Fiber-Optic Closed-Loop Liquid-Level Control System Ein Fiber-Optisches Flussigkeitsfullstand Mess- und Kontrollsystem

摘要

This paper describes a novel point fiber-optic liquid-level sensor. The sensor head is made of two fusion-spliced multimode fibers and the light at its boundary is sensitive to the refractive index of the surrounding medium. THe sensor's response time to the four different liquids is experimentally studied. A closed-loop control system is established with two sensor heads controlling the water level within a range corresponding to the two sensor's positions, each has a level-resolution better than ±0.15 mm. A special sensor holder structure is proposed to minimize the droplet collection problem puzzling with this type of sensors. The system has been operated during a long-term continuous trial with water and remains operational for one year. The simpleness in fabrication and the non-electrical nature in field make the sensor competitive to traditional liquid-level sensors in chemical industry and other harsh environmental applications.