SYMMETRIZING A VIBRONIC SENSOR

Abstract

A device for determining and/or monitoring a process variable of a medium comprises a sensor unit with a mechanically vibrating fork having a first and a second vibrating element and having a first piezoelectric element arranged in the first vibrating element. An electronic unit of the device is designed to excite mechanical vibrations in the mechanically vibratable unit, receive the mechanical vibrations of the vibratable unit and convert same into a first reception signal, generate the excitation signal on the basis of the first reception signal such that there is a specifiable phase shift between the excitation signal and the first reception signal, and ascertain the process variable using the first reception signal. The electronic unit has an adjustable impedance element connected in series to the first piezoelectric element.

Claims

1-15. (canceled)

16. A device for determining and/or monitoring at least one process variable of a medium, comprising: a sensor unit including a mechanically vibratable unit in the form of a vibrating fork having a first and a second vibrating element and further having a first piezoelectric element that is at least partly arranged in the first vibrating element; and an electronic unit including a first adjustable impedance, wherein the electronic unit is designed to excite mechanical vibrations in the mechanically vibratable unit via an excitation signal, receive the mechanical vibrations of the vibratable unit and convert the received mechanical vibrations into a first reception signal, generate the excitation signal on the basis of the first reception signal such that a specifiable phase shift is provided between the excitation signal and the first reception signal, and calculate the process variable using the first reception signal, wherein the first adjustable impedance element is connected in series to the first piezoelectric element.

17. The device according to claim 16, wherein the sensor unit further includes a second piezoelectric element, wherein the second piezoelectric element is at least partly arranged in the second vibrating element.

18. The device according to claim 17, wherein the electronic unit further includes a second adjustable impedance element, wherein the second adjustable impedance element is connected in series to the second piezoelectric element.

19. The device according to claim 18, wherein each of the first and second adjustable impedance elements is an adjustable resistor, a potentiometer, or a switched-capacitor filter.

20. The device according to claim 19, wherein the electronic unit is further designed to adjust an impedance of the first and second impedance elements as a function of a frequency, a quality, and/or an amplitude of the reception signal.

21. The device according to claim 20, wherein the electronic unit is further designed to emit a transmission signal and receive a second reception signal and determine the at least one process variable using the first and/or second reception signals (E.sub.S).

22. The device according to claim 16, further comprising: a unit, including a temperature sensor in the form of a resistor element or a thermocouple, for determining and/or monitoring the temperature.

23. The device according to claim 16, further comprising: a unit for determining and/or monitoring a pressure of the medium; and/or a unit for determining and/or monitoring a conductivity and/or a capacity of the medium.

24. A method for symmetrizing a first and a second vibrating element of a vibrating fork, which is part of a sensor unit of a device for determining and/or monitoring at least one process variable of a medium, wherein a first piezoelectric element is at least partly arranged in the first vibrating element, and wherein an electronic unit of the device includes a first adjustable impedance element connected in series to the first piezoelectric element, and wherein the method comprising: exciting mechanical vibrations in the first vibrating element via a symmetrizing excitation signal and receiving a first symmetrizing reception signal; exciting mechanical vibrations in the second vibrating element via the symmetrizing excitation signal and receiving a second symmetrizing reception signal; comparing the first and second symmetrizing reception signals on the basis of a first or second frequency, an amplitude and/or a quality ascertained from the first and/or second symmetrizing reception signals; and adjusting the at least one impedance element based on the comparison.

25. The method according to claim 24, further comprising: adjusting the at least one impedance element such that the first and second frequency, the amplitude and/or the quality each have the same value.

26. The method according to claim 25, further comprising: mechanically blocking one vibrating element while vibrations are excited in the other vibrating element.

27. The method according to claim 24, wherein the sensor unit includes a second piezoelectric element and the second piezoelectric element is at least partly arranged in the second vibrating element, wherein the electronic unit of the device further includes a second impedance element and the second impedance element is connected in series to the second piezoelectric element, and wherein the first and second impedance element are adjusted based on the comparison.

28. The method according to claim 27, wherein the at least one impedance element is adjusted such that the amplitude of the first and/or second symmetrizing reception signal is at a maximum.

29. The method according to claim 28, wherein a presence of corrosion and/or sediment in a region of at least one of the vibrating elements is inferred based on a change in the amplitude of the first and/or second symmetrizing reception signal over time.

30. The method according to claim 29, wherein in the case of the presence of corrosion and/or sediment, at least one impedance element is adjusted such that an influence of the corrosion or the sediment on the first and/or second symmetrizing reception signal is reduced or compensated.

