一种新型光纤光栅应变计的温度补偿方法研究

Research on New Temperature Compensation Method for Fiber Bragg Grating Strain Sensor

目的:为了降低光纤光栅应变传感器的温度影响程度,提高监测盾构隧道结构应变的准确性,需对该类传感器的温度补偿方法进行优化。方法:介绍了一种常用光纤光栅应变传感器的结构及工作原理,采用铝合金和铜2种已知热膨胀系数的材料作为传感器附着基底,开展了自由及约束状态下光纤光栅应变传感器的温度循环试验,基于测试结果,提出了在2种状态下的温度补偿方式,并对补偿后的可靠性进行了分析。将该类传感器应用于宁波轨道交通1号线天童庄出入段盾构隧道的管片应变监测,获取了温度影响下应变传感器的测试结果。结果及结论:相关试验及应用表明:在自由状态下应变计的温度系数近似等于光栅本身光学效应的温度系数加上温补光栅附着金属的膨胀系数。在约束下,应变光栅的温度系数近似等于光栅本身光学效应的温度系数加上待测基材的膨胀系数,该温度补偿方法能有效减少光纤光栅应变计进行温度补偿的误差,实际应用中得到了可靠的监测效果。

Objective:In order to reduce the impact of temperature on FBG(fiber Bragg grating)strain sensors and improve the accuracy of monitoring strain in shield tunnel structures,the temperature compensation method for this type of sensor needs to be optimized.Method:The structure and working principle of a commonly used FBG strain sensor are introduced.Two known thermal expansion coefficient materials,aluminum alloy and copper,are used as sensor attachment substrates.Temperature cycling tests are conducted in free and constrained states.Based on the test results,temperature compensation methods are proposed for two states,and the reliability of the compensation is analyzed.The sensors are applied to the strain monitoring of shield tunnel segment at the Tiantongzhuang Depot access of Ningbo Metro Line 1,and the test results of the strain sensors under temperature influence are obtained.Result&Conclusion:Relevant tests and applications show that the temperature coefficient of the strain sensor in free-state is approximately equal to the temperature coefficient of the grating′s own optical effect plus the expansion coefficient of the temperature-compensation grating attachment metal.In the constrained state,the temperature coefficient of the strain grating is approximately equal to the temperature coefficient of the grating′s own optical effect plus the expansion coefficient of the substrate material ready for testing.This temperature compensation method effectively reduces the error in temperature compensation for FBG strain sensors,resulting in reliable monitoring in practical applications.