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WO2019001760A1 - Dispositif de mesure et procédé servant à déterminer une grandeur fluidique - Google Patents

Dispositif de mesure et procédé servant à déterminer une grandeur fluidique Download PDF

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Publication number
WO2019001760A1
WO2019001760A1 PCT/EP2018/000296 EP2018000296W WO2019001760A1 WO 2019001760 A1 WO2019001760 A1 WO 2019001760A1 EP 2018000296 W EP2018000296 W EP 2018000296W WO 2019001760 A1 WO2019001760 A1 WO 2019001760A1
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WO
WIPO (PCT)
Prior art keywords
measuring tube
fluid
vibration transducer
electrodes
electrode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/EP2018/000296
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German (de)
English (en)
Inventor
Michael MAYLE
Peter Ploss
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Diehl Metering GmbH
Original Assignee
Diehl Metering GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Diehl Metering GmbH filed Critical Diehl Metering GmbH
Publication of WO2019001760A1 publication Critical patent/WO2019001760A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
    • B06B1/0644—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element
    • B06B1/0662—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element with an electrode on the sensitive surface
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
    • B06B1/0688—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction with foil-type piezoelectric elements, e.g. PVDF
    • B06B1/0692—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction with foil-type piezoelectric elements, e.g. PVDF with a continuous electrode on one side and a plurality of electrodes on the other side
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H1/00—Measuring characteristics of vibrations in solids by using direct conduction to the detector
    • G01H1/12—Measuring characteristics of vibrations in solids by using direct conduction to the detector of longitudinal or not specified vibrations

Definitions

  • the invention relates to a measuring device for determining a fluid quantity concerning a fluid and / or a fluid flow of the fluid with a control device, a measuring tube receiving the fluid and / or a flow-through measuring tube and a first and a second spaced apart arranged on the measuring tube piezoelectric vibration transducer, wherein the control means of the first and / or the second vibration transducer are driven to excite a guided through a side wall of the measuring tube shaft, wherein the guided wave stimulates compression oscillations of the fluid via the fluid to the other Vibration converter feasible and there can be detected by the control device for determining measurement data, wherein the fluid size can be determined depending on the measured data.
  • the invention relates to a method for determining a fluid size.
  • ultrasonic counters One way to measure a flow through a measuring tube, are ultrasonic counters.
  • at least one ultrasonic transducer is used to couple an ultrasonic wave into the fluid flowing through the measuring tube, whereby it is guided on a straight path or after several reflections on walls or special reflector 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.
  • US Pat. No. 4,735,097 A proposes to use ultrasonic transducers for simplifying the measurement setup, which are fastened to the outside of the measuring tube. These are used to induce guided waves in the measuring tube, whereby a lower accuracy in the arrangement of the ultrasonic transducers on the measuring tube is required.
  • a wedge-shaped element is used whose longest side is pressed onto the tube wall and at the shortest side of which a piezoelectric element is arranged. This is vibrated to induce a guided wave in the tube wall via the wedge-shaped element.
  • the disadvantage here is that the measurement setup used is relatively complex and large-scale. Thus, in many measurement situations in which a flow measurement is desired, it is not or only with high wall usable.
  • piezoelectric element Seer modes are necessarily excited, typically, high excitation efficiencies are not typically achieved
  • a relatively elaborate, high-precision lithography is required to apply the required electrode structure with sufficient accuracy, while still often not achieving sufficient mode purity of the excitation.
  • excitation of a model-pure guided wave is highly relevant for use in an ultrasound counter, since 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 , Thus, if different modes are excited, then different propagation paths for the compression vibrations in the fluid, which can possibly be excluded by a complex signal evaluation result.
  • the invention is therefore an object of the invention to provide a measuring device, in particular an ultrasonic meter, which uses guided waves for the determination of measured data, with a small space requirement and a simple structure to be realized and preferably as pure as possible excitation of guided waves to be achieved.
  • the object is achieved by a measuring device of the type mentioned above, wherein either the first and / or the second vibration transducer each have exactly one measuring tube side electrode and exactly one Meßrohrabgewandte electrode, which are opposite to the side wall of the measuring tube parallel side surfaces of the respective vibration transducer are arranged, or wherein the first and / or the second vibration transducer a plurality of measuring tube side electrodes and at least one measuring tube facing away from the electrode or a plurality of measuring tube facing away Electrodes and at least one measuring tube-side electrode, wherein the control device is adapted to specify the voltages between the electrodes such that the sign of the voltage between a respective measuring tube side electrode and a respective electrode facing away electrode for all pairs of measuring tube side and measuring tube facing away electrodes of the respective Vibration converter is the same.
