Method for determining the flow rate of a fluid medium through a pipeline and a measuring device

Abstract

The invention relates to a method for determining the flow rate of a fluid medium through a pipeline (10) using a measuring device (12) comprising a first and a second transducer (14a, 14b) for generating and receiving ultrasonic waves, wherein the two transducers (14a, 14b) are arranged in a sensor housing (16) at a predetermined measuring distance (a) from each other, with the following steps for determining a pipe wall thickness (s) for a flow rate calculation: Aligning the two transducers (14a, 14b) in a measuring state along an axial direction (AX) of the pipeline (10) onto a pipe wall (18) of the pipeline (10) in order to determine a flow velocity of the fluid medium by means of an ultrasonic transit-time measurement through the pipeline (10). Determining the pipe wall thickness (s) of the pipeline (10) using a Rayleigh-Lamb wave equation for the pipeline (10) in order to calculate a volume flow rate through a pipe cross-section (A).The invention further relates to a measuring device for determining the flow rate of a fluid medium.

Description

[0001] The invention relates to a method for determining the flow rate of a fluid medium through a pipeline. Furthermore, the invention relates to a measuring device for determining the flow rate of a fluid medium through a pipeline.

[0002] Flow measurement methods and ultrasonic flow measuring devices, or ultrasonic flow meters (USD or UDM for short), are already known from the prior art. Such devices measure the flow velocity of a flowing medium, in particular a gas or liquid, in a pipeline using ultrasonic waves. For this purpose, the flow measuring devices have two axially spaced-apart measuring transducers, each of which emits an ultrasonic measuring signal and receives an ultrasonic measuring signal from the other transducer. These measuring signals are coupled into the pipeline and transmitted through the pipe wall into the medium. After passing through a measuring section within the pipeline, the measuring signals are in turn coupled out from the medium via the pipe wall to the receiving measuring transducer.The flow velocity of the medium can be determined based on the transit time difference of the ultrasonic measurement signals traveling with or against a flow direction. Such ultrasonic flow measuring devices are becoming increasingly popular for flow measurements because they can be used over a wide measuring range and can also be easily clamped onto the outside of the pipeline without having to penetrate the pipeline, interrupt the pipeline, or influence or disrupt the flow cross-section within the pipeline.

[0003] To calculate the flow rate from the flow velocity of the fluid medium, the inner diameter of the pipeline must be known. However, the geometry of the pipeline, in particular the inner diameter or the wall thickness of the pipe wall, cannot be determined in many cases or cannot be determined accurately in the area of ​​the measuring device. In particular, it may happen that the inner diameter of the pipeline is not accessible from the outside. In most cases, an operator does not have geometric information and is therefore unable to obtain an accurate flow measurement without manually calibrating the device against the measured values ​​of a reference flow measuring device. However, such a calibration process is very time-consuming. In other words, with state-of-the-art flow measuring devices, the operator must manually calibrate and enter information about the pipe wall thickness and the outer diameter.This step is very time-consuming and prevents simple and versatile handling.

[0004] An exemplary flow measurement method is known from US 11,215,489 B2. In this method, two measuring transducers are arranged on a pipe wall along an axial direction, with both measuring transducers emitting Lamb waves in order to determine the flow velocity of the fluid from the transit time difference between the two Lamb waves. To calibrate the measuring device, the frequency of the Lamb wave is varied until the signal amplitude is maximum and the Lamb wave propagates with a single wave mode. A calculation of the wall thickness of the pipe is not taken into account. This method of measuring flow using Lamb waves has the disadvantage that complex measuring electronics and measuring transducers must be used to vary the frequencies, and the frequency selection must at least be monitored by an operator in order to reliably detect a maximum signal amplitude.Furthermore, the geometry of the pipeline can only be determined using a large number of separate measurements, whereby an ultrasonic wave must be transmitted through the fluid in the axial and radial directions of the pipeline. In particular, the selection of the frequency already depends on the fluid present in the pipe, and measurement errors can occur if the fluid within the pipe changes.

[0005] US 6,575,043 B1 also describes a method for measuring flow in a pipeline, whereby two transducers can be arranged on a pipe wall at a variable distance from each other. Lamb waves are coupled into the pipe wall, and the attenuation of the Lamb waves is measured over a specified distance in order to determine different fluid phases within the pipeline.

