A liquid level sensor based on spiral macro-bending plastic optical fiber

Abstract

Liquid level sensing refers to the monitoring of liquid level height information under working or static conditions. Compared with traditional liquid level monitoring methods, optical fiber liquid level sensor has advantages of immunity to electromagnetic interference, excellent electronic insulation and remote operation. The light propagates in the fiber through total internal reflection. When the fiber is bent, a large number of cladding modes will be generated. These cladding modes will have Fresnel reflection at the interface between the bent cladding and environment. When the high refractive index medium is in contact with or close to the fiber cladding, part of the cladding mode light will leak into the external medium, resulting in light energy loss. Therefore, according to the basic working principle of optical fiber macro-bending loss, a new type of spiral plastic optical fiber (POF) liquid level sensor was designed. The POF with a diameter of 0.5 mm was used as the sensing optical fiber, and then it was spirally wound and fixed on a self-designed square cylinder. The liquid level was monitored by the designed sensor, and the effects of environment and liquid temperature on the test process were analyzed. The results show: (i) the measuring range of the liquid level sensing system is within 80 mm and it has good repeatability; (ii) the resolution and sensitivity are 1.03 mm and 0.088 dB/mm, respectively; (iii) the influence of temperature on the sensor is less than 0.06 dB/℃.