  • a vibration converter which, similar to the interdigital transducers discussed at the beginning, has side faces lying parallel to the side wall, ie in particular rests flat on the side wall or a coupling layer or another coupling element.
  • a small space requirement is realized.
  • an interdigital transducer which is locally differently polarized via the comb-like meshing electrode structures
  • Expansion and compression vibrations can be excited in most piezoelectric vibration transducers with higher efficiency than shearing vibrations, thus enabling more efficient vibration excitation.
  • the measuring device according to the invention which can be in particular an ultrasonic meter, can thus be particularly compact and allows a particularly efficient vibration excitation. The same applies if the vibration transducer is used to detect the vibrations. Due to the efficient vibration coupling the signal acquisition is improved.
  • a high mode purity for the excited guided wave can be achieved.
  • a high mode purity can be achieved by selecting the dimensions of the vibration transducer, ie in particular the piezo element used, even when using a single electrode on each side.
  • the vibration transducer is disposed on the sidewall such that two of its side surfaces are substantially parallel to the sidewall.
  • the vibration transducer may in particular be parallel to the outer surface of the side wall, if the outer surface and the inner surface of the side wall are shaped differently and / or are angled to one another. It is of course possible that there are production-related slight deviations from the parallelism.
  • the angle of inclination of the side surfaces of the vibration transducer to the side wall or to its outer surface may be less than 1 °, less than 3 ° or less than 5 °.
  • the vibration transducer may be an ultrasonic transducer.
  • the guided wave is in particular an acoustic ultrasonic wave.
  • the vibration transducer or the piezoelectric element which forms the vibration transducer can in particular be cuboidal. Measurements can be made on a fluid flow flowing through the measuring tube, but also on a fluid in the measuring tube.
  • the measuring device can also have more than two vibration transducers. By way of example, an oscillation emitted by a first oscillation converter can be divided by several second ones
  • Vibration transformers are detected, for. to consider different propagation paths or to validate measurement data.
  • a vibration transport for detecting fluid properties is known in principle in the prior art. For example, in ultrasound counters, transit time differences of a transit time of a vibration between a first and a second ultrasound transducer and vice versa are often detected and from this a flow velocity can be determined.
  • 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 relation in the fluid.
  • 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.
  • a speed of sound in the fluid and / or a composition of the fluid for example a mixing ratio of different components.
  • 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.
  • relationships 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.
  • the control device can specify the voltages for the electrodes as the respective temporal voltage curve. Alternatively, it is also possible that only the measuring tube-facing electrodes or only the measuring tube-side electrodes, a voltage waveform is fed and the respective other electrodes are at a fixed predetermined voltage potential.
  • the control device can act in particular on all the electrodes of a respective side surface of the vibration transducer with the same voltage.
  • the control device can be set up to predetermine the voltages between the electrodes in such a way that substantially no voltage drops between the measuring tube-side electrodes of the respective vibration converter and / or that substantially no voltage drops between the electrodes of the respective vibration converter facing away from the measuring tube. All electrodes of one side can thus be approximately at the same potential.
  • Potential differences can result, for example, from slight differences in the resistance of the supply lines.
  • the voltage difference between the electrodes of one side can be smaller by a factor of 100 or 1000 than the maximum voltage between electrodes of the different sides in the context of a voltage curve used for the control.
  • the first and / or the second vibration transducer may have exactly one measuring tube-side electrode and / or exactly one measuring tube facing away from the electrode.
  • the first and / or the second oscillation converter may have a plurality of strip-shaped electrodes whose distance corresponds to the wavelength of the guided wave, and / or the first and / or the second oscillation converter have a plurality of strip-shaped electrodes facing away from the measuring tube Distance of the wavelength of the guided wave corresponds.
  • Such structuring of the electrodes of at least one side face of the vibration transducer can be used to improve the mode selectivity of the excitation.
  • the wavelength of the guided wave can be predetermined by the excitation geometry and an excitation signal supplied by the control device, in particular an excitation frequency.
  • the excitation frequency can be fixed for the measuring device or adjusted as a function of operating parameters, for example as a function of an operating temperature, which can be detected, for example, via a temperature sensor of the measuring device.
