DE102015107567A1 - Arrangement comprising an ultrasonic transducer and clamp-on ultrasonic flowmeter - Google Patents

Abstract

The invention relates to an arrangement comprising an ultrasonic transducer, which is provided for emitting and receiving ultrasonic measuring signals, and a wall of a container and / or a tube, wherein i the ultrasonic transducer has a coupling element, via which the ultrasonic measuring signals under a predetermined input or Auskoppelwinkel coupled into the container and / or pipe or be coupled out of the container and / or the pipe, and ii the arrangement comprises a control / evaluation, based on the measured signals or based on measurement data, the are derived from the measured signals, determines the volume and / or mass flow of a flowing medium in the pipe or container and / or determines the level of the medium in the container, characterized in that the coupling element (11, 12) consists of a block of a consists of silicon-containing glass, and a clamp-on ultrasonic flowmeter

Description

The invention relates to an arrangement comprising an ultrasonic transducer and a clamp-on ultrasonic flowmeter.

Ultrasonic flowmeters are widely used in process and automation technology. They allow the volumetric and / or mass flow of a medium in a pipeline to be determined without contact.

The known ultrasonic flowmeters operate either on the Doppler principle or on the transit time difference principle. When running time difference principle, the different duration of ultrasonic measurement signals in the flow direction and against the flow direction of the medium is evaluated. For this purpose, the ultrasonic measuring signals are alternately transmitted or received by the ultrasonic transducers in the flow direction and counter to the flow direction of the medium. From the transit time difference of the ultrasonic measuring signals, the flow rate and thus at a known diameter of the pipe volume flow or at known or measured density of the medium mass flow can be determined.

In the Doppler principle, ultrasonic measurement signals are coupled into the flowing medium at a predetermined frequency. The reflected in the medium ultrasonic measurement signals are evaluated. On the basis of an occurring between the coupled and the reflected ultrasonic measurement signal frequency shift can also determine the flow rate of the medium or the volume and / or mass flow.

The use of flow meters, which operate on the Doppler principle, is only possible if in the medium air bubbles or impurities are present at which the ultrasonic measurement signals are reflected. Thus, the use of such ultrasonic flowmeters compared to the ultrasonic flowmeters, which operate on the transit time difference principle, rather limited.

With regard to the types of measuring instruments, a distinction is made between ultrasonic flow transducers, which are inserted into the pipeline, and clamp-on flow measuring devices, in which the ultrasonic transducers are pressed from the outside to the pipeline by means of a clamping closure. Clamp-on flowmeters are for example in the EP 0 686 255 B1 , of the U.S. Patent 4,484,478 or the U.S. Patent 4,598,593 described.

In both types of ultrasonic flowmeters, the ultrasonic measuring signals are radiated and / or received at a predetermined angle in the pipe or in the measuring tube, in / in which the flowing medium is located. In order to achieve optimum impedance matching, the ultrasonic measuring signals are coupled via a feed body or a coupling wedge in the pipeline or coupled out of the pipeline. The main component of an ultrasonic transducer is at least one piezoelectric element which generates and / or receives the ultrasonic measuring signals.

The ultrasonic measuring signals generated in a piezoelectric element are passed via the coupling wedge or the flow body and - in the case of a clamp-on Durchlflußmeßgeräts - on the pipe wall in the liquid medium. Since the velocities of sound in a liquid and in plastic are different from each other, the ultrasonic waves are refracted in the transition from one medium to the other. The angle of refraction itself is determined according to Snell's law, ie the angle of refraction in the transition from one medium to another is dependent on the ratio of the velocities of sound c _m , c _{n of} the two media n, m.

Mathematically, the Snellius law can preferably be represented according to the following abbreviated formula: c _n / sin α _n = c _m / sin α _m = const. (1)

c_n:

die Schallgeschwindigkeit z.B. im Koppelkeil, beispielsweise aus Kunststoff gefertigt ist;

c_m:

die Schallgeschwindigkeit z. B. im Medium, bei dem es sich beispielsweise um Wasser handelt;

α_n:

den Winkel zwischen dem Schallpfad und dem senkrechten Lot auf die Grenzfläche des Koppelkeils beim Durchstoßpunkt des Ultraschall-Meßsignals durch die Grenzfläche;

α_m:

den Winkel zwischen dem Schallpfad und dem senkrechten Lot auf die Grenzfläche des Mediums beim Durchstoßpunkt des Ultraschall-Meßsignals durch die Grenzfläche.