[0006] The scientific article by MCAUGHEY, Kevin L., et al., entitled “Ultrasonic thickness measurements of sub-millimetre thickness sheets”, E-journal of nondestructive testing & ultrasonics, 2012, discloses a thickness measurement of very thin metal plates using Lamb waves.

[0007] The object of the invention is to propose a method for flow measurement which, while avoiding the problems known from the prior art, reduces user interaction with a measuring device and susceptibility to errors in the measuring method and enables more precise flow measurement.

[0008] Furthermore, the object is to provide a device for carrying out the method.

[0009] The problem is solved with regard to the method by the features of independent claims 1 and 2 and with regard to the device by the features of claim 7.

[0010] Advantageous embodiments of the invention are specified in the subclaims.

[0011] According to a first aspect of the invention, a method for determining a flow of a fluid medium through a pipeline by means of a measuring device is claimed, wherein the measuring device has a first and a second measuring transducer for generating and receiving ultrasonic waves, wherein the two measuring transducers are arranged in a sensor housing at a predetermined measuring distance from one another, wherein the pipeline is formed from a metallic material. The method comprises the following steps for calculating the flow. The sequence represents a preferred sequence and can preferably be modified as desired. In a preferred first step, the two measuring transducers are aligned along an axial direction of the pipeline onto a pipe wall of the pipeline in order to determine a flow velocity of the fluid medium by means of an ultrasonic transit time measurement.In a preferred second step, ultrasonic waves with a predetermined measuring frequency are generated by means of the first measuring transducer along the axial direction of the pipeline in such a way that a Lamb wave with at least one transverse wave mode and at least one longitudinal wave mode is coupled into the pipe wall, wherein the measuring frequency is predetermined based on the expected propagation velocities of the wave modes of the Lamb wave within the metallic pipeline. In a preferred third step, the Lamb wave traveling through the pipe wall is received and coupled out by means of the second measuring transducer, wherein the propagation time of the Lamb wave is measured. In a preferred fourth step, the transverse velocity and the longitudinal velocity are determined from the propagation time of the Lamb wave over the measuring distance in the axial direction.Preferably, before or after determining the pipe wall thickness, an ultrasonic transit time measurement is performed using bulk ultrasonic waves with a predetermined radiation angle, wherein the bulk ultrasonic waves are coupled into the fluid medium within the pipeline by means of the measuring transducers. In a preferred fifth step, the wall thickness of the pipeline is determined using a Rayleigh-Lamb wave equation for the pipeline. In a preferred sixth step, a volume flow of the fluid medium through a pipe cross-section is calculated from the measured pipe wall thickness, a predetermined outer diameter of the pipeline, and a measured flow velocity.

[0012] A flow velocity measurement using ultrasonic transit time measurement, in particular a so-called time-of-flight measurement, can be performed before or preferably after determining the pipe wall thickness. For the ultrasonic transit time measurement, a volume ultrasonic wave, in particular a longitudinal wave, is preferably used. This wave is coupled into the fluid medium, passes through the fluid medium, and is reflected by the pipe wall. Preferably, an ultrasonic wave is emitted along a flow direction and against a flow direction of the fluid medium in order to determine the flow velocity of the fluid medium from the difference in the measured transit times of the counter-propagating ultrasonic waves.

[0013] The volume flow is preferably calculated from the following equation: Q=v*A with a volume flow Q, a flow velocity v and the pipe cross-section A, where the pipe cross-section is calculated as follows: A=(πd2) / 4 with an inner diameter d of the pipeline, which is calculated from the outer diameter D of the pipeline and the pipe wall thickness s: d=D−2*s.

[0014] A volume ultrasonic wave is used to determine the flow velocity, particularly since the propagation of the ultrasonic wave within the fluid medium is not frequency-dependent and the propagation time can be calculated more easily. Preferably, a radiation angle for the volume ultrasonic wave depends on an angled arrangement of the transducers relative to the axial direction of the pipeline, with the arrangement and radiation angle preferably being known in advance and preferably fixed by the arrangement of the transducers within the sensor housing. In contrast, the radiation angle for Lamb waves is frequency-dependent, which is why complex user input for frequency selection would be required to determine the flow velocity.

