Spread-spectrum time-domain reflectometry

Spread-spectrum time-domain reflectometry is a measurement technique to identify faults, usually in electrical wires, by observing reflected spread spectrum signals. SSTDR is a type of time-domain reflectometry that can be advantageous to other systems due to the ability to use SSTDR in high-noise and live environments. Additionally, SSTDR systems have the additional benefit of being able to precisely locate the position of the fault. Specifically, This SSTDR is accurate to within a few centimeters for wires carrying 400-Hz aircraft signals as well as MilStd 1553 data bus signals. AN SSTDR system has the ability to be run on a live wire because the spread spectrum signals can be isolated from the system noise and activity.

A conceptual illustration of an SSTDR system is depicted below-left. At the most basic level, the system works by sending spread spectrum signals down a wireline and waiting for those signals to be reflected back to the SSTDR system. The observed (i.e. reflected back) signal is than correlated with a copy of the sent signal. Mathematical algorithms are applied against both the shape and timing of the signals to locate either the short or the end of an open circuit.

The graph below-right demonstrates the type of output that would be generated by an 80 ft wire that is either open at the end or has a short at the 80 ft. mark. As the picture illustrates, the reflected signal will be inverted when the signal hits a short circuit and will be right side-up for an open circuit.

See also

• Spread Spectrum
• Time-domain reflectometry

External links

• Furse, Cynthia, Smith, Paul, Safavi, Mehdi, and Lo, Chet."Feasibility of Spread Spectrum Sensors for Location of Arcs on Live Wires".IEEE SENSORS JOURNAL, VOL. 5, NO. 6, DECEMBER 2005
• Furse, Cynthia, Smith, Paul, and Lo, Chet."Spread Spectrum Sensors for Critical Fault Location on Live Wire Networks". STRUCTURAL CONTROL AND HEALTH MONITORING, June 2005.