WO2022053265A1

WO2022053265A1 - Ultrasonic transducer and clamp-on ultrasonic flowmeter

Info

Publication number: WO2022053265A1
Application number: PCT/EP2021/072741
Authority: WO
Inventors: Achim Wiest; Andreas Berger; Beat Kissling
Original assignee: Endress+Hauser Flowtec Ag
Priority date: 2020-09-11
Filing date: 2021-08-16
Publication date: 2022-03-17

Abstract

The invention relates to an ultrasonic transducer (10) of a clamp-on ultrasonic flow meter (1), comprising: - a transducer element (11), in particular a piezo element, for generating and detecting ultrasonic signals; and - a coupling element (12) having a first side (12.1) and a second side (12.2), the transducer element being situated on a side surface (12.11) of the first side, the second side having a side surface (12.21) comprising a recess structure with at least one recess (12.3), which recess structure reduces a bearing surface of the side surface, - wherein the side surface of the second side defines a reference surface, a circular environment (U) having a diameter (D) being assigned to each point in a central region of the reference surface, which environment is completely covered by the reference surface, in each environment (U) a surface ratio of recess surface to bearing surface being at least 0.5, wherein the following applies: D=WL/2.

Description

description

Ultrasonic Transducers and Clamp-On Ultrasonic Flow Meters

The invention relates to an ultrasonic transducer and a clamp-on ultrasonic flow meter for measuring a flow rate or a volume flow of a medium flowing through a pipeline.

In the case of clamp-on ultrasonic flowmeters, ultrasonic transducers are attached to an outside of a measuring tube, by means of which ultrasonic signals are radiated into the measuring tube and ultrasonic signals emerging from the measuring tube are detected. Ultrasonic transducers for such measuring devices have a coupling element which is set up to transmit the ultrasonic signals between the measuring tube and a transducer element, as can be seen, for example, from DE102010063535A1. A critical aspect of such coupling elements is the acoustic resistance between the coupling element and the pipeline, which makes it difficult for sound to pass between the coupling element and the pipeline and vice versa.

The object of the invention is to propose an ultrasonic transducer and a clamp-on ultrasonic flowmeter with such an ultrasonic transducer, in which a good and robust sound transmission can be guaranteed.

The object is achieved by an ultrasonic transducer according to independent claim 1 and by a clamp-on ultrasonic flow meter according to independent claim 5.

An ultrasonic transducer according to the invention of a clamp-on ultrasonic flow meter comprises:

A transducer element, in particular a piezo element, for generating and detecting ultrasonic signals;

A coupling element with a first side and a second side, the coupling element being set up in particular to be acoustically coupled to a medium-carrying pipeline via the second side and to transmit ultrasonic signals between the transducer element and the pipeline and vice versa,

RECTIFIED SHEET (RULE 91) ISA/EP Description wherein the transducer element is arranged on a side surface of the first side, the second side having a side surface with a depression structure with at least one depression, which depression structure reduces a bearing surface of the side surface, the ultrasonic signals that can be generated by the transducer elements having a central frequency, which central frequency is im A wavelength is assigned to the coupling element, with the side surface of the second side defining a reference surface without taking the depression into account, with each point in a central region of the reference surface being assigned a circular area with a diameter which area is completely covered by the reference area, characterized in that in each environment, an area ratio of the depression area to the contact area is at least 0.25 and in particular at least 0.5, us preferably at least 0.75, and the area ratio is at most 15, and in particular particular is at most 10 and preferably at most 8, where the following applies: diameter=wavelength/2.

In this way, when using the ultrasonic transducer with a given contact pressure, an average surface pressure of the bearing surface on a measuring tube can be increased. By complying with the minimum value of the area ratio in each environment U, a disturbing Lamb wave generation in a measuring tube wall can be avoided. By complying with the maximum value, a sufficient contact surface is guaranteed.

The indentation area corresponds to the portion of the reference area that covers an indentation. The reference surface is thus a continuation of the bearing surface across the indentations.

RECTIFIED SHEET (RULE 91) ISA/EP description

In this case, the ultrasonic transducer is preferably set up to radiate ultrasonic signals along one direction into a measuring tube.