[0015] According to a second aspect, the invention relates to a method for determining a flow of a fluid medium through a pipeline by means of a measuring device, wherein the measuring device has a first and a second measuring transducer for generating and receiving ultrasonic waves, wherein the two measuring transducers are arranged in a sensor housing at a predetermined measuring distance from one another, wherein the pipeline is formed from a metallic material. The method comprises the following steps for calculating the flow. The sequence represents a preferred sequence and can preferably be modified as desired. These are preferably steps for calibrating the measuring device, wherein the geometry of the pipeline is determined.In a preferred first step, the two measuring transducers are aligned along an axial direction of the pipeline onto a pipe wall in order to determine a flow velocity of the fluid medium through the pipeline using an ultrasonic time-of-flight measurement. In a preferred second step, ultrasonic waves with a predetermined measuring frequency are generated by the first measuring transducer along a circumferential direction of the pipeline in such a way that a Lamb wave with at least one transverse wave mode and at least one longitudinal wave mode is coupled into the pipe wall, wherein the measuring frequency is predetermined based on the expected propagation velocities of the wave modes of the Lamb wave within the metallic pipeline. In a preferred third step, the Lamb wave propagating through the pipe wall is received and coupled out by the first measuring transducer, wherein the time-of-flight of the Lamb wave is measured.In a preferred fourth step, the transverse velocity and the longitudinal velocity are determined from the travel time of the Lamb wave over a circumference of the pipeline with a predetermined outer diameter. Preferably before or after determining the pipe wall thickness, an ultrasonic travel time measurement is carried out using volume ultrasonic waves with a predetermined radiation angle, wherein the volume ultrasonic waves are coupled into the fluid medium within the pipeline by means of the measuring transducers. In a preferred fifth step, the wall thickness of the pipeline is determined using a Rayleigh-Lamb wave equation for the pipeline. In a preferred sixth step, a volume flow of the fluid medium through a pipe cross-section is calculated from the measured pipe wall thickness, the predetermined outer diameter of the pipeline, and a measured flow velocity.

[0016] In other words, according to the first aspect of the invention, a Lamb wave is generated along the axial direction, and according to the second aspect of the invention, a Lamb wave is generated along the circumferential direction within the pipe wall to determine the pipe wall thickness. It may also be preferable for the method of the first aspect to be modified in accordance with the second aspect of the invention such that a Lamb wave is emitted along the axial direction and the circumferential direction, and the propagation time is preferably determined by the measuring distance and the circumference of the pipeline.

[0017] Preferably, the measured transverse and longitudinal velocities specify the material parameters for the pipeline. A single measurement frequency is preferably used as the predetermined measurement frequency, with the pipe wall thickness remaining as an unknown parameter of the Rayleigh-Lamb wave equation for the pipeline and can be evaluated using the Rayleigh-Lamb wave equation itself.

[0018] The Lamb wave is preferably a complex oscillation wave that arises from the interaction between transverse waves and longitudinal waves and propagates parallel to the pipe wall. A transverse wave is also preferably understood to be a shear wave within the pipe wall. The Lamb wave more preferably propagates across the entire wall thickness of the pipe. Transverse waves preferably oscillate perpendicular to their propagation direction, and longitudinal waves preferably oscillate along their propagation direction, with the propagation direction preferably aligned parallel to the axial direction of the pipe. The Lamb waves within the pipe wall exhibit a dispersive property that depends on the frequency of the Lamb wave and the pipe wall thickness.Further preferably, the propagation of the generation of Lamb wave modes in the pipe wall depends on a relationship between the wall thickness and the wavelength used. Advantageously, for a given measurement frequency or wavelength, this dependence on the number of modes can also be exploited to determine the wall thickness by comparing it with the Rayleigh-Lamb equation.

[0019] Further preferably, the two transducers for generating and / or receiving the transverse and longitudinal wave modes of the Lamb wave are arranged at an angle of incidence relative to the axial direction.

[0020] Furthermore, it may be preferred that the measuring transducer is designed to oscillate in a direction transverse and longitudinal to the axial direction.

[0021] Particularly preferably, the measuring transducers are designed as piezoelectric measuring transducers with a polarization such that the measuring transducer generates and measures an oscillation transversely and / or longitudinally in the axial direction.

