DE102018109807B4 - Ultrasonic transducer and flow meter - Google Patents

Abstract

Ultrasonic transducer (10) of a clamp-on ultrasonic flowmeter (1), which flowmeter is set up to measure a flow rate or a volumetric flow rate of a medium flowing through a measuring tube (20), the ultrasonic transducer comprising: at least one transducer element (11 ), in particular a piezoelectric transducer element, which is set up to generate and/or detect ultrasonic signals;a coupling element (12), which is set up to conduct ultrasonic signals between the converter element and the measuring tube and vice versa;wherein the converter element is arranged on a first , the side (12.1) of the coupling element facing away from the measuring tube and is acoustically and mechanically coupled thereto;wherein the transducer element is set up to emit ultrasonic signals along a surface normal (11.1) of the transducer element, with a spatial emission profile of the ultrasonic signal having a central area (Z) With has a first wavefront and an outer area (A) with a second wavefront, with normal vectors of the first wavefront having at most a maximum angle β1 to the surface normal, and normal vectors of the second wavefront having at least a minimum angle β2 to the surface normal, with the coupling element on a second, facing the measuring tube Side (12.2) has a second side surface (12.21) with a contact area (12.22), which second side surface is set up by means of the contact area to be acoustically and mechanically coupled to the measuring tube, whereby by applying the coupling element to the measuring tube in the direction of a measuring tube axis or measuring tube center line of the measuring tube, a third side (12.3) and a fourth side (12.4) opposite the third side are defined, wherein the coupling element has a masking device (13) which is set up to block the second wave front at least in sections at the transient to at least partially prevent entry into the measuring tube, the coupling element having a lateral surface (12.51), characterized in that the blanking device has at least one gap group (13.1) with at least one gap (13.11), which gap protrudes from the lateral surface into the coupling element, wherein the gap is configured to protrude into a spatial propagation region of the second wavefront, wherein the at least one gap is an air gap.

Description

The invention relates to an ultrasonic transducer of a clamp-on ultrasonic flowmeter, and the clamp-on ultrasonic flowmeter, the flowmeter being set up to measure a flow rate or a volume flow of a medium flowing through a measuring tube.

Clamp-on ultrasonic transducers according to the prior art usually have a transducer element and a coupling element, with the transducer element being attached to a side of the coupling element facing away from the measuring tube. Ultrasonic signals generated by the transducer element thus run through the coupling element to the measuring tube and are coupled into the measuring tube via a measuring tube wall. The following writings are mentioned here as examples: DE102015107567A1 , DE 202015104291 U1 , U.S. 2002/0011120 A1 and US6062091A .

The transducer elements usually have a disc-shaped geometry, and the generation of an ultrasonic signal is based on a forced rapid change in thickness of the transducer element. This change in thickness generates an ultrasonic signal with a wavefront which is approximately flat in a central area and which can be used for an ultrasonic flow measurement.

However, interference components of the ultrasonic signal occur in an edge area of such transducer elements, which have a non-planar wavefront and enter the measuring tube at different points than the planar wavefront. These interference components increase an interference noise level in the measuring tube in a very reliable manner and worsen a signal/noise ratio.

It is therefore the object of the invention to propose an ultrasonic transducer and a clamp-on ultrasonic flow meter in which the influence of the interference component on the signal-to-noise ratio is reduced.

