Research On Optical Fiber Sensors Of Multi-parameter Test In High-temperature Pipelines

High-temperature pipelines are widely used in large-scale nuclear power plants,and their safe operation is very important to the safety of human life and the reliability in nuclear power plants.Therefore,it is necessary to monitor the health status of pipeline structure of nuclear power system in real time.High-temperature pipelines operate under high pressure,strong vibration and strong electromagnetic interference,which makes it difficult for traditional electronic sensors to work normally in this environment.However,fiber optic sensors have the advantages of anti-electromagnetic interference,resistance to high temperature and high pressure,et al,showing great application potential for monitoring of high-temperature pipelines in nuclear power plants.In order to meet the requirements of pressure and acceleration monitoring in hightemperature pipelines,and then detect whether leakage and vibration damage occur in pipelines.In this thesis,two kinds of high temperature resistant optical fiber sensors have been developed,including fiber Bragg Grating(FBG)pressure sensors and fiber FabryPerot(F-P)acceleration sensors.The main research work is as follows:For the measurement of pressure parameters,a FBG pressure sensor based on rectangular diaphragm bas been designed and encapsulated.The FBG for measuring pressure have been encapsulated by two ways: full-cover pasting and pre-pull pasting at both ends,and the encapsulated sensors are verified by experiments.By comparing the temperature and pressure cross sensitivity of the two encapsulated pressure sensors,the results show that the pre-pull pasting encapsulated pressure sensor at both ends has less cross sensitivity.The pressure sensor with pre-pull pasting at both ends has been tested at200℃ for 2 hours,and the pressure characteristics are studied in the pressure range of0～11MPa,it shows that the pressure sensitivity before and after the high temperature is basically the same,and the pressure sensing characteristics are better.For the measurement of acceleration parameters,based on the optical fiber F-P acceleration sensing model of the double beam,the fiber F-P acceleration sensor has been designed and manufactured by using metal double beam,and the related characteristics are studied.In consideration of the high temperature and high pressure environment of pipelines operation,two acceleration sensors with different cavity lengths have been fabricated by laser welding,and the static experiments shows that the sensitivity of the accelerometer with smaller cavity length is higher.The dynamic response characteristics and temperature characteristics of the acceleration sensor with small cavity length are studied,the results show that the frequency response of the sensor is good in the range of10～200Hz,but the cross sensitivity of temperature acceleration is large.In order to reduce the influence of temperature on acceleration measurement,an optical fiber F-P acceleration sensor with small volume and light weight has been designed and manufactured by using a quartz double beam with aluminum plated film as elastic structure.The research shows that the sensor has good frequency response characteristics in 10 ～ 200 Hz frequency range,and the acceleration sensitivity is0.559nm/g,the resolution is 2.25 mg,and the temperature acceleration cross sensitivity of the sensor in the temperature range of 50～250℃ is 0.049g/℃.