VIBRONIC SENSOR

Abstract

A vibronic sensor used to determine a process variable of a medium in a container comprises a mechanically vibratable unit, a drive/receiving unit, and an electronic unit. The drive/receiving unit excites mechanical vibrations in the mechanically vibratable unit via an electric excitation signal and receives the mechanical vibrations of the mechanically vibratable unit and convert same into an electric reception signal. The electronic unit is designed to generate the excitation signal on the basis of the reception signal and determine the process variable from the reception signal. The electronic unit includes an adaptive filter and is designed to set the filter characteristic of the adapter filter to produce a target phase offset between the excitation and reception signals. The sensor also has a detection unit to determine a phase offset between the excitation signal and the reception signal and/or the amplitude of the reception signal using a quadrature demodulation.

Claims

1-12. (canceled)

13. A vibronic sensor for determining and/or monitoring at least one process variable of a medium in a container comprises: a mechanically vibratable unit; a drive/receiving unit; an electronic unit including a first adaptive filter; and a detection unit, wherein the drive/receiving unit is designed to excite mechanical vibrations in the mechanically vibratable unit via an electrical excitation signal and is further designed to receive mechanical vibrations of the mechanically vibratable unit and convert the received mechanical vibrations into an electrical reception signal, wherein the electronic unit is designed to generate the electrical excitation signal on the basis of the electrical reception signal and to determine the at least one process variable from the electrical reception signal, wherein the electronic unit is designed to set a filter characteristic of the first adaptive filter to produce a target phase offset between the electrical excitation signal and the electrical reception signal, and wherein the detection unit is designed to determine a phase offset between the electrical excitation signal and the electrical reception signal and an amplitude of the reception signal using a quadrature demodulation.

14. The vibronic sensor according to claim 13, wherein the detection unit includes a first and/or a second reference unit for generating a first and/or a second reference signal for performing the quadrature demodulation.

15. The vibronic sensor according to claim 14, wherein the first and/or second reference unit is/are designed to generate the first and/or second reference signal on the basis of the electrical reception signal.

16. The vibronic sensor according to claim 15, wherein one of the two reference units includes a first phase shifter for generating one of the reference signals with a phase offset of +/−90° with respect to the electrical reception signal.

17. The vibronic sensor according to claim 16, wherein the first phase shifter is a second adaptive filter of identical design to the first adaptive filter, an all-pass filter, or a Hilbert transform.

18. The vibronic sensor according to claim 17, wherein one of the two reference units includes a second phase shifter for generating one of the reference signals with a phase offset of 0° with respect to the electrical reception signal.

19. The vibronic sensor according to claim 18, wherein the second phase shifter is a multiplier, an adaptive filter, or a resonator filter.

20. The vibronic sensor according to claim 13, wherein the electronic unit is designed to set the target phase offset by setting a center frequency of the first adaptive filter via a phase control unit.

21. The vibronic sensor according to claim 13, wherein the target phase offset is 90°, 45°, or 0°.

22. The vibronic sensor according to claim 17, wherein the first adaptive filter and/or the second adaptive filter is a resonator filter, a bandpass filter, a low-pass filter, or a 2nd order low-pass filter.

23. The vibronic sensor according to claim 13, wherein the electronic unit is designed to alternately execute a first and a second operating mode, wherein the drive/receiving unit is designed to excite mechanical vibrations in the mechanically vibratable unit via the electrical excitation signal during the first operating mode, wherein the electronic unit is designed, during the second operating mode, to interrupt the excitation of the mechanically vibratable unit by the excitation signal, to receive the mechanical vibrations of the mechanically vibratable unit and convert the received mechanical vibrations into the electrical reception signal, to set a value of the filter characteristic of the first adaptive filter such that there is a specifiable phase offset between the excitation signal and the reception signal, and to determine the at least one process variable from the electrical reception signal.

