VIBRONIC SENSOR

Abstract

A device for determining and/or monitoring at least one process variable of a medium in a container includes four, rod-shaped elements arranged on a membrane, three piezoelectric elements and an electronics system, wherein one first and one second rod-shaped element are arranged and configured such that they form a mechanically vibratable unit, wherein the device is configured to excite the vibratable unit via an excitation signal to create mechanical oscillations, to receive the mechanical oscillations of the vibratable unit, to convert them into a first received signal, to transmit a transmitted signal, and to receive a second received signal, and wherein the electronics system is configured to determine the at least one process variable based on the first and/or second received signal.

Claims

1-15. (canceled)

16. A device for determining and/or monitoring at least one process variable of a medium in a container, the device comprising: four, rod-shaped elements disposed on a membrane, including a first element and a second element, wherein the first element and the second element are arranged and configured as to define a mechanically vibratable unit; three piezoelectric elements; and an electronics system, wherein the device is configured to: excite the vibratable unit via an excitation signal to generate mechanical oscillations; receive the mechanical oscillations of the vibratable unit and convert the mechanical oscillations into a first received signal; transmit a transmitted signal; and receive a second received signal, and wherein the electronics system is configured to determine the at least one process variable based on the first received signal and/or the second received signal.

17. The device of claim 16, comprising four piezoelectric elements.

18. The device of claim 16, wherein at least one piezoelectric element of the three piezoelectric elements is arranged at least partially within the first element or the second element.

19. The device of claim 16, wherein the at least one process variable is a fill-level, a density, a viscosity, an acoustic velocity, a Reynolds number, or a variable derived from at least one of the preceding process variables.

20. The device of claim 16, wherein the electronics system is configured to determine at least two different process variables based upon the first received signal and/or the second received signal.

21. The device of claim 16, wherein the four, rod-shaped elements including a third element and a fourth element, wherein the first element and the second element are configured identically and are arranged opposite each other relative to a center point of a surface of the membrane on which the first and second elements are disposed, and wherein the third and the fourth rod-shaped elements are configured identically and are arranged opposite each other relative to the center point of the surface of the membrane on which the third and fourth elements are disposed

22. The device of claim 21, wherein an angle between a first connecting line between the first and second elements and a second connecting line between the third and fourth elements are substantially perpendicular to each other.

23. The device of claim 21, wherein the first and second elements each have a same length, and the third and fourth elements each have a different same length, wherein the length of the first and second elements is greater than the length of the third and fourth elements.

24. The device of claim 21, wherein the first and second elements each have a same base area, and the third and fourth elements each have a different same base area, wherein the base area of the first and second elements is greater than the base area of the third and fourth elements.

25. The device of claim 21, wherein the third element and/or fourth element are configured and arranged as a baffle such that the baffle generates vortices in the medium when the medium is flowing across the device, wherein the vortices have a speed-dependent, vortex shedding frequency from the baffle, wherein the vortex shedding frequency is determined based on pressure fluctuations, caused by the vortices, using the vibratable unit, and wherein a Strouhal number of the medium, a Reynolds number of the medium, and/or a variable derived from the Strouhal number and/or the Reynolds number is determined based on the vortex shedding frequency.

26. A method for determining and/or monitoring at least one process variable of a medium in a container, the method comprising: exciting a mechanically vibratable unit of a sensor unit with an excitation signal to generate mechanical oscillations; receiving the mechanical oscillations of the vibratable unit; converting the mechanical oscillations into a first received signal; transmitting a transmitted signal; and receiving a second received signal, wherein the at least one process variable is determined based upon the first received signal and/or second received signal.

