Patent Application
20240385021
The present invention relates to a vibronic sensing element for mass flow and density measurement with eccentric excitation.
The density of a medium guided in the measuring tube is determined by means of a vibronic sensing element on the basis of the eigenfrequencies of vibration modes of the measuring tube. Ideally, the medium is incompressible, so that the medium follows the vibrations of the measuring tube. However, if the medium is compressible, e.g., due to gas content of the medium, the mass flow measurement and the density measurement can be flawed, because the medium begins to oscillate with respect to the measuring tube. The influence of this so-called resonator effect can be corrected by detecting the eigenfrequencies of two vibration modes, wherein, essentially, a sound velocity of the medium is determined for which corresponding density measurement values for the medium result from the two eigenfrequencies. Details on this are disclosed, for example, in DE 10 2015 122 661 A1. The first and second symmetric vibration modes, i.e., the f1 mode and the f3 mode, are usually excited for this purpose. However, in some sensing elements, the eigenfrequency of the second symmetric vibration mode f3 can be high enough that it is within the range of the resonance frequency of the medium, so that a stable excitation of the second symmetric vibration mode cannot be reliably ensured. In this case, the first antisymmetric vibration mode is an attractive alternative, because the eigenfrequency of this mode is lower, and thus a greater distance from the resonance frequency of the measuring tube is to be expected.
The yet unpublished patent application DE 10 2020 123 999.8 discloses a vibronic measuring arrangement having a single, slightly eccentrically arranged exciter, which is suitable for exciting antisymmetric modes in addition to symmetric modes. This fulfills its purpose, but is problematic insofar as excitation also of the first symmetric vibration mode also includes an eccentric portion which causes a zero point error, in particular a damping-dependent zero point error, during flow measurement. Although this zero point error can be determined and can be rectified in a correction, this means additional effort and possibly compromises during operation of the measuring device.
US 2003/0131669 A1 discloses a vibronic sensing element having two eccentrically-arranged exciter arrangements, which are positioned symmetrically, with respect to the center of the measuring tube, at a great distance from one another. The selection of the modes to be excited is made via the frequency and the phase relationship of the exciter signals that are applied to the two exciters. Deviations in the phase relationship or unequal amplitudes of the exciter signals necessarily result in the excitation of other, undesirable modes. This can lead to undetected measurement errors.
It is therefore the object of the invention to remedy this situation.
The vibronic sensing element according to the invention comprises: an oscillator having at least one first measuring tube for guiding a medium; at least one electrodynamic exciter arrangement for exciting the oscillator to bring about bending vibrations of the at least one first measuring tube; at least one inlet-side sensor arrangement for detecting the bending vibrations of the at least one first measuring tube; at least one outlet-side sensor arrangement for detecting the bending vibrations of the at least one first measuring tube; and a measuring and operating circuit configured to apply at least one exciter signal to the electrodynamic exciter arrangement, detect sensor signals of the inlet-side and outlet-side sensor arrangements, and determine a density measurement value and/or a mass flow rate measurement value on the basis of the sensor signals, the electrodynamic exciter arrangement comprising a first exciter assembly, which is fastened to the at least one first measuring tube, and a second exciter assembly, in respect of which the at least one first measuring tube is to be excited such as to vibrate, the first exciter assembly having a center of gravity located, up to manufacturing tolerances, in a measuring tube transverse plane, which runs perpendicularly to the at least one first measuring tube and in respect of which the at least one first measuring tube has a substantially mirror symmetric profile, the electrodynamic exciter arrangement comprising a first electrodynamic exciter, the exciter arrangement comprising a second electrodynamic exciter and at least one first compensation mass body, the first exciter assembly comprising a first component of the first electrodynamic exciter and a first component of the second electrodynamic exciter and the first compensation mass body, the second exciter assembly comprising a second component of the first electrodynamic exciter and a second component of the second electrodynamic exciter, the first electrodynamic exciter being configured to exert an exciter force on the at least one first measuring tube, said exciter force acting between the first component and the second component of the first electrodynamic exciter, an effective center of the first exciter force being located in the measuring tube transverse plane (EQ), the second electrodynamic exciter being configured to exert a second exciter force on the at least one measuring tube, said second exciter force acting between the first component and the second component of the second electrodynamic exciter, an effective center of the second exciter force being located outside the measuring tube transverse plane, the measuring and operating circuit being configured to apply a first exciter signal, the frequency of which corresponds to a present eigenfrequency of a symmetric vibration mode of the oscillator, only to the first electrodynamic exciter, and the measuring and operating circuit (70) being configured to apply a second exciter signal, the frequency of which corresponds to a present eigenfrequency of an antisymmetric vibration mode of the oscillator, only to the second electrodynamic exciter.
