WO2008152060A1 - Method for measurement and/or monitoring of a flow parameter and corresponding device - Google Patents

Method for measurement and/or monitoring of a flow parameter and corresponding device Download PDF

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Publication number
WO2008152060A1
WO2008152060A1 PCT/EP2008/057295 EP2008057295W WO2008152060A1 WO 2008152060 A1 WO2008152060 A1 WO 2008152060A1 EP 2008057295 W EP2008057295 W EP 2008057295W WO 2008152060 A1 WO2008152060 A1 WO 2008152060A1
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WO
WIPO (PCT)
Prior art keywords
measuring tube
transducer elements
amplitudes
transducer
mechanical vibrations
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PCT/EP2008/057295
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German (de)
French (fr)
Inventor
Matthias Roost
Original Assignee
Endress+Hauser Flowtec Ag
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Application filed by Endress+Hauser Flowtec Ag filed Critical Endress+Hauser Flowtec Ag
Publication of WO2008152060A1 publication Critical patent/WO2008152060A1/en

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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
    • G01F1/76—Devices for measuring mass flow of a fluid or a fluent solid material
    • G01F1/78—Direct mass flowmeters
    • G01F1/80—Direct mass flowmeters operating by measuring pressure, force, momentum, or frequency of a fluid flow to which a rotational movement has been imparted
    • G01F1/84—Coriolis or gyroscopic mass flowmeters
    • G01F1/845—Coriolis or gyroscopic mass flowmeters arrangements of measuring means, e.g., of measuring conduits
    • G01F1/8468—Coriolis or gyroscopic mass flowmeters arrangements of measuring means, e.g., of measuring conduits vibrating measuring conduits
    • G01F1/849—Coriolis or gyroscopic mass flowmeters arrangements of measuring means, e.g., of measuring conduits vibrating measuring conduits having straight measuring conduits

Definitions

  • the invention relates to a method for measuring and / or
  • At least one flow parameter of a medium which medium flows through at least one measuring tube, wherein the measuring tube is at least temporarily excited by at least one transducer element, which is acted upon by an excitation signal to mechanical vibrations, being received by at least one transducer element, the mechanical vibrations of the measuring tube, and wherein from the transducer element at least one of the mechanical vibrations of the measuring tube corresponding receiving signal is generated.
  • the invention relates to a device for measuring and / or monitoring at least one flow parameter of a medium, which medium flows through at least one measuring tube, with at least one transducer element, which excites the measuring tube at least temporarily to mechanical vibrations, starting from an excitation signal, and at least one Transducer element which receives the mechanical vibrations of the measuring tube and generates a corresponding to the mechanical vibrations of the measuring tube receiving signal.
  • the flow parameter is, for example, the flow rate, the flow rate or the mass flow rate of the medium.
  • the medium is for example a liquid, a gas or generally a fluid which is present in one or more phases.
  • the measuring device is a meter tube or a two-meter tube system.
  • Coriolis meter which has two vibration exciters and a centrally arranged vibration receiver. By deposition or abrasion processes or by extraordinary parameters of the medium or the processes occurring, it can cause changes to the vibration exciters, or to the vibration receiver and thus to a loss of measurement accuracy come. Furthermore, asymmetries in the vibration excitation or associated measurement uncertainties in the vibration detection can occur.
  • the document WO 2006/036139 A1 describes a Coriolis meter, which has two vibration exciters and two vibration receivers mounted parallel thereto. In order to determine specific vibration variables of the measuring tube, the two vibration exciters are operated alternately. Either one or the other thus stimulates the measuring tube to oscillate. The vibrations occurring in each case are absorbed by the vibration receiver.
  • vibration converter which serve both the excitation of vibrations, as well as their detection (DE 103 51 310 A1).
  • the associated electronics for controlling the converter is in a special task, i. either designed for excitement or detection.
  • transducer elements which consist of piezoelectric material is described for example in the not yet published application DE 10 2005 059 070.
  • the invention has the object, the measurement of
  • This object is achieved by the invention by a method and a device.
  • the amplitude of the excitation signal of the transducer element is varied over time.
  • the amplitude of the excitation signal is thus not constant in time, but it is varied, ie the power at which the measuring tube is excited by the transducer element to mechanical vibrations is variable over time.
  • the amplitude of the generated vibrations each time-dependent.
  • This variation of the amplitude makes it possible to detect and quantify asymmetries and to take them into account when evaluating the received signals, ie when determining the flow parameter.
  • the reception property of the vibration-receiving transducer elements is varied over time.
  • the gain function for the reception is suitably varied, so that an override of the receiving unit is avoided. For example, when the excitation signal is increased, the gain of the receiving unit is appropriately reduced.
  • An embodiment of the method according to the invention provides that the amplitude of the excitation signal of the transducer element is varied continuously over time.
  • the amplitude changes continuously, i. no hard transitions are provided, but the variation in amplitude is continuous and uniform.
  • An embodiment of the method according to the invention includes that the measuring tube is at least temporarily excited by at least two transducer elements, which are each acted upon by an excitation signal to mechanical vibrations, and that the amplitudes of the respective excitation signals of the two transducer elements are varied over time.
  • two transducer elements are provided, the two excitation signals are varied over time. If the respective received signals are measured at the two locations of the transducer elements, the asymmetries can be calculated therefrom. The values obtained from this then serve to more accurately determine the flow parameter.
  • the two transducer elements are preferably located along an imaginary longitudinal axis of the measuring tube at different locations.
  • the measuring tube is thus superimposed on two points continuously excited to a vibration in the fundamental mode.
  • the excitation power is oscillating on the two Distributed transducer elements or the associated locations of the measuring tube.
  • This location-modulated excitation generates a continuous measurement-zero-point variation, which results from the different resonance properties when excited at different points on the measuring tube with different transducer elements.
  • the term zero point refers to the phases which result from the constituents of the measuring instrument itself in the received signal and which, if necessary, are subject to drift due to deposits or abrasion or due to process conditions such as, for example, the temperature.
  • Excitation (local) modulation allows the determination of the zero point of the mechanical system and additionally the system of transducer elements. Thus, asymmetries can be considered appropriately.
  • the measured value for the flow parameter is determined independently by evaluating the relative movement of the measuring tube at the two positions of the transducer elements in the frequency range of the mechanical resonance of the measuring system and corrected with the zero point of the mechanical system and the transducer system.
  • An embodiment of the method according to the invention provides that the amplitudes of the respective excitation signals of the two transducer elements are varied continuously over time. Even with two transducer elements thus a discrete and hard transition between the suggestions is avoided.
  • An embodiment of the method according to the invention includes that the amplitudes of the respective excitation signals of the two transducer elements are varied with a function dependent on a predefinable modulation frequency. Both transducer elements are thus subjected to excitation signals, which are modulated with a mathematical function dependent on a predefinable modulation frequency. Therefore, the variations of the two excitation signals are directly connected to each other, so that therefore the variation of one amplitude with a corresponding variation of the other amplitude accompanied.
  • An embodiment of the method according to the invention provides that the amplitudes of the respective excitation signals of the two transducer elements are varied with a sinusoidal function dependent on the predefinable modulation frequency.
  • An embodiment of the method according to the invention includes that the amplitudes of the respective excitation signals of the two transducer elements are varied such that the sum of the amplitudes is substantially constant over time.
  • the amplitude of the other excitation signal is correspondingly larger. In other words, the full power of the vibration excitation oscillates between the two transducer elements back and forth.
  • An embodiment of the method according to the invention provides that the modulation frequency of the function with which the amplitudes of the respective excitation signals of the two transducer elements are varied will dictate such that the modulation frequency is less than the frequency of the mechanical vibrations of the measuring tube.
  • the measuring tube is excited to the fundamental, so that the modulation frequency is below the fundamental frequency of the measuring tube.
  • An embodiment of the method according to the invention includes that the modulation frequency of the function, with which the amplitudes of the respective excitation signals of the two transducer elements are varied, will dictate such that the modulation frequency is greater than the frequency band within which the flow parameter varies. Depending on the medium or the process to which the medium is subjected, changes in the flow parameter may occur. This means that the flow parameter can also be subject to temporal variations. In this embodiment, consideration is given to this fluctuation in that the modulation frequency is higher than the bandwidth of this frequency.
  • the object is achieved for the device in that at least one control unit is provided which varies the amplitude of the excitation signal of the transducer elements in time.
  • the measuring device is thus designed such that a control unit is provided which varies the amplitude of the excitation signal of the transducer element over time, ie the power with which the measuring tube is excited by the transducer element to mechanical vibrations, is not constant over time, but changes over currently.
  • An embodiment of the device according to the invention includes that two transducer elements are provided, which stimulate the measuring tube, at least temporarily starting from each excitation signal to mechanical vibrations, as well as receive the mechanical vibrations of the measuring tube and one corresponding to the mechanical vibrations of the measuring tube Generate receive signal.
  • two transducer elements are provided which serve both the generation of the vibrations and their detection.
  • the transducer elements are mounted in the roots of the measuring tube or the measuring tubes.
  • the attachment in the roots of the measuring tube is particularly advantageous for the embodiment in which the transducer elements consist of piezoelectric elements.
  • at least one transducer element is mounted at the point of highest deflection of the Coriolis vibration mode of the measuring tube. This applies in particular to electrodynamic transducer elements.
  • only two transducer elements are provided. In this case, the invention makes it possible to measure the zero point properties of a measuring system having two excitation points for limited symmetry and to calculate them in the calculation of the Flow parameter, eg the mass flow measured value to be considered.
  • An embodiment of the device according to the invention provides that it is the piezoelectric elements in the two transducer elements.
  • An embodiment of the device includes that the control unit varies the amplitudes of the respective excitation signals of the two transducer elements in time.