  • the excitation geometry of the measuring device can be optimized to a defined frequency and wavelength of the guided wave in order to stimulate a guided wave with exactly these parameters as modestly as possible.
  • the wavelength and frequency of the guided wave to be excited are thus predetermined by the structural design of the measuring device.
  • An adaptation of an excitation frequency as has been explained above, can only serve to change the mode structure of the vibration transducer and / or of the measuring tube or of its side wall, for. B. due to a change in temperature to compensate.
  • the guided wave can be a lamb wave. Excitation of Lamb waves takes place when the wall thickness is comparable to the wavelength of the transverse wave of the solid. Such guided waves are combined pressure and shear waves and thus also lead to a deflection of the inner surface of the side wall in the direction of the fluid or away from the fluid. This deflection in turn causes compression waves in the fluid. The entire area within which the guided wave propagates on the side wall can thus serve as an excitation surface for a compression oscillation of the fluid. Conversely, a compression vibration of the fluid in a wall region of the side wall can excite a corresponding Lamb wave, which is then guided in the side wall to the other vibration transducer.
  • a mode selectivity of the excitation can be realized by an appropriate tuning of the vibration transducer and of the measuring tube or its side wall to one another. It is therefore possible that the first and / or the second Vibration converter and the measuring tube are formed such that a natural vibration of the vibration transducer has the same frequency and the same wavelength as the guided wave. If only relatively low oscillation modes, ie only relatively low spatial frequencies, are taken into account, then the oscillation converter has only a finite number of natural oscillation modes. For the teaching according to the invention, in particular compression oscillation modes perpendicular to the side wall are relevant here, since they are particularly strongly coupled into the side wall.
  • the measuring tube or its excited sidewall for guided waves in particular for Lamb waves or Rayleigh waves, has a dispersion relation which describes a clear relationship between their frequency and wavelength for each mode. If an excitation of the vibration transducer with a frequency corresponding to the frequency of a natural vibration of the vibration transducer, so results in a standing wave with a defined frequency and wavelength. If now the dimensions and the other parameters of the vibration transducer are chosen such that this combination of frequency and wavelength lies on or close to a branch of the dispersion relation for guided waves in the measuring tube or in the excited sidewall, then almost exclusively the branch associated with it Vibration mode excited. A mode selectivity can thus be achieved solely by using a correspondingly dimensioned vibration transducer or piezoelectric element.
  • a side length of the lateral faces of the vibration transducer parallel to the sidewall of the measuring tube may be the product of the wavelength of the guided wave with a scaling factor, the scaling factor being the sum of a natural number, that is an integer, and a number between 0.05 and 0.45 , in particular between 0.15 and 0.35.
  • This side length may in particular be the extent of the vibration transducer in a direction in which the guided wave is to be radiated, that is, for example, in a flow direction of the measuring tube. It has been found within the scope of the invention that optimum mode selectivity is unexpectedly achieved not at the side of integer or half-integer multiples of the wavelength but at approximately five quarters, nine quarters, thirteen quarters, etc. of the wavelength.
  • the concrete optimal scaling factors also depend on the specific electrode structure and the type of coupling of the vibration transducer to the measuring tube or the side wall.
  • An optimum value in the intervals given above can be obtained, for example, by a simulation of the sample. be determined empirically or empirically.
  • the side length of the vibration transducer in the propagation direction of the guided wave may be 4.1 mm.
  • a thickness perpendicular to the sidewall of the measuring tube can be chosen to match the frequency of the natural vibration of the vibratory transducer to the frequency of the guided wave at that wavelength.
  • the thickness can be about 2 mm.
  • the width of the vibration transducer perpendicular to the direction of propagation can be selected substantially freely and, for example, be 10 to 20 mm, for example, to extend over a large part of the width of the measuring tube.
  • the wavelength of the guided wave can be between 1, 6 mm and 2.2 mm, in particular between 1, 8 mm and 2 mm.
  • the control device can thus be set up to excite a guided wave having said wavelength and in particular a defined frequency.
  • the first and / or the second vibration transducer may be coupled to the measuring tube via a viscous coupling layer.
  • the coupling layer may have a viscosity of less than 10 8 mPas (millipascal seconds), in particular a viscosity between 0.6 mPas and 10 6 mPas.
  • a silicone oil can be used as a viscous coupling layer whose properties can be further adjusted by additives, for example introduced particles.
