Vibration sensor

Abstract

The invention relates to a vibration sensor having a mechanically vibratable unit (1) and a transducer device (2) which has a transmitter component (20) and a receiver component (21) and is delimited at the end faces by two insulating discs (23). Two of the three contacting electrodes (9, E+, S+, GND) are used to transmit the excitation and received signals. The other contacting electrode (GND) is provided between the receiver component (21) and the transmitter component (20) and is electrically connected to the housing (3) of the vibration sensor.

Description

[0001] Vibration sensor

[0002] The invention relates to a vibration sensor. The vibration sensor serves, for example, to determine and / or monitor a process parameter of a medium. The process parameter 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 rods. Such sensors have a mechanically vibrating 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 processed. For measurement purposes, it is used, for example, that the vibration frequency or amplitude changes when the mechanically vibrating unit transitions from an uncovered to a state 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 transducer device that converts between electrical signals and mechanical vibrations. Piezoelectric elements are often used for this purpose; these elements have a polarized ceramic surface and at least one electrode on one end face for electrical contact. To increase the generated mechanical force, it is known to arrange several piezoelectric elements in a stack. For electrical contact, it is then necessary to connect each element individually or at least to the others.

[0005] In the prior art, it is known that all piezoelectric elements alternately function as transmitters or receivers. Another known variant involves some of the piezoelectric elements acting as transmitters and others as receivers. It is important to note that the piezoelectric elements function not only as transducers but also as electrical components. In particular, capacitive coupling occurs between the transmitter piezoelectric elements and the receiver piezoelectric elements. This direct coupling between transmitter and receiver can be very strong, potentially rendering this type of transducer unsuitable for use in a vibration sensor, as the transmitter or excitation signal would have too strong an effect on the receiver.The invention is based on the objective of proposing a vibration sensor in which the capacitive coupling in the transducer device between a transmitter and a receiver component is avoided as far as possible.

[0006] The problem is solved by a vibration sensor comprising a mechanically vibrating unit, a transducer device, and a housing, wherein the transducer device excites the mechanically vibrating unit to mechanical vibrations and receives mechanical vibrations from the mechanically vibrating unit, wherein the transducer device is arranged in the housing, wherein the transducer device has at least one transmitter component and one receiver component, wherein the transmitter component excites the mechanically vibrating unit to mechanical vibrations based on electrical excitation signals, wherein the receiver component receives the mechanical vibrations from the mechanically vibrating unit and converts them into electrical reception signals, wherein the transducer device is bounded at its end face by two insulating disks, each of which forms one of the two insulating disks of the transmitter component or the other of the receiver component.is assigned to the receiver component, wherein the converter device has three contact electrodes, wherein one of the three contact electrodes is arranged between the transmitter component and the associated insulating disk and serves to transmit the excitation signals, wherein one of the three contact electrodes is arranged between the receiver component and the associated insulating disk and serves to transmit the received signals, and wherein one of the three contact electrodes is arranged between the transmitter component and the receiver component and serves to provide an electrical connection to the housing.

[0007] The converter device consists of a transmitter component and a receiver component. An insulating disc is located at the end face of each component, adjacent to and thus associated with the respective transmitter or receiver component. Therefore, the converter device has the following structure: insulating disc, transmitter component, receiver component, and insulating disc.

[0008] Three contact electrodes are provided for the electrical connection of the transducer device. These allow the transmitter component to be supplied with excitation signals and the receiver component to receive the signals. The contact electrodes are arranged as follows and each has the following function: A transmit contact electrode is located between the transmitter component and its associated insulating disc; this electrode receives the excitation signals. A receive contact electrode is located between the receiver component and its insulating disc; this electrode receives the signals. A ground contact electrode, connected to the housing, is located between the receiver component and the transmitter component. If the housing is grounded in the application, the ground contact electrode is connected to ground.This electrically isolates the receiver and transmitter components. An electrical connection to the housing is established via a contact electrode, ensuring an equal ground potential between the stack and the housing.

[0009] Here and in the following, "ground" or "earth" refers to the electrical reference potential with which the electronic components—e.g., as part of an electronic device—operate to generate the electrical (transmit-excitation) signals for vibration excitation and / or to receive and process the electrical (receive) signals. In particular, it is preferably the reference potential for fundamental frequency excitation.

