What are the principles and applications of fiber optic sensors in process industries?

Fiber optic sensors use light properties (intensity, phase, wavelength, polarization) for measurement. Types include: Fiber Bragg Grating (FBG) for distributed temperature and strain sensing (wavelength shift with temperature/strain), intensity-based sensors for level and proximity, interferometric sensors for high-precision displacement and vibration. Advantages: immunity to EMI, intrinsically safe, distributed sensing over long distances (DTS systems for pipeline leak detection), multi-point measurement on single fiber, and operation in harsh environments. Applications: downhole temperature profiling, pipeline integrity monitoring, fire detection, and transformer winding temperature.