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Fiber Optics in Sensors and Contr ol Systems

FIGURE 3.41 Eight-port active star coupler. 165

required taps exceed the number of available I/O ports, or should it
be desirable to place these tap boxes at several locations in the sys-
tem, the active star couplers may be jumpered together optically by
tying a pair of I/O ports on one coupler to that on another in a hub-
and-spoke system.
With the active star coupler serving as the hub of the data bus
network, any message broadcast by a unit on the network is retrans-
mitted to all other units on the network. A response of these other
units is broadcast back to the rest of the network through the star, as
in an electrical wired data bus network.

3.13 Configurations of Fiber Optics for Sensors
Fiber-optic sensors for general industrial use have largely been
restricted to applications in which their small size has made them
convenient replacements for conventional photoelectric sensors.
Until recently, fiber-optic sensors have almost exclusively employed
standard bundle technology, whereby thin glass fibers are bundled
together to form flexible conduits for light.
Recently, however, the advances in fiber optics for data communi-
cations have introduced an entirely new dimension into optical sens-
ing technology. Combined with novel but effective transducing tech-
nology, they set the stage for a powerful class of fiber-optic sensors.

3.13.1 Fiber-Optic Bundles
A typical fiber-optic sensor probe, often referred to as a bundle
(Fig. 3.42), is 1.25 to 3.15 mm in diameter and made of individual
fiber elements approximately 0.05 mm in diameter. An average