VIBRONIC SENSOR FOR MASS FLOW AND DENSITY MEASUREMENT

Description

[0001] The present invention relates to a vibronic sensor for mass flow and density measurement with eccentric excitation.

[0002] The density of a medium conveyed in a measuring tube is determined using a vibronic sensor based on the natural frequencies 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 becomes compressible, for example due to gas loading of the medium, the mass flow measurement and the density measurement can be inaccurate because the medium begins to vibrate relative to the measuring tube. The influence of this so-called resonator effect can be corrected by detecting the natural frequencies of two vibration modes, essentially determining a speed of sound of the medium for which the two natural frequencies yield consistent density measurements for the medium. Details are disclosed, for example, in DE 10 2015 122 661 A1.Typically, the first and second symmetrical oscillation modes, i.e., the f1 mode and the f3 mode, are excited for this purpose. US 2015 377 673 A1 also discloses a Coriolis flowmeter whose measuring tube is to be excited in two oscillation modes. However, in some sensors, the natural frequency of the second symmetrical oscillation mode, f3, can be so high that it lies in the range of the medium's resonant frequency, meaning that stable excitation of the second symmetrical oscillation mode cannot be reliably guaranteed. In this case, the first antisymmetrical oscillation mode is an attractive alternative, since the natural frequency of this mode is lower, and thus a greater distance from the resonant frequency of the measuring tube can be expected.

[0003] The as yet unpublished patent application DE 10 2020 123 999.8 discloses a vibronic measuring arrangement with a single, slightly eccentrically arranged exciter, which is suitable for exciting not only the symmetric but also the antisymmetric modes. This serves its purpose, but is problematic in that the excitation of even the first symmetric oscillation mode also has an eccentric component, which causes a zero-point error in the flow measurement, particularly one that is damping-dependent. This zero-point error can be determined and corrected with a correction, but this entails additional effort and potentially compromises in the operation of the measuring device.

[0004] US 2003 / 0131669 A1 discloses a vibronic sensor with two eccentrically arranged excitation arrays positioned symmetrically with respect to the center of the measuring tube at a large distance from each other. The modes to be excited are selected based on the frequency and phase relationship of the excitation signals applied to the two exciters. Deviations in the phase relationship or unequal amplitudes of the excitation signals inevitably result in the excitation of other, undesired modes. This can lead to undetected measurement errors.

[0005] It is therefore the object of the invention to remedy this situation.

[0006] The vibronic measuring sensor according to the invention comprises: an oscillator with at least one first measuring tube for guiding a medium; at least one electrodynamic excitation arrangement for exciting the oscillator to flexural vibrations of the at least one first measuring tube; at least one inlet-side sensor arrangement for detecting the flexural vibrations of the at least one first measuring tube; at least one outlet-side sensor arrangement for detecting the flexural vibrations of the at least one first measuring tube; and a measuring and operating circuit configured to apply at least one excitation signal to the electrodynamic excitation arrangement, to detect sensor signals from the inlet-side and outlet-side sensor arrangements, and to determine a density measurement value and / or a mass flow rate measurement value based on the sensor signals, wherein the electrodynamic excitation arrangement has a first excitation assembly,which is attached to the at least one first measuring tube, and a second exciter assembly, with respect to which the at least one first measuring tube is to be excited to oscillate, wherein the first exciter assembly has a center of gravity which, except for manufacturing tolerances, lies in a transverse measuring tube plane which runs perpendicular to the at least one first measuring tube, and with respect to which the at least one first measuring tube has a substantially mirror-symmetrical profile; wherein the electrodynamic exciter arrangement comprises a first electrodynamic exciter, wherein the exciter arrangement comprises a second electrodynamic exciter and at least one first balancing mass body, wherein the first exciter assembly comprises a first component of the first electrodynamic exciter and a first component of the second electrodynamic exciter and the first balancing mass body,wherein the second exciter assembly comprises a second component of the first electrodynamic exciter and a second component of the second electrodynamic exciter, wherein the first electrodynamic exciter is configured to exert an excitation force on the at least one first measuring tube, which acts between the first and the second component of the first electrodynamic exciter, wherein an effective center of the first excitation force is located in the measuring tube transverse plane (EQ), wherein the second electrodynamic exciter is configured to exert a second excitation force on the at least one measuring tube, which acts between the first and the second component of the second electrodynamic exciter, wherein an effective center of the second excitation force is located outside the measuring tube transverse plane, wherein the measuring and operating circuit is configured to apply a first excitation signal only to the first electrodynamic exciter,whose frequency corresponds to a current natural frequency of a symmetrical oscillation mode of the oscillator, and wherein the measuring and operating circuit (70) is configured to apply only to the second electrodynamic exciter a second excitation signal whose frequency corresponds to a current natural frequency of an antisymmetrical oscillation mode of the oscillator.