Description

[0034] The invention is explained in greater detail with reference to the following figures. The following is shown:

[0035] FIG. 1: a schematic drawing of a vibronic sensor according to the prior art,

[0036] FIG. 2 a plurality of possible embodiments of a sensor unit that are known per se from the prior art and are suitable for carrying out the method according to the invention, and

[0037] FIG. 3: an exemplary embodiment of a device according to the invention with two adjustable impedance elements.

[0038] In the figures, identical elements are respectively provided with the same reference signs.

[0039] FIG. 1 shows a vibronic sensor 1 having a sensor unit 2. The sensor has a mechanically vibratable unit 4, in the form of a vibrating fork, which is partially dipped into a medium M which is located in a reservoir 3. The vibrating unit 4 is excited by the excitation/receiving unit 5 to mechanical vibrations and can, for example, be excited by means of a piezoelectric stack drive or bimorphic drive. Other vibronic sensors have electromagnetic drive/receiving units 5, for example. It is possible to use a single drive/receiving unit 5 which serves both to excite the mechanical vibrations and to detect them. However, it is likewise conceivable to realize one each, a drive unit and a receiving unit. Furthermore depicted in FIG. 1 is an electronics unit 6 by means of which the signal acquisition, evaluation, and/or feed takes place.

[0040] FIG. 2 shows, by way of example, various sensor units 2, which are suitable for carrying out a method according to the invention. The mechanically vibratable unit 4 shown in FIG. 2a comprises two vibrating elements 9a, 9b, which are mounted on a base 8 and which are therefore also referred to as fork teeth. Optionally, a paddle may respectively also be formed on the end sides of the two vibrating elements 9a, 9b [not shown here]. In each of the two vibrating elements 9a, 9b, a cavity 10a, 10b, especially, a pocket-like cavity, is respectively introduced, in which at least one piezoelectric element 11a, 11b of the drive/receiving unit 5 is respectively arranged. Preferably, the piezoelectric elements 11a and 11b are embedded in the cavities 10a and 10b. The cavities 10a, 10b can be such that the two piezoelectric elements 11a, 11b are located completely or partly in the region of the two vibrating elements 9a, 9b. Such an arrangement along with similar arrangements are extensively described in DE102012100728A1.

[0041] Another possible exemplary embodiment of a sensor unit 2 is depicted in FIG. 2b. The mechanically vibratable unit 4 has two vibrating elements 9a, 9b, which are aligned in parallel to one another and are configured here in a rod-shaped manner. They are mounted on a disk-shaped element 12 and can be excited separately from one another to vibrate mechanically. Their vibrations can likewise be received and evaluated separately from one another. The two vibrating elements 9a and 9b respectively have a cavity 10a and 10b, in which at least one piezoelectric element 11a and 11b is respectively arranged in the region facing the disk-shaped element 12. With respect to the embodiment according to FIG. 2b, reference is again made to the as yet unpublished German patent application with reference number DE102017130527A1.

[0042] As shown schematically in FIG. 2b, according to the invention, the sensor unit 2 is supplied on the one hand with an excitation signal A such that mechanical vibrations are excited in the vibratable unit 4. The vibrations are generated by means of the two piezoelectric elements 11a and 11b. It is conceivable both for both piezoelectric elements to be supplied with the same excitation signal A and for the first vibrating element 11a to be supplied with a first excitation signal A.sub.1 and the second vibrating element 11b to be supplied with a second excitation signal A.sub.2. It is also conceivable for a first reception signal E.sub.A to be received on the basis of the mechanical vibrations, or for each vibrating element 9a, 9b to receive a separate reception signal E.sub.A1 or E.sub.A2.

[0043] In addition, a transmission signal S is emitted from the first piezoelectric element 11a and is received in the form of a second reception signal E.sub.S by the second piezoelectric element 11b. Since the two piezoelectric elements 11a and 11b are arranged at least in the region of the vibrating elements 9a and 9b, the transmission 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 transmission signal S is preferably an ultrasonic signal, especially a pulsed ultrasonic signal, especially at least one ultrasonic pulse. However, it is also conceivable for the transmission signal S to be emitted by the first piezoelectric element 11a in the region of the first vibrating element 9a and to be reflected at the second vibrating element 9b. In this case, the second reception signal E.sub.S is received by the first piezoelectric element 11a. In this case, the transmission signal S passes through the medium M twice, which leads to a doubling of a transit time r of the transmission signal S.