  • the layer thickness of the coupling layer can be between 10 and 100 ⁇ m.
  • a viscous coupling layer is advantageous in the ultrasonic transducer according to the invention for several reasons. On the one hand, this can achieve that there is no or only a slight coupling between the vibration transducer and the measuring tube or the side wall of the measuring tube with respect to shear forces. As a result, the vibration transducer and the measuring tube or its side wall with respect to their eigenmodes or the modes of the guided waves can be considered in good nutrition as separate systems, whereby the design of the vibration transducer for mode-selective excitation is facilitated.
  • the advantage is also achieved that tensions between the vibration transducer and the measuring tube are avoided with a change in temperature.
  • the measuring tube which is formed for example of metal or plastic, and the vibration transducer, the off a piezoceramic with applied electrodes, different thermal expansion coefficients. Due to the viscous coupling layer, these different expansions can be compensated without causing tension and thus, for example, an adhesive layer can become brittle over time.
  • the coupling layer is electrically insulating.
  • the measuring tube-side electrode of the vibration transducer for example, be isolated by the coupling layer of the measuring tube, if this is conductive.
  • the coupling layer may be, for example, a thin elastomeric film. It may be a film with a thickness between 5 pm and 80 pm, for example, be provided with a thickness of 20 pm.
  • a dielectric elastomer can be used.
  • the measuring tube-side electrode may be formed, for example, as an electrode plate, which extends beyond the vibration transducer to facilitate their contact.
  • the coupling layer could be electrically conductive. In particular, the electrodes may be contacted via the coupling layer.
  • the coupling layer may have a conductivity of more than 1 S / m (Siemens / meter), in particular more than 10 3 S / m. Preferably, even greater conductivities are realized. However, the said relatively low conductivities may be sufficient since no large currents have to be transported.
  • the coupling layer may contain metallic particles. On the one hand, this can serve to produce the abovementioned conductivity; on the other hand, the viscosity of the layer can be adjusted as required by adding particles.
  • the invention relates to a method for determining a fluid size concerning a fluid and / or a fluid flow of the fluid by a measuring device comprising a control device, a measuring tube receiving the fluid and / or by the fluid flow-through and a first and a second spaced apart on the measuring tube arranged piezoelectric vibration transducer, wherein the control means of the first and / or the second vibration transducer are driven to excite a guided through a side wall of the measuring tube shaft, wherein the guided wave stimulates compression oscillations of the fluid to the via the fluid are guided in each case to other vibration converters and detected there by the control device for determining measured data, the fluid size being determined by the control device as a function of the measured data.
  • a vibration transducer which either has exactly one measuring tube side electrode, and exactly one measuring tube facing electrode, which are arranged on opposite, parallel to the side wall of the measuring tube side surfaces of the respective vibration transducer, or a plurality of measuring tube-side electrodes and at least one measuring tube facing away from the electrode or electrodes and at least one measuring tube side electrode, wherein the control device specifies the voltages between the electrodes such that the sign of the voltage between a respective measuring tube side electrode and a respective Meßrohrab- facing electrode for all pairs from measuring tube side and measuring tube facing away electrodes of the respective vibration transducer is the same.
  • the inventive method can be further developed with those features that have been explained to the ultrasonic transducer according to the invention. Here, the advantages mentioned there are achieved.
  • FIG. 1 shows an embodiment of a measuring device according to the invention
  • FIG. 4 shows a detailed view of a further exemplary embodiment of a measuring device according to the invention, for example the tuning of the vibration converter and the measuring tube to each other for mode-selective excitation of the guided wave, and a further embodiment of a measuring device according to the invention.
  • FIG. 1 shows a measuring device, for example an ultrasonic counter, for detecting a fluid quantity concerning a fluid and / or a fluid flow of the fluid.
  • the measuring device 1 has a control device 2, a measuring tube 3 and a first and second ten spaced from each other on the measuring tube 3 arranged piezoelectric vibration transducer 5, 6.
  • the fluid is guided in an inner space 4 of the measuring tube 3 in the longitudinal direction 16 of the measuring tube 3.
  • a transit time difference of the signal propagation time from the first vibration transducer 5 to the second vibration transducer 6 and vice versa can be determined by the control device 2.
