Apparatus for determining fill level of a fill substance in a container with process isolation having at least two plastics

1. An apparatus for determining or monitoring the fill level of a fill substance located in a container in a process, comprising:

a signal producing unit, which produces high-frequency measuring signals;

an in-coupling/out-coupling unit, which couples the high-frequency measuring signals into an antenna unit, respectively out of the antenna unit; said antenna unit has a hollow conductor and an antenna element widening toward the fill substance; and

said antenna unit transmits the high-frequency measuring signals in the direction of the surface of the fill substance and receives echo signals reflected on the surface of the fill substance; and

a control/evaluation unit, which ascertains the fill level of the fill substance in the container based on travel time of the measuring signals, wherein:

in or on said antenna unit a process isolation is provided, which is at least approximately transparent for the high-frequency measuring signals and which protects said in-coupling/out-coupling unit against influences of the process;

said process isolation is an isostatically pressed, molded part, which is manufactured of at least two plastics having different physical and/or chemical properties; and

each of said at least two plastics is provided in respectively defined regions of said process isolation.

2. The apparatus as claimed in claim 1 , wherein:

said two plastics comprise a first plastic having a first dielectric constant (DK 1 ) and a second plastic having a second dielectric constant (DK 2 ); and

said two dielectric constants (DK 1 , DK 2 ) are at least approximately equal.

3. The apparatus as claimed in claim 1 , wherein:

said process isolation is embodied gas tightly.

4. The apparatus as claimed in claim 1 , wherein:

said first plastic has a higher temperature, pressure- and/or chemical durability than said second plastic.

5. The apparatus as claimed in claim 4 , wherein:

said first plastic with the higher temperature, pressure- and/or chemical durability is arranged in the defined region of said process isolation, which faces the process, respectively contacts the process.

6. The apparatus as claimed in claim 5 , wherein:

the defined region, in which said first plastic is arranged, is essentially embodied as a surface layer.

7. The apparatus as claimed in claim 1 , wherein:

the thickness of the surface layer of said first plastic amounts preferably to λ/4, wherein λ is the wavelength of the high-frequency measuring signals or the center wavelength of a pulse of the high-frequency measuring signals.

8. The apparatus as claimed in claim 1 , wherein:

said process isolation has a gasket, which is composed of said first plastic or a third plastic, which has a high temperature- and chemical durability comparable to that of said first plastic; and

the diameter of said gasket is greater than the maximum diameter of said antenna element.

9. The apparatus as claimed in claim 8 , wherein:

said first plastic or said third plastic is PTFE or PEEK and said second plastic is PP.

10. The apparatus as claimed in claim 8 , wherein:

electrically conductive particle are introduced into said first plastic and/or the said third plastic.