In the case of an exciter which has a coaxial arrangement of a rotationally-symmetrical magnet with a rotationally-symmetrical coil, the effective center of the exciter force lies on the common axis of the rotational symmetry. In other embodiments, the center of the exciter force for an electromagnetic exciter is to be determined as the center of gravity of the integral of the force density between magnet and coil.
In one development of the invention, the first component of the second electrodynamic exciter has a first center of gravity, wherein the first compensation mass body has a second center of gravity, wherein a distance of a common center of gravity of the first center of gravity and of the second center of gravity from the measuring tube transverse plane is not more than 5%, especially not more than 2% of the distance of the first center of gravity from the second center of gravity.
In one development of the invention, the total mass of the first component of the second electrodynamic exciter and of the first compensation mass body is not more than one times, especially not more than half of, the mass of the first component of the first electrodynamic exciter.
In one development of the invention, the at least one first measuring tube has a free vibration length which extends between an inlet-side fixation of the measuring tube and an outlet-side fixation of the measuring tube, wherein the center of the second exciter force FE2 is spaced apart from the measuring tube transverse plane (EQ) by no less than 1% of the free vibration length and no more than 10% of the free vibration length.
In one development of the invention, one of the components of the first electrodynamic exciter has a first exciter coil, wherein one of the components of the second electrodynamic exciter has a second exciter coil, wherein the inductance of the first exciter coil is not less than two times, especially not less than four times, the inductance of the second exciter coil.
In one development of the invention, the other of the components of the first electrodynamic exciter has a first magnet, wherein the other components of the second electrodynamic exciter comprises a second magnet, wherein an orthogonal projection of the first magnet and an orthogonal projection of the second magnet onto a plane running perpendicularly to the vibration direction of the at least one measuring tube overlap with an orthogonal projection of the first exciter coil and an orthogonal projection of the second exciter coil, respectively, onto this plane.
In one development of the invention, the area of the overlapping orthogonal projections of the components of the first electrodynamic exciter is at least two times, for example at least three times and especially at least four times, the area of the overlapping orthogonal projections of the components of the second electrodynamic exciter.
In one development of the invention, the distance of the second electrodynamic exciter from the sensor arrangement closest thereto is not less than four times, especially not less than eight times, the distance of the second electrodynamic exciter from the first electrodynamic exciter.
In one development of the invention, a principal axis of inertia of the first exciter assembly runs in the measuring tube transverse plane (EQ).
In one development of the invention, the first exciter assembly is fastened to the at least one measuring tube by means of a joint, wherein the measuring tube transverse plane (EQ) runs through a center of gravity of the joint.
In one development of the invention, the first exciter assembly has a first carrier body on which the second exciter coil and the at least one first compensation mass body are arranged, wherein the first carrier body is symmetrical with respect to the measuring tube transverse plane EQ.
In one development of the invention, the oscillator also has a second measuring tube, wherein the first measuring tube and the second measuring tube have a mirror symmetric profile relative to one another with respect to a sensing element longitudinal plane, wherein the sensing element longitudinal plane runs perpendicularly to the measuring tube transverse plane EQ.
