Polytec OFV-3001, Руководство пользователя

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D-1
D Functional Description of the Controller
Appendix D: Functional Description of the Controller
D.1 Overview
The main function of the controller is to demodulate the radio frequency signal
(RF signal) provided by the interferometer in the sensor head. The frequency
of the signal is the carrier of the velocity information and the phase is the
carrier of the displacement information. Secondary functions such as human
interfacing, display and filters improve the user friendliness of the vibrometer.
An overview of the functional structure of the controller is shown in
figure D.1 .
The RF signal from the sensor head (sensor input) initially passes the
functional block signal conditioning where it is pre-processed to optimally
drive the following blocks. Subsequently the signal path is split up into the
branches velocity signal decoding (below) and displacement signal decoding
(above). If the controller is fully equipped there are two velocity decoders
installed (demodulator I and demodulator II).
The velocity is modulated on the radio frequency of the input signal. In the
velocity decoder, an AC voltage is generated which is proportional to the
instantaneous velocity of the object with the aid of so-called FM
demodulators. In the displacement decoder, optionally the phase of the RF
signal is demodulated. In doing so, an AC voltage is generated which is
proportional to the instantaneous position of the object.
The individual demodulators require different reference frequencies which are
in a fixed relationship to the driver frequency of the Bragg cell in the
interferometer. They are generated in the central oscillator block,
synchronized with the driver signal for the Bragg cell.
Figure D.1: Block diagram of the controller OFV-3001
S i g n a l
C o n d i t i o n i n g O s c i l l a t o r
L e v e l
D e t e c t o r
S i g n a l
L e v e l
D i s p l a y
S i g n a l L e v e l
S e n s o r
I n p u t
B r a g g C e l l
D r i v e O u t
O u t p u t
f
L O
f
B
f
m o d
D
D f
V
D e m o d u l a t o r I
D f
V
D e m o d u l a t o r I I
f
m o d
D
V
m o d
V
m o d
S w i t c h
C o n t r o l B u s
L o w P a s s A m p l i f i e r
V e l o
F r o n t P a n e l
V e l o c i t y
O u t p u t
S y s t e m C o n t r o l
R S - 2 3 2
I E E E - 4 8 8
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 )
j
r e f
j
m o d
P C - b a s e d
D i s p l a c e m e n t D e c o d e r
A m p l i f i e r
D i s p l a c e m e n t
O u t p u t
D i s p