Sensor device and method for determining and/or monitoring a process variable of a medium in a container

A method for determining and/or monitoring a process variable of a medium capable of filling a container to a plurality of different fill levels using a sensor device,

• wherein the sensor device comprises:
• a crystal body that includes at least two defects or at least two crystal bodies that each including at least one defect, wherein the at least two defects, or the at least two crystal bodies, are configured to be arranged linearly and perpendicular to ground on a wall of the container;
• a magnetic field device configured to generate a magnetic field, wherein the magnetic field device is arranged to generate the magnetic field in a region of the crystal body, or of the at least two crystal bodies, and in a region of the medium within the container such that a change in the magnetic field in the region of the crystal body, or of the at least two crystal bodies, is amplified;
• an excitation unit configured to generate an excitation signal to optically excite the at least two defects of the crystal body or of the at least two crystal bodies;
• a detection unit configured to detect a magnetic field-dependent fluorescence signal emitted from the crystal body, or from the at least two crystal bodies, in a manner dependent upon the magnetic field;
• and
• an evaluation unit configured to determine at least one characteristic of the process variable based on the fluorescence signal,
• wherein the method comprises:
• generating the magnetic field in the region of the crystal body, or of the at least two crystal bodies, and in the region of the medium inside the container;
• stimulating the at least two defects;
• detecting the fluorescence signal emitted from the crystal body, or from the at least two crystal bodies;
• determining a gradient of the magnetic field from the fluorescence signal, wherein the gradient of the magnetic field is determined based on the at least two defects, which are arranged linearly and perpendicular to ground;
• and
• determining the at least one characteristic of the process variable based on the gradient of the magnetic field, wherein the process variable includes a fill level or a limit level of the medium, and the magnetic field in the region of the medium is dependent on a change to the fill level.