In one development of the invention, the second exciter assembly is fastened to the second measuring tube opposite the first exciter assembly, wherein the center of gravity of the second exciter assembly lies in the measuring tube transverse plane EQ up to manufacturing tolerances.
In one development of the invention, a principal axis of inertia of the second exciter assembly runs in the measuring tube transverse plane EQ.
In one development of the invention, the second exciter assembly has a second carrier body on which the second magnet and a second compensation mass body are arranged, wherein the second carrier body is symmetrical with respect to the measuring tube transverse plane EQ.
In one development of the invention, if the sensing element comprises only a single measuring tube, the exciter assembly carrying the magnets is arranged on the measuring tube, while the exciter assembly carrying the coils is fixed to a comparatively stiff carrier tube or frame of the sensing element. With this arrangement, the measuring tube is to be excited such as to vibrate relative to the carrier tube or frame. In this way, the wiring along the measuring tube is omitted. The same applies to the arrangement of the sensors.
In one development of the invention, the measuring and operating circuit is configured to excite the first symmetric vibration mode and the first antisymmetric vibration mode, to determine the eigenfrequencies of the first symmetric vibration mode and of the first antisymmetric vibration mode, and on the basis of the eigenfrequencies of the first symmetric vibration mode and of the first antisymmetric vibration mode a density measurement value or mass flow measurement value for a medium guided in the measuring tube, wherein the density measurement value or the mass flow measurement value is corrected with respect to a resonator effect due to gas content of the medium.
The invention is now explained in more detail on the basis of the exemplary embodiments shown in the figures.
In the figures:
The sensing element 1 shown in
The exciter arrangement 11 is arranged on the measuring tubes 10.1, 10.2 in such a way that the center of mass of the exciter assembly overall lies in a measuring tube transverse plane EQ which intersects the measuring tubes perpendicularly and in respect of which each of the measuring tubes has a mirror symmetric profile. The exciter arrangement comprises a first electrodynamic exciter 15, the exciter force of which acts between the measuring tubes symmetrically with respect to the measuring tube transverse plane in order to excite symmetric bending vibration modes of the measuring tubes 10.1, 10.2. The exciter arrangement also comprises a second electrodynamic exciter 18, the exciter force of which acts between the measuring tubes parallel to the measuring tube transverse plane and at an offset to the measuring tube transverse plane of approximately 5% in the longitudinal direction of the measuring tubes in order to excite antisymmetric bending vibration modes of the measuring tubes 10.1, 10.2. The exciter arrangement moreover has a compensation mass 19 for compensating the mass of the second electrodynamic exciter 18 in order to keep the center of mass of the exciter arrangement in the measuring tube transverse plane.
Details regarding the exciter arrangement 11 are now explained with reference to
As is customary, the exciter arrangement 11 and the sensor arrangements 12a, 12b have electrodynamic transducers; for each of these transducers, a magnet is arranged on one of the measuring tubes and a coil is arranged on the other. This principle is known per se and does not need to be explained in more detail here. The special feature of the sensing element according to the invention is that, in addition to the excitation of symmetric bending vibration modes, the exciter arrangement 11 also allows excitation of antisymmetric bending vibration modes of the oscillator or of the measuring tubes of the oscillator, and the exciter arrangement is nevertheless balanced with respect to its mass distribution. For this purpose, the exciter arrangement 11 comprises a first exciter assembly 11.1 on a first measuring tube 10.1, as illustrated in
The first exciter assembly 11.1 shown in
The second exciter assembly 11.2 shown in
The second ring segment 14.2 is in particular structurally identical to the first ring segment 14.1, and the second carrier body 16.2 is in particular structurally identical to the first carrier body 16.1.
