VIBRONIC SENSOR

Description

[0001] The invention relates to a method for determining and / or monitoring the density and / or viscosity of a medium in a container by means of a vibronic sensor and to a device suitable for carrying out the method.

[0002] Vibronic sensors are widely used in process and / or automation technology. In the case of level gauges, they feature at least one mechanically vibrating unit, such as a tuning fork, a rod, or a diaphragm. During operation, this unit is excited into mechanical vibrations by a drive / receiver unit, often in the form of an electromechanical transducer unit, which in turn can be, for example, a piezoelectric or electromagnetic drive. In the case of flow meters, however, the mechanically vibrating unit can also be designed as a vibrating tube through which the respective medium flows, as in a measuring device operating on the Coriolis principle.

[0003] The applicant manufactures a wide variety of corresponding field devices, which, in the case of level measuring devices, are marketed, for example, under the names LIQUIPHANT or SOLIPHANT. The underlying measuring principles are known in principle from numerous publications. The drive / receiver unit excites the mechanically vibrating unit to mechanical vibrations by means of an electrical excitation signal. Conversely, the drive / receiver unit can receive the mechanical vibrations of the mechanically vibrating unit and convert them into an electrical reception signal. Accordingly, the drive / receiver unit is either a separate drive unit and a separate receiver unit, or a combined drive / receiver unit.

[0004] In many cases, the drive / receiver unit is part of a feedback-controlled electrical resonant circuit, which excites the mechanically oscillating unit to produce mechanical vibrations. For example, for resonant oscillation, the resonant circuit condition must be met, according to which the gain factor is ≥1 and all phases occurring in the resonant circuit are multiples of 360°.

[0005] To excite and fulfill the resonant circuit condition, a specific phase shift between the excitation signal and the received signal must be ensured. Therefore, a predefined value for the phase shift, i.e., a setpoint for the phase shift between the excitation signal and the received signal, is often set. Various solutions for this, both analog and digital methods, are known from the prior art. In principle, the phase shift can be set, for example, by using a suitable filter, or it can be controlled to a predefined phase shift, the setpoint, by means of a control loop. For example, DE102006034105A1 discloses the use of an adjustable phase shifter.The additional integration of an amplifier with an adjustable gain factor for further control of the oscillation amplitude was described in DE102007013557A1. DE102005015547A1 proposes the use of an all-pass filter. The phase shift can also be adjusted using a so-called frequency scan, as disclosed, for example, in DE102009026685A1, DE102009028022A1, and DE102010030982A1. Alternatively, the phase shift can be controlled to a predefinable value using a phase-locked loop (PLL). An excitation method based on this is the subject of DE00102010030982A1.

[0006] Both the excitation signal and the received signal are characterized by their frequency ω, amplitude A, and / or phase Φ. Accordingly, changes in these quantities are typically used to determine the respective process variable, such as a predetermined fill level of a medium in a container, or the density and / or viscosity of a medium, or the flow rate of a medium through a pipe. In the case of a vibronic level switch for liquids, for example, a distinction is made between whether the vibrating unit is submerged in the liquid or oscillating freely. These two states, the free state and the submerged state, are distinguished, for example, by their different resonant frequencies, i.e., a frequency shift. The density and / or viscosity, in turn, can only be determined with such a measuring device if the vibrating unit is submerged in the medium.

[0007] As described, for example, in DE10050299A1, the viscosity of a medium can be determined using a vibronic sensor based on the frequency-phase curve (Φ=g(ω)). This method is based on the dependence of the damping of the vibrating unit on the viscosity of the respective medium. The lower the viscosity, the steeper the frequency-phase curve. To eliminate the influence of density on the measurement, the viscosity is determined based on a frequency change caused by two different phase values, i.e., by a relative measurement. This can be achieved either by setting two different phase values ​​and determining the corresponding frequency change, or by scanning a predefined frequency band and determining when at least two predefined phase values ​​are reached.

[0008] Furthermore, DE102007043811A1 discloses the ability to infer a change in viscosity from a change in the natural frequency and / or resonance frequency and / or phase angle, and / or to determine the viscosity based on correspondingly defined dependencies of the vibrations of the vibrating unit on the viscosity of the respective medium. This approach also requires taking into account the dependence of the viscosity determination on the density of the medium.

