METHOD FOR OPERATING A VIBRONIC SENSOR

Abstract

A method for determining and/or monitoring a predeterminable fill level of a medium in a container using a vibronic sensor having at least one sensor unit with a mechanically vibratable unit, comprises exciting the mechanically vibratable unit with an excitation signal to produce mechanical vibrations, and receiving the mechanical vibrations in the form of a reception signal, determining an amplitude and a frequency of the reception signal, comparing the frequency and amplitude of the reception signal with a predeterminable frequency limit value and a predeterminable amplitude limit value, and determining a reaching of the predeterminable fill level on the basis of the comparison.

Claims

1-10. (canceled)

11. A method for determining and/or monitoring a predeterminable fill level of a medium in a container using a vibronic sensor having at least one sensor unit with a mechanically vibratable unit, the method comprising: exciting the mechanically vibratable unit with an excitation signal to produce mechanical vibrations; receiving mechanical vibrations in the form of a reception signal; determining an amplitude and a frequency of the reception signal; comparing the frequency and the amplitude of the reception signal with a predeterminable frequency limit value and a predeterminable amplitude limit value; and determining a reaching of the predeterminable fill level on the basis of the comparison.

12. The method according to claim 11, wherein the comparing includes checking whether the frequency of the reception signal exceeds or falls below the predeterminable frequency limit value.

13. The method according to claim 11, wherein the comparing includes checking whether the amplitude of the reception signal exceeds or falls below the predeterminable amplitude limit value.

14. The method according to claim 11, further comprising: recording the frequency and/or amplitude of the reception signal a function of time.

15. The method according to claim 11, further comprising: when the frequency of the reception signal exceeds or falls below the predeterminable frequency limit value while the amplitude of the reception signal remains constant, determining the vibratable unit is covered by a fluid.

16. The method according to claim 11, further comprising: when the amplitude of the reception signal exceeds or falls below the predeterminable amplitude limit value, determining the vibratable unit is covered by a foam or that a sediment is present in the medium.

17. The method according to claim 16, further comprising: when the frequency of the reception signal remains constant, determining a deposition of sediment in the region of the vibratable unit.

18. The method according to claim 16, further comprising: when frequency of the reception signal changes but does not exceed or fall below the predeterminable frequency limit value, determining a presence of the sediment in the medium or coverage by the foam.

19. The method according to claim 11, wherein the predeterminable amplitude limit value and/or the predeterminable frequency limit value are each a value for the amplitude and/or the frequency of the reception signal corresponding to a resonance vibration of the vibratable unit in the fundamental mode and in air.

20. The method according to claim 11, wherein the vibratable unit is a vibrating fork with a membrane and two vibrating rods attached to the membrane.

Description

[0026] The invention and its advantages are described in more detail with reference to the following figures, FIG. 1 and FIG. 3. In the figures:

[0027] FIG. 1 shows a vibronic sensor according to the prior art;

[0028] FIG. 2 shows a vibratable unit of a vibronic sensor in the form of a vibrating fork; and

[0029] FIG. 3 shows diagrams of the frequency and amplitude for different media for illustrating the procedure according to the invention.

[0030] FIG. 1 shows a vibronic sensor 1. A sensor unit 3 having 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 tank 2a. Mechanical vibrations are excited in the vibratable unit 4 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.

