MONITORING THE CONDITION OF A VIBRONIC SENSOR

Abstract

A method for monitoring condition of a vibronic sensor for determining and/or monitoring at least one process variable of a medium in a containment and having at least one sensor unit having a mechanically oscillatable unit includes: exciting the mechanically oscillatable unit by means of an excitation signal such that mechanical oscillations are executed, and receiving the mechanical oscillations in the form of a received signal, determining a measured value for amplitude and a measured value for frequency of the received signal, comparing the measured values for amplitude and frequency with reference values for amplitude and frequency, and ascertaining a condition indicator from the comparison.

Claims

1-12. (canceled)

13. A method for monitoring condition of a vibronic sensor for determining and/or monitoring at least one process variable of a medium in a containment and having at least one sensor unit having a mechanically oscillatable unit, the method comprising: exciting the mechanically oscillatable unit by means of an excitation signal such that mechanical oscillations are executed; receiving the mechanical oscillations in the form of a received signal; determining a measured value for amplitude and a measured value for frequency of the received signal; comparing the measured values for amplitude and frequency with respective reference values for amplitude and frequency; and ascertaining a condition indicator from the comparison.

14. The method as claimed in claim 13, further comprising: ascertaining a deviation between the measured values and the respective reference values for frequency and/or amplitude, wherein the condition indicator is ascertained based on the deviation.

15. The method as claimed in claim 14, further comprising: ascertaining whether the deviation for frequency and/or for amplitude exceeds a predeterminable limit value.

16. The method as claimed in claim 13, wherein the reference values for amplitude and frequency are values for amplitude and frequency corresponding to a resonant oscillation of the oscillatable unit in a fundamental oscillation mode and in air.

17. The method as claimed in claim 13, wherein the mechanically oscillatable unit is excited in air to mechanical resonant oscillations in the fundamental oscillation mode, and wherein the received signal represents resonant oscillations of the oscillatable unit in the fundamental oscillation mode.

18. The method as claimed in claim 13, wherein the condition indicator is information with reference to: an accretion, corrosion, or abrasion in the region of the oscillatable unit; a defect in the region of a driving/receiving unit by means of which the exciting of the oscillatable unit occurs such that mechanical oscillations are executed; or a defect of an electronics of a sensor which comprises the oscillatable unit.

19. The method as claimed in claim 13, wherein the oscillatable unit is an oscillatory fork comprising a membrane and two oscillatory tines secured to the membrane.

20. The method as claimed in claim 13, wherein when no measured value is ascertainable for amplitude and the measured value for frequency is less than the reference value, such indicates the presence of corrosion and/or abrasion on the oscillatory tines and/or a hard accretion in the region of the membrane.

21. The method as claimed in claim 14, wherein when the deviation between the measured value and the reference value for amplitude is less than a predeterminable limit value and the measured value for frequency is less than the reference value, such indicates a hard accretion in the region of the oscillatory tines and/or corrosion and/or abrasion in the region of the membrane.

22. The method as claimed in claim 13, wherein when the measured value for amplitude and the measured value for frequency are less than their respective reference values, such indicates a soft accretion in the region of the oscillatory tines and/or media residues in the region of the oscillatable unit.

23. The method as claimed in claim 14, wherein when the measured value for amplitude is less than the reference value and the deviation between the measured value and the reference value for frequency is less than a predeterminable limit value, such indicates a defect in the region of the driving/receiving unit in the region of at least one piezoelectric element of the driving/receiving unit and/or a defect in the field of the electronics.

24. The method as claimed in claim 13, wherein the method is embodied according to the TO-Link standard.

Description

[0034] The invention as well as its advantages will now be more exactly described based on the appended drawing, the figures of which show as follows:

[0035] FIG. 1 a vibronic sensor according to the state of the art, and

[0036] FIG. 2 an oscillatable unit of a vibronic sensor in the form of an oscillatory fork.