[0009] For determining and / or monitoring the density of a medium, a method and a device are disclosed in DE10057974A1, by means of which the influence of at least one disturbance variable, for example viscosity, on the vibration frequency of the mechanically vibrating unit is determined and compensated accordingly. DE102006033819A1 further describes how to set a predefinable phase shift between the excitation signal and the received signal, at which the effects of changes in the viscosity of the medium on the mechanical vibrations of the mechanically vibrating unit are negligible. The density is essentially determined according to the formula ρ Med = 1 K f 0 , Vak + C ⋅ t + A ⋅ t 2 f T , P , Med 2 ⋅ 1 + D ⋅ p − 1

[0010] Determined, where K is the density sensitivity of the mechanically oscillating unit, F 0,vak is the frequency of the mechanical oscillations in vacuum, C and A are the linear and quadratic temperature coefficients of the mechanically oscillating unit, respectively, t is the process temperature, F 0,med is the frequency of the mechanical oscillations in the medium, D is the pressure coefficient, and p is the pressure of the medium.

[0011] However, the empirical assumption that the measurement is independent of viscosity for a specific, predefined phase shift leads to fundamental limitations. Above a certain viscosity, accurate density measurement can no longer be guaranteed using the described measurement principles. Therefore, a maximum permissible viscosity must be determined for each medium, up to which density determination should be performed. To circumvent this problem, a vibronic sensor and a method for its operation have been disclosed in the as-yet-unpublished German patent application number 102015102834.4, by means of which density and / or viscosity can be determined in a broader range of applications. The analytical measurement principle proposed therein takes into account the interactions between the vibrating unit and the medium.The sensor operates at two different, predefined phase shifts, and the process parameters density and / or viscosity are determined from the respective response signal. Reference is made in full below to the German patent application with file number 102015102834.4.

[0012] Based on the prior art, the present invention aims to expand the scope of application for determining density and / or viscosity using a vibronic sensor.

[0013] This problem is solved by the features of method claim 1 and by the features of device claim 8.

[0014] Regarding the method, the problem is solved by a method for determining and / or monitoring the density and / or viscosity of a medium in a container using a vibronic sensor. A vibrating unit is excited to mechanical vibrations by means of an electrical excitation signal, and the mechanical vibrations of the vibrating unit are received and converted into an electrical receive signal. The excitation signal is generated from the receive signal such that at least one predefinable phase shift exists between the excitation signal and the receive signal, and a frequency of the excitation signal is determined from the received signal if the predefinable phase shift is present.According to the invention, an attenuation and / or a quantity dependent on the attenuation is / are further determined from the received signal when the predefinable phase shift is present, and at least from the attenuation and / or the quantity dependent on the attenuation, and from the frequency of the excitation signal, the density and / or the viscosity of the medium are determined. analytically The method is applicable both when a single, predefined phase shift is set between the excitation signal and the received signal, and when two or more predefined phase shifts are used. In particular, a first and a second phase shift can be set alternately at predefined time intervals.

[0015] Damping D, also known as damping coefficient, damping measure, or Lehr's damping measure, generally describes the behavior of an oscillating system after excitation. It is usually a dimensionless quantity that, in principle, indicates the energy loss of the oscillating system. A quantity very closely related to damping is the quality factor Q, also known as the quality factor or resonance sharpness, of an oscillating system. A high quality factor Q corresponds, for example, to low damping D. Therefore, determining the density and / or viscosity based on the quality factor Q of the oscillating unit, which is mathematically related to the damping D, also falls within the scope of protection of the present invention.It should be noted that both damping and quality are generally known quantities to those skilled in the art in the field of mechanical vibration theory, so that the respective formulas and relationships are deliberately omitted here.

[0016] The method according to the invention offers the advantage of being based on an analytical foundation for determining the density and / or viscosity of a medium using a vibronic sensor. It is a particularly easy-to-implement measurement principle. In contrast to the method described in German patent application no. 102015102834.4, the setting of two different phase shifts is no longer essential. The method according to the invention, as well as the corresponding sensor, can be used universally and independently of the viscosity of the respective medium. This applies particularly to highly viscous media in which the vibratory unit can just barely perform a vibrational movement.In addition to the aforementioned simplifications and the expansion of the application range of various media, the solution according to the invention is further characterized by high accuracy with regard to the determination of the process parameters density and / or viscosity.

