A radar signal is emitted via an antenna, reflected on the product surface and received after a time t. The radar principle used is FMCW (Frequency Modulated Continuous Wave). The FMCWradar transmits a high frequency signal whose frequency increases linearly during the measurement phase (called the frequency sweep).
The signal is emitted, reflected on the measuring surface and received with a time delay, t. Delay time, t=2d/c, where d is the distance to the product surface and c is the speed of light in the gas above the product. For further signal processing the difference ¦¤f is calculated from the actual transmit frequency and the receive frequency.
The difference is directly proportional to the distance. A large frequency difference corresponds to a large distance and vice versa. The frequency difference ¦¤f is transformed via a Fourier transformation (FFT) into a frequency spectrum and then the distance is calculated from the spectrum. The level results from the difference between tank height and measuring distance.