[0037] FIG. 1 shows a vibronic sensor 1, including a sensor unit 3 with an oscillatable unit 4 in the form of an oscillatory fork, which is partially immersed in a medium 2 located in a container 2a. The oscillatable unit 4 is excited by means of the exciter/receiving unit 5, such that mechanical oscillations are executed. The exciter/receiving unit 5 can be, for example, a piezoelectric stack- or bimorph drive. It is understood, however, that also other embodiments of a vibronic sensor fall within the scope of the invention. Also included is an electronics unit 6, by means of which signal registration,—evaluation and/or—feeding occurs.

[0038] FIG. 2 shows in a side view an oscillatable unit 4 in the form of an oscillatory fork, such as used, for example, in the vibronic sensor 1 sold by the applicant under the mark LIQUIPHANT. Oscillatory fork 4 includes, formed on a membrane 7, two oscillatory tines 8a,8b, on which are terminally formed two paddles 9a,9b. The oscillatory tines 8a,8b together with the paddles 9a,9b are frequently also referred to as fork tines. In order to cause the mechanically oscillatable unit 4 to execute mechanical oscillations, a force is exerted on the membrane 7 by means of a driving/receiving unit 5 secured by material bonding to the side of the membrane 7 opposite that carrying the oscillatory tines 8a,8b. The driving/receiving unit 5 is an electromechanical transducer unit, and comprises, for example, a piezoelectric element, or an electromagnetic drive (not shown). Either the driving/receiving unit 5 is comprised of separate driving and receiving units, or it is a combined driving/receiving unit. In the case, in which the driving/receiving unit 5 comprises a piezoelectric element 9, the force exerted on the membrane 7 is generated by applying an excitation signal U.sub.E, for example, in the form of an alternating electrical voltage. A change of the applied electrical voltage effects a change of the geometric shape of the driving/receiving unit 5, thus, a contraction or an expansion within the piezoelectric element, in such a manner that the applying of an alternating electrical voltage as excitation signal U.sub.E brings about an oscillation of the membrane 7 connected by material bonding with the driving/receiving unit 5.

[0039] Conversely, the mechanical oscillations of the oscillatable unit are transmitted via the membrane to the driving/receiving unit 5 and converted into an electrical, received signal U.sub.R. The particular process variable, for example, a predeterminable fill level of medium 2 in the container 2a, or the density or viscosity of the medium 2, can then be ascertained based on the received signal U.sub.R.

[0040] An option for monitoring condition of the vibronic sensor will now be explained based on comparing a measured frequency f and a measured amplitude A of the oscillatable unit 4 for an exciting at the fundamental oscillation mode of the oscillatable unit 4. In a first step, reference values f.sub.ref, A.sub.ref for amplitude and frequency are ascertained, wherein the oscillatable unit 4 is excited to execute resonant oscillations in air.

[0041] For ascertaining information with reference to condition of the sensor 1 during ongoing operation, the oscillatable unit is excited anew by means of a excitation signal U.sub.E, such that mechanical oscillations are executed in the fundamental oscillation mode and the received signal U.sub.R representing the oscillations is received and evaluated as regards frequency f and amplitude A. At this point in time, the oscillatable unit 4 is not covered by medium. These values f, A are then compared, for example, with their reference values f.sub.ref, A.sub.ref and deviations of the measured values f, A from reference values f.sub.ref, A.sub.ref are ascertained.

[0042] For example, a predeterminable limit value can be defined. If the deviation exceeds this limit value, then, in given cases, a problem is present, or the sensor 1 needs to be serviced. The method of the invention offers, thus, the advantage of predictive maintenance.

REFERENCE CHARACTERS

[0043] 1 vibronic sensor [0044] 2 medium [0045] 2a container [0046] 3 sensor unit [0047] 4 oscillatable unit [0048] 5 driving/receiving unit [0049] 6 electronics unit [0050] 7 membrane [0051] 8a,8b oscillatory tines [0052] 9a,9b paddles [0053] U.sub.E excitation signal [0054] U.sub.R received signal [0055] f frequency [0056] f.sub.ref reference value for frequency [0057] A amplitude [0058] A.sub.ref reference value for amplitude