Research On Fiber Bragg Grating Seepage Pressure Sensor And The Temperature Compensation Performance

The traditional seepage pressure monitoring system based on mechanical and electrical test equipment is difficult to meet the need of actual measurement because of the widespread weaknesses such as weak electromagnetic interference resistance,poor long-term stability,zero drift and dynamic drift large faults.In recent years,the fiber Bragg grating(FBG)as the new generation of smart sensing technique has a broad application prospect in the field of structural health monitoring of large civil engineering,because it has the advantages of simple structure,good reliability,high corrosion resistance,strong electromagnetic interference resistance,and being easy to reuse network and embed.Although the study of the seepage pressure measurement by using FBG has achieved some success,the research on this field remains to be further explored,especially in the technology of fiber Bragg grating osmotic pressure sensor designing.Aiming at designing the FBG seepage pressure sensors for different using environment and improving their various performance indicators,corresponding research work was carried out as follows:(1)The thesis firstly summarizes predecessor's research results.In the field of pressure measurement,optical fiber sensing technologies are mainly EFPI,F-P and FBG,as well as the technology development by combining FBG with F-P.By comparison,the FBG sensor with high precision is more suitable for osmotic pressure measurement.In this thesis,the sensor was redesigned based on the shortcomings of the existing FBG osmotic pressure sensor to improve the performance of the sensor.(2)Secondly,the FBG's strain sensing properties and temperature sensing properties are analyzed in theory,and the mechanism of its temperature strain cross-sensitivity characteristics is understood further.For FBG's strain and temperature cross-sensitivity,it must make temperature compensation in the osmotic pressure measurement to improve the accuracy.At the same time,the different methods of temperature compensation are analyzed and selected for specific applied environment.(3)And then two types of osmotic pressure sensors,which are FBG osmotic pressure sensor with corrugated pipe and equal strength beam and FBG osmotic pressure sensor with flat diaphragm structure,are designed based on the fiber Bragg grating strain sensitive features.Differential sensing structure model and pull rod sensing structure model are established in theory,and the main mechanical performances of sensitive element are analyzed through simulated analysis.Also the specific parameters of various components are determined by using the SoildWorks and ANSYS software to model and simulate.(4)According to the design drawings,two sensors are processed and assembled,and the FBG is pasted.Then various performance tests are completed for the sensor.According to the pressure experiments and temperature compensation experiments,two sensors have good pressure sensing properties.And through the temperature compensation structure,the linearity,repeatability and hysteresis characteristics are greatly improved,so the measurement accuracy of the sensor is also improved.