27. The method of claim 26, wherein the at least one process variable determined is a flow characteristic of the medium.

28. The method of claim 26, wherein the vibratable unit includes a first rod-shaped element and a second rod-shaped element, wherein the sensor unit further includes a third rod-shaped element and/or a fourth rod-shaped element, wherein the third element and/or fourth element are configured as a baffle, which is configured and arranged to generate vortices in the medium when the medium is flowing across the sensor unit, wherein the vortices have a speed-dependent, vortex shedding frequency from the baffle, wherein a vortex shedding frequency is determined based on pressure fluctuations, caused by the vortices, via the vibratable unit, and wherein a Strouhal number of the medium, a Reynolds number of the medium, and/or a variable derived from the Strouhal number and/or the Reynolds number is determined based on the vortex shedding frequency.

29. The method of claim 28, wherein the at least one process variable determined is a flow characteristic of the medium, and wherein the flow characteristic is determined using the Strouhal number and/or the Reynolds number.

30. The method of claim 29, wherein the excitation signal and the transmitted signal are generated in a first operating mode, wherein the at least one process variable is determined in the first operating mode based on the first received signal and/or second received signal, and wherein the flow characteristic of the medium is determined in a second operating mode.

31. The method of claim 26, wherein a viscosity and/or a density of the medium is determined based on the first received signal, and wherein a Reynolds number of the medium is taken into account for determining the viscosity and/or density.

Description

[0037] The invention and its advantageous embodiments are described in more detail below with reference to the figures, FIG. 1-FIG. 3. The following are shown:

[0038] FIG. 1: a schematic drawing of a vibronic sensor according to the prior art;

[0039] FIG. 2: an exemplary embodiment of a device according to the invention; and

[0040] FIG. 3: an illustration for determining the Reynolds number by means of the device shown in FIG. 2.

[0041] FIG. 1a shows a vibronic sensor 1. The sensor has a sensor unit 2 having a mechanically vibratable unit 4 in the form of an oscillating fork, which is partially immersed in a medium M, which is located in a tank 3. The vibratable unit 4 is excited by the excitation/receiving unit 5 to vibrate mechanically and can be, for example, by means of a piezoelectric stack drive or bimorphic drive. Other vibronic sensors have, for example, electromagnetic driving/receiving units 5. It is possible to use a single driving/receiving unit 5, which serves to excite the mechanical vibrations and to detect them. However, it is also conceivable to implement one driving unit and one receiving unit each. FIG. 1 further shows an electronics system 6, by means of which the signal acquisition, evaluation, and/or feeding takes place.

[0042] FIG. 1b shows a vibratable unit 4 in the form of an oscillating fork, as is integrated in the vibronic sensor 1 marketed by the applicant under the name LIQUIPHANT, for example. The oscillating fork 4 comprises two, rod-shaped elements 9a, 9b which are mounted on a membrane 8 and on the end of each of which a paddle 10a, 10b is integrally formed. These are therefore also referred to as fork prongs. The driving/receiving unit 5 is fastened to the side of the membrane 8, facing away from the rod-shaped elements 9a, 9b, by means of an integrally-bonded and/or force-fitting connection. For the exemplary embodiment shown, it is assumed that the driving/receiving unit 5 comprises at least one piezoelectric element. During continuous operation, a force is applied to the membrane 8 via the application of an excitation signal U.sub.A, e.g., in the form of an electrical alternating voltage which is generated in the electronics system 6. A change in the applied electrical voltage causes a change in the geometric shape of the driving/receiving unit 5, i.e., a contraction or a relaxation within the piezoelectric element such that the application of an electrical alternating voltage as an excitation signal U.sub.A causes an oscillation of the membrane 8 integrally bonded to the driving/receiving unit 5, and therefore of the mechanically vibratable unit 4.

[0043] In a device 1 according to the invention, as shown by way of example in FIG. 3, the sensor unit 2 comprises four, rod-shaped elements 9a-9d, formed on the membrane 8, and four piezoelectric elements 11a-11d. The first rod-shaped element 9a and the second rod-shaped element 9b form the vibratable unit 4. In each case, one piezoelectric element 11a-11d is introduced into one of the rod-shaped elements 9a-9b.

