Intermittent Fault Location on Live Electrical Wiring Systems 2008-01-2932
Intermittent wiring faults are among the most frustrating, time consuming, and expensive problems to diagnose in electrical systems. These sporadic problems occur when wires are wet, vibrating, under pressure, or when the system is in a particular configuration during use. Then when the system is stable and/or powered down, the problems disappear. The best and often the only time to locate these faults is while the faulty wiring is live and in operation. This paper will describe new technology for locating intermittent faults on live wiring systems without interfering with their operation. Spread spectrum time domain reflectometry (SSTDR) has been developed for locating these intermittent faults on live aircraft wires. A pseudo noise (PN) code is injected on the wire, well below the noise margin of the system. The PN code can be self-correlated to give the characteristics of the wiring system - its branches, loads, sources, etc. When an intermittent fault occurs, SSTDR detects and locates the fault. Unlike systems that use voltage and current measurements to detect faults, this method locates impedance changes to the wiring system. It is therefore complimentary to current/voltage analysis methods commonly used for arc fault circuit breakers. It is also highly immune to electromagnetic interference and noise caused by switching loads, etc. This technology is currently being miniaturized into an application specific integrated circuit (ASIC) that can be integrated into many types of electrical systems. The methodology, specifications, and simulated performance of the ASIC are described in detail. Methods to integrate this technology into existing and new electrical systems are also described.