Vibronic measuring sensor for mass flow and density measurement with a monitoring function
The vibronic sensor uses dual electrodynamic exciters with samarium-cobalt and AINiCo magnets to ensure long-term stability and accurate monitoring of measuring tube conditions, addressing the challenge of undetected changes due to corrosion and abrasion, thus maintaining precise mass flow and density measurements.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ENDRESS HAUSER FLOWTEC AG
- Filing Date
- 2025-12-03
- Publication Date
- 2026-07-02
AI Technical Summary
Existing vibronic sensors for mass flow and density measurement face challenges in accurately monitoring changes due to abrasion, corrosion, or deposit formation on components like permanent magnets, which can impair measurement accuracy and go undetected, especially at high temperatures.
The sensor employs two electrodynamic exciters with excitation magnets made of different hard magnetic materials, one with samarium-cobalt for excitation and another with AINiCo, ensuring long-term stability and reliable detection of changes in measuring tube conditions by using excitation frequencies that are independent of aging effects.
This configuration allows for more reliable monitoring of changes in the measuring tube, enhancing the sensor's ability to detect corrosion, abrasion, or deposit formation, thereby maintaining accurate mass flow and density measurements.
Smart Images
Figure EP2025085380_02072026_PF_FP_ABST
Abstract
Description
[0001] Vibronic sensor for mass flow and density measurement with monitoring function
[0002] The present invention relates to a vibronic sensor for mass flow and density measurement with monitoring function.
[0003] Patent EP 3894802 B1 relates to a method for monitoring a sensor with at least one vibrating measuring tube for mass flow and density measurement. In these sensors, the measuring tube is excited to vibrate by an electrodynamic exciter, and the vibrations are detected by electrodynamic sensors, with the ratio between a vibration signal amplitude and an excitation signal amplitude being considered as a monitoring parameter. Such monitoring is particularly necessary when measuring tubes can change their vibration characteristics due to abrasion, corrosion, or deposit formation, which can impair the measurement accuracy of the sensors.Besides the measuring tubes, other components of the sensor that affect the monitored parameter can also exhibit variable properties, making it difficult to attribute observed changes in the monitored parameter to specific causes. Candidates for components with variable properties include the permanent magnets of electrodynamic exciters and vibration sensors. These permanent magnets can age, particularly at high temperatures, which causes a decrease in the monitored parameter. Since this counteracts an increase in the monitored parameter, for example, due to corrosion of the measuring tube, this combination of changes in sensor components can go undetected.
[0004] It is therefore the object of the present invention to remedy this situation. This object is achieved according to the invention by the measuring sensor according to independent claim 1.
[0005] The vibronic sensor according to the invention comprises: an oscillator with at least one first measuring tube for guiding a medium; a first electrodynamic exciter for exciting the oscillator to bending vibrations of the at least one first measuring tube, wherein the first electrodynamic exciter comprises a first excitation coil and a first excitation magnet, which interact to excite the bending vibrations; at least one second electrodynamic exciter for exciting the oscillator to bending vibrations of the at least one first measuring tube, wherein the at least one second electrodynamic exciter comprises at least one second excitation coil and at least one second excitation magnet, which interact to excite the bending vibrations; at least one inlet-side electrodynamic sensor arrangement for detecting the bending vibrations of the at least one first measuring tube;and at least one outlet-side electrodynamic sensor arrangement for detecting the bending vibrations of the at least one first measuring tube; a measuring and operating circuit configured to drive the electrodynamic exciters with excitation signals; and to detect sensor signals of the electrodynamic sensor arrangements in order to determine a mass flow rate measurement and / or a density measurement, as well as to determine a monitoring parameter which depends on the state of the measuring tube; characterized in that the first excitation magnet comprises a first hard magnetic material, and the second excitation magnet comprises a second hard magnetic material, wherein the coercive field strength of the first hard magnetic material has a larger value H; c _i exhibits as the coercive field strength of the second hard magnetic material H c 2 , and where the energy product of the first hard magnetic material has a larger value (B ■ H) max_i exhibits as the energy product of the second hard magnetic material (B ■ H) max_2; wherein the coercive field strength and the energy product of the first hard magnetic material exhibit lower long-term stability at temperatures of not less than 280°C than the coercive field strength and the energy product of the second hard magnetic material; wherein the measuring and operating circuit is configured to drive the first electrodynamic exciter with an excitation current of a first excitation frequency corresponding to a natural frequency of a bending vibration of the at least one measuring tube, to drive the second electrodynamic exciter with an excitation current of a second excitation frequency which causes an excitation of a bending vibration of the measuring tube out of resonance, to determine the mass flow rate and / or the density value based on the vibrations of the at least one measuring tube at the first excitation frequency, and to determine a value of the monitoring parameter based on the vibrations of the measuring tube at the second excitation frequency.
