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.

中文翻译：

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基于TDR的新型传感电缆，可提高桥梁冲刷监测的性能

时域反射法（TDR）用于桥梁冲刷过程的实时监控已经历了几个开发阶段。最近提出的捆绑式TDR传感电缆的概念是一项重大变化，它具有两方面的优势，其中包括两组绝缘钢绞线并连接到中心同轴电缆，从而形成紧凑的传感电缆，该优点包括自下而上的传感机制。尽管如此，仍有很大的空间可以提高其测量灵敏度和信噪比（SNR）。还需要改变波导配置，以避免在现场实施中观察到的绝缘磨损的不利影响。这项研究评估了用于构造感应波导的三种新型导体和绝缘体配置，包括平衡的两导体波导（I型），一个不平衡的三导体波导，中间导体上有绝缘涂层（II型），不平衡的三导体波导，两个外导体上有绝缘涂层（III型）。在所有情况下，特别是通过用非导线代替某些钢绞线来扩大两组钢绞线（即波导导体）之间的间距，以提高测量灵敏度并避免由于绝缘磨损而导致的短路情况。实验结果表明，III型在所有方面均具有最佳性能。因此，基于III型配置提出了一种新的改进的TDR传感电缆。考虑到在大多数现场条件下的长距离测量，通过全面的实验进一步评估了其性能。有关提高测量灵敏度和SNR的详细讨论，