[0007] For an exciter featuring a coaxial arrangement of a rotationally symmetric magnet and a rotationally symmetric coil, the effective center of the excitation force lies on the common axis of rotational symmetry. For other designs, the center of the excitation force for an electrodynamic exciter is determined as the center of gravity of the integral of the force density between the magnet and the coil.

[0008] In a further development of the invention, the first component of the second electrodynamic exciter has a first center of gravity, wherein the first balancing mass body has a second center of gravity, wherein a distance of a common center of gravity of the first center of gravity and the second center of gravity from the measuring tube transverse plane is not more than 5%, in particular not more than 2% of the distance of the first center of gravity from the second center of gravity.

[0009] In a further development of the invention, the total mass of the first component of the second electrodynamic exciter and of the first balancing mass body is not more than one time, in particular not more than half the mass of the first component of the first electrodynamic exciter.

[0010] In a further development of the invention, the at least one first measuring tube has a free oscillation length which extends between an inlet-side fixing of the measuring tube and an outlet-side fixing of the measuring tube, wherein the center of the second excitation force FE2 is spaced from the transverse plane (EQ) of the measuring tube by not less than 1% of the free oscillation length and not more than 10% of the free oscillation length.

[0011] In a further development of the invention, one of the components of the first electrodynamic exciter has a first excitation coil, wherein one of the components of the second electrodynamic exciter has a second excitation coil, wherein the inductance of the first excitation coil is not less than twice, in particular not less than four times, the inductance of the second excitation coil.

[0012] In a further development of the invention, the other of the components of the first electrodynamic exciter has a first magnet, wherein the other component of the second electrodynamic exciter comprises a second magnet, wherein an orthogonal projection of the first magnet and the second magnet onto a plane which is perpendicular to the direction of oscillation of the at least one measuring tube overlaps with an orthogonal projection of the first excitation coil or the second excitation coil onto this plane.

[0013] In this development of the invention, the area of ​​the overlapping orthogonal projections of the components of the first electrodynamic exciter is at least twice, for example at least three times and in particular at least four times the area of ​​the overlapping orthogonal projections of the components of the second electrodynamic exciter.

[0014] In a further development of the invention, the distance of the second electrodynamic exciter from the sensor arrangement closest to it is not less than four times, in particular not less than eight times the distance of the second electrodynamic exciter from the first electrodynamic exciter.

[0015] In a further development of the invention, a main axis of inertia of the first excitation assembly runs in the measuring tube transverse plane (EQ).

[0016] In a further development of the invention, the first excitation 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.

[0017] In a further development of the invention, the first excitation assembly has a first carrier body on which the second excitation coil and the at least one first balancing mass body are arranged, wherein the first carrier body is formed symmetrically with respect to the measuring tube transverse plane EQ.

[0018] In a further development of the invention, the oscillator further comprises a second measuring tube, wherein the first measuring tube and the second measuring tube extend mirror-symmetrically to one another with respect to a measuring sensor longitudinal plane, wherein the measuring sensor longitudinal plane extends perpendicular to the measuring tube transverse plane EQ.

[0019] In a further development of the invention, the second excitation assembly is fastened to the second measuring tube opposite the first excitation assembly, wherein the center of gravity of the second excitation assembly lies in the measuring tube transverse plane EQ except for manufacturing tolerances.

[0020] In a further development of the invention, a main axis of inertia of the second excitation assembly runs in the measuring tube transverse plane EQ.

[0021] In a further development of the invention, the second excitation assembly has a second carrier body on which the second magnet and a second balancing mass body are arranged, wherein the second carrier body is formed symmetrically with respect to the measuring tube transverse plane EQ.

[0022] If the sensor comprises only a single measuring tube, according to a further development of the invention, the excitation assembly, which carries the magnets, is arranged on the measuring tube, while the excitation assembly, which carries the coils, is fixed to a comparatively rigid support tube or frame of the sensor. With this arrangement, the measuring tube can be excited to oscillate relative to the support tube or frame. This eliminates the need for cabling along the measuring tube. The same applies to the arrangement of the sensors.