In one embodiment, the indentations each have a minimum depth of 0.1 millimeters and in particular 0.2 millimeters and preferably 0.5 millimeters and/or a maximum depth of 20 millimeters and in particular 15 millimeters and preferably 10 millimeters.

In one configuration, the side surface of the second side has a curvature.

In this way, the coupling element can advantageously be placed on a curved outer surface of a measuring tube.

In one configuration, the coupling element is made from a metal such as aluminum or steel, or from a ceramic such as aluminum oxide, zirconium oxide or silicon nitride, or from a metallic or non-metallic glass.

In this way it is resistant to high temperatures and can be used at temperatures of over 200°C.

In one configuration, the area ratio is at most 2 and in particular at most 1.5.

An upper limit for the area ratio ensures good ultrasonic signal transmission between the coupling element and the pipeline, since otherwise there would only be a small contact area. In addition, it is ensured that mechanical stability of the coupling element is guaranteed in the area of the bearing surface. If the contact surface is too small, high contact pressures can lead to undesired deformations of the coupling element.

A clamp-on ultrasonic flow meter according to the invention for measuring the flow rate or the volume flow of a medium flowing through a pipeline comprises:

RECTIFIED SHEET (RULE 91) ISA/EP Description of a measuring tube for guiding the medium, at least one pair of ultrasonic transducers according to one of the preceding claims, an electronic measuring/operating circuit for operating the ultrasonic transducers, for evaluating measurement signals and providing flow measurement values.

The measuring tube can be part of an existing pipeline to which the ultrasonic transducers are subsequently attached, or installed in a pipeline together with the ultrasonic transducers.

In one embodiment, the outside of the measuring tube has at least one flat surface designed to accommodate at least one ultrasonic transducer.

In one embodiment, the measuring tube has an outer radius, with the side surface of the second side of the coupling element having a curvature, which curvature has a radius of curvature, the radius of curvature being at most 10 percent larger than the outer radius, and the radius of curvature corresponding at least to the value of the outer radius .

In this way, the coupling element rests securely and sturdily on the measuring tube. This is advantageous for measuring tubes with a round cross-section without a flat contact surface for ultrasonic transducers. A radius of curvature slightly larger than the outer radius also makes it easier to use a metal foil between the coupling element and the measuring tube.

In one embodiment, a metal foil is arranged between each ultrasonic converter and the measuring tube, which is set up to further improve an acoustic coupling between the ultrasonic converter and the measuring tube.

The metal foil has the property that an existing surface roughness of the measuring tube for the coupling element is smoothed out. The film at least partially adapts to the surface of the measuring tube.

In particular, the metal foil has an acoustic index between the acoustic index of the measuring tube and the acoustic index of the coupling element. This will

RECTIFIED SHEET (RULE 91) ISA/EP Description of the sound transition between the measuring tube and the coupling element and vice versa further improved.

In one embodiment, an average surface pressure of the ultrasonic transducers on the measuring tube is at least 0.1 megapascal, and in particular at least 1 megapascal and preferably at least 10 megapascals.

A corresponding surface pressure improves the coupling and smoothes the metal foil when present. The surface pressure can be adjusted by a person skilled in the art depending on the material of the metal foil and a process temperature.

In one embodiment, the flow meter is suitable for carrying media with a temperature above 200 degrees.

The invention is described below using exemplary embodiments.

Fig. 1 outlines an exemplary schematic clamp-on ultrasonic flow meter,

Fig. 2 outlines a detailed view of an ultrasonic transducer shown in Fig. 1,

3 a) to c) outline various exemplary configurations according to the invention of a coupling element of an ultrasonic transducer of a clamp-on ultrasonic flowmeter,

Fig. 4 outlines cross sections of exemplary depressions according to the invention,

5 outlines exemplary configurations of a bearing surface of the coupling element.

