A Novel Pulse Echo Correlation Tool for Transmission Path Testing and Fault Diagnosis

Abstract

In this paper a novel pulse sequence testing methodology is presented [22] as an alternative to Time Domain Reflectometry (TDR) for transmission line health condition monitoring, faultfinding and location. This scheme uses Pseudo Random Binary Sequence (PRBS) injection for transmission line testing and fault location with cross correlation (CCR) techniques to build a unique response profile, as a characteristic signature, to identify the type of fault, if any, or load termination present as well as its distance from the point of stimulus insertion. This fault characterization strategy can be applied to a number of industrial application scenarios embracing high frequency (HF) printed circuit board (PCB) and integrated circuit (IC) device operation, overhead lines and underground cables in inaccessible locations, which rely on a transmission line pathway or via common to all cases either for signal propagation or power conveyance.As an improved time-domain methodology PRBS enabled fault finding can be performed online at low amplitude levels for normal uncorrelated signal traffic disturbance rejection and to average out the presence of transmission link extraneous noise pickup over several PRBS cycles for the purpose of multiple fault coverage, resolution and identification. This unique troubleshooting tool is due to the perturbation of the transmission line with a special pseudonoise (pN) sequence of uncorrelated pulses of random polarity and the subsequent CCR measurement of their aggregate response at the test node input for line fault identification and localisation. Based on the distinct spike-like attribute of the PRBS autocorrelation (ACR) function, a pre-location fault measurement relies on the relative time displacement of the device/system conditioned PRBS cross-correlated echo response from the ACR peak for accurate fault/load location and identification. This measured time translation of the correlation peaks can be subsequently used to determine the propagation delay of the reflected response from the fault/load-termination of the unit under test (UUT). This procedure not only results in fault/load parameter identification but also of the reflection transit time from the fault interface and thus the distance of the fault from the point of stimulus insertion.In this paper a lumped parameter circuit model is presented to emulate generalized transmission line, using the well-known pSpice simulation package, for a range of known load terminations mimicking fault conditions in a range of application scenarios encountered in practice. Numerous line behavioural simulations for various fault conditions, known apriori, with measured CCR response demonstrate the capability of and establishes confidence in the effectiveness of the PRBS test method in fault type identification and location. The accuracy of the method is further validated through theoretical calculation using known lumped parameters, fault termination conditions and link distance in transmission line simulation.