'
')XQFWLRQDO'HVFULSWLRQRIWKH&RQWUROOHU
The velocity decoder is followed by a low pass filter which suppresses spuri-
ous RF components and limits the bandwidth of the output signal to reduce
background noise. Via the system control, various cutoff frequencies can be
set for the low pass filter.
The last block in each signal path is an amplifier which scales the output sig-
nals and can optimally drive subsequent signal processing units.
The system control manages the communication of the controller with the
environment via the front panel and PC interfaces and also the internal setting
of all parameters for the individual functional blocks.
Not included in the block diagram is the power supply unit which generates all
supply voltages for the sensor head and the controller.
'6LJQDO&RQGLWLRQLQJ
The RF signal from the sensor head first of all has to be pre-processed to
optimally drive the various demodulators. The signal conditioning includes the
following functions:
Measurement of the input signal level
Stabilization of the signal amplitude
Limitation of the bandwidth
Drop-out reduction via the tracking filter
Down-mixing of the frequency
0HDVX UHPHQW
RIWKH LQS XW
VLJ QDOO HY HO
The measurement of the input signal level is required to provide the user with
information of the back scattering properties of the object and as a help to
optimally focus the laser beam. The level is converted to a logarithmically
scaled DC voltage. This signal is visualized on the sensor head and on the
controller as a bar display and is available at the BNC jack SIGNAL for exter-
nal usage.
6WDE LOL ]DW LRQ
RIWKHVLJQDO
DPSOLW XGH
Stabilization of the signal amplitude is necessary for the following signal pro-
cessing steps as the input signal level can fluctuate by several orders of mag-
nitude due to the extremely different back scattering properties of the objects.
/LPLWDWLRQRI
WKHEDQGZLGWK
Limitation of the bandwidth at the input of the signal processing electronics is
required because, for low velocities, only a narrow section of the system
bandwidth is occupied by the FM signal. In the remaining bandwidth only
noise is recorded. For this reason, at the input section of the controller, a swit-
chable filter is installed which limits the noise bandwidth depending on the
velocity measurement range set. As this is carried out right at the input, how-
ever, the bandwidth limitation also affects the displacement decoding and
under certain circumstances has to be taken into consideration (refer also to
section 4.2.3, Optimizing the RF bandwidth).
'URSRXW
UHGXFWLRQYLD
WKHWUDFNLQJ
ILOWHU
Drop-out reduction via the tracking filter plays a very important role in optical
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
signal amplitude of the dark speckle can lead to loss of signal, so-called drop-
outs. When decoding the velocity, this interruption of the input signal causes
short but high noise signals, so-called spikes which make it very difficult to
analyze the output signal. These drop-outs are effectively reduced by a so-
called tracking filter integrated in the input section of the controller. This is
To Next Page
Loading...
Need help?
General