• mindestens ein Wandlerelement, insbesondere ein piezoelektrisches Wandlerelement, welches dazu eingerichtet ist, Ultraschallsignale zu erzeugen und/oder zu erfassen;
• ein Koppelelement, welches dazu eingerichtet ist, Ultraschallsignale zwischen dem Wandlerelement und dem Messrohr sowie umgekehrt zu leiten;
• wobei das Wandlerelement auf einer ersten, dem Messrohr abzuwendenen Seite des Koppelelements angeordnet ist und mit diesem akustisch und mechanisch gekoppelt ist;
• wobei das Wandlerelement dazu eingerichtet ist, Ultraschallsignale insbesondere entlang einer Oberflächennormalen des Wandlerelements abzustrahlen, wobei ein räumliches Abstrahlprofil des Ultraschallsignals einen Zentralbereich mit einer ersten Wellenfront und einen Außenbereich mit einer zweiten Wellenfront aufweist,
• wobei Normalenvektoren der ersten Wellenfront maximal einen Maximalwinkel β₁ zur Oberflächennormalen aufweisen, und wobei Normalenvektoren der zweiten Wellenfront zumindest einen Mindestwinkel β₂ zur Oberflächennormalen aufweisen,
• wobei das Koppelelement auf einer zweiten, dem Messrohr zuzuwendenden Seite eine zweite Seitenfläche mit einem Kontaktbereich aufweist, welche zweite Seitenfläche mittels des Kontaktbereichs dazu eingerichtet ist, mit dem Messrohr akustisch und mechanisch gekoppelt zu werden,
• wobei durch Anlegen des Koppelelements an ein Messrohr in Richtung einer Messrohrachse des Messrohrs eine dritte Seite und eine der dritten Seite gegenüberliegende vierte Seite definiert ist,
• wobei dass das Koppelelement eine Ausblendeeinrichtung aufweist, welche dazu eingerichtet ist, die zweite Wellenfront zumindest abschnittsweise am Übertreten in das Messrohr zumindest teilweise zu hindern,
• wobei das Koppelelement eine Mantelfläche aufweist, wobei die Ausblendeeinrichtung mindestens eine Spaltgruppe mit mindestens einem Spalt aufweist, welcher Spalt von der Mantelfläche in das Koppelelement hineinragt,
• wobei der Spalt dazu eingerichtet ist, in einen räumlichen Ausbreitungsbereich der zweiten Wellenfront hineinzuragen,
• wobei der Spalt ein Luftspalt ist.

The object of the invention is achieved by an ultrasonic transducer according to the invention comprising:

• at least one transducer element, in particular a piezoelectric transducer element, which is set up to generate and/or detect ultrasonic signals;
• a coupling element which is set up to conduct ultrasonic signals between the transducer element and the measuring tube and vice versa;
• wherein the transducer element is arranged on a first side of the coupling element, facing away from the measuring tube, and is acoustically and mechanically coupled thereto;
• wherein the transducer element is set up to emit ultrasonic signals in particular along a surface normal of the transducer element, wherein a spatial emission profile of the ultrasonic signal has a central area with a first wavefront and an outer area with a second wavefront,
• wherein normal vectors of the first wavefront have at most a maximum angle β ₁ to the surface normal, and wherein normal vectors of the second wavefront have at least a minimum angle β ₂ to the surface normal,
• wherein the coupling element has a second side face with a contact area on a second side facing the measuring tube, which second side face is set up by means of the contact area to be acoustically and mechanically coupled to the measuring tube,
• wherein a third side and a fourth side opposite the third side are defined by placing the coupling element on a measuring tube in the direction of a measuring tube axis of the measuring tube,
• wherein the coupling element has a suppression device which is set up to at least partially prevent the second wavefront from entering the measuring tube at least in sections,
• wherein the coupling element has a lateral surface, wherein the blanking device has at least one gap group with at least one gap, which gap protrudes from the lateral surface into the coupling element,
• wherein the gap is set up to protrude into a spatial propagation area of the second wavefront,
• where the gap is an air gap.

A portion of the ultrasonic signal that impinges on the gap is partially reflected back and partially penetrates the gap and loses intensity in the process.

In one configuration, the gap has a thickness, the thickness being perpendicular to the second side surface, the thickness of the gap being greater than 0.02 mm, and in particular greater than 0.05 mm and preferably greater than 0.1 mm, and/or smaller than 1.5 mm and in particular less than 1.2 mm and preferably less than 1 mm.

By limiting the gap to a maximum thickness, structural integrity of the coupling element can be maintained; a minimum thickness ensures that the thickness of the gap is greater than the maximum amplitudes of the ultrasonic signals that occur in the coupling element.

In one configuration, at least one gap group comprises a plurality of gaps, which gaps are offset from one another in a direction perpendicular to the second side surface, the perpendicular direction in each case defining a height of each gap with respect to the second side surface.

In this way, an intensity of interfering ultrasonic signal components can be further reduced.

In one embodiment, an offset between adjacent columns is dimensioned in such a way that a total reflection of the ultrasonic signal occurs, or that the ultrasonic signal enters the blanking device and is successively weakened there.

In one embodiment, the lowest gap in a gap group in terms of height is an air gap, with at least one further gap being filled with an acoustically damping material, for example a foam material or a plastic.

Due to a high difference in the acoustic impedances of the gap and the coupling element compared to gaps filled with acoustically damping materials, a larger proportion of the signal is increasingly reflected back at the air gap and passes through the gaps filled with acoustically damping material a second time.

