WO2015028180A1

WO2015028180A1 - Ultrasonic transducer and ultrasonic flow meter

Info

Publication number: WO2015028180A1
Application number: PCT/EP2014/064597
Authority: WO
Inventors: Achim Wiest; Sascha Grunwald; Gebhard GSCHWEND; Pierre Ueberschlag
Original assignee: Endress+Hauser Flowtec Ag
Priority date: 2013-08-29
Filing date: 2014-07-08
Publication date: 2015-03-05
Also published as: DE102013109349A1

Abstract

The invention relates to an ultrasonic transducer (1), in particular for a flow meter or a level gauge, comprising a housing (1a) and a piezo element (7) arranged inside the housing (1a) for generating or receiving ultrasonic signals, wherein the housing (1a) comprises a housing portion having a housing wall (3a) through which housing wall (3a) the ultrasonic signals are transmitted from the piezo element (7) to a medium, and wherein near said housing portion the housing wall (3a) has at least one metallic layer on a face (8) which can be impinged upon by a medium. The invention further relates to an ultrasonic flow meter and to a device for determining the fill level of a measurement medium in a container.

Description

Ultrasonic transducer and ultrasonic flowmeter

The present invention relates to an ultrasonic transducer according to the preamble of claim 1 and an ultrasonic flowmeter.

In the field of ultrasonic transducer assemblies is already a variety of different

Structures and sequence of layers known.

Ultrasonic transducers are known which have sensor housings end faces from which ultrasound signals emerge from the ultrasound transducer or to which are emitted

Ultrasonic signals enter the ultrasonic transducer. These sensor housings are made of either metal or plastic (e.g., polyvinylidene fluoride). Plastic end faces are more likely to be used with clamp-on flowmeters that are not exposed to direct contact with the sample. Metal sensor housings are predominantly used in so-called in-line devices, in which the end face is in contact with the medium.

Inline devices in which the ultrasonic transducer is fixed in the measuring tube, often the problem arises that the acoustic properties, respectively the acoustic impedances Z ,, from the metallic housing wall are poorly adapted to the medium to be measured, resulting in reflections R of the can cause acoustic wave.

It is therefore an object of the present invention to provide an ultrasonic transducer in which the above-described problems occur only reduced. The invention solves this problem by an ultrasonic transducer having the features of claim 1.

An inventive ultrasonic transducer, in particular for a flow meter or a level gauge, comprises a housing and a piezoelectric element disposed within the housing for generating or receiving ultrasonic signals, wherein the housing has a housing portion through which the ultrasonic signals are transmitted from the piezoelectric element to a medium, wherein the housing has a housing wall in the region of this housing section which has at least one metallic layer on an end face which can be acted upon by a medium.

This housing wall is preferably made of plastic or alternatively of aluminum.

The said housing portion may be integrally formed on the housing. Thus, the housing may be formed, for example, as a plastic injection molded article. Alternatively, in the case of a multi-part housing, said housing section may be formed merely as part of a single component of the housing. The end face can in particular be flat. However, other geometric design variants, such as conical, convex or concave end surfaces are conceivable. Through the housing wall, a better coupling of the ultrasonic signal to the medium, compared with the previously used steel housings. At the same time, the

Housing wall no or only a marginal small volume increase, provided they are provided with a metallic layer. This layer has the function of a

Diffusion barrier layer. It may be formed in a particularly preferred variant as a coating. Alternatively, the layer can also during the manufacturing process of

Housing wall to be connected to the same. This can e.g. during injection molding of the housing wall by casting the plastic onto a metal foil.

Advantageous embodiments of the invention are the subject of the dependent claims.

It is advantageous if the housing section is completely made of plastic and provided with a metallic layer.

It is advantageous if the metallic layer has a metal species selected from the following metals: copper, nickel, gold and chromium. These metals are on the one hand

comparatively diffusion-tight and have good chemical and mechanical resistance.

The plastic may in particular be a polyetherimide, a polyethylene and / or a polyamide. These dimensionally stable plastics allow a good adaptation between the piezo element and the measuring medium.

The housing portion is preferably formed as a cap and therefore individually exchangeable and manufacturable.

To protect the housing wall from diffusion of the coupling medium has the

Housing wall on the medium-contacting face opposite surface advantageously a metallic layer. The volume increase of the housing wall upon contact of the housing section with a medium is preferably less than 0.5 vol.%.

For a particularly reliable diffusion barrier of a layer in the form of a coating, it is advantageous if the layer thickness of the metallic coating is 0.5 to 500 μm.

