Track Sensors System Based On Fiber Bragg Gratings

The track sensors system based on fiber Bragg grating (FBG) is mainly used for the rail surface strain sensing. Taking advantage of the measured strain, such information as the load and temperature stress impact on the rail can be obtained. In order to access the track deformation by quasi-distributed measuring the strain of rail, a number of FBG sensors should be installed on the rails and networked.In this paper the track sensors system technology utilizing FBG is studied from two aspects of theoretical analysis and experimental verification. Firstly, the mechanism of FBG sensor is introduced, and the model between FBG wavelength shift and strain induced by the wheel load or temperature stress is produced. Then in accordance with the principles of a point to a line, the design for different sensors and sensor networks is described.As the demodulation technology based on matched gratings is free from the temperature disturbance, a sensing technology solution that can achieve the rail location strain is given with the analysis of strain and deformation in different rail conditions. The solution has a good performance.As the demodulation technology based on the matched gratings needs a pair of FBGs whose center wavelengths of the reflection spectra are identical, a demodulation method based on semi-freedom package grating is proposed. Then, the wavelength shift can be obtained by the intensity demodulation method using only a grating. Numerical simulation and experiment results show that semi-freedom packaged fiber grating sensor can be used for strain measuring from 0 to 500μεand has a good linearity.Finally, according to the analysis of track sensors system, a multiplexed fiber grating sensor network using the optical time-domain-reflectometry technology is designed in accordance with the characteristics such as linear distribution, long distance and large number of measurement points. And optical code division multiple access (OCDMA) technology is used to solve the noise problem. In order to eliminate the crosstalk, the Golay complementary sequences with a close-zero cross-correlation are used. Therefore, all the FBG sensors without overlapped reflection spectra can be demodulated simultaneously. Numerical simulation results indicate that FBG sensors can be accurately demodulated without multiple-access-interference (MAI) taking advantages of the Golay sequence.