[0022] The invention, according to the first and second aspects, has recognized that the dispersive property of the Lamb wave can be exploited to determine the wall thickness of the pipeline automatically by the flow measuring device itself without manual measurement. Preferably, there is an automated measurement of the pipe parameters, which eliminates the need to manually enter information about the pipe dimensions in order to calibrate ultrasonic flow meters for accurate measurements. In particular, the dispersion of the Lamb wave can be exploited to determine the material of the pipeline, wherein the wall thickness of the pipeline can be determined by the method according to the invention by comparison with a preferably analytically calculated Rayleigh-Lamb dispersion equation. This also makes it possible to determine an inner diameter for pipelines with a known outer diameter that cannot be measured manually from the outside.In other words, the method according to the invention can provide an operator with a measuring device that reduces user interaction and improves the reliability and reproducibility of a flow measurement. Furthermore, flow measurement can be enabled for pipelines with an internal diameter that is difficult to measure. Furthermore, by measuring the pipe wall thickness directly in the flow measurement area, a local pipe cross-section can be precisely determined, which also allows for a more precise calculation of the volume flow. In particular, this enables reliable and highly accurate flow measurement with minimal operator intervention.

[0023] Using the Lamb wave to determine pipe wall thickness also has the advantage that the Lamb wave propagates within the pipe wall itself, and its propagation velocity is not influenced by the surrounding fluid. This allows the pipe wall thickness of a pipeline to be measured even when the fluid to be measured later is not yet present or a second fluid is present. This independence also increases the reliability of flow measurement.

[0024] According to a preferred embodiment of the first and second aspects, the pipe wall thickness is determined as an unknown geometric parameter of the pipeline by means of curve fitting and / or inversion algorithms from the Rayleigh-Lamb equation.

[0025] In particular, the Rayleigh-Lamb equation can be calculated in the form of velocity curves as a function of the product of a frequency and the wall thickness as a graph for different pipe materials as reference graphs for different wave modes. The wall thickness can be determined by fitting the curves to the reference graphs, preferably using the measured transverse and longitudinal propagation velocities and the predetermined measurement frequency.

[0026] Particularly preferably, an outer diameter of the pipeline is determined manually by an operator, in particular if a measurement is carried out on standardized pipes. In this case, the outer diameter is further preferably transmitted via wireless input means to an evaluation unit of the measuring device in order to determine an inner diameter of the pipeline for the flow measurement together with the measured wall thickness. This can advantageously simplify user interaction with the measuring device. Preferably, the input means are designed as a control computer with a user interface. Alternatively or additionally, it can be provided that the input means are formed in the sensor housing. Further preferably, the outer diameter is already preconfigured and the measuring device is intended for measurements on pipes with a known outer diameter.Preferably, the outer diameter is determined in the area of ​​a mounting point of the measuring device in order to be able to measure a local precise flow.

[0027] According to an alternative or additional embodiment, following a determination of the pipe wall thickness according to the first aspect by measuring the Lamb wave along the axial direction, the Lamb wave can be emitted at least partially along a circumferential direction of the pipeline, wherein the outer diameter of the pipeline is determined from a measurement of the travel time of the Lamb wave in the circumferential direction. Particularly preferably, the Lamb wave propagates several times around the pipe, wherein the outer diameter is calculated from a measurement of the arrival time of successive round trips. In particular, the previously calculated propagation velocity of the Lamb wave is used, in particular for a defined wave mode. The outer diameter D is then derived from the speed of sound c, the travel time t, and the pipe wall thickness s, preferably as follows: D=(ct) / π+s According to the invention, the pipeline is made of a metallic material, in particular steel or aluminum, wherein the measuring frequency is predetermined based on the expected propagation velocities for the pipeline.

[0028] Advantageously, the method can be adapted for metallic materials, whereby, in particular, an adjustment of the measurement frequency is not required for metallic materials. This advantageously simplifies the method, whereby an operator advantageously does not have to adjust or change the measurement frequency.

