Vibration sensor

Abstract

The invention relates to a vibration sensor comprising a mechanically vibrating unit (1) and a transducer device (2) which causes the mechanically vibrating unit (1) to mechanically vibrate and / or receives mechanical vibrations. The transducer device (2) has a piezo element (3) with two end faces (30, 31) and an outer casing (32). Each end face (30, 31) is provided with an electrode (33, 34) which extends from one end face (30, 31) to the respective other end face (31, 30) via the outer casing (32).

Description

[0001] Vibration sensor

[0002] The invention relates to a vibration sensor. The vibration sensor is used, for example, to determine and / or monitor a process variable of a medium. The process variable is, for example, the fill level, and the medium is, for example, a liquid, a gas, or a bulk material.

[0003] Vibration sensors are known in the art, for example, in the form of tuning forks or single-rod sensors. Such sensors have a mechanically oscillating unit that is excited to mechanical vibrations by a drive / receiver unit. The vibrations resulting from the interaction with a medium to be measured or monitored are received by the drive / receiver unit and sent for evaluation. For example, a measurement exploits the fact that the vibration frequency or amplitude changes when the mechanically oscillating unit transitions from an uncovered state to one covered by the medium. This allows, for example, the monitoring of the fill level of the medium in a container.

[0004] The drive / receiver unit typically contains a converter device that converts between electrical signals and mechanical vibrations. Piezoelectric elements are often used for this purpose. These elements feature a polarized ceramic and at least one electrode applied to one end face for electrical contact. If the mechanical force to be generated is to be increased, it is common practice to arrange several piezoelectric elements in a stack. For electrical contact, it is then necessary to contact all the elements individually or at least with each other. This is very complex and costly.

[0005] Examples of different designs of piezoelectric elements are described in the following publications: DE 103 50 086 B4, DE 10 2019 111 384 B3, DE 10 2016 113 447 A1, DE 1648 582 A, or EP 0 985 916 A1. The invention is based on the object of proposing a vibration sensor that is as simple as possible to manufacture with regard to the piezoelectric elements.

[0006] The object is achieved by a vibration sensor with a mechanically oscillatable unit and with a transducer device, wherein the transducer device excites the mechanically oscillatable unit to mechanical vibrations and / or receives mechanical vibrations from the mechanically oscillatable unit, wherein the transducer device has at least one piezo element, wherein the piezo element has two end faces and an outer casing, wherein an electrode is applied to each end face, and wherein each electrode is guided from one end face of the two end faces via the outer casing to the respective other end face of the two end faces.

[0007] The vibration sensor according to the invention has a mechanically oscillating unit (e.g. in the form of a tuning fork, a single rod, or a diaphragm) and a transducer device that converts between electrical signals and the mechanical vibrations of the mechanically oscillating unit and / or vice versa. The transducer device has at least one piezo element for this purpose. The piezo element has two end faces and an outer casing. On each end face there is an electrode for electrical contact. Furthermore, each electrode is guided via the outer casing to the other end face. Thus, there are two electrodes on each end face, which are preferably electrically insulated from one another. The electrodes themselves extend from one end face across the outer casing to the other end face. This offers the advantage that both sides of the piezo element can be contacted via each end face.It is therefore not necessary to connect a single contact to each end face; it is sufficient to connect two contacts to one end face. This significantly simplifies the contacting effort.

[0008] Furthermore, this makes it easier to arrange multiple piezo elements in a stack and connect them electrically. Finally, with a suitable arrangement and design, the contacts of the different piezo elements also face each other. Therefore, one design provides for the transducer device to have at least two piezo elements, for the at least two piezo elements to be arranged one above the other in a stack, and for the at least two piezo elements to be directly electrically connected to each other. The electrodes must have a geometry such that the mechanical contact surfaces are sufficiently large for electrical contact. The piezo elements are preferably of the same design.

[0009] To ensure adequate contact, one design provides for the piezo elements to be pressed together by a mechanical force. This eliminates the need for solder or adhesive connections, for example. This avoids, among other things, the disadvantage of adhesive connections, which is the potential for settling effects, which can lead to a reduction in the preload or preload force and thus change the stiffness of the overall system.

