An instrumentation system automates the detection and location of faults in multiconductor electrical cables. It can accelerate diagnoses of aircraft, automotive, or industrial cables, while reducing the incidence of errors and of damage caused by test probes.

The Automated Cable-Analyzer System includes a time-domain reflectometer and a switching matrix controlled by a laptop computer, which also analyzes the test data. The switching matrix addresses designated pairs of wires in the cable, in a sequence specified via software.

The system (see figure) includes a time-domain reflectometer (TDR), which is a conventional pulse/echo cable-testing instrument. The system also includes a switching matrix containing relay switches, power-supply circuitry, a cable jumper and an assortment of adapters for mating to a variety of cables, digital control circuitry, and a computer that performs control and data-processing functions. The computer can be programmed to automatically cause the switching matrix to connect the ACAS to different pairs of wires in the cable under test and to analyze and store the measured data.

When connected to the various pairs of wires, the ACAS launches pulses into the cables and samples the reflections. The digitized reflection signals are processed to locate faults, using a real-time algorithm and/or a more thorough post-processing algorithm. Optionally, post-processing can include comparisons with data acquired previously from cables in known conditions.

This work was done by Michael T. Pham of Johnson Space Center.For further information, access the Technical Support Package (TSP) free on-line at under the Electronic Systems category,or circle no. 122 on the TSP Order Card in this issue to receive a copy by mail ($5 charge).