Wang Kai, Lin Chih-Ping, Jheng Wei-Hao
Department of Civil Engineering, National Chiao Tung University, No. 1001 Ta-Hsueh Rd., Hsinchu City 300, Taiwan.
Yijhu Township Office, No. 389, Renli Village, Yijhu Town, Chiayi County 624, Taiwan.
Sensors (Basel). 2020 Nov 21;20(22):6665. doi: 10.3390/s20226665.
The use of time domain reflectometry (TDR) for real-time monitoring of bridge scour process has gone through several stages of development. The recently-proposed concept of bundled TDR sensing cable, in which two sets of insulated steel strands are twisted around and connected to a central coaxial cable to form a compact sensing cable, is a major change that has several advantages including the bottom-up sensing mechanism. Nevertheless, there is big room for improving its measurement sensitivity and signal to noise ratio (SNR). Changes in waveguide configuration also need to be made to avoid the adverse effect of insulation abrasion observed in field implementation. This study evaluated three new conductor and insulator configurations for constructing the sensing waveguide, including a balanced two-conductor waveguide (Type I), an unbalanced three-conductor waveguide with insulation coating on the middle conductor (Type II) and an unbalanced three-conductor with insulation coating on the two outer conductors (Type III). In all cases, the spacing between the two sets of steel strands (i.e., the waveguide conductors) was especially enlarged by replacing some steel strands with non-conductor wires to increases measurement sensitivity and avoid shorted conditions due to insulation abrasion. Experimental results show that Type III has the best performance on all counts. A new improved TDR sensing cable was hence proposed based on Type III configuration. Its performance was further evaluated by a full-scale experiment to take into consideration the long range of measurement in most field conditions. Detailed discussions on improvements of measurement sensitivity and SNR, limitation of sensing range, and mitigating the adverse effect of insulation abrasion are presented.
将时域反射仪（TDR）用于桥梁冲刷过程的实时监测经历了几个发展阶段。最近提出的捆绑式TDR传感电缆概念，即两组绝缘钢绞线缠绕并连接到一根中心同轴电缆上形成紧凑的传感电缆，是一项重大变革，具有包括自下而上传感机制在内的诸多优点。然而，在测量灵敏度和信噪比（SNR）方面仍有很大的提升空间。还需要对波导配置进行改变，以避免在现场实施中观察到的绝缘磨损的不利影响。本研究评估了三种用于构建传感波导的新型导体和绝缘体配置，包括平衡双导体波导（I型）、中间导体带有绝缘涂层的不平衡三导体波导（II型）以及两个外部导体带有绝缘涂层的不平衡三导体波导（III型）。在所有情况下，通过用非导体线替换一些钢绞线来特别增大两组钢绞线（即波导导体）之间的间距，以提高测量灵敏度并避免因绝缘磨损导致的短路情况。实验结果表明，III型在各方面表现最佳。因此，基于III型配置提出了一种改进的TDR传感电缆。通过全尺寸实验进一步评估了其性能，以考虑大多数现场条件下的长距离测量。文中还对测量灵敏度和信噪比的提高、传感范围的限制以及减轻绝缘磨损的不利影响进行了详细讨论。