[0029] Furthermore, the invention relates to a method according to a third aspect for determining a flow of a fluid medium through a pipeline by means of a measuring device, comprising a first and a second measuring transducer for generating and receiving ultrasonic waves, wherein the two measuring transducers are arranged in a sensor housing at a predetermined measuring distance from one another, with the following steps for calculating the flow. Here, too, the following sequence is preferred and can preferably be modified as desired. After a preferred first step, the two measuring transducers are aligned along an axial direction of the pipeline onto a pipe wall of the pipeline in order to determine a flow velocity of the fluid medium by means of an ultrasonic transit time measurement through the pipeline.In a preferred second step, an ultrasonic wave with a predetermined measurement frequency is generated and coupled into the pipe wall by means of the first measuring transducer along a radial direction of the pipeline. After a preferred third step, the ultrasonic wave is coupled out and received by means of the first measuring transducer, wherein the propagation time and the reflected signal strength of the coupled out ultrasonic wave are measured. In particular, this is an echo measurement method, wherein an interface on the inner pipe wall reflects the coupled ultrasonic waves. In particular, the reflected energy of the reflected ultrasonic wave at the inner pipe wall can be determined.

[0030] Preferably, a reflection coefficient is determined from a ratio of an input signal strength and the reflected signal strength.

[0031] According to a preferred fourth step, an acoustic impedance of the pipe wall is determined from the measured reflected signal strength. Preferably, the acoustic impedance is determined from the measured reflection coefficient and a known acoustic impedance of the fluid medium in the pipe. In particular, a Fresnel equation is used, where the reflection coefficient R is calculated from the acoustic impedance Zr of the pipe wall and the acoustic impedance Zm of the fluid medium as follows: R=Zm−ZrZm+Zr Preferably, the acoustic impedance of the fluid medium is predetermined or known and in particular indicates the acoustic impedance of the fluid medium to be measured within the pipeline.

[0032] According to a preferred fifth step, the propagation velocity of the ultrasonic wave is determined from the acoustic impedance of the pipe wall, and the pipe wall thickness of the pipeline is calculated from the measured propagation time of the ultrasonic wave. Preferably, the pipe wall thickness can subsequently be used to determine an inner diameter of the pipeline in order to determine a flow rate of the fluid medium.

[0033] The acoustic impedance of the pipe wall depends in particular on a product of the material density and the propagation velocity. Preferably, a control unit of the measuring device has a list of acoustic impedances of commonly used reference materials, in particular for metals and / or plastics, particularly preferably for steel, copper, aluminum, and / or PVC plastic. The material of the pipe wall, its density, and propagation velocity can be derived, preferably by comparing the measured impedance with the reference impedances of the reference materials.

[0034] Additionally or alternatively, it is also conceivable for the control unit to have a list of values ​​for reflected energy and transmitted energy for various material surfaces, in particular between the pipe materials steel, copper, aluminum, and / or PVC plastic and the fluid medium, preferably water. Reference signal strengths on various materials are preferably determined or estimated using reference measurements, with a known fluid medium, particularly preferably the fluid medium to be measured, preferably being filled into the pipeline. Sound velocity information can also be derived from such a list of reference material transitions by comparing it with the measured signal strength.

[0035] The echo measurement method described above is particularly preferably used for pipelines made of plastic materials.

[0036] Furthermore, the invention also relates to a measuring device for determining a flow of a fluid medium through a pipeline, which is configured to operate the aforementioned methods, comprising two measuring transducers for generating and receiving ultrasonic waves, wherein the two measuring transducers are arranged in a sensor housing at a predetermined measuring distance from each other, wherein in a measuring state for determining the flow, the two measuring transducers are aligned along an axial direction of the pipeline and arranged on a pipe wall in order to determine a flow velocity of the fluid medium by means of an ultrasonic transit time measurement through the pipeline, wherein the pipeline is formed from a metallic material, wherein the measuring transducers are configured with a control unit to couple in and out transverse and longitudinal wave modes of a Lamb wave at a predetermined frequency at the wall,wherein the measuring device for determining a wall thickness of the pipeline has an evaluation unit, wherein wave velocities of the transverse and longitudinal wave modes can be evaluated from the different propagation times of the transverse and longitudinal wave modes by means of the evaluation unit, wherein the evaluation unit is designed to calculate a wall thickness of the pipe wall by means of a comparison of the measured transverse and longitudinal wave velocities and a Rayleigh-Lamb equation for the pipeline, wherein a volume flow of the fluid medium through a pipe cross-section can be calculated from the measured pipe wall thickness, a predetermined outer diameter of the pipeline and a measured flow velocity.

