Patent Application
20250155271
The invention relates to a fill level measuring device, or meter, which can be used at small, lateral openings of the containers.
In automation technology, especially for process automation, field devices are often applied, which serve for registering diverse measured variables. The measured variable to be determined can be, for example, a fill level, a flow, a pressure, the temperature, the pH value, the redox potential, a conductivity or the dielectric value of a medium in a process plant. For registering the corresponding measured values, the field devices comprise suitable sensors based on suitable measuring principles. A large number of different field device types are manufactured and sold by the Endress+Hauser group of companies.
For fill level measurement of fill substances in containers, radar based measuring methods have proven themselves, since they are robust and are distinguished by low-maintenance. A central advantage of radar based measuring methods is their ability to measure fill level virtually continuously. In the context of the invention, the terminology “radar” refers to radar signals with frequencies between 0.03 GHz and 300 GHz. Usual frequency bands, at which fill level measurement is performed, lie at 2 GHZ, 26 GHZ, 79 GHz, and 120 GHz. Two established measuring principles, in such case, are the pulse travel time principle (also known as “pulse radar”) and the FMCW principle (“Frequency Modulated Continuous Wave”). A fill level measuring device working according to the pulse travel time method is described, for example, in disclosure document DE 10 2012 104 858 A1. A typical construction of FMCW based fill level measuring devices is presented, by way of example, in disclosure document DE 10 2013 108 490 A1. The FMCW and pulse radar measuring principles are described in greater detail in “Radar Level Detection, Peter Devine, 2000”.
Since radar based, fill level measuring devices determine fill level indirectly, in that they measure from above the fill substance surface, fill level measuring devices according to the state of the art are so designed that they are mounted on the top of the container. For this, the containers need a corresponding connection means, such as a flange connection, on top. Often, such connections need to be supplied by retrofitting, while, in contrast, lateral connections are often present per se on containers, for example, as unused inlets or outlets, or as connections for pressure- or temperature measurement. A lateral installation on a container wall can bring the danger that the container wall is struck by the main radiation lobe of the transmitted radar signal, whereby disturbance reflections can arise, which lead to an incorrect fill level measurement.
DE10 2020 106 020 A1 describes a radar based, fill level measuring device, which is mounted laterally on the container, wherein its antenna arrangement extends from there inwardly into the container in the form of a hollow tube. In such case, the antenna arrangement is designed to transmit the radar signal vertically downwards with an asymmetric bundling. In this way, the possibility of a reflection on the container wall is lessened. In the case of the fill level measuring device shown there, the asymmetric bundling is implemented via a corresponding aperture. In such case, the cross section of the hollow tube, in whose end region the asymmetric aperture is arranged, needs to have a sufficiently large cross section of especially greater than DN50. For, in order for the transmitted radar signal to have a sufficient bundling, thus a sufficient asymmetry, the aperture needs to be dimensioned correspondingly large.
Depending on process plant, however, lateral openings of containers are often only available with small diameter of significantly less than DN50.
An object of the invention, therefore, is to provide a fill level measuring device, by means of which the fill level can be determined via a small, lateral opening of the container.
The invention achieves this object by a radar based, fill level measuring device for measuring a fill level of a fill substance in a container, comprising:
According to the invention, the fill level measuring device is distinguished by features that both the radar-bundling means as well as also the primary radiator have, in each case, an asymmetric aperture, which is larger in parallel with the tube axis than orthogonal to the tube axis. Optimally in this connection, the ratio of the asymmetry is set, for example at 3:1, equally for the aperture of the primary radiator and the aperture the radar-bundling means. In this way, there results, in total, that the radar signal is transmitted with a main radiation lobe flattened toward the container wall. This acts, thus, advantageously, in that the antenna arrangement does not need to extend far into the container and the radar signal, in spite of this, is not undesirably reflected on the container-wall. Because the radar-bundling means and the primary radiator are symmetrically designed, the antenna arrangement is so compactly designable that it works also in the case of container openings with diameter smaller than DN50. Nevertheless, in total, an aperture is implementable, which is sufficiently large and asymmetrical. In this connection, sufficient asymmetry is present, when the aperture of the radar-bundling means, and of the primary radiator is larger in parallel with tube axis than orthogonally to the tube axis at least by a factor of 1.5, especially a factor 3. For maximizing the transmitting power, it is additionally advantageous that the radar-bundling means and the primary radiator are adapted to one another in such a manner that the primary radiator illuminates the outer contour of the radar-bundling means with the radar signal with −10 dB with respect to the main radiation axis of the directional characteristic.
Also the choice of the frequency band, in which the radar signal is produced, influences the minimum size of the antenna arrangement, since the radar signal at given aperture is better bundled, or focused, with rising frequency. Accordingly, the transmitting/receiving unit is advantageously designed to produce the radar signal with a frequency of at least 60 GHz, especially at least 120 GHZ.
The radar-bundling means can, for example, be designed lens shaped and be made of a radar-focusing plastic, such as PE, PEEK or PTFE. According to the invention, the design of the radar-bundling means, as well as also the design of the primary radiator, are, however, not fixedly predetermined, as long as an appropriately asymmetric bundling results. The primary radiator can, accordingly, be designed, for example, as patch antenna, or antenna array, as electrically conductive coupling-pin, or as slit-hollow conductor antenna. In such case, the primary radiator can be an integral component of the transmitting/receiving unit, such that both are arranged in the antenna arrangement in the focal point of the radar-bundling means. In this way, conduction losses between the transmitting/receiving unit and the primary radiator are minimized. However, the implementing of explosion protection requirements is made difficult in the case of this design, because the transmitting/receiving unit as active, i.e. electrical current containing, component is located in the antenna arrangement and, thus, in the container interior. In order to avoid this, the transmitting/receiving unit can be arranged in a special housing of the fill level measuring device, which in the secured state is located outside of the container. In such case, the primary radiator for transmitting the radar signal is connected with the transmitting/receiving unit, for example, via a waveguide, especially a hollow conductor, a dielectric waveguide, a microstrip conductor or a coaxial cable.