It is advantageous if the coating has a first layer of 5-100 nm arranged on the plastic. This layer preferably serves as an adhesion-promoting layer and may, for example, also be a metallic layer. The second upper or

medium-loadable metallic layer serves as the actual diffusion barrier and preferably has a layer thickness of 350-3000 nm. The medium with which the metallic layer is applied is in the case of

Flowmeter primarily the measuring medium. In the case of a fill level measuring device, this does not necessarily have to be the measuring medium, but it can also be, for example, condensed liquid drops, solvent vapors or the like, which are arranged above the measuring medium.

Between the plastic of the housing wall and a first layer of a metallic coating formed as a metallic coating, a conductive ink is preferably provided. This is advantageous to apply a galvanic coating. With such

Coating method, even larger layer thicknesses can be applied to the housing wall. A conductive ink creates optimum conductivity and a good conductivity

Surface adhesion for the galvanic coating system.

Alternatively or additionally, the housing wall or the housing section may consist of a conductive plastic. This allows a better attachment of an electrode (cathode) of the galvanic plant on the object to be coated.

The housing of the ultrasonic transducer can advantageously be constructed in several parts, wherein the cap is connected to a support sleeve for fixing the ultrasonic transducer in the wall of a measuring tube or a container, wherein the connection is made via a soft solder. To connect to the support sleeve, both the cap and the support sleeve in

Connection region have a metallic coating or consist of metal. The soft solder creates a cohesive and tight connection between the cap and

Stützhülse.Alternativ adhesive, in particular an epoxy resin or a silicone, for

Connection of the parts are used.

According to the invention, an ultrasonic flowmeter for determining the

Flow rate or the volume flow of a measuring medium, a measuring tube and at least two arranged along the measuring tube ultrasonic transducer according to claim 1, such that the ultrasonic transducers are partially in contact with the measuring medium. The determination of the flow rate or the volume flow is preferably carried out by means of the known transit time difference method. Depending on the operating mode, each of the two ultrasonic transducers functions both as transmitter of

Ultrasonic signals to the complementary ultrasonic transducer and as a receiver of ultrasonic signals from the complementary ultrasonic transducer.

According to the invention, a device for determining the level of a

Measuring medium in a container, the container, with an inner volume which is bounded by a container wall, and an ultrasonic level gauge with at least one ultrasonic transducer according to claim 1, which is fixed in the container wall and wherein at least the housing portion protrudes into the inner volume of the container.

Further advantageous embodiments of the invention are the subject of the dependent claims. The subject matter of the invention will be explained in more detail below with reference to an exemplary embodiment in the attached figures. They show:

Fig. 1 sectional view of a first ultrasonic transducer according to the invention; FIG. 2 is a perspective view of the first ultrasonic transducer; FIG.

Fig. 3 is a schematic representation of an ultrasonic flowmeter according to the invention; and

Fig. 4 is a schematic representation of an ultrasonic level gauge according to the invention.

1 and 2 show an ultrasonic transducer 1 of an ultrasonic flowmeter or a level gauge. In the following, the application of the ultrasonic transducer 1 with respect to an in-line flowmeter will be explained in more detail. representational

However, the ultrasonic transducer for a flowmeter described below does not differ from that of a level gauge. It should be noted, however, that in the case of the in-line flowmeter, the ultrasonic transducer is in direct contact with a measurement medium, whereas in the case of the level gauge (see FIG. 4)

Ultrasonic transducer in many applications is not necessarily in contact with the measuring medium M1, but with another medium M2 (solvent vapors, condensation droplets, air, etc.) in contact.

The ultrasound transducer (1) of FIG. 1 has a housing 1 a, which in FIGS. 1 and 2 has a two-part construction. Within the housing 1 a, a piezoelectric element 7 is arranged, which, depending on whether it is in a transmitting or receiving operation,

Transmits ultrasonic signals into the measuring medium or receives ultrasonic signals from the measuring medium. Between the piezoelectric element and the measuring medium, a housing section is arranged, which is formed in FIGS. 1 and 2 as a cap 3. The housing section has a housing wall made of plastic 3a, through which housing wall 3a the

Ultrasonic signals are transmitted from the piezoelectric element 7 to the measuring medium.

The housing wall has an end face 8 that can be acted upon by a medium, which is shown in FIGS. 1 and 2 as a flat end face.

The housing can of course be constructed in one piece or composed of more than two parts.

In the present embodiment, the ultrasonic transducer 1 also consists of a

Support sleeve 2 and the cap 3 mounted thereon with the end face 8. The support sleeve 2 may consist of a plastic or of a metal, such as stainless steel. It has a cavity, the arrangement of electronic components and / or for performing a non-illustrated line for signal picking up a received ultrasonic signal and / or Power supply of a piezoelectric element. The cavity can be potted by means of a potting material.

