DE102022129944A1 - Method for examining a wall using Lamb waves and a measuring device therefor - Google Patents

Abstract

The invention relates to a method (100) for examining a state of a wall of an immersion sensor or a container, such as a tank, a bottle, a measuring tube or the like, which is wetted with a medium. In a first method step (101), Lamb waves of a Lamb wave mode are generated on a first section of the wall by means of a first ultrasonic transducer (11). In a second method step (102), the Lamb waves running through the wall are detected by means of the first ultrasonic transducer (11) and/or by means of at least one second ultrasonic transducer (12). In a third method step (103), based on a reference value of a local wall thickness, a reference value and a measured value are used for at least one of the following measured variables in order to determine a current local wall thickness by means of an electronic measuring/operating circuit: phase velocity and/or group velocity and/or amplitude and/or intensity of the Lamb wave mode, frequency of the Lamb wave mode, temperature of the wall. In a fourth method step (104), the current local From the wall thickness a statement can be made about the condition of the wall.

Description

The invention relates to a method for examining a condition of a wall of an immersion sensor or a container by means of Lamb waves and a measuring device for implementing the method.

The DE102015107752A1 discloses a method for determining a pipe wall resonance frequency of a pipeline in the area of a measuring point. EP2335062B1 describes a method for examining a structure such as a measuring tube, in which ultrasonic signals are radiated into a liquid medium in order to subsequently make a statement about a coating on a surface of the structure.

The disadvantage is that an examination cannot be carried out in this way if there is no medium or the measuring tube is only partially filled.

The object of the invention is therefore to propose a method and a measuring device in which a condition of a wall of the measuring device or of a container can be determined in a robust and precise manner.

The object is achieved by a method according to independent claim 1 and by a measuring device according to independent claim 7, as well as by a use of such a measuring device according to independent claim 10.

• Phasengeschwindigkeit und/oder Gruppengeschwindigkeit und/oder Amplitude und/oder Intensität der Lambwellenmode, Frequenz der Lambwellenmode, Temperatur der Wandung,
• wobei in einem vierten Verfahrensschritt aus der aktuellen lokalen Wandstärke eine Aussage zu einem Zustand der Wandung abgeleitet wird.

In a method according to the invention for examining a state of a wall of an immersion sensor or a container such as a tank, a bottle, a measuring tube or the like, which can be wetted in particular with a liquid medium, in a first method step Lamb waves of a Lamb wave mode are generated on/in a first section of the wall by means of a first ultrasonic transducer,
wherein in a second method step the Lamb waves running in the wall are detected by means of the first ultrasonic transducer and/or by means of at least one second ultrasonic transducer,
characterized in that
in a third method step, based on a reference value of a local wall thickness, a reference value and a measured value are used for at least one of the following measured variables in order to determine a current local wall thickness by means of an electronic measuring/operating circuit:

• Phase velocity and/or group velocity and/or amplitude and/or intensity of the Lamb wave mode, frequency of the Lamb wave mode, temperature of the wall,
• In a fourth process step, a statement about the condition of the wall is derived from the current local wall thickness.

By comparing the reference value and the measured value of at least one measured variable, a current local wall thickness can be calculated using a mathematical-physical model. It is not necessary to radiate ultrasonic signals into a liquid medium.

In this way, it is possible to determine whether, for example, corrosion or the build-up of deposits on the wall has changed the vibration capacity of a wall. Corrosion, for example, leads to a reduction in the wall thickness, at least locally, which reduces the area moment of inertia of the wall. This results in a shift in the natural frequencies of vibrations of the wall. Deposits lead to an apparently higher mass of the wall and thus to a reduction in the natural frequencies of the wall.

By comparing a reference state with an actual state, conclusions can be drawn about changes in physical boundary conditions that influence lamb waves.

In one embodiment, when determining the current local wall thickness, a deviation between a reference value and a corresponding measured value is weighted with a coefficient.

In this way, a current local wall thickness can be better quantified.

In one embodiment, the at least one coefficient is determined experimentally or by simulations.

In one embodiment, a first signal propagation time of the Lamb wave mode between transmission and reception by means of the first ultrasonic transducer and/or at least one second ultrasonic transducer deviates from a second signal propagation time of an ultrasonic signal passing through the medium and generated with the Lamb wave by at least 10% of the first signal propagation time.