  • the amplitudes of the two excitation signals of the two transducer elements are varied over time, i. the vibrations which generate the two transducer elements are superimposed with a modulation of the amplitudes.
  • asymmetries can then be detected and considered accordingly in the determination of the flow parameter.
  • An embodiment of the device according to the invention provides that the control unit varies the amplitudes of the respective excitation signals of the two transducer elements in time with a function dependent on a modulation frequency.
  • FIG. 1 shows a schematic representation of a Coriolis measuring device in a first variant
  • FIG. 2 shows a schematic representation of a Coriolis measuring device in a second variant
  • Fig. 3 a non-scale representation of the relevant frequencies in the method according to the invention.
  • a measuring tube 1 is shown, through which here, for example, for clarity from left to right the - flows or flows - not shown here - medium.
  • the medium is, for example, a liquid, a gas, a powder, a mixture or, in general, a fluid that can flow.
  • the first transducer element 2 On the input side of the measuring tube 1 is the first transducer element 2, which is for serves to excite the measuring tube 1 to mechanical vibrations.
  • the oscillation generation serves the outlet side, the second transducer element 3.
  • a further transducer element 4 is arranged, via which the mechanical vibrations of the measuring tube 1 are received.
  • the localization of the receiving transducer element 4 is only an example here. In the embodiment shown here, only one measuring tube 1, which is flowed through by the medium, is shown. However, the invention can also be applied to a system with two measuring tubes.
  • the control unit 5 acts on the two exciting transducer elements 2, 3 each with an excitation signal, which is, for example, an alternating electrical current. It takes place with an impressed current excitation and the resulting voltage is then measured. A phase match of current and voltage means that the measurement system resonates.
  • the frequency of the excitation signal preferably corresponds to the frequency of the fundamental vibrations of the measuring tube 1.
  • the amplitude of the excitation signal determines the oscillation amplitude to which the measuring tube 1 is excited by the corresponding transducer element 2, 3.
  • the third transducer element 4 shown here receives the mechanical vibrations of the measuring tube 1 and generates therefrom a received signal, which is usually also an electrical alternating voltage. From the phase difference between the excitation signal and the received signal, the flow parameter, e.g. determine the flow or mass flow of the medium.
  • the measuring tube 1 is excited once on the inlet side and then on the outlet side to vibrate.
  • asymmetric vibrations are generated.
  • the amplitudes of the excitation signals are changed continuously, so that an abrupt behavior of the vibration excitation is avoided.
  • the amplitude of each excitation signal is modulated with a sine function.
  • the two excitation signals are in this way with each other coupled, that a decreasing amplitude is connected at an excitation signal with a correspondingly increasing amplitude of the other excitation signal. The sum of the amplitudes of the two excitation signals is thus constant in time.
  • the embodiment with two excitation transducer elements and a receive transducer element is only an example. It can also be provided more transducer elements with different mounting location.
  • the transducer elements 2, 3 themselves, as well as their mechanical coupling to the measuring tube 1 can not be realized identically in general for the two positions in which they are located. This thus existing coupling asymmetry is just as the measuring tube symmetry itself exposed to the temperature and influenced by drifting mechanical forces. For exact determination of the measuring tube asymmetry, therefore, the zero point properties of the transducer elements must each be determined separately. That It must be determined which phases are thus independent of the influence of the flow parameter, as only thus can be reliably determined which phase of the flow parameters generated in conjunction with the Coriolis effect.
  • the asymmetry is measured.
  • the group delay of the transducer elements has to be measured.
  • such a measurement can take place outside the normal measuring mode or during the measuring mode.
  • at one of the two positions of the two transducer elements 2, 3 a not shown here additional transducer element in the most symmetrical arrangement possible to the existing transducer element.
  • the already existing transducer element 2 or 3 is used for Coupling of the excitation energy according to the described location-modulated method.
  • the additional - not shown here, but located at the same location as the transducer element 2 or 3 - transducer element allows the measurement of the relative group delay over the existing transducer element. It is to the group delay between the sensor signals of the two transducer elements, which are located at the same place, measured, and this for both positions.
  • the relative group delay between two transducers at the same position shows the superposition of the term of the one converter with a modulated duration of the other converter at the same place.
  • the amount of modulation of the superimposed transducer group delay can be determined by demodulation and corresponds to the current duration of the exciting transducer element at the respective position.
  • the transducer group delay per position, i. the respective one
  • Transducer element zero point can be used to determine the exact, mechanically relative movement between the two positions of the transducer elements along the measuring tube 1. In turn, directly from the flow parameters, such as the mass flow can be determined.
  • S 1 is the oscillation amplitude at the transducer position i at time t
  • a 1 the amplitude maximum at the transducer position i, f ( ⁇ the mechanical natural frequency or the resonance frequency of the measuring system and ⁇ , ⁇ f m , d additional phase angle at the transducer position i caused by mechanical asymmetry and excitation locus modulation with / ⁇ n () d .
  • T 12 is the transit time difference between the transducer positions for
  • T fleets the transit time difference, caused by the mass flow of the medium through the measuring tube and 7 ⁇ nod the transit time difference, resulting from the excitation at the two different locations 1 and 2.
  • / mod is the oscillation frequency for the spatial modulation of the excitation.
  • the excitation and reception transducer elements of FIG. 1 have each collapsed to form a transducer element.
  • this variant is more advantageous than that of FIG. 1, since only two transducer elements are used here.
  • the excitation force is impressed on the measuring tube via a current and the deflection is measured via the measured voltage-in the electrodynamic case, the deflection speed.
  • transducer elements are used using piezoelectric transducers, with two transducer elements each being located at the same location relative to a longitudinal axis of the measuring tube in order to compensate for the transit time differences of the transducer elements.
  • the electro-mechanical transducer elements are mounted at two different positions on the measuring tube, for example, especially in the roots of the measuring tube.
  • the introduction of the exciter power and the measurement of the measuring tube movement with two different transducer elements take place at the same position on the measuring tube, wherein the one element performs the excitation function and the other the receiving function.
  • FIG. 2 it is shown that in each case a single transducer element assumes both functions.
  • the electro-mechanical transducer element may be an electro-dynamic coil system or a piezoelectric element.
  • the control unit 5 is also here for a measuring circuit with two
  • the measuring tube 1 as a whole is continuously excited by the transducer elements 2, 3 or by the control unit 5, so that the natural frequency (resonant frequency) of the mechanical system is maintained in the fundamental mode.
  • the excitation power at the two transducer elements 2, 3 on the measuring tube 1 is modulated with a predetermined modulation frequency fmod between zero and the currently required exciter power.
  • the modulation takes place in such a way that the sum of the two exciter powers at both converter elements 2, 3 is not modulated and corresponds to the currently required exciter power, i. the sum of the two amplitudes is constant.
  • the measured value for the flow parameter is thereby determined by utilizing the Coriolis effect from the relative movement between the two positions of the two transducer elements 2, 3. It is specifically the difference of the eigenvector phase angles.
  • a with respect to the excitation modulation mechanical and electrical asymmetry of the transducer system, e.g. by drift, temperature, etc., is expressed in the modulation of the measured value of the flow parameter with the modulation frequency fmod of the excitation.
  • the modulation is due to the fact that in asymmetry between the positions of the two transducer elements 2, 3 different eigenvector phase angles and amplitudes are measured.
  • This "zero point" modulation is thus a measure of the asymmetry of the system of the transducer elements and the measuring tube mechanism.
  • the asymmetry can be measured or calculated by demodulation with the modulation frequency of the amplitudes of the excitation signals. Based on this measured zero point information, the measured value for the flow parameter with respect to the converter-system asymmetry can then be corrected.
  • Fig. 3 is not drawn to scale and purely schematically the ratio of frequencies occurring.
  • the two excitation signals which are applied to the first 2 and the second excitation transducer element 3 in order to excite the measuring tube 1 in the fundamental mode to mechanical vibrations have in this embodiment, the same frequency, which corresponds to the fundamental frequency of the measuring tube 1: fG.
  • the frequency with which the amplitudes of the excitation signals are modulated: fmod is smaller than the fundamental frequency fG.
  • the modulation frequency fmod is higher than the frequency bandwidth Dfs within which the flow parameter can vary.
  • the lowest value of the frequency bandwidth Dfs is 0 Hz, i. the flow parameter is constant.
  • the amplitude and even the phase position of the mechanical zero point can be determined.
  • Coriolis phase difference which is proportional to the mass flow, superimposed with the zero-point modulation frequency. This can be filtered from the measured value. The separated
  • Zero Point Displacement Amplitude is a measure of the rigidity of the mechanical system and can be used as an independent measure for other compensation and monitoring purposes (eg for density, viscosity, abrasion, etc.).

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  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Measuring Volume Flow (AREA)

Abstract

The invention relates to a method for measurement and/or monitoring of at least one flow parameter of a medium, wherein said medium flows through a measurement tube (1), wherein the measurement tube (1) is excited at least temporarily into mechanical vibrations by at least one transducer element (2, 3) to which an excitation signal is applied, wherein at least one transducer element (4) receives the mechanical vibrations of the measurement tube (1), and wherein at least one reception signal corresponding to the mechanical vibrations of the measurement tube (1) is generated by the transducer element (4). According to the invention, the amplitude of the excitation signal of the transducer element (2, 3) is varied with time. In addition, the invention relates to a corresponding device.

