Study On Multi-points Measuring Technology For Fiber Fabry-Perot Strain Sensing

Large bridge plays an important role in traffic, military and daily life. Health monitoring for large bridge is an important means to insure it run safely. Strain, which reflects the stress and damage condition of the structure, is the most important parameter in bridge monitoring. For the huge body and complicated structure, it always needs dozens of strain sensors fixed on key positions to reflect the state of bridge completely.Compared with traditional electric resistance strain gauge and fiber grating sensor, fiber Fabry-Perot strain sensor has the advantages of simple structure, corrosion resistance, anti electromagnetic interference, low sensitivity towards temperature, excellent long-time stability, and very suitable to use in bridge monitoring. For the principle of the fiber Fabry-Perot sensor, the application is limited because of the bad multiplexing ability.At present, methods for multi-points measurement of fiber Fabry-Perot sensor are always sensor multiplexing and changing measure channel using optical switch. The research on sensor multiplexing still remains in the tow sensors series or parallel connection. The multiplexing ability is limited. Using switching channel method, the cost will be increased with the channel number.To measure more fiber Fabry-Perot strain sensors with less cost, research below is carried out.1. The basic principle and modulation demodulation method of fiber Fabry-Perot sensor is analyzed. Discrete gap transform method is chosen for demodulation.2. Different technologies of sensor multiplexing are studied. Using space division multiplex, multi strain sensors can be measured without any other additional device. Series and parallel mixed multiplexing structure is proposed. The characteristic of the output signal is analyzed. The experimentation of four sensors mixed multiplexing is set up, and the result shows that mixed multiplexing is feasible.3. Base on the requirement of the number of measure points and the stability in bridge strain monitoring, the hardware system and measuring software of multi-channel stain measuring apparatus for fiber Fabry-Perot sensors are designed. This system is able to monitor strain state independently, and measuring software can be called by other application software to measure strain. In long term monitoring, measuring...