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Tag Archives: Magnitude of Reflection

Non-Contact Connections for Reflectometry and Location of Faults in Cable Shields

The following slides were presented at the 2012 Aircraft Airworthiness & Sustainment Conference in Baltimore, Maryland on April 4, 2012. To view all slides, view the .PDF.
Non-Contact Connections for Reflectometry and Location of Faults in Cable Shields: Dr. Cynthia Furse, Dr. Brian Jones, Lucas Thomson

 

Time delay between Incident and Reflected Pulses tells distance to fault. The challenge: MANY faults cannot be replicated on the ground. Tests can't interfere with aircraft signals and aircraft signals can't interfere with tests.

 

TDR: Time  -  FDR: Frequency  -  NDR: Noise  -  STDR: Spectral  -  SSTDR: Spread Spectrum

 

'Hard' Fault is an open/short or near open/short that produces a LARGE electrical change to the system and produces a LARGE reflection to reflectometry. A 'Soft' Fault is caused by small impedance changes (corrosion, water, aging materials, etc.) and it produces a SMALL (maybe undetectable) electrical change to the system and it produces a SMALL reflection ot reflectometry.

 

'Hard' Fault: Open/Short or Near Open/Short  -  'Soft' Fault: Small impedance changes (corrosion, water, aging materials, etc.)  -  'Intermittent' Fault: Any fault (large or small) that appears and then disappears with time; 'Dry Arc' (vibration/stress induced; 'Wet Arc' (Moisture induced); 'No Fault Found"

 

Miswire: 8%; Failure due to corrosion: 7%; Short due to corrosion: 1%; Unspecified Failure: 6%; Short circuit unspecified cause (includes arcing incidents): 3%; Loose connection: 2%; Insulation failure: 3%; Chafed wire insulation leading to short circuit and/or arcing: 32%; Connector Failure: 9%; Broken Wires: 10%; and Other: 18%

 

Simulated Wire: TDR Signal & Partial wire fault location (high impedance short) with partial signal reflection due to a high impedance short circuit.

 

Live testing can locate up to 72% of wiring failures. Broken wires: 10%; Connector failure: 9%;  Miswire: 8%; Failure due to corrosion: 7%; Short due to corrosion: 1%; Unspecified failure: 6%; Short circuite unspecified cause (includes arcing incidents): 3%; Loose connection: 2%; Insulation failure: 3%; Chafed wire insulation leading to short circuit and/or arcing: 32%; and Other: 18%

 

During this 1 minute test, LiveWire SSTDR arc fault technology detected and reported the fault location more than 15 times prior to AFCB trip.