In connection with the transmitting/receiving unit, the terminology “unit” in the context of the invention means, in principle, any electronic circuit, which is suitably designed for the contemplated application. It can, thus, depending on requirement, refer to an analog circuit for producing, or processing, corresponding analog signals. It can also be a digital circuit, such as an FPGA or a storage medium in cooperation with a program. In such case, the program is designed to perform the corresponding method steps, thus to apply the required computer operations of the particular unit. In this context, various electronic units of the dielectric value measuring device can, within the scope of the invention, potentially also use a shared physical memory, or be operated by means of the same physical, digital circuit.
The invention will now be explained in greater detail based on the appended drawing. The figures of the drawing show as follows:
For understanding the invention,
As a rule, the fill level measuring device 1 is connected via a bus system, such as, for instance, “Ethernet”, “PROFIBUS”, “HART” or “wireless HART”, with a superordinated unit 4, for example, a process control system or a decentral database. In this way, on the one hand, information concerning the operating state of the fill level measuring device 1 can be communicated. However, also information concerning the fill level L can be transmitted via the bus system, in order, in given cases, to control in- or outgoing flows of the container 3.
In order to be able reliably to ascertain the fill level L, the fill level measuring device 1 needs in the case of lateral arrangement to be arranged at a container opening 31, which is located above the maximum fill level L of the fill substance 2. In such case, the installed height h above the floor of the container 3 is known and furnished in the fill level measuring device 1. Additionally, the fill level measuring device 1 is secured and oriented in such a manner pressure- and media-tightly at the container opening 31 that only the tubular antenna arrangement 12 of the fill level measuring device 1 extends horizontally into the container 3, while the additional components of the fill level measuring device 1 are arranged outside of the container 3. For installation of the fill level measuring device 1, the tube-shape of the antenna arrangement 12 does need, moreover, to be sufficiently compactly designed that during mounting of the fill level measuring device 1 it can be led through the container opening 31. In such case, depending on process application, there can be available laterally only a very small container opening, for example, having a diameter of DN20. After lead through of the antenna arrangement 12, the fill level measuring device 1 can be secured to the lateral opening of the container 31 by means of a suitable securement means, such as a flange connection.
The antenna arrangement 12 is so designed that via its end region 121 protruding out into the container, radar signals SHF within a predefined frequency band are transmitted in the direction of the surface of the fill substance 2. After reflection on the fill substance surface, the fill level measuring device 1 receives the reflected received signals, in turn, via this end region 121. In such case, the signal travel time t between transmitting and receiving the radar signal SHF is, according to
proportional to the distance d between the fill level measuring device 1 and the fill substance 2, wherein c corresponds to the radar-propagation velocity of the appropriate speed of light. The signal travel time t can be determined by the fill level measuring device 1, for example, by means of the FMCW method or by means of the pulse travel time method. In this way, the fill level measuring device 1 can associate the measured travel time t with distance d, for example, based on a corresponding calibration. In this way, the fill level measuring device 1 can, in turn, determine the fill level L according to
when the installed height h is furnished in the fill level measuring device 1. For producing the transmitted radar signal SHF and for determining the signal travel time t and the corresponding fill level value L based on the incoming, received signal, the fill level measuring device 1 includes a correspondingly designed transmitting/receiving unit 11, in which, for example, the FMCW—or the pulse travel time, measuring principle is implemented. In the case of the embodiment shown in
The frequency, and frequency band, at which the signal production unit 11 of the fill level measuring device 1 produces the radar signal SHF, is decisively selected as a function of the character of the fill substance 2: For a highly accurate fill level measurement, inherently an as high as possible frequency band is advantageous, since higher frequency bands permit greater bandwidth. In reference to the invention, a high frequency band of 60 Ghz or higher is, moreover, advantageous, since for a given aperture ap, ao, the corresponding radar-bundling means 122 can be compactly dimensioned.
Starting from the antenna arrangement 12, which protrudes orthogonally inwardly from the container wall 31 and, thus, is horizontally oriented, the axis of the main radiation lobe of the radar signal SHF extends perpendicularly to the fill substance 2. As can be seen from comparison of the front view and the side view of the fill level measuring device 1 in
A corresponding aperture ap, ao within the antenna arrangement 12 compact enough that the antenna arrangement 12 can be used also for the smallest container openings 31 comprises, according to the invention, a primary radiator 123 and a radar-bundling means 122, in whose focus the primary radiator 123 is arranged. In such case, not only the radar-bundling means 122 has a correspondingly asymmetric aperture ap, ao, but, instead, also the primary radiator 123. Additionally, the apertures ap, ao of the primary radiator 123 and the radar-bundling means 122 have the same ratio of asymmetry. The ratio can be set, for example, at 3:1.
An example of an embodiment of the antenna arrangement 12 of the invention is shown in
Schematically,
As shown in
The variant of the antenna arrangement 12 shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 132 553.6 | Dec 2021 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/082662 | 11/21/2022 | WO |
