Field device with radar sensor and vibration limit level sensor and method for operating a field device

Abstract

The invention relates to a field device (10) with a radar sensor for measuring a filling level and with a vibration limit level sensor, wherein the radar sensor has a transmitting and receiving unit and an antenna (14), wherein the vibration limit switch has a drive unit (34) and a mechanical oscillator (24) connected thereto, wherein the antenna (14) serves at the same time as a mechanical oscillator (24). The invention also relates to a method for operating a field device (10).

Description

[0001] Field device with radar sensor and vibration limit level sensor and method for operating a field device

[0002] The invention relates to a field device with a radar sensor for measuring a fill level and with a vibration limit sensor according to claim 1. The invention also relates to a method for operating a field device according to claim 10.

[0003] In process automation technology, field devices are often used to record and / or influence process variables. Field devices can include, in particular, actuators, sensors, data collectors (data loggers), and measuring transducers. "Field" refers to the area outside of control rooms. Such field devices are often connected to higher-level units, such as control systems or control units. These higher-level units are used for process control, process visualization, and / or process monitoring.

[0004] State-of-the-art field devices typically comprise a housing, a sensor unit, and an electronic module with sensor electronics located within the housing. The measured process variables are typically evaluated, and the results can be used, for example, to generate a switching command and / or a proportional analog or digital output variable, or to display physical properties or process variables.

[0005] One example of a field device is a level measuring device that operates according to the radar principle. Level measuring devices for determining and / or monitoring a fill level in a container are known in various designs. Radar level measuring devices, for example level measuring devices that operate according to the time-of-flight principle, emit electromagnetic radiation pulses of a specific wavelength and then detect the temporal progression of the reflected electromagnetic radiation as an echo curve. This detects, among other things, reflections on the surface of the liquid to be measured or of the filling material in the container. The reflections combine to produce a signal that is measured as a function of time and is detected and displayed as a time-dependent echo curve, usually with several maxima. The fill level of the filling material in the container is then determined from the progression of this echo curve.

[0006] Another example of a field device is a vibrating point level sensor (also called a vibronic point level sensor). A vibrating point level sensor typically has a membrane that can be excited to vibrate via a drive, by means of which one or more mechanical oscillators arranged on the membrane can be excited to vibrate. Depending on the coverage level of the at least one mechanical oscillator with a filling material, as well as the viscosity of this filling material, the at least one mechanical oscillator oscillates at a characteristic frequency and amplitude, which can be detected by the vibrating point level sensor and converted into a measurement signal.

[0007] The underlying objective of the invention is to provide a field device that requires minimal installation effort, requires minimal space, and provides particularly reliable measurements. Furthermore, a method for operating a field device is to be provided that makes it as easy as possible to measure a fill level and a limit level.

[0008] The object is achieved according to the invention with the features of the independent claims. Further practical embodiments and advantages are described in conjunction with the dependent claims.

[0009] A field device according to the invention comprises a radar sensor for measuring a fill level and a vibration limit sensor for determining a limit level. The radar sensor is intended to continuously determine the change in a fill level, e.g. in a container, whereas the vibration limit sensor is intended to detect the reaching of a maximum limit level. The field device is a combined field device, with the two different sensor types being arranged in or on a housing. The radar sensor and the vibration limit sensor are integrated into a single field device. The field device has, in particular, only one housing and shared sensor electronics. The radar sensor has a transmitting and receiving unit and an antenna. In particular, the antenna is a horn antenna which is conical in shape. A radar chip serves, in particular, as the transmitting and receiving unit.In particular, the electromagnetic waves generated at the transmitting unit are transmitted via a waveguide to the antenna, where they are coupled. The antenna serves to focus the emitted radiation onto the medium to be measured and to bundle the radiation reflected by the medium.

[0010] The vibration level sensor comprises a drive unit and at least one mechanical oscillator connected to it. The at least one mechanical oscillator is excited to oscillate, in particular by a piezoelectric drive or by an inductive drive via a membrane. The mechanical oscillator can be a single-rod oscillator or a tuning fork, as explained in more detail below.

[0011] According to the invention, the antenna also serves as a mechanical oscillator. This means that radar radiation is coupled into the antenna and focused by it, and the antenna, in its function as a mechanical oscillator, is also excited to oscillate by the drive unit.

