Research focussing on the fundamental problems of line neutrality and autocalibration of optical fibre sensors and the implementation of fibre optic temperature, pressure and other types, such as displacement sensors, into the same network has been undertaken. It was intended to develop a distributed fibre optic sensor network to monitor environmental changes in industrial and civil engineering appplications.
A multiplex system has been developed which is able to connect up to 8 intensity modulated temperature and pressure sensors. A new set of fibre optic pressure transducers has been developed for different ranges and different applications. The sensors show good repeatability and promise good lifetime with an accuracy of 1%. Temperature sensors have also been developed with an accuracy of better tha 0.5 degrees.
An expanded sensor system is being tested in a large dam hydroelectric power station, and by a gas pipeline company.
Fibre optic sensors provide a method of reliable, passive monitoring of environmental changes for industrial and civil engineering applications. More recently they gained interest as a sensor technology issue with great promise in measuring various variables such as : temperature, pressure, level, flow and other analogue parameters because of its high data rates, safety inflammable or explosive atmospheres, immunity to electromagnetic-interferences and hence longevity in hostile environments.
The system is based on a network of fibre optic intensity modulated sensors interrogated by a time delay frequency multiplexing technique used for processing the signals of the multiple sensor system.
The major advantage of optical fibres for this sensor system is the possibility of passive sensing, that is, sensing without the use of electrical components in the sensor head. The long term stability of the proposed system is an essential requirement.