[0044] On the one hand, such a device can be acted upon by an excitation signal A such that the vibratable unit 4 is excited to create mechanical oscillations. The oscillations are generated by means of the two piezoelectric elements 11a and 11b. It is conceivable for both piezoelectric elements to be acted upon by the same excitation signal A as well as for the first vibrating element 11a to be acted upon by means of a first excitation signal A.sub.1 and the second vibrating element 11b to be acted upon by means of a second excitation signal A.sub.2. It is also conceivable for a first received signal E.sub.A to be received on the basis of the mechanical oscillations, or for a first received signal E.sub.A1 or E.sub.A2 to be separately received from each vibrating element 9a, 9b.

[0045] In addition, a transmitted signal S is emitted from the third piezoelectric element 11c and is received in the form of a second received signal E.sub.S by the fourth piezoelectric element 11d. Since the two piezoelectric elements 11c and 11d are arranged in the region of the rod-shaped elements 9c and 9d, the transmitted signal S passes through the medium M, provided that the sensor unit 2 is in contact with the medium M, and is influenced accordingly by the properties of the medium M. The transmitted signal S is preferably an ultrasonic signal, in particular a pulsed ultrasonic signal, and in particular at least one ultrasonic pulse. In other embodiments, the fourth piezoelectric element 11d can be omitted. The transmitted signal S is then reflected at the fourth rod-shaped element 11d and received by the third piezoelectric element 11c. In this case, the transmitted signal S passes through the medium M twice, which leads to a doubling of a transit time T of the transmitted signal S.

[0046] The first rod-shaped element 9a and the second rod-shaped element 9b are designed identically for the embodiment shown. They have the same base area G1 and length L1, and are arranged symmetrically to one another on opposite sides of a center point P of the surface O, facing the medium M, of the membrane 8. The third rod-shaped element 9c and fourth rod-shaped element 9d are also designed identically, have the same base area G2 and length L2, and are arranged symmetrically to one another on opposite sides of a center point P of the surface O, facing the medium M, of the membrane 8. The length L1 and base area G1 of the first rod-shaped element 9a and second rod-shaped element 9b are each greater than the length L2 and base area G2 of the third rod-shaped element 9c and fourth rod-shaped element 9d.

[0047] In addition to this shown embodiment of a device 1 according to the invention, numerous other variants are also conceivable, which likewise fall within the present invention.

[0048] Finally, FIG. 3 illustrates the determination of the Reynolds number RE. A view from above of the sensor unit 2 from FIG. 2 is shown. The first rod-shaped element 9a and the second rod-shaped element 9b form the vibratable unit 4. The third rod-shaped element 9c and fourth rod-shaped element 9d form a flow unit 12 for generating vortex flows W, which are detected by the vibratable unit 4. The third rod-shaped element 12c is used as a baffle.

LIST OF REFERENCE SIGNS

[0049] 1 Vibronic sensor [0050] 2 Medium [0051] 3 Container [0052] 4 Vibratable unit [0053] 5 Driving/receiving unit [0054] 6 Electronics system [0055] 8 Membrane [0056] 9, 9a-9d Rod-shaped elements [0057] 10, 10a, 10b Paddle [0058] 11a-11d Piezoelectric elements [0059] 12 Unit for ultrasonic measurement and for generating vortex flows [0060] A Excitation signal [0061] S Transmitted signal [0062] E.sub.A First received signal [0063] E.sub.S Second received signal [0064] L1, L2 Length of the rod-shaped elements [0065] G1, G2 Base areas of the rod-shaped elements [0066] b, b.sub.1-b.sub.4 Base sides of the vibrating elements [0067] d1, d2 Distance from the center point of the membrane [0068] M Medium [0069] W Vortex flow [0070] P Center point of the membrane [0071] O Surface, facing the medium, of the membrane [0072] f Vortex shedding frequency [0073] SR Strouhal number [0074] RE Reynolds number