[0010] The advantage of connecting the central electrode to the housing, and thus to ground, will be explained again. Consider an arrangement of receiver and transmitter components in a stack enclosed by insulating discs. The transducer device is coupled to the mechanically oscillating unit for mechanical force transmission, typically by clamping the transducer device between two solid components, usually made of steel (one embodiment, for example, uses a pressure screw that presses the transducer device against a diaphragm via a hemispherical force transmission component). This results in capacitive coupling across the insulating discs. The central ground connection prevents this capacitive coupling between the receiver and transmitter components.

[0011] One embodiment provides that the housing includes a diaphragm, that the mechanically oscillating unit is coupled to the diaphragm, that the transducer device is arranged between the diaphragm and a pressure screw, and that a hemispherical intermediate component is located between the transducer device and the diaphragm. In one embodiment, the housing, the pressure screw, and / or the intermediate component are made of a metal, e.g., steel. The hemispherical intermediate component ensures good force transmission between the diaphragm and the transducer device. The pressure screw, which in one embodiment is threaded into the housing, generates the preload against the diaphragm.

[0012] One embodiment provides that the transmitter and receiver components are arranged along a longitudinal axis such that the transmitter component is located in front of the receiver component in the direction of the diaphragm. In this embodiment, the transmitter component is positioned in front of the receiver component in the direction of the diaphragm. This also places the transmitter component closer to the mechanically vibrating unit, and the mechanical vibrations received by the receiver component are initially transmitted via the transmitter component.

[0013] In an alternative embodiment, the transmitter component and the receiver component are arranged along a longitudinal axis such that the receiver component is located in front of the transmitter component in the direction of the diaphragm. In this embodiment, the receiver component is closer to the mechanically vibrating unit.

[0014] One embodiment involves the mechanically oscillating unit being a rocker fork. A rocker fork has at least two fork tines, which in one embodiment are attached to the aforementioned diaphragm of the housing.

[0015] One embodiment includes the fact that the transmitter component and the receiver component each have several piezoelectric elements – preferably flat, disc-shaped or ring-shaped – which are mechanically connected and electrically contacted in pairs, particularly through diffusion processes; that the piezoelectric elements of the transmitter component and the receiver component each have essentially the same geometric dimensions; that the piezoelectric elements each have two end faces and an outer shell; that an electrode is applied to each end face; and that each electrode is led from one end face of the two end faces, via the outer shell, to the other end face of the two end faces.

[0016] In the aforementioned configuration, both the transmitter and receiver components each have several piezoelectric elements, which essentially have the same geometric dimensions. In one embodiment, the piezoelectric elements are disk-shaped, so that both the transmitter and receiver components consist of stacks of such disks. The disks can also have an internal recess, giving them a ring shape. The special feature of the piezoelectric elements used is the so-called double re-contacting: Each of the two end faces of the piezoelectric elements has an electrode that serves for electrical contact. Thus, if, for example, one electrode is contacted with the positive terminal of an electrical conductor and the other – opposite – electrode is contacted with a negative terminal, the piezoelectric element will contract or expand accordingly.In this configuration, the piezoelectric elements are polarized such that the polarization is perpendicular to the end faces and runs from one end face to the other. The double re-contacting is achieved by guiding each electrode over the outer edge of the piezoelectric element to the opposite end face. Therefore, it is possible, for example, to contact both electrodes from one end face.

[0017] The aforementioned piezoelectric elements are mechanically and electrically connected within their respective stacks—that is, with regard to the transmitter and receiver components. This connection is achieved, for example, through diffusion processes under pressure and temperature. Materials used include, for example, Ag, Ag-Sn, Ag-Sn-Au, Ti-Ni-Au, and Ni-Au. Alternatively or additionally, diffusion welding is also possible.

[0018] One embodiment provides that the piezoelectric elements have a recess in their outer casing. This recess allows, for example, easier assembly by inserting the piezoelectric elements into a sleeve with a detent that corresponds to the recess.

[0019] One embodiment provides that the transmitter component and the receiver component have a different number of piezoelectric elements. A further embodiment provides that the transmitter component has more piezoelectric elements than the receiver component. One embodiment includes a transmitter component with five piezoelectric elements and a receiver component with three piezoelectric elements.

[0020] One embodiment provides that the vibration sensor further comprises an electronic device, and that the electronic device is configured such that it supplies the transducer device with excitation signals and receives the received signals. In one embodiment, the electronic device evaluates the received signals with regard to determining and / or monitoring a process variable, e.g., fill level, density, or viscosity, of a medium.

