A novel FBG sensor for accurate and real time liquid level monitoring

We present a very simple and versatile fiber optic sensing platform for real time and continuous liquid level measurement. It includes a proper mass suspended in the liquid with one end fixed to a Fiber Bragg Grating (FBG) strain sensor, while the other fiber termination is fixed to a rigid support. When the liquid level increases inside the tank, the load exerted by the suspended mass on the optical fiber is reduced as a consequence of the increase of the buoyant force acting on the immersed mass, thus leading to a reduction of the strain applied to the FBG. Here, just as proof of principle, we exploited an aluminum cylindrical mass having a radius of 8mm, and experimentally demonstrated the capability of the realized platform to measure the water level inside a beaker over a range of 25 cm with a sensitivity of ~27pm/cm and a resolution of ~0.1% of the full scale reading (FSR).