光纖光柵應變管之研發

Abstract

本研究主要目的是發展光纖光柵感測系統應用於地層滑動之監測技術，以光纖感測器結合應變管在地層滑動長期監測上的應用，發展發展一解析度高、穩定度高的自動化監測系統。 傳統地層滑動監測工具主要包括手拉式測傾儀、孔內測傾儀及應變管等。手拉式測傾儀是藉由測傾儀在孔內移動，量測各點傾斜度，累積得到傾斜管位移量，精度高，自動化所需成本較高；孔內測傾儀作用與測傾儀類似，但直接將孔內測傾儀串接安裝於傾斜管內，但由於傾斜管內空間狹小，單一孔內能監測的數量有限；應變管是直接將應變片黏貼於傾斜管表面，藉由量測彎曲應變計算傾斜管變形，十分適合自動化監測系統，但由於電子訊號相互干擾等問題，應變片間距受到侷限，影響監測精度。 光纖光柵應變管是利用光纖光柵感測系統單線多點感測及光纖傳輸不受電磁干擾等特性，以光纖光柵感測器取代應變片，克服應變管感測點間距限制及線路過於繁雜的缺點，提高監測品質。本論文敘述光纖光柵應變量測之基本原理以及光纖光柵應變管之設計與實際應用之狀況與心得。

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.