A team of researchers at NASA’s Armstrong Flight Research Center have developed a new manufacturing process that improves the ability of fiber optic sensing systems to measure temperature and liquid levels when operating in humid environments. The process involves eliminating moisture from the optical fiber coating, then completing the sensor assembly within humidity-controlled conditions. The resulting sensor hardware provides precise and accurate measurements even when operating in a humid environment. Originally designed to monitor a rocket’s cryogenic fuel levels in conjunction with NASA’s patented Fiber Optic Sensing System (FOSS), this technology can be used in many industrial, food, and medical applications.
Armstrong’s multi-patented FOSS system has long been used to measure temperature and liquid levels in cryogenic environments. When the sensing system’s fibers trapped humidity from the surrounding environment before their submersion into cryogenic liquids, the moisture adversely affected outputs. The new manufacturing process solves this problem, increasing reliability and accuracy not only of NASA’s FOSS but also any fiber optic sensing system.
Armstrong has developed a two-step process to assemble the sensors. First, the bare sensor fiber is inserted into an oven to expel all moisture from the fiber coating. Then, the moisture-free fiber is placed inside a humidity-controlled glovebox to prevent it from absorbing any new moisture. While inside the glovebox, the fiber is inserted into a loose barrier tubing that isolates the fiber yet is still thin enough to provide adequate thermal transfer. The tubing can be further purged with various gases while it is inside the glovebox to provide additional moisture isolation.
This innovation is particularly useful for fiber optic systems that measure temperature and that identify any temperature stratifications within cryogenic liquids. The innovation eliminates erroneous readings that can occur due to moisture collection on the fiber sensors.