Portland, Ore. -- A diagnostic spark that finds defects in wiring systems as complex as those on aircraft has been developed by researchers at Sandia National Laboratories. The Pulsed Arrested Spark Discharge (PASD) enables engineers to pinpoint the location of future short circuits before they occur, by exposing weaknesses that would eventually cause the short, according to the researchers.
Ordinarily, a 10,000 to 15,000-volt, 200-amp test signal would fry any electronics under test, but when it only lasts 10 nanoseconds, it can't damage wiring systems, said Sandia National Laboratory electrical engineer Larry Schneider.
Airplanes have miles of wiring harnesses, with many of the wires running hundreds of feet between connections. In the past, airlines have had to wait for shorts to develop before they could be diagnosed, possibly risking debilitating failures. Intermittent electrical short circuits in aging airliners often make cabin lights blink, but they have also caused fatal crashes, such as flights SwissAir 111 and TWA 800. If PASD had been used to precondition their wiring harnesses, then those aircraft could have been maintained short-free by replacing problem wires before they failed in flight.
PASD pulses actually improve the performance of wiring harnesses, according to the laboratory, since they burn off any foreign matter that might be bridging a hot line to ground, thereby preconditioning the wiring system and raising its overall breakdown voltage.
If the PASD "finds a defect in the insulation, it will break that defect down and collapse the impedance to zero there, reflecting the balance of the energy from the pulse back to its source," said Schneider. "We calculate the distance to the short from the propagation velocity of the pulse--in the manner of time-domain reflectometry. We can tell within a foot where the short is."
"PASD is a direct test of dielectric strength--that's its unique capability," said Schneider. "There is no other way available today to find small defects in complex wiring systems."
The Sandia lab, which holds several patents on the PASD system, recently licensed it to Astronics Advanced Electronic Systems of Redmond, Wash., where it was added to the company's ArcSafe tester. ArcSafe, which is the size of a suitcase, now uses PASD pulses riding on top of a variable-voltage direct current. It includes automated test sequences to test complete aircraft wiring harnesses automatically.
The Sandia research was funded for this project with $2 million over four years by the National Nuclear Security Administration, the U.S. Navy and the Federal Aviation Administration.