[0021] One embodiment provides that the insulating discs are made of a piezoelectric material, in particular of the same material as the piezoelectric elements of the transmitter component and the receiver component.

[0022] One embodiment includes the three contact electrodes being essentially identical, each having a base and a contact tab, and the contact tabs of the contact electrodes projecting from the stacks of piezoelectric elements in the transmitter and receiver components. Another embodiment provides that the three contact electrodes are arranged such that there is an angular distance of essentially 90° between two pairs of immediately adjacent contact tabs.

[0023] The geometry of the three contact electrodes can certainly differ. However, for manufacturing purposes, it is generally simpler if all contact electrodes are identical, so that only one type needs to be kept in stock. The following descriptions therefore refer to identically designed contact electrodes, although at least one contact electrode may have a different geometry. It should be noted that the contact electrodes can also be referred to as soldering or welding lugs.

[0024] One embodiment includes the fact that the base surfaces are essentially designed as a flat disc with an essentially crescent-shaped outer contour, and that the outer contour essentially consists of a partial circular contour and an inwardly projecting, smoothly sloping recessed section.

[0025] For the preceding design, the coupling between those piezo elements belonging to the transmitter component and the receiver component, respectively, and which have direct contact with each other in the overall stack of the transducer device, was considered.

[0026] Extensive investigations and modeling have shown that at least two types of coupling occur. The first is a direct coupling with a phase of 0°: This is the pressure acting on the receiver component when the transmitter component expands along its longitudinal axis and, for example, acts against the membrane to which the mechanically oscillating unit is attached. The second is a transverse coupling with a phase shift of 180°: Due to the change in length of the transmitter component, its diameter changes because the volume must remain constant. This creates a transverse force that also acts on the receiver component.

[0027] Studies have shown that a crescent-shaped contact electrode provides an optimal ratio of direct to cross-coupling, preventing the transmitting component from negatively affecting the receiving component. In particular, both direct and cross-coupling occur.

[0028] The crescent shape can alternatively be described as a half-moon shape. The key feature is that the contact electrode has a circular side opposite which there is a recess, similar to a crescent or a waxing or waning moon. One design provides that the contact tab merges into the base surface in the area of ​​the partial circular contour.

[0029] One embodiment involves the contact flag being essentially a rectangular strip, and the contact flag having a narrower width adjacent to the base than in the area beyond. The strip-shaped contact flag thus hangs from the base and initially has a narrower width, followed by a wider one.

[0030] One embodiment provides that each base surface has a notch. In a further embodiment, the notch is located essentially diametrically opposite the deepest extension of the respective recessed section. The notch of the contacting electrode is particularly relevant for the design of the piezoelectric element, in which the piezoelectric element has a notch-like recess on its outer surface. This recess is advantageous, for example, when several piezoelectric elements are arranged with the correct orientation relative to each other, e.g., in a sleeve with an alignment lug, and then connected to one another.

[0031] The invention is explained in more detail with reference to the following figures.

[0032] Fig. 1 schematically shows the cross-sectional structure of a vibration sensor.

[0033] Fig. 2 shows a section through a first embodiment of a converter device,

[0034] Fig. 3 shows a spatial representation of one side of a piezoelectric element,

[0035] Fig. 4 shows the other side of the piezoelectric element of Fig. 3,

[0036] Fig. 5 shows a top view of a design of a contacting electrode and

[0037] Fig. 6 shows a top view of another embodiment of a contacting electrode.

[0038] Fig. 1 shows a so-called tuning fork as an example of a design of the vibration sensor.

[0039] The mechanically oscillating unit 1 has two so-called fork tines connected to a diaphragm 4. On the opposite, and therefore inner, side of the diaphragm 4, a transducer device 2 is located in a housing 3 (indicated here). In this example, the transducer device 2 has several disc-shaped piezoelectric elements 7 arranged in a stack. The transducer device 2 is clamped between a pressure screw 5 and a hemispherical intermediate component 6, and is thus subject to a preload relative to the diaphragm 4. Also shown is an electronic device 8, which is connected to the contact electrodes S+, E+. This device generates the excitation signals and evaluates the received signals.