In this way, a disturbing interaction between the ultrasonic signals passing through the wall and the ultrasonic signals passing through a medium at the location of a receiving ultrasonic transducer can be avoided or attenuated.

In one embodiment, at least two of the first ultrasonic transducers and/or the at least one second ultrasonic transducer receive Lamb waves generated by the first ultrasonic transducer.

In one embodiment, at least two different path lengths of Lamb waves are established between a generating ultrasonic transducer and a receiving ultrasonic transducer.

In one embodiment, a compensation of transmitter dynamics and receiver dynamics is carried out based on the received Lamb waves with different path lengths.

In one embodiment, a wall thickness profile is created using measured values for the local wall thickness from the at least two of the first ultrasonic transducers and/or the at least one second ultrasonic transducer.

• zumindest einen ersten Ultraschallwandler zum Erzeugen von Ultraschallsignalen, wobei der zumindest eine erste Ultraschallwandler und/oder zumindest ein zweiter Ultraschallwandler dazu eingerichtet ist, zumindest eines der Ultraschallsignale zu erfassen;
• eine elektronische Mess-/Betriebsschaltung zum Aufnehmen von Messsignalen des zumindest einen Ultraschallwandlers und zum Bereitstellen von Messwerten einer lokalen Wandstärke.

A measuring device according to the invention for implementing the method comprises:

• at least one first ultrasonic transducer for generating ultrasonic signals, wherein the at least one first ultrasonic transducer and/or at least one second ultrasonic transducer is configured to detect at least one of the ultrasonic signals;
• an electronic measuring/operating circuit for receiving measuring signals from the at least one ultrasonic transducer and for providing measured values of a local wall thickness.

In one embodiment, the at least one ultrasonic transducer is designed to be arranged on a wall of a container such as a tank, a bottle, a measuring tube or the like.

In one embodiment, the measuring device further comprises a wall on which the at least one first ultrasonic transducer is arranged,
wherein the measuring device is designed to be immersed in a medium within a container such as a tank, a bottle, a measuring tube or the like.

In one embodiment, the electronic measuring/operating circuit is configured to use a decrease in a local wall thickness of the wall to provide a measured value for corrosion or abrasion of the container.

• 1 skizziert den Ablauf eines beispielhaften erfindungsgemäßen Verfahrens.
• 2 a) bis c) skizziert beispielhafte erfindungsgemäße Messgeräte.
• 3 skizziert beispielshafte Messrohrquerschnitte.
• 4 skizziert ein beispielhaftes Eintauchmessgerät.

In the following, the invention is described using embodiments.

• 1 outlines the sequence of an exemplary method according to the invention.
• 2 a) to c) outline exemplary measuring devices according to the invention.
• 3 outlines exemplary measuring tube cross-sections.
• 4 outlines an example immersion measuring device.

• Phasengeschwindigkeit der Lambwellenmode, Frequenz der Lambwellenmode, Temperatur der Wandung.

1 outlines the sequence of an exemplary method according to the invention, wherein in a first method step 101 Lamb waves of a Lamb wave mode are generated on a first section of the wall by means of a first ultrasonic transducer 11. The wall can be used to form an immersion sensor 14.1 (see 4 ), where the wall is immersed in a medium. The wall can also be part of a container such as a measuring tube, a tank or a bottle, see also 2 and 3 . In a second method step 102, the Lamb waves passing through the wall are detected by means of the first ultrasonic transducer 11 and/or by means of at least one second ultrasonic transducer 12. According to the invention, in a third method step 103, based on a reference value of a local wall thickness, a reference value and a measured value are determined for at least one of the following measured variables used to determine a current local wall thickness using an electronic measuring/operating circuit:

• Phase velocity of the Lamb wave mode, frequency of the Lamb wave mode, temperature of the wall.