Here represents:

c _n:

the speed of sound, for example, in the coupling wedge, for example made of plastic;

c _m :

the speed of sound z. In the medium, which is, for example, water;

α _n :

the angle between the sound path and the perpendicular perpendicular to the interface of the coupling wedge at the point of penetration of the ultrasonic measuring signal through the interface;

α _m:

the angle between the sound path and the perpendicular Lot on the interface of the medium at the point of penetration of the ultrasonic measurement signal through the interface.

With mostly wedge-shaped coupling elements or plastic precursor bodies, a good impedance matching can generally be achieved; However, the speed of sound of plastic shows a relatively strong temperature dependence. Typically, that changes Sound velocity of plastic from about 2500 m / s at 25 ° C to about 2200 m / s at 130 ° C. In addition to the temperature-induced change in the transit time of the ultrasonic measurement signals in the plastic of the coupling wedge, the propagation direction of the ultrasonic measurement signals in the flowing medium also changes. Both changes have an unfavorable effect on the measurement accuracy in an ultrasonic flowmeter operating according to the transit time difference method. In addition, the propagation velocity in certain media also has a strong temperature dependence.

To reduce the temperature dependence of the coupling elements, it is from the WO 02/39069 A2 become known to expand the coupling element of a plurality of arcuate segments. Preferably, the segments are made of metal. The individual segments are arranged separately from each other and extend from a contact plane, which faces the piezoelectric element, to a base plate, which is in communication with the pipe wall. The length of the individual segments is dimensioned so that the ultrasonic measurement signals are radiated or received at the base plate at a predetermined angle. However, this embodiment is relatively expensive.

The invention has for its object to provide a clamp-on ultrasonic measuring device, the accuracy of which is relatively insensitive to temperature changes of the medium and / or the environment responds.

The object is achieved by an arrangement having the features of claim 1.

This arrangement comprises an ultrasonic transducer and a wall of a pipe or a container. The ultrasonic transducer is placed from the outside to a continuous wall area. To avoid air between the ultrasonic transducer and the wall, a coupling grease can additionally be used in a known manner.

The ultrasonic transducer is provided for transmitting and receiving ultrasonic measurement signals. Usually, for this purpose at least transducer element, e.g. a piezoelectric transducer element provided. These can be arranged one above the other as a single stack or as a so-called stack with several transducer elements. They convert a tension into mechanical movements and, conversely, can generate tension from mechanical movements. The mechanical movements are delivered in the form of ultrasonic waves via a coupling element and over the wall of the tube or container in the medium.

In the vast majority of cases, the ultrasonic transducer is associated with a level measuring device when arranged on a container. Since the invention has particular advantages, especially with hot media, level measurement can be applications from the field of hot sterilization or the like.

In the vast majority of cases, the ultrasonic transducer is associated with a flow meter when placed on a pipe.

The ultrasound transducer has a coupling element, via which the ultrasound measuring signals are coupled into the container and / or tube at a predetermined coupling-in or outcoupling angle, or are coupled out of the container and / or the tube. Corresponding coupling elements have been known for some time.

The arrangement comprises a control / evaluation unit which, based on measurement signals or on the basis of measurement data derived from the measurement signals, the volume and / or mass flow of a flowing medium in the pipe or container or alternatively or additionally to the level of a determined in the container medium. Usually, the ultrasound transducer and the control / evaluation unit are to be understood as a structural unit, which may be e.g. are integrated in an ultrasonic flowmeter or a level gauge.

The aforementioned coupling element according to the invention consists of a block of a silicon-containing glass. The glasses are based based preferably on silica and / or silicates. However, they can be enriched with a very high level of heavy metal species. These heavy metal species, e.g. Heavy metal oxides may also contain more than 50% by weight, e.g. 60-70 wt.%, To be contained in the silicon-based glass. The glass is an inorganic glass and not plastic glass, e.g. Acrylic glass.

In a preferred embodiment, the silicon-containing glass comprises at least 10% by weight of a silicon species such as e.g. Silica or a silicate, it preferably comprises at least 20% by weight of a silicon species.

In addition to the aforementioned coupling element, it is also possible to provide further coupling elements which can be combined to form a unit under the form and optionally also material connection. It is sufficient if one of these coupling elements is designed as a glass or silicate block.

