Device for determining and / or monitoring at least one process variable of a medium
Patent Information
- Application Number
- EP2023814379
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-12-16
- Filing Date
- 2023-11-28
- Publication Date
- 2025-10-22
AI Technical Summary
Existing vibronic sensors in process and automation technology face challenges in easily inserting and securely connecting the drive/receiver unit to the mechanically oscillatable unit, leading to complex and costly manufacturing processes, and thermomechanical stresses due to differing thermal expansion coefficients.
A device featuring a mechanically oscillatable unit with a first cylindrical bore to accommodate a tubular piezoelectric element, reducing manufacturing complexity and thermomechanical stresses, and optionally incorporating a temperature sensor within the piezoelectric element for improved measurement accuracy.
Simplifies the manufacturing process, reduces costs, and enhances measurement accuracy by minimizing thermomechanical stresses and allowing for space-efficient integration of temperature sensors.
Smart Images
Figure 1.1
Abstract
Description
[0001] Device for determining and / or monitoring at least one process variable of a medium
[0002] The invention relates to a device for determining and / or monitoring at least one process variable of a medium.
[0003] Vibronic sensors are widely used in process and / or automation technology. In the case of level measuring devices, they comprise at least one mechanically oscillating unit, such as a tuning fork, a single-rod sensor, or a diaphragm. During operation, this unit is excited to mechanical vibrations by a drive / receiver unit, often in the form of an electromechanical transducer unit, which in turn can be, for example, a piezoelectric drive or an electromagnetic drive. The applicant manufactures a wide variety of corresponding field devices and markets them, for example, under the names LIQUIPHANT or SOLIPHANT. The underlying measurement principles are known from numerous publications. The drive / receiver unit excites the mechanically oscillating unit to mechanical vibrations using an electrical excitation signal.Conversely, the drive / receiver unit can receive the mechanical vibrations of the mechanically oscillating unit and convert them into an electrical reception signal. Accordingly, the drive / receiver unit is either a separate drive unit and a separate receiver unit, or a combined drive / receiver unit.
[0004] In many cases, the drive / receiver unit is part of a feedback electrical oscillating circuit, which is used to excite the mechanically oscillating unit to mechanical oscillations. For example, for a resonant oscillation, the oscillating circuit condition must be met, according to which the gain factor is >1 and all phases occurring in the oscillating circuit are a multiple of 360°. To excite and fulfill the oscillating circuit condition, a certain phase shift must be ensured between the excitation signal and the received signal. Therefore, a predeterminable value for the phase shift, i.e., a target value for the phase shift between the excitation signal and the received signal, is often set.For this purpose, a wide variety of solutions, both analogue and digital methods, have become known from the state of the art, as described, for example, in the documents DE102006034105A1, DE 102007013557A1, DE 102005015547A1, DE102009026685A1, DE102009028022A1, DE102010030982A1 or DE00102010030982A1.
[0005] Both the excitation signal and the received signal are characterized by their frequency w, amplitude A and / or phase <t>Accordingly, changes in these variables are usually used to determine the respective process variable. The process variable can be, for example, a fill level, a specified fill level, or the density or viscosity of the medium, as well as the flow rate. In a vibronic point level switch for liquids, for example, a distinction is made between whether the oscillating unit is covered by the liquid or is freely oscillating. These two states, the free state and the covered state, are differentiated, for example, based on different resonance frequencies, i.e., based on a frequency shift.
[0006] The drive / receiver unit is typically designed as a piezoelectric element in the form of a rectangular disk and is inserted into a pocket-like cavity of the oscillating unit. The cavity is then filled with a potting material so that the drive / receiver unit is force-fitted to a wall of the cavity. The potting material is preferably selected so that a very good force coupling is achieved between the drive / receiver unit and the oscillating unit after potting. Such a drive / receiver unit is described, for example, in DE102012100728A1. To create the cavity, the area of the oscillating unit intended for the cavity is usually eroded using a spark erosion removal process. However, such removal processes are complex and cost-intensive.It is therefore an object of the present invention to provide a device in which the drive-receiving unit can be easily introduced into the oscillatable unit.
[0007] According to the invention, the object is achieved by a device for determining and / or monitoring at least one process variable of a medium, comprising an electronics unit and a sensor unit with a mechanically oscillatable unit and at least one first tubular piezoelectric element, wherein the device is designed to excite the mechanically oscillatable unit by means of a first excitation signal to mechanical oscillations in a first oscillation mode and to receive the mechanical oscillations of the mechanically oscillatable unit in the first oscillation mode and to convert them into an electrical received signal, wherein the electronics unit is set up to determine the at least one process variable from the received signal, and wherein the mechanically oscillatable unit has at least one first cylindrical bore in an end region, into which the at least first piezoelectric element is at least partially introduced.