[0044] In addition to these two embodiments shown of an device 1 according to the invention, numerous other variants are also conceivable, which likewise fall within the present invention. For example, for the embodiments according to figures FIG. 2a and FIG. 2b, it is possible to use only one piezoelectric element 11a, 11b and to arrange it at least in one of the two vibrating elements 9a, 9b. In this case, the piezoelectric element 9a serves to generate the excitation signal and the transmission signal S, and to receive the first E.sub.1 and the second reception signal E.sub.2. In this case, the transmission signal is reflected at the second vibrating element 9b without piezoelectric element 11b.

[0045] Another exemplary possibility is depicted in FIG. 2c. Here, a third piezoelectric element 11c is provided in the region of the membrane 12. The third piezoelectric element 11c serves to generate the excitation signal A and to receive the first reception signal E.sub.1; the first 11a and the second piezoelectric element 11b serve to generate the transmission signal S or to receive the second reception signal E.sub.2. Alternatively, it is possible, for example, to generate the excitation signal A and the transmission signal S and receive the second reception signal E.sub.2 with the first 11a and/or the second piezoelectric element 11b, wherein the third piezoelectric element 11c serves to receive the first reception signal E.sub.1. It is also possible to generate the transmission signal S with the first 11a and/or the second piezoelectric element 11b and the excitation signal A with the third piezoelectric element 11c and to receive the first E.sub.1 and/or the second reception signal E.sub.2 with the first 11a and/or the second piezoelectric element 11b. In the case of FIG. 2c, it is also possible for other embodiments to dispense with the first 11a or the second piezoelectric element 11b.

[0046] Yet another possible embodiment of the device 1 is the subject matter of FIG. 2d. Starting from the embodiment of FIG. 2b, the device comprises a third 9c and a fourth vibrating element 9d. However, the latter do not serve to generate vibrations. Rather, a third 11c and a fourth piezoelectric element 11d are respectively arranged in the additional elements 9c, 9d. In this case, the vibronic measurement is carried out by means of the first two piezoelectric elements 11a, 11b and the ultrasonic measurement by means of the other two piezoelectric elements 11c, 11d. Here as well, a piezoelectric element, e.g., 11b and 11d, can be dispensed with depending on the measurement principle. For reasons of symmetry, however, it is advantageous to always use two additional vibrating elements 9c, 9d.

[0047] In the embodiments shown, the piezoelectric elements 11 each also serve for vibration excitation and detection and thus have a dual function. In other embodiments, at least one piezoelectric element 11 arranged in at least one of the vibrating elements 9 can also serve exclusively for symmetrizing the vibrating fork, while the electromechanical transducer unit 5 is a separate component. The at least one piezoelectric element 11, which is at least partly arranged in one of the vibrating elements 9, is preferably arranged in a region which decisively influences the rigidity of the respective vibrating element, for example in the root region, i.e., in an end region, which is attached to the membrane 8 or the disk-shaped element 12, of the vibrating element 9.

[0048] An exemplary embodiment of a device 1 according to the invention in which the mechanically vibratable unit 4 is configured similarly to that of FIG. 2a is shown in FIG. 3. In addition to various components combined with the reference symbol 6 in the box, the electronic unit 6 comprises two electrically adjustable impedance elements 13a, 13b, each of which is connected in series to the two piezoelectric elements 11a, 11b. In other embodiments, only one impedance element 13 can also be provided, which is connected in series to one of the piezoelectric elements 11.

[0049] The rigidity of the vibrating elements 9a, 9b can be directly influenced by means of the impedance elements 13a, 13b. As a result, an identical vibration behavior of the two vibrating rods 9a, 9b, i.e., a symmetry between both vibrating elements 9a, 9b, can in turn be achieved. The impedance/impedances can be adjusted in a suitable manner as part of the manufacturing process, before commissioning at the place of use or during continuous operation.

LIST OF REFERENCE SIGNS

[0050] 1 Vibronic sensor [0051] 2 Sensor unit [0052] 3 Reservoir [0053] 4 Vibratable unit [0054] 5 Drive/receiving unit [0055] 6 Electronic unit [0056] 8 Base [0057] 9a, 9b Vibrating elements [0058] 10a, 10b Cavities [0059] 11a, 11b Piezoelectric elements [0060] 12 Disk-shaped element [0061] 13, 13a, 13b Impedance element [0062] M Medium [0063] P.sub.1-P.sub.3 Process variables [0064] A Excitation signal [0065] S Transmission signal [0066] E.sub.A First reception signal [0067] E.sub.S Second reception signal [0068] Δ.sub.ϕ Specifiable phase shift [0069] ρ Density of the medium [0070] v Viscosity of the medium [0071] v.sub.M Sound velocity in the medium [0072] T Transit time