[0023] In a further development of the invention, the measuring and operating circuit is configured to excite the first symmetrical oscillation mode and the first antisymmetrical oscillation mode, to determine the natural frequencies of the first symmetrical oscillation mode and the first antisymmetrical oscillation mode on the basis of the natural frequencies of the first symmetrical oscillation mode and the first antisymmetrical oscillation 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 regard to a resonator effect due to a gas loading of the medium.

[0024] The invention will now be explained in more detail with reference to the embodiments shown in the drawings.

[0025] It shows: Fig. 1a : a representation of an embodiment of a measuring sensor according to the invention; Fig. 1b :a schematic side view of a first excitation assembly of the sensor from Fig. 1a viewed from the direction of the second excitation assembly; Fig. 1c : a schematic side view of a second excitation assembly of the sensor from Fig. 1a viewed from the direction of the first excitation assembly; Fig. 2 : a diagram of the vibration modes of a sensor; and Fig. 3 : a flow diagram for determining the density and mass flow of a compressible medium using the measuring sensor according to the invention.

[0026] The Fig. 1a The sensor 1 shown for measuring mass flow and density comprises an oscillator 10 with two essentially parallel, curved measuring tubes 10.1, 10.2 and an excitation arrangement 11 that acts between the measuring tubes 10 to excite them to bending vibrations against each other. Furthermore, the sensor 1 has two sensor arrangements 12a, 12b that are arranged symmetrically to the transverse plane of the measuring tube in order to detect the measuring tube vibrations as a relative movement of the mutually vibrating measuring tubes 10.1, 10.2. The measuring tubes 10.1, 10.2 extend between two flow dividers (not shown) that fluidically combine the measuring tubes 10.1, 10.2 and are each connected to a flange 30a, 30b that serves to install the sensor 1 in a pipeline. The measuring tubes 10.1, 10.2 are also connected to each other on the inlet and outlet sides by at least one coupling plate 13a, 13b each, wherein the free oscillation length I of the measuring tubes 10.1, 10.2 is defined by the coupling plates 13a, 13b. A rigid support tube 60 extends between the flow dividers, connecting the flow dividers to one another in order to suppress oscillations of the flow dividers against one another in the frequency range of the bending oscillation modes of the oscillator 10. The support tube 60 further carries an electronics housing 80, shown only schematically here, in which a measuring and operating circuit 70 is contained, which is configured to operate the measuring sensor and carry out the method according to the invention.

[0027] The exciter arrangement 11 is arranged on the measuring tubes 10.1, 10.2 such that the center of mass of the exciter assembly lies in a transverse measuring tube plane EQ, which intersects the measuring tubes perpendicularly and with respect to which each of the measuring tubes has a mirror-symmetrical profile. The exciter arrangement comprises a first electrodynamic exciter 15, whose excitation force acts symmetrically to the transverse measuring tube plane between the measuring tubes to excite symmetrical bending vibration modes of the measuring tubes 10.1, 10.2. Furthermore, the exciter arrangement comprises a second electrodynamic exciter 18, whose excitation force acts parallel to the transverse measuring tube plane and offset approximately 5% in the longitudinal direction of the measuring tubes from the transverse measuring tube plane between the measuring tubes to excite antisymmetrical bending vibration modes of the measuring tubes 10.1, 10.2.In addition, the exciter arrangement has a balancing mass 19 to balance the mass of the second electrodynamic exciter 18 in order to keep the center of mass of the exciter arrangement in the transverse plane of the measuring tube.

[0028] Details of the excitation arrangement 11 are now given on the basis of the Fign. 1b und 1c explained.

[0029] The excitation arrangement 11 and the sensor arrangements 12a, 12b comprise, as usual, electrodynamic transducers, with a magnet arranged on one of the measuring tubes and a coil on the other for the transducers. This principle is known per se and needs no further explanation here. The special feature of the measuring sensor according to the invention is that the excitation arrangement 11, in addition to the excitation of symmetrical bending vibration modes, also enables the excitation of antisymmetrical bending vibration modes of the oscillator or its measuring tubes, while still being balanced with regard to its mass distribution. The excitation arrangement 11 comprises a first excitation assembly 11.1 on a first measuring tube 10.1, as shown in Fig. 1b is shown, and a second excitation assembly 11.2, which is arranged opposite the first excitation assembly 11.1 on a second measuring tube 10.2, as Fig. 1c shows.

