DE102018003802A1 - Measuring device for determining a fluid size - Google Patents

Abstract

Measuring device for determining a fluid quantity concerning a fluid and / or a fluid flow of the fluid with a control device (2), a measuring tube (3) accommodating the fluid and / or by the fluid, and a first vibration transducer (5) arranged on the measuring tube (3) ), wherein the first vibration converter (5) comprises exactly one vibration device (16) or a plurality of spaced vibration devices (16), the vibration device (16) or the vibration devices (16) each consisting of a vibration body (17) and a measuring tube side electrode (18 ), which is arranged on a measuring tube side side surface (19) of the respective oscillating body (17), and a Meßrohrabgewandten electrode (20) on one of the measuring tube side side surface (19) opposite, Meßrohrrabgewandten side surface (21) of the oscillating body (17) is arranged , consists or consist, wherein the measuring tube-side electrode (18) and the Meßrohrabgewandte Elek (19) extend on a respective further side surface (22, 23) of the oscillating body (17) which is angled to the measuring tube side and the measuring tube facing side surface (19, 21), wherein by the control device (2) a voltage between the measuring tube side and the Meßrohrabgewandten electrode (18, 20) is variable in order to excite by the vibrating means (16) or by the vibrating means (16) of the first vibration transducer (5) together in a side wall (9) of the measuring tube (3) guided wave, the direct via the side wall (9) or indirectly at least partially via the fluid to a on the measuring tube (3) arranged second vibration transducer (6) or back to the first vibration transducer (5) feasible and there detectable by the control device (2) for determining measurement data is, wherein the fluid size can be determined by the control device (2) in dependence of the measured data.

Description

The invention relates to a measuring device for determining a fluid size which relates to a fluid and / or a fluid flow of the fluid.

One way to measure a flow through a measuring tube, are ultrasonic meters. In these at least one ultrasonic transducer is used to couple an ultrasonic wave into the fluid flowing through the measuring tube, which is guided on a straight path or after multiple reflections on walls or special reflection elements to a second ultrasonic transducer. From the transit time of the ultrasonic wave between the ultrasonic transducers or from a transit time difference at a permutation of transmitter and receiver, a flow rate through the measuring tube can be determined.

From the article G. Lindner, "Sensors and actuators based on surface acoustic waves propagating along solid-liquid interfaces", J. Phys. D: Appl. Phys. 41 (2008) 123002 , it is known to use for excitation of guided waves so-called interdigital transducers in which a piezoelectric element is used, which has comb-like intermeshing control lines to achieve excitation of certain excited modes of guided waves. Since shear modes of the piezoelectric element are necessarily excited, typically high excitation efficiencies are not achieved. In addition, a relatively complex, high-precision lithography is required to apply the required electrode structure with sufficient accuracy, although often sufficient mode purity of the excitation is not achieved.

However, excitation of a model pure guided wave is highly relevant for use in an ultrasound counter because the angle at which compression vibrations are radiated into the fluid depends on the phase velocity of the guided wave, which is typically different in different excitation modes at the same excited frequency. If different modes are excited, then different propagation paths for the compression oscillations in the fluid result, which can possibly be eliminated by a complex signal evaluation.

The invention is therefore an object of the invention to provide a measuring device that uses guided waves for measurement, with a small space requirement and simple design preferably a possible modest excitation of guided waves should be possible.

The object is achieved by a measuring device of the type mentioned above, comprising a control device, a fluid receiving and / or flowed through by the fluid measuring tube and disposed on the measuring tube, the first vibration transducer, wherein the first vibration transducer exactly one or more vibration device comprising spaced oscillating means, wherein the vibrating means or the vibrating means each of a vibrating body and a measuring tube side electrode which is arranged on a measuring tube side side surface of the respective oscillating body, and a Meßrohrrabgewandten electrode which is disposed on one of the measuring tube side side surface opposite, Meßrohrrabgewandten side surface of the vibrating body exists or exist, with the measuring tube side electrode and the measuring tube remote electrode extending to a respective further side surface of the oscillating body, the angled z u is the measuring tube side and the measuring tube facing away side surface, wherein by the control device, a voltage between the measuring tube side and the Meßrohrrabgewandten electrode is variable to jointly by the vibrating means or by the vibrating means of the first vibration transducer to excite a guided in a side wall of the measuring tube, the directly on the side wall or indirectly via the fluid to a arranged on the measuring tube second vibration transducer or back to the first vibration transducer and detectable there by the control device for determining measured data, wherein the fluid size can be determined by the control device in dependence of the measured data.

