Polymer Optical Fiber Continuous Liquid Level Sensor for Dynamic Measurement

The effect of cladding mode frustrated total internal reflection (CMFTIR) in macrobend polymer optical fiber is first used to achieve continuous liquid-level dynamic sensing. However, the difficulty is that the CMFTIR sensing signal is so weak as to be drowned into background noises. To solve this problem, the sensors with the parallel (twisted) helical macrobend coupling structure (PHMBCS and THMBCS) are designed to obtain dark-filed coupling signal which is found to be excellent on signal-to-noise ratio. The experiment shows that the sensor can dynamically measure the continuous change of water level, and the curve tracks are related to the speed of water flow. The result offers the possibility to calculate the real-time speeds of the level change. The measurement range of PHMBCS is 70 mm, and THMBCS reaches 350 mm. Better linearity is realized using THMBCS. The average level resolutions of the sensors with two structures are both less than 0.3 mm, and the measurement results show a very good consistency. The sensor, which has a good prospect of application, meets the needs of dynamic measurement of liquid level, especially under complicated electromagnetic and flammable environment.