Fig. 1 sketches a schematic side view of an exemplary clamp-on ultrasonic flow meter 1 for measuring a flow rate or a volume flow of a medium flowing through a pipeline, which has a measuring tube 20 with a measuring tube axis 23, two ultrasonic transducers mounted on an outer side 21 of the measuring tube 10 and an electronic measuring Z operating circuit 30 for operating the ultrasonic transducer and for evaluating measurement signals and providing

RECTIFIED SHEET (RULE 91) ISA/EP description

flow readings. Each ultrasonic transducer has a migrating element 11 and a coupling element 12 . The converter element can be a piezo element. The measuring tube can be part of an existing pipeline to which the ultrasonic transducers are subsequently attached, or installed in a pipeline together with the ultrasonic transducers. The ultrasonic transducers are configured here by way of example in such a way that a 2-traverse path of ultrasonic signals through the measuring tube with a reflection on an inner wall of the measuring tube results. Configurations with one truss or three or more trusses are also known to a person skilled in the art and he will choose one that is suitable for him. Each ultrasonic transducer has a migrating element 11 and a coupling element 12 .

FIG. 2 sketches a close-up of an ultrasonic transducer shown in FIG. 1, the transducer element being arranged on a side surface 12.11 of a first side 12.1 of the coupling element, facing away from the measuring tube. The coupling element is acoustically coupled to the measuring tube via a side surface 12.21 of a second side 12.2 facing the measuring tube. As shown here, a metal foil 40 can be arranged between the measuring tube 20 and the coupling element 12, which is set up to compensate for unevenness of the measuring tube on the outside in the area of the ultrasonic transducer and thus to produce an improved acoustic contact. According to the invention, the side surface 12.21 of the second side has an indentation structure, which is shown in Figs. 3 a) to c) is explained in more detail.

3 a) outlines an exemplary depression structure with a plurality of parallel depressions 12.3, which run parallel to a short edge of the side surface of the second side, only two depressions being identified for the sake of clarity. The indentations reduce a bearing surface 12.4 of the side surface. Here, too, only two areas of the bearing surface are marked for the sake of clarity.

The side surface 12.21 of the second side without considering the indentation defines a reference surface, with each point in a central area of the reference surface being assigned a circular environment U with a diameter, which environment is completely covered by the reference surface. The central area of the reference surface, i.e. the union of all surroundings U.

RECTIFIED SHEET (RULE 91) ISA/EP description

According to the invention, in each environment U the area ratio of the depression area to the contact area is at least 0.25 and in particular at least 0.5 and preferably at least 0.75, and the area ratio is at most 15 and in particular at most 10 and preferably at most 8, with the following applying: diameter=wavelength/ 2. It is therefore valid that the minimum value of the area ratio is maintained not only over the entire lateral surface, but also locally within each of the surroundings U defined here.

When using the ultrasonic transducer, a lower limit of the area ratio increases a surface pressure for a given contact pressure, while the upper limit ensures that there is sufficient contact area.

FIG. 3b) outlines an embodiment in which the depressions run parallel to a long edge of the side surface of the second side.

3c) sketches examples of further conceivable shapes of the indentations, such as zigzag, running at an angle to one another, crossing one another, arc-shaped, or indentations in the form of bores.

The ones in Figs. The depressions shown in FIGS. 3 a) to c) and their orientations to one another are purely exemplary and can also be combined with one another.

4 outlines three exemplary cross sections through elongated indentations, the cross sections having a triangular shape, a rectangular shape, or a circular shape. Other cross-sectional shapes are conceivable. The same applies to circular indentations such as bores.

Fig. 5 sketches two front views of two exemplary configurations of measuring tube 20 and coupling element 12, in which case the measuring tube can be partially flat on the outside, so that a coupling element with a flat side surface 12.21 on the second side can be placed on the measuring tube.

Alternatively, the coupling element can also have a side surface 12.21 on the second side

RECTIFIED SHEET (RULE 91) ISA/EP Description having a curvature 12.212, which is adapted to a curvature of the outside with a radius of curvature 12.2121.

