Vibronic Sensor

Abstract

A vibronic sensor for determining and/or monitoring at least one process variable of a medium in a container. The sensor at least comprising: a unit which can oscillate mechanically; a driving/receiving unit; and an electronic unit. The driving/receiving unit is designed to excite, by means of an electrical excitation signal, mechanical oscillations in the unit which can oscillate mechanically and is designed to receive the mechanical oscillations of the unit which can oscillate mechanically, and to convert them into an electrical receiving signal. The electronic unit is designed to generate the excitation signal on the basis of the receiving signal and to determine the at least one process variable from the receiving signal; The electronic unit comprises at least one adaptive filter; and the electronic unit is designed to set the filter characteristic of the adaptive filter in such a way that there is a target phase shift between the excitation signal and the receiving signal.

Claims

1-21. (canceled)

22. A vibronic sensor for determining and/or monitoring at least one process variable of a medium in a container, comprising: at least one unit which can oscillate mechanically; a driving/receiving unit ; and an electronics unit, wherein: said driving/receiving unit is designed to excite, via an electrical excitation signal, mechanical oscillations in said unit which can oscillate mechanically and to receive the mechanical oscillations of said unit which can oscillate mechanically, and to convert them into an electrical receiving signal; said electronics unit is designed to generate the excitation signal on the basis of the receiving signal and to determine the at least one process variable from the receiving signal; said electronics unit comprises at least one adaptive filter; and said electronics unit is designed to set the filter characteristic of said adaptive filter in such a way that there is a target phase shift between the excitation signal and the receiving signal.

23. The vibronic sensor according to claim 22, wherein: said electronics unit is designed to set said target phase shift by setting the center frequency of said adaptive filter.

24. The vibronic sensor according to claim 22, wherein: said electronics unit comprises a phase control unit, which controls the center frequency of said adaptive filter in such a manner that there is a specifiable value for said phase shift between an input signal and an output signal of said adaptive filter.

25. The vibronic sensor according to claim 22, wherein: said electronics unit comprises a ring memory and/or a phase shifter, by which said target phase shift can be set.

26. The vibronic sensor according to claim 22, wherein: the bandwidth of said adaptive filter is adjustable.

27. The vibronic sensor according to claim 22, wherein: said adaptive filter is a resonator filter.

28. The vibronic sensor according to claim 22, wherein: said adaptive filter is a band pass filter—especially, a low-pass filter—especially, a second-order low-pass filter.

29. The vibronic sensor according to claim 22, wherein: said phase control unit is based upon the principle of a lock-in amplifier.

30. The vibronic sensor according to claim 22, wherein: said target phase shift is 90°, 45°, or 0°.

31. The vibronic sensor according to claim 22, wherein: at least a first and a second target phase shift are alternately adjustable.

32. The vibronic sensor according to claim 22, wherein: said electronics unit comprises an amplitude control unit for controlling the amplitude of the excitation signal to a specifiable value or to a value within a specifiable interval.

33. The vibronic sensor according to claim 22, wherein: said electronics unit is designed to perform a frequency search to excite said oscillating unit in the event that a specifiable lower threshold value for the amplitude is not reached and to successively set the center frequency of said adaptive filter to consecutive, discrete excitation frequencies within a specifiable frequency interval.

34. The vibronic sensor according to claim 22, wherein: the process variable is a pre-determined fill level, density, and/or viscosity of the medium in the container.

35. The vibronic sensor according to claim 22, wherein: said oscillating unit is a membrane, a rod, or a vibrating fork.

36. The vibronic sensor according to claim 22, wherein: said driving/receiving unit is an electromagnetic or a piezoelectric driving/receiving unit.

37. A method for operating a vibronic sensor for determining and/or monitoring at least one process variable of a medium in a container, comprising: exciting a mechanical oscillating unit to mechanical oscillations via an electrical excitation signal; and receiving said mechanical oscillations of said mechanical oscillating unit; converting said mechanical oscillations of said mechanical oscillating unit into an electrical receiving signal; creating said excitation signal originating from said receiving signal; and determining said at least one process variable, wherein: the filter characteristics of an adaptive filter comprised in an electronics unit of said sensor are determined in such a manner that there is a target phase shift between said excitation signal and said receiving signal.

38. The method according to claim 37, wherein: the center frequency of the adaptive filter is controlled in such a manner that there is a target phase shift between the excitation signal and the receiving signal.

