission standard, e.g., to a building automation server. The calibration unit can be integrated with the control and evaluation unit as an electronic unit of the ultrasonic flow meter. In particular, it can be a program-controlled unit of common, standardized design in which the functions of the control and evaluation unit and the calibration unit are implemented by software.

[0028] Exemplary embodiments of the invention are explained in more detail below with reference to the figures. The figures show:

[0029] Fig. 1 a schematic view of a

[0030] Ultrasonic flow meter;

[0031] Fig. 2 a schematic view of a

[0032] Ultrasound transducer with coupling body and swivel joint;

[0033] Fig. 3 a schematic view of a

[0034] Actuator with motor and spindle;

[0035] Fig. 4 is a schematic illustration of the

[0036] Determination of the propagation speed of an ultrasound signal in the material of a pipe;

[0037] Fig. 5 is a schematic illustration of the

[0038] Determining the wall thickness of a pipe;

[0039] Fig. 6 is a schematic illustration of the

[0040] Determining the pipe's inner diameter.

[0041] In the following figure description, the same reference symbols and terms are used for the same elements.

[0042] Fig. 1 schematically shows a top view of an ultrasonic flow measuring device according to the invention, arranged on a pipe 1 and calibrated using the inventive method. The device comprises two ultrasonic transducers 2, 3 spaced apart from each other in the longitudinal direction of the pipe 1, i.e., in the flow direction of a fluid flowing in the pipe 1. These transducers have a directional characteristic, with each having a transmission and reception characteristic aligned along a principal direction. The ultrasonic transducers 2, 3 (and thus their principal directions) are aligned at an angle to the pipe axis and to each other in a symmetrical V-shape, as can be seen in Fig. 1. The ultrasonic transducers 2, 3 are arranged on the same side of the pipe 1, and the emitted ultrasonic signal is reflected along a corresponding V-shaped path, indicated at 4, at the opposite pipe wall.Correct alignment of the ultrasonic transducers 2 and 3 relative to each other, adapted to the diameter of the pipe 1, is crucial for precise and reliable flow measurement. A motorized actuator 5 is provided for setting the correct alignment, i.e., the angle. An electronic calibration unit 6 controls the actuator 5 to automatically adjust the angle to the pipe diameter. For this purpose, the calibration unit 6 is connected not only to the actuator but also to the ultrasonic transducers 2 and 3. The calibration unit 6 is programmed to adjust the angle until an ultrasonic signal emitted by one ultrasonic transducer 2 is received by the other ultrasonic transducer 3 with maximum signal strength. Due to the directional characteristics of the ultrasonic transducers 2 and 3, the correct adaptation of the V-shape to the pipe geometry is then achieved.In this configuration, the tip of the V-shape lies on the inner surface of the opposite pipe wall, while the reflected ultrasonic signal falls precisely onto the receiving ultrasonic transducer 3, in the direction of its maximum sensitivity.

[0043] As shown in more detail in Fig. 2, each ultrasonic transducer 2, 3 is associated with a coupling element 7, 8 for coupling ultrasound into the tube 1, to which the respective ultrasonic transducer 2, 3 is connected via a rotary joint 9, 10. The actuator 5 sets the angle between the principal axes of the two ultrasonic transducers 2, 3 by synchronously rotating the ultrasonic transducers 2, 3 in opposite directions about the axes of rotation of the rotary joints 9, 10. The rotary joints 9, 10 each have a cylindrical sliding bearing, the joint gap of which is filled with an ultrasound-transmitting coupling medium, e.g., a gel.

[0044] As shown in Fig. 3, the actuator 5 comprises an electric motor 11 and a spindle 12 driven by the motor to convert a rotation of the spindle 12 into a linear motion. This linear motion, via leverage, causes the ultrasonic transducers 2, 3 to rotate in the opposite direction (synchronously) about their axes of rotation. The rotational movements of the two ultrasonic transducers 2, 3 must be synchronized such that, as can be seen in Fig. 3, the angles a, a' that the principal axes 13, 14 enclose with a direction 15 perpendicular to the tube axis are always equal (a = a'), i.e., the symmetrical V-shape is maintained. For this purpose, the spindle 12 has two threaded sections 16, 17 with different pitches. The ultrasonic transducer 2 is coupled to the motor 11, i.e., the motor moves in the direction parallel to the spindle 12 when the angle is set. The other ultrasonic transducer 3 is coupled to a nut 18 running on the threaded section 16.A nut 19 running on the other threaded section is stationary. This is, for example, coupled to a (not shown) housing of the ultrasonic flow measuring device.