The principal axes of inertia of the first exciter assembly 11.1 and of the second exciter assembly 11.2 in the measuring tube transverse plane run parallel to one another, and in particular mirror-symmetrically to one another, with respect to a sensing element longitudinal plane which runs between the two measuring tubes 10.1, 10.2, wherein the two measuring tubes are arranged mirror-symmetrically to one another with respect to the sensing element longitudinal plane.
The first exciter coil 15.1 and the second exciter coil 18.1 are each configured to be fed by the measuring and operating circuit 70 with an alternating current signal which is specific to the exciter coil and the frequency of which corresponds to the present eigenfrequency of a bending vibration mode to be excited. For the first exciter coil 15.1 these are the frequencies of the symmetric bending vibration modes, and for second exciter coil 18.1 these are the frequencies of the antisymmetric bending vibration modes. Of course, alternating current signals of different frequencies of the symmetry class in question can also be superimposed, for example with the present eigenfrequencies of the first symmetric and the second symmetric bending vibration mode for the first exciter coil 15.1 and with the present eigenfrequencies of the first antisymmetric bending vibration mode and the second antisymmetric bending vibration mode for the second exciter coil 18.1. The resulting magnetic fields produce alternating attractive and repulsive forces on the corresponding exciter magnet 15.2, 18.2 which lies opposite the field-generating exciter coil, and as a result the two measuring tubes 10.1, 10.2 of the oscillator are caused to vibrate relative to each other in the selected bending vibration modes.
The exciter magnets 15.2, 18.2 and the exciter coils 15.1, 18.1 as well as the two compensation mass bodies 19.1, 19.2 are preferably rotationally symmetrical, with the axis of rotation running substantially in the direction of the vibrations of the measuring tubes. In particular, the exciter magnets 15.2, 18.2, the exciter coils 15.1, 18.1, and the two compensation mass bodies 19.1, 19.2 have cylindrical symmetry, at least in sections.
The mode-dependent deflection of a measuring tube is shown schematically in
The first antisymmetric vibration mode has to be excited only so much that the value of its eigenfrequency can be determined, which is possible already at a minimum vibration amplitude. The second electrodynamic exciter 18 can therefore be dimensioned much smaller and lighter than the first electrodynamic exciter 15, with which the first symmetric bending vibration mode, i.e., the so-called bending vibration utilization mode, is to be excited.
The positions of the sensor arrangements 12a, 12b are selected symmetrically, in the longitudinal direction z, with respect to the measuring tube center of the measuring tubes, such that the deflections of the vibration sensors produce a sufficient measurement signal in the case of both vibrations in the drive mode and the first antisymmetric vibration mode.
The measuring and operating circuit is configured to excite the first symmetric vibration mode and the first antisymmetric vibration mode by feeding the respectively associated exciter coil with an exciter current, to determine the eigenfrequencies of the first symmetric vibration mode and of the first antisymmetric vibration mode, and on the basis of the eigenfrequencies of the first symmetric vibration mode and of the first antisymmetric vibration mode a density measurement value or mass flow measurement value for a medium guided in the measuring tube, the density measurement value or the mass flow measurement value being corrected with respect to a resonator effect due to gas content of the medium. The influence of this so-called resonator effect can be corrected by detecting the eigenfrequencies of two vibration modes, wherein, essentially, a sound velocity of the medium is determined for which corresponding density measurement values for the medium result from the two eigenfrequencies. Details for this are disclosed, for example, in DE 10 2015 122 661 A1, wherein the first and second symmetric vibration modes are to be evaluated according to the teaching described therein. With reference to
To provide a correct mass flow rate measurement value, a preliminary mass flow rate measurement value 150 is first determined. In a next step 160, a flow correction factor is determined on the basis of the density error or density correction factor, as is also disclosed in DE 10 2015 122 661 A1. In a last step 170, a correct mass flow rate measurement value is determined, in which the preliminary mass flow rate measurement value is corrected with the correction factor.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 123 412.3 | Sep 2021 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/072689 | 8/12/2022 | WO |
