The city has a water leak. They are not sure where the leak is. >They can n ot dig up a whole city block to find it so they use a >clever trick. They p ut two microphones about 50 feet apart where the >leak seems to be. Then th en record the random sound of water hissing >out of the pipe. The two micro phones are wired to left and right >channel of the recorder. By adjusting t he time delay of the right or >left microphone they can find the sweet spot where the random noise >from one microphone matches the random noise of th e other >microphone. Once the delay is know they know where the leak is >wi thin 1 or 2 feet. That is a clever trick. "
Hah, I can top that one.
We had a power outage, traced to a break somewhere in an underground line. It was one of those ancient coaxial feeders, and it ran a good quarter mil e through the woods, maybe more, it's been a while. How to find the break?
We hired this specialist with a thumper, which is a pulsed high voltage DC. It makes a noise like a gunshot when the arc jumps the gap. You walk the route of the line (which you never know exactly because your drawings are always a little sketchy) and listen.
Usually this works. Not this time - it arced for a while, then somehow the arc welded the break back together. No more pulses, no way to find the sp ot, we just turned the power back on and let it go.