Strain sensing is widely used in safety monitoring of high temperature pressure pipes in oil companies and power plants. A novel high-temperature strain sensor was researched based on FBG(Fiber Bragg Grating) and the elastic high-temperature alloy in this paper. First, high-temperature Polyimide fiber FBG was prepared and tested in high temperature chamber. Second, a novel T strain gauge structure of three FBG was designed and fabricated on the elastic high-temperature alloy. This strain gauge could be applied in measurement of two-dimensional high-temperature strain sensing. In the end, a equi-intensity cantilever was adopted to test the high-temperature FBG strain sensor and testing results verified that the T type FBG strain sensor was suitable for high-temperature strain sensing with reliable performance in 300°C environment.
Fiber Bragg Grating (FBG) sensing technology is widely used in detection of temperature, strain and etc. Now the application of FBG sensor is limited below 200°C. Application over 200°C is still an engineering challenge since no suitable FBG strain gauge. In this paper, FBG strain gauge structure which consists of three FBGs is designed and fabricated based on the theoretical strain and stress analysis. This strain gauge can be used for the real-time high temperature strain monitoring situation. The elastic high-temperature alloy (10MoWVNb) is chosen as the substrate. The three FBGs with a similar performance are fabricated on the substrate by high-temperature glue. Among the three FBGs, FBG1 is used for the horizontal strain monitoring, FBG2 is used for the longitudinal strain monitoring, and FGB3 is used for high temperature cross-sensitive compensation. The fabricated high temperature FBG gauge is demonstrated suitable for high temperature strain monitoring by experiment.
Pressure pipelines have been applied widely in the chemical industry, the petroleum enterprises and the electrical power plants. Leakage and explosion accidents happened frequently owing to the weakness of the pressure pipeline. To monitoring the pressure pipeline weakness, a novel method is presented by using optical FBG (FBG: Fiber Bragg Grating) sensors to carry on the real-time monitoring of the pressure piping surface strains. A typical pressure pipeline was fabricated with weak position of L shaped, Tee shaped and U shaped joints. The strains of the weak position were analyzed by the ANSYS software, and then the same weak positions were monitored by experimental method of FBG sensor. The FBG sensor was verified a feasible means to monitoring the pressure pipeline by comparing the ANSYS software results with the experimental results of FBG sensors.
An online safety warning system based on FBG sensing elements was developed to prevent the leakage or explosion of the high temperature and pressure pipeline. On the basis of using optical sensing interrogator, a computer monitoring software has been designed to monitor the surface strain of the high temperature pipeline, and this software was written in LabVIEW,including signal analysis, real-time view, data management and related functions. Combining the software and GSM module, a SMS warning and reversing controlling system has been developed into the remote safety warning system.
Micro-resonators could be fabricated directly on the optical fiber top by micro mechanical process. The micro optical fiber resonator has more great advantages comparing with the traditional optical excited micro silicon resonators, such as being optically positioned easily between the resonator and the optical fiber end. By this way, the optical excited light through the fiber core is thus put on the micro resonator accurately and then partially reflected by the Fabry-Perot interferometer formed between fiber top and resonator surface. The reflected light from F-P interferometer was sent to the opto-electric detector PIN to demodulate the detected parameter. A matched metal layer can be deposited atop of the resonator in order to increase the optical excitation efficiency. Firstly mechanism analysis of optical excited bi-layered resonator is given by fully considering Longitudinal thermal strain effect and Bi-coating effect, and then the typical theoretical models were setup including the resonating frequency and resonant amplitude, and temperature sensing feature was simulated by computer software. The simulation results indicated that the average frequency sensitivity of temperature sensing is about 29Hz/°C.
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