Abstract

This study has designed, developed, and tested a high temperature sensor based on Fiber Bragg grating. The new introduced interrogation system makes the sensor suitable for installation inside the power transformer. Unlike the existing fiber Bragg grating based temperature sensors, the interrogation system of the sensor is based on amplitude modulation (AM). The distinctive characteristics of the designed temperature sensor, in addition to inherent advantages of FBG is, its real-time monitoring, small size, and low cost. The sensor is tested in harsh environment at temperature starting from -27 ºC to 400 ºC. The long-term stability and reliability of the designed sensors of one sensor head is tested in furnace at 400 ºC for 338 hours. Furthermore, the sensor head was under test in 600 ºC for about 18 hours. The sensor head which is used in this experiment is fiber Bragg grating Corning SMF-28, Ge-doped optical fibers with 4% Ge content in its core. It was loaded with hydrogen prior to writing with 248 nm excimer laser. The Bragg wavelength of the two prepared sensors head for this work is around 1530 nm and 1550 nm.
In this study, we used Amplified spontaneous emission (ASE) light source as an input light for the sensor head. ASE light source makes it possible to have linear input light in two different ranges with 4 nm span. The sensors head Bragg wavelength is designed in the range in which the ASE light source spectrum is linear. The sensor has the Photodiode (PD) to convert the Bragg reflected spectrum power into its equivalent current.