Page 421 - Sensors and Control Systems in Manufacturing

Industrial Sensors and Contr ol
• Star network with reflective sensors (Fig. 7.49c). 375
• Star network with reflective sensors; one or more sensors can
be replaced by a separate star network, in order to obtain a
tree network (Fig. 7.49d).
• Star network that can also be operated with transmissive sen-
sors (Fig. 7.49e).
• Ladder network with two star couplers. A star coupler is
replaced by several access couplers, the number required
being equal to the number of sensors (Fig. 7.49f).
Topological modifications, especially of sensor arrays and ladder
networks, may be desirable in order to incorporate reference paths of
transmissive (dummy sensors) or reflective sensors (splices, open
fiber end).
The transmit and return fibers, or fiber highway, generally share
a common single-fiber path in networks using reflective sensors.
When a suitable fiber-optic network topology is required, various
criteria must be considered:

• The sensor type, encoding principle, and topology to be used
• The proposed multiplexing scheme, required number of sen-
sors, and power budget
• The allowable cross-communication level
• The system cost and complexity constraints
• The reliability (i.e., the effect of component failure on system
performance)

7.31 Power Line Fault-Detection Systems for Power
Generation and Distribution Industries
In power distribution lines, faults such as short circuits, ground faults,
and lightning strikes on the conductors must be detected in a very
short time to prevent damage to equipment and power failure, and to
enable quick repair. If the transmission line is divided in sections and
a current or magnetic-field sensor is mounted in each section, a faulty
section can be determined by detection of a change of the level and
phase of the current on the power line. A system was developed as a
hybrid optical approach to a fault-locating system that detects the phase
and current difference between two current transformers on a com-
posite fiber-optic ground wire (OPGW) wherein, due to induction,
current is constantly passing (Fig. 7.50). The signal from a local elec-
trical sensor, powered by solar cells and batteries, is transmitted over
a conventional optical-fiber communication link. By three-wavelength