According to the invention it is thus proposed to excite a guided in the measuring tube shaft, which is used in the context of determining the fluid size by a vibrating device or together by a plurality of vibrating devices, in which the Meßrohrrabgewandte electrode and the measuring tube side electrode respectively on at least one respective further side surface of the vibrating body which may be formed, for example, by a block of piezoelectric material. In this case, it is known that guiding the measuring tube-side electrode along a further side surface or up to the side facing away from the measuring tube facilitates contacting of this electrode. In the context of the invention, however, it has been found that an asymmetrical electrode structure in which, for example, the measuring tube side electrode is at least partially guided around the oscillating body, while the measuring tube remote electrode is arranged exclusively on the side facing away from the measuring tube, the eigenmodes of the vibrating device influenced in a manner that at an as pure as possible desired excitation of guided waves in the side wall of the measuring tube can be a hindrance. From an asymmetric Arrangement of the electrodes results on the one hand asymmetry of the mechanical properties of the vibrating device and on the other hand, an asymmetric field distribution in the vibrating body when applying a voltage to the electrodes. It has been recognized that even in the case where substantially plane guided waves are excited perpendicular to the direction in which this asymmetry occurs, such asymmetry may prevent or at least aggravate mode-specific excitation. However, it has been recognized that such an asymmetry can be remedied by the fact that the electrode facing away from the measuring tube also extends to a further side face of the oscillating body or even extends up to the measuring tube-side side face. As a result, the symmetry of the electrodes and thus the symmetry of the entire oscillating device can be increased. It has been recognized that this is advantageous for exciting mode-pure vibrations.

If, for example, a substantially plane guided wave, for example in the longitudinal direction of the measuring tube, to be excited, this can be achieved that dimensions of the measuring device are tuned to a wavelength of a desired vibration mode to enhance their excitation, or to the wavelength of a attenuating vibration mode are tuned to suppress an excitation of this vibration mode or to reduce an amplitude of this vibration mode. If the measuring tube is excited, for example, in a plurality of excitation regions whose center distance corresponds to half the wavelength of a specific vibration mode at a currently used excitation frequency, then this oscillation mode is attenuated in the case of in-phase excitation or excitation with the same polarity and if the excitation is 180 ° resp a reverse polarity of the excitation in the excitation regions amplified. If, however, the distance between the centers of the excitation regions is an integer multiple of the wavelength of the corresponding oscillation mode, then the inverse relationship holds.

An in-phase excitation in spaced excitation regions can be achieved, for example, by coupling a vibrating device to the sidewall of the measuring tube only in these excitation regions. This is possible for example by a corresponding structuring of the side wall of the measuring tube, that is, for example, by the provision of spaced elevations or depressions, or by the use of a correspondingly structured coupling element between the oscillating device and the side wall.

Alternatively or additionally, a plurality of spaced-apart oscillation devices can be used, which are each coupled to one or more excitation regions. These can be operated in phase to achieve in-phase excitation in the associated excitation regions. Alternatively, the excitation signal may be inverted or phase shifted for portions of the vibrators to achieve phase shifted or inverted excitation.

Irrespective of the specific implementation of the excitation in the different excitation regions, subunits guided in the wall in each case can be excited by the oscillating device or oscillating devices in a plurality of spaced-apart excitation regions, which superimpose to the respective overall wave, the distance between the centers of the excitation regions and the excitation frequency are selected such that a vibration mode to be damped is at least partially extinguished by a destructive interference of the partial wave at least in a direction of propagation. In particular, when the vibrating device or the vibrating devices are to be operated resonantly, ie a natural vibration of the vibrating device or vibrating devices to be used for a particularly efficient excitation, asymmetric natural oscillations can reduce the achievable mode purity. This is avoided by the inventively provided increase in the symmetry by pulling both the Meßrohrabgewandten electrode and the measuring tube side electrode to a respective further side surface or this effect is reduced.

For a variety of measurement tasks, for example, to determine a flow, the shaft guided in the side wall to stimulate a compression vibration in the fluid. Lamb waves in the sidewall may preferably be excited for this purpose. These are combined pressure and shear waves, which results in a deflection of the inner surface of the wall in the direction of the fluid or away from the fluid even when excited on the outside of the wall of the measuring tube. As a result, compression waves are triggered in the fluid. The entire area within which the guided wave propagates on the wall can thus serve as an excitation surface for the compression oscillation of the fluid. Conversely, the compression vibration of the fluid in an extended area of the wall can in turn excite a guided wave that can be detected by the respective receiving vibration transducer. In this case, by the selected distance of the excitation regions and optionally by a choice of the sign or the phase in the superimposition of the measured signals detected in different excitation regions Wavelength selectivity and thus a mode selectivity of the measurement can be achieved. In the case of Lamb waves, two oscillation modes can always be excited even at low excitation frequencies, with the result that, as a result of the above-described damping of one of these oscillation modes, a largely pure mode excitation or measurement can take place.

