The design, development and performance characteristics of a fibre optic drag-force flow sensor

We present the design, development and performance characteristics of an optical fibre drag-force flow sensor to measure the speed and direction of fluid flow. Multidirectional fluid flow measurement is made possible by vectorial addition of the orthogonal flow components. The flow sensor comprises a fibre optic strain gauge developed by the authors, a cantilever-deflecting element made of rubber, and a drag element. The fibre optic strain gauge was designed and developed by inserting grooves into a multimode plastic optical fibre. As the fibre bends, the variation in the angle of the grooves causes an intensity modulation of the light transmitted through the fibre. The flow sensor has a repeatability of 0.3%, negligible hysteresis, and measures the wind velocity up to 30 m s-1 with a magnitude resolution of 1.4 m s-1 and a direction resolution of 5.9°. The flow sensor would be ideally suited for industrial and environmental applications.