[0008] In the device according to the invention, at least the first piezoelectric element is inserted into the first cylindrical bore. Such bores are considerably easier to manufacture than pocket-shaped cavities used to accommodate piezoelectric elements, as known from the prior art described above. Instead of complex erosive manufacturing processes, simpler and more cost-effective machining processes, such as drilling, can be used.
[0009] In addition, the use of the at least first tubular piezoelectric element reduces thermomechanical stresses in the region of the at least first tubular piezoelectric element. As a rule, the thermal expansion coefficients of the mechanically oscillating unit, the at least first piezoelectric element, and any potting material used to connect the at least first piezoelectric element to the at least first cylindrical bore differ from one another, so that stresses arise in the region of the at least first piezoelectric element under the influence of temperature. Due to the tubular design of the at least first piezoelectric element, it expands, particularly in the direction of its longitudinal axis.Conventional disc- or plate-shaped piezoelectric elements expand both radially and axially, resulting in greater thermomechanical stresses than tubular piezoelectric elements. The at least first piezoelectric element is designed in the form of a tube or a tube section.
[0010] The mechanically oscillating unit is, for example, a membrane, a single rod, an arrangement of at least two oscillating elements, or a tuning fork. The at least first piezoelectric element can serve, on the one hand, as a drive / receiver unit for generating the mechanical oscillations of the mechanically oscillating unit, which are generated by the excitation signal. In the case where the oscillating unit is covered by a medium, the mechanical oscillations are in turn influenced by the properties of the medium, so that a statement about the at least one process variable can be generated based on the received signal, which represents the oscillations of the oscillating unit.
[0011] In one embodiment, the sensor unit has at least a second tubular piezoelectric element, wherein the mechanically oscillatable unit is a tuning fork with a first oscillating element and a second oscillating element, wherein the at least first piezoelectric element is at least partially inserted into a first cylindrical bore of the first oscillating element and the at least second piezoelectric element is at least partially inserted into a second cylindrical bore of the second oscillating element. In a further embodiment, the device comprises a temperature sensor. The temperature influences the mechanical properties of the sensor unit and a wide variety of process variables of the medium. By additionally determining and / or monitoring the temperature, the measuring accuracy of the device can be significantly improved and the functionality of the device expanded.In particular, the temperature sensor is a thermocouple or a resistance element.
[0012] In a further development, the temperature sensor is inserted into at least the first cylindrical bore. By inserting the temperature sensor into at least the first cylindrical bore together with at least the first piezoelectric element, space is saved and the process temperature is optimally evaluated.
[0013] In a further embodiment, the temperature sensor is arranged in a cavity enclosed by the at least first piezoelectric element. The temperature sensor is thus located inside the tube of the at least first piezoelectric element and is thus arranged in a particularly space-saving manner.
[0014] An alternative embodiment provides that the temperature sensor is arranged in an end region of the at least first piezoelectric element. Preferably, the temperature sensor is arranged in an end region of the at least first piezoelectric element facing away from the mechanically oscillatable unit.
[0015] In a further development, the at least first piezoelectric element is electrically connected to the end region of the mechanically oscillatable unit by means of a conductive adhesive or a soldering point.
[0016] In a further embodiment, an outer wall of the at least first piezoelectric element is configured as a first conductive electrode, at least in a first section, and an inner wall of the at least first piezoelectric element is configured as a second conductive electrode, at least in a second section. The first and second conductive electrodes are thus partially or completely formed by the outer wall and the inner wall.
[0017] In a further development, the at least first piezoelectric element has a peripheral contact configured such that the first conductive electrode can be electrically contacted by means of a third section of the inner wall, or that the second conductive electrode can be electrically contacted by means of a fourth section of the outer wall. The peripheral contact ensures that both the first conductive electrode and the second conductive electrode can be contacted either on the inner wall or the outer wall. If the first conductive electrode is formed by the outer wall, at least in the first section, the first section can be drawn toward the inner wall such that it forms a third section in the region of the inner wall.Alternatively, the second portion may be drawn toward the outer wall in such a way that it forms a fourth portion of the outer wall when the second conductive electrode is formed at least by the second portion of the inner wall.
[0018] In a further embodiment, the at least first piezoelectric element is electrically connected to an electrical connection element via the outer wall and / or the inner wall. In particular, the electrical connection element is a cable or a circuit board. Any temperature sensor present can also be arranged on the circuit board.
[0019] Preferably, the mechanically oscillatable unit is connected to a housing by means of its end region.
[0020] Advantageously, the at least first piezoelectric element at least partially contacts a wall of the at least first cylindrical bore. The invention will be explained in more detail below with reference to the following figures, Figs. 1-7. They show:
[0021] Fig. 1 : a schematic representation of a device according to the invention, which is attached to a container.
[0022] Fig. 2: a schematic representation of a first embodiment of the sensor unit.