By comparing the reference value and the measured value of at least one measured variable, a current local wall thickness can be calculated using a mathematical-physical model. It is not necessary to radiate ultrasonic signals into a liquid medium.

mit cph als Phasengeschwindigkeit einer Lambwellenmode in der Wandung, T als Temperatur der Wandung, t als lokale Wandstärke und f als Frequenz einer angeregten Lambwellenmode, wobei _r Referenzwerte kennzeichnet und wobei _m Messwerte kennzeichnet. kT, kt und kf bezeichnen Proportionalitätskoeffizienten bzgl. des Einflusses der Abweichungen zwischen Messwert und Referenzwert der einzelnen Messgrößen auf den Messwert der Phasengeschwindigkeit. Diese Koeffizienten können beispielsweise experimentell oder per Simulation bestimmt, oder auch abgeschätzt werden.For example, the following physical model can be used: $$\text{cph\_m}=\text{cph\_r}+\left(\text{T\_m}-\text{T\_r}\right)*\text{kT}+\left(\text{t\_m}-\text{t\_r}\right)*\text{kt}+\left(\text{f\_m}-\text{f\_r}\right)*\text{kf},$$

with cph as the phase velocity of a Lamb wave mode in the wall, T as the temperature of the wall, t as the local wall thickness and f as the frequency of an excited Lamb wave mode, where _r denotes reference values and where _m denotes measured values. kT, kt and kf denote proportionality coefficients with regard to the influence of the deviations between the measured value and the reference value of the individual measured variables on the measured value of the phase velocity. These coefficients can be determined experimentally or by simulation, or even estimated.

By converting to t_m we get: $$\text{t\_m}=\text{t\_r}+\left(\text{cph\_m}-\text{cph\_r}-\left(\text{T\_m}-\text{T\_r}\right)*\text{kT}-\left(\text{f\_m}-\text{f\_r}\right)*\text{kf}\right)/\text{kt}$$

This model is purely exemplary; nonlinear influences or other measured variables can also be included.

After a measured value for a local wall thickness has been determined, a statement about the condition of the wall can then be derived from the current local wall thickness in a fourth method step 104.

Properties of the Lamb wave mode are also influenced by a medium wetting the wall, or for example by its speed of sound and density. However, the uncertainty that arises when these measured variables are not taken into account when determining a local wall thickness can be estimated using Gaussian error propagation. For example, it can be shown that if a medium is in a speed of sound range between 600 m/s and 2100 m/s and a density range between 0.7 g/cm^3 and 1.5 g/cm^3, there is an uncertainty of approx. 6% in the measured value of the local wall thickness. For many applications, this already allows a satisfactory statement to be made about the condition of a wall. If the speed of sound and/or density of a medium wetting the wall are known more precisely than in the ranges given as examples, the uncertainty can be reduced significantly further.

In one embodiment, at least two of the at least one first ultrasonic transducer 11 and/or the at least one second ultrasonic transducer 12 are designed to receive Lamb waves generated by the first ultrasonic transducer. For example, this can create a local wall thickness profile, which enables further insights into the state of the wall, see for example 2 a) and b).

In one embodiment, at least two path lengths of the Lamb waves between the generating ultrasonic transducer and the receiving ultrasonic transducer are different. This makes it possible, for example, to compensate for transmitter dynamics and receiver dynamics based on the received Lamb waves with different path lengths. The background to this is that each ultrasonic transducer has an influence on a Lamb wave mode.

2 a) to c) outline exemplary embodiments of measuring devices 10 according to the invention for implementing the method 100 according to the invention, wherein the measuring devices each comprise a media-containing container 14 such as a measuring tube, wherein first ultrasonic transducers 11 and second ultrasonic transducers 12 are arranged on an outer side of a wall 14.1 of the container. An electronic measuring/operating circuit 13 as shown by way of example in 2 a) shown, is designed to detect the ultrasound transducers, to record and evaluate measurement signals from the ultrasonic transducers and to provide measured values of at least one measured variable. In addition to the measured variables listed above, this can be, for example, a media speed, i.e. a flow rate in the case of a measuring tube as a container. First ultrasonic transducers are at least designed to excite and in particular to detect Lamb waves, and second ultrasonic transducers are at least designed to detect and in particular to excite Lamb waves.

The ultrasonic transducers can be used as 2 a) and b) can be used in pairs, for example as in 2c) shown, only a first ultrasonic transducer 11 can be used and a reflector 15 can be used to reflect generated Lamb waves.

Instead of the two pairs shown, only a few ultrasonic transducers or more than two pairs of ultrasonic transducers can be installed. 2 a) to c) are to be interpreted purely as examples.

3 shows exemplary cross-sections of measuring tubes which can be used in measuring devices according to the invention. Such measuring tubes can have a round cross-section or a rectangular cross-section.

