基于锚固区外置光纤光栅传感器的FAST工程拉索索力监测研究

Monitoring Cable Force of FAST Project Based on Fiber Bragg Grating Sensor External Installed on Anchorage Zone

500 m口径球面射电望远镜(Five-hundred-meter aperture spherical radio telescope,FAST)工程是我国重大科学工程。索网作为反射面的主要支承结构以及角度调整机构,其索力的实时有效监测对该工程的安全评估与维护起重要作用。提出在拉索的锚杯外壁耦合光纤光栅(Fiber Bragg grating,FBG)传感器测量应变值换算索力的方法。详细理论分析了拉索锚杯的轴向应力应变分布规律,推导出其与拉索索力的关系式;据此选择采用量程为1500με的光纤应变计,沿轴向安装于锚杯内孔大端附近的外壁;并采取了专用安装底座和保护外壳将补偿的温度传感器与应变传感器进行一体固定保护,确保了传感器的安全耐用及温度一体性。该工程的316根拉索索力监测使用了FBG传感器,索网安装完毕后均存活有效。在索网调节期间,将B区边缘索FBG传感器所测数据与辅助调索的测力传感器的进行比较,相对误差在5%以内,满足工程需求。

The five-hundred-meter aperture spherical radio telescope（FAST） is a major scientific project in China. The cable net is the main support structure and angle adjusting mechanism of reflector, which effective real-time health monitoring to the cable force plays a vital role in evaluating the safety and maintenance of FAST. A measurement method for cable force by coupling the fiber Bragg grating（FBG） sensor on the surface of cable anchoring cup is presented. The axial stress distribution of the anchoring cup is analyzed theoretically, which relationship with cable force is derived. FBG sensor with measure range of 1 500μ is selected and installed along the axial direction on the outer surface of the anchoring cup near the bigger end of inner cone hole. The safety, durability and temperature integration of sensor are secured by the special installation base and protective shell. 316 cables are installed FBG sensors to monitor the cable tension force and each senor is effective after cable net knitting. During the adjustment of the cable net, the measured data of the FBG sensors of the edge cable of the B area is compared with the force measuring by the adjustment system, and the relative error is less than 5%, which meets the engineering requirements.