Description

Beschreibung description
Verfahren zur Messung und/oder Überwachung eines Strömungsparameters und entsprechende VorrichtungMethod for measuring and / or monitoring a flow parameter and corresponding device
[0001] Die Erfindung bezieht sich auf ein Verfahren zur Messung und/oderThe invention relates to a method for measuring and / or
Überwachung mindestens eines Strömungsparameters eines Mediums, welches Medium mindestens ein Messrohr durchströmt, wobei das Messrohr zumindest temporär von mindestens einem Wandlerelement, welches mit einem Anregungssignal beaufschlagt wird, zu mechanischen Schwingungen angeregt wird, wobei von mindestens einem Wandlerelement die mechanischen Schwingungen des Messrohres empfangen werden, und wobei von dem Wandlerelement mindestens ein zu den mechanischen Schwingungen des Messrohres korrespondierendes Empfangssignal erzeugt wird. Weiterhin bezieht sich die Erfindung auf eine Vorrichtung zur Messung und/oder Überwachung mindestens eines Strömungsparameters eines Mediums, welches Medium mindestens ein Messrohr durchströmt, mit mindestens einem Wandlerelement, welches ausgehend von einem Anregungssignal das Messrohr zumindest temporär zu mechanischen Schwingungen anregt, und mit mindestens einem Wandlerelement, welches die mechanischen Schwingungen des Messrohres empfängt und ein zu den mechanischen Schwingungen des Messrohres korrespondierendes Empfangssignal erzeugt. Bei dem Strömungsparameter handelt es sich beispielsweise um die Durchflussgeschwindigkeit, den Durchfluss oder den Massendurchfluss des Mediums. Dabei ist das Medium beispielsweise eine Flüssigkeit, ein Gas oder allgemein ein Fluid, welches in einer oder in mehreren Phasen vorliegt. Bei der Messvorrichtung handelt es sich beispielsweise um ein Einmessrohr- oder um ein Zweimessrohr-System.Monitoring at least one flow parameter of a medium, which medium flows through at least one measuring tube, wherein the measuring tube is at least temporarily excited by at least one transducer element, which is acted upon by an excitation signal to mechanical vibrations, being received by at least one transducer element, the mechanical vibrations of the measuring tube, and wherein from the transducer element at least one of the mechanical vibrations of the measuring tube corresponding receiving signal is generated. Furthermore, the invention relates to a device for measuring and / or monitoring at least one flow parameter of a medium, which medium flows through at least one measuring tube, with at least one transducer element, which excites the measuring tube at least temporarily to mechanical vibrations, starting from an excitation signal, and at least one Transducer element which receives the mechanical vibrations of the measuring tube and generates a corresponding to the mechanical vibrations of the measuring tube receiving signal. The flow parameter is, for example, the flow rate, the flow rate or the mass flow rate of the medium. In this case, the medium is for example a liquid, a gas or generally a fluid which is present in one or more phases. By way of example, the measuring device is a meter tube or a two-meter tube system.
[0002] Bekannt ist im Stand der Technik (z.B. DE 10 2005 034 749 A1) ein[0002] It is known in the art (e.g., DE 10 2005 034 749 A1)
Coriolismessgerät, welches zwei Schwingungserreger und einen mittig dazu angeordneten Schwingungsempfänger aufweist. Durch Ablagerungsoder Abrasionsprozesse oder durch außergewöhnliche Parameter des Mediums oder der auftretenden Prozesse kann es zu Veränderungen an den Schwingungserregern, bzw. am Schwingungsempfänger und somit zu einem Verlust an Messgenauigkeit kommen. Weiterhin können Asymmetrien bei der Schwingungserregung bzw. damit verbundene Messunsicherheiten bei der Schwingungsdetektion auftreten.Coriolis meter, which has two vibration exciters and a centrally arranged vibration receiver. By deposition or abrasion processes or by extraordinary parameters of the medium or the processes occurring, it can cause changes to the vibration exciters, or to the vibration receiver and thus to a loss of measurement accuracy come. Furthermore, asymmetries in the vibration excitation or associated measurement uncertainties in the vibration detection can occur.
[0003] Das Dokument WO 2006/036139 A1 beschreibt ein Coriolismessgerät, welches zwei Schwingungserreger und zwei jeweils parallel dazu angebrachte Schwingungsempfänger aufweist. Um spezielle Schwingungsgrößen des Messrohres bestimmen zu können, werden die beiden Schwingungserreger alternierend betrieben. Entweder das eine oder das andere regt somit das Messrohr zu Schwingungen an. Die dabei auftretenden Schwingungen werden jeweils durch die Schwingungsempfänger aufgenommen.The document WO 2006/036139 A1 describes a Coriolis meter, which has two vibration exciters and two vibration receivers mounted parallel thereto. In order to determine specific vibration variables of the measuring tube, the two vibration exciters are operated alternately. Either one or the other thus stimulates the measuring tube to oscillate. The vibrations occurring in each case are absorbed by the vibration receiver.
[0004] Bekannt sind im Stand der Technik weiterhin Schwingungswandler, welche sowohl der Erregung von Schwingungen, als auch deren Detektion dienen (DE 103 51 310 A1). Die zugehörige Elektronik zur Ansteuerung des Wandlers ist dabei auf eine spezielle Aufgabe, d.h. entweder auf Erregung oder Detektion hin ausgestaltet.Also known in the prior art vibration converter, which serve both the excitation of vibrations, as well as their detection (DE 103 51 310 A1). The associated electronics for controlling the converter is in a special task, i. either designed for excitement or detection.
[0005] Die Verwendung von Wandlerelementen, die aus piezoelektrischem Material bestehen, ist beispielsweise in der noch nicht veröffentlichten Anmeldung DE 10 2005 059 070 beschrieben.The use of transducer elements, which consist of piezoelectric material is described for example in the not yet published application DE 10 2005 059 070.
[0006] Problematisch sind Asymmetrien im Messaufbau, welche zusätzlicheAre problematic asymmetries in the test setup, which additional
Phasen im Messsignal verursachen und die somit auch die Bestimmung des Strömungsparameters beeinflussen.Cause phases in the measurement signal and thus also influence the determination of the flow parameter.
[0007] Daher liegt der Erfindung die Aufgabe zugrunde, die Messung desTherefore, the invention has the object, the measurement of
Strömungsparameters dahingehend zu verbessern, dass Asymmetrien des Messaufbaus bei der Messung berücksichtigt werden.To improve flow parameters so that asymmetries of the measurement setup are taken into account in the measurement.
[0008] Diese Aufgabe löst die Erfindung durch ein Verfahren und eine Vorrichtung.This object is achieved by the invention by a method and a device.
[0009] Die Aufgabe wird erfindungsgemäß für das Verfahren dadurch gelöst, dass die Amplitude des Anregungssignals des Wandlerelements zeitlich variiert wird. Die Amplitude des Anregungssignals ist somit nicht zeitlich konstant, sondern sie wird variiert, d.h. die Leistung, mit welcher das Messrohr durch das Wandlerelement zu mechanischen Schwingungen angeregt wird, ist zeitlich variabel. Somit ist auch die Amplitude der erzeugten Schwingungen jeweils zeitabhängig. Diese Variation der Amplitude erlaubt es, Asymmetrien zu erkennen, zu quantifizieren und diese entsprechend bei der Auswertung der Empfangssignale, d.h. bei der Bestimmung des Strömungsparameters zu berücksichtigen. In einer weiteren Ausgestaltung wird auch die Empfangseigenschaft der die Schwingungen empfangenden Wandlerelemente zeitlich variiert. In dieser Ausgestaltung wird beispielsweise die Verstärkungsfunktion für den Empfang passend variiert, so dass eine Übersteuerung der Empfangseinheit vermieden wird. Beispielsweise wird bei einer Erhöhung des Anregungssignals die Verstärkung der Empfangseinheit passend zurückgefahren.The object is achieved for the method in that the amplitude of the excitation signal of the transducer element is varied over time. The amplitude of the excitation signal is thus not constant in time, but it is varied, ie the power at which the measuring tube is excited by the transducer element to mechanical vibrations is variable over time. Thus, the amplitude of the generated vibrations each time-dependent. This variation of the amplitude makes it possible to detect and quantify asymmetries and to take them into account when evaluating the received signals, ie when determining the flow parameter. In a further embodiment, the reception property of the vibration-receiving transducer elements is varied over time. In this embodiment, for example, the gain function for the reception is suitably varied, so that an override of the receiving unit is avoided. For example, when the excitation signal is increased, the gain of the receiving unit is appropriately reduced.
[0010] Eine Ausgestaltung des erfindungsgemäßen Verfahrens sieht vor, dass die Amplitude des Anregungssignals des Wandlerelements zeitlich kontinuierlich variiert wird. In dieser Ausgestaltung ist vorgesehen, dass sich die Amplitude kontinuierlich ändert, d.h. es sind keine harten Übergänge vorgesehen, sondern die Variation der Amplitude ist kontinuierlich und gleichmäßig.An embodiment of the method according to the invention provides that the amplitude of the excitation signal of the transducer element is varied continuously over time. In this embodiment, it is provided that the amplitude changes continuously, i. no hard transitions are provided, but the variation in amplitude is continuous and uniform.
[0011] Eine Ausgestaltung des erfindungsgemäßen Verfahrens beinhaltet, dass das Messrohr zumindest temporär von mindestens zwei Wandlerelementen, welche jeweils mit einem Anregungssignal beaufschlagt werden, zu mechanischen Schwingungen angeregt wird, und dass die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente zeitlich variiert werden. In dieser Ausgestaltung sind zwei Wandlerelemente vorgesehen, deren beide Anregungssignale zeitlich variiert werden. Werden an den beiden Orten der Wandlerelemente die jeweiligen Empfangssignale gemessen, so lassen sich daraus die Asymmetrien berechnen. Die daraus erhaltenen Werte dienen anschließend der genaueren Bestimmung des Strömungsparameters. Die beiden Wandlerelemente befinden sich vorzugsweise längs einer imaginären Längsachse des Messrohres an unterschiedlichen Orten.An embodiment of the method according to the invention includes that the measuring tube is at least temporarily excited by at least two transducer elements, which are each acted upon by an excitation signal to mechanical vibrations, and that the amplitudes of the respective excitation signals of the two transducer elements are varied over time. In this embodiment, two transducer elements are provided, the two excitation signals are varied over time. If the respective received signals are measured at the two locations of the transducer elements, the asymmetries can be calculated therefrom. The values obtained from this then serve to more accurately determine the flow parameter. The two transducer elements are preferably located along an imaginary longitudinal axis of the measuring tube at different locations.
