Polytec PSV 300, Руководство по оборудованию

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   
                                                     
The system control manages communication of the controller with the The system control manages communication of the controller with the
environment via the front panel and
environment via the front panel and worksta workstation interfaces and also the tion 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 to pre-processed to
optimally drive the various demodulators. The optimally drive the various demodulators. The signal conditioning includes the signal conditioning includes the
following functions: following functions:
 
Measurement of the input signal level Measurement of the input signal level
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Stabilization of the signal amplitude Stabilization of the signal amplitude
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Limitation of the bandwidth Limitation of the bandwidth
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Dropout reduction via the tracking filter Dropout reduction via the tracking filter
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Down-mixing of the Down-mixing of the frequency frequency
 
  
  
 
 
The measurement of the input signal level is The measurement of the input signal level is required to provide the user with required to provide the user with
information of the back scattering proper information of the back scattering properties of the object and as a ties of the object and as a help to help to
optimally focus the laser beam. The level optimally focus the laser beam. The level is converted to a is converted to a logarithmicall logarithmically y
scaled DC voltage. This signal is visualized on the scaled DC voltage. This signal is visualized on the scanning head and on the scanning 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 for the BNC jack SIGNAL for
external usage. external usage.
 
  
  


Stabilization of the signal amplitude is necessary for the following signal Stabilization 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 of fluctuate by several orders of
magnitude due to the magnitude due to the extremely diffe extremely different back scattering properties of the rent back scattering properties of the
objects. objects.
   
 
 
Limitatio Limitation of n of the bandwidth at the input the bandwidth at the input of the signal of the signal processing electronics is processing electronics is
required because, for low velocities, only a required because, for low velocities, only a narrow section of the system narrow section of the system
bandwidth is occupied by the FM bandwidth is occupied by the FM signal. In the remaining bandwidth only signal. In the remaining bandwidth only
noise is recorded. For this reason, at the input section of the controller, a noise is recorded. For this reason, at the input section of the controller, a
switchable filter is installed which limits the noise bandwidth depending on the
switchable 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 optical very important role in optical
signal processing. The light scattered back from the object has a speckled signal 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 low nature, 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-called of signal, so-called
dropouts. When decoding the dropouts. When decoding the velocity velocity, this , this interruption of the interruption of the input signal input signal
causes short but high noise signals, so-called spikes which make it very causes short but high noise signals, so-called spikes which make it very
difficult to analyze the output signal. These dropouts are effectively reduced
difficult 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 controller controller..
This is done by This is done by an electronic circuit to regenerate high an electronic circuit to regenerate high frequency signals frequency 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 o the tracking filter is based on replacing n 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 voltage voltage
controlled oscillator which is synchronized with the frequency and the phase controlled oscillator which is synchronized with the frequency and the phase
of the input signal. Suitable circuit design can make it possible to maintain the
of the input signal. Suitable circuit design can make it possible to maintain the
synchronized condition approximately, even if the input signal is temporarily
synchronized condition approximately, even if the input signal is temporarily
lost. The mechanical analog for this design is a flywheel which may lose a lost. 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 but the driving force is briefly interrupted but
continues to run at almost the same number of revolutions per minute and can continues to run at almost the same number of revolutions per minute and can