[0045] Fig. 4 illustrates the procedure for determining the propagation speed (speed of sound) of the ultrasonic signal in the pipe wall material. The angle of the ultrasonic transducers 2 and 3 is set to a value βk such that an ultrasonic signal emitted by one transducer 2 propagates as a surface wave (indicated at 20) along the pipe wall and is received by the other transducer 3. The propagation speed is then derived from the travel time of the ultrasonic signal 20 from one transducer 2 to the other transducer 3 and from the known distance between the transducers 2 and 3. The condition for the generation of the surface wave is given by βk = arcsin(Ck / a). Here, Ck and ci are the speeds of sound in the material of the coupling body 7 and in the material of the pipe wall, respectively, the latter of which is initially unknown.Therefore, using the calibration device 6, an angle can first be set that fulfills the above condition for the material copper (or another material). The angle is then varied until the ultrasonic signal received by the ultrasonic transducer 3 is at its maximum. Based on the angle βk then set and the speed of sound ci determined from the transit time at this angle, it can be checked against the above condition whether the result is consistent and whether the desired surface wave has actually been generated. If this is not the case, the variation of the angle is continued until the correct value of the speed of sound is found.

[0046] Fig. 5 illustrates a possible procedure for determining the wall thickness of pipe 1. An ultrasonic signal is emitted by the ultrasonic transducer 2 at an angle β such that the ultrasonic signal propagates between the outer surface 21 and the inner surface 22 of the pipe wall under multiple total internal reflections (indicated at 23). The wall thickness of pipe 1 is then derived from the measured transit time of the ultrasonic signal, the value of the angle β, and the previously determined propagation velocity ci of the ultrasonic signal in the material of pipe 1. Suitable formulas for this purpose are known. Due to the signal propagation pattern with multiple reflections, the transit time depends characteristically on the wall thickness of pipe 1. In Fig. 5, each ultrasonic transducer 2, 3 is associated with an acoustic sump 24, 25, which attenuates any portion of the ultrasonic wave that is not totally reflected, i.e.,The light emanating from the outer surface 21 is directly detected by the ultrasonic transducer 3. This component would distort the time-of-flight measurement. In this calibration step, to generate propagation with total internal reflection, an angle β of, for example, 70° can initially be used. The angle is then varied until the ultrasonic signal received by the ultrasonic transducer 3 is maximized.

[0047] Figure 6 illustrates the procedure for adjusting the angle to match the inner diameter 26 of the tube 1. The path 27, 27' of the ultrasonic propagation from the emitting ultrasonic transducer 2 to the receiving ultrasonic transducer 3 is shown for two different angle settings. With the path 27', the angle is set too shallow. This angle would correspond to a smaller inner diameter 26'. The steeper angle, on the other hand, matches the actual inner diameter 26 of the tube 1. At this angle, the apex of the V-shaped path 27 of the directed ultrasonic wave lies on the inner surface 22 of the opposite tube wall, and the reflected ultrasonic signal falls precisely on the receiving ultrasonic transducer 3. With this angle setting, the signal strength of the ultrasonic signal received by the ultrasonic transducer 3 is at its maximum. As shown in Figure 6, the angle 27 is 27'.As can be seen in Figure 6, refraction of the ultrasonic wave occurs at the transitions between coupling bodies 7, 8 and the pipe wall on the one hand, and between the pipe wall and the fluid flowing in the pipe on the other. This affects the length of the propagation path. This must be taken into account when deriving the flow velocity from the measured transit time. All the necessary parameters for this (sound velocities in the different media, wall thickness of pipe 1) are known after calibration. The inner diameter 26 of the pipe can also be directly derived from the parameters available after calibration, which is a prerequisite for determining, for example, the volumetric flow rate.

[0048] - Patent claims -

Claims

Patent claims 1. Method for calibrating an ultrasonic flow measuring device coupled to a pipe (1) for measuring a flow velocity and / or a volume flow rate of a fluid in a pipe (1) with two spaced-apart ultrasonic transducers (2, 3) each having a transmission and reception characteristic oriented along a principal direction, wherein the principal directions of the ultrasonic transducers (2, 3) are aligned at an angle to each other in a symmetrical V-shape, comprising the following method steps: Determination of the propagation speed of an ultrasonic signal propagating as a surface wave through the pipe wall; Determining the wall thickness of the pipe by measuring the transit time of an ultrasonic signal through the pipe wall; Determination of the pipe inner diameter by derivation from the value of the adapted angle and the distance of the ultrasonic transducers, adjustment of the angle to the determined pipe geometry by means of at least one motorized actuator (5) that sets the angle and an electronic calibration device (6) that interacts with the actuator (5).