[0012] In dieser Ausgestaltung wird somit das Messrohr überlagert an zwei Punkten kontinuierlich zu einer Schwingung im Grundmode angeregt. Dabei wird die Anregungsleistung pendelnd auf die beiden Wandlerelemente bzw. die damit verbundenen Orte des Messrohrs verteilt. Diese ortsmodulierte Anregung generiert eine kontinuierliche Messwert-Nullpunkt-Variation, welche sich aus den unterschiedlichen Resonanz-Eigenschaften bei Anregung an verschiedenen Punkten am Messrohr mit verschiedenen Wandlerelementen ergibt. Der Ausdruck Nullpunkt bezieht sich dabei auf die Phasen, welche sich durch die Bestandteile des Messgerätes selbst im Empfangssignal ergeben und welche ggf. bedingt durch Ablagerungen oder Abrasion oder durch Prozessbedingungen wie z.B. der Temperatur einer Drift unterliegen. Die kontinuierliche Auswertung der relativen Bewegung der Messrohre an den beiden Wandlerpositionen im Frequenzband derIn this embodiment, the measuring tube is thus superimposed on two points continuously excited to a vibration in the fundamental mode. The excitation power is oscillating on the two Distributed transducer elements or the associated locations of the measuring tube. This location-modulated excitation generates a continuous measurement-zero-point variation, which results from the different resonance properties when excited at different points on the measuring tube with different transducer elements. The term zero point refers to the phases which result from the constituents of the measuring instrument itself in the received signal and which, if necessary, are subject to drift due to deposits or abrasion or due to process conditions such as, for example, the temperature. The continuous evaluation of the relative movement of the measuring tubes at the two transducer positions in the frequency band of the
Anregungs-(Orts-)Modulation erlaubt die Bestimmung des Nullpunktes des mechanischen Systems und zusätzlich des Systems der Wandlerelemente. Somit können also Asymmetrien passend berücksichtigt werden. Der Messwert für den Strömungsparameter wird unabhängig durch Auswertung der relativen Bewegung des Messrohrs an den beiden Positionen der Wandlerelemente im Frequenzbereich der mechanischen Resonanz des Messsystems ermittelt und mit dem Nullpunkt des mechanischen Systems und des Wandlersystems korrigiert.Excitation (local) modulation allows the determination of the zero point of the mechanical system and additionally the system of transducer elements. Thus, asymmetries can be considered appropriately. The measured value for the flow parameter is determined independently by evaluating the relative movement of the measuring tube at the two positions of the transducer elements in the frequency range of the mechanical resonance of the measuring system and corrected with the zero point of the mechanical system and the transducer system.
[0013] Eine Ausgestaltung des erfindungsgemäßen Verfahrens sieht vor, dass die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente zeitlich kontinuierlich variiert werden. Auch bei zwei Wandlerelementen wird somit ein diskreter und harter Übergang zwischen den Anregungen vermieden.An embodiment of the method according to the invention provides that the amplitudes of the respective excitation signals of the two transducer elements are varied continuously over time. Even with two transducer elements thus a discrete and hard transition between the suggestions is avoided.
[0014] Eine Ausgestaltung des erfindungsgemäßen Verfahrens beinhaltet, dass die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente mit einer von einer vorgebbaren Modulationsfrequenz abhängigen Funktion variiert werden. Beide Wandlerelemente werden somit mit Anregungssignalen beaufschlagt, die mit einer von einer vorgebbaren Modulationsfrequenz abhängigen mathematischen Funktion moduliert sind. Daher sind die Variationen der beiden Anregungssignale miteinander direkt verbunden, so dass also die Variation der einen Amplitude mit einer entsprechenden Variation der anderen Amplitude einhergeht.An embodiment of the method according to the invention includes that the amplitudes of the respective excitation signals of the two transducer elements are varied with a function dependent on a predefinable modulation frequency. Both transducer elements are thus subjected to excitation signals, which are modulated with a mathematical function dependent on a predefinable modulation frequency. Therefore, the variations of the two excitation signals are directly connected to each other, so that therefore the variation of one amplitude with a corresponding variation of the other amplitude accompanied.
[0015] Eine Ausgestaltung des erfindungsgemäßen Verfahrens sieht vor, dass die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente mit einer von der vorgebbaren Modulationsfrequenz abhängigen Sinus-Funktion variiert werden.An embodiment of the method according to the invention provides that the amplitudes of the respective excitation signals of the two transducer elements are varied with a sinusoidal function dependent on the predefinable modulation frequency.
[0016] Eine Ausgestaltung des erfindungsgemäßen Verfahrens beinhaltet, dass die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente derartig variiert werden, dass die Summe der Amplituden zeitlich im Wesentlichen konstant ist. In dieser Ausgestaltung ist somit vorgesehen, dass in dem Fall, dass die eine Amplitude mit der Zeit kleiner wird, die Amplitude des anderen Anregungssignals entsprechend größer wird. Mit anderen Worten: Die volle Leistung der Schwingungserregung pendelt zwischen den beiden Wandlerelementen hin und her.An embodiment of the method according to the invention includes that the amplitudes of the respective excitation signals of the two transducer elements are varied such that the sum of the amplitudes is substantially constant over time. In this embodiment, it is thus provided that in the case that the one amplitude decreases with time, the amplitude of the other excitation signal is correspondingly larger. In other words, the full power of the vibration excitation oscillates between the two transducer elements back and forth.
[0017] Eine Ausgestaltung des erfindungsgemäßen Verfahrens sieht vor, dass die Modulationsfrequenz der Funktion, mit welcher die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente variiert werden, derartig vorgeben wird, dass die Modulationsfrequenz kleiner als die Frequenz der mechanischen Schwingungen des Messrohres ist. In einer Ausgestaltung wird das Messrohr zur Grundschwingung angeregt, so dass die Modulationsfrequenz unterhalb der Grundfrequenz des Messrohres liegt.An embodiment of the method according to the invention provides that the modulation frequency of the function with which the amplitudes of the respective excitation signals of the two transducer elements are varied will dictate such that the modulation frequency is less than the frequency of the mechanical vibrations of the measuring tube. In one embodiment, the measuring tube is excited to the fundamental, so that the modulation frequency is below the fundamental frequency of the measuring tube.
[0018] Eine Ausgestaltung des erfindungsgemäßen Verfahrens beinhaltet, dass die Modulationsfrequenz der Funktion, mit welcher die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente variiert werden, derartig vorgeben wird, dass die Modulationsfrequenz größer ist als das Frequenzband, innerhalb dessen der Strömungsparameter variiert. Je nach Medium bzw. je nach Prozess, welchem das Medium unterworfen ist, kann es zu Veränderungen im Bereich des Strömungsparameters kommen. D.h. auch der Strömungsparameter kann zeitlichen Variationen unterworfen sein. In dieser Ausgestaltung wird auf diese Fluktuation Rücksicht genommen, indem die Modulationsfrequenz höher als die Bandbreite dieser Frequenz liegt. [0019] Die Aufgabe wird erfindungsgemäß für die Vorrichtung dadurch gelöst, dass mindestens eine Steuereinheit vorgesehen ist, welche die Amplitude des Anregungssignals der Wandlerelemente zeitlich variiert. Das erfindungsgemäße Messgerät ist somit derartig ausgestaltet, dass eine Steuereinheit vorgesehen ist, welche die Amplitude des Anregungssignals des Wandlerelements zeitlich variiert, d.h. die Leistung, mit welcher das Messrohr durch das Wandlerelement zu mechanischen Schwingungen angeregt wird, ist nicht zeitlich konstant, sondern ändert sich über der Zeit.An embodiment of the method according to the invention includes that the modulation frequency of the function, with which the amplitudes of the respective excitation signals of the two transducer elements are varied, will dictate such that the modulation frequency is greater than the frequency band within which the flow parameter varies. Depending on the medium or the process to which the medium is subjected, changes in the flow parameter may occur. This means that the flow parameter can also be subject to temporal variations. In this embodiment, consideration is given to this fluctuation in that the modulation frequency is higher than the bandwidth of this frequency. The object is achieved for the device in that at least one control unit is provided which varies the amplitude of the excitation signal of the transducer elements in time. The measuring device according to the invention is thus designed such that a control unit is provided which varies the amplitude of the excitation signal of the transducer element over time, ie the power with which the measuring tube is excited by the transducer element to mechanical vibrations, is not constant over time, but changes over currently.
[0020] Die oben getätigten Ausführungen über das erfindungsgemäße Verfahren gelten entsprechend auch hier für die erfindungsgemäße Vorrichtung bzw. umgekehrt beziehen sich die Aussagen über die Messvorrichtung entsprechend auch auf das Verfahren.The statements made above on the method according to the invention apply mutatis mutandis to the device according to the invention or vice versa relate the statements about the measuring device accordingly to the process.
[0021] Eine Ausgestaltung der erfindungsgemäßen Vorrichtung beinhaltet, dass zwei Wandlerelemente vorgesehen sind, welche sowohl ausgehend von jeweils einem Anregungssignal das Messrohr zumindest temporär zu mechanischen Schwingungen anregen, als auch die mechanischen Schwingungen des Messrohres empfangen und jeweils ein zu den mechanischen Schwingungen des Messrohres korrespondierendes Empfangssignal erzeugen. In dieser Ausgestaltung sind zwei Wandlerelemente vorgesehen, welche sowohl der Erzeugung der Schwingungen als auch deren Detektion dienen.An embodiment of the device according to the invention includes that two transducer elements are provided, which stimulate the measuring tube, at least temporarily starting from each excitation signal to mechanical vibrations, as well as receive the mechanical vibrations of the measuring tube and one corresponding to the mechanical vibrations of the measuring tube Generate receive signal. In this embodiment, two transducer elements are provided which serve both the generation of the vibrations and their detection.