[0012] By integrating the antenna and mechanical oscillator into a single component, both sensors – point level and fill level – are integrated into a single field device and, above all, into a single mechanical system. Additional mechanical components are no longer required. Integration into a single field device and a single mechanical system also saves space, as only one through-hole is required for inserting the field device into a container, as opposed to two openings for each field device.

[0013] Furthermore, the reliability of the field device is increased because the detection of the limit level, i.e., a maximum or minimum permissible level, can be achieved using two principles. Particularly in the vicinity of the radar sensor, where the accuracy of the level measurement is lower, the vibrating limit level sensor serves as a second measurement method.

[0014] In a practical embodiment, the antenna is constructed in at least two parts and has a first antenna part and a second antenna part. The first antenna part forms a first mechanical oscillator and the second antenna part a second mechanical oscillator. The two-part antenna horn thus serves simultaneously to shape and focus the radar beams and as a tuning fork for detecting the limit level. The two-part design facilitates vibration excitation and, in addition, two counter-oscillating mechanical oscillators can better compensate for possible imbalances. If the antenna is constructed in at least two parts, a free space or slot is formed between the individual antenna parts. This is advantageous because it allows air to escape from the area of ​​the antenna when the medium to be measured reaches the antenna.

[0015] In a further practical embodiment, the first antenna part and the second antenna part extend over an arc section of an imaginary cone or an imaginary conical antenna. This means that the first antenna part and the second antenna part form part of an imaginary conical antenna horn. In particular, the first antenna part and the second antenna part each extend over an angular range of 20 to 180°, and preferably over an angular range greater than 40° and less than 180°. The focusing of the emitted radar radiation and the collection of the reflected radar radiation are maintained at a high level of quality.

[0016] In particular, the first antenna part and the second antenna part are designed as half-shells of a cone, and a slot is formed between each of the two half-shells. In particular, the slot width remains constant over the length of the slot. However, the slot can also have a varying slot width and, for example, be designed to taper in one direction.

[0017] Except for the slot, the two half-shells form a conical antenna horn. The separation by the slot decouples the first and second antenna sections, or the first and second mechanical oscillators, so that they can oscillate at a sufficient frequency and amplitude. The two half-shells form a nearly closed antenna, allowing the radar radiation to be focused particularly well.

[0018] In another practical embodiment, the first antenna part and the second antenna part are plate-shaped. The plates, in particular, have a trapezoidal base area, with the width of the base area increasing in the direction of the process. In this embodiment, the mechanical oscillators have a particularly large base area to ensure contact with as much medium as possible. This embodiment is particularly suitable for viscous media or for measuring a limit level in bulk materials.

[0019] In particular, the first antenna part and the second antenna part increase their distance from a housing toward the end of the process. The antenna parts moving away from each other continue to ensure good focusing of the radar radiation.

[0020] In particular, the first antenna part and the second antenna part are symmetrical with respect to a mirror plane extending in the axial direction. This avoids imbalances in two mechanical oscillators and ensures good centering of the radar radiation.

[0021] In another practical embodiment, the drive unit for causing the antenna or mechanical oscillator to vibrate is arranged off-center along a central axis through the field device. In particular, the field device is rotationally symmetrical, and the central axis extends centrally through the field device. As explained below, a waveguide is arranged centrally in the field device to couple the radar radiation centrally into the antenna.

[0022] In particular, the drive unit is ring-shaped. Ring-shaped here means that the drive unit is arranged surrounding an inner region. The drive unit can have a square or circular ring-shaped geometry. The drive unit can have a closed or open geometry and can only partially or completely surround the inner region. In particular, the drive unit is circular and extends over the base of the first mechanical oscillator and the second mechanical oscillator. In particular, the drive unit comprises a piezo element which expands and contracts radially or axially when a voltage is applied, thus causing a membrane and thereby the at least one mechanical oscillator to oscillate.The drive unit can also be designed so that it extends over only part of the mechanical oscillator and, in particular, is located only at the base of a mechanical oscillator. For example, a piezo element, an electromagnet, or another oscillating drive element can drive a mechanical oscillator. The movement of the piezo element, electromagnet, or other oscillating drive element can then be indirectly transmitted to the other mechanical oscillator. A suitable transmission mechanism, such as a rotatably mounted lever, can be provided for this purpose.