4 outlines an exemplary measuring device 10 according to the invention in the form of an immersion sensor for implementing the method 100 according to the invention. A wall 15 designed for immersion in a medium, which is located, for example, in a container 17, has on an outer side of the wall 15 a first ultrasonic transducer 11 for generating Lamb waves and a second ultrasonic transducer 12 for detecting Lamb waves. With regard to possible arrangements of ultrasonic transducers, the same applies to 2 a) to c). An electronic measuring/operating circuit 13 is designed to control the ultrasonic transducers according to the embodiments in 2 a) to c).

List of reference symbols

10

Measuring device

11

first ultrasonic transducer

12

second ultrasonic transducer

13

electronic measuring/operating circuit

14

container

14.1

Wall

15

Wall for immersion

16

reflector

17

container

100

Proceedings

101

first procedural step

102

second process step

103

third procedural step

104

fourth procedural step

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 102015107752 A1 [0002]
• EP 2335062 B1 [0002]

Claims (10)

Method (100) for examining a state of a wall (15) of an immersion sensor or a container (14) that can be wetted with a particularly liquid medium, such as a tank, a bottle, a measuring tube or the like, wherein in a first method step (101) Lamb waves of a Lamb wave mode are generated in a first section of the wall by means of at least one first ultrasonic transducer (11), wherein in a second method step (102) the Lamb waves running through the wall are detected by means of the at least one first ultrasonic transducer (11) and/or by means of at least one second ultrasonic transducer (12), characterized in that in a third method step (103), based on a reference value of a local wall thickness, a reference value and a measured value are used for at least one of the following measured variables in order to determine a current local wall thickness by means of an electronic measuring/operating circuit: phase velocity and/or group velocity and/or amplitude and/or intensity of the Lamb wave mode, frequency of the Lamb wave mode, temperature of the wall, wherein in a fourth method step (104) a statement about the condition of the wall is derived from the current local wall thickness. Procedure according to Claim 1 , whereby when determining the current local wall thickness, a deviation between a reference value and a corresponding measured value is weighted with a coefficient. Procedure according to Claim 2 , wherein the at least one coefficient is determined experimentally or by simulations. Method according to one of the preceding claims, wherein a first signal propagation time of the Lamb wave mode between transmission and reception by means of the first ultrasonic transducer (11) and/or at least one second ultrasonic transducer (12) deviates from a second signal propagation time of an ultrasonic signal passing through the medium and generated with the Lamb wave by at least 10% of the first signal propagation time. Method according to one of the preceding claims, wherein at least two of the first ultrasonic transducer (11) and/or the at least one second ultrasonic transducer (12) receive Lamb waves generated by the first ultrasonic transducer, wherein at least two different path lengths of the Lamb waves are set up between the generating ultrasonic transducer and the receiving ultrasonic transducer, wherein a compensation of transmitter dynamics and receiver dynamics is carried out on the basis of the received Lamb waves with different path lengths. Method according to one of the preceding claims, wherein at least two of the first ultrasonic transducers (11) and/or the at least one second ultrasonic transducer (12) receive Lamb waves generated by the first ultrasonic transducer, wherein a wall thickness profile is created using measured values for the local wall thickness from the at least two of the first ultrasonic transducers (11) and/or the at least one second ultrasonic transducer (12). Measuring device (10) for implementing the method comprising: at least one first ultrasonic transducer (11) for generating ultrasonic signals, wherein the at least one first ultrasonic transducer and/or at least one second ultrasonic transducer (12) is configured to detect at least one of the ultrasonic signals; an electronic measuring/operating circuit (13) for receiving measuring signals from the at least one ultrasonic transducer (11, 12) and for providing measured values of a local wall thickness. Measuring device according to Claim 7 , wherein the at least one ultrasonic transducer (11, 12) is adapted to be arranged on a wall (14.1) of a container (14) such as a tank, a bottle, a measuring tube or the like. Measuring device according to Claim 8 , wherein the measuring device has a wall (15) for immersion in a medium, on which wall the at least one first ultrasonic transducer (11) is arranged, wherein the measuring device is designed to be immersed in a medium within a container such as a tank, a bottle, a measuring tube or the like. Use of a measuring device according to Claim 9 , wherein the electronic measuring/operating circuit (13) is designed to use a change in a local wall thickness of the wall to provide a measured value for corrosion, abrasion or deposits on the wall (14.1, 15).

Images