[0022] Vorteilhafterweise sind die Wandlerelemente in den Wurzeln des Messrohrs bzw. der Messrohre angebracht. Die Anbringung in den Wurzeln des Messrohres ist insbesondere für die Ausgestaltung vorteilhaft, in welcher die Wandlerelemente aus piezo-elektrischen Elementen bestehen. In einer anderen Ausgestaltung ist zumindest ein Wandlerelement an dem Punkt der höchsten Auslenkung der Coriolis-Schwingungsmode des Messrohres angebracht. Dies gilt insbesondere für elektrodynamische Wandlerelemente. In einer Ausgestaltung sind genau nur zwei Wandlerelemente vorgesehen. Dabei erlaubt es die Erfindung, die Nullpunkteigenschaften, welche ein Messsystem mit zwei Anregungspunkten wegen beschränkter Symmetrie besitzt, messtechnisch zu erfassen und in der Berechnung des Strömungsparameters, z.B. des Massenfluss-Messwertes zu berücksichtigen.Advantageously, the transducer elements are mounted in the roots of the measuring tube or the measuring tubes. The attachment in the roots of the measuring tube is particularly advantageous for the embodiment in which the transducer elements consist of piezoelectric elements. In another embodiment, at least one transducer element is mounted at the point of highest deflection of the Coriolis vibration mode of the measuring tube. This applies in particular to electrodynamic transducer elements. In one embodiment, only two transducer elements are provided. In this case, the invention makes it possible to measure the zero point properties of a measuring system having two excitation points for limited symmetry and to calculate them in the calculation of the Flow parameter, eg the mass flow measured value to be considered.
[0023] Eine Ausgestaltung der erfindungsgemäßen Vorrichtung sieht vor, dass es sich bei den zwei Wandlerelementen um piezoelektrische Elemente handelt.An embodiment of the device according to the invention provides that it is the piezoelectric elements in the two transducer elements.
[0024] Eine Ausgestaltung der erfindungsgemäßen Vorrichtung beinhaltet, dass die Steuereinheit die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente zeitlich variiert. In dieser Ausgestaltung werden die Amplituden der beiden Anregungssignale der beiden Wandlerelemente zeitlich variiert, d.h. die Schwingungen, welche die beiden Wandlerelemente erzeugen, werden mit einer Modulation der Amplituden überlagert. Ausgehend von dem Verhalten des Systems auf die Modulation der Amplituden lassen sich dann Asymmetrien erkennen und entsprechend bei der Bestimmung des Strömungsparameters berücksichtigen.An embodiment of the device according to the invention includes that the control unit varies the amplitudes of the respective excitation signals of the two transducer elements in time. In this embodiment, the amplitudes of the two excitation signals of the two transducer elements are varied over time, i. the vibrations which generate the two transducer elements are superimposed with a modulation of the amplitudes. On the basis of the behavior of the system on the modulation of the amplitudes, asymmetries can then be detected and considered accordingly in the determination of the flow parameter.
[0025] Eine Ausgestaltung der erfindungsgemäßen Vorrichtung sieht vor, dass die Steuereinheit die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente zeitlich mit einer von einer Modulationsfrequenz abhängigen Funktion variiert.An embodiment of the device according to the invention provides that the control unit varies the amplitudes of the respective excitation signals of the two transducer elements in time with a function dependent on a modulation frequency.
[0026] Die Erfindung wird anhand der nachfolgenden Zeichnungen näher erläutert. Es zeigt:The invention will be explained in more detail with reference to the following drawings. It shows:
[0027] Fig. 1 : eine schematische Darstellung eines Coriolis-Messgerätes in einer ersten Variante,1 shows a schematic representation of a Coriolis measuring device in a first variant,
[0028] Fig. 2: eine schematische Darstellung eines Coriolis-Messgerätes in einer zweiten Variante, und2 shows a schematic representation of a Coriolis measuring device in a second variant, and
[0029] Fig. 3: eine nicht-maßstabsgerechte Darstellung der relevanten Frequenzen beim erfindungsgemäßen Verfahren.Fig. 3: a non-scale representation of the relevant frequencies in the method according to the invention.
[0030] In der Fig. 1 ist ein Messrohr 1 dargestellt, durch welches hier beispielsweise für die Verdeutlichung von links nach rechts das - hier nicht dargestellte - Medium strömt oder fließt. Bei dem Medium handelt es sich beispielsweise um eine Flüssigkeit, um ein Gas, um ein Pulver, um ein Gemisch oder allgemein um ein fließfähiges Fluid. Eingangsseitig des Messrohres 1 befindet sich das erste Wandlerelement 2, welches dafür dient, das Messrohr 1 zu mechanischen Schwingungen anzuregen. Der Schwingungserzeugung dient auslaufseitig das zweite Wandlerelement 3. Mittig zwischen diesen beiden Wandlerelementen 2, 3 ist ein weiteres Wandlerelement 4 angeordnet, über welches die mechanischen Schwingungen des Messrohres 1 empfangen werden. Die Lokalisierung des Empfangswandlerelements 4 ist hier nur beispielhaft. In der hier dargestellten Ausgestaltung ist nur ein Messrohr 1 , welches vom Medium durchströmt wird, dargestellt. Die Erfindung lässt sich jedoch auch auf ein System mit zwei Messrohren anwenden.In Fig. 1, a measuring tube 1 is shown, through which here, for example, for clarity from left to right the - flows or flows - not shown here - medium. The medium is, for example, a liquid, a gas, a powder, a mixture or, in general, a fluid that can flow. On the input side of the measuring tube 1 is the first transducer element 2, which is for serves to excite the measuring tube 1 to mechanical vibrations. The oscillation generation serves the outlet side, the second transducer element 3. In the middle between these two transducer elements 2, 3, a further transducer element 4 is arranged, via which the mechanical vibrations of the measuring tube 1 are received. The localization of the receiving transducer element 4 is only an example here. In the embodiment shown here, only one measuring tube 1, which is flowed through by the medium, is shown. However, the invention can also be applied to a system with two measuring tubes.
[0031] Die Steuereinheit 5 beaufschlagt die beiden Anrege-Wandlerelemente 2, 3 jeweils mit einem Anregungssignal, wobei es sich beispielsweise um einen elektrischen Wechselstrom handelt. Es findet mit einem eingeprägten Strom die Anregung statt und die sich einstellende Spannung wird dann gemessen. Eine Phasen-Übereinstimmung von Strom und Spannung bedeutet, dass das Messsystem in Resonanz schwingt. Die Frequenz des Anregungssignals entspricht dabei vorzugsweise der Frequenz der Grundschwingungen des Messrohres 1. Die Amplitude des Anregungssignals bestimmt die Schwingungsamplitude, zu welcher das Messrohr 1 durch das entsprechende Wandlerelement 2, 3 angeregt wird.The control unit 5 acts on the two exciting transducer elements 2, 3 each with an excitation signal, which is, for example, an alternating electrical current. It takes place with an impressed current excitation and the resulting voltage is then measured. A phase match of current and voltage means that the measurement system resonates. The frequency of the excitation signal preferably corresponds to the frequency of the fundamental vibrations of the measuring tube 1. The amplitude of the excitation signal determines the oscillation amplitude to which the measuring tube 1 is excited by the corresponding transducer element 2, 3.
[0032] Das hier dargestellte dritte Wandlerelement 4 empfängt die mechanischen Schwingungen des Messrohres 1 und erzeugt daraus ein Empfangssignal, bei welchem es sich üblicherweise ebenfalls um eine elektrische Wechselspannung handelt. Aus der Phasendifferenz zwischen dem Anregungssignal und dem Empfangssignal lässt sich dann der Strömungsparameter, z.B. der Durchfluss oder der Massendurchfluss des Mediums bestimmen.The third transducer element 4 shown here receives the mechanical vibrations of the measuring tube 1 and generates therefrom a received signal, which is usually also an electrical alternating voltage. From the phase difference between the excitation signal and the received signal, the flow parameter, e.g. determine the flow or mass flow of the medium.
[0033] Erfindungsgemäß wird das Messrohr 1 einmal einlaufseitig und dann auslaufseitig zu Schwingungen angeregt. Es werden somit asymmetrisch Schwingungen erzeugt. Insbesondere werden die Amplituden der Anregungssignale kontinuierlich verändert, so dass ein abruptes Verhalten der Schwingungserregung vermieden wird. In einer Ausgestaltung wird die Amplitude jedes Anregungssignals mit einer Sinus-Funktion moduliert. Weiterhin sind dabei die beiden Anregungssignale derartig miteinander gekoppelt, dass eine abnehmende Amplitude bei einem Anregungssignal mit einer entsprechend zunehmenden Amplitude des anderen Anregungssignals verbunden ist. Die Summe der Amplituden der beiden Anregungssignale ist somit zeitlich jeweils konstant.According to the invention, the measuring tube 1 is excited once on the inlet side and then on the outlet side to vibrate. Thus, asymmetric vibrations are generated. In particular, the amplitudes of the excitation signals are changed continuously, so that an abrupt behavior of the vibration excitation is avoided. In one embodiment, the amplitude of each excitation signal is modulated with a sine function. Furthermore, the two excitation signals are in this way with each other coupled, that a decreasing amplitude is connected at an excitation signal with a correspondingly increasing amplitude of the other excitation signal. The sum of the amplitudes of the two excitation signals is thus constant in time.