  • this transit time depends on a velocity component of the fluid parallel to a propagation direction of an ultrasound beam 15 through the fluid. From this transit time, a fluid velocity averaged over the path of the respective ultrasound beam 15 in the direction of the respective ultrasound beam 15 and thus approximately an averaged flow velocity in the volume traversed by the ultrasound beam 15 can thus be determined.
  • Such waves can be excited if the thickness 23 of the side wall 7 is comparable to the wavelength of the transverse wave of the solid, which results from the ratio of the sound velocity of the transverse wave of the solid and the excited frequency.
  • a relatively simple constructed vibration transducer is used to excite such a guided wave.
  • the oscillation converter 5 is formed from a block 8 made of piezoceramic, on whose opposite, parallel to the side wall 7 of the measuring tube 3 side surfaces in each case an electrode 9, 10 is arranged.
  • blocks of other piezoelectric materials, such as a composite piezoelectric ceramic could be used.
  • the measuring tube facing away electrode can be contacted directly.
  • an electrically conductive, viscous coupling layer 11 is used, via which the electrode 9 can be contacted.
  • the coupling layer may for example consist of silicone oil, wherein in addition metallic particles 22 are introduced into the coupling layer 11 in order to achieve a sufficient conductivity.
  • sealing elements 12 are provided.
  • a sheet-metal electrode which can protrude beyond the piezoelectric main body. This is particularly advantageous if an insulating coupling layer is to be used.
  • a sheet-metal electrode may, for example, rest loosely on the piezoelectric main body and be held there only by a contact pressure.
  • the coupling layer also serves to reduce or eliminate a coupling between the vibration transducer 5 and the side wall 7 and the measuring tube 3 with respect to a transmission of shear forces. In essence, therefore, only forces perpendicular to the side wall 7 are transmitted.
  • This extensive decoupling makes it possible to use the eigenmodes of the vibration converter 5, which, as will be explained in more detail later, for the mode-selective excitation of guided waves in the measuring tube 3 or in the side wall 7, approximately isolated from the coupling to the measuring tube 3 consider.
  • the excited Lamb wave is a combined shear and pressure wave.
  • a local deformation of the inner surface 24 of the side wall 7 results from the guided along the side wall 7 guided wave.
  • This results in a radiation of a compression wave in the fluid in the entire area within which the guided wave propagates.
  • This is illustrated schematically in FIG. 1 by the ultrasound beams 15, which are spaced apart from one another in the longitudinal direction 16.
  • a further guided wave in the side wall 7 is excited by the incoming compression waves, which is represented by the arrow 14 and is detected by the control device 2 via the vibration converter 5.
  • the radiation of the corresponding compression waves takes place in the Rayleigh angle 17, which depends on the speed of sound in the fluid and the phase velocity of the guided wave.
  • the dispersion relation for Lamb waves in the side wall 7 typically has several branches in the relevant frequency range.
  • the control device 2 Upon excitation with a given frequency given by the control device 2, it would thus be possible for different oscillation modes to be used for the lambda. Wave are excited, the different phase velocities and thus have different Rayleigh angle 17. Since the ultrasonic beams 5 involved in the measuring process would cover different paths in this case, a multipath propagation would result, which can significantly complicate the signal evaluation of the signals received at the vibration converter 6.
  • an exclusive or at least substantially exclusive excitation of a single vibration mode should take place.
  • Such a mode selectivity can be achieved if the dimensions shown in FIGS. 2 and 3 of the vibration transducer 5 or of the block 8 made of piezoceramics are correctly selected and a corresponding excitation frequency for the excitation by the control device 2 is used.
  • the eigenmodes can be defined in terms of their wavelength and their frequency. In this case, slight changes in the adaptation of the width 20 may occur, which can be considered in the context of the design of the vibration converter 5.
  • the coupling via the coupling layer 1 1 can, especially when using high viscosities, slightly influence the wavelengths or frequencies of corresponding eigenmodes.
  • the vibration transducer 5 has a natural vibration having the same frequency and the same wavelength as the guided wave to be generated.
  • the excitation via the guided wave vibration transducer 5 not only imposes a defined frequency but also a defined wavelength, whereby a mode-selective excitation takes place.
  • the side length 19 of the vibration converter 5 corresponds to approximately nine quarters of the wavelength of the excited Lamb wave in the side wall 7.
  • the measurement accuracy or the robustness of the measurement can z. B. be further improved by the fact that an additional vibration transducer 18 is provided, can be detected by the sig- nalauf 1952 for a portion of the path between the vibration transducers 5, 6. As a result, a flow variable determined from the signal propagation time can be validated and / or corrected.
