A quasi-distributed level sensor based on a bent side-polished plastic optical fibre cable

A flexible quasi-distributed liquid level sensor based on the changes in the light transmittance in a plastic optical fibre (POF) cable is proposed. The measurement points are constituted by small areas created by side-polishing on a curved fibre and the removal of a portion of the core. These points are distributed on each full turn of a coil of fibre built on a cylindrical tube vertically positioned in a tank. The changes between the refractive indices of air and liquid generate a signal power proportional to the position and level of the liquid. The sensor system has been successfully demonstrated in the laboratory, and experimental results of two prototypes with 15 and 18 measurement points in a range of 33 mm and 39 mm respectively and a resolution of 0.08 mm with bend radii of 5 mm and 8 mm are presented.