ABSTRACT

The overall size of most civil structures poses many problems for the sensor system, some of which can possibly be overcome through the use of fiber optic sensors [1, 2, 3, 4]. One of the major problems with conventional sensor systems is the cabling. A sensing system on a major structure may require more than 100 data channels. A conventional electronic analog sensor cable requires at least five high-quality parallel wires (two for signal transmission, two for power supply, and one for shielding) inside a weatherproofed jacket with strain relief for each transducer. These cables can be very expensive, heavy and bulky. Many cabling problems can be reduced significantly with the use of fiber optic cables, which can carry the excitation and signal light over the same line, can be multiplexed, and are relatively light in weight. The immunity of fiber optic sensors to electromagnetic interference is also a significant advantage. The long cable lengths associated with the use of conventional electronic sensors can cause the formation of large antennas which can pick up noise, create ground loops, and are susceptible to lightning strikes. Fiber optic cables are relatively immune to these problems. Another advantage of optical fibers is that they are resistant to corrosion, which can be a serious prob­ lem for long term monitoring systems that are exposed to the environment aggression. As an additional advantage, fiber optic sensors can be configured to measure quantities that are distributed over a distance. Distributed sensing may be useful in many applications, due to the large size of the structure.