[0037] The invention is explained in more detail below using exemplary embodiments with reference to the drawings.

[0038] They show schematically: Fig. 1a Side view of a pipeline with measuring device, Fig. 1b Front view of the pipeline according to the Fig. 1a.

[0039] In the following description of the preferred embodiments, like reference numerals designate like or comparable components.

[0040] The Fig. 1a shows a pipeline 10 having a cylindrical pipe wall 18 and an interior space 13 enclosed by the pipe wall 18. The pipeline 10 has a cylindrical coordinate system with an axial direction AX, a radial direction R, and a circumferential direction U. An ultrasonic flow measuring device 12 is arranged on the outside of the pipe wall 18. The measuring device 12 has a first measuring transducer 14a and a second measuring transducer 14b, each designed as an ultrasonic transducer and spaced from one another in the axial direction AX. To determine a flow velocity of a fluid medium in the interior space 13 of the pipeline 10, ultrasonic measuring signals or ultrasonic waves are coupled into and out of the pipeline 10 by the measuring transducers 14a, 14b, which for this purpose pass through the pipe wall 18.Preferably, the transducers 14a, 14b may have a coupling element (not shown here) in order to couple the ultrasonic waves into and out of the pipe wall 18.

[0041] Furthermore, the measuring device 12 has a housing 16 which accommodates the measuring transducers 14a, 14b and also has means (not shown) for fastening the measuring device 12 to the pipeline 10, in particular clamping means.

[0042] The Fig. 1a further shows that the two transducers 14a, 14b are arranged at a predefined and fixed measuring distance a from each other. According to a first aspect of the invention, the first transducer 14a is preferably configured to couple a Lamb wave 20, schematically represented by arrows, along the axial direction AX to the pipe wall 18, wherein the Lamb wave 20 is in turn coupled out by the second transducer 14b at the pipe wall 18. A Lamb wave is thereby excited with transverse and longitudinal wave modes 22a, 22b, which have different propagation velocities and are schematically represented as arrows with different propagation angles. By evaluating the propagation times of the wave modes 22a, 22b over the measuring distance a, the propagation velocities of the transverse and longitudinal wave modes 22a, 22b can be determined, which preferably specify the material parameters for the material of the pipeline 10 and the pipe wall 18.The Lamb wave 20 is preferably generated with a predefined measurement frequency. Using the measured propagation velocities of the transverse and longitudinal wave modes, as well as the measurement frequency, the pipe wall thickness s can be determined by comparison with a Rayleigh-Lamb equation for the pipe geometry. The measuring device 12 preferably has a control unit 24 for the comparison and determination of the pipe wall thickness s. Preferably, a volume flow of a fluid medium through a pipe cross-section A can subsequently be calculated from the calculated pipe wall thickness s based on the measured pipe wall thickness s, a predetermined outer diameter D of the pipe 10, and a measured flow velocity.

[0043] Preferably, the measuring device 12 is used to couple an ultrasonic wave, in particular a longitudinal wave or volume wave, into the interior 13 and the fluid medium, wherein the flow velocity of the fluid medium is determined based on the transit time of the ultrasonic wave through the fluid medium.

[0044] Advantageously, the measurement of the volume flow does not require manual input of the pipe wall thickness s, but is performed automatically by the measuring device 12 itself. This can advantageously simplify operation of the measuring device 12 and make the flow measurement process more reliable and precise. Furthermore, flow measurement is also possible on pipelines 10 where an inner diameter d cannot be determined without destruction or is difficult to access from the outside 11.

[0045] According to a second aspect of the invention, the Lamb shaft 20, as shown in Fig.1b, preferably coupled in a circumferential direction U. The Lamb wave 20 travels through the pipe wall 18 preferably along the circumferential direction U. Based on the travel times of the transverse and longitudinal wave modes of this Lamb wave 20 and a previously known outer diameter D, the pipe wall thickness s can also be determined here by comparison with the Rayleigh-Lamb equation for the pipeline.