[0030] The Fig. 1b The first excitation assembly 11.1 shown comprises a first ring segment 14.1, which partially surrounds the first measuring tube 10.1 symmetrically to the transverse plane of the measuring tube and is integrally joined to the first measuring tube 10.1, for example, by brazing. The first ring segment 14.1 holds a planar first carrier body 16.1, which runs essentially perpendicular to the transverse plane of the measuring tube and is designed symmetrically to the transverse plane of the measuring tube. The first carrier body 16.1 has a slotted first excitation component carrier 16.1.1 and a slotted first balancing mass carrier 16.1.2 and carries in its center a first excitation coil 15.1 of the first electrodynamic exciter 15. The first excitation component carrier 16.1.1 carries a second excitation coil 18.1 of the second electrodynamic exciter 18, which is connected to the first excitation component carrier 16.1 by means of a pin which is inserted in a slot in the first excitation component carrier 16.1.1 engages, positioned, and is fixed to the latter, for example, by soldering, gluing, or screwing. The first balancing mass carrier 16.1.2 carries a first balancing mass body 19.1, which is positioned by means of a pin that engages in a slot of the first balancing mass carrier 16.1.2 and is fixed to the latter, for example, by soldering, gluing, or screwing. The first balancing mass body 19.1 is matched to the mass of the second excitation coil 18.1 such that the common center of gravity lies in the measuring tube transverse plane. In particular, the first balancing mass body 19.1 and the second excitation coil 18.1 have the same mass. A principal axis of inertia of the first excitation assembly 11.1 runs in the measuring tube transverse plane EQ.

[0031] The Fig. 1c The second excitation assembly 11.2 shown comprises a second ring segment 14.2, which partially surrounds the second measuring tube 10.2 symmetrically to the transverse plane of the measuring tube and is integrally joined to the second measuring tube 10.2, for example, by brazing. The second ring segment 14.2 holds a particularly planar second carrier body 16.2, which runs essentially perpendicular to the transverse plane of the measuring tube and is designed symmetrically to the transverse plane of the measuring tube. The second carrier body 16.2 has a slotted second excitation component carrier 16.2.1 and a slotted second balancing mass carrier 16.2.2 and carries in its center a first excitation magnet 15.2 of the first electrodynamic exciter 15. The second excitation component carrier 16.2.1 carries a second excitation magnet 18.2 of the second electrodynamic exciter 18, which is pivotally mounted on the second excitation component carrier 16.2 by means of a pin which is inserted into a slot in the second excitation component carrier 16.2.1 engages, is positioned, and is fixed to the latter, for example, by soldering, gluing, or screwing. The second balancing mass carrier 16.2.2 carries a second balancing mass body 19.2, which is positioned by means of a pin that engages in a slot of the second balancing mass carrier 16.2.2 and is fixed to the latter, for example, by soldering, gluing, or screwing. The second balancing mass body 19.2 is matched to the mass of the second excitation magnet 18.2 such that the common center of gravity lies in the measuring tube transverse plane EQ. In particular, the second balancing mass body 19.2 and the second excitation magnet 18.2 have the same mass. A principal axis of inertia of the second excitation assembly 11.2 runs in the measuring tube transverse plane EQ.

[0032] The second ring segment 14.2 is in particular identical in construction to the first ring segment 14.1 and the second carrier body 16.2 is in particular identical in construction to the first carrier body 16.1.

[0033] The main axes of inertia of the first excitation assembly 11.1 and the second excitation assembly 11.2 in the transverse plane of the measuring tube run parallel to each other and in particular mirror-symmetrically to each other with respect to a measuring sensor longitudinal plane which runs between the two measuring tubes 10.1, 10.2, wherein the two measuring tubes are arranged mirror-symmetrically to each other with respect to the measuring sensor longitudinal plane.