[0040] The section in Fig. 2 shows a transducer device 2 with a transmitter component 20 and a receiver component 21. The diaphragm 4 is located below the lower insulating disk 23, as shown in the embodiment of Fig. 1. The longitudinal axis 22 of the transducer device 2 is perpendicular to the diaphragm 4. An insulating disk 23 is arranged at each end face.

[0041] Between the two components 20, 21 and their respective insulating discs 23, there is a contact electrode 9, designated here as E+, S+, and GND for their functions. Between the transmitter component 20 and the receiver component 21 is the ground contact electrode GND, which is electrically connected to the housing 3 (see Fig. 1). Since the housing 3 is connected to ground, the middle contact electrode GND is also electrically connected to ground. The two other contact electrodes E+ and S+ serve to apply the excitation signals to the transmitter component 20 and to tap the received signals from the receiver component 21, respectively. Preferably, ground is also the reference potential with which the electronic device 8 performs the fundamental frequency excitation.

[0042] Comparing the section in Fig. 2 with the structure in Fig. 1, it becomes clear that capacitive coupling occurs across the insulating discs 23 to the metallic components (intermediate component 6, membrane 4, pressure screw 5). This coupling is prevented by the electrical connection to the grounded housing 3.

[0043] Figures 3 and 4, described together below, show a disc-shaped piezoelectric element 7. An electrode 73, 74, made of silver or at least partially of silver (e.g., Cr-Ag), is applied to each end face 70, 71. These electrodes serve for electrical contact. The electrodes 73, 74 are preferably applied with a uniform but minimal thickness. Therefore, a sputtering process is preferably used. The outer sheath 72 allows each of the electrodes 73, 74 to be redirected to the opposite end face 71, 70. Thus, each end face 70, 71 has an area that is electrically separated from the electrode 73, 74 by a gap and belongs to the opposite electrode 74, 73. The polarization of the piezoelectric element 7 runs from one end face 70, 71 to the other.In the example shown, the piezo element 7 also has a recess 75, which is intended to simplify assembly.

[0044] The individual piezo elements 7 are directly connected to each other mechanically and electrically in a stack for the receiver component 21 and the transmitter component 20.

[0045] The double contacting necessitates that the number of essentially identical piezoelectric elements 7 in the respective stacks of the receiver component 21 and the transmitter component 20 is odd. In one embodiment, the transmitter component 20 has more piezoelectric elements 7 than the receiver component 21. For example, there are five piezoelectric elements 7 for the transmitter component 20 and three piezoelectric elements 7 for the receiver component 21.

[0046] Fig. 5 shows an embodiment of a contacting electrode 9.

[0047] The disc-shaped base 90 is located within the geometry of the transducer device 2, and the contact tab 91 protrudes from the stack of piezoelectric elements 2. Further electrical contact with the other components of the vibration sensor, and in particular with the electronic device 8, is made via the contact tab 91.

[0048] The base 90 is almost a full circle, but deviates from this in one crucial section. The outer contour 92 consists of a partial circle contour 93 and a curved recessed section 94, which results in the crescent shape of the base 90. The transition between the partial circle contour 93 and the recessed section 94 is rounded.

[0049] The contact flag 91 transitions into the base area 90 in the area of ​​the partial circle contour 93.

[0050] In the illustrated embodiment, the outer contour 92 has an inwardly projecting notch 95, which corresponds to the recess 75 in the piezoelectric elements 7 of the embodiment shown in Figs. 3 and 4. If the piezoelectric elements 7 are designed as closed discs and therefore without a recess 75, the notch 95 can also be omitted.

[0051] Fig. 6 also shows a contact electrode 9 with a crescent-shaped base 90. Here, too, a notch 95 is present, which in the illustrated embodiment is located diametrically opposite the deepest part of the recessed section 94. The contact lug 91 is strip-shaped and has two different widths. Adjacent to the base 90, there is a section with a smaller width and then a section with a larger width. The narrower section facilitates bending of the contact lug 91 during manufacturing, and the wider section enables good and reliable contact with other connection elements.

[0052] In the embodiments shown in Figs. 5 and 6, the contact flag 91 transitions into the base surface 90 in the area of ​​the partial circle contour 93. However, the two embodiments differ in the affected angular range.

