The system control manages communication of the controller with theThe system control manages communication of the controller with the
environment via the front panel and environment via the front panel and workstaworkstation interfaces and also thetion interfaces and also the
internal setting of all parameters for the internal setting of all parameters for the individual functional blocks.individual functional blocks.
The RF signal from the scanning head first of all has to be The RF signal from the scanning head first of all has to be pre-processed topre-processed to
optimally drive the various demodulators. The optimally drive the various demodulators. The signal conditioning includes thesignal conditioning includes the
following functions:following functions:
Measurement of the input signal levelMeasurement of the input signal level
Stabilization of the signal amplitudeStabilization of the signal amplitude
Limitation of the bandwidthLimitation of the bandwidth
Dropout reduction via the tracking filterDropout reduction via the tracking filter
Down-mixing of the Down-mixing of the frequencyfrequency
The measurement of the input signal level is The measurement of the input signal level is required to provide the user withrequired to provide the user with
information of the back scattering properinformation of the back scattering properties of the object and as a ties of the object and as a help tohelp to
optimally focus the laser beam. The level optimally focus the laser beam. The level is converted to a is converted to a logarithmicalllogarithmicallyy
scaled DC voltage. This signal is visualized on the scaled DC voltage. This signal is visualized on the scanning head and on thescanning head and on the
controller as a bar controller as a bar display and is available at display and is available at the BNC jack SIGNAL forthe BNC jack SIGNAL for
external usage.external usage.
Stabilization of the signal amplitude is necessary for the following signalStabilization of the signal amplitude is necessary for the following signal
processing steps as the input signal level can processing steps as the input signal level can fluctuate by several orders offluctuate by several orders of
magnitude due to the magnitude due to the extremely diffeextremely different back scattering properties of therent back scattering properties of the
objects.objects.
LimitatioLimitation of n of the bandwidth at the input the bandwidth at the input of the signal of the signal processing electronics isprocessing electronics is
required because, for low velocities, only a required because, for low velocities, only a narrow section of the systemnarrow section of the system
bandwidth is occupied by the FM bandwidth is occupied by the FM signal. In the remaining bandwidth onlysignal. In the remaining bandwidth only
noise is recorded. For this reason, at the input section of the controller, anoise is recorded. For this reason, at the input section of the controller, a
switchable filter is installed which limits the noise bandwidth depending on theswitchable filter is installed which limits the noise bandwidth depending on the
velocity measurement range set.velocity measurement range set.
The dropout reduction via tracking filter plays a The dropout reduction via tracking filter plays a very important role in opticalvery important role in optical
signal processing. The light scattered back from the object has a speckledsignal processing. The light scattered back from the object has a speckled
nature, i.e. at any instant the detector sees a light or a dark speckle. The lownature, i.e. at any instant the detector sees a light or a dark speckle. The low
signal amplitude of the dark speckle can signal amplitude of the dark speckle can lead to loss lead to loss of signal, so-calledof signal, so-called
dropouts. When decoding the dropouts. When decoding the velocityvelocity, this , this interruption of the interruption of the input signalinput signal
causes short but high noise signals, so-called spikes which make it verycauses short but high noise signals, so-called spikes which make it very
difficult to analyze the output signal. These dropouts are effectively reduceddifficult to analyze the output signal. These dropouts are effectively reduced
by a so-called tracking filter integrated in by a so-called tracking filter integrated in the input section of the the input section of the controllercontroller..
This is done by This is done by an electronic circuit to regenerate high an electronic circuit to regenerate high frequency signalsfrequency signals
based on the principle of the phase locked loop (PLL).based on the principle of the phase locked loop (PLL).
The principle of signal regeneration by The principle of signal regeneration by the tracking filter is based othe tracking filter is based on replacingn replacing
the input signal with a the input signal with a distorted amplitude by a stable signal from a distorted amplitude by a stable signal from a voltagevoltage
controlled oscillator which is synchronized with the frequency and the phasecontrolled oscillator which is synchronized with the frequency and the phase
of the input signal. Suitable circuit design can make it possible to maintain theof the input signal. Suitable circuit design can make it possible to maintain the
synchronized condition approximately, even if the input signal is temporarilysynchronized condition approximately, even if the input signal is temporarily
lost. The mechanical analog for this design is a flywheel which may lose alost. The mechanical analog for this design is a flywheel which may lose a
small portion of its energy if small portion of its energy if the driving force is briefly interrupted butthe driving force is briefly interrupted but
continues to run at almost the same number of revolutions per minute and cancontinues to run at almost the same number of revolutions per minute and can
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