FMCW method
The radar gauge transmits microwaves towards the surface of the liquid. The microwave signal has a continuously varying frequency around 10 GHz. When the signal has travelled down to the liquid surface and back to the antenna, it is mixed with the signal that is being transmitted at that moment.
The frequency of the transmitted signal has changed slightly during the time it takes for the echo signal to travel down to the surface and back again. When mixing the transmitted and the received signal the result is a signal with a low frequency proportional to the distance to the surface.
This signal provides a measured value with high accuracy. The method is called the FMCW-method (Frequency Modulated Continuous Wave).
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