[0006] The long-term stability LX(t) of a quantity X can, for example, be described as the difference between one and the magnitude of the relative change of the quantity X(t) after a time t relative to an initial value X(0), i.e., LX(t) = 1 - |(x(t) - x(0)) / (X(0)|. The time t can, for example, be several months, in particular 2, 3, or 4 months. In connection with the present invention, the quantity X can, in particular, be the coercive field strength, the energy product, or a remanent flux density of a hard magnetic material.
[0007] The value of the monitoring parameter can depend, in particular, on the ratio of a sensor signal amplitude to an excitation current amplitude of the same frequency. By using the second hard magnetic material, which exhibits greater long-term stability than the first hard magnetic material, the influence of a change in the excitation magnet on the monitoring parameter is reduced, thus enabling more reliable detection of changes in at least one measuring tube due to corrosion, abrasion, or deposit formation.
[0008] In a further development of the invention, the first hard magnetic material exhibits a first remanent flux density value B. r _i, where the second hard magnetic material has a second remanent flux density value B r 2 exhibits, with the first remanent flux density exhibiting lower long-term stability at temperatures of not less than 280°C than the second remanent flux density.
[0009] In a further development of the invention, the at least one inlet-side electrodynamic sensor arrangement and the at least one outlet-side electrodynamic sensor arrangement each comprise an electrodynamic sensor with a sensor coil and a sensor magnet, which has a third hard magnetic material that differs from the first hard magnetic material.
[0010] In a further development of the invention, the first hard magnetic material contains at least samarium and cobalt.
[0011] In a further development of the invention, the second hard magnetic material comprises at least iron, aluminum, nickel and cobalt.
[0012] In a further development of the invention, the third hard magnetic material comprises at least iron, aluminium, nickel and cobalt and in particular has the same composition as the second hard magnetic material.
[0013] In a further development of the invention, the at least one measuring tube extends in a mirror-symmetric manner with respect to a transverse plane of the measuring tube which intersects a guide curve of the measuring tube, wherein the first electrodynamic exciter is arranged symmetrically to the transverse plane of the measuring tube, wherein an excitation force field of the first electrodynamic exciter acts symmetrically to the transverse plane of the measuring tube.
[0014] In a further development of the invention, the at least one measuring tube is mirror-symmetric with respect to a measuring tube transverse plane which intersects a guide curve of the measuring tube, wherein an excitation force field of the at least one second electrodynamic exciter acts symmetrically to the measuring tube transverse plane.
[0015] In a further development of the invention, the at least one measuring tube is mirror-symmetric with respect to a measuring tube transverse plane which intersects a guide curve of the measuring tube, wherein an excitation force field of the at least one second electrodynamic exciter acts asymmetrically to the measuring tube transverse plane.
[0016] In a further development of the invention, exactly one second electrodynamic exciter is included, wherein the second exciter magnet has a center of gravity, wherein the at least one measuring tube has a free oscillation length extending between an inlet-side fixing of the measuring tube and an outlet-side fixing of the measuring tube, wherein the center of gravity of the second exciter magnet is spaced not less than 1%, in particular not less than 2% of the free oscillation length and for example not more than 10% of the free oscillation length from the transverse plane (EQ) of the measuring tube.
[0017] In a further development of the invention, the measuring sensor has exactly two second electrodynamic exciters, each of which has a center of gravity, wherein the centers of gravity of the two second electrodynamic exciters are arranged symmetrically to the transverse plane of the measuring tube.
[0018] In a first embodiment of this further development of the invention, the two second excitation coils of the two second electrodynamic exciters are connected in series, wherein the polarities of the second excitation coils are matched to the polarity of the second excitation magnets such that both second electrodynamic exciters operate in phase. This results in, in particular, the excitation of a symmetrical measuring tube oscillation.
