High-precision Optical Fiber Liquid Level Sensor

This paper describes a novel fiber-optic level sensor designed to measure the level of benzene, diesel oil or other chemical liquid discretely or continuously. Owing to all-fiber-based system and the needle type of single fiber sensor head, it has many merits such as immunity to electromagnetic interference, simple structure, high measurement precision, high sensitivity and low drift. The experiment results demonstrated that the level measurement accuracy of ±0.5 mm has been achieved in a range of 2m and the maximum optical modulation depth of the sensor is 21dB. So it could be used for level control and measurement of flammable and explosive oil and other chemical liquids, specially for the precise measurement of liquid level in small tanks.The single fiber sensor head was investigated experimentally and theoretically. Two kinds of sensor head fabrication methods were demonstrated and compared, which are the electrical arc melting and mechanical grinding respectively. A mathematic model of fiber tip reflection was established by the method of ray-tracing. It is found that the sensor tip with a 90° conical tip has the maximum optical modulation depth. The contamination mechanism of the sensor head has been studied for increasing the operating life time of the sensor system. Two different working medium, oil and water, were tested respectively. A new improved method of fiber tip fabrication was put forward, which is a coating technique of sol-gel TiO2 film on the surface of the fiber tip for improve its anti-pollution capacity. The experiment result in the water demonstrated that the working life of the coated fiber tip was much better than uncoated one.