Fiber-optic high-temperature sensing system and its field application

This paper presents the development of a sapphire-based fiber-optic sensing system for temperature monitoring in harsh environment, including sensor and system design, implementation, laboratory tests and field demonstration. The sensor is built with single-crystal sapphire fiber and sapphire wafer. As the sensing element, the wafer constitutes an extrinsic Fabry-Perot interferometer (EFPI) by its two surfaces. Its optical thickness has significant thermal dependence and provides temperature information through white light interferometry. The sensors were tested to 1600°C with 0.2% full scale accuracy and 0.5°C resolution. They were further demonstrated in industrial environment. A complete sensing system was developed around the sensor for temperature monitoring in a coal gasifier at the Tampa Electric Company's Polk Power Station. It consists of three major components: 1) Sensors and their packaging which were installed in the coal gasifier, 2) Optical interrogation unit for detection and transmission of sensor signal, and 3) Processing and control unit for signal demodulation. The system continuously operated and delivered temperature readings for seven months.