[0034] Die Ausgestaltung mit zwei Anregungs-Wandlerelementen und einem Empfangs-Wandlerelement ist dabei nur beispielhaft. Es können auch mehr Wandlerelemente mit unterschiedlichem Anbringungsort vorgesehen sein.The embodiment with two excitation transducer elements and a receive transducer element is only an example. It can also be provided more transducer elements with different mounting location.
[0035] Die Bestimmung der Gruppenlaufzeit der Wandlerelemente sei noch einmal bezüglich des Wandler-Nullpunkts und bezüglich der Ausgestaltung mit nur zwei Positionen der Wandlerelemente relativ zu einer imaginären Längsachse des mindestens einen Messrohres mit anderen Worten beschrieben:The determination of the group delay of the transducer elements is described once again with respect to the converter zero point and with respect to the embodiment with only two positions of the transducer elements relative to an imaginary longitudinal axis of the at least one measuring tube:
[0036] Die Wandlerelemente 2, 3 selbst, sowie deren mechanische Ankopplung an das Messrohr 1 können im Allgemeinen für die beiden Positionen, an denen sie sich befinden, nicht identisch realisiert werden. Diese somit bestehende Ankopplungsasymmetrie ist ebenso, wie die Messrohrsymmetrie selbst der Temperatur ausgesetzt und durch driftende mechanische Kräfte beeinflusst. Zur exakten Bestimmung der Messrohrasymmetrie müssen daher die Nullpunkt-Eigenschaften der Wandlerelemente jeweils separat bestimmt werden. D.h. es muss ermittelt werden, welche Phasen somit unabhängig vom Einfluss des Strömungsparameters gegeben sind, da nur somit sicher bestimmt werden kann, welche Phase der Strömungsparameter in Verbindung mit dem Coriolis-Effekt erzeugt.The transducer elements 2, 3 themselves, as well as their mechanical coupling to the measuring tube 1 can not be realized identically in general for the two positions in which they are located. This thus existing coupling asymmetry is just as the measuring tube symmetry itself exposed to the temperature and influenced by drifting mechanical forces. For exact determination of the measuring tube asymmetry, therefore, the zero point properties of the transducer elements must each be determined separately. That It must be determined which phases are thus independent of the influence of the flow parameter, as only thus can be reliably determined which phase of the flow parameters generated in conjunction with the Coriolis effect.
[0037] Es wird also die Asymmetrie ausgemessen. Dies bedeutet konkret, dass die Gruppenlaufzeit der Wandlerelemente ausgemessen werden muss. Eine solche Ausmessung kann dabei prinzipiell außerhalb des normalen Messbetriebes oder während des Messbetriebes erfolgen. Dazu wird an einer der beiden Positionen der beiden Wandlerelemente 2, 3 ein hier nicht dargestelltes zusätzliches Wandlerelement in möglichst symmetrischer Anordnung zum bereits vorhandenen Wandlerelement angebracht. Das bereits vorhandene Wandlerelement 2 bzw. 3 dient zur Einkopplung der Anregungsenergie gemäß dem beschriebenen orts-moduliertem Verfahren. Das zusätzliche - hier nicht dargestellte, sich aber am gleichen Ort wie das Wandlerelement 2 bzw. 3 befindliche - Wandlerelement erlaubt die Messung der relativen Gruppenlaufzeit gegenüber dem bereits vorhandenen Wandlerelement. Es wird dazu die Gruppenlaufzeit zwischen den Sensorsignalen der beiden Wandlerelemente, welche sich jeweils am gleichen Ort befinden, ausgemessen, und dies jeweils für beide Positionen.Thus, the asymmetry is measured. This means concretely that the group delay of the transducer elements has to be measured. In principle, such a measurement can take place outside the normal measuring mode or during the measuring mode. For this purpose, at one of the two positions of the two transducer elements 2, 3 a not shown here additional transducer element in the most symmetrical arrangement possible to the existing transducer element. The already existing transducer element 2 or 3 is used for Coupling of the excitation energy according to the described location-modulated method. The additional - not shown here, but located at the same location as the transducer element 2 or 3 - transducer element allows the measurement of the relative group delay over the existing transducer element. It is to the group delay between the sensor signals of the two transducer elements, which are located at the same place, measured, and this for both positions.
[0038] Bei pendelnder Anregung zwischen den beiden Positionen zeigt die relative Gruppenlaufzeit zwischen zwei Wandlern an der gleichen Position die Überlagerung der Laufzeit des einen Wandlers mit einer modulierten Laufzeit des jeweils anderen Wandler am gleichen Ort.When oscillating excitation between the two positions, the relative group delay between two transducers at the same position shows the superposition of the term of the one converter with a modulated duration of the other converter at the same place.
[0039] Der Betrag der Modulation der überlagerten Wandler-Gruppenlaufzeiten lässt sich durch Demodulation bestimmen und entspricht der aktuellen Laufzeit des anregenden Wandlerelements an der jeweiligen Position.The amount of modulation of the superimposed transducer group delay can be determined by demodulation and corresponds to the current duration of the exciting transducer element at the respective position.
[0040] Die Wandler-Gruppenlaufzeit pro Position, d.h. der jeweiligeThe transducer group delay per position, i. the respective one
Wandlerelement-Nullpunkt kann verwendet werden, um die exakte, mechanisch relative Bewegung zwischen den beiden Positionen der Wandlerelemente längs des Messrohrs 1 zu bestimmen. Daraus wiederum kann direkt der Strömungsparameter, beispielsweise der Massenfluss bestimmt werden.Transducer element zero point can be used to determine the exact, mechanically relative movement between the two positions of the transducer elements along the measuring tube 1. In turn, directly from the flow parameters, such as the mass flow can be determined.
[0041] Die Schwingungen an einer Position i des Wandlerelements längs der imaginären Längsachse des Messrohres lassen sich im Resonanzfall mit folgender Formel beschreiben: S1 = A1 * sm(2τfGt + φχfm)dj))The vibrations at a position i of the transducer element along the imaginary longitudinal axis of the measuring tube can be described in the case of resonance with the following formula: S 1 = A 1 * sm (2τf G t + φχf m) d j))
[0042] Dabei ist S1 die Schwingungsamplitude an der Wandlerposition i zur Zeit t, A1 das Amplitudenmaximum an der Wandlerposition i, f(ι die mechanische Eigenfrequenz bzw. die Resonanzfrequenz des Messsystems und φ,{fm,d.t) ein zusätzlicher Phasenwinkel an der Wandlerposition i verursacht durch mechanische Asymmetrie und Anregungsorts-Modulation mit /ιn()d . In dem Fall, dass die Wandlerelemente an zwei Orten längs der Längsachse positioniert sind, ergeben sich somit zwei Gleichungen für i = 1 und i = 2. [0043] Aus diesen beiden Gleichungen lässt sich die Laufzeitdifferenz zwischen den beiden Orten ermitteln. Sie ergibt sich nach Demodulation der beiden Signale S1 und S2 mit f(ι , d.h. nach Frequenztranslation bzw. Faltung mit fG , Phasendifferenzbildung und Umrechnung in Laufzeit zu:In this case, S 1 is the oscillation amplitude at the transducer position i at time t, A 1 the amplitude maximum at the transducer position i, f (ι the mechanical natural frequency or the resonance frequency of the measuring system and φ, {f m , d additional phase angle at the transducer position i caused by mechanical asymmetry and excitation locus modulation with / ιn () d . Thus, in the case where the transducer elements are positioned at two locations along the longitudinal axis, there are two equations for i = 1 and i = 2. From these two equations, the transit time difference between the two locations can be determined. It results after demodulation of the two signals S 1 and S 2 with f (ι , ie after frequency translation or convolution with f G , phase difference formation and conversion in transit time to:
Tn -Tflm+Tmύd *sm(2πfmj)Tn -T flm + T mύd * sm (2πf m j)
[0044] Dabei ist T12 die Laufzeitdifferenz zwischen den Wandlerpositionen zurIn this case, T 12 is the transit time difference between the transducer positions for
Zeit t nach der Demodulation, T flυu die Laufzeitdifferenz, verursacht durch den Massenfluss des Mediums durch das Messrohr und 7^nod die Laufzeitdifferenz, resultierend aus der Anregung an den beiden unterschiedlichen Orten 1 und 2. Wobei die letztere Laufzeit sich durch mechanische Randbedingungen verändern kann. Weiterhin ist /mod die Pendelfrequenz für die Ortsmodulation der Anregung.Time t after the demodulation, T fleets the transit time difference, caused by the mass flow of the medium through the measuring tube and 7 ^ nod the transit time difference, resulting from the excitation at the two different locations 1 and 2. Where the latter term can change due to mechanical boundary conditions , Furthermore, / mod is the oscillation frequency for the spatial modulation of the excitation.
[0045] Nach einer Filterung der /mod -Anteile mit einem einfachen Tiefpass mit der Bedingung: Δ/s < fc < fmod , wobei / die Grenzfrequenz des Tiefpassfilters ist ergibt sich: T12 =T flu]l .After filtering the / mod parts with a simple low pass with the condition: Δ / s <f c <f mod , where / the cutoff frequency of the low-pass filter is: T 12 = T flu] l .
[0046] In der Fig. 2 ist eine zweite Variante des Messsystems dargestellt.2, a second variant of the measuring system is shown.
