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A long time ago, I supported a wind speed detection system consisting of an impeller, a small electric generator, a 12 gauge cable running a few miles, and a voltmeter. The entire thing was calibrated through a resistive bridge–attach an electric motor to the generator, run it at a series of fixed speed, and adjust the resistive bridge until the voltmeter, marked in knots of wind speed, read correctly.
The primary problem in this system was the several miles of 12 gauge cable. It was often damaged, requiring us to dig the cable up (shovel ready jobs!), strip the cable back, splice the correct pairs together, seal it all in a plastic container filled with goo, and bury it all again. There was one instance, however, when we could not get the wind speed system adjusted correctly, no matter how we tried to tune the resistive bridge. We pulled things apart and determined there must be a problem in one of the (many) splices in the several miles of cable.
At first, we ran a Time Domain Reflectometer (TDR) across the cable to see if we could find the problem. The TDR turned up a couple of hot spots, Continue reading