[0019] In a second embodiment of this further development of the invention, the two second excitation coils of the two second electrodynamic exciters are connected in series, the polarities of the second excitation coils being matched to the polarity of the second excitation magnets such that both electrodynamic exciters operate in opposite phases. This results, in particular, in the excitation of an antisymmetric measuring tube oscillation. This provides access to monitoring the modal stiffness of the corresponding antisymmetric bending vibration mode of the measuring tube, which modal stiffness directly affects the calibration factor for the mass flow measurement.
[0020] The invention will now be explained in more detail with reference to the exemplary embodiments shown in the drawings. These show:
[0021] Fig. 1a: a representation of a first embodiment of a measuring sensor according to the invention; Fig. 1b: a schematic side view of a first excitation assembly of the measuring sensor from Fig. 1a viewed from the direction of the second excitation assembly;
[0022] 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;
[0023] Fig. 2a: a schematic side view of a first excitation assembly of a second embodiment of a measuring sensor according to the invention, viewed from the direction of the second excitation assembly;
[0024] Fig. 2b: a schematic side view of a second excitation assembly of the sensor from Fig. 2a, viewed from the direction of the first excitation assembly;
[0025] Fig. 3a: a schematic side view of a first excitation assembly of a third embodiment of a measuring sensor according to the invention, viewed from the direction of the second excitation assembly; and
[0026] Fig. 3b: a schematic side view of a second excitation assembly of the sensor from Fig. 3a, viewed from the direction of the first excitation assembly.
[0027] The measuring instrument 1 shown in Fig. 1a for measuring mass flow rate and density comprises an oscillator 10 with two substantially parallel, curved measuring tubes 10.1, 10.2, and an excitation arrangement 11 with two electrodynamic exciters 15, 18, which act between the measuring tubes 10 to excite them to bending vibrations relative to each other. Furthermore, the measuring instrument 1 has two electrodynamic sensors 12a, 12b, which are arranged symmetrically to a transverse plane EQ of the measuring tubes in order to detect the measuring tube vibrations as the relative motion of the oscillating measuring tubes 10.1, 10.2 relative to each other. The measuring tubes 10.1, 10.2 extend between two (not shown) flow dividers, which fluidically combine the measuring tubes 10.1, 10.2 and are each connected to a flange 30a, 30b, which serves for installing the sensor 1 in a pipeline. The measuring tubes 10.1, 10.The two flow dividers are connected to each other on the inlet and outlet sides by at least one coupling plate 13a, 13b, whereby the coupling plates 13a, 13b define the free oscillation length I of the measuring tubes 10.1, 10.2. A rigid support tube 60 extends between the flow dividers, connecting them to suppress oscillations between the flow dividers in the frequency range of the bending modes of the oscillator 10. The support tube 60 also carries an electronics housing 80, shown here only schematically, which contains a measuring and operating circuit 70 configured to operate the sensor.
[0028] The excitation arrangement 11 is arranged on the measuring tubes 10.1 and 10.2 such that their center of mass lies in a transverse plane EQ of the measuring tubes, which intersects the measuring tubes perpendicularly and with respect to which each of the measuring tubes has a mirror-symmetric orientation. The excitation arrangement comprises a first electrodynamic exciter 15, whose excitation force acts symmetrically to the transverse plane of the measuring tubes between the measuring tubes in order to excite symmetric bending modes of the measuring tubes 10.1 and 10.2. Furthermore, the excitation arrangement comprises a second electrodynamic exciter 18, whose excitation force acts parallel to the transverse plane of the measuring tubes and offset by approximately 5% in the longitudinal direction of the measuring tubes to the transverse plane of the measuring tubes between the measuring tubes in order to excite a proportion of an antisymmetric bending mode of the measuring tubes 10.1 and 10.2.In addition, the exciter arrangement has a balancing mass 19 to compensate for 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.
[0029] Details of the pathogen arrangement 11 will now be explained with reference to Figs. 1b and 1c.