2. Method according to claim 1, wherein each ultrasonic transducer (2, 3) is associated with a coupling body (7, 8) provided for ultrasonic coupling into the tube (1), with which the respective ultrasonic transducer (2, 3) is connected via a rotary joint (9, 10), wherein the actuator (5) adjusts the angle by synchronous, opposite rotation of the ultrasonic transducers (2, 3) about the axes of rotation of the rotary joints (9, 10).

3. Method according to claim 2, wherein the rotary joints (9, 10) each have a cylindrical sliding bearing, the joint gap of which is filled with an ultrasound-transmitting coupling medium, in particular a coupling fluid.

4. Method according to claim 2 or 3, wherein the actuator (5) drives a spindle (12) by means of a motor (11), a linear movement is generated by rotating the spindle (12) and this linear movement causes a counter-clockwise rotation of the ultrasonic transducers (2, 3) about the respective axes of rotation by means of a lever action.

5. Method according to claim 4, wherein the spindle (12) has two thread sections (16, 17) with different pitch and / or number of threads.

6. Method according to claim 4, wherein the spindle (12) has a first section with a right-hand thread and a second section with a left-hand thread.

7. Method according to any one of claims 1 to 6, wherein the calibration device (6) for automatically adjusting the angle to the pipe geometry adjusts the angle until an ultrasonic signal emitted by one ultrasonic transducer (2) is received by the other ultrasonic transducer (3) with maximum signal strength.

8. Method according to any one of claims 1 to 7, wherein the temperature on an outer surface of the tube (1) is detected by means of a temperature sensor.

9. Method according to any one of claims 1 to 8, wherein the ultrasonic flow measuring device is attached to the pipe (1) by means of a fastening device, thereby establishing an ultrasonic transmitting connection between the ultrasonic transducers and the pipe wall.

10. Method according to any one of claims 1 to 9, wherein the ultrasonic transducers (2, 3) and optionally the temperature sensor are controlled and read out by a connected electronic control and evaluation unit, which controls the ultrasonic transducers, receives measurement signals from the ultrasonic transducers and derives flow measurement values ​​from them, and transmits the flow measurement values ​​via an interface, in particular wirelessly.

11. Method according to one of the preceding claims, wherein, to determine the propagation speed of the ultrasonic signal, the angle is adjusted such that an ultrasonic signal emitted by one of the ultrasonic transducers (2) is propagated as a surface wave along the pipe wall and is received by the other ultrasonic transducer (3), wherein the propagation speed is derived from the transit time of the ultrasonic signal from one to the other ultrasonic transducer (2, 3) and from the distance between the ultrasonic transducers (2, 3).

12. Method according to one of the preceding claims, wherein, to determine the wall thickness of the pipe (1 ), an ultrasonic signal is emitted in a direction perpendicular to the pipe axis by means of one of the two ultrasonic transducers (2, 3) and an ultrasonic signal reflected at the inner surface (22) of the pipe is detected, wherein the wall thickness of the pipe (1 ) is derived from the transit time of the ultrasonic signal, i.e. from the detected duration of the time interval between emission and detection and from the propagation speed of the ultrasonic signal in the material of the pipe (1 ).

13. Method according to one of the preceding claims, wherein, to determine the wall thickness of the pipe (1) by means of an ultrasonic transducer (2), an ultrasonic signal is emitted at an angle such that the ultrasonic signal propagates under total internal reflection between the outer surface (21) and the inner surface (22) of the pipe wall, wherein the wall thickness of the pipe (1) is determined from the transit time of the ultrasonic signal, i.e., from the detected duration of the time interval between emission by means of one ultrasonic transducer (2) and detection by means of the other ultrasonic transducer. (3) is derived from the value of the angle and from the propagation speed of the ultrasonic signal in the material of the tube (1).

14. Ultrasonic flow measuring device for measuring a flow velocity and / or a volume flow rate of a fluid in a pipe (1), comprising two spaced-apart ultrasonic transducers (2, 3), each having a transmission and reception characteristic oriented along a principal direction, wherein the principal directions of the ultrasonic transducers (2, 3) are aligned at an angle to each other in a symmetrical V-shape, and comprising at least one angle-adjusting motor actuator (5) and an electronic calibration device (6) cooperating with the actuator (5), provided and configured to automatically adjust the angle to a pipe geometry by carrying out the method according to one of claims 1 to 13. - Summary -

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