Device for determining or monitoring the filling level of a filling material stored in a container

1. A device for determining or monitoring the fill level of a filing material stored in a container in a process, comprising:

a control/evaluation unit;

at least one process separation device;

an antenna unit;

a signal generating unit which generates high-frequency measurement signals; and

a coupling/decoupling unit which couples said high-frequency measurement signals to said antenna unit or decouples said high-frequency measurement signals from said antenna unit, wherein:

said antenna unit emits high-frequency measurement signals in a direction of a surface of the filling material and receives the echo signals reflected by the surface of the filling material;

said control/evaluation unit determines the filing level of the filling material in the container from a transit time of said high-frequency measurement signals;

said at least one process separation device is provided in or on said antenna unit, which said at least one process separation device protects said coupling/decoupling unit from influences of the process;

said at least one process separation device is produced at least partially from a dielectric material with a specified porosity; and

said at least one process separation device is configured to be at least approximately transparent to said high-frequency measurement signals;

wherein the dielectric material is aluminum oxide, and

the porosity is selected in such a way that the dielectric constant of the process isolating element is in the range between 1 and 5.

2. The device according to claim 1 , wherein:

said at least one process separation device is arranged such that at least one segment of its surface coming into contact with the process is produced from a closed porous dielectric material.

3. The device according to claim 1 , wherein:

an inner core of said at least one process separation device is designed to be open porous;

a protective layer is applied at least on the segment of said at least one process separation device coming into contact with the process; and

said protective layer consists of a closed porous or essentially pore-free dielectric material.

4. The device according to claim 3 , wherein:

the thickness of each of the two protective layers is preferably λ/2, where λ denotes the wavelength of the high-frequency measurement signals or the center wavelength of a pulse of high-frequency measurement signals.

5. The device according to claim 1 , wherein:

a second process separation device is provided that is arranged in front of a first process separation device when viewed in the direction of emission of the high-frequency measurement signals; and

said second process separation device is made of a closed porous dielectric material or wherein said second process separation device consists of an open porous core and a closed porous or essentially pore-free protective layer that surrounds the open porous core.

6. The device according to claim 5 , wherein:

the porosity of the dielectric material of said second process separation device is dimensioned in such a way that the dielectric material has a specified dielectric constant.

7. The device according to claim 1 , wherein:

a second process separation device is provided that is arranged in front of a first process separation device when viewed in the direction of emission of the high-frequency measurement signals; and

said second process separation device is completely made of an open porous dielectric material.

8. The device according to claim 1 , wherein:

the dielectric material is a temperature-resistant plastic or a ceramic.