[0046] Alternatively or additionally, it is also conceivable that by means of the aforementioned measurement of the Lamb wave 20 along the circumferential direction U and a previously determined pipe wall thickness s by measuring the Lamb wave 20 in the axial direction AX, the outer diameter D is determined by the measured time of flight along the circumferential direction U. In other words, the first measuring transducer 14a or the second measuring transducer 14b can be arranged and configured such that a Lamb wave 20 in the circumferential direction U is coupled in and / or out at the pipe wall 18. The measuring transducer 14a thus emits a Lamb wave 20 in the circumferential direction, is switched to receive mode and can detect the circulating Lamb wave, so that the pipe wall thickness s can be determined from this by comparison with the Rayleigh-Lamb equation and / or the pipe outer diameter can be determined from the time of flight.

[0047] According to a preferred embodiment, the transducers 14a, 14b can be configured and arranged to couple and decouple an ultrasonic measurement signal for detecting an ultrasonic Doppler effect. Such a procedure can be used, for example, to detect the velocities of particles and / or air bubbles in the fluid medium.

[0048] According to an additional or alternative embodiment, the measuring transducers 14a, 14b can be configured to determine the pipe wall thickness s using an echo method. For this purpose, the first and / or the second measuring transducer 14a, 14b couples an ultrasonic wave in a radial direction R onto the pipe wall 18. The ultrasonic wave is reflected back on the inside of the pipe wall 18. The first and / or the second measuring transducer 14a, 14b decouples the ultrasonic wave again and determines the propagation time of the ultrasonic wave as well as a signal strength. The reflected signal strength depends on the acoustic impedances of the pipeline 10 and the fluid medium located in the interior 13. The impedance of the pipeline 10 can be determined from the signal strength and the previously known impedance of the fluid medium, which in turn determines the propagation speed of the ultrasonic wave within the pipe wall 18.Together with the measured propagation time and the propagation velocity, the pipe wall thickness s can then be determined. The pipe wall thickness s can preferably be determined by means of the control unit 24 of the measuring device 12, wherein the control unit 24 more preferably has a reference list of reference impedances and / or reference signal strengths for various reference materials in order to determine the propagation velocity from the measured propagation time. The reference list is preferably designed for the reference materials steel, copper, aluminum and / or PVC plastic. More preferably, the reference signal strengths are designed as reflected energy and transmitted energy between the reference materials and a known medium within the pipeline 10.

