Development of an optic fiber grating pipe strain gauge
|關鍵字:||光纖光柵;應變管;地滑;optic fiber grating;pipe strain gauge;land slide|
The main objective of this research is to develop an optic fiber Bragg grating based pipe strain gauge as a means to perform long term ground movement monitoring. This new automated system has a superior resolution and higher stability than currently available electronic devices. The ground movement has traditionally been monitored using the inclinometer probe, in place inclinometer or pipe strain gauge. The inclinometers measured the inclination at a regular interval as it is pulled upward to the ground surface. In general, the inclinometer system has a rather desirable resolution but it is expensive to automate the system. The in-place inclinometer system installed multiple inclinometer probes on a permanent basis. Because of the transmission cables usually take up a lot of space in the inclinometer casing, only limited number of sensor probes could be installed in the casing. Pipe strain gauge, which was a flexible pipe attached with a series of strain gauges at regular intervals. The strain gages measured the flexural strain distribution of the flexible pipe. Integrating the strains would then yield the amount of pipe movement. The pipe strain gages can be automated but the number of strain gauges had to be limited, and there was inevitable electronic noises in the strain gages. FBG pipe strain gauge overcame the disadvantages of the traditional pipe strain gauge, by replacing the electronic strain gauges with fiber Bragg grating sensors. The fiber optic sensors were not affected by the electromagnetic interference, and multiple FBG sensors can be installed on a single optic fiber. The number of FBG sensors can be significantly expanded and the signal to noise ratio was much improved. The thesis describes the basic principles of fiber Bragg grating, design of the FBG pipe strain gages and lessons learned from field application of the new ground movement monitoring system.