Heavy metals in the context of the present invention include all metals with a density of more than 5 g / cm ³ .

Due to the use of a block of glass or silicate, the absorption of moisture e.g. Humidity through the coupling element at higher temperatures relatively low.

Advantageous embodiments are the subject of the dependent claims.

It is advantageous if the block of silicon-containing glass is designed as a coupling wedge. This applies in particular when used in a clamp-on flowmeter as the angle at which the ultrasonic signal enters the pipe wall and later also into the measuring medium is correspondingly precisely defined and changes only slightly with temperature changes.

The coupling wedge may advantageously have an angle of 20-60 °, wherein a vertex of the angle is the Auflagegläche the coupling wedge on the container and / or the tube

It is advantageous if the block of silicon-containing glass in each case has a content of a heavy metal species of more than 50 percent by weight. As a result, the density of the material is increased and adapted to the remaining elements of the arrangement. The heavy metal species is preferably a metal oxide.

It is advantageous if the block of silicon containing glass consists of heavy flint glass. has an acoustic impedance which is higher than that of plastic, whereby lower losses of signal components can be achieved by reflection

The density of the block is advantageously at least 3.5 g / cm ³ , preferably 4.0 to 8.5 g / cm ³ at 25 ° C.

The thermal coefficient of linear expansion of the block is preferably in the range of up to a maximum of 9.5 · 4 · 10 ^-8 K ^-1 (static measurement), in particular up to a maximum of 5 · 4 · 10 ^-8 K ^-1 .

The ultrasonic transducer has a sound-generating ultrasonic transducer element which is fixed in a form-fitting manner on one side of the coupling element. The positive connection can be achieved for example by a spring element which presses the transducer element against the coupling element.

The ultrasonic transducer element or the transducer element can also be fixed in a material-locking manner by means of an adhesion promoter on one side of the coupling element. Due to the adapted thermal expansion, the temperature does not rise when the ultrasonic transducer element is released.

According to one use of the arrangement according to one of the preceding claims for positioning a side of the on a wall of a pipe and / or a container with an outside temperature of this wall of more than 130 ° C. These high temperatures are usually problematic for coupling elements.

An inventive clamp-on ultrasonic flowmeter has at least two arrangements according to one of claims 1-10. The arrangements may preferably be configured in a one or two truss arrangement.

The invention will be explained in more detail with reference to the following drawings.

It shows:

1 a schematic representation of a known clamp-on ultrasonic flowmeter in two-truss arrangement; and

2 : A schematic representation of an arrangement of a clamp-on ultrasonic transducer on a pipe.

In 1 is schematically a clamp-on flowmeter 1 in a so-called two-truss arrangement 10 shown. For the present variant, this means that the signal traverses the tube cross-section twice before entering the medium, before it is received by. There are also other arrangements, such as Eintraversenanordnungen known. These arrangements can also be used in the same way in the context of the present invention

The flowmeter 1 determines the volume flow and / or the mass flow of the medium 10 in the tube 7 according to the known transit time difference method.

Essential components of the clamp-on ultrasonic flowmeter 1 are the two ultrasonic transducers 3 . 4 and the control / evaluation unit 9 , The two ultrasonic transducers 3 . 4 are by means of a in the 1 not shown separately fastening device to the pipe 7 appropriate. Corresponding fastening devices are well known from the prior art and are also offered and distributed by the applicant. The pipe 7 with a given inner diameter di is from the medium 2 flows through in the flow direction S.

An ultrasonic transducer 3 ; 4 comprises as essential components at least one piezoelectric element 5 ; 6 , which generates and / or receives the ultrasonic measuring signals, and a coupling wedge or a leading body 11 ; 12 , The ultrasonic measuring signals are transmitted via the coupling wedges 11 . 12 into the medium 10 flowed through pipe 7 coupled in or out of the pipe 7 decoupled. The coupling wedges 11 ; 12 determine the direction of irradiation or emission of the ultrasonic measuring signals from the tube or from the medium; above that they serve to optimize the impedance matching of the ultrasonic measuring signals during the transition into the tube 7 or from the pipe 7 ,

The two ultrasonic transducers 3 . 4 are positioned at a distance L from each other, wherein the distance L is chosen so that the highest possible energy shares that of an ultrasonic transducer 3 ; 4 emitted ultrasonic measuring signals in the respective other ultrasonic transducer 4 ; 3 Will be received. The optimal positioning depends on a large number of different system and / or process variables. These system and process variables are, for example, the inner diameter di of the tube 7 to the thickness of the pipe wall 8th to the speed of sound c _{3 of} the material from which the tube 7 is made, or the speed of sound c _{4 of} the medium 10 , In addition, the speed of sound in the different materials such as coupling wedge, pipe wall and medium have a more or less strong temperature dependence.