Insbesondere sind nur zwei Wandlerelemente 2, 3 vorgesehen, welche sowohl der Schwingungserzeugung, als auch dem Empfangen der Schwingungen dienen. D.h. die Anregungs- und Empfangs-Wandlerelemente der Fig. 1 sind jeweils zu einem Wandlerelement zusammengefallen. Somit ist diese Variante vorteilhafter als die der Fig. 1 , da hier nur zwei Wandlerelemente Verwendung finden. Dadurch ergeben sich ein Kostenvorteil, eine einfachere Mechanik und eine bessere mechanische Symmetrie. In einer Ausgestaltung wird bei elektrodynamischen Wandlerelementen über einen Strom die Anregungskraft auf das Messrohr eingeprägt und über die gemessene Spannung wird die Auslenkung - im elektrodynamischen Fall die Auslenkungsgeschwindigkeit -gemessen. In einer weiteren Ausgestaltung werden unter Benutzung von piezoelektrischen Wandlern vier Wandlerelemente verwendet, wobei jeweils zwei Wandlerelemente relativ zu einer Längsachse des Messrohres an der gleichen Stelle lokalisiert sind, um die Laufzeitdifferenzen der Wandlerelemente auszugleichen. [0047] Die elektro-mechanischen Wandlerelemente sind an zwei verschiedenen Positionen am Messrohr, z.B. speziell in den Wurzeln des Messrohrs, angebracht. In einer alternativen Ausgestaltung erfolgen das Einbringen der Erreger-Leistung und das Messen der Messrohrbewegung mit zwei verschiedenen Wandlerelementen an derselben Position am Messrohr, wobei das eine Element die Anregungsfunktion und das andere die Empfangsfunktion übernimmt. Hier in der Fig. 2 ist dargestellt, dass jeweils ein einziges Wandlerelement jeweils beide Funktionen übernimmt.In particular, only two transducer elements 2, 3 are provided, which serve both the vibration generation, as well as the receiving of the vibrations. That is to say, the excitation and reception transducer elements of FIG. 1 have each collapsed to form a transducer element. Thus, this variant is more advantageous than that of FIG. 1, since only two transducer elements are used here. This results in a cost advantage, a simpler mechanics and a better mechanical symmetry. In one embodiment, in the case of electrodynamic transducer elements, the excitation force is impressed on the measuring tube via a current and the deflection is measured via the measured voltage-in the electrodynamic case, the deflection speed. In a further embodiment, four transducer elements are used using piezoelectric transducers, with two transducer elements each being located at the same location relative to a longitudinal axis of the measuring tube in order to compensate for the transit time differences of the transducer elements. The electro-mechanical transducer elements are mounted at two different positions on the measuring tube, for example, especially in the roots of the measuring tube. In an alternative embodiment, the introduction of the exciter power and the measurement of the measuring tube movement with two different transducer elements take place at the same position on the measuring tube, wherein the one element performs the excitation function and the other the receiving function. Here in FIG. 2 it is shown that in each case a single transducer element assumes both functions.
[0048] Hier - wie in der Ausgestaltung der Fig. 1 - kann das elektro-mechanische Wandlerelement ein elektro-dynamisches Spulensystem oder eine piezoelektrisches Element sein.Here - as in the embodiment of Fig. 1 - the electro-mechanical transducer element may be an electro-dynamic coil system or a piezoelectric element.
[0049] Die Steuereinheit 5 steht auch hier für eine Messschaltung mit zweiThe control unit 5 is also here for a measuring circuit with two
Anschlüssen zur Ausgabe von zwei unabhängig steuerbaren Strompegeln zur unabhängigen Anregung an den zwei Positionen der Wandlerelemente 2, 3 am Messrohr 1 , sowie zwei oder vier Spannungs-Eingängen zur unabhängigen Erfassung der Messrohrbewegung an den zwei Positionen am Messrohr 1.Terminals for the output of two independently controllable current levels for independent excitation at the two positions of the transducer elements 2, 3 on the measuring tube 1, and two or four voltage inputs for independent detection of the Meßrohrbewegung at the two positions on the measuring tube. 1
[0050] Das Messrohr 1 als Ganzes wird dabei durch die Wandlerelemente 2, 3 bzw. durch die Steuereinheit 5 kontinuierlich angeregt, so dass die Eigenfrequenz (Resonanzfrequenz) des mechanischen Systems im Grundmode aufrechterhalten bleibt.The measuring tube 1 as a whole is continuously excited by the transducer elements 2, 3 or by the control unit 5, so that the natural frequency (resonant frequency) of the mechanical system is maintained in the fundamental mode.
[0051] Auch bei der hier gezeigten Ausgestaltung wird wie bei der Variante der Fig. 1 eine Nullpunkts-Modulation vorgenommen:Also in the embodiment shown here, as in the variant of FIG. 1, a zero-point modulation is performed:
[0052] Die Anregungsleistung an den beiden Wandlerelementen 2, 3 am Messrohr 1 wird mit einer vorgebbaren Modulationsfrequenz fmod zwischen Null und der aktuell notwendigen Erregerleistung moduliert. Dabei findet die Modulation derartig statt, dass die Summe der beiden Erregerleistungen an beiden Wandlerelementen 2, 3 nicht moduliert ist und der aktuell notwendigen Erregerleistung entspricht, d.h. die Summe der beiden Amplituden ist konstant.The excitation power at the two transducer elements 2, 3 on the measuring tube 1 is modulated with a predetermined modulation frequency fmod between zero and the currently required exciter power. In this case, the modulation takes place in such a way that the sum of the two exciter powers at both converter elements 2, 3 is not modulated and corresponds to the currently required exciter power, i. the sum of the two amplitudes is constant.
[0053] Der Messwert für den Strömungsparameter wird dabei unter Ausnutzung des Coriolis-Effekts aus der relativen Bewegung zwischen den beiden Positionen der beiden Wandlerelemente 2, 3 bestimmt. Dabei handelt es sich konkret um die Differenz der Eigenvektor-Phasenlagen.The measured value for the flow parameter is thereby determined by utilizing the Coriolis effect from the relative movement between the two positions of the two transducer elements 2, 3. It is specifically the difference of the eigenvector phase angles.
[0054] Eine bezüglich der Anregungsmodulation mechanische und elektrische Asymmetrie des Wandlersystems, z.B. durch Drift, Temperatur, etc., äußert sich in der Modulation des Messwertes des Strömungsparameters mit der Modulationsfrequenz fmod der Anregung.A with respect to the excitation modulation mechanical and electrical asymmetry of the transducer system, e.g. by drift, temperature, etc., is expressed in the modulation of the measured value of the flow parameter with the modulation frequency fmod of the excitation.
[0055] Die Modulation liegt darin begründet, dass bei Asymmetrie zwischen den Positionen der beiden Wandlerelemente 2, 3 unterschiedliche Eigenvektor-Phasenlagen und Amplituden gemessen werden. Diese „Nullpunkf'-Modulation ist somit ein Maß für die Asymmetrie des Systems der Wandlerelemente und der Messrohr-Mechanik. Die Asymmetrie lässt sich dabei durch Demodulation mit der Modulationsfrequenz der Amplituden der Anregungssignale ausmessen bzw. ausrechnen. Ausgehend von dieser gemessenen Nullpunkt-Information lässt sich dann der Messwert für den Strömungsparameter bezüglich der Wandler-System-Asymmetrie korrigieren.The modulation is due to the fact that in asymmetry between the positions of the two transducer elements 2, 3 different eigenvector phase angles and amplitudes are measured. This "zero point" modulation is thus a measure of the asymmetry of the system of the transducer elements and the measuring tube mechanism. The asymmetry can be measured or calculated by demodulation with the modulation frequency of the amplitudes of the excitation signals. Based on this measured zero point information, the measured value for the flow parameter with respect to the converter-system asymmetry can then be corrected.
[0056] In der Fig. 3 ist nicht maßstabsgerecht und rein schematisch das Verhältnis der auftretenden Frequenzen dargestellt. Die beiden Anregungssignale, mit welchen das erste 2 und das zweite Anregungs-Wandlerelement 3 beaufschlagt werden, um das Messrohr 1 in der Grundmode zu mechanischen Schwingungen anzuregen, haben in dieser Ausgestaltung die gleiche Frequenz, welche der Grundfrequenz des Messrohrs 1 entspricht: fG. Die Frequenz, mit welcher die Amplituden der Anregungssignale moduliert werden: fmod ist kleiner als die Grundfrequenz fG. Gleichzeitig ist die Modulationsfrequenz fmod höher als die Frequenzbandbreite Dfs, innerhalb der der Strömungsparameter variieren kann. Der unterste Wert des Frequenzbandbreite Dfs liegt dabei bei 0 Hz, d.h. der Strömungsparameter ist konstant.In Fig. 3 is not drawn to scale and purely schematically the ratio of frequencies occurring. The two excitation signals which are applied to the first 2 and the second excitation transducer element 3 in order to excite the measuring tube 1 in the fundamental mode to mechanical vibrations have in this embodiment, the same frequency, which corresponds to the fundamental frequency of the measuring tube 1: fG. The frequency with which the amplitudes of the excitation signals are modulated: fmod is smaller than the fundamental frequency fG. At the same time, the modulation frequency fmod is higher than the frequency bandwidth Dfs within which the flow parameter can vary. The lowest value of the frequency bandwidth Dfs is 0 Hz, i. the flow parameter is constant.
[0057] Erfindungsgemäß werden somit keine diskrete Anregungs-Zustände erzeugt, sondern es findet, um Diskontinuität der Anregung bzw. Transienten beim Übergang von einem zum anderen Anregungszustand zu vermeiden, ein kontinuierlicher bzw. sinusförmiger Übergang der örtlichen Anregung statt.Thus, according to the invention, no discrete excitation states are generated, but instead of avoiding discontinuity of the excitation or transients during the transition from one excited state to another, a continuous or sinusoidal transition of the local excitation takes place.