[0023] As already described above, the waveguide, which transmits radar radiation from the transmitting and receiving unit to the antenna, extends particularly along the central axis. The waveguide is arranged so that it is concentric with the antenna. In particular, the waveguide is also arranged within the annular drive unit. The waveguide is arranged particularly centrally with respect to the first antenna part and the second antenna part, so that radar radiation is coupled centrally between the two antenna parts.

[0024] The invention also relates to a method for operating a field device, in particular a field device as described above, wherein a field device is mounted on a container, wherein a fill level in the container is continuously detected by means of a radar sensor, and wherein a limit level is detected by means of a vibration limit sensor when a minimum or maximum fill level is reached. An antenna is set into vibration and simultaneously serves as a mechanical oscillator.

[0025] In particular, a first antenna part and a second antenna part are set into oscillation and at the same time radar radiation is transmitted by means of the antenna, or the first antenna part and the second antenna part.

[0026] Further practical embodiments and advantages are described below in conjunction with the figures. They show:

[0027] Fig. 1 shows a field device according to a first embodiment in a perspective view obliquely from above, Fig. 2 shows a field device according to a second embodiment in a perspective view obliquely from above,

[0028] Fig. 3 a field device according to a third embodiment in a perspective view obliquely from above

[0029] Fig. 4 shows a field device according to a fourth embodiment with a drive in a schematic representation in cross section and

[0030] Fig. 5 shows a field device according to a fifth embodiment with a drive in a schematic cross-sectional view.

[0031] Fig. 1 shows a field device 10 according to a first embodiment. The field device 10 has a housing 12 in which sensor electronics are arranged (not visible). At its end facing the process, the field device 10 has a conical antenna 14 (antenna horn) with a first antenna part 16 and a second antenna part 18. The first antenna part 16 is simultaneously a first mechanical oscillator 20, and the second antenna part 16 is simultaneously a second mechanical oscillator 22.

[0032] In this respect, the field device 10 comprises both a radar sensor for measuring a fill level, wherein the first antenna part 16 and the second antenna part 18 serve as part of an antenna horn 14. The field device 10 further comprises a vibration limit level sensor, wherein the first mechanical oscillator 20 and the second mechanical oscillator 22 serve as two parts of a mechanical oscillator (tuning fork) 24 to detect a limit level.

[0033] Two measuring principles can be realized via a common mechanism 14, 24.

[0034] According to the first embodiment of the field device 10, the first antenna part 16 and the second antenna part 18 are designed as half-shells, each separated from the other by a slot 26. The two half-shells 16, 18 are each shaped as part of a cone. The slots 26 have a constant slot width w over their length. Fig. 1 also shows that a matching cone 28 is arranged in a section adjacent to the housing between the first antenna part 16 and the second antenna part 18.

[0035] In conjunction with Fig. 2 to Fig. 5, further embodiments are shown below, wherein the same reference numerals are used for identical or at least functionally equivalent elements as for the description of the first embodiment.

[0036] Fig. 2 shows a field device 10 according to a second embodiment. The field device 10 differs from the first embodiment essentially in the design of the first antenna part 16 and the second antenna part 18. The first antenna part 16 and the second antenna part 18 extend here over an arc section on an imaginary cone. The mechanical oscillators 20, 22 are curved. The angular range of the respective arc sections is approximately 60°. The distance between the first antenna part 16 and the second antenna part 18 increases starting from the housing 12, so that the mechanical oscillators 20, 22 are spread apart from each other.

[0037] Fig. 3 shows a third embodiment of a field device 10. The field device 10 differs from the first and second embodiments in the design of the antenna parts 16, 18, the mechanical oscillators 20, 22, and the housing 12.

[0038] The housing 12 has a rectangular cross-section here. However, it is also conceivable to have a circular design for the housing 12 with the antenna parts 16, 18 shown.

[0039] The first antenna part 16 or the first mechanical oscillator 20 and the second antenna part 18 or the second mechanical oscillator 22 are plate-shaped and have a trapezoidal base. The width of the first antenna part 16 and the second antenna part 18 increases from the housing 12 toward the process. The mechanical oscillators 20, 22 are accordingly flat and not curved. The distance between the first antenna part 16 and the second antenna part 18 increases from the housing 12.

[0040] In Figs. 4 and 5 two further embodiments are described, which differ in the type of drive for the mechanical oscillator 24.

