Polytec PSV 300, Hardware Manual

Page: 89 / 105

   
                                                       
drive a subsequent mechanism without disruption. It is easy to see that this drive a subsequent mechanism without disruption. It is easy to see that this
effect gets better, the higher the inertia of the wheel is. At the same time the
effect gets better, the higher the inertia of the wheel is. At the same time the
flywheel however
flywheel however, loses the ability to , loses the ability to follow rapid changes in the follow rapid changes in the revolutions revolutions
per minute, i.e. the per minute, i.e. the dynamic response of the drive system gets worse. The dynamic response of the drive system gets worse. The
same correlation also applies to the same correlation also applies to the electronic trackin electronic tracking filter which thus g filter which thus
always represents a compromise between the regeneration effect and the always represents a compromise between the regeneration effect and the
dynamic tracking behavior of the
dynamic tracking behavior of the input signal. Basically input signal. Basically, good , good dropout dropout
elimination or noise suppression is always involved with limited dynamic elimination or noise suppression is always involved with limited dynamic
response. If the response. If the maximum acceleration is exceeded, the maximum acceleration is exceeded, the synchroniza synchronization tion
between the input signal and the oscillator is lost (the tracking filter loses lock) between the input signal and the oscillator is lost (the tracking filter loses lock)
which leads to drastic signal distortions at the
which leads to drastic signal distortions at the signal output. Practical advice signal output. Practical advice
for setting the tracking filter can be found in for setting the tracking filter can be found in sec sec tio tio n n 4.2 4.2 .3 .3 ..
The internal structure of the The internal structure of the tracking filter circuit is shown in tracking filter circuit is shown in fi fi gu gu re re C. C. 2 2 . The . The
function of the voltage controlled oscillator (VCO) has already been function of the voltage controlled oscillator (VCO) has already been
mentioned. The control signal which synchronizes the oscillator is generated
mentioned. The control signal which synchronizes the oscillator is generated
in the phase
in the phase detector which monitors the phase difference between the input detector which monitors the phase difference between the input
signal and the oscillator signal. The signal and the oscillator signal. The dynamic characteris dynamic characteristics of the tics of the
configuration are mainly determined by the internal low pass filter. The configuration are mainly determined by the internal low pass filter. The
maximum acceleratio
maximum acceleration which the tracking filter can n which the tracking filter can still follow depends on the still follow depends on the
filter bandwidth. The low pass time constant is switched between SLOW and filter bandwidth. The low pass time constant is switched between SLOW and
FAST via the system control and thus adapts the dynamic characteristics to
FAST via the system control and thus adapts the dynamic characteristics to
the application. The tracking filter can be turned off via a bypass if the
the application. The tracking filter can be turned off via a bypass if the
accelerations are too high or in the case of good
accelerations are too high or in the case of good optical signals. optical signals.
 
 
 


Down-mixi Down-mixing of the ng of the frequency in the input frequency in the input section is required to convert the section is required to convert the
carrier frequency of the input signal from 40.4 carrier frequency of the input signal from 40.4 MHz originally to lower MHz originally to lower
intermediate frequencies. With these intermediate intermediate frequencies. With these intermediate frequencies, the velocity frequencies, the velocity
decoder can work optimally in decoder can work optimally in the individual measurement ranges. Down- the individual measurement ranges. Down-
mixing is carried out by a mixing is carried out by a mixing process which does not affect the modulation mixing process which does not affect the modulation
content of the FM signal. content of the FM signal. The variable frequency f The variable frequency f
LO LO
is produced by the so- is produced by the so-
called local oscillator in a called local oscillator in a fixed relationship to the drive frequency of fixed relationship to the drive frequency of the the
Bragg cell. Bragg cell.
Figure C.2: Block diagram of the tracking filter circuit Figure C.2: Block diagram of the tracking filter circuit
     
 
 
 
   
 
 
 
 
 
 
 
   