[0010] One embodiment consists in the converter device having at least one contacting electrode, and the contacting electrode being electrically connected to at least one piezoelectric element. Electrical signals can be transmitted to or discharged from the converter device via a contacting electrode (another term is, for example, a soldering lug).

[0011] One embodiment provides for the transducer device to have a sleeve, and for the at least one piezo element to be arranged in the sleeve. The sleeve encloses the transducer device and, in one embodiment, also serves as thermal insulation against potentially higher temperatures arising from the application, through a suitable choice of material.

[0012] One embodiment consists in that the at least one piezo element is arranged in the sleeve in a rotationally fixed manner via a recess and a locking lug. The rotationally fixed positioning is particularly advantageous when several piezo elements are electrically contacted with one another via their electrodes solely by mechanical force. In this case, care must be taken to ensure the correct orientation of the electrodes or piezo elements relative to one another in order to ensure optimal overlap between the electrodes of the individual piezo elements arranged one above the other. According to one embodiment, the sleeve has at least one radially inward-projecting support at its end. The support, which can also be referred to as a shoulder, serves as protection against the piezo element or other components arranged in the stack falling out of the sleeve, e.g. during assembly.

[0013] In one embodiment, the circumferentially interrupted support consists of several circumferentially distributed locking arms.

[0014] On the opposite end of the sleeve, there is, in one embodiment, a shoulder that also narrows the diameter compared to the diameter of the interior of the sleeve. On this end, in one embodiment, the coupling element is located, which has a spherically tapered end and, conversely, an outer diameter that increases inward. This causes the spherical end to protrude from the sleeve, while at the same time, the coupling element as a whole is held against falling out by the shoulder of the sleeve.

[0015] One embodiment consists in the piezo element being designed as a circular disc.

[0016] The invention is explained in more detail with reference to the following figures.

[0017] Fig. 1 shows schematically the structure of a vibration sensor,

[0018] Fig. 2 shows a section through a converter device,

[0019] Fig. 3 shows a spatial representation of the converter device of Fig. 2,

[0020] Fig. 4 shows a stack of piezo elements,

[0021] Fig. 5 shows a front side of a piezo element and

[0022] Fig. 6 shows the other end face of the piezo element of Fig. 5. Fig. 1 shows a so-called tuning fork as an example of a design of the vibration sensor.

[0023] The mechanically oscillating unit 1 has two so-called fork tines connected to a diaphragm 5. On the opposite side of the diaphragm 5, in a housing 4 (shown here), there is a transducer device 2, which, in the example shown, has several disc-like piezo elements 3 arranged in a stack. The piezo elements 3 are clamped between a pressure screw 6 and a coupling element 7. The coupling element 7 for clamping relative to the diaphragm 5 has the shape of a hemisphere.

[0024] The section in Fig. 2 shows that, in the exemplary embodiment, several piezo elements 3 and three insulation disks 11 are located between the pressure screw 6 and the coupling element 7. The piezo elements 3 are surrounded by a sleeve 9. A contacting electrode 8 extends from a window 10 in the sleeve 9 and is in contact with a piezo element 3 in the stack. The sleeve 9 is attached to the pressure screw 6, for example, via snap hooks.

[0025] Fig. 3 shows that the sleeve 9 is designed in two parts for easy assembly. This can be seen at the front separation point. The two housing halves each have a raised portion at their upper ends for mutual locking.

[0026] The sleeve 9 has several windows 10 for the contacting electrodes 8 (an alternative term is solder lug). On the top side, a locking lug 12 is visible in the sleeve 9, which engages the matching recesses 35 of the piezo elements 3 or the insulation discs (see Fig. 4 - Fig. 6).

[0027] At the upper end of the sleeve 9 is an inwardly projecting shoulder 13, which in this design consists of three individual locking arms (see Fig. 2). The shoulder 13 ensures that the end face of the sleeve 9 has a smaller diameter than the interior of the sleeve 9. Therefore, components located in the sleeve 9 are prevented from falling out. This simplifies manufacturing. On the underside of the sleeve 9 - see Fig. 2 - there is also an inwardly projecting shoulder, which holds the coupling element 7 there.

