Polytec OFV-3001, User Manual

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2-1
2 Introduction
2 Introduction
2.1 System Overview
Polytec vibrometers are instruments for non-contact measurement of surface
vibrations based on laser interferometry. The vibrometer consists of the
controller OFV-3001 and the sensor head OFV-303/-353 or OFV-511/-512.
The signal paths in the vibrometer are shown schematically in
figure 2.1 .
The beam of a helium neon laser is focused on the object under investigation,
scattered back from there and coupled back into the interferometer in the
sensor head. The interferometer compares the phase
ϕ
mod
and frequency f
mod
of the object beam with those of the internal reference beam
ϕ
0
and f
0
. The
frequency difference is proportional to the instantaneous velocity and the
phase difference is proportional to the instantaneous position of the object.
In the controller, the resulting signal is decoded using the velocity decoder
and optionally the displacement decoder. Two voltage signals are generated
which are respectively proportional to the instantaneous VELOCITY and to
the instantaneous position (DISPLACEMENT) of the object. Both signals are
available at the front of the controller as an analog voltage and can be
processed further externally. Additional functions such as filters and signal
level display raise the level of comfort for the vibrometer user. The settings of
the vibrometer are selected via the display of the controller or via PC
interfaces.
To display and analyze measurement results on a workstation, the Polytec
Vibrometer Software (VibSoft) is available optionally. The software is
described in a separate manual.
Figure 2.1: Signals in the vibrometer
S e n s o r h e a d
f
0
j
0
f
m o d
j
m o d
F r e q u e n c y
P h a s e
D
f
V e l o c i t y
d e c o d e r
V
D i s p l a c e m e n t
d e c o d e r ( o p t i o n a l )
D j
V
v ( t )
x ( t )
O b j e c t
x ( t )
v ( t ) = d x / d t