In one embodiment, the first side has a coupling surface that faces the third side and is inclined with respect to the second side surface, on which coupling surface the transducer element is arranged,
wherein a first gap group is arranged on the third side of the coupling element, and/or wherein a second gap group is arranged on the fourth side of the coupling element.

In one configuration, the second side has a reflective surface facing the third side, sloping with respect to the second side surface and/or a reflective surface facing the fourth side, sloping with respect to the second side surface, which reflective surface is set up in each case to reflect the ultrasonic signal in a spatial propagation area of the partially reflect back the second wavefront in the coupling element.

In this way, the interfering portion of the ultrasonic signal is reflected back into the coupling element, at least in certain areas, and scattered.

In one configuration, the oblique reflection surface has a notch which is set up to scatter the ultrasonic signal that is reflected back.

With an appropriate design, a notch can support the scattering of the interfering ultrasonic signal component.

In one configuration, the second side surface has a depression which is set up to prevent the second wave front from entering the measuring tube at least in sections, the depression delimiting the contact area at least in sections.

In one configuration, the second side surface has an edge surface which delimits the depression.

A stable seat of the coupling element on the measuring tube can be ensured by setting up an edge surface.

In one embodiment, the following applies: β ₁ <15° and/or β ₂ >15°.

In one embodiment, the following applies: β ₁ <10° and/or β ₂ >10°

In one embodiment, the following applies: β ₁ <5° and/or β ₂ >5°

In one embodiment, β ₁ is selected such that an ultrasonic signal amplitude falls by less than 12 dB, and in particular less than 9 dB, and preferably less than 6 dB compared to a maximum value of a spatial amplitude distribution, or β ₂ is selected such that a minimum drop of 12 dB and in particular 9dB and preferably 6dB occurs.

• Mindestens ein Paar Ultraschallwandler mit Ultraschallwandlern nach einem der vorigen Ansprüche, welche Ultraschallwandler entlang einer Messrohrachse des Messrohrs versetzt zueinander am Messrohr angeordnet sind, wobei die Ultraschallwandler eines Paars dazu eingerichtet sind, wechselseitig Ultraschallsignale zu senden und zu empfangen;
• eine elektronische Mess-/Betriebsschaltung zum Betreiben der Ultraschallwandler sowie zum Generieren von Durchflussmesswerten.

A clamp-on ultrasonic flow meter according to the invention for measuring a flow rate or a volume flow of a medium flowing through a measuring tube according to the transit time difference principle comprises:

• At least one pair of ultrasonic transducers with ultrasonic transducers according to one of the preceding claims, which ultrasonic transducers are arranged offset to one another on the measuring tube along a measuring tube axis of the measuring tube, the ultrasonic transducers of a pair being arranged thereto are configured to reciprocally transmit and receive ultrasonic signals;
• an electronic measurement/operation circuit for operating the ultrasonic transducers and for generating flow measurement values.

The invention is described below using exemplary embodiments.

1 outlines the structure of a clamp-on ultrasonic transducer according to the prior art; 2 outlines the structure of a variant of a clamp-on ultrasonic transducer according to the invention; 3 outlines the structure of a further clamp-on ultrasonic transducer according to the invention; 4 outlines a top view of a second side of an ultrasonic transducer according to the invention; and 5 outlines a setup of a clamp-on ultrasonic flow meter.

1 shows a schematic structure of a typical clamp-on ultrasonic transducer 10 with a transducer element 11 and a coupling element 12, the transducer element being attached to a coupling surface 12.11 on a first side 12.1 of the coupling element facing away from a measuring tube 20. The coupling element is set up to conduct ultrasonic signals between the transducer element and the measuring tube and vice versa. As a result, the coupling element has a second side surface 12.21 with a contact area 12.22 on a second side 12.2 facing the measuring tube, which second side surface is set up by means of the contact area to be acoustically and mechanically coupled to the measuring tube. The transducer element is set up, among other things, to generate ultrasonic signals and to radiate them into the coupling element along a surface normal 11.1 of the transducer element, with a spatial radiation profile of the ultrasonic signal having a central region Z with a first, approximately flat wavefront and an outer region A with a second, curved wavefront . Normal vectors of the first, approximately planar wave front have a maximum angle β ₁ to the surface normal, normal vectors of the second wave front have at least a minimum angle β ₂ to the surface normal. Since only the ultrasonic signal component from the central area can be used to measure an ultrasonic flow, the ultrasonic signal component from the outer area represents a disruptive component, which also enters the measuring tube and therefore worsens the signal-to-noise ratio. For example, the angle β ₁ can be less than 15° and in particular less than 10° and preferably less than 5°, and β ₂ can be greater than 15° and in particular greater than 10° and preferably greater than 5°.