The cap 3 is made of plastic. This has the advantage of a significantly improved

Impedance matching between the measuring medium and the piezo element. This will be illustrated by the following formula:

The two indices stand for any media through which an ultrasonic signal is sent. Typical values for acoustic impedances are:

Water 1, 5 MRayl

Polyetherimide 2.5 MRayl

Aluminum 17 MRayl

Piezo element 18 ... 30 MRayl

Steel 42 MRayl

Also, the minimum of the reflection / maximum of the transmission of an intermediate layer Z ₂ - eg between piezoceramic Z-ι and water Z ₃ at a value of Z ₂ = ^ Z _x * Z _3rd

to find.

It follows that the difference for a typical inline ultrasonic transducer made with a steel housing with water is a worse combination than a plastic housing with water.

A corresponding plastic may be, for example, a polyetherimide (PEI), a polyethylene (PE) or a polyamide (PA). In particular, PEI is due to its high

Temperature resistance of up to 170 ° C is preferred.

Aluminum enclosures are also possible, which do not withstand the chemical processes but are protected by a suitable coating. Aluminum is no longer acoustically usable in a corrosive attack due to surface changes occurring and is only conditionally pressure-stable. These metallic housings have the advantage of better zone separation in the Ex area.

The cap 3 also has a cylindrical basic shape and a cavity which merges on one side into the cavity of the support sleeve 2. The cap 3 has the end face the said flat end face 8. Alternatively, pointed, concave or convex end faces are possible in further advantageous embodiment variants of the invention. Parallel to this flat end face 8 a planar piezoelectric element 7 is arranged in the cavity of the cap 3. Between the piezoelectric element 7 and the cap 3 further layers, respectively coupling and adaptation layers for better transmission of an ultrasonic signal from the piezoelectric element to the housing wall 3a or the cap wall can be arranged. An adaptation layer has the function of amplifying the transmission of the ultrasonic level between two materials or media (eg between piezo element and air). This is made possible by an adaptation of the acoustic impedance. The matching layer has a

Impedance, which lies between the impedances of the two materials to be adapted. The thickness of an adaptation layer is preferably close to the quarter-wave, ie a quarter of the wavelength of the ultrasound signal in the material of the matching layer.

A coupling layer has the function of coupling two active layers, e.g. the piezoelectric element and an adaptation layer. It is classically made of glue or one

Liquid like oil or fat. The layer thickness is usually lower than that of a matching layer and is usually below lambda tenths.

The support sleeve 2 also has two threads 2a and 6, wherein the thread 6 is provided for connection to a holder of a measuring tube of an ultrasonic transducer and the thread 2a is provided for connecting a signal transmission and / or power supply cable, not shown, for connecting the ultrasonic transducer to an evaluation unit of the ultrasonic flowmeter.

The support sleeve 2 has a joining edge 5. This joining edge 5 limits a receptacle in which the cap 2 is used in some areas. An overlap region 9 is inserted into the receptacle of the support sleeve.

Of course, the said overlap region 9 of the cap 3 can also be arranged on the inner circumference, provided that the support sleeve with geometric modification of the cap in a

Except the cap is plugged. Between the overlap region 9 of the cap 3 and the support sleeve 2, a seal may be used.

At the overlap region 9, a sealing groove 10 connects. In the sealing groove 10, a sealing ring can be used. It improves the tightness of the ultrasonic transducer 1 when it is mounted in a measuring tube relative to the measuring medium.

The end face 8 and, depending on the wall thickness, a part of the edge surface 11 adjoining the end face is in normal operation of the ultrasonic transducer 1 in an ultrasonic flowmeter in direct contact with the measuring medium.

The cap 3 is made of plastic and thus has a housing wall 3a made of plastic, which is arranged between the piezoelectric element 7 and the measuring medium. In the present embodiment, the ultrasonic signals generated by the piezoelectric element 7, in particular in the region of the end face 8, enter the measuring medium.

At least the end face 8 of the plastic cap is formed as a metallic layer in the form of a coating 4a. A metallic layer e.g. as a thin film can be defined as a cover layer of the cap also in the manufacturing process on the cap, e.g.

can be cast, but it can also be applied as a coating. The metallic layer on the cap prevents or reduces the diffusion of the measuring medium into the plastic material of the cap 3.

Therefore, the ultrasonic transducers according to the invention can be particularly preferably used in in-line ultrasonic flowmeters, in which the end face 8 of

Ultrasonic transducer permanently in contact with the measuring medium. Also at

Level gauges can also deposit condensation droplets on the surface of the ultrasonic transducer which tend to diffuse. Solvent vapors can also accumulate and are able to diffuse into plastic material.