[0030] The excitation arrangement 11 and the sensor arrangements 12a, 12b, as usual, have electrodynamic transducers, wherein a magnet 15.2, 18.2 is arranged on one of the measuring tubes and a coil (15.1, 18.1) on the other. This principle is known per se and need not be explained in detail here. The special feature of the measuring transducer according to the invention lies in the fact that the excitation arrangement 11 has two electrodynamic exciters with excitation magnets made of different hard magnetic materials. Thus, the first electrodynamic exciter 15 has an excitation magnet 15.2, which comprises a samarium-cobalt magnet, for example, a magnet available under the trademark RECOMA, or, for example, SmCo5. With this excitation magnet, maximum vibration amplitudes of the symmetrical bending vibration modes can be achieved for a given excitation current. Samarium-cobalt magnets are specified for operating temperatures up to 350°.This is entirely sufficient for the purpose of exciting bending vibrations for flow and density measurement, even if the excitation force amplitude currently decreases by a few percent at high temperatures. However, monitoring the measuring tube condition based on signal amplitudes can be affected by such a change. Therefore, a second electrodynamic exciter 18 is provided for the monitoring function. This exciter is located outside the transverse plane of the measuring tube and has a second excitation magnet 18.2 that is an AINiCo magnet specified for operating temperatures up to 550 °C. While the vibration amplitudes that can be excited with this magnet for a given excitation current are considerably lower than those achievable with a samarium-cobalt magnet, they are still sufficient.However, the excitation force amplitude is considerably more stable over the long term, meaning that changes in the sensor signal amplitudes at the excitation frequency of the second electrodynamic exciter, which is, for example, 1.1 to 1.4 times the natural frequency of the symmetrical bending vibration mode, are largely independent of aging of the second excitation magnet.
[0031] The excitation arrangement 11 thus comprises a first excitation assembly 11.1 on a first measuring tube 10.1, as shown in Fig. 1b, 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 shown in Fig.
[0032] Figure 1c shows the first excitation assembly 11.1, which comprises a first ring segment 14.1 that partially surrounds the first measuring tube 10.1 symmetrically to the transverse plane of the measuring tube and is joined to the first measuring tube 10.1 by a material bond, for example by brazing. The first ring segment 14.1 holds a first support body 16.1, which is planar in particular and extends substantially perpendicular to the transverse plane of the measuring tube. The first support body 16.1 has a slotted first excitation component carrier 16.1.1 and a slotted first compensating 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 by means of a pin that is in a slot of the first excitation component carrier 16.1.The first compensating mass carrier 16.1.2 carries a first compensating mass body 19.1, which is positioned by means of a pin that engages in a slot of the first compensating mass carrier 16.1.2 and is fixed to the latter, for example, by soldering, gluing, or screwing. The first compensating mass body 19.1 is matched to the mass of the second excitation coil 18.1 such that their common center of gravity lies in the transverse plane of the measuring tube. In particular, the first compensating 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 transverse plane EQ of the measuring tube.
[0033] The second excitation assembly 11.2 shown in Fig. 1c 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 joined to the second measuring tube 10.2 by a material bond, for example by brazing. The second ring segment 14.2 holds a second support body 16.2, which is planar in particular and extends substantially perpendicular to the transverse plane of the measuring tube, and is symmetrical to the transverse plane of the measuring tube. The second support body 16.2 has a slotted second excitation component carrier 16.2.1 and a slotted second compensating 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 connected by means of a pin that is in a slot of the second excitation component carrier 16.2.The second compensating mass carrier 16.2.2 carries a second compensating mass body 19.2, which is positioned by means of a pin that engages in a slot of the second compensating mass carrier 16.2.2 and is fixed to the latter, for example, by soldering, gluing, or screwing. The second compensating mass body 19.2 is matched to the mass of the second excitation magnet 18.2 such that their common center of gravity lies in the transverse plane EQ of the measuring tube. In particular, the second compensating 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 transverse plane EQ of the measuring tube.
[0034] The second ring segment 14.2 is in particular identical in construction to the first ring segment 14.1 and the second support body 16.2 is in particular identical in construction to the first support body 16.1.
[0035] The principal axes of inertia of the first exciter assembly 11.1 and the second exciter assembly 11.2 in the transverse plane of the measuring tube run parallel to each other and in particular are mirror-symmetric to each other with respect to a sensor longitudinal plane which runs between the two measuring tubes 10.1, 10.2, wherein the two measuring tubes are arranged mirror-symmetric to each other with respect to the sensor longitudinal plane.
[0036] 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, this is the frequency of the symmetrical bending vibration mode, which in particular has no nodes, and for the second excitation coil 18.1, this is 1.1 to 1.4 times the excitation frequency of the bending vibration mode.
[0037] The excitation magnets 15.2, 18.2 and the excitation coils 15.1, 18.1 as well as the two compensating mass bodies 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.
[0038] In particular, the excitation magnets 15.2, 18.2, the excitation coils 15.1, 18.1, and the two compensating mass bodies 19.1, 19.2 exhibit at least section-by-section cylindrical symmetry.
