KROHNE OPTIWAVE 5200 C/F Handbook page 59

OPTIWAVE 5200 C/F
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8.1 Measuring principle
A radar signal is emitted via an antenna, reflected from the product surface and received after a time t. The radar principle used is
FMCW (Frequency Modulated Continuous Wave).
The FMCW-radar 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 Δf 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 Δf 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.
Figure 8-1: Measuring principle of FMCW radar
1 Transmitter
2 Mixer
3 Antenna
4 Distance to product surface, where change in frequency is proportional to distance
03/2012 - 4001904901 - HB OPTIWAVE 5200 R01 en
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