39. The method according to claim 37, wherein: the bandwidth of the adaptive filter is determined.

40. The method according to claim 37, wherein: the target phase shift is set at 90°, 45°, or 0°.

41. The method according to claim 37, wherein: at least a first and a second target phase shift are alternately set.

42. The method according to claim 37, wherein: the amplitude of the excitation signal is set to a specifiable value or to a value within a specifiable interval.

Description

[0044] The invention, as well as its advantageous embodiments, are more closely described below with reference to FIG. 1 and FIG. 2. Illustrated are:

[0045] FIG. 1: a schematic drawing of a vibronic sensor according to the prior art,

[0046] FIG. 2: a block diagram of an electronics unit according to the invention.

[0047] A vibronic sensor 1 is shown in FIG. 1. A vibration-capable unit 4 is depicted in the form of an oscillating fork which is submerged partially into a medium 2, which is located in a container 3. The vibration-capable unit is stimulated by the triggering / receiving unit 5 to mechanical vibrations and can, for example, be a piezoelectric stack- or bi-morph actuator. However, it is naturally understood that other embodiments of a vibronic sensor also fall under the invention. In addition, an electronics unit 6 is illustrated, by means of which the signal reception, evaluation, and/or storage are accomplished.

[0048] A block diagram of an electronics unit according to the invention is the subject of FIG. 2. The receiving signal U.sub.E first passes through an analog/digital converter 10 before it is supplied to the adaptive filter 7. The filter characteristics of the adaptive filter are set in such a manner that there is an appropriate phase shift φ.sub.filter between the input signal and the output signal of the adaptive filter. This produces a target phase shift φ.sub.soll=360°−φ.sub.Filter between the excitation signal and the receiving signal. A target phase shift can also be set between the excitation signal and the receiving signal via an appropriate adjustment of the filter characteristics. For example, a phase control unit 8 can be used that controls the center frequency f.sub.m of the adaptive filter in such a manner that there is a target phase shift φ.sub.soll between the excitation signal and the receiving signal. Phase control unit 8, in turn, can be based upon the principle of a lock-in amplifier, for example.

[0049] The quality Q of adaptive filter 7 can be set by the so-called Lehr damping ratio D, among others. The following relationship can be used for this: Q=1/2 D, wherein the Lehr damping ratio, in turn, is determined from the mechanical properties of the oscillating unit.

[0050] Quality Q of adaptive filter 7 is additionally related via the relationship B=fm/Q to the quality Q and the center frequency of the adaptive filter f.sub.m. An embodiment of the invention includes the ability to set quality Q of adaptive filter 7 or its bandwidth B.

[0051] Receiving signal U.sub.E is characterized by its frequency, its amplitude, and its phase. The phase control of phase control unit 8 is accomplished by setting center frequency f.sub.m of adaptive filter 7 to the input frequency of the adaptive filter, so that the frequency at which the oscillating unit oscillates is known at every instant.

[0052] Furthermore, according to a different embodiment, an amplitude control unit 9 can be integrated into electronics unit 6. By means of amplitude control unit 9, the amplitude A of the excitation signal U.sub.A comprises a specifiable value or a value within a specifiable interval. For example, a standard P1 controller can be used for this purpose.

[0053] An advantage of the invention is that, by using an adaptive filter 7 to excite mechanical oscillating unit 4, no additional filter is needed for filtering the signal prior to evaluation.

[0054] Before excitation signal U.sub.A is transmitted via output stage 11 of the electronics unit to sensor unit 13, it passes through a digital/analog converter 10a. Optionally, receiving signal U.sub.E received by sensor unit 13 can also be passed through an anti-aliasing filter 14 before it is further transmitted to analog/digital converter 10 after passing through input stage 12.

LIST OF REFERENCE CHARACTERS

[0055] 1 Vibronic sensor [0056] 2 Medium [0057] 3 Container [0058] 4 Oscillating unit [0059] 5 Electromechanical transducer [0060] 6 Electronics unit [0061] 7 Adaptive filter [0062] 8 Phase control unit [0063] 9 Amplitude control unit [0064] 10,10a Analog/digital converter, digital/analog converter [0065] 11 Output stage [0066] 12 Input stage [0067] 13 Sensor unit [0068] 14 Anti-aliasing filter [0069] U.sub.A Excitation signal [0070] U.sub.E Reception signal [0071] f.sub.m Center frequency of the adaptive filter [0072] A.sub.soll Target value of the amplitude [0073] φ Phase [0074] φ.sub.soll Target phase shift between excitation signal and receiving signal [0075] φ.sub.filter Phase shift between input signal and output signal of the adaptive filter [0076] Q Quality [0077] B Bandwidth