Measuring Frequencies Of The Turbine Blade Based On Fiber Bragg Grating

Fiber Bragg grating (FBG) is a novel optics fiber sensing unit with many advantages such as light weight, slim body, low loss transmission, chemical stability, immunity to electromagnetic interference etc., and possesses special virtues, immunity to laser resource instability, buried easily into the materials and made a distributed sensing network. This paper presents a measuring technique about the frequencies of the turbine blade based on the FBG. The blade is a twisted one made up of hardening and tempering 2Cr13-5 with T-type blade root in low pressure cylinder, and 25 2mm length without shroud band and lashing wire. In this work, two FBGs were used, one was annealed with package, while the other one wasn't. The frequencies of the blade have been measured without constraint condition by that two gratings, the former are 1005.00Hz, 2048.00Hz, 2297.25Hz, 2786.00Hz, the latter are 1005.00Hz, 2048.00Hz, 2297.25Hz, 2786.00Hz. The results were obtained with constraint condition by that two FBGs, the former are 921.50Hz, 1482.00Hz, 2454.75Hz, the latter are 927.00Hz, 1479.75Hz, 2472.75Hz. An acceleration transducer was also employed in this work to make a comparison, the results without constraint condition are 1005.00Hz, 2048.00Hz, 2297.00Hz, 2786.00Hz, while the ones with constraint condition are 917.00Hz, 1480.75Hz, 2454.25Hz. Obviously, it is a feasible method to measure the frequencies based on the FBG because their results are approximately equal. Furthermore, interrogator and wavelength division multiplexing (WDM) of the FBG, which is beneficial to make sensing network to measure many parameters simultaneously, have also been investigated.