LED光源影像應用於水位量測之研究

Abstract

本研究目的為在易淹水地區之水位計開發，克服一般市售水位計造價昂貴，且無法廣設於易淹水地區之問題，其優點為硬體設備造價低廉、內部元件取得容易、儀器架設方便、量測精確度高、且未來發展性強。 本研究設計之試驗儀器，為三角光學式測距水位計。影像擷取鏡頭使用市售價格低廉之網路攝影機，計算部分利用三角測距量測法(Optical Triangulation Method) 結合光學形心法(Centroid Method)，追蹤計算EPS浮板上之光源形心位置及變化量，反推其水位。 試驗部分為靜態及動態水位試驗，靜態水位試驗使用靜穩之蓄水槽，放入三角光學式測距水位計並於相同水位進行二組不同解析度，計算與實際水位誤差量比較；動態水位試驗則固定試驗水槽中之流量，調整尾水板，以不同之水槽水位進行誤差測試。最後，與市售二種壓力式及一種浮筒式水位計檢校報告實測值進行相對誤差分析比較。 試驗結果顯示三角光學式測距水位計之靜水位誤差範圍，符合美國國家環境保護局所提出量測精度須小於±0.01ft之規範。

This study aims at the development of water level gauge for flood-prone areas. To overcome common level gauges, expensive cost and not being able to applied to flood-prone areas, this research focuses on five directions: low cost of hardware of the instrument, the availability of internal components, the convenience to set up the instrument, high accuracy of measurement, and the potential of development in the future. Optical triangulation water level gauge is designed in this study. Webcam with low price is used to capture the image in this study. The combination of optical triangulation method and centroid method is applied in the calculation. By tracing the position and the variation of the centroid of light source on the EPS kickboard, water level can be deduced. Experiments of water level are divided into static and dynamic parts. In the experiment of static water level, optical triangulation water level gauge was put in the static sink and measured with two different resolutions; measurements for the two resolutions were compared with the actual water level, and the both error were calculated and compared, too. As for dynamic experiment, flux of water was fixed, and the inaccuracy was measured by putting the optical triangulation water level gauge into sinks with different water levels. The measurements were compared with two submersible pressure sensors and another float sensor. Measurement of the triangulation water level gauge reveals that error range of the static water level is smaller than 0.01ft, which is the standard of precision of measurement set by United States Environmental Protection Agency.