Wide-range reflective optical fiber liquid-level sensor

To achieve accurate, continuous, and online monitoring of liquid levels over a wide range, we investigate a liquid level sensor based on reflective optical fiber. The theoretical model of liquid level measurement by sensor is constructed. The sensor consists of a receiving fiber, an incident fiber, an elastic diaphragm, and a reflective sheet. To enhance the sensitivity of the sensor, the effects of the incident fiber diameter, number of receiving fibers, spacing between incident and receiving fibers, and optical path on the sensor’s reflection spectrum and sensitivity were investigated. The effects of liquid level dynamic change rate, vibration, temperature, and working fluid on sensor measurements were further investigated. For the as-fabricated sensor with an incident fiber of 2000 μm diameter, three receiving fibers of 1000 μm diameter, a fiber core spacing of 100 μm, an initial optical path of 10 mm, and an elastic diaphragm thickness of 5 mm, liquid level sensitivity reached 8 nW/cm. Over a measurement range of 0 to 5 m, with liquid level variation rates of 10 to 100 cm/min, temperatures of 0°C to 70°C, and horizontal and circular vibration frequencies and powers of 1 to 2.6 Hz and 15 and 32 W, respectively, output of the sensor maintained a linear relationship with the liquid level, showing minimal influence from variation rates, temperature, vibrations, and working fluid with a maximum relative measurement error of 3.2%.