[0034] The first excitation coil 15.1 and the second excitation coil 18.1 are each configured to be supplied by the measuring and operating circuit 70 with an alternating current signal specific to the excitation coil, the frequency of which corresponds to the instantaneous natural frequency of a bending vibration mode to be excited. For the first excitation coil 15.1, these are the frequencies of the symmetrical bending vibration modes, and for the second excitation coil 18.1, these are the frequencies of the antisymmetrical bending vibration modes. Of course, alternating current signals of different frequencies of the respective symmetry class can also be superimposed, for example, with the instantaneous natural frequencies of the first symmetrical and second symmetrical bending vibration modes for the first excitation coil 15.1 and with the instantaneous natural frequencies of the first antisymmetrical bending vibration mode and the second antisymmetrical bending vibration mode for the second excitation coil 18.1.The resulting magnetic fields cause alternating attractive and repulsive forces on the excitation magnets 15.2 18.2, which are opposite the field-generating excitation coil, whereby the two measuring tubes 10.1, 10.2 of the oscillator are set into oscillation against each other in the selected bending vibration modes.

[0035] The excitation magnets 15.2, 18.2 and the excitation coils 15.1, 18.1, as well as the two balancing masses 19.1, 19.2, are preferably designed to be rotationally symmetrical, with the axis of rotation running essentially in the direction of the vibrations of the measuring tubes. In particular, the excitation magnets 15.2, 18.2, the excitation coils 15.1, 18.1, and the two balancing masses 19.1, 19.2 exhibit cylindrical symmetry, at least in sections.

[0036] The mode-dependent deflection of a measuring tube is Fig. 2 shown schematically. Here, the curve a(f 1 ) shows the bending line of a measuring tube for the first symmetrical oscillation mode, which is also called the drive mode or f 1 mode. The curve a(f 2 ) shows the bending line of the measuring tube for the first antisymmetrical oscillation mode, in which the measuring tube is deflected by the Coriolis forces when a mass flow flows through the measuring tube oscillating with the first symmetrical oscillation mode. The first antisymmetrical oscillation mode has an oscillation node in the longitudinal direction of the measuring tube in the middle of the tube at z = 0. An exciter at this position would not be able to excite an oscillation of the first antisymmetrical oscillation mode. Therefore, the second electrodynamic exciter 18 is positioned here such that its excitation force F E2 acts between the measuring tubes offset by approximately 2.5% of the measuring tube length, i.e. approximately 5% of half the measuring tube length, compared to the transverse plane of the measuring tube.The measuring tube length is the length of a measuring tube center line following the curved course of a measuring tube between the points shown in . Fig. 1a illustrated coupling plates 13a, 13b. In the offset position, the second electrodynamic exciter 18 can excite the first antisymmetric oscillation mode by applying an excitation force F E2 with the resonance frequency of the first antisymmetric oscillation mode.

[0037] The first antisymmetric vibration mode only needs to be excited to the extent that its natural frequency can be determined, which is possible even with a minimal vibration amplitude. Therefore, the second electrodynamic exciter 18 can be much smaller and lighter than the first electrodynamic exciter 15, which is used to excite the first symmetric bending vibration mode, the so-called useful bending vibration mode.

[0038] The positions of the sensor arrangements 12a, 12b are selected in the longitudinal direction z symmetrically to the center of the measuring tubes so that deflections of the vibration sensors produce a sufficient measurement signal both during vibrations in the drive mode and the first antisymmetric vibration mode.

[0039] The measuring and operating circuit is configured to excite the first symmetrical oscillation mode and the first antisymmetrical oscillation mode by feeding the respectively associated excitation coil with an excitation current, to determine the natural frequencies of the first symmetrical oscillation mode and the first antisymmetrical oscillation mode on the basis of the natural frequencies of the first symmetrical oscillation mode and the first antisymmetrical oscillation 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 regard to a resonator effect due to a gas loading of the medium.The influence of this so-called resonator effect can be corrected by detecting the natural frequencies of two vibration modes, essentially determining a sound velocity of the medium for which the two natural frequencies yield consistent density measurements for the medium. Details of this are disclosed, for example, in DE 10 2015 122 661 A1, according to the teaching described therein, the first and second symmetric vibrations are gungsmode are to be evaluated. Based on Fig. 3The method 100 for which the measuring and operating circuit is designed is now explained. In a first step 110, the first symmetrical and the first antisymmetrical oscillation modes, i.e. the f 1 mode and the f 2 mode, are excited. In a second step 120, a preliminary density measurement value ρ 1 , ρ 2 is determined based on the natural frequencies of the excited modes. For incompressible media, the two density measurements essentially agree. If deviations exist, a correction factor is determined in the next step 130, which depends on the speed of sound of the compressible medium. Accordingly, as disclosed in DE 10 2015 122 661 A1, the speed of sound is first determined, which leads to the observed ratio of the preliminary density measurements.Based on the speed of sound and one of the natural frequencies, a density error and a correction factor can then be determined, with which a corrected density measurement value ρ corr is then determined in the next step 140.