In the case shown, the distance L of the two ultrasonic transducers 3 . 4 so dimensioned that the ultrasonic measuring signals, which correspond to the transit time difference method alternately from the two ultrasonic transducers 3 . 4 be sent and received via the sound path SP in the medium 10 flowed through pipe 7 spread. The sound path SP has two traverses, so two crossings of the tube 7 on. The trusses can run diametrically or cordially.

2 schematically shows an embodiment of the ultrasonic transducer according to the invention 21 on average. The ultrasonic transducer according to the invention consists of at least two sub-elements, a sound-generating transducer element 20 , For example, a piezoelectric transducer element, and a coupling wedge 22 , also called flow body. successively from the ultrasonic measurement signals received from the transducer element 22 be sent and / or received.

The coupling / Auskoppelwinkel is essentially by the geometry of the Kopelkeils 22 determined, ie the geometry of the coupling wedge 22 is chosen so that as much energy as possible is the interface between the coupling wedge 22 and one of a medium 24 flowed through pipe 23 happens. The coupling or decoupling of a high energy component of the ultrasonic measurement signal is of crucial importance for a good measurement accuracy. In order to achieve the reliable measurement results over any period of time, it is also important that a specified optimized coupling / decoupling angle subsequently also remains constant. As mentioned, any deviation from the given value leads to a deterioration of the measurement accuracy. The problem is a permanent constancy of the Einstrahl- / failure angle in particular because the sound velocities in the different materials change more or less pronounced depending on the temperature.

Since the speeds of sound in liquids and plastics are different, the ultrasonic waves are refracted during the transition from one medium to another. The angle of refraction is determined by Snell's law. The angle of refraction is thus dependent on the ratio of the propagation velocities in the two media. Usually, as a coupling wedge, plastic materials, e.g. Polyetheretherketone or polyimides used. However, these tend to absorb water, which changes the material properties, or the speed of sound of an ultrasonic signal in the material changes.

As has been shown, silicates or even glasses of other silicon-containing inorganic materials are less problematic in terms of water absorption than plastic materials. Therefore, they are better suited as material for a coupling wedge.

Due to their high density, silicates and glasses of inorganic siliceous materials, each with a heavy metal species content of more than 50 weight percent, are particularly well suited as a coupling wedge material. They have a thermal expansion, which corresponds much closer to the thermal expansion of a piezoelectric transducer element than in the previously known plastic coupling wedges. As a result, a transducer element can be glued to the coupling wedge, without this solves the coupling wedge due to different thermal expansions. A preferred average thermal expansion coefficient (20 ° C, 300 ° C) is in the range of 4.0 4 · 10 ^-8 K ^-1 to 9.5 4 · 10 ^-8 K ^-1 (static measurement).

The thermal stability is also higher with silicates or glasses of silicon-containing inorganic materials than with plastic materials.

Particularly preferably, the material of the coupling wedge is a so-called heavy flint glass. These have mostly as heavy metal species lead oxide with more than 60 wt.%, Preferably more than 65 wt.%, On.

Straight heavy flint glass has an acoustic impedance which is higher than that of plastic, whereby lower losses of signal components can be achieved by reflection.

The sound velocities within a glass with high heavy metal contents and particularly preferably of heavy flint glass are relatively low due to the high density. This results in a very favorable angle for the construction of the coupling wedge. This can for example be a 45 °, so a similar angle as in the previously used plastic coupling wedges

An exemplary heavy flint glass, which has proven to be especially good for use at temperatures above 130 ° C is a glass Schott AG, which at the time of the first application present invention the name RD 50 wearing.

