The strain of structure is an important parameter in the structural health monitoring of spacecraft. FBG (Fiber Bragg Grating) sensors have the advantages of small size, light weight, anti-electromagnetic interference andeasy to network, which is suitable for the strain measurement of spacecraft structure. In order to improve the accuracy and in-orbit reliability of the strain measurement of spacecraft structure, an FBG strain sensor with metal encapsulation is designed, in which the structure of metal elastomer is optimized by finite element analysis. Meanwhile, a calibration method for the FBG strain sensor is presented, in which the clamping displacement sensitivity, strain transfer coefficient and temperature compensation coefficient are calculated. At last, the FBG strain sensor is verified by ground environmental tests, whose relative error of strain measurement is less than 1.6%, and it has been successfully applied to the in-orbit real-time structure strain measurement of the new spacecraft of China.
In order to achieve the high accuracy measurement of strain parameters of spacecraft structure with optical fiber sensors, a demodulation approach based on the composite wavelength reference of Fabry-Perot(F-P) etalon and acetylene(C2H2) gas cell is presented. In the approach, an adaptive threshold method is used to resolve the difficulty of peaks searching of F-P etalon waveform, which is caused by poor flatness of light source. Meanwhile, the strain sensitivity coefficient of optical fiber sensors is accurately obtained by a two-step method, so as to eliminate the influences of the sensor substrate and the bonding layer on the measurement. Finally, the measuring results of strain sensors are compensated with the temperature sensor to improve the measurement precision of strain parameters. The experiments results show that when the temperature variation range is 85°C(-25°C~60°C), the FBG wavelength demodulation deviation of the approach in this paper is within 3pm, while the relative measuring error of strain parameters is within 4%, which can realize the stable and high-precision measurement of the strain parameters of spacecraft structure.
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