The general principle of the radar level gauge is that the radar emits electromagnetic waves on the top of the tank, and the electromagnetic waves are received by the radar after being reflected by the medium. The frequency difference öf between the received signal and the transmitted signal is proportional to the distance R from the surface of the medium: R=C (speed)*öf (frequency difference)/2/K (frequency modulation slope) Because the speed of light C and the frequency modulation slope K are known, the frequency diference öf can be estimated to obtain the distance R from the radar installation position to the material surface, and then through the known total height of the tank, subtract the spatial distance from the radar to the material surface (referred to as Empty height) to get the height of the material level.