By the metallic coating on the plastic wall of the cap 3 is a

Volume increase of the plastic by swelling preferably reduced to less than 0.5 vol%, or particularly preferably completely prevented. Due to the defined wall thickness of the cap in the region of the end face 8 during operation of the ultrasonic flowmeter, a more accurate measurement can take place.

Typical aggressive media that attack the plastic of the cap

for example, low molecular weight alcohols such as ethanol or methanol, tetrahydrofuran (THF), acetone or acetonitrile and hydrocarbons such as gasoline or diesel.

The metallic coating may be a single-layer or multi-layer coating.

A single-layer or multi-layer coating can preferably by

Vapor deposition, for example by vapor deposition, sputtering, arc,

Electron beam or laser beam evaporation take place. Also, a metal spraying and / or flame spraying using injection wires according to DIN EN ISO 14919 and

Metal spray powder according to DIN EN 1274 can be used advantageously for the job.

Also paintable metal coatings comprising at least one binder and more than 50 wt.%, Preferably more than 90 wt.% Metal particles can be used as a coating material. However, in the case of a single-layer coating, these are to be regarded as a less preferred embodiment variant than the abovementioned coating methods, since the binder can be partially dissolved depending on the measuring medium or a swelling can occur which, however, is lower compared to the plastic of the cap 3. Also preferred is a wet-chemical application of the topmost metal layer to the cap.

As a preferred method, the metal layer may be deposited by electrochemical deposition. Particularly preferred is a galvanic deposition or a chrome plating. Particularly in the case of galvanic deposition, the layer thickness of the coating can be adjusted by regulating the current density and / or the current intensity and / or the residence time in the electroplating bath.

The prerequisite for electrochemical deposition is a conductive surface.

For example, in the case of a multilayer coating, this may be applied to the plastic, for example as a layer of conductive ink (for example silver or graphite conductive ink).

Alternatively, the plastic material of the plastic cap metal particles, carbon or graphite particles are added during their production, so that the plastic cap is conductive even without additional conductive coating. This also has the advantage that an electrode in the subsequent electroplating is easier to connect to an electrode of a galvanic plant. Preferred metal species for the coating, in particular the galvanic coating copper, nickel and / or gold. A chromium plating of the plastic surface of the cap can be advantageous.

Of course, several different metal layers can be deposited one above the other galvanically on the substrate, so the end face. A preferred layer sequence is, for example, the plastic substrate of the cap, a chromium layer, a copper layer and a nickel layer.

The chromium layer and / or the copper layer can preferably be applied by means of PVD methods. Subsequently, the nickel layer can be applied galvanically.

Another advantage of the metallic coating is a better wettability of the

Metal coating of the face opposite to the pure plastic surface with the

Measuring medium. This results in a better acoustic adjustment between

Ultrasonic transducer surface and measuring medium.

The coating 4a in FIG. 1 preferably extends at least as far as the sealing groove 10, at which the ultrasonic transducer is sealed in a receptacle of the measuring tube. If a metallic coating is also provided in the overlapping region 9 of the cap 3, a gas-tight connection between the cap 3 and the support sleeve 2 can be achieved by soldering, in particular by means of a soft solder. By combining a plastic housing, especially inline sensors with a metallic coating instead of the usual steel housing, a higher

Sensitivity, higher accuracy, wider bandwidth, and better SNR ratio.

The medium resistance of the ultrasonic transducer can be determined by the choice of

Coating metal to be matched to individual measuring media.

In an embodiment as a cap, this can be used in existing ultrasonic transducers

be replaced without replacing the entire ultrasonic transducer.

In Fig. 2 also an inner coating 4b of the cap 3 is shown. This inner coating serves to protect the cap 3 from a coupling medium, e.g. Coupling fat may contain the hydrocarbon in the sensor. This inner coating is preferably also formed as a metallic coating.

Fig. 3 shows an ultrasonic flowmeter with a measuring tube 13 one and two

Ultrasonic transducer pairs 14 and 15 include the ultrasonic transducers 14A, 14B, 15A and 15B. However, it is also possible to provide only one ultrasonic transducer pair. These are connected to an evaluation unit 16. Determining the flow rate and the

Volume flow can be done in this structure using the transit time difference method. The ultrasonic transducers 14A, 14B, 15A, 15B can be designed in accordance with the exemplary embodiments illustrated in FIGS. 1 and 2. 4 shows an arrangement with an ultrasonic fill level measuring device which is arranged on or in a container 17. The container 17 contains a measuring medium M1 located therein and a further measuring medium M2, for example solvent vapors. The fill level measuring device comprises an ultrasonic transducer 18 and an evaluation unit 19 connected thereto. As can be seen, the ultrasonic transducer 18 is arranged on the lid or on the upper side of the container 17 on its container wall 17A. The ultrasonic transducer 18 is designed according to the embodiment shown in Fig. 1 or 2.