24. A method for operating a vibronic sensor for determining and/or monitoring at least one process variable of a medium in a container, the method comprising: providing the vibronic sensor, including: a mechanically vibratable unit; a drive/receiving unit; an electronic unit including a first adaptive filter; and a detection unit, wherein the drive/receiving unit is designed to excite mechanical vibrations in the mechanically vibratable unit via an electrical excitation signal and is further designed to receive mechanical vibrations of the mechanically vibratable unit and convert the received mechanical vibrations into an electrical reception signal, wherein the electronic unit is designed to generate the electrical excitation signal on the basis of the electrical reception signal and to determine the at least one process variable from the electrical reception signal, wherein the electronic unit is designed to set a filter characteristic of the first adaptive filter to produce a target phase offset between the electrical excitation signal and the electrical reception signal, and wherein the detection unit is designed to determine a phase offset between the electrical excitation signal and the electrical reception signal and an amplitude of the reception signal using a quadrature demodulation; exciting mechanical vibrations in the mechanically vibratable unit by the electrical excitation signal; receiving mechanical vibrations of the mechanically vibratable unit and converting the received mechanical vibrations into the electrical reception signal; generating the electrical excitation signal on the basis of the electrical reception signal; setting a filter characteristic of the first adaptive filter thereby setting the target phase offset between the electrical excitation signal and the electrical reception signal, wherein the phase offset between the electrical excitation signal and the electrical reception signal and/or an amplitude of the electrical reception signal is determined using a quadrature demodulation; and determining the at least one process variable from the electrical reception signal.

Description

[0041] The invention and its advantageous embodiments are described in more detail below with reference to the figures, FIG. 1-FIG. 3. The following is shown:

[0042] FIG. 1: a schematic drawing of a vibronic sensor according to the prior art,

[0043] FIG. 2: a block diagram of a first embodiment of an electronic unit according to the invention, and

[0044] FIG. 3: a block diagram of a further embodiment of an electronic unit according to the invention for illustrating the performance of two operating modes.

[0045] FIG. 1 shows a vibronic sensor 1. A vibratable unit 4 is depicted in the form of a vibrating fork which is partially immersed in a medium 2, which is located in a container 3. Mechanical vibrations are excited in the vibratable unit by the excitation/receiving unit 5, and the vibratable unit can, for example, be a piezoelectric stack drive or bimorph drive. However, it is naturally understood that other embodiments of a vibronic sensor also fall under the invention. Furthermore, an electronic unit 6 by means of which the signal detection, signal evaluation and/or signal supply takes place is shown.

[0046] A block diagram of a first exemplary embodiment for an electronic unit according to the invention is the subject matter of FIG. 2.

[0047] Mechanical vibrations are excited in the vibratable unit 4 by means of the excitation signal U.sub.A. The reception signal U.sub.E representing these vibrations first passes through an analog/digital converter D/A before it is supplied to the first adaptive filter 7. In continuous operation, the filter characteristic of the adaptive filter 7 is set so that there is a specifiable phase offset ϕ.sub.soll=360°−ϕ.sub.Filter between the excitation signal U.sub.A and the reception signal U.sub.E, wherein ϕ.sub.filter is the phase offset between the input signal and the output signal of the adaptive filter 7. A control then controls the phase appropriately on the basis of the phase offset Δϕ detected in each case. For further details on a setting of the target phase offset ϕ.sub.soll by means of an adaptive filter 7, refer to DE102014119061A1.

[0048] By means of the detection unit 10, the amplitude 11a of the reception signal U.sub.E and the phase offset 11b Δϕ between the excitation signal U.sub.A and the reception signal are determined. According to the invention, the detection unit 10 is designed to determine the phase offset Δϕ using a quadrature demodulation. In this manner, a high degree of accuracy can be achieved with regard to the determination, which determination is also advantageously independent of the respective signal amplitudes. Before entering the detection unit 10, the respective input signals here each pass through a low-pass filter 9a, 9b, which is optional in itself.