[0058] Da beispielsweise ein sinusförmiger Wechsel zwischen den Anregungsorten stattfindet, kann zu jedem beliebigen Zeitpunkt durch Demodulation mit der Modulations- oder Pendelfrequenz (=Nullpunkt-Modulationsfrequenz), d.h. z.B. nach jedem Sample die Amplitude und sogar die Phasenlage des mechanischen Nullpunktes bestimmt werden. Durch das erfindungsgemäße Verfahren ist somit dieFor example, as a sinusoidal change between the Excitation places takes place, at any time by demodulation with the modulation or pendulum frequency (= zero point modulation frequency), ie for example after each sample, the amplitude and even the phase position of the mechanical zero point can be determined. The inventive method is thus the
Coriolis-Phasendifferenz, welche proportional zum Massenfluss ist, überlagert mit der Nullpunkt-Modulationsfrequenz. Diese kann aus dem Messwert gefiltert werden. Die separierteCoriolis phase difference, which is proportional to the mass flow, superimposed with the zero-point modulation frequency. This can be filtered from the measured value. The separated
Nullpunkt-Verschiebungs-Amplitude ist ein Maß für die Starrheit des mechanischen Systems und kann für weitere Kompensations- und Überwachungszwecke (z.B. für Dichte, Viskosität, Abrasion, etc.) als unabhängiger Messwert genutzt werden. Zero Point Displacement Amplitude is a measure of the rigidity of the mechanical system and can be used as an independent measure for other compensation and monitoring purposes (eg for density, viscosity, abrasion, etc.).
BezugszeichenlisteLIST OF REFERENCE NUMBERS
Tabelle 1
Figure imgf000017_0001
Table 1
Figure imgf000017_0001

Claims

Ansprüche claims
1. Verfahren zur Messung und/oder Überwachung mindestens eines Strömungsparameters eines Mediums, welches Medium mindestens ein Messrohr (1) durchströmt, wobei das Messrohr (1) zumindest temporär von mindestens einem1. A method for measuring and / or monitoring at least one flow parameter of a medium, which medium flows through at least one measuring tube (1), wherein the measuring tube (1) at least temporarily from at least one
Wandlerelement (2, 3), welches mit einem Anregungssignal beaufschlagt wird, zu mechanischen Schwingungen angeregt wird, wobei von mindestens einem Wandlerelement (4) die mechanischenTransducer element (2, 3), which is acted upon by an excitation signal is excited to mechanical vibrations, wherein of at least one transducer element (4), the mechanical
Schwingungen des Messrohres (1) empfangen werden, und wobei von dem Wandlerelement (4) mindestens ein zu den mechanischenVibrations of the measuring tube (1) are received, and wherein of the transducer element (4) at least one of the mechanical
Schwingungen des Messrohres (1) korrespondierendes Empfangssignal erzeugt wird, dadurch gekennzeichnet, dass die Amplitude des Anregungssignals des Wandlerelements (2, 3) zeitlich variiert wird.Vibrations of the measuring tube (1) corresponding received signal is generated, characterized in that the amplitude of the excitation signal of the transducer element (2, 3) is varied over time.
2. Verfahren nach Anspruch 1 , dadurch gekennzeichnet, dass die Amplitude des Anregungssignals des Wandlerelements (2, 3) zeitlich kontinuierlich variiert wird.2. The method according to claim 1, characterized in that the amplitude of the excitation signal of the transducer element (2, 3) is varied continuously over time.
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass das Messrohr (1) zumindest temporär von mindestens zwei3. The method according to claim 1 or 2, characterized in that the measuring tube (1) at least temporarily of at least two
Wandlerelementen (2, 3), welche jeweils mit einem Anregungssignal beaufschlagt werden, zu mechanischen Schwingungen angeregt wird, und dass die Amplituden der jeweiligen Anregungssignale der zweiTransducer elements (2, 3), which are each acted upon by an excitation signal is excited to mechanical vibrations, and that the amplitudes of the respective excitation signals of the two
Wandlerelemente (2, 3) zeitlich variiert werden.Transducer elements (2, 3) are varied over time.
4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, dass die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente (2, 3) zeitlich kontinuierlich variiert werden.4. The method according to claim 3, characterized in that the amplitudes of the respective excitation signals of the two transducer elements (2, 3) are varied continuously in time.
5. Verfahren nach mindestens einem der Ansprüche 3 bis 4, dadurch gekennzeichnet, dass die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente (2, 3) mit einer von einer vorgebbaren Modulationsfrequenz (fmod) abhängigen Funktion variiert werden.5. The method according to at least one of claims 3 to 4, characterized in that the amplitudes of the respective excitation signals of the two transducer elements (2, 3) are varied with a function dependent on a predefinable modulation frequency (fmod).
6. Verfahren nach Anspruch 5, dadurch gekennzeichnet, dass die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente (2, 3) mit einer von der vorgebbaren Modulationsfrequenz (fmod) abhängigen Sinus-Funktion variiert werden.6. The method according to claim 5, characterized in that the amplitudes of the respective excitation signals of the two transducer elements (2, 3) are varied with one of the predetermined modulation frequency (fmod) dependent sine function.
7. Verfahren nach mindestens einem der Ansprüche 3 bis 6, dadurch gekennzeichnet, dass die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente (2, 3) derartig variiert werden, dass die Summe der Amplituden zeitlich im Wesentlichen konstant ist.7. The method according to at least one of claims 3 to 6, characterized in that the amplitudes of the respective excitation signals of the two transducer elements (2, 3) are varied such that the sum of the amplitudes is temporally substantially constant.
8. Verfahren nach Anspruch 5 oder 6, dadurch gekennzeichnet, dass die Modulationsfrequenz (fmod) der Funktion, mit welcher die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente (2, 3) variiert werden, derartig vorgeben wird, dass die Modulationsfrequenz (fmod) kleiner als die Frequenz (fG) der mechanischen Schwingungen des Messrohres (1) ist.8. The method according to claim 5 or 6, characterized in that the modulation frequency (fmod) of the function with which the amplitudes of the respective excitation signals of the two transducer elements (2, 3) are varied, such pretend that the modulation frequency (fmod) smaller as the frequency (fG) of the mechanical vibrations of the measuring tube (1).
9. Verfahren nach Anspruch 5, 6 oder 8, dadurch gekennzeichnet, dass die Modulationsfrequenz (fmod) der Funktion, mit welcher die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente (2, 3) variiert werden, derartig vorgeben wird, dass die Modulationsfrequenz (fmod) größer ist als das Frequenzband (Dfs), innerhalb dessen der Strömungsparameter variiert.9. The method of claim 5, 6 or 8, characterized in that the modulation frequency (fmod) of the function with which the amplitudes of the respective excitation signals of the two transducer elements (2, 3) are varied, such will pretend that the modulation frequency (fmod ) is greater than the frequency band (Dfs) within which the flow parameter varies.
10. Vorrichtung zur Messung und/oder Überwachung mindestens eines Strömungsparameters eines Mediums, welches Medium mindestens ein Messrohr (1) durchströmt, mit mindestens einem Wandlerelement (2, 3), welches ausgehend von einem10. Device for measuring and / or monitoring at least one flow parameter of a medium, which medium flows through at least one measuring tube (1), with at least one transducer element (2, 3), which starting from a
Anregungssignal das Messrohr (1) zumindest temporär zu mechanischen Schwingungen anregt, und mit mindestens einem Wandlerelement (4), welches die mechanischenExcitation signal the measuring tube (1) at least temporarily to mechanical Exciting vibrations, and with at least one transducer element (4), which is the mechanical
Schwingungen des Messrohres (1) empfängt und ein zu den mechanischenVibrations of the measuring tube (1) receives and one to the mechanical
Schwingungen des Messrohres (1) korrespondierendes Empfangssignal erzeugt, dadurch gekennzeichnet, dass mindestens eine Steuereinheit (5) vorgesehen ist, welche die Amplitude des Anregungssignals des Wandlerelements (2, 3) zeitlich variiert.Vibrations of the measuring tube (1) generates corresponding received signal, characterized in that at least one control unit (5) is provided, which varies the amplitude of the excitation signal of the transducer element (2, 3) in time.
11. Vorrichtung nach Anspruch 10, dadurch gekennzeichnet, dass zwei Wandlerelemente (2, 3) vorgesehen sind, welche sowohl ausgehend von jeweils einem Anregungssignal das Messrohr (1) zumindest temporär zu mechanischen Schwingungen anregen, als auch die mechanischen Schwingungen des Messrohres (1) empfangen und jeweils ein zu den mechanischen Schwingungen des Messrohres (1) korrespondierendes Empfangssignal erzeugen.11. The device according to claim 10, characterized in that two transducer elements (2, 3) are provided, which excite the measuring tube (1) at least temporarily to mechanical vibrations, both starting from an excitation signal, as well as the mechanical vibrations of the measuring tube (1). receive and each generate a to the mechanical vibrations of the measuring tube (1) corresponding to the received signal.
12. Vorrichtung nach Anspruch 10 oder 11 , dadurch gekennzeichnet, dass es sich bei den zwei Wandlerelementen (2, 3) um piezoelektrische Elemente handelt.12. Device according to claim 10 or 11, characterized in that the two transducer elements (2, 3) are piezoelectric elements.
13. Vorrichtung nach Anspruch 11 oder 12, dadurch gekennzeichnet, dass die Steuereinheit (5) die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente (2, 3) zeitlich variiert.13. The apparatus of claim 11 or 12, characterized in that the control unit (5) varies the amplitudes of the respective excitation signals of the two transducer elements (2, 3) in time.
14. Vorrichtung nach Anspruch 13, dadurch gekennzeichnet, dass die Steuereinheit die Amplituden der jeweiligen Anregungssignale der zwei Wandlerelemente (2, 3) zeitlich mit einer von einer Modulationsfrequenz (fmod) abhängigen Funktion variiert. 14. The device according to claim 13, characterized in that the control unit varies the amplitudes of the respective excitation signals of the two transducer elements (2, 3) in time with one of a modulation frequency (fmod) dependent function.
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