KROHNE BM 70 M - Manual (Page 6)

6 BM 70 M
As the transmit frequency is changed during a short time interval by FMCW radar the transmitted
frequency has to follow the nominal frequency within micro seconds. This ensues via modern, fast
electronic and processors.
Microprocessor
control
Reference
oscillator
Phase
detector
Microwave
oscillator
Loop
filter
Antenna
PLL structure
2.2 Signal processing (digital)
The radar signals are digitally processed by a microprocessor. The processing system is based
on intelligent procedures that allow for plausibilities and history.
The following diagram describes the path of internal signal processing:
After automatic gain control, the measuring signal is filtered, digitized and converted into a
frequency spectrum by means of the Fourier transform. Plausibility of the value obtained is
assessed with the aid of the so-called empty-tank spectrum, which contains information about
constant interference reflectors. Interpolation of the spectrum helps to improve resolution of the
measured value.
O O
O O
V
Fourier
spectrum
interpolation
850.97:2
plausi-
bility
transform
filter
analog to
digital
spectrum
measurement
signal
gain
switch
gain
control
conversion
corrected
empty tank spectrum
distance