[0017] In an advantageous embodiment, a predefinable phase shift of essentially + / -90° is chosen. Generally, a phase shift between the excitation signal and the received signal is preferably set that corresponds to a resonant oscillation of the oscillating unit, particularly in the fundamental mode. A purely mechanical oscillator, for example, performs resonant mechanical oscillations with a phase shift of -90°. However, depending on the type of drive / receiver unit and / or the design and selection of the electronic unit's components, it may also be necessary to consider additional phase shifts that may be caused. In the case of the LIQUIPHANTEN marketed by the applicant, for example, an additional phase shift of +180° is generated, so that the phase shift between the excitation signal and the received signal is usually set to +90° for a resonant oscillation.For other configurations of a vibronic sensor, phase shifts of + / -45° or 0° between the excitation signal and the received signal may also be advantageous.

[0018] The drive / receiver unit can, for example, include a piezoelectric element. Alternatively, the drive / receiver unit can be electromagnetic or magnetostrictive.

[0019] A particularly preferred embodiment of the method according to the invention provides that a predefinable change in the density and / or viscosity of the medium is monitored.

[0020] Another particularly preferred embodiment of the method provides that a predetermined fill level or limit level of the medium in the container is determined and / or monitored.

[0021] According to the invention, a vibronic sensor, or level switch, that switches according to determinable limit values ​​for the density and / or viscosity of a medium can be implemented. For example, interfaces or boundary layers between two different media arranged one above the other, or between different states of a medium arranged one above the other, e.g., foam formation, can be monitored in situ. Detection of interfaces or boundary levels is advantageously possible according to the invention, and in contrast to other methods for determining density and / or viscosity from the prior art, due to the comparatively high speed in determining the respective process parameter.

[0022] One embodiment of the method according to the invention includes determining at least one reference damping and / or a value dependent on the reference damping when the vibrating unit is at least partially, preferably completely, immersed in a reference medium, or when the vibrating unit is excited to mechanical vibrations in the absence of a medium by means of an electrical excitation signal. The reference medium is preferably a medium of known density and viscosity. Mechanical vibration in the absence of a medium can be understood to mean vibration of the mechanically vibrating unit in air as well as in a vacuum.

[0023] The mechanical vibrations of the mechanically oscillating unit, whether immersed in a reference medium or in the absence of a medium, are then received and converted into an electrical signal. Preferably, the excitation signal is generated from the received signal in such a way that a predefinable phase shift exists between the excitation signal and the received signal. A reference frequency for the excitation signal is then determined from the received signal when the predefinable phase shift is present. Furthermore, the reference damping can be determined from the received signal when the predefinable phase shift is present.

[0024] It is advantageous to use a mathematical model with at least one equation of motion for the vibrational motion of the oscillating unit to determine the density and / or viscosity. This equation of motion takes into account the interaction of the oscillating unit with the medium in the form of a pressure force and a frictional force generated by the medium surrounding the oscillating unit, as well as a frictional force resulting from uniform motion of the oscillating unit within the medium. Thus, the interactions between the oscillating unit and the respective medium, as well as the mutual influence of the two quantities, density and viscosity, are considered when determining the density and / or viscosity.In order to obtain an analytical solution to the equation of motion, the oscillatory motion, which in reality corresponds to a bending oscillation, is approximated by a torsional oscillation. Furthermore, two elliptical cylinders of different dimensions serve as an approximation of the geometry of the oscillating unit for each of the two fork tines.

[0025] It should be noted that any other geometry can be chosen for the oscillatory unit without loss of generality. In this case, however, the geometric coefficients must be adjusted accordingly.

[0026] A particularly preferred embodiment of the present invention includes the damping and / or the reference damping and / or the quantity dependent on the damping and / or reference damping. based on a slope of a phase of the received signal at the frequency and / or reference frequency, of the excitation signal when the predefinable phase shift is present, based on the time course of the amplitude of the received signal after a switch-off of the excitation signal, and / or based on a modulation of the excitation signal is determined.

[0027] For example, German patent DE 10050299A1 discloses how to calculate the viscosity of a medium based on the slope of the phase between the excitation signal and the received signal. A variant of the inventive method, however, provides to determine the attenuation and / or a dependent quantity from the slope of the phase at the frequency of the excitation signal, given a predefinable phase shift.

[0028] A measurement of the temporal evolution of the amplitude of the received signal after switching off the excitation signal, i.e., the decay behavior of the vibrations of the mechanically oscillating unit, is known from DE102007043811A1. According to the invention, the damping or a quantity dependent on the damping is inferred from the decay behavior, and the density and / or viscosity are then determined based on the damping.

