中空式光纖光柵荷重元之研發

Abstract

地錨荷重計為現今量測地錨預力的主要工具，目前傳統荷重計多為電子式，但電子式感測器會因周圍電磁波干擾問題，電子迴路也易受潮損壞，而光纖光柵（Fiber Bragg Grating，FBG）具有不怕雷擊、不易受電磁波與水干擾、穩定耐用等優點，故本研究目的希望利用光纖感測優勢來研發光纖式地錨荷重計。本研究以光纖光柵受拉可提高量測範圍的概念設計了兩種機制，首先是套筒式，其優點在於能提高荷重元的解析度，但因機制以及光柵黏貼處理上較複雜導致實驗結果不如預期理想，於是設計了三環式將機制以及黏貼過程簡單化，但無法提高解析度。製作微型荷重元進行1噸的壓力測試來確認機制的可行性後，再製作全尺寸荷重計進行30噸的壓力測試，而光柵應變以及壓力的變化與理論分析是相符的，最後再進行溫度的率定並以電阻式荷重元溫度補償方式來修正溫度改變造成的影響。

Load cell has been used as a primary tool to monitor the pre-stress conditions for earth anchors. The currently used load cells are mostly electrical, the electric circuit is prone to electromagnetic interference (EMI) and humidity induced short circuit. Optical fiber Bragg grating (FBG) has the advantage of being durable and immune to lightning, EMI and humidity. This research intends to develop an FBG based load cell to take advantage of these unique capabilities. The load cell was designed so that the FBG was always subject to tensile strain to increase the range of measurement. A two layer, coaxial design was used first. However, the attachment of FBG was rather complicated, and thus this scheme was abandoned. A three layer, coaxial design was then experimented to simplify the process of attaching the FBG’s. A down sized, 1 ton capacity load cell was made to verify the design mechanism test its performance first. Afterwards, a full sized 30 ton load cell was made. The relationship between FBG readings and applied load meets the theoretical derivations. The scheme for temperature compensation in FBG load cell follows the same procedure typically used in electric load cells.