[0041] Fig. 4 shows a fourth embodiment of the field device 10. The field device 10 has a housing 12 and a first antenna part 14 and a second antenna part 16 arranged thereon. Sensor electronics 30 are arranged in the housing 12, which also includes the transmitting and receiving element (not explicitly shown) for the radar sensor. Starting from the sensor electronics 30, a waveguide 32 extends along a central axis M through the field device 10. The waveguide 32 extends concentrically to the antenna 14 formed by the first antenna part 16 and the second antenna part 18. For coupling the radar radiation into the antenna 14, a matching cone 28 is arranged at the end of the housing 12 facing the process.

[0042] An annular piezoelectric element 36 is arranged in the housing 12 as the drive unit 34 for the first mechanical oscillator 20 and the second mechanical oscillator 22. The piezoelectric element 36 is connected to the sensor electronics 30 via an electrical connection 40.

[0043] Basically, two different variants of piezo elements 36 are conceivable. These can oscillate in the axial direction as indicated by arrow 38 or in the radial direction as indicated by arrow 40. The piezo element 36 extends in a ring around the central axis M and the waveguide 32. The drive unit 34 causes the mechanical oscillators 20, 22 to oscillate via a membrane 42.

[0044] Fig. 5 shows a fifth embodiment of a field device 10, wherein this embodiment shows a drive unit 34 that is modified compared to Fig. 4. The drive unit 34 is asymmetrical and includes a drive element in the form of a piezoelectric element 36 for only one mechanical oscillator 20, which can expand in the axial or radial direction (see arrow 38 or arrow 40). The movement of the piezoelectric element 36 is transmitted indirectly to the second mechanical oscillator 22. Here, via a bending beam 44 with a pivot bearing 46.

[0045] List of reference symbols

[0046] 10 field device

[0047] 12 housings

[0048] 14 Antenna

[0049] 16 first antenna part

[0050] 18 second antenna part

[0051] 20 first mechanical oscillator

[0052] 22 second mechanical oscillator

[0053] 24 mechanical oscillator (tuning fork)

[0054] 26 slot

[0055] 28 adjustment cones

[0056] 30 Sensor electronics

[0057] 32 waveguides

[0058] 34 Drive unit

[0059] 36 Piezo element

[0060] 38 Arrow (axial direction)

[0061] 40 Arrow (radial direction)

[0062] 42 membrane

[0063] 44 bending beams

[0064] 46 pivot bearings

Claims

Patent claims 1. Field device with a radar sensor for measuring a fill level and a vibration limit sensor, wherein the radar sensor has a transmitting and receiving unit and an antenna (14), wherein the vibration limit switch has a drive unit (34) and a mechanical oscillator (24) connected thereto, wherein the antenna (14) simultaneously serves as a mechanical oscillator (24).

2. Field device according to the preceding claim, characterized in that the antenna (14) is formed in at least two parts and has a first antenna part (16) and a second antenna part (18), and wherein the first antenna part (16) is a first mechanical oscillator (20) and the second antenna part (18) is a second mechanical oscillator (22).

3. Field device according to the preceding claim, characterized in that the first antenna part (16) and the second antenna part (18) each extend over an arc section of an imaginary conical antenna.

4. Field device according to one of the two preceding claims, characterized in that the first antenna part (16) and the second antenna part (18) are designed as half-shells of a cone and a slot (26) is formed between each of the half-shells.

5. Field device according to one of the three preceding claims, characterized in that the first antenna part (16) and the second antenna part (18) are plate-shaped.

6. Field device according to one of the four preceding claims, characterized in that the first antenna part (16) and the second antenna part (18) increase their distance from a housing (20) in the direction of a process end.

7. Field device according to one of the preceding claims, characterized in that the drive unit (34) for displacing the at least one mechanical oscillator (24, 20, 22) is arranged off-center of a central axis (M) through the field device (10).

8. Field device according to one of the preceding claims, characterized in that the drive unit (43) is annular.

9. Field device according to one of the preceding claims, characterized in that a waveguide (32) for transmitting radar radiation extends along the central axis (M).

10. Experience for operating a field device (10), wherein the field device (10) has a radar sensor and a fill level sensor, wherein by means of one field device a fill level is continuously detected by means of the radar sensor and a limit level is detected by means of the vibration limit level sensor, wherein an antenna (14) is set into vibration and simultaneously serves as a mechanical oscillator (24).

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