Modeling Reflections in a Complex Cable Structure with Impedance Mismatches

Abstract

Reflections may occur in cables and transmission lines due to several reasons, such as junctions, so-called soft faults, or due to a mismatch between the terminating resistors and the characteristic impedance of the transmission line in the worst case as short circuits or open circuits, so called hard faults. For fault diagnostic based on Time-domain Reflectometry in complex cables, it is important to model the influence of impedance mismatches on the reflected signals to attribute the reflection peaks to the corresponding fault. In this paper, we propose an all-in-one model for the effect of impedance mismatches i.e. junctions, soft and hard faults, and mismatch between the cables and the connected devices at their ports. The model validation is carried out on a cable network modeled with distributed RLCG cable models. For simulation, a cable network has been defined with a direct path of 240 m, including two soft faults and two junctions, with an impedance mismatch between the cable and the reflectometer device. The results show good conformity between the analytical model and the simulation results. The deviations are in the range of 0.955 mV corresponding to 0.312 % of the simulated reflected signal, and the soft faults showed the highest participation in voltage deviation.