2 shows a schematic exemplary structure of an ultrasonic transducer according to the invention. The coupling element 12 has a blanking device with two gap groups 13.1, each with two gaps 13.11, which are introduced into the lateral surface 12.51 on the third side 12.3 and the fourth side 12.4. The gaps are filled with air. An ultrasonic signal component impinging on the gap is partly reflected back and partly attenuated, the intensity of the back reflection depending, among other things, on the acoustic properties of the coupling element and of the material filling the gap. In this way it can be achieved that mainly the central area of the ultrasonic signal enters the measuring tube and the entry of the outer area of the ultrasonic signal is largely prevented.

The gaps are offset from one another in a direction perpendicular to the second face, the perpendicular direction defining a height 13.13 of each gap relative to the second face. An ultrasonic transducer according to the invention is not limited to the number of gaps shown here and the gap groupings shown. For example, an ultrasonic transducer according to the invention can also only have a gap on the third side 12.3 and/or the fourth side 12.4. However, more than two columns can also be arranged per column group. Different gap groups can have different gap numbers.

3 shows another ultrasonic transducer according to the invention, wherein the coupling element on the second side 12.2 has a reflective surface 13.2 facing the third side 12.3 and a gap group 13.1 on the fourth side 12.4. The reflection surface reflects part of the outer area of the ultrasonic signal back into the coupling element and thereby reduces the portion of the ultrasonic signal that contributes to the noise. As an alternative to in 3 In the embodiment shown, an ultrasonic transducer according to the invention can also have a coupling element without a gap and at least one reflection surface 13.2, which faces the third side 12.3 or the fourth side 12.4. When columns with reflection surfaces are combined, column groups with any number of columns with reflection surfaces can be arranged on the third side and/or the fourth side. In the 3 The embodiment shown is not to be interpreted as limiting. The reflective surface 13.2 can also have a notch with one or more notches. With an appropriate design, a notch can support the scattering of the interfering ultrasonic signal component. The indentation can have a pyramid structure or an egg cup structure, for example. Alternatively, the notch can also have an irregular structure.

In general, all surfaces apart from the contact surface 12.22 and the coupling surface 12.11 can each have a notch for scattering reflected ultrasonic signals.

4 shows a top view of an exemplary second side 12.2 of the coupling element according to the invention. The second side 12.2 has a contact area 12.22, which is designed to be in contact with the measuring tube. The contact area is surrounded by a depression 12.23, which is designed to prevent at least part of the outer area from entering the measuring tube. For example, the depression can be at least partially filled with an acoustically damping material. The depression is surrounded by an edge surface 12.24, by means of which a secure and stable support of the coupling element on the measuring tube can be ensured. As an alternative to creating a depression in the coupling element, the contact area 12.22 can be produced by attaching a disk and/or the edge surface 12.24 by attaching a support ring.

5 outlines a clamp-on ultrasonic flowmeter 1 with a measuring tube 20, which is set up to carry a medium, two ultrasonic transducers 10 according to the invention arranged thereon and an electronic measuring/operating circuit 777, which is set up to operate the ultrasonic transducers as well to generate flow measurements. The clamp-on ultrasonic flow meter, for example, works according to a transit time difference principle.

reference list

1

Clamp-On Ultrasonic Flow Meter

10

ultrasonic transducer

11

transducer element

11.1

surface normal

12

coupling element

12.1

first page

12.11

coupling surface

12.2

second page

12.21

second side face

12.22

contact area

12.23

deepening

12.24

edge surface

12.3

third party

12.4

fourth page

12.51

lateral surface

13

blanking device

13.1

cleft group

13.11

gap

13.12

offset

13.13

Height

13.2

reflection surface

20

measuring tube

777

electronic measurement/operation circuit

A

outdoor area

Z

central area

Claims (13)