In the measuring device according to the invention, the measuring tube side and the measuring tube facing side surface to each other and / or to an outer surface of the measuring tube may be substantially parallel, that is, they may include, for example, an angle of less than 5 °, less than 3 ° or less than 1 °. The further side surfaces may in particular be substantially perpendicular to the measuring tube side and / or the measuring tube facing side surface, that is, for example, with the vertical angle of less than 5 °, less than 3 ° or less than 1 °. The further side surfaces may in particular be substantially parallel to each other. The oscillating body may in particular be cuboid.

The electrodes may cover the further side surface on which they are arranged substantially completely, that is to say for example at least 70% or at least 80%. The measuring tube-side electrode may extend over the further side surface to the side facing away from the measuring tube and partially cover it and vice versa.

If a plurality of oscillating devices are used in the measuring device according to the invention, they can be arranged at a distance from one another, in particular in a longitudinal direction and / or in a transverse direction of the measuring tube. Preferably, all oscillating means are arranged at the same height in the direction perpendicular to the side wall of the measuring tube. In particular, oscillating devices or oscillating bodies are not stacked one above the other in the direction perpendicular to the side wall of the measuring tube. The spaced arrangement of the vibrating means means in particular that touch neither the vibrating body nor the electrodes of the various vibrating devices.

The measuring device according to the invention makes it possible to carry out measurements on a fluid flow flowing through the measuring tube, but also on a fluid in the measuring tube. The use of a vibration transport for detecting fluid properties is known in principle in the prior art. For example, transit times or transit time differences of a vibration are detected in ultrasonic counters already explained in the introduction, and from this a flow velocity or a flow rate can be determined. However, other measurement data can also be evaluated to determine fluid properties. For example, a signal amplitude at the receiving vibration transducer can be evaluated to detect a damping of the vibration during transport through the fluid. Amplitudes can also be evaluated frequency-dependent and absolute or relative amplitudes of specific spectral ranges can be evaluated in order to detect a spectrally different damping behavior in the fluid. Phase relationships of different frequency bands can also be evaluated in order, for example, to obtain information about the dispersion behavior of the measurement path. Preferably, information about the dispersion behavior of the pressure wave in the fluid and / or about the dispersion behavior of the guided wave in the side wall can be determined. Alternatively or additionally, it is also possible to evaluate changes in the spectral composition or the amplitude over time, for example within a measuring pulse.

By evaluating these variables, for example a flow rate and / or a flow volume and / or a density, temperature and / or viscosity of the fluid can be determined as fluid quantities. Additionally or alternatively, for example, a speed of sound in the fluid and / or a composition of the fluid, for example a mixing ratio of different components, can be determined. Various approaches for obtaining these fluid quantities from the above-explained measured variables are known in the prior art and are therefore not to be shown in detail. For example, correlations between one or more measured variables and the fluid size can be determined empirically, and it is possible, for example, to use a look-up table or a corresponding formula to determine the fluid size.

In some cases, it may also be possible to determine a fluid size exclusively as a function of the transport of the guided wave through the side wall of the measuring tube. For example, a pressure of the fluid can lead to a deformation of the force or a force on the side wall, whereby the properties of the side wall with respect to the transport of guided waves, in particular the speed of sound, can change. By detecting a transit time or the like can thus be concluded that the pressure of the fluid.

The measuring tube-side electrode can only at the measuring tube side side surface and exactly one of the other side surfaces and the Meßrohrabgewandte electrode exclusively on the side facing away from the measuring tube and exactly one other of the other side surfaces be arranged. Alternatively, the measuring tube side and the Meßrohrrabgewandte electrode may be disposed on a respective further side surface and the measuring tube side side surface and the measuring tube facing away side surface. In the first case, similar vibration modes are achieved, as in the case where the electrode facing away from the measuring tube is arranged exclusively on the side facing away from the measuring tube and the measuring tube side electrode is arranged exclusively on the measuring tube side side surface. It can thus be used for vibrational excitation, the entire base surface of the vibrating body, yet a slight contact can be achieved by providing the electrodes on the side surfaces. In the second case, guiding the measuring tube-facing electrode to the measuring tube-side side surface and vice versa, as will be explained in more detail later, leads to parts of the oscillating body being essentially field-free and thus not being excited to oscillate. This can be advantageous in order to support the oscillating device or to carry out a contacting in a non-oscillating or slightly oscillating region.

