FIBEROPTIC SENSOR TECHNOLOGY HANDBOOK

site measurement of a physical parameter to be represented
in a form (baseband signal) that can be directly
and immediately processed and transmitted to another
location, where it can be further processed and exploited
for any desired use or application. Most, if
not all, applications will require that the signal from
a sensor be telemetered to a location other than the
point of its generation. There are virtually no limits
on the range of telemetering distances that may be required.
llus, many fiberoptic sensors permit direct
optical data transmission without conversion to electrical
signals until photodetection. This section will
be devoted to the configuration and use of fiberoptic
sensor arrays, the telemetering of their outputs to
other locations, and the reconversion of these signals
to useful forms. Topics include system considerations,
sensor systems, data transmission, data link analysis,
repeater design, cable and connector design, and the
budgeting of time, power and cost in telemetry systems.
These topics may be summarized as:
FIBEROPTIC:
TELEMETRY SYSTEMS
SYSTEN GENERAL CONSIDEIbiTIONS
LINR ANALYSIS: RISETINE, POWER,
AND COST BUDGETS
SENSOR SYSTEMS
REPEATER DESIGN
CABLE AND CONNECTOR DESIGN
END-TERMINAL RECEIVER CONSIDERATIONS
The basic components of a telemetry system, from the
sensors of the variations of a physical parameter to
the instruments for displaying, recording, or simply
using a representation of the variation at some destination
user location are shown in Fig. 6.12.
P
?
PHYSICAL
PARAMETER
0TRANSDUCER
I
El
s-f(p)
ENCODER
MOOULATOR
MULTIPLEXER
CONVERTER
TRANSMITTER
SOURCE
YEND INSTRUMENT
DISPLAY
SOUND
RECORD
COMPUTE
E@
TRANSMISSION
I
SINK
Fig. 6.12 Basic components of a fiberoptic array
telemetry system.
6.2.2 Fiberoptic Telemetry System Basic
Configurations
Perhaps the most general telemetry system
configuration is the multisource (sensor array), multiuser
(user-array) general communication network-connected
system shown in Fig. 6.13. The simplest system
ARRAY
SOURCE
FIBEROPTIC
CABLES
1
m------
Fig. 6.13
FIBEROPTIC, RADIO,
OR WIRE
L
TRANS-
MISSION
SYSTEM
-----El .
---b
Generalized fiberoptic telemetry system.
is a single sensor connected to a single output device
via a single channel. Many variations are poasible,
for example the multisource, multiplexed, single user,
fiberoptic data link configuration shown in Fig. 6.14.
El-
1
FIBEROPTIC
CABLES
SIGNAL
CONDl-
4 TIONER
I 1’
. . .
‘B-J
5
ṅ
Fig. 6.14
FOCABLE
USER END INSTRUMENTS
RECORDER
DISPLAY DEVICE
LOUDSPEAKER
COMPUTER
TRANSMITTER
0
photodetector
AND DEMUX
A multisource multiplexed single-uaer fiberoptic
sensor array telemetry system.
6.2.1 Fiberoptic Telemetry System Design OptiOnS
Mny options are open to the designer of a
fiberoptic telemetry system. These include the determination
of the overall system configuration; the design
and selection of fiberoptic senaors, cables, and
connectors; the design and selection of transmitters
and receivers; and the specification of system parameters,
such as signal-to-noise ratios, distortion
limits, permissible bit error-rates, multiplexing
schemes, modulation methods, and the coding, sensing,
and detection arrangements.
6-6
Various arrangements for the transmission of
signals from a fiberoptic sensor array to many users
via different types of fiberoptic data links are ahown
in Fig. 6.15. The simplex, half-duplex, full-duplex,
and multiplex schemes illustrated in Fig. 6.15 describe
various system configurations with different capabilities.
These configurations may be connected to operate
as one-way-at-a-time, two-way alternate, or two-way
simultaneous systems. For example, two simplex channels
could be associated for operating a two-way simultaneous
data link.