[0049] Detection of the phase Δϕ by means of the quadrature demodulation requires two reference signals R1, R2, which are advantageously generated from the reception signal U.sub.E in the embodiment shown here. Advantageously, no further signal sources are required to generate the reference signals R1, R2. The reference signals R1, R2 can be generated in a particularly simple manner. A first reference unit 8a is used to generate a first reference signal R1 with a phase offset of +90° with respect to the reception signal U.sub.E and, for this purpose, comprises here by way of example a second adaptive filter, which is of identical design to the first adaptive filter 7. Alternatively, other elements that are not identical in design to the first adaptive filter 7 can be used; for example, an adaptive bandpass filter can also be used. The first reference unit 8a can also comprise multiple components to generate a phase offset of +/−90°.

[0050] A second reference unit 8b is used to generate a second reference signal R2 with a phase offset of 0° with respect to the reception signal U.sub.E and, here, comprises a multiplier for this purpose. Moreover, it should be noted that there are numerous other alternatives available that are familiar to those skilled in the art.

[0051] A further exemplary embodiment of an electronic unit 6 according to the invention is the subject matter of FIG. 3. For this embodiment, two different operating modes are performed, and the electronic unit 6 comprises a switching element 13 for switching back and forth between the two operating modes.

[0052] With regard to the performance of two operating modes, reference is made to DE102016111134A1. In the first operating mode, also referred to as the excitation sequence, an excitation signal U.sub.A is applied to the vibratable unit 4, and mechanical vibrations are induced. The vibratable unit 4 thus stores vibration energy in this manner. The reception signal U.sub.E coming from the vibratable unit 4 is superimposed on the excitation signal U.sub.A. During the excitation sequence, no active measurement or setting is made with respect to the currently present phase offset Δϕ between the excitation signal U.sub.A and the reception signal U.sub.E. The filter characteristic of the adaptive filter 7 remains constant.

[0053] During the second operating mode 16, also referred to as the measurement/control sequence, the application of the excitation signal U.sub.A to the sensor unit 4, 5 is interrupted by means of the switching element 13. The vibratable unit 4 now vibrates at its natural resonant frequency f.sub.0 and performs a damped resonant vibration accordingly. The excitation signal U.sub.A is now no longer superimposed on the reception signal U.sub.E, so that a suitable signal evaluation can be carried out in an evaluation unit 14 of the electronic unit 6 designed for this purpose, which here by way of example has a digitally controlled oscillator DCO and a unit for detecting a zero crossing 15. The control of the current phase offset Δϕ between excitation signal U.sub.A and reception signal U.sub.E is continued. For example, to control the current phase offset Δϕ, the center frequency f.sub.m of the adaptive filter 7 can be suitably set. Thus, during the successive measurement/control sequences, various internal parameters and/or values of the parameters used for control and phase measurement are successively changed until, for example, resonant excitation of the sensor unit 4, 5 occurs.

LIST OF REFERENCE SIGNS

[0054] 1 Vibronic sensor [0055] 2 Medium [0056] 3 Container [0057] 4 Vibratable unit [0058] 5 Electromechanical converter unit [0059] 6 Electronic unit [0060] 7 Adaptive filter [0061] 8, 8a, 8b Reference units [0062] 9, 9a, 9b Low-pass filter [0063] 10 Detection unit [0064] 11a, 11 b Detection of amplitude (a) and phase (b) [0065] 12 Control unit [0066] 13 Switching element [0067] 14 Evaluation unit [0068] 15 Unit for detecting a zero crossing [0069] U.sub.A Excitation signal [0070] U.sub.E Reception signal [0071] f.sub.m Center frequency of the adaptive filter [0072] f.sub.0 Resonant frequency of the vibratable unit [0073] A.sub.I Amplitude [0074] Δϕ Phase offset [0075] ϕ.sub.soll Specifiable phase offset between excitation signal and reception signal [0076] ϕ.sub.filter Phase offset between input signal and output signal of the adaptive filter