In the second case discussed, the partial surface of the measuring tube-facing side surface covered by the measuring tube-side electrode can be substantially smaller, for example at least a factor of 3, at least by a factor of 5 or at least 10 times smaller than the partial surface of the measuring tube facing away from the measuring tube facing electrode Side surface and vice versa. The extension of the respective electrodes to the side surfaces not assigned to them can serve exclusively for contacting the electrode or for providing non-oscillating regions or for producing symmetry, with an excessively large coverage area being disadvantageous.

The measuring tube facing away from the electrode and the measuring tube side electrode are insulated from each other. In the region of the oscillating device, the insulation can be effected, in particular, in that a region of the oscillating body is not provided with a conductive coating between the electrodes. By adapting the width or shape of this non-conductive coated partial area, it is possible in particular to adapt the electrical impedance of the oscillating device, since the capacitance between the electrodes depends on this. Thus, it is possible to adapt an electrical resonance frequency of a resonant circuit by adjusting the width or shape of this partial area. The shape of the electrodes and / or the degree of coverage of the vibrating body by the electrodes can also be used to specify a mechanical resonance frequency of the vibrating element.

The measuring tube facing away from the electrode, the measuring tube facing away inner side surface and the side surface to which it extends almost completely, so for example to cover at least 80% or 90%. Likewise, the measuring tube side electrode can almost completely cover the measuring tube side side surface and the associated further side surface.

The measuring tube side electrode and the measuring tube facing away from the electrode or the respective oscillating device may each have a 2-fold rotational symmetry. In other words, when the entire oscillating device is rotated, the measuring tube-side electrode is imaged by 180 ° about an axis of symmetry onto the electrode facing away from the measuring tube, and vice versa. This corresponds to a point symmetry of a section through the oscillating device perpendicular to the symmetry axis with respect to the two electrodes. Preferably, the entire vibrating element, apart from the polarization of the vibrating body, so for example, the piezoelectric material, so rotationally symmetrical. Obviously, due to production or design, slight deviations from the aforementioned rotational symmetry may occur. By way of example, the shape of the measuring tube-side electrode can deviate from the shape of the electrode facing away from the measuring tube by a maximum of 1 mm or 2 mm or 5 mm or by not more than 1%, 3% or 5% of the longest side length of the oscillating body.

A symmetrical configuration of the electrodes or of the entire oscillating device also results in a corresponding symmetry of the oscillation modes. Compared to oscillating devices in which only one of the electrodes is guided on the further side wall or the opposite side wall, thus the eigenmodes are less disturbed, which as explained above, may be advantageous for a mode-pure excitation. In addition, such a rotational symmetry of the oscillating device ensures that, apart from a polarization of the oscillating body, it is insignificant whether the measuring tube side side surface of the oscillating body or accidentally due to a faulty structure, the actual measuring tube facing side surface of the oscillating body is arranged towards the measuring tube. Such a "wrong" arrangement of the vibrating device on the measuring tube can thus be compensated by the fact that the polarity of the drive is reversed accordingly. As a result, the structure of the measuring device can potentially be simplified or a faulty arrangement of the oscillating devices on the measuring tube does not necessarily lead to a necessary rejection of the faulty built measuring device, but this can be used after simple corrective action.

The measuring tube-side electrode can cover at least 50% of the measuring tube-side side surface and / or the electrode facing away from the measuring tube facing the side surface facing away from the measuring tube. In addition or as an alternative, the measuring tube-side and the measuring tube-facing electrode may cover at least 50% of the respective further side surface on which they are arranged. Particularly preferably, the side surfaces are substantially completely covered by the respective electrode. If only the measuring tube facing away from the electrode side electrode disposed on the side facing away from the measuring tube, and vice versa, the respective electrode can cover the respective side surface substantially completely. If both electrodes are arranged on the side facing away from the measuring tube and the measuring tube side, then the available degree of coverage is lower, since space must remain for the respective other electrode and a non-conducting insulation strip lying between the electrodes.

The, the respective or each oscillating device may be cuboid, wherein the measuring tube side and the measuring tube facing side surface are spanned by a longitudinal direction and a transverse direction of the cuboid, wherein the vibrating device in the transverse direction at a first edge a first edge region and at an opposite second edge a second edge region In the first edge region, only the measuring tube-side electrode is arranged both on the measuring tube-side side surface and on the measuring tube-facing side surface, and in the second edge region, only the measuring tube-remote electrode is arranged both on the measuring tube-side side surface and on the measuring tube-facing side surface. When a voltage is applied between the electrodes, the edge regions of the oscillating device or of the oscillating body are thus largely field-free and, for example, there is no or only slight deformation of the oscillating body in the edge region, for example in the case of a piezoelectric vibrating body. The edge regions thus do not oscillate or have a significantly lower amplitude than other regions of the oscillating device and are therefore particularly suitable for supporting or contacting the oscillating device, wherein influencing of the eigenmodes of the oscillation during holding or contacting in these regions can be largely avoided ,

Preferably, the measuring tube side electrode is arranged on the further side surface, which limits the oscillating body in the first edge region in the transverse direction and vice versa.