[0023] Fig. 3: a schematic representation of a second embodiment of the sensor unit.
[0024] Fig. 4a: a cross-sectional view of a third embodiment of the sensor unit.
[0025] Fig. 4b: a schematic representation of the third embodiment of the sensor unit.
[0026] Fig. 5: a detailed view of the at least first piezoelectric element.
[0027] Fig. 6: a first embodiment of the contact.
[0028] Fig. 7: a second embodiment of the contact.
[0029] Fig. 1 shows an exemplary device 1 according to the invention with an electronics unit 3 and a sensor unit 4. The device 1 is attached to a container 30, such as a pipe or a tank. A medium 2 is introduced into the container 30. The sensor unit 4 comprises a mechanically oscillatable unit 5 and at least one first piezoelectric element e (here concealed by the housing 28 of the device 1). The device 1, in particular the electronics unit 3, is designed to excite the mechanically oscillatable unit 5 to mechanical oscillations in a first oscillation mode by means of a first excitation signal and to receive the mechanical oscillations of the mechanically oscillatable unit 5 in the first oscillation mode and to convert them into an electrical received signal. The electronics unit 3 is further designed to determine the at least one process variable of the medium 2 from the received signal.The process variable of medium 2 is, for example, a fill level, a density or a viscosity.
[0030] Fig. 2 shows a first embodiment of the sensor unit. The mechanically oscillatable unit 5 has at least one first cylindrical bore 8 in an end region 7, into which the at least first piezoelectric element 6 is at least partially inserted. For example, the at least first piezoelectric element 6 is electrically connected to the end region 7 of the mechanically oscillatable unit 5 by means of a conductive adhesive or a solder joint. Piezoelectric elements typically have a thermal expansion coefficient of approximately 6 10' 6 K' 1 The mechanically vibrating unit can be made of stainless steel with a thermal expansion coefficient of (16-18)- 10 -6 K -1 A conventional adhesive as a potting material typically has a thermal expansion coefficient of (40-60)- 10' 6 K' 1 Due to the different thermal expansion coefficients, thermomechanical stresses arise. The tubular design of the at least first piezoelectric element 6 reduces these stresses compared to a disk- or plate-shaped design of the at least first piezoelectric element, since large areas that expand are present only in the axial direction, but not in the radial direction.
[0031] The mechanically oscillatable unit 5 is optionally connected to a housing 28 in its end region 7. The device 1 can optionally comprise a temperature sensor 14. The temperature sensor 14 can be introduced into the at least one first cylindrical bore 8 and arranged, for example, in an end region 16 of the at least first piezoelectric element 6, as shown in Fig. 2. The temperature sensor 14 is preferably arranged in an end region 16 of the at least first piezoelectric element 6 facing away from the mechanically oscillatable unit 5, as shown in Fig. 3. Fig. 3 shows a second embodiment of the sensor unit 4. In this example, the sensor unit 4 comprises a tuning fork 10 with a first oscillating element 11 and a second oscillating element 12. The first oscillating element 11 has the first cylindrical bore 8, into which the at least first piezoelectric element 6 is introduced.The second oscillating element 12 has a second cylindrical bore 13 into which at least a second piezoelectric element 9 is inserted. The at least first piezoelectric element 6 and the at least second piezoelectric element 9 are preferably arranged such that they each at least partially touch a wall 29 of the respective cylindrical bore 8, 13. In Fig. 3, a temperature sensor 14 is provided only in the first oscillating element 11. However, a second, redundant temperature sensor can also be provided, in particular in the second cylindrical bore 13.
[0032] Alternatively, the temperature sensor 14 can also be arranged in a cavity 15 enclosed by the at least first piezoelectric element 6, as shown in Fig. 4a-b. For this alternative, the temperature sensor 14 must be dimensioned such that it is smaller in at least two dimensions than an inner radius of the at least first piezoelectric element 6.
[0033] Fig. 5 shows a detailed view of an exemplary first piezoelectric element 6. The at least first piezoelectric element 6 has an outer wall 17 and an inner wall 20. At least a first section 18 of the outer wall 17 is designed as a first conductive electrode 19. At least a second section 21 of the inner wall 20 is designed as a second conductive electrode 22. In the selected example, the inner wall 20 is designed entirely as a second conductive electrode 22, and the outer wall 17 is designed entirely as a first conductive electrode 19.
[0034] For easy electrical contacting, the at least first piezoelectric element 6 can have a peripheral contact 23, as shown in Figures 6 and 7. The peripheral contact is designed, for example, such that the second conductive electrode 22 can be electrically contacted by means of a fourth section 25 of the outer wall 17 (see Figure 6). The electrical contacting of the first conductive electrode 19 and the second conductive electrode 20 can be achieved from the outer wall 17 by means of an electrical connection element 26 (not shown).
