Fill-level measuring device and apparatus for determining the dielectric constant
A fill-level measuring device for determining the fill level of a process medium in a container by means of a travel-time method. The fill-level measuring device is distinguished by features including that the fill-level measuring device has structure for determining the dielectric constant of a second medium, which is located between the measuring device and the process medium. The structure for determining the dielectric constant comprises at least one waveguide for a high-frequency measuring signal, wherein such waveguide is filled at least sectionally with a dielectric and embodied and arrangeable in such a manner that the dielectric forms with the second medium an interface, at which a significant fraction of the measuring signal supplied to the second medium via the waveguide is reflected. Furthermore, an apparatus for determining the dielectric constant and a system of such an apparatus and a fill-level measuring device are proposed.
1. A fill-level measuring device for determining the fill level of a process medium in a container by means of a travel-time method, comprising:
means for determining the dielectric constant of an atmosphere above the process medium, which is located between the fill-level measuring device and the process medium, said means for determining the dielectric constant comprises at least one waveguide for a high-frequency measuring signal, said waveguide is filled at least sectionally with a dielectric and embodied and arrangeable in such a manner that the dielectric forms with the atmosphere an interface, at which a fraction of the measuring signal supplied to the atmosphere via the waveguide is reflected, wherein the dielectric constant of the atmosphere is ascertained by comparing the amplitude of the measuring signal with the amplitude of the reflected signal, and determining the dielectric constant of the atmosphere from the ratio of the amplitudes; and
at least one electronics unit, which is embodied, based on a signal transmitted toward the process medium and reflected on the process medium to determine a measured value for the fill level, and to ascertain as a function of the measured dielectric constant of the atmosphere above the process medium, a corrected measured value for the fill level.
2. The fill-level measuring device as claimed in claim 1 , wherein:
there is furnished in said electronics unit at least one correction value and/or a correction formula for correction of the measured value for the fill level as a function of the dielectric constant of the atmosphere; and
said electronics unit is embodied to correct the measured value for the fill level in accordance with the correction value and/or the correction formula.
3. The fill-level measuring device as claimed in claim 1 , wherein:
the fill-level measuring device is embodied as an ultrasonic measuring device, a radar measuring device with guided signal or a radar measuring device utilizing freely propagating waves.
4. An apparatus for determining the dielectric constant of a medium in a container, comprising:
a waveguide for a high-frequency measuring signal; and
an electronics unit, wherein:
said waveguide is filled at least sectionally with a dielectric and embodied in such a manner and introducible into the container such that the dielectric forms with the medium an interface, at which a significant fraction of the measuring signal propagating in said waveguide toward the medium is reflected; and
said electronics unit is embodied to receive the signal reflected on said interface and to compare the amplitude of the measuring signal with the amplitude of the reflected signal, and to determine the dielectric constant of the medium from the ratio of the amplitudes.
5. The apparatus as claimed in claim 4 , wherein:
the dielectric has a frustoconically shaped end.
6. The apparatus as claimed in claim 4 , wherein:
at least one cooling fin is formed on the apparatus.
7. The apparatus as claimed in claim 4 , wherein:
said waveguide is embodied as a hollow conductor or as a coaxial conductor.
8. A system for determining a fill level of a process medium in a container, at least comprising:
a fill-level measuring device for determining the fill level of the process medium by means of a travel-time method; and
at least one apparatus for determining the dielectric constant of a medium in a container, comprising: a waveguide for a high-frequency measuring signal; and an electronics unit, wherein: said waveguide is filled at least sectionally with a dielectric and embodied in such a manner and introducible into the container such that the dielectric forms with the medium an interface, at which a significant fraction of the measuring signal propagating in said waveguide toward the medium is reflected; and said electronics unit is embodied to receive the signal reflected on said interface and to compare the amplitude of the measuring signal with the amplitude of the reflected signal, and to determine the dielectric constant of the medium from the ratio of the amplitudes.