8
TECHNICAL DATA
68
OPTIWAVE 1010
www.krohne.com
10/2016 - 4003537403 - MA OPTIWAVE 1010 R03 en
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
Δ
f is calculated from the actual transmitted
frequency and the received frequency. The difference is directly proportional to the distance. A
large frequency difference corresponds to a large distance and vice versa. The frequency
difference
Δ
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
the maximum distance and the measured 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
5
Differential time delay,
Δ
t
6
Differential frequency,
Δ
f
7
Frequency transmitted
8
Frequency received
9
Frequency
10
Time