RECTIFIED SHEET (RULE 91) ISA/EP description

Reference List

1 clamp-on ultrasonic flow meter

10 ultrasonic transducers

11 transducer element

12 coupling element

12.1 first page

12.11 Face of First Page

12.2 second page

12.21 Face of the second side

12.212 camber

12.2121 radius of curvature

12.3 Deepening

12.4 Bearing Surface

20 measuring tube

21 outside

21.1 flat surface

22 outer radius

23 longitudinal axis

30 electronic measurement/operation circuit

40 metal foil

T depth

RECTIFIED SHEET (RULE 91) ISA/EP description

U circular environment

RECTIFIED SHEET (RULE 91) ISA/EP

Claims

patent claims

1. Ultrasonic transducer (10) of a clamp-on ultrasonic flowmeter (1) comprising:

A transducer element (11), in particular a piezo element, for generating and detecting ultrasonic signals;

A coupling element (12) with a first side (12.1) and a second side (12.2), the coupling element being set up in particular to be acoustically coupled to a media-carrying pipeline via the second side and to transmit ultrasonic signals between the transducer element and the pipeline and vice versa , wherein the transducer element is arranged on a first side surface (12.11) of the first side, the second side having a second side surface (12.21) with a depression structure with at least one depression (12.3), which depression reduces a bearing surface (12.4) of the side surface, wherein the ultrasonic signals that can be generated by the transducer elements have a central frequency, to which central frequency in the coupling element a wavelength is assigned, wherein the side surface (12.21) of the second side defines a reference surface without taking the depression into account, each point in a central area of the reference surface having a circular Environment (U) is associated with a diameter, which environment is completely covered by the reference surface, characterized in that in each environment (U) an area ratio of depression surface to bearing surface is at least 0.25 and in particular at least 0.5 and preferably at least 0.75, and wherein the area ratio is at most 15, and in particular at most 10 and preferably at most 8, where the following applies: diameter=wavelength / 2.

2. Ultrasonic transducer according to claim 1, wherein the indentations (12.3) each have a minimum depth of 0.1 millimeters and in particular 0.2 millimeters and preferably 0.5 millimeters and/or a maximum depth of 20 millimeters and in particular 15 millimeters and preferably 10 millimeters.

3. Ultrasonic transducer according to claim 1 or 2, wherein the side surface (12.21) of the second side has a curvature (12.211) which is in particular concave.

4. Ultrasonic transducer according to one of the preceding claims, wherein the coupling element (12) is made of a metal such as aluminum or steel, or of a ceramic such as aluminum oxide, zirconium oxide or silicon nitride, or of a metallic or non-metallic glass.

5. Ultrasonic transducer according to one of the preceding claims, wherein the area ratio is a maximum of 2 and in particular a maximum of 1.5

6. Clamp-on ultrasonic flow meter (1) for measuring the flow rate or volumetric flow of a medium flowing through a pipeline, comprising: a measuring tube (20) for guiding the medium, at least one pair of ultrasonic transducers (10) according to one of the preceding claims , wherein the ultrasonic transducers are fastened to an outside (21) of the measuring tube, an electronic measuring/operating circuit (30) for operating the ultrasonic transducers, for evaluating measurement signals and providing flow measurement values.

7. Flow meter according to claim 6, wherein the measuring tube (20) on the outside (21) has at least one flat surface (21.1) set up to accommodate at least one ultrasonic transducer.

8. Flow meter according to claim 6, wherein the measuring tube (20) has an outer radius (22), the side surface of the second side of the coupling element having a bulge (12.212), which bulge has a radius of curvature (12.2121), the radius of curvature being a maximum of 10 percent is greater than the outer radius, and the radius of curvature is at least equal to the value of the outer radius.

9. Flow meter according to one of claims 6 to 8, wherein a metal foil (40) is arranged between each ultrasonic transducer (10) and the measuring tube (20), which is designed to improve acoustic coupling between the ultrasonic transducer and measuring tube.

10. Flow meter according to one of claims 6 to 9, wherein an average surface pressure of the contact surface of the ultrasonic transducer (10) on the measuring tube (20) is at least 0.5 megapascals, and in particular at least 3 megapascals and preferably at least 10 megapascals.

11 . Flow meter according to one of claims 6 to 10, wherein the flow meter (1) is suitable for carrying media at a temperature above 200 degrees.