[0053] Reference symbol

[0054] 1 mechanically oscillating unit

[0055] 2 Converter device

[0056] 3 cases

[0057] 4 membranes

[0058] 5 pressure screw

[0059] 6 hemispherical intermediate components

[0060] 7 Piezoelectric element

[0061] 8 Electronic device

[0062] 9 Contact electrode

[0063] 20 transmitter components

[0064] 21 Receiver component

[0065] 22 Longitudinal axis

[0066] 23 insulating disc

[0067] 70, 71 Front

[0068] 72 Outer jacket

[0069] 73, 74 electrode

[0070] 75 recess

[0071] 90 square meters of floor space

[0072] 91 Contact flag

[0073] 92 Outer contour

[0074] 93 Partial circle contour

[0075] 94 Return section

[0076] 95 notch

[0077] E+, S+, GND,

[0078] Contact electrode

Claims

Patent claims 1. Vibration sensor, comprising a mechanically oscillating unit (1), a transducer device (2), and a housing (3), wherein the transducer device (2) excites the mechanically oscillating unit (1) to mechanical vibrations and receives mechanical vibrations from the mechanically oscillating unit (1), wherein the transducer device (2) is arranged in the housing (3), wherein the transducer device (2) comprises at least one transmitter component (20) and one receiver component (21), wherein the transmitter component (20) excites the mechanically oscillating unit (1) to mechanical vibrations based on electrical excitation signals, wherein the receiver component (21) receives the mechanical vibrations from the mechanically oscillating unit (1) and converts them into electrical reception signals, wherein the transducer device (2) is bounded at its end face by two insulating disks (23).wherein one of the two insulating discs (23) is assigned to the transmitter component (20) and the receiver component (21), respectively, wherein the converter device (2) has three contact electrodes (9, E+, S+, GND), wherein of the three contact electrodes (9, E+, S+, GND) one contact electrode (S+) is arranged between the transmitter component (20) and the assigned insulating disc (23) and serves to transmit the excitation signals, wherein of the three contact electrodes (9, E+, S+, GND) one contact electrode (E+) is arranged between the receiver component (21) and the assigned insulating disc (23) and serves to transmit the received signals, and wherein of the three contact electrodes (9, E+, S+, GND) one contact electrode (GND) is arranged between the transmitter component (20) and the receiver component (21) and serves to provide an electrical connection to the housing (3).

2. Vibration sensor according to claim 1, wherein the housing (3) has a diaphragm (4), wherein the mechanically oscillating unit (1) is coupled to the diaphragm (4), wherein the transducer device (2) is arranged between the diaphragm (4) and a pressure screw (5), and wherein a hemispherical intermediate component (6) is located between the transducer device (2) and the membrane (4).

3. Vibration sensor according to claim 1 or 2, wherein the mechanically oscillating unit (1) is a vibrating fork.

4. Vibration sensor according to one of claims 1 to 3, wherein the transmitter component (20) and the receiver component (21) each have several piezoelectric elements (7) – preferably flat, disc-shaped or ring-shaped – which are mechanically connected and electrically contacted in pairs, particularly by diffusion processes, wherein the piezoelectric elements (7) of the transmitter component (20) and the receiver component (21) each have essentially the same geometric dimensions, wherein the piezoelectric elements (7) each have two end faces (70, 71) and an outer sheath (72), wherein an electrode (73, 74) is applied to each end face (70, 71), and wherein each electrode (73, 74) is guided from one end face (70, 71) of the two end faces (70, 71) via the outer sheath (72) to the respective other end face (71, 70) of the two end faces (70, 71).

5. Vibration sensor according to one of claims 1 to 4, wherein the three contact electrodes (9, E+, S+, GND) are substantially identical and each have a base surface (90) and a contact flag (91), wherein the contact flags (91) of the contact electrodes (9, E+, S+, GND) each protrude from the stacks of the piezoelectric elements (7) of the transmitter component (20) and the receiver component (21), wherein the base surfaces (90) each are substantially designed as a flat disk with a substantially crescent-shaped outer contour (92), and wherein the outer contour (92) consists substantially of a partial circle contour (93) and an inwardly projecting smooth receding section (94).

6. Vibration sensor according to claim 5, wherein the contact flag (91) transitions into the base surface (90) in the area of ​​the partial circle contour (93).

7. Vibration sensor according to claim 5 or 6, wherein the contact flag (91) is essentially designed as a rectangular strip, and wherein the contact flag (91) has a narrower width adjacent to the base surface (90) than in the following area.

Images