[0040] To provide a correct mass flow rate measurement, a preliminary mass flow rate measurement is first determined 150. In a next step 160, a flow correction factor is determined based on the density error or density correction factor, as also disclosed in DE 10 2015 122 661 A1. In a final step 170, a correct mass flow rate measurement is determined by correcting the preliminary mass flow rate measurement with the correction factor.

Claims

1. Vibronic transducer (1), comprising: an oscillator (10) with at least one first measuring tube (10.1, 10,2) for guiding a medium; at least one electrodynamic exciter arrangement (11) for exciting the oscillator (10) to bending oscillations of the at least one first measuring tube (10.1, 10, 2); at least one sensor arrangement (12a) on the inlet side for detecting the bending vibrations of the at least one first measuring tube (10.1, 10, 2); at least one sensor arrangement (12b) on the outlet side for detecting the bending vibrations of the at least one first measuring tube (10.1, 10, 2); and a measuring and operating circuit (70) which is set up to apply at least one excitation signal to the electrodynamic exciter arrangement (11) and to detect sensor signals from the sensor arrangements (12a, 12b) on the inlet side and outlet side, and to determine a measured density value and / or a measured mass flow rate value on the basis of the sensor signals, wherein the electrodynamic exciter arrangement has a first exciter assembly (11.1, 11.2) which is fastened to the at least one first measuring tube (10.1, 10.2), and a second exciter assembly (11.2) with respect to which the at least one first measuring tube is to be excited to oscillate, wherein the first exciter assembly (11.1, 11.2) has a center of gravity which, apart from manufacturing tolerances, lies in a measuring tube transverse plane (EQ) which extends perpendicularly to the at least one first measuring tube (10.1, 10.2).1, 11.2) has a center of gravity which, apart from manufacturing tolerances, lies in a measuring tube transverse plane (EQ) which runs perpendicular to the at least one first measuring tube (10.1, 10.2), and with respect to which the at least one first measuring tube (10.1, 10.2) has a substantially mirror-symmetrical course; wherein the electrodynamic exciter arrangement (11) comprises a first electrodynamic exciter (15), wherein the exciter arrangement (11) comprises a second electrodynamic exciter (18) and at least one first equalizing mass body (19.1, 19.2), wherein the first exciter assembly comprises a first component of the first electrodynamic exciter and a first component of the second electrodynamic exciter and the first equalizing mass body, wherein the second exciter assembly comprises a second component of the first electrodynamic exciter and a second component of the second electrodynamic exciter, wherein the first electrodynamic exciter (18) is arranged to exert an excitation force (FE1) on the at least one first measuring tube (10.1, 10.2), which acts between the first and the second component of the first electrodynamic exciter, wherein an effective center of the first excitation force (FE1) is localized in the transverse plane (EQ) of the measuring tube, the second electrodynamic exciter being set up to exert a second excitation force (FE2) on the at least one measuring tube (10.1, 10.2), which acts between the first and the second component of the second electrodynamic exciter, an effective center of the second excitation force (FE2) being localized outside the transverse plane (EQ) of the measuring tube, wherein the measuring and operating circuit (70) is arranged to apply a first excitation signal only to the first electrodynamic exciter, the frequency of which corresponds to a current natural frequency of a symmetrical oscillation mode of the oscillator, and wherein the measuring and operating circuit (70) is arranged to apply a second excitation signal only to the second electrodynamic exciter, the frequency of which corresponds to a current natural frequency of an antisymmetrical oscillation mode of the oscillator.

2. Measuring transducer (1) according to claim 1, wherein the first component of the second electrodynamic exciter has a first center of gravity, wherein the first balancing mass body has a second center of gravity, wherein a distance of a common center of gravity of the first center of gravity and the second center of gravity from the measuring tube transverse plane is not more than 5%, in particular not more than 2%, of the distance of the first center of gravity from the second center of gravity.

3. Measuring sensor (1) according to claim 1 or 2, wherein the total mass of the first component of the second electrodynamic exciter and of the first equalizing mass body is not more than one times, in particular not more than half, the mass of the first component of the first electrodynamic exciter.