[0039] The positions of the electrodynamic vibration sensors 12a, 12b are selected symmetrically in the longitudinal direction z with respect to the center of the measuring tubes such that deflections of the vibration sensors produce a sufficient measurement signal even during vibrations in the bending mode. Preferably, the sensor magnets also feature AINiCo magnets. While this results in lower measurement signal amplitudes, they are independent of the aging of the sensor magnets.
[0040] The embodiment shown in Figures 2a and 2b comprises a first electrodynamic exciter 25 with a first excitation coil 25.1 and a first excitation magnet 25.2 comprising a samarium-cobalt magnet, whose center of gravity lies in the transverse plane EQ of the measuring tube. The embodiment further comprises two second electrodynamic exciters 28, 29, each with a second excitation coil 28.1, 29.1 and a second excitation magnet 28.2, 29.2 comprising an AINiCo magnet. The two second electrodynamic exciters 28, 29 are arranged symmetrically to each other with respect to the transverse plane of the measuring tubes 20.1, 20.2 and have a common center of gravity in the transverse plane of the measuring tubes. The two second excitation coils are connected in series. Depending on the polarity ratio of the excitation coils and excitation magnets, a strictly symmetrical or strictly antisymmetrical excitation of an oscillation of the measuring tubes 21.1 can be achieved.By exciting and monitoring the antisymmetric oscillation, more direct monitoring of changes in the calibration factor for flow measurement is possible. The coils of the three electrodynamic exciters are combined in a first excitation assembly 21.1, which is mounted on one of the measuring tubes 20.1. The excitation magnets of the three electrodynamic exciters are combined in a second excitation assembly 21.2, which is mounted on a second of the measuring tubes 20.2.
[0041] The embodiment shown in Figures 3a and 3b comprises a first electrodynamic exciter 35 with a first excitation coil 35.1 and a first excitation magnet 35.2, which includes a samarium-cobalt magnet, and whose center of gravity lies in the transverse plane EQ of the measuring tube. The embodiment further comprises a second electrodynamic exciter 38 with a second excitation coil 38.1 and a second excitation magnet 38.2, which includes an AINiCo magnet. The coils of the two electrodynamic exciters are combined in a first excitation assembly, which is mounted on a first of the measuring tubes 30.1. The excitation magnets of the two electrodynamic exciters are combined in a second excitation assembly, which is mounted on a second of the measuring tubes 30.2. The second electrodynamic exciter 28 has its center of gravity in the transverse plane of the measuring tube. It enables symmetrical excitation of an oscillation of the measuring tubes 30.1, 30.2.
Claims
Patent claims 1. Vibronal sensor (1), comprising: an oscillator (10) with at least one first measuring tube (10.1, 10.2; 20.1, 20.2; 30.1, 30.2) for guiding a medium; a first electrodynamic exciter (15; 25; 35) for exciting the oscillator (10) to bending vibrations of the at least one first measuring tube (10.1, 10.2; 20.1, 20.2; 30.1, 30.2), wherein the first electrodynamic exciter (15; 25; 35) comprises a first excitation coil (15.1; 25.1; 35.1) and a first excitation magnet (15.2; 25.2; 35.2); which interact to excite the bending vibrations; at least one second electrodynamic exciter (18; 28, 29; 38) for exciting the oscillator (10) to bending vibrations of the at least one first measuring tube (10.1, 10.2; 20.1, 20.2; 30.1, 30.2); wherein the at least one second electrodynamic exciter (18; 28, 29; 38) comprises at least one second excitation coil (18.1; 28.1, 28.2; 38.1) and at least one second excitation magnet (18.2; 28.2, 29.2; 38.2); which interact to excite the bending vibrations; at least one inlet-side electrodynamic sensor arrangement (12a) for detecting the bending vibrations of the at least one first measuring tube (10.1, 10.2; 20.1, 20.2; 30.1, 30.2); and at least one outlet-side electrodynamic sensor arrangement (12b) for detecting the bending vibrations of the at least one first measuring tube (10.1, 10,2; 20.1, 20,2; 30.1, 30,2); a measuring and operating circuit designed to drive the electrodynamic exciters with excitation signals; and to acquire sensor signals from the electrodynamic sensor arrangements in order to determine a mass flow rate measurement and / or a density measurement, as well as to determine a value of a monitoring parameter which depends on a state of the measuring tube; characterized by the fact that the first excitation magnet has a first hard magnetic material, and the second excitation magnet has a second hard magnetic material, whereby the coercive field strength of the first hard magnetic material has a larger value H c _i exhibits as the coercive field strength of the second hard magnetic material H c 2 , and where the energy product of the first hard magnetic material has a larger value (B ■ H)max_i than the energy product of the second hard magnetic material (B ■ H) max_2; where the coercive field strength and the energy product of the first hard magnetic material exhibit lower long-term stability at temperatures of not less than 280°C than the coercive field strength and the energy product of the second hard magnetic material; the measuring and operating circuit is set up for this purpose, to drive the first electrodynamic exciter with an excitation current of a first excitation frequency that corresponds to a natural frequency of a bending vibration of the at least one measuring tube, to drive the second electrodynamic exciter with an excitation current of a second excitation frequency that causes an excitation of a bending vibration of the measuring tube out of resonance, to determine the mass flow rate and / or density value based on the vibrations of at least one measuring tube with the first excitation frequency, and to determine the value of the monitoring parameter based on the vibrations of the measuring tube with the second excitation frequency.