  • electrodes 9, 10 can be used, which are substantially over the entire side surfaces of the vibration transducer 5 and of the block 8 of piezoceramic extend.
  • the mode selectivity of the excitation can be further improved if a plurality of electrodes facing away from the measuring tube or electrodes on the measuring tube side are used. An example of this is shown in FIG. In this case, a measuring tube-side electrode is also used. However, two separate electrodes 25, 26 are arranged on the side facing away from the measuring tube which is easier to contact. The distance 27 between the centers of these electrodes 25, 26 corresponds approximately to the wavelength of the Lamb wave to be excited.
  • the electrodes 25, 26 are supplied by the control device, a common drive signal, whereby the electrodes 25, 26 are at the substantially same potential.
  • a defined wavelength is imparted to the excitation of the oscillation converter 5, so that, in particular, an eigenmode having corresponding wavelengths with high purity can be excited. Accordingly, a higher mode purity for the generated Lamb wave in the measuring tube 3 or in the side wall 7 can be achieved.
  • the effect of a corresponding choice of the dimensions of the vibration transducer 5 is shown schematically in FIG.
  • the respective deflections of the vibration transducer 5 and the side wall 7 are greatly exaggerated in order to illustrate the operating principle.
  • a natural oscillation of the oscillation converter 5 is excited.
  • the nodes 29, 30 and the bellies 28 of the vibration are stationary.
  • the side length 19 of the vibration transducer 5 in the propagation directions of the guided wave, indicated by the arrow 13 is greater than twice the wavelength 31.
  • the fixed nodes 29, 30 and bellies 28 also in the Sidewall 7 excited Lamb wave imparted a fixed wavelength. Since an excitation with a fixed frequency and a fixed wavelength, results in a mode-pure excitation.
  • FIG. 6 Sidewall was reflected. However, this is not necessary for the explained measuring principle, so that an arrangement as shown in FIG. 6 can also be used.
  • the basic structure here corresponds to the structure shown in FIG. 1, wherein the first and second vibration transducers 5, 6 are arranged on opposite side walls. In an embodiment not shown it would be possible to use such an arrangement, wherein the ultrasonic waves are repeatedly reflected during the propagation through the fluid on the side walls.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Electromagnetism (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Measuring Volume Flow (AREA)

Abstract

L'invention concerne un dispositif de mesure (1) servant à déterminer une grandeur fluidique, comportant un tube de mesure (3) et un premier et un second transducteur de vibrations piézoélectrique (5, 6), le premier et/ou le second transducteur de vibrations (5, 6) pouvant être commandés pour exciter un arbre guidé par le biais d'une paroi latérale (7) du tube de mesure (3), l'arbre guidé excitant les vibrations de compression du fluide, celles-ci pouvant être guidées vers l'autre transducteur de vibrations (5, 6) respectif au moyen du fluide et y être déterminées, le premier et/ou le second transducteur de vibrations (5, 6) présentant respectivement exactement une électrode du côté du tube de mesure (9) et exactement une électrode du côté opposé au tube de mesure (10), ou le premier et le second transducteur de vibrations (5, 6) présentant plusieurs électrodes du côté du tube de mesure (9) et au moins une électrode du côté opposé au tube de mesure (10, 25, 26) ou inversement. Le dispositif de commande (2) est destiné à prédéfinir les tensions entre les électrodes (9, 10, 25, 26), de sorte que le signe de la tension entre une électrode respective du côté du tube de mesure (9) et une électrode respective du côté opposé au tube de mesure (10, 25, 26) est identique pour toutes les paires constituées d'électrodes du côté du tube de mesure et du côté opposé au tube de mesure (9, 10, 25, 26) du transducteur de vibrations (5, 6) respectif.
PCT/EP2018/000296 2017-06-29 2018-06-07 Dispositif de mesure et procédé servant à déterminer une grandeur fluidique Ceased WO2019001760A1 (fr)

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Application Number Priority Date Filing Date Title
DE102017006181.5 2017-06-29
DE102017006181.5A DE102017006181A1 (de) 2017-06-29 2017-06-29 Messeinrichtung und Verfahren zur Ermittlung einer Fluidgröße

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WO2019001760A1 true WO2019001760A1 (fr) 2019-01-03

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