Chet Lo

Feasibility of spread spectrum sensors for location of arcs on live wires

Spread spectrum methods are an important emerging class of sensors that have the potential to locate small, intermittent faults on energized aircraft power circuit wires. Previous work has demonstrated the use of these methods for hard faults (open and short circuits). This paper extends that work to the location of typical intermittent faults that plague aircraft maintainers. Test results on 200-ft-long realistic aircraft wires demonstrate the feasibility of these techniques to locate both wet and dry arcs while the system is powered with 400-Hz 115-V ac power running a variety of aircraft lighting loads. The capability of the system to function with either the aircraft structure or a paired wire as the return path to ground is demonstrated. These results indicate that spread spectrum methods have significant promise for locating intermittent faults on wires as they occur in flight or other modes of operation, such as landing and takeoff, taxiing, and other critical times when possible vibration, etc., may cause intermittent faults.

Noncontact Probes for Wire FaultLocation With Reflectometry

This paper describes an approach to locate wire faults using reflectometry without physical contact with the wire conductor. This noncontact method is capable of locating faults on both dead and live powered wires with todays reflectometry technologies, and it does not require any modification or disconnection of the existing wiring system. With proper configuration, this method can detect wire faults with an accuracy of 3 in, which is comparable to direct connection systems

Mixed-signal reflectometer for location of faults on aging wiring

Location of faults on aging cables is of great interest to maintainers of aircraft, cars, power distribution systems, communication systems, etc. One class of methods for locating faults is frequency domain reflectometry (FDR), using sine waves as the forcing function. A new frequency domain method called mixed-signal reflectometry (MSR) is described in this paper and compared to data from phase detection FDR (PDFDR) methods. The MSR is less expensive and smaller than the PDFDR and has very similar performance. A prototype system using the 100-200-MHz bandwidth with 256 40-kHz steps is shown to have a resolution of about 10 cm, very similar to a PDFDR in the same frequency band.

Modeling and simulation of branched wiring network

This paper presents a method to analyze the reflectometry responses of a branched network of non-ideal wires. A modified bounce diagram that uses a transition matrix to keep track of signal flow is used. This approach is further improved by including the complex propagation constant to include the frequency dependent filtering effect (phase delay and attenuation) of the non-ideal transmission lines