C-3
C Basics of the Measurement Procedure
C.3 Optical Configuration in the Sensor Head OFV-511/-512
In Polytec’s vibrometers, the velocity and displacement measurement is
carried out using a modified Mach-Zehnder interferometer.
OFV-511
The optical configuration in the sensor head OFV-511 is shown schematically
in
.
The light source is a helium neon laser which provides a linear polarized
beam. The polarizing beam splitter BS1 splits the beam into the object beam
and the reference beam.
The object beam passes through the polarizing beam splitter BS2 and is
focused into the fiber with an input coupler. The beam is then emitted from the
end of the fiber, passes through a
λ
/ 4 plate and is focused using the fiber
head or the mini sensor on the object and scattered back from there. The
polarizing beam splitter BS2 then functions as an optical directional coupler
together with the
λ
/ 4 plate, and deflects the object beam to the beam splitter
BS3. As both arms of the "internal" interferometer are symmetrical, the optical
path difference vanishes within the interferometer. The resulting path
difference is equal to twice the distance between the beam splitter BS2 and
the object.
The Bragg cell in the reference arm generates the additional frequency offset
to determine the sign of the velocity.
The resulting interference signal of the object beam and reference beam is
converted into an electrical signal in the photo detector and subsequently
decoded in the controller.
Figure C.2: Optical configuration of the interferometer in the sensor head OFV-511
B S 1
O b j e c t
P r i s m
B r a g g C e l l
B S 3
B S 2
L a s e r
D e t e c t o r
C o u p l e r
F i b e r H e a d
o r
M i n i S e n s o r
R e f e r e n c e
B e a m
O b j e c t B e a m
F i b e r
l / 4
Summary of Contents for OFV-3001
Page 28: ...3 16 3 First Steps...
Page 54: ...5 12 5 Operating the Vibrometer...
Page 94: ...D 10 D Functional Description of the Controller...