The oscillating device can be fastened to a holding device in the first and / or the second edge region and / or the measuring tube-side electrode can be electrically contacted in the first edge region and / or the electrode facing away from the measuring tube can be electrically contacted in the second edge region. The holding device can be, for example, a housing or a carrier for the oscillating elements, which or in particular predetermines the relative arrangement of a plurality of oscillating devices used in a vibrating transducer to achieve, for example, a tuning of distances of excitation regions and a wavelength used for excitation, as explained above has been.

The measuring tube side and the measuring tube facing away electrode can be electrically contacted on the side facing away from the measuring tube or on the other side surface, on which the respective electrode extends. This is advantageous because corresponding contact areas can be easily accessible even after an arrangement on the measuring tube. In the case of a lateral contacting or contacting of the side facing away from the measuring tube in the above-explained edge regions, contacting also takes place in areas which oscillate less, with which the contacts are less mechanically stressed.

The oscillating body can be formed from a piezoelectric material, for example from a piezoceramic. Preferably, exactly one block of piezoelectric material is used as oscillating body, which is contacted by exactly two electrodes, namely the measuring tube side and the measuring tube facing away from the electrode.

The measuring tube-side electrode can mechanically contact the measuring tube or a coupling element which couples the measuring tube to the vibrating element. The coupling element may in particular be insulating. In particular, the measuring device according to the invention preferably does not use oscillating elements or oscillating bodies stacked perpendicularly to the side face of the measuring tube. In other words, the oscillating devices are preferably not stacked or a stack height of exactly one oscillating device is used. Preferably, all vibrating means of a vibration transducer lie in a plane which extends parallel to the side wall of the measuring tube.

The measuring tube facing away from the side surface can apart from the electrode arranged away from the measuring tube or the thereto arranged measuring tube facing away from and measuring tube-side electrodes at least outside the edge regions cantilevered. In particular, neither the measuring tube facing side surface nor that portion of the measuring tube facing away from the electrode, which is arranged on the side facing away from the measuring tube, outside of the edge regions in contact with a further component of the measuring device. In this way, a disturbance of the eigenmode of the oscillating device or a damping of the oscillation can be avoided.

• 1 ein Ausführungsbeispiel einer erfindungsgemäßen Messeinrichtung,
• 2 eine Detailansicht eines Schwingungswandlers der in 1 gezeigten Messeinrichtung, und
• 3 eine Detailansicht eines Schwingungswandlers eines weiteren Ausführungsbeispiels einer erfindungsgemäßen Messeinrichtung.

Further advantages and details of the invention will become apparent from the following embodiments and the accompanying drawings. Here are shown schematically:

• 1 an embodiment of a measuring device according to the invention,
• 2 a detailed view of a vibration transducer of in 1 shown measuring device, and
• 3 a detailed view of a vibration transducer of another embodiment of a measuring device according to the invention.

1 shows a measuring device 1 for determining a fluid size which relates to a fluid and / or a fluid flow. The fluid is in this case in a by the arrow 7 shown direction through an interior 4 a measuring tube 3 guided. In order to determine the fluid size, in particular a flow volume, can by the control device 2 a transit time difference between the maturities of a first vibration transducer 5 to a second vibration transducer 6 and vice versa. This exploits that this transit time of a velocity component of the fluid parallel to a propagation direction of an ultrasonic beam 8th depends on the fluid. From this runtime can thus one on the path of the respective ultrasonic beam 8th average flow velocity in the direction of the respective ultrasound beam 8th and thus approximately an average flow velocity in that of the ultrasound beam 8th traversed volumes are determined.

On the one hand, an arrangement of the vibration transducer 5 . 6 outside the measuring tube 3 and on the other hand to reduce sensitivity to different flow velocities at different positions of the airfoil is achieved by the first vibration transducer 5 not directly an ultrasonic beam 8th , ie a pressure wave, in which fluid is induced. Instead, it is through the vibration transducer 5 a guided wave in the side wall 9 of the measuring tube 3 stimulated. The excitation occurs at a frequency chosen such that a Lamb wave in the sidewall 9 is stimulated. Such waves can be excited when the thickness 10 the side wall 9 comparable to the wavelength of the transverse wave in the solid, which results from the ratio of the sound velocity of the transverse wave in the solid and the excited frequency.