4. Measuring transducer (1) according to one of claims 1 to 3, wherein the at least one first measuring tube (10.1, 10.2) has a free oscillation length extending between an inlet-side fixation of the measuring tube and an outlet-side fixation of the measuring tube (10.1, 10.2), wherein the center of the second excitation force FE2 is spaced not less than 1% of the free oscillation length and not more than 10% of the free oscillation length from the measuring tube transverse plane (EQ).

5. Measuring transducer (1) according to one of the preceding claims, wherein one of the components of the first electrodynamic exciter (15) comprises a first excitation coil (15.1), and wherein one of the components of the second electrodynamic exciter (18) comprises a second excitation coil (18.1), wherein the inductance of the first excitation coil (15.1) is not less than twice, in particular not less than four times, the inductance of the second excitation coil (18.1).

6. The transducer (1) according to claim 3, wherein the other of the components of the first electrodynamic exciter (15) comprises a first magnet (15.2), and wherein the other of the components of the second electrodynamic exciter (18) comprises a second magnet (18.2), wherein an orthogonal projection of the first magnet (15.2) and the second magnet (18.2) onto a plane perpendicular to the direction of oscillation of the at least one measuring tube is aligned with an orthogonal projection of the first excitation coil (15.1) or the second excitation coil (18.1) onto this plane, wherein the area of the overlapping orthogonal projections of the components of the first electrodynamic exciter is at least twice, for example at least three times and in particular at least four times the area of the overlapping orthogonal projections of the components of the second electrodynamic exciter.

7. Measuring sensor according to one of the preceding claims, wherein the distance of the second electrodynamic exciter from the sensor arrangement nearest to it is not less than four times, in particular not less than eight times, the distance of the second electrodynamic exciter from the first electrodynamic exciter.

8. Measuring sensor (1) according to one of the preceding claims, wherein a main axis of inertia of the first exciter assembly (11.1) extends in the transverse plane (EQ) of the measuring tube.

9. Measuring sensor (1) according to one of the preceding claims, characterized in that the first exciter assembly (11.1) is fastened to the at least one measuring tube (10.1) by means of a joining point, the transverse plane (EQ) of the measuring tube running through a centre of gravity of the joining point.

10. Measuring sensor (1) according to one of the preceding claims, wherein the first exciter assembly (11.1) has a first carrier body (16.1), on which the second exciter coil (18.1) and the at least one first equalizing mass body (19.1) are arranged, wherein the first carrier body (16.1) is designed symmetrically with respect to the measuring tube transverse plane (EQ).

11. Measuring transducer (1) according to one of the preceding claims, wherein the oscillator (10) further comprises a second measuring tube (10.2), wherein the first measuring tube (10.1) and the second measuring tube (10.2) extend mirror-symmetrically to each other with respect to a longitudinal plane of the measuring transducer, wherein the longitudinal plane of the measuring transducer extends perpendicular to the transverse plane (EQ) of the measuring tube.

12. Measuring sensor (1) according to claim 11, wherein the second exciter assembly (11.2) is fastened to the second measuring tube (10.2) opposite the first exciter assembly (11.1), wherein the center of gravity of the second exciter assembly (11.2) lies in the transverse plane (EQ) of the measuring tube except for manufacturing tolerances.

13. Measuring sensor (1) according to claim 11 or 12, wherein a main axis of inertia of the second exciter assembly (11.2) extends in the transverse plane (EQ) of the measuring tube.

14. Measuring sensor (1) according to one of the preceding claims, wherein the second exciter assembly (11.2) has a second carrier body (16.2), on which the second magnet (18.2) and a second equalizing mass body (19.2) are arranged, wherein the second carrier body (16.2) is designed symmetrically with respect to the transverse plane (EQ) of the measuring tube.

15. Measuring sensor (1) according to one of the preceding claims, wherein the measuring and operating circuit (70) is set up to excite the first symmetrical oscillation mode and the first antisymmetrical oscillation mode, to determine the natural frequencies of the first symmetrical oscillation mode and the first antisymmetrical oscillation mode on the basis of the natural frequencies of the first symmetrical oscillation mode and the first antisymmetrical oscillation 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 a gas loading of the medium. the measured mass flow rate value is corrected with respect to a resonator effect due to gas loading of the medium.