[0029] For determining the attenuation by modulating the excitation signal, reference is again made to the as yet unpublished German patent application with file number 102015101891.8. With this method for determining and / or ascertaining the attenuation, it is advantageously sufficient to set only a single, predefinable phase shift between the excitation signal and the received signal, which corresponds to excitation of the sensor at a single frequency.

[0030] All three documents relating to the determination and / or analysis of damping or the quantity dependent on damping are hereby incorporated by reference in full.

[0031] It should be noted that, in addition to the three methods mentioned above for determining damping and / or at least one dependent parameter, further methods are conceivable, all of which fall within the scope of the present invention. The advantage of determining damping to determine density and / or viscosity lies in the fact that the inventive analytical determination of density and / or viscosity becomes possible with the aid of damping.

[0032] Preferably, the vibrating unit for determining the density and / or viscosity is arranged in a defined position within the container such that it is immersed in the medium to a determinable immersion depth, in particular completely.

[0033] With regard to the device, the problem underlying the invention is solved by a vibronic sensor for determining and / or monitoring at least one process parameter of a medium in a container with at least one electronic unit and one oscillating unit, wherein the electronic unit is designed to carry out at least one embodiment of the method according to the invention.

[0034] Advantageously, the electronic unit includes a memory unit. This memory unit can store, for example, the reference attenuation, the reference frequency, or other constants and / or parameters.

[0035] In a preferred configuration of the vibronic sensorThe electronic unit is configured to supply the oscillating unit with an excitation signal, which is composed of an excitation carrier signal with an excitation carrier frequency and an excitation modulation signal with an excitation modulation frequency, and to receive a receive signal from the oscillating unit, which is composed of a receive carrier signal and a receive modulation signal. Furthermore, the electronic unit is configured to determine at least the attenuation D and / or the reference attenuation D0 from the phase shift between the excitation modulation signal and the receive modulation signal and / or at least from the receive carrier signal.

[0036] It is advantageous if the mechanically oscillating unit is a tuning fork, a single rod, or a diaphragm.

[0037] The embodiments mentioned in connection with the device according to the invention are also applicable, mutatis mutandis, to the method according to the invention and vice versa.

[0038] In summary, the present invention offers the following advantages over the prior art: The density can be determined independently of the viscosity of the medium, and to determine the density and / or viscosity it may be sufficient to set a single phase shift between the excitation signal and the received signal. The analytical formulas according to the invention for density and / or viscosity are more accurate than the formulas known from the prior art, and the speed at which the density and / or viscosity can be determined is significantly increased compared to methods known from the prior art.

[0039] The invention and its advantageous embodiments are described in more detail below with reference to Figures 1 to 3. These show: Fig. 1 : a schematic sketch of a vibronic sensor according to the state of the art, and Fig. 2 : a schematic drawing of a rocker fork.

[0040] In Fig. 1 A vibronic sensor 1 is shown. It depicts a vibrating unit 4 in the form of a vibrating fork, which is partially immersed in a medium 2 contained in a container 3. The vibrating unit is excited to mechanical vibrations by means of the excitation / receiving unit 5 and can, for example, be a piezoelectric stack or bimorph drive. It is understood, however, that other embodiments of a vibronic sensor also fall within the scope of the invention. Furthermore, an electronic unit 6 is shown, by means of which the signal acquisition, evaluation, and / or power supply is carried out.

[0041] In Fig. 2A vibrating unit 4 in the form of a vibrating fork, such as that integrated into the vibronic sensor 1 marketed by the applicant under the name LIQUIPHANT, is shown. The vibrating fork 4 comprises two vibrating rods 7a, 7b, or fork tines, mounted on a membrane 8. To set the vibrating rods 7a, 7b into mechanical vibration, a force is applied to the membrane 8 by means of a drive / receiver unit 5, which is bonded to the side of the membrane 8 facing away from the vibrating rods 7a, 7b. The drive / receiver unit 5 is an electromechanical transducer unit and comprises, for example, a piezoelectric element 9 or an electromagnetic drive. The drive unit 5 and the receiver unit are either designed as two separate units or as a combined drive / receiver unit. The drive / receiver unit 5 is shown in detail in the drawing on the right.A piezoelectric element 9 is arranged on a steatite disk 10 and is equipped with electrodes 11 for applying the excitation signal and for tapping off the received signal.