2. Sensor (1) according to claim 1, wherein the first hard magnetic material has a first remanent flux density value B r _i exhibits, where the second hard magnetic material has a second remanent flux density value B r 2 exhibits wherein the first remanent flux density exhibits lower long-term stability at temperatures of not less than 280°C than the second remanent flux density.
3. Sensor (1) according to claim 1 or 2, wherein the at least one inlet-side electrodynamic sensor arrangement (12a) and the at least one outlet-side electrodynamic sensor arrangement (12b) each comprise an electrodynamic sensor with a sensor coil and a sensor magnet, which has a third hard magnetic material that differs from the first hard magnetic material.
4. Sensor (1) according to one of the preceding claims, wherein the first hard magnetic material comprises at least samarium and cobalt.
5. Sensor (1) according to one of the preceding claims, wherein the second hard magnetic material comprises at least iron, aluminium, nickel and cobalt.
6. Sensor (1) according to claim 3 or a claim dependent on claim 3, wherein the third hard magnetic material comprises at least iron, aluminium, nickel and cobalt, and in particular has the same composition as the second hard magnetic material.
7. Measuring sensor according to one of the preceding claims, wherein the at least one measuring tube is mirror-symmetric with respect to a measuring tube transverse plane which intersects a guide curve of the measuring tube, wherein the first electrodynamic exciter is arranged symmetrically to the measuring tube transverse plane, wherein an excitation force field of the first electrodynamic exciter acts symmetrically to the measuring tube transverse plane.
8. A measuring sensor according to any one of the preceding claims, wherein the at least one measuring tube is mirror-symmetric with respect to a transverse plane of the measuring tube which intersects a guide curve of the measuring tube, wherein an excitation force field of the at least one second electrodynamic exciter acts symmetrically with respect to the transverse plane of the measuring tube.
9. A measuring sensor according to any one of claims 1 to 7, wherein the at least one measuring tube is mirror-symmetric with respect to a transverse plane of the measuring tube which intersects a guide curve of the measuring tube, wherein an excitation force field of the at least one second electrodynamic exciter acts asymmetrically with respect to the transverse plane of the measuring tube.
10. Sensor (1) according to claim 9, wherein the sensor has exactly one second electrodynamic exciter, wherein the exciter magnet has a center of gravity, wherein the at least one measuring tube (10.1, 10.2) has a free oscillation length extending between an inlet-side fixing of the measuring tube and an outlet-side fixing of the measuring tube (10.1, 10.2), wherein the center of gravity is spaced not less than 1%, in particular not less than 2% of the free oscillation length and for example not more than 10% of the free oscillation length from the transverse plane (EQ) of the measuring tube.
11. Sensor (1) according to one of claims 1 to 7, wherein the sensor has exactly two second electrodynamic exciters, each having a center of gravity, wherein the centers of gravity of the two second electrodynamic exciters are arranged symmetrically to the transverse plane of the measuring tube.
12. Sensor (1) according to claim 11, wherein the two second excitation coils of the two second electrodynamic exciters are connected in series, wherein the polarities of the second excitation coils are matched to the polarity of the second excitation magnets such that both second electrodynamic exciters act in phase.
13. Sensor (1) according to claim 11, wherein the two second excitation coils of the two second electrodynamic exciters are connected in series, wherein the polarities of the second excitation coils are matched to the polarity of the second excitation magnets such that both electrodynamic exciters act in opposite phase.