LIST OF REFERENCE NUMBERS

I ultrasonic transducer 1 a housing

2 support sleeve

2a thread

3 cap

3a housing wall 4a coating

4b internal coating

5 joining edge

6 threads

7 piezo element

8 face

9 overlap area

10 sealing groove

I I edge area

12 connection adapter

13 measuring tube

14 ultrasonic transducer pair

14A ultrasonic transducer 14B ultrasonic transducer

15 Ultrasonic transducer pair 15A Ultrasonic transducer 15B Ultrasonic transducer

16 evaluation unit

17 containers

17A tank wall

18 ultrasonic transducer 19 evaluation unit

M measuring medium

M1 measuring medium

M2 further medium

Claims

claims

Ultrasonic transducer (1), in particular for a flow meter or a

Level gauge, comprising a housing (1 a) and within the housing (1 a) arranged piezoelectric element (7) for generating or for receiving

Ultrasonic signals, wherein the housing (1 a) has a housing section with a

Housing wall (3 a), through which housing wall (3 a)

Ultrasonic signals from the piezoelectric element (7) are transmitted to a medium, characterized in that the housing wall (3a) at one with a medium

acted upon end face (8) has at least one metallic layer.

Ultrasonic transducer according to claim 1, characterized in that the

Housing (3a) at least in the region of the housing portion made of plastic or aluminum and is provided on the medium can be acted upon with the end face (8) with the metallic layer.

Ultrasonic transducer, according to claim 2, characterized in that the

Housing section completely made of plastic and is provided with the metallic layer.

Ultrasonic transducer according to one of the preceding sections, characterized in that the metallic layer comprises at least one layer of a metal species selected from the following metals: copper, nickel, gold and chromium.

Ultrasonic transducer according to one of the preceding claims, characterized in that the plastic is a polyetherimide, a polyethylene and / or a polyamide.

Ultrasonic transducer according to one of the preceding claims, characterized in that the housing portion is formed as a cap (3).

Ultrasonic transducer according to one of the preceding claims, characterized in that the housing wall (3a) on one of the medium-contacting end face (8) opposite surface has a metallic layer.

Ultrasonic transducer according to one of the preceding claims, characterized in that the volume increase of the housing wall (3a) upon contact of the

Housing section with a medium less than 0.5 vol.%

Ultrasonic transducer according to one of the preceding claims, characterized in that the metallic layer on the end face (8) and / or on the said end face (8) opposite surface as a metallic coating (4a, 4b) is formed, wherein the layer thickness of the metallic coating (4a, 4b) is 0.5-500 μιη.

10. Ultrasonic transducer according to one of the preceding claims, characterized in that the metallic layer on the end face (8) and / or on this end face (8) part of a multilayer metallic coating (4a, 4b), wherein a first layer arranged on the plastic has 5-100 nm and comprises a second layer of 350-3000 nm. 1 1. Ultrasonic transducer according to one of the preceding claims, characterized in that between the housing wall (3a) made of plastic and a first layer of the metallic coating (4a, 4b) is provided a conductive ink.

12. Ultrasonic transducer according to one of the preceding claims, characterized in that the housing wall (3a) or the housing portion of a conductive

Plastic exist.

13. Ultrasonic transducer according to claim 5, characterized in that the housing (1 a) of the ultrasonic transducer (1) is constructed in several parts, wherein the cap (3) with a support sleeve (2) for fixing the ultrasonic transducer (1) in the wall of a

Measuring tube or a container is connected, wherein the connection is made via a soft solder.

14. An ultrasonic flowmeter for determining the flow rate or the volume flow rate of a measuring medium (M) with a measuring tube (13) and at least two arranged along the measuring tube ultrasonic transducers (14A, 14B or 15A, 15B) according to claim 1, such that the ultrasonic transducer (14A , 14B, 15A, 15B) are partially in contact with the measuring medium (M). 15. Device for determining the level of a measuring medium (MI) in a container

(17), comprising the container (17), with an inner volume which is bounded by a container wall (17A), and an ultrasonic level gauge with at least one ultrasonic transducer (18) according to claim 1, which in the

Container wall (17A) is fixed and wherein at least the said

Housing portion of the ultrasonic transducer (18) protrudes into the inner volume of the container (17).