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EP-4741778-A1 - LEVEL MEASURING DEVICE

EP4741778A1EP 4741778 A1EP4741778 A1EP 4741778A1EP-4741778-A1

Abstract

The invention relates to a level measuring device for determining the level of a medium in a container, comprising a signal generation device configured to generate an electrical signal comprising a step function or a pulse function; a measuring line connected, in particular electrically, to the signal generation device and extending from a process connection into the medium, wherein the measuring line serves to guide the electrical signal into the container and towards the medium, the electrical signal being at least partially reflected at the surface of the medium and the reflected signal influencing the electrical signal; and an evaluation unit configured to determine the level of the medium based on the influenced electrical signal.

Inventors

  • Baldischweiler, Boris
  • WEBER, THOMAS

Assignees

  • SICK AG

Dates

Publication Date
20260513
Application Date
20241111

Claims (15)

  1. Level measuring device (12) for determining the level of a medium (14) in a container (16), comprising: a signal generating device configured to generate an electrical signal comprising a step function or an impulse function; a measuring line (20) which is connected to the signal generating device, in particular electrically, and extends from a process connection (22) into the medium (14), wherein the measuring line (20) serves to conduct the electrical signal into the container (16) and towards the medium (14), wherein the electrical signal is at least partially reflected at the surface of the medium (14) and the reflected signal influences the electrical signal; and an evaluation unit (24) which is designed to determine the fill level of the medium (14) based on the influenced electrical signal.
  2. Level measuring device (12) according to claim 1, wherein evaluation unit (24) is designed to determine a substitution quantity based on the influenced electrical signal, which is proportional to a transit time of the electrical signal from the process connection (22) to the medium surface and back and/or to a distance between the medium surface and the process connection (22), and to determine the fill level of the medium (14) based on the substitution quantity, where the substitution quantity does not correspond to the propagation time of the electrical signal.
  3. Level measuring device (12) according to claim 2, wherein the influenced electrical signal has a pulse shape, wherein the evaluation unit (24) is configured to generate a rectangular signal based on a pulse width of one, in particular a first, pulse of the influenced electrical signal, the width of which essentially corresponds to the pulse width of the influenced electrical signal, and to determine the substitution quantity based on the rectangular signal.
  4. Level measuring device (12) according to claim 3, wherein the evaluation unit (24) is configured to generate the square wave signal based on the influenced electrical signal using a threshold filter, wherein the square wave signal essentially assumes the value 0 when the influenced electrical signal is less than a predetermined threshold, and assumes a predefined non-zero value when the influenced electrical signal is greater than the predetermined threshold, wherein the evaluation unit (24) is configured to perform an integration of the square wave signal using an integrator component in order to determine an integration value, and to determine the fill level of the medium (14) based on the integration value.
  5. Level measuring device (12) according to claim 4, wherein the evaluation unit (24) is configured to determine the specified threshold value as a function of the impedance difference between a reference impedance, which represents the impedance of the measuring line for the section which does not extend into the medium, and a medium impedance, which represents the impedance of the measuring line for the section which extends into the medium.
  6. Level measuring device (12) according to claim 4 or 5, wherein the evaluation unit (24) is configured to continuously adjust the specified threshold of the threshold filter or at specified time intervals, in particular to reduce it.
  7. Level measuring device (12) according to one of claims 4 to 6, wherein the evaluation unit (24) comprises several threshold filters with different threshold values.
  8. Level measuring device (12) according to one of claims 4 to 7, wherein the evaluation unit (24) is configured to sample an integration signal generated by the integration of the square wave signal by means of an ADC with a sampling frequency of less than 10 MHz, less than 1 MHz, less than 100 kHz, less than 10 kHz or less than 1 kHz in order to determine the integration value.
  9. Level measuring device (12) according to one of the preceding claims, wherein the measuring line (20) does not comprise a coaxial cable.
  10. Level measuring device (12) according to one of the preceding claims, wherein the electrical signal comprises a plurality of rectangular pulses and the influenced electrical signal comprises a plurality of, in particular similar, pulses, wherein the evaluation unit (24) is configured to determine a DC component of the influenced electrical signal and to determine the fill level of the medium (14) based on the DC component of the influenced electrical signal.
  11. Level measuring device (12) according to claim 10, wherein the signal generation device is configured to generate the rectangular pulses of the electrical signal at variable time intervals.
  12. Level measuring device (12) according to one of the preceding claims, wherein the reference impedance (20) is larger, in particular 5 times, 10 times, 12 times or 15 times larger, than the medium impedance (14).
  13. Level measuring device (12) according to one of the preceding claims, wherein the measuring line (20), in particular as a coplanar line or micro-strip line, is arranged together with the evaluation unit (24) and the signal generation device on the same printed circuit board (66).
  14. Method for determining the fill level of a medium (14) in a container (16), comprising the steps: Generating an electrical signal in the form of a step function using a signal generation device, Conducting the electrical signal via a measuring line (20) into the container (16) and towards the medium (14), wherein the measuring line (20) extends into the medium (14), Reflecting part of the electrical signal from the surface of the medium (14), wherein the reflected signal influences the electrical signal, and Determining the fill level of the medium (14) based on the influenced electrical signal using an evaluation unit (24).
  15. Method according to claim 14, where the electrical signal is transmitted with an essentially constant fundamental impedance.