[0042] If the drive / receiver unit 5 includes a piezoelectric element 9, the force exerted on the membrane 8 is generated by applying an excitation signal UA, for example in the form of an alternating electrical voltage. A change in the applied electrical voltage causes a change in the geometric shape of the drive / receiver unit 5, i.e., a contraction or relaxation within the piezoelectric element 9, such that the application of an alternating electrical voltage as an excitation signal UA causes the membrane 8, which is bonded to the drive / receiver unit 5, to vibrate.

[0043] As described at the outset, the objective of the present invention is to extend the scope of application for determining density and / or viscosity using a vibronic sensor 1. The analytical model used according to the invention to describe the vibrational motions of a vibronic sensor 1 largely corresponds to that described in the previously unpublished German patent application with file number 102015102834.4, to which full reference has already been made. Therefore, the complete derivation of the analytical model is not repeated here.

[0044] The following explanations, without loss of generality, refer to a resonant oscillation with a phase shift of Δφ = 90° between the excitation signal UA and the received signal UE, and a reference frequency ω₀, which corresponds to an undamped oscillation of the oscillating unit 4 in a vacuum. These considerations can be extended to other cases (different phase shift Δφ, reference medium 2 instead of an undamped oscillation in a vacuum) as needed.

[0045] According to the invention, the reference frequency ω 0 is now related to the frequency ω of the excitation signal UA of the oscillating unit 4 when the predefinable phase shift Δφ is present. This results in ω 0 2 ω 90 2 = 1 + a 1 pη ω 90 + a 2 ρ

[0046] This includes ρ the density and η the viscosity of the medium, while the coefficients a 1 and a 2 describe geometric sensor constants.

[0047] Furthermore, will the damping D 0 of the sensor in a vacuum affects the damping D 90 of the vibronic sensor in the medium, so the result D 90 ω 0 D 0 ω 90 = 1 + a 3 ρηω 90 + a 4 η + a 5 where a 3 - a 5 also describe geometric sensor constants.

[0048] The density can then be calculated using the following formulas: ρ = A C − B AE + BD − BG − A 2 E 2 − 2 ABDE + 2 ABEG + 4 CFAD − 4 CFAG + B 2 D 2 − 2 B 2 DG + B 2 G 2 C 2 BE − 2 CF

[0049] However, the following applies to viscosity: η = AE 2 − E A 2 E 2 − 2 ABDE + 2 ABEG + 4 CFAD − 4 CFAG + B 2 D 2 − 2 B 2 DG + B 2 G 2 + F 2 CD − 2 CG − BDE + BEG 2 CF 2 − 2 BEF

[0050] The symbols marked with capital letters represent abbreviations for the following terms: A = ω 0 2 ω 90 2 − 1 B = a 1 ω 90 C = a 2 D = D 90 ω 0 D 0 ω 90 − 1 E = a 3 ω 90 F = a 4 G = a 5

[0051] To determine the density ρ and / or viscosity η According to the invention, the following steps are carried out on a medium 2: Before commissioning the vibronic sensor: 1. Determining the sizes ω 0 and D0 in each case in a vacuum, and 2. Determination, in particular experimental determination of the geometric sensor constants a 1 - a 5 in a suitable number of selectable so-called balancing media of known density ρ and viscosity η .

[0052] During operation of the vibronic sensor: 3. Continuous measurement / determination of ω 90 and D 90, and 4. Continuous calculation of density ρ and the viscosity η.

[0053] To determine and / or ascertain the damping D According to the invention, several different possibilities exist for the vibronic sensor 1. For example, the damping can be adjusted. D 90 of the vibronic sensor 1 when the predefinable phase shift Δφ = 90° between the excitation signal UA and the received signal UE is present, based on the slope of the phase d φ d ω at the frequency ω90 will be determined. In this case, the following applies: d φ d ω ω = ω 90 = 1 D 90 ω 90 and thus D 90 = 1 d φ d ω ω = ω 90 ⋅ ω 90 Reference symbol list

