Fault location on shielded cables: Electromagnetic modelling and improved measurement data processing

Abstract: This paper analyses the performance of the time domain reflectometry (TDR) technique when it is applied to the location of faults on cables. Different types of defects, which can arise on coaxial cables, are modelled and their reflection coefficients are calculated. The results, validated by experimental data, are compared to the typical noise that affects this kind of measurement to assess the sensitivity of the technique. Shield damage to a shielded twisted pair and a shielded multiwire cable is also examined: these examples represent more critical situations because the effect of cable and mismatching losses limits the dynamic range of the measurement. In both cases, the TDR allows us to locate faults that strongly affect the propagation of the signal on the transmission line, but the reflections produced by small defects are often masked by the noise. A data processing technique based on the comparison with a reference measurement and the use of the statistical correlation are then implemented. In this way, the reflections produced by the faults are much more visible and an overall enhancement of the technique sensitivity is achieved.