Diagnostics and Prognostics of Wiring Integrity via Joint Time-Frequency Domain Reflectometry

The integrity of the wiring in the electric power system of an aircraft is vital to its safe operation. To ensure the wiring integrity, it must be tested to determine if any incipient defects exist. For this purpose, joint time-frequency domain reflectometry (JTFDR) has proven to be effective on shielded, coaxial cable. This paper demonstrates the ability of JTFDR to also effectively detect and locate incipient defects on the more challenging unshielded twisted-pair cables. Though these cables have greater attenuation and are more susceptible to interference, the versatility and configurability of JTFDR allow it to be successful for detection and location of the defects. This paper also addresses age capability of JTFDR for cable prognostics. Using a heat chamber to simulate accelerated thermal aging, coaxial cables are exposed to extreme heat monitored over time. The time-frequency cross-correlation function employed by JTFDR provides indices that are monitored and analyzed to determine if a cable has been aged permanently by the exposure or if it is still operable. Monitoring these JTFDR indices may also be used to predict both hard faults before they occur and the remaining life of the cable.