[0054] 1 Vibronic sensor 2 Medium 3 Container 4 Oscillating unit 5 Electromechanical transducer unit 6 Electronic unit 7a, 7b Oscillating rods of the oscillating unit 8 Membrane 9 Piezoelectric element 10 Steatite disk 11 Electrodes UA Excitation signal UE Received signal ΔΦ Predefinable phase shift ρ Density of the medium v ​​Viscosity of the medium ω, ω 90 Oscillation frequency of the oscillating unit in a medium, or oscillation frequency at a phase shift ΔΦ=90° ω 0 Reference frequency of the oscillating unit φ(ω) Phase response of the oscillating unit a 1 -a 5 geometric sensor constants

Claims

1. A method for determining and / or monitoring the density (ρ) and / or the viscosity (v) of a medium (3) in a container (2) using a vibronic sensor (1), wherein a unit capable of oscillating (4) is caused to mechanically oscillate using an electrical excitation signal (UA), and the mechanical oscillations of the unit capable of mechanically oscillating (4) are received and converted into an electrical received signal (UE), wherein the excitation signal (UA) is generated based on the received signal (UE) in such a way that there is at least one specifiable phase shift (Δϕ) between the excitation signal (UA) and the received signal (UE), wherein the received signal (UE) is used to determine a frequency (f) of the excitation signal (UA) if there is a specifiable phase shift (Δϕ), wherein the received signal (UE) is used to determine a damping (D) and / or a variable dependent on the damping (D) if there is a specifiable phase shift (Δϕ), and wherein the density (ρ) and / or the viscosity (v) of the medium is / are analytically determined at least from the damping (D) and / or from the variable dependent on the damping (D), and from the frequency (f) of the excitation signal (UA).

2. The method as claimed in claim 1, wherein ±90° is mainly selected as the specifiable phase shift (Δϕ).

3. The method as claimed in at least one of the preceding claims, wherein a specifiable change in the density (ρ) and / or the viscosity (v) of the medium (2) is monitored.

4. The method as claimed in claim 1 or 2, wherein a specifiable fill level or limit level of the medium (2) in the container (3) or a limit level between a first and a second medium (2) is monitored.

5. The method as claimed in at least one of the preceding claims, wherein at least one reference damping (D0) and / or a variable dependent on the reference damping (D0) is / are determined for the event that the unit capable of oscillating (4) is at least partially immersed in a reference medium (2), or in the case that the unit capable of oscillating (4) is caused to mechanically oscillate using an electrical excitation signal (UA) in the absence of a medium (2).

6. The method as claimed in at least one of the preceding claims, wherein a mathematical model with at least one equation of motion for an oscillatory movement of the unit capable of oscillating (4) is used to determine the density and / or the viscosity, said equation of motion considering the interaction between the unit capable of oscillating (4) and the medium (2) in the form of a compressive force (FD) and a friction force (FR) produced by the medium surrounding the unit capable of oscillating, as well as a friction force (FSP) caused by a uniform movement of the unit capable of oscillating (4) within the medium (2).

7. The method as claimed in at least one of the preceding claims, wherein the damping (D) and / or the reference damping (D0) or the variable dependent on the damping (D) and / or reference damping (D0) is / are determined - based on a slope of a phase (ϕ) of the received signal (UE) at the frequency (f) and / or reference frequency (f0) of the excitation signal if the specifiable phase shift (Δϕ) is present, - using the temporal profile of the amplitude (A) of the received signal (UE) after the excitation signal (UA) is deactivated, and / or using a modulation of the excitation signal (UA).

8. A vibronic sensor for determining and / or monitoring at least one process variable of a medium (2) in a container (3) at least with an electronic unit (6) and a unit capable of oscillating (4), wherein the electronic unit (6) is configured to carry out at least one method as claimed in at least one of the preceding claims.

9. The vibronic sensor as claimed in claim 8, wherein the electronic unit (6) comprises a storage unit.

10. The vibronic sensor as claimed in claim 8 or 9, wherein the electronic unit (4) is configured to supply the unit capable of oscillating (4) with an excitation signal (UA) which is made up of an excitation carrier signal with an excitation carrier frequency and an excitation modulation signal with an excitation modulation frequency, and to receive a received signal (UE) from the unit capable of oscillating (4), which is made up of a received carrier signal and a received modulation signal, and wherein the electronic unit (6) is configured to determine at least the damping (D) and / or the reference damping (D0) from the phase shift (Φ) between the excitation modulation signal and the received modulation signal and / or at least from the received carrier signal.

11. The vibronic sensor as claimed in claim 9 or 10, wherein the unit capable of mechanically oscillating (4) is an oscillating fork, a single bar or a membrane.