[0035] Alternatively, the peripheral contact 23 can be configured such that the first conductive electrode 19 can be electrically contacted by means of a third section 24 of the inner wall 20, as shown in Fig. 7. In this case, the first conductive electrode 19 and the second conductive electrode 20 can be easily electrically connected to an electrical connection element 26, for example, a cable or a circuit board. If a circuit board is used as the electrical connection element 26, the temperature sensor 14 can also be arranged on it.
[0036] List of reference symbols
[0037] 1 device
[0038] 2 Medium
[0039] 3 Electronic unit
[0040] 4 Sensor unit
[0041] 5 mechanically oscillating unit
[0042] 6 first piezoelectric element
[0043] 7 End area of the mechanically oscillating unit
[0044] 8 first cylindrical bore
[0045] 9 second piezoelectric element
[0046] 10 Tuning fork
[0047] 11 first oscillating element
[0048] 12 second oscillating element
[0049] 13 second cylindrical bore
[0050] 14 Temperature sensor
[0051] 15 cavity
[0052] 16 End region of the first piezoelectric element
[0053] 17 Outer wall of the first piezoelectric element
[0054] 18 first section
[0055] 19 first conductive electrode
[0056] 20 Inner wall of the first piezoelectric element
[0057] 21 second section
[0058] 22 second conductive electrode
[0059] 23 To contact
[0060] 24 third section
[0061] 25 fourth section
[0062] 26 electrical connection element
[0063] 28 housings
[0064] 29 Wall of the first cylindrical bore
[0065] 30 containers< / t>
Claims
Patent claims Device (1) for determining and / or monitoring at least one process variable of a medium (2) comprising an electronics unit (3) and a sensor unit (4) with a mechanically oscillatable unit (5) and at least one first tubular piezoelectric element (6), wherein the device (1) is designed to excite the mechanically oscillatable unit (5) by means of a first excitation signal to mechanical oscillations in a first oscillation mode and to receive the mechanical oscillations of the mechanically oscillatable unit (5) in the first oscillation mode and to convert them into an electrical received signal, wherein the electronics unit (3) is set up to determine the at least one process variable from the received signal, and wherein the mechanically oscillatable unit (5) has at least one first cylindrical bore (8) in an end region (7),into which the at least first piezoelectric element (6) is at least partially inserted. Device (1) according to claim 1, wherein the sensor unit (4) comprises at least a second tubular piezoelectric element (9), wherein the mechanically oscillatable unit (5) is a tuning fork (10) with a first oscillating element (11) and a second oscillating element (12), wherein the at least first piezoelectric element (6) is at least partially inserted into a first cylindrical bore (8) of the first oscillating element (11) and the at least second piezoelectric element (9) is at least partially inserted into a second cylindrical bore (13) of the second oscillating element (12). Device (1) according to one of claims 1-2, wherein the device (1) comprises a temperature sensor (14).
4. Device (1) according to claim 3, wherein the temperature sensor (14) is inserted into the at least first cylindrical bore (8).
5. Device (1) according to one of claims 3-4, wherein the temperature sensor (14) is arranged in a cavity (15) enclosed by the at least first piezoelectric element (6).
6. Device (1) according to one of claims 3-4, wherein the temperature sensor (14) is arranged in an end region (16) of the at least first piezoelectric element (6).
7. Device (1) according to one of claims 3-6, wherein the temperature sensor (14) is a thermocouple or a resistance element.
8. Device (1) according to one of claims 1-7, wherein the at least first piezoelectric element (6) is electrically connected to the end region (7) of the mechanically oscillatable unit (5) by means of a conductive adhesive or a soldering point.
9. Device (1) according to one of claims 1-8, wherein an outer wall (17) of the at least first piezoelectric element (6) is designed as a first conductive electrode (19) at least in a first section (18) and an inner wall (20) of the at least first piezoelectric element (6) is designed as a second conductive electrode (22) at least in a second section (21).
10. Device (1) according to claim 9, wherein the at least first piezoelectric element (6) has a contact (23) which is designed such that the first conductive electrode (19) can be electrically contacted by means of a third section (24) of the inner wall (20) or that the second conductive electrode (22) can be electrically contacted by means of a fourth section (25) of the outer wall (17). Device (1) according to one of claims 9-10, wherein the at least first piezoelectric element (6) is electrically connected to an electrical connection element (26) by means of the outer wall (17) and / or the inner wall (20). Device (1) according to claim 11, wherein the electrical connection element (26) is a cable or a printed circuit board. Device (1) according to one of claims 1-12, wherein the mechanically oscillatable unit (5) is connected to a housing (28) by means of the end region (7). Device (1) according to one of claims 1-13, wherein the at least first piezoelectric element (6) at least partially contacts a wall (29) of the first cylindrical bore (8).