Claims

[1] Method for determining a flow of a fluid medium through a pipeline (10) by means of a measuring device (12), comprising a first and a second measuring transducer (14a, 14b) for generating and receiving ultrasonic waves, wherein the two measuring transducers (14a, 14b) are arranged in a sensor housing (16) with a predetermined measuring distance (a) from each other, wherein the pipeline (10) is formed from a metallic material, with the following steps for flow calculation: - Aligning the two measuring transducers (14a, 14b) along an axial direction (AX) of the pipeline (10) to a pipe wall (18) of the pipeline (10) in order to determine a flow velocity of the fluid medium by means of an ultrasonic transit time measurement through the pipeline (10), - generating ultrasonic waves with a predetermined measuring frequency by means of the first measuring transducer (14a) along the axial direction (AX) of the pipeline (10) such that a Lamb wave (20) with at least one transverse wave mode (22a) and at least one longitudinal wave mode (22b) is coupled into the pipe wall (18), wherein the measuring frequency is predetermined based on the expected propagation velocities of the wave modes (22a, 22b) of the Lamb wave (20) within the metallic pipeline (10), - receiving and decoupling the Lamb wave (20) passing through the pipe wall (18) by means of the second transducer (14b) and determining a transverse velocity and a longitudinal velocity of the wave modes (22a, 22b) from the measured transit time over the measuring distance (a) in the axial direction (AX), - Determining the pipe wall thickness (s) of the pipeline (10) using a Rayleigh-Lamb wave equation for the pipeline (10) - Carrying out the ultrasonic transit time measurement by means of volume ultrasonic waves with predetermined radiation angles, which are coupled into the fluid medium within the pipeline (10) by means of the measuring transducers (14a, 14b), - Precise calculation of a volume flow of the fluid medium through a pipe cross-section (A) from the measured pipe wall thickness (s), a predetermined outer diameter (D) of the pipeline (10) and a measured flow velocity. [2] Method for determining a flow of a fluid medium through a pipeline (10) by means of a measuring device (12), comprising a first and a second measuring transducer (14a, 14b) for generating and receiving ultrasonic waves, wherein the two measuring transducers (14a, 14b) are arranged in a sensor housing (16) with a predetermined measuring distance (a) from one another, wherein the pipeline (10) is formed from a metallic material, with the following steps for determining a pipe wall thickness (s) for a flow calculation: - Aligning the two measuring transducers (14a, 14b) along an axial direction (AX) of the pipeline (10) to a pipe wall (18) of the pipeline (10) in order to determine a flow velocity of the fluid medium by means of an ultrasonic transit time measurement through the pipeline (10), - generating ultrasonic waves with a predetermined measuring frequency by means of the first measuring transducer (14a) along a circumferential direction (U) of the pipeline (10) such that a Lamb wave (20) with at least one transverse wave mode (22a) and at least one longitudinal wave mode (22b) is coupled into the pipe wall (18), wherein the measuring frequency is predetermined based on the expected propagation velocities of the wave modes (22a, 22b) of the Lamb wave (20) within the metallic pipeline (10), - receiving and decoupling the Lamb wave (20) passing through the pipe wall (18) by means of the first transducer (14a) and determining a transverse velocity and a longitudinal velocity of the wave modes (22a, 22b) from the measured propagation time over a circumference of the pipe (10) with a predetermined outer diameter (D), - Determining the pipe wall thickness (s) of the pipeline (10) by means of a Rayleigh-Lamb wave equation for the pipeline (10), - Carrying out the ultrasonic transit time measurement by means of volume ultrasonic waves with predetermined radiation angles, which are coupled into the fluid medium within the pipeline (10) by means of the measuring transducers (14a, 14b), - Precise calculation of a volume flow of the fluid medium through a pipe cross-section (A) from the measured pipe wall thickness (s), the predetermined outer diameter (D) of the pipeline (10) and a measured flow velocity. [3] Method according to claim 1 or 2, characterized by that the pipe wall thickness (s) is determined as an unknown parameter using curve fitting and / or inversion algorithms from the Rayleigh-Lamb equation. [4] Method according to one of claims 1 to 3, characterized bythat an operator manually determines an outer diameter (D) of the pipeline (10) and transmits it via input means to the measuring device (12) in order to determine an inner diameter (d) of the pipeline (10) for the flow calculation. [5] Method according to one of claims 1, 3 or 4, characterized by that following a determination of the pipe wall thickness (s) by measuring the Lamb wave (20) along the axial direction (AX), the Lamb wave (20) is emitted at least partially along the circumferential direction (U) of the pipeline (10) and the outer diameter (D) of the pipeline (10) is determined from a measurement of the travel time of the Lamb wave (20). [6] Method according to one of claims 1 to 5, characterized by that the pipeline (10) is made of steel or aluminum. [7] A measuring device for determining a flow of a fluid medium through a pipeline (10), which is designed to operate a method according to one of claims 1 to 6, comprising a first and a second measuring transducer (14a, 14b) for generating and receiving ultrasonic waves, wherein the two measuring transducers (14a, 14b) are arranged in a sensor housing (16) with a predetermined measuring distance (a) from one another, wherein the two measuring transducers (14a, 14b) are aligned in a measuring state for determining the flow along an axial direction (AX) of the pipeline (10) and are arranged on a pipe wall in order to determine a flow velocity of the fluid medium by means of an ultrasonic transit time measurement through the pipeline (10), wherein the pipeline (10) is made of a metallic material, wherein the measuring transducers (14a, 14b) are arranged to couple transverse and longitudinal wave modes (22a, 22b) of a Lamb wave (20) with a predetermined frequency into and out of the pipe wall (18), wherein the measuring device (12) for determining a pipe wall thickness (s) has a control unit (24), wherein wave velocities of the transverse and longitudinal wave modes (22a,22b) can be evaluated from the different travel times of the transverse and longitudinal wave modes (22a,22b) by means of the control unit (24), wherein the control unit (24) is designed to calculate a pipe wall thickness (s) of the pipeline (10) by means of a comparison of the measured transverse and longitudinal wave velocities and a Rayleigh-Lamb equation for the pipeline (10), wherein a volume flow of the fluid medium through a pipe cross-section (A) can be calculated from the measured pipe wall thickness (s), a predetermined outer diameter (D) of the pipeline (10) and a measured flow velocity.

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