[0031] FIG. 2 shows a side view of a vibratable unit 4 in the form of a vibrating fork, as is integrated in the vibronic sensor 1 marketed by the applicant under the name LIQUIPHANT, for example. The vibrating fork 4 comprises two vibrating rods 8a,8b which are integrally formed on a membrane 7 and on the end of each of which a paddle 9a,9b is integrally formed. The vibrating rods 8a,8b together with the paddles 9a,9b are frequently also referred to as fork prongs. In order to mechanically vibrate the mechanically vibratable unit 4, a force is applied to the membrane 8 by means of a drive/receiving unit 5 which is firmly mounted on the side of the membrane 8 facing away from the vibrating rods 7a,7b. The drive/receiving unit 5 is an electromechanical transducer unit and comprises, for example, a piezoelectric element or also an electromagnetic drive [not shown]. The drive unit 5 and the receiving unit are constructed as two separate units or as a combined drive/receiving unit. In the case that the drive/receiving unit 5 comprises a piezoelectric element 9, the force applied to the membrane 7 is generated by applying an excitation signal UA for example in the form of an electrical AC voltage. A change in the applied electrical voltage causes a change in the geometric shape of the drive/receiving unit 5, i.e., a contraction or a relaxation within the piezoelectric element such that the application of an electrical AC voltage as excitation signal UA causes a vibration of the membrane 7 that is firmly bonded to the drive/receiving unit 5. Conversely, the mechanical vibrations of the vibratable unit are transmitted via the membrane to the drive/receiving unit 5 and converted into an electrical reception signal U.sub.E. The predeterminable fill level of the medium 2 in the tank 2a can then be determined on the basis of the reception signal U.sub.E, for example on the basis of an amplitude A, frequency f, or phase of the reception signal U.sub.E.

[0032] The method according to the invention allows for a significantly higher accuracy in the determination of the predeterminable filling level in an expanded field of application. Various preferred embodiments are shown in this context by way of example in FIG. 3.

[0033] In a first step, reference values f.sub.ref, A.sub.ref are determined for the amplitude and the frequency, wherein the vibratable unit 4 is excited to produce resonance vibrations in air. To determine a statement about the predeterminable fill level during continuous operation, the vibratable unit 4 is excited by means of an excitation signal UA to produce mechanical vibrations in the fundamental mode, and the reception signal U.sub.E representing the oscillations is received and evaluated with respect to the frequency f and amplitude A. The values f, A are compared to the respective reference values f.sub.ref, A.sub.ref and, for example, a deviation of the measured values f, A from the reference values f.sub.ref, A.sub.ref is determined or it is checked whether the frequency f and/or amplitude A exceeds or falls below the respectively predeterminable limit value f.sub.ref or A.sub.ref.

[0034] FIG. 3 shows exemplary diagrams of the frequency f and amplitude A in which, for different situations, the frequency f and amplitude A in each case is shown as a function of the immersion depth t of the vibratable unit 4 into the medium 2. In the case of coverage of the vibratable unit 4 with a liquid medium 2, the frequency f changes while the amplitude A remains substantially constant or changes only to a minor extent, as illustrated in FIG. 3a.

[0035] If, on the other hand, a change in amplitude A, in particular above a predeterminable amplitude limit value A.sub.ref, can be detected, one can conclude that the vibrating unit 4 is covered by a foam or that a sediment is present in the medium, as illustrated in FIG. 3b. Without the additional consideration, it would be impossible to distinguish between a freely vibrating vibratable unit 4 and a coverage by foam or sediment. This can lead to considerable problems because the reaching of the predeterminable limit value may possibly not be correctly displayed.

[0036] Moreover, in order to be able to distinguish between a sediment and a foam, an additional consideration of the frequency f can be helpful for example in the presence of a change in amplitude A, as in the case of FIG. 3b. If the frequency f remains substantially constant, there may be, for example, a deposition of sediment in the region of the vibratable unit 4. If, on the other hand, a change in the frequency f is also detected which, however, does not exceed a predeterminable limit value for the frequency, for example, one may conclude that a sediment is present in the medium 2 or that the vibratable unit 4 is covered by a foam.

[0037] In addition to the possibilities mentioned, numerous further embodiments of the method according to the invention are conceivable, which allow for further conclusions to be drawn from the consideration of the frequency and amplitude with respect to the determination of a statement about the limit level, which also fall under the present invention.

REFERENCE SYMBOLS

[0038]

TABLE-US-00001 1 Vibronic sensor 2 Medium 2a Container 3 Sensor unit 4 Vibratable unit 5 Drive/receiving unit 6 Electronic unit 7 Membrane 8a, 8b Vibrating rods 9a, 9b Paddles U.sub.A Excitation signal U.sub.E Reception signal f Frequency f.sub.ref Frequency reference value A Amplitude A.sub.ref Amplitude reference value a Freely vibrating vibratable unit b Vibratable unit covered with medium t Immersion depth of the vibratable unit