The through the vibration converter 5 in the sidewall 9 excited guided wave is schematically by the arrow 11 shown. The guided wave excites compressional vibrations of the fluid which are radiated into the fluid throughout the guided wave propagation path. This is schematically represented by the ultrasound beams staggered in the direction of flow 8th shown. The radiation is angled to the side wall 9 under the Rayleigh angle 14 , The radiated ultrasound beams 8th be on the opposite side wall 12 reflected and via the fluid back to the sidewall 9 guided. There, the impinging ultrasound beams are stirring 8th again a guided wave in the sidewall 9 at, which is indicated schematically by the arrow 13 is shown and by the vibration transducer 6 can be recorded to determine the term. Alternatively or additionally, it is possible to transmit the emitted ultrasonic waves via a vibration converter 15 to capture that on the sidewall 12 is arranged. In the example shown, the ultrasonic beams 8th on her path to the vibration converter 6 . 15 not or only once on the side walls 9 . 12 reflected. It would of course be possible to use a longer measuring section, the ultrasonic beams 8th several times on the side walls 9 . 12 be reflected.

In order to achieve a largely mode-pure excitation or a mode selectivity when detecting a vibration, are in the vibration transducers 5 . 6 each used one or more vibrating devices that the side wall 9 of the measuring tube 3 in contact with each other in the longitudinal direction of the measuring tube spaced excitation areas. This can be achieved by using a plurality of spaced oscillating devices or by a corresponding shaping of the side wall 9 or one, in particular insulating, coupling element, between the side wall 9 and the respective oscillating device is arranged. This makes it possible to use relatively simply constructed vibrating devices, which are described in detail below with reference to FIG 2 be explained.

2 shows a detail view of in 1 schematically illustrated vibration transducer 5 wherein a section through one of two used vibrating means 16 is being used. The vibrating equipment 16 are perpendicular to the image plane in 2 , So in the longitudinal direction of the tube, spaced from each other. Thus, by the operation of the vibrating means 16 the side wall 9 be excited in spaced excitation regions. This can be used for example to a largely pure mode excitation of a Lamb wave in the sidewall 9 to realize.

If relatively low excitation frequencies are used, lambda waves with exactly two wavelengths in the material of the sidewall are at a certain excitation frequency 9 excitable. The wavelengths depend on the dispersion relation in the sidewall 9 from. Now, for example, the distance between the centers of the vibrating devices 16 chosen such that it corresponds to half the wavelength of a vibration mode to be damped at this excitation frequency and the excitation is in-phase or with the same excitation signal, the vibration mode to be damped by superimposing the by the two vibrating devices 16 excited partial vibrations largely extinguished. The same applies if the distance corresponds to an integer multiple of the wavelength of the mode to be damped and the excitation takes place with the polarity reversed or with 180 ° phase offset. By spacing the vibrating means by a quarter of a wavelength of a vibration mode and an excitation with a phase shift of 90 °, a direction-selective radiation can be achieved. Thus, by appropriate choice or specification of an excitation frequency, the distance between the oscillating means and a relative polarity or phase position of the excitations of the various vibration means different excitation patterns can be realized.

To a simple structure of the vibrating equipment 16 To realize these are by a vibrating body 17 , For example, a block of a piezoelectric material, a measuring tube-side electrode 18 and a Meßrohrrabgewandte electrode 20 educated. The measuring tube side electrode 18 is primarily on the measuring tube side side surface 19 of the vibrating body 17 arranged and the Meßrohrrabgewandte electrode 20 primarily on the side facing away from the measuring tube 21 of the vibrating body 17 , The measuring tube side electrode 18 also extends over another side surface 22 and in a border section 27 on the side facing away from the measuring tube 21 , This allows contacting of both electrodes 18 . 20 on the side facing away from the measuring tube 21 ,

Would only the measuring tube side electrode 18 around the oscillating body 17 led to the top of the arrangement, this would cause the vibrating device 16 both with regard to their mechanical design and with regard to the resulting field distribution when a voltage is applied between the electrodes 18 . 20 would be asymmetrical. This would lead to asymmetric eigenmodes of the vibrating device 16 to lead. It has been recognized that this can lead to a lower mode purity or a lower mode selectivity when vibration is detected during vibration excitation. To avoid this is in the vibrating device 16 also the measuring tube facing away from the electrode 20 along one of the further side surfaces 22 opposite another side surface 23 to the opposite side of the vibrating body 17 led and is in the edge area 28 also on the measuring tube facing side surface 19 arranged. This leads to the measuring tube-side electrode 18 and the Meßrohrrabgewandte electrode 20 a 2-fold rotational symmetry about the symmetry axis 26 to each other. This corresponds in the illustrated sectional representation of a point symmetry with respect to the intersection of the axis of symmetry 26 with the picture plane.