Ultrasonic transducer (10) of a clamp-on ultrasonic flowmeter (1), which flowmeter is set up to measure a flow rate or a volumetric flow rate of a medium flowing through a measuring tube (20), the ultrasonic transducer comprising: at least one transducer element (11 ), in particular a piezoelectric transducer element, which is set up to generate and/or detect ultrasonic signals; a coupling element (12) which is set up to conduct ultrasonic signals between the transducer element and the measuring tube and vice versa; wherein the transducer element is arranged on a first side (12.1) of the coupling element facing away from the measuring tube and is acoustically and mechanically coupled thereto; wherein the transducer element is set up to emit ultrasonic signals along a surface normal (11.1) of the transducer element, wherein a spatial emission profile of the ultrasonic signal has a central region (Z) with a first wavefront and an outer area (A) with a second wavefront, with normal vectors of the first wavefront have at most a maximum angle β ₁ to the surface normal, and wherein normal vectors of the second wavefront have at least a minimum angle β ₂ to the surface normal, the coupling element having a second side surface (12.21) with a contact area (12.22) on a second side (12.2) facing the measuring tube has, which second side surface is set up by means of the contact area to be acoustically and mechanically coupled to the measuring tube, wherein by applying the coupling element to the measuring tube in the direction of a measuring tube axis or measuring tube center line of the measuring tube, a third side (12.3) and a fourth side (12.4) opposite the third side, wherein the coupling element has a blanking device (13) which is set up to at least partially prevent the second wavefront from entering the measuring tube at least in sections, wherein the coupling element has a lateral surface (12.51), characterized in that the blanking device has at least one gap group (13.1) with at least one gap (13.11), which gap projects from the lateral surface into the coupling element, the gap being set up to extend into a spatial propagation area of the second wavefront, wherein the at least one gap is an air gap. ultrasonic converter claim 1 , wherein the gap (13.11) has a thickness, the thickness being perpendicular to the second side surface, the thickness of the gap being greater than 0.02 mm, and in particular greater than 0.05 mm and preferably greater than 0.1 mm, and/or less than 1.5 mm and in particular is less than 1.2 mm and preferably less than 1 mm. ultrasonic converter claim 1 or 2 , wherein the at least one gap group (13.1) comprises a plurality of gaps (13.11), which gaps are offset from one another in a direction perpendicular to the second side face, the perpendicular direction in each case defining a height (13.13) of each gap with respect to the second side face. ultrasonic converter claim 3 , where for an offset (13.12) of adjacent columns, the following applies: V=n*λ/2, where λ is a mean wavelength of the ultrasonic signal, and where n is a natural number. ultrasonic converter claim 3 or 4 , wherein the lowest gap of a gap group in terms of height (13.13) is an air gap, and at least one further gap is filled with an acoustically damping material, for example a foam material or a plastic. Ultrasonic transducer according to one of the preceding claims, wherein the first side has a coupling surface (12.11) facing the third side and inclined with respect to the second side surface, on which coupling surface the transducer element is arranged, the first gap group being arranged on the third side of the coupling element, and /or wherein a second gap group is arranged on the fourth side of the coupling element. Ultrasonic transducer according to one of the preceding claims, wherein the second side has a reflective surface (13.2) facing the third side and sloping with respect to the second side surface and/or a reflective surface (13.2) facing the fourth side and sloping with respect to the second side surface, which reflective surface respectively is set up to partially reflect the ultrasonic signal back into the coupling element in a spatial propagation range of the second wave front. ultrasonic converter claim 7 , wherein the oblique reflection surface (13.2) has a notch (13.21) which is designed to scatter the reflected ultrasonic signal. Ultrasonic transducer according to one of the preceding claims, wherein the second side surface has a depression (12.23) which is set up to prevent the second wavefront from entering the measuring tube at least in sections, the depression delimiting the contact area at least in sections. ultrasonic converter claim 9 , wherein the second side surface has an edge surface (12.24) which delimits the depression (12.23). Ultrasonic transducer according to any of the above Claims 1 until 8th , wherein the contact area (12.22) is produced by attaching a disc to the coupling element and/or an edge surface (12.24) by attaching a support ring to the coupling element. Ultrasonic transducer according to one of the preceding claims, wherein the following applies: β ₁ <15°, in particular <10°, preferably <5° and/or β ₂ >15°, in particular >10°, preferably >5°. Clamp-on ultrasonic flow meter (1) for measuring a flow rate or a volume flow of a medium flowing through a measuring tube (20) according to the transit time difference principle, comprising: At least one pair of ultrasonic transducers (10) with ultrasonic transducers according to one of the preceding claims, which ultrasonic transducers are arranged offset to one another on the measuring tube along a measuring tube axis of the measuring tube, the ultrasonic transducers of a pair being set up to transmit and receive ultrasonic signals alternately; an electronic measurement/operation circuit (777) for operating the ultrasonic transducers and for generating flow measurements.

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