Twisted tapered plastic optical fibers for continuous liquid level sensing

Abstract A low-cost liquid level sensor capable of continuous liquid level sensing is proposed in this work. The sensor is based on twisted tapered plastic optical fibers (POFs) which is fabricated by twisting the tapered POFs around each other. The tapered structure could enhance the evanescent field and the light transmission from one POF to the other. The changes of liquid level can lead to the variations of light intensity at two output ends of the probe and by monitoring the changes of the coupling ratio, the liquid level can be measured. Experimental results show that a linear response with the sensitivity of 0.65%/mm and response time of 3.2 s is obtained when the probe is with active fiber diameter of 150 µm and the passive fiber diameter of 250 µm. In addition, the influences of tapered POFs diameters, the liquid refractive index and the temperature on the sensing performance are investigated, and the repeatability and the dynamic performance for the probe are also tested.