Distributed Temperature Measurements Along a Heated Tube Using All-Fiber Bragg Grating Optical Sensors

Abstract

This study presents the application of Optical Frequency Domain Reflectometry (OFDR) technique for distributed fiber optic temperature measurements along a heated tube. The sensor consisted of a 0.5 m long commercially available all-Fiber Bragg Grating (FBG) fiber with 9 mm grating length, 10 mm pitch spacing, and a central wavelength of 1550 nm. The all-FBG sensors were installed along the outside surface of a heated Inconel tube with an outside diameter of 13 mm and a length of 500 mm, and used to measure surface temperatures during free-convection tests at atmospheric pressure in both air and water. The OFDR technique measures the reflected spectral shifts from all-FBG sensors, which are then converted to temperatures through calibration using thermocouples. Temperature distributions recorded along the heated tube up to 160 °C in air, and up to 76 °C in water, are reported to demonstrate sensor performance. Preliminary results show that all-FBG sensor accuracy is within ±5% of thermocouple measurements at steady-state conditions.