[0028] During production, for example, the individual components are inserted into one housing half. The other housing half is then applied so that the raised portions engage each other to lock them together. In the resulting assembled sleeve 9, the locking lugs 12 prevent the components from twisting relative to each other and protect the supports 13 from falling out.

[0029] In an alternative design (not shown), a hinge, e.g., a film hinge, is provided. For assembly, in this variant, the sleeve 9 is opened to accommodate the components. Then, the sleeve 9 is closed again, and a snap-in of the previously mentioned protrusions ensures fixation.

[0030] In Fig. 4, it can be seen on the outer casings 32 of the piezo elements 3 how an electrode 34 extends continuously from bottom to top, thus creating a continuous electrical contact. The insulating disks 11 as the upper and lower ends of the stack, respectively, as well as the insulating disk 11 in the stack, result in a total of two separate stacks of piezo elements 3, which separately serve to excite and receive the mechanical vibrations. It can be seen that only four contacting electrodes 8 are sufficient for this. Furthermore, there are no further electrical connections between the piezo elements 3. On the rear side, the recess 35 can be seen, which engages with the locking lug 12 of the sleeve 9.

[0031] Fig. 5 and Fig. 6 show the two end faces 30, 31 of a piezo element 3. On each of the end faces 30, 31 there is a largely circular electrode 33, 34. Each electrode 33, 34 borders in sections on the edge of the end face 30, 31 in order to be guided in this area to the opposite end face 31, 30. This occurs via the part of the electrode 33, 34 that extends along the outer casing 32 of the piezo element 3. On the respective opposite end faces 31, 30 there is a significantly smaller extension of the electrode 33, 34. The smaller area is possible because the purpose of the recontacting is electrical contact. The electrodes 33, 34 are designed here such that on each end face 30, 31 the two sections for the respective non-contacting from one end face 31, 30 to the other are opposite each other.

[0032] List of reference symbols for mechanically oscillating unit

[0033] converter device

[0034] Piezo element

[0035] Housing

[0036] membrane

[0037] pressure screw

[0038] coupling element

[0039] Contacting electrode

[0040] sleeve

[0041] Window

[0042] Insulating disc

[0043] locking lug

[0044] Edition

[0045] Front side of the piezo element

[0046] Front side of the piezo element

[0047] Outer jacket of the piezo element

[0048] electrode

[0049] electrode

[0050] recess

Claims

Patent claims 1 . Vibration sensor, with a mechanically oscillatable unit (1 ) and with a transducer device (2), wherein the transducer device (2) excites the mechanically oscillatable unit (1 ) to mechanical vibrations and / or receives mechanical vibrations from the mechanically oscillatable unit (1 ), wherein the transducer device (2) has at least one piezo element (3), wherein the piezo element (3) has two end faces (30, 31 ) and an outer casing (32), wherein an electrode (33, 34) is applied to each end face (30, 31 ), and wherein each electrode (33, 34) is guided from one end face (30, 31 ) of the two end faces (30, 31 ) via the outer casing (32) to the respective other end face (31, 30) of the two end faces (30, 31 ).

2. Vibration sensor according to claim 1, wherein the transducer device (2) has at least two piezo elements (3), wherein the at least two piezo elements (3) are arranged one above the other in a stack, and wherein the at least two piezo elements (3) are directly electrically contacted with one another.

3. Vibration sensor according to claim 1 or 2, wherein the transducer device (2) has at least one contacting electrode (8), and wherein the contacting electrode (8) is electrically conductively contacted with at least one piezo element (3).

4. Vibration sensor according to one of claims 1 to 3, wherein the transducer device (2) has a sleeve (9), and wherein the at least one piezo element (3) is arranged in the sleeve (9).

5. Vibration sensor according to claim 4, wherein the at least one piezo element (3) is arranged in the sleeve (9) via a recess (35) and a locking lug (12) in a rotationally fixed manner.

6. Vibration sensor according to claim 4 or 5, wherein the sleeve (9) has at least one radially inwardly projecting support (13) at its end.

7. Vibration sensor according to one of claims 1 to 6, wherein the piezo element (3) is designed as a circular disc.

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