The density of the RD 50 is 5.05 g / cm ³ . However, silicates or inorganic glasses each having a proportion of a heavy metal species of more than 50 percent by weight have proven to be advantageous as ultrasonic coupling wedge, which have a density of more than 3.5 g / cm ³ . Particularly good sound-conducting properties even at temperatures above 100 ° C., silicon-containing glasses each having a proportion of a heavy metal species of more than 50 weight percent, which have a density between 4-6 g / cm ³ . The aforementioned densities can be determined for example by means of a pycnometer at 25 ° C in water.

In addition to or as an alternative to lead species, other metal species may also be added to the glass. These are preferably metal oxides, e.g. Tungsten oxide.

Typical sound velocities within the aforementioned wedge-shaped anorg. Glass bodies each having a heavy metal species content of more than 50% by weight are preferably 2500-3500 m / s at 25 ° C.

The above-described coupling wedge is preferably used in a Messanordung for ultrasonic flow measurement. The preferred applied

Flow measurement method is the so-called transit time difference measurement method.

However, it is also possible to fill the level e.g. to determine hot media in a pipe or a container by means of the aforementioned ultrasonic arrangement. In this case, the coupling element or the lead body does not need to be wedge-shaped as a coupling wedge but may be designed as a block, for example as a cylinder, as a rectangle, as a cuboid, as a prism or in another form. The same applies to the flow measurement according to the Doppler method here, the Einstahlwinkel can be 90 °, but the signal can also be introduced at a different angle in the medium.

LIST OF REFERENCE NUMBERS

1

 Clamp-on ultrasonic flowmeter

2

 medium

3

 ultrasound transducer

4

 ultrasound transducer

5

 Piezoelectric element

6

 Piezoelectric element

7

 Pipe / container

8th

 pipe wall

9

 Control / evaluation unit

10

 Two-Travers arrangement

11

 Coupling element / flow body

12

 Coupling element / flow body

20

 transducer element

21

 ultrasound transducer

22

 coupling wedge

23

 pipe

24

 medium

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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 assumes no liability for any errors or omissions.

Cited patent literature

• EP 0686255 B1 [0006]
• US 4484478 [0006]
• US 4598593 [0006]
• WO 02/39069 A2 [0012]

Claims (12)

Arrangement comprising an ultrasonic transducer, which is provided for emitting and receiving ultrasonic measuring signals, and a wall of a container and / or a tube, wherein i the ultrasonic transducer has a coupling element, via which the ultrasonic measuring signals under a predetermined coupling or. Decoupling angle coupled into the container and / or pipe or be coupled out of the container and / or the tube, and ii the arrangement comprises a control / evaluation unit, which are based on the measurement signals or based on measurement data derived from the measurement signals determines the volume and / or mass flow of a flowing medium in the pipe or container and / or determines the level of the medium in the container, characterized in that the coupling element ( 11 . 12 ) consists of a block of silicon-containing glass. Arrangement according to claim 1, characterized in that the block of silicon-containing glass is designed as a coupling wedge. Arrangement according to claim 1 or 2, characterized in that the block of silicon-containing glass each having a proportion of a heavy metal species of more than 50 weight percent. Arrangement according to claim 3, characterized in that the silicon-containing glass is designed as Schwerflintglas. Arrangement according to one of the preceding claims, characterized in that the density of the block is at least 3.5 g / cm ³ , preferably 4.0 to 8.5 g / cm ³ at 25 ° C. Arrangement according to one of the preceding claims, characterized in that the heavy metal species is a metal oxide. Arrangement according to one of the preceding claims, characterized in that the thermal coefficient of linear expansion of the block is in the range of up to a maximum of 9.5 4 · 10 ^-8 K ^-1 (static measurement), preferably less than 5 · 10 ^-8 K ^-1 . Arrangement according to one of the preceding claims, characterized in that the ultrasonic transducer has a sound-generating ultrasonic transducer element which is fixed in a form-fitting manner on one side of the coupling element. Arrangement according to claim 8, characterized in that the ultrasonic transducer element is also fixed material fit by means of a bonding agent on one side of the coupling element. Arrangement according to claim 2, characterized in that the coupling wedge an angle of 20-60 °, wherein a vertex of the angle is the Auflagegläche of the coupling wedge on the container and / or the tube. Use of the arrangement according to one of the preceding claims for positioning a side of the on a wall of a pipe and / or a container with an outside temperature of this wall of more than 130 ° C. Clamp-on ultrasonic flowmeter with at least two arrangements according to one of claims 1-10.

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