Description

The present invention relates to a level measuring device for determining the level of a medium in a container. Precisely determining the fill level in tanks is a common requirement in various industrial applications. Several technologies are available to address this challenge. For example, optical, radar-based, capacitive, or conductive sensors, tuning forks, floats, or wired time-of-flight (TOF) methods can be used to measure the fill level. In wired TOF methods, an electrical pulse is sent through a cable that extends into the liquid in the tank. Since the cable has different effective impedances for the section that does not extend into the liquid and the section that does, the electrical pulse sent through the cable is reflected at the liquid surface, i.e., at the boundary between the two different impedances. Based on the travel time of the electrical pulse from a process port to the liquid surface and the travel time of the reflected signal from the liquid surface back to the process port, the fill level of the tank can be determined. However, evaluating the pulse in wired TOF (Time-of-Flight) methods places high demands on the transmitting and receiving equipment, as this must provide high resolutions, often down to the picosecond range, which increases complexity and costs. Another disadvantage is that Measuring transit time often requires many consecutive excitation signals, which negatively impacts energy consumption. Furthermore, existing methods result in high emissions of high-frequency interference, as portions of the high-frequency pulse signal can be radiated by the measuring probe, which acts as an antenna. Therefore, such applications are often limited to use in metallic containers. It is an object of the present invention to remedy the aforementioned disadvantages and to provide an improved level measuring device for determining the level of a medium in a container and a corresponding method. This task is solved by the subject matter of the independent claims. A first aspect of the invention relates to a level measuring device for determining the level of a medium in a container, comprising: a signal generating device configured to generate an electrical signal comprising a step function or an impulse function; a measuring line which is connected to the signal generating device, in particular electrically, and extends or can extend from a process connection into the medium, wherein the measuring line serves to guide the electrical signal into the container and in the direction of the medium, wherein the electrical signal is preferably reflected at least partially at the surface of the medium and the reflected signal influences the electrical signal; and an evaluation unit which is configured to determine the fill level of the medium based on the influenced electrical signal. The invention is therefore based on the understanding that the reflection of the electrical signal at the surface of the medium influences or alters the original electrical signal, and that this alteration manifests itself in the form of the The system reflects the influenced electrical signal, allowing the transit time of the electrical signal, and thus the fill level of the medium, to be determined indirectly based on this signal. Specifically, the fill level of the medium is determined without directly measuring or determining the transit time of the electrical signal to the medium's surface and back (Time of Flight). The influenced electrical signal is, in particular, the step response or impulse response of the system to the applied input signal. When the transit time of the electrical signal is mentioned herein, unless otherwise stated, this refers to the transit time of the electrical signal from the process connection (or from the signal generation device) to the surface of the medium and the transit time of the reflected signal from the surface of the medium back to the process connection (and thus to the evaluation unit). The signal generation device is, for example, a voltage source that generates a voltage having at least the form of a step function or pulse function and feeds this voltage into the level measuring device. The signal generation device is particularly capable of rapidly switching on or feeding the electrical signal into the system, i.e., with a rise time shorter than 10 ns, 1 ns, or 100 ps. This ensures, for example, that the level measuring device is capable of performing measurements with a corresponding level of accuracy and resolution. A rapid rise of the electrical signal can also be generated, for example, by "instantly" feeding a constant electrical signal into the system by switching a switch. For example, the switch can be designed as part of the signal generation device and switch the electrical signal on and off. In other words, the switch connects the signal generated by the signal generation device to a remaining part of the level measuring device and separates it again, so