Due to the arrangement of the electrodes shown 18 . 20 is the vibrating body 17 in the border areas 27 . 28 even with a concern of a voltage between the electrodes 18 . 20 largely field-free, whereby these areas are not or compared with the central region of the vibrating body 17 swing with a significantly reduced amplitude. This allows the contacts 24 . 25 for contacting the electrodes in these areas and an attachment via a holding device 29 , which attacks in these areas, the vibration of the vibrating device 16 not or at most slightly disturb or dampen.

To make a short circuit between the electrodes 18 . 20 To avoid are insulating areas 30 provided in which the vibrating body 17 not provided with a conductive coating. The shape and dimensions of the areas 30 influences the mechanical and electrical properties of the vibrating device 16 , In particular, affects the shape and width of the area 30 on the capacitance between the electrodes 18 . 20 from and thus, for example, to a resonant frequency of a resonant circuit, the resonant excitation of the vibrating device 16 can be used. In the context of the design process or production can thus, for example, by adjusting the width of the area 30 or a laser trimming the area 30 a desired electrical and / or mechanical resonance frequency can be realized.

3 shows one of the 2 corresponding detail view of another embodiment of a measuring device. Here, components with the same function are denoted by the same reference numerals. This in 3 The embodiment shown differs primarily by the formation of the electrodes 18 . 20 from the in 2 shown embodiment. Instead of the electrodes 18 . 20 in the respective border areas 27 . 28 to the respective opposite side surface 19 . 21 to draw, is a measuring tube side electrode 18 used exclusively along the measuring tube-side side surface 19 and exactly one more side surface 22 of the vibrating body 17 extends and a Meßrohrrabgewandte electrode 20 , which extends exclusively along the side facing away from the measuring tube 21 and exactly one more side surface 23 of the vibrating body 17 extends. Also, this arrangement of the electrodes has a 2-fold rotational symmetry with respect to the axis of symmetry 26 on. Thus, also in this case, the symmetry of the eigenmodes of the vibrations of the vibrating device 16 not disturbed. A contact is in this case, for example, via contacts 24 . 25 on the side surfaces 22 . 23 possible.

Another difference to that in 2 shown embodiment is that while in 2 the measuring tube side electrode 18 in direct contact with the side wall 9 of the measuring tube 3 is in 3 one between the electrode 18 and the side wall 9 arranged coupling element 31 is being used. This may be, for example, a thin elastic or viscous layer, on the one hand for holding the vibrating device 16 can serve on the side wall and on the other hand can serve that only perpendicular to the side wall 9 a force transfer between the vibrating device 16 and sidewall 9 is possible. As a result, for example, a coupling of shear modes of the side wall 9 and the vibrating device 16 be reduced or avoided, whereby the eigenmodes of the vibrating device 16 essentially independent of the vibration modes in the sidewall 9 can be considered. Such a coupling element can also be used to the vibrating device 16 in spaced apart excitation regions with the sidewall 9 of the measuring tube 3 to pair. For example, the coupling element 31 through in the direction perpendicular to the image plane in 3 be formed spaced strips. In this way, the excitation discussed above in spaced excitation regions, which can serve for the mode-pure excitation of Lamb waves or the like, even when using a single oscillating device 16 respectively.

The embodiments shown relate to a measuring device which detects a flow of a fluid, in which the propagation velocity of compression waves in the fluid is evaluated. The described embodiment of the vibrating device 16 However, it can also be used for other measuring devices that measure fluid size and in this case use guided waves in side walls of a measuring tube. For example, temperatures, pressures or the like can be detected. In some embodiments it may also be possible, instead of using two vibration transducers on the measuring tube, to use only one vibration transducer to which the guided wave is returned directly or through the fluid, for example by being reflected at a reflection element or after circulating around the measuring tube in the flow tube Side wall 9 ,

LIST OF REFERENCE NUMBERS

1

measuring device

2

control device

3

measuring tube

4

inner space

5

vibration transducer

6

vibration transducer

7

arrow

8th

ultrasonic beam

9

Side wall

10

thickness

11

arrow

12

Side wall

13

arrow

14

Rayleigh angle

15

vibration transducer

16

oscillating device

17

oscillating body

18

electrode

19

side surface

20

electrode

21

side surface

22

side surface

23

side surface

24

Contact

25

Contact

26

axis of symmetry

27

border area

28

border area

29

holder

30

Area

31

coupling element

QUOTES INCLUDE IN THE DESCRIPTION

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Cited non-patent literature

• G. Lindner, "Sensors and actuators based on surface acoustic waves propagating along solid-liquid interfaces", J. Phys. D: Appl. Phys. 41 (2008) 123002 [0003]

