Deflection is one of the key parameters that reflects the state of a bridge. However, deflection measurement is difficult for a bridge that is under operation. Most existing sensors and measuring techniques often do not meet the requirements for health monitoring for various types of bridges. Therefore, based on changes of optical fiber intensity, a novel sensing system using connected pipes to measure bridge deflection in different positions is proposed in this paper. As an absolute reference, the liquid level position along the structure is adopted for the deflection measurement, and an additional external reference to the ground is not needed in this system. The proposed system consists of three parts: connected pipes to connect the measurement points along the structure, liquid to fill in the connected pipes, and the sensing element to detect the change of level. A plastic optical fiber sensor based on the intensity change is used as the sensing element of the developed system. Then, a set of experimental tests are conducted for performance evaluation purposes. Results show that this system has an accurate linear response and high reliability under various environmental conditions. The deflection of the test beam measured by the sensor agrees with linear variable differential transformer (LVDT) within an error margin of 2.1%. The proposed system shows great potential applicability for future health monitoring of long-span bridges.

中文翻译：

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用于桥挠度测量的塑料光纤传感系统。

挠度是反映桥梁状态的关键参数之一。然而，挠度测量对于正在运行的桥梁是困难的。现有的大多数传感器和测量技术通常都无法满足各种类型桥梁的健康监测要求。因此，基于光纤强度的变化，本文提出了一种新的传感系统，该系统使用连接的管道来测量桥梁在不同位置的挠度。作为绝对参考，将采用沿结构的液位位置进行挠度测量，并且在此系统中不需要对地面的附加外部参考。拟议的系统由三部分组成：用于连接沿结构的测量点的连接管，用于填充连接管的液体，感测元件检测电平的变化。基于强度变化的塑料光纤传感器被用作开发系统的传感元件。然后，进行一组实验测试以评估性能。结果表明，该系统在各种环境条件下均具有精确的线性响应和高可靠性。传感器测得的测试光束的偏转与线性可变差动变压器（LVDT）的误差范围为2.1％。拟议的系统在未来大跨度桥梁健康监测方面显示出巨大的潜在适用性。结果表明，该系统在各种环境条件下均具有精确的线性响应和高可靠性。传感器测得的测试光束的偏转与线性可变差动变压器（LVDT）的误差范围为2.1％。拟议的系统在未来大跨度桥梁健康监测方面显示出巨大的潜在适用性。结果表明，该系统在各种环境条件下均具有精确的线性响应和高可靠性。传感器测得的测试光束的偏转与线性可变差动变压器（LVDT）的误差范围为2.1％。拟议的系统在未来大跨度桥梁健康监测方面显示出巨大的潜在适用性。