Claims (10)

Measuring device for determining a fluid quantity concerning a fluid and / or a fluid flow of the fluid with a control device (2), a measuring tube (3) accommodating the fluid and / or by the fluid, and a first vibration transducer (5) arranged on the measuring tube (3) ), wherein the first vibration converter (5) comprises exactly one vibration device (16) or a plurality of spaced vibration devices (16), the vibration device (16) or the vibration devices (16) each consisting of a vibration body (17) and a measuring tube side electrode (18 ), which is arranged on a measuring tube side side surface (19) of the respective oscillating body (17), and a Meßrohrabgewandten electrode (20) on one of the measuring tube side side surface (19) opposite, Meßrohrrabgewandten side surface (21) of the oscillating body (17) is arranged , consists or consist, wherein the measuring tube-side electrode (18) and the Meßrohrabgewandte Elek (19) extend on a respective further side surface (22, 23) of the oscillating body (17) which is angled to the measuring tube side and the measuring tube facing side surface (19, 21), wherein by the control device (2) a voltage between the measuring tube side and the Meßrohrabgewandten electrode (18, 20) is variable in order to excite by the vibrating means (16) or by the vibrating means (16) of the first vibration transducer (5) together in a side wall (9) of the measuring tube (3) guided wave, the direct via the side wall (9) or indirectly at least partially via the fluid to a on the measuring tube (3) arranged second vibration transducer (6) or back to the first vibration transducer (5) feasible and there detectable by the control device (2) for determining measurement data is, wherein the fluid size can be determined by the control device (2) in dependence of the measured data. Measuring device according to Claim 1 , characterized in that either the measuring tube-side electrode (18) exclusively at the measuring tube side side surface (19) and exactly one of the further side surfaces (22) and the Meßrohrabgewandte electrode (20) exclusively on the measuring tube facing away side surface (21) and exactly another of the other Side surfaces (23) is arranged, or that the measuring tube side and the Meßrohrrabgewandte electrode (18, 20) on the respective further side surface (22, 23) and the measuring tube side side surface (19) and the Meßrohrabgewandten side surface (21) are arranged. Measuring device according to Claim 1 or 2 , characterized in that the measuring tube-side electrode (18) and the Meßrohrabgewandte electrode (20) of the or the respective oscillating means (16) to each other have a 2-fold rotational symmetry. Measuring device according to one of the preceding claims, characterized in that the measuring tube side electrode (18) the measuring tube side side surface (19) and / or the measuring tube remote electrode (20) the Meßrohrabgewandte side surface (21) covered at least 50% and / or that the measuring tube side and the measuring tube facing away from the electrode (18, 20) at least 50% cover the respective further side surface (22, 23) on which they are arranged. Measuring device according to one of the preceding claims, characterized in that the or the respective oscillating device (16) is cuboidal, wherein the measuring tube side and the measuring tube facing side surface (19, 21) are spanned by a longitudinal direction and a transverse direction of the cuboid, wherein the oscillating means (16 ) in the transverse direction at a first edge of a first edge region (27) and at an opposite second edge has a second edge region (28), wherein in the first edge region (27) both on the measuring tube side side surface (19) and on the side facing away from the measuring tube ( 21) only the measuring tube side electrode (28) is arranged and in the second edge region (28) both on the measuring tube side side surface (19) and on the measuring tube facing side surface (21) exclusively the measuring tube remote electrode (20) is arranged. Measuring device according to Claim 5 , characterized in that the or the respective oscillating device (16) in the first and / or the second edge region (27, 28) is attached to a holding device (29) and / or that the measuring tube-side electrode (18) in the first edge region ( 27) and / or the Meßrohrabgewandte electrode (20) in the second edge region (28) are electrically contacted. Measuring device according to one of the preceding claims, characterized in that the measuring tube side and the measuring tube facing away from the electrode (18, 20) electrically on the side facing away from the measuring tube (21) or on the respective further side surface (22, 23), to which the respective electrode (18 , 20), are contacted. Measuring device according to one of the preceding claims, characterized in that the oscillating body (17) is formed from a piezoelectric material. Measuring device according to one of the preceding claims, characterized in that the measuring tube-side electrode (18) the measuring tube (3) or a coupling element (31), the measuring tube (3) with the vibrating device (16) couples, mechanically contacted. Measuring device according to one of the preceding claims, characterized in that the Meßrohrabgewandte side surface (21) apart from the measuring tube facing away from the electrode electrode (20) or the measuring tube facing away from the measuring tube side electrodes (18, 20) free-swinging at least outside the edge regions (27, 28) is arranged.

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