3 ms·
How can they tell where is the cable damage? If the cable is all underground, surely they didn’t dig up the whole thing? Can they measure that from one end? Do
by cm2187 6y ago
How can they tell where is the cable damage? If the cable is all underground, surely they didn’t dig up the whole thing? Can they measure that from one end? Do they do a binary search by digging and testing?
- morsch 6y agohttps://en.m.wikipedia.org/wiki/Optical_time-domain_reflectometer https://en.m.wikipedia.org/wiki/Optical_time-domain_reflecto...
- walrus01 6y agoOTDR - optical time domain reflectometer, you connect it to the fiber at one end and it'll tell you where the break is, accurate to plus or minus 20-30 meters
- segfaultbuserr 6y agoIf you want to understand how TDR works, watch this classic tutorial from the mid-50s in the AT&T archive. The first 5 minutes, showing the reflection of an open and short circuit is enough. * AT&T Archives: Similiarities of Wave Behavior https://www.youtube.com/watch?v=DovunOxlY1k https://www.youtube.com/watch?v=DovunOxlY1k Many are surprised when they learned that it's possible to detect the location of a break in the mains wiring or an Ethernet cable, just by doing an electrical test from one end of the cable (some Ethernet cards even have builtin TDR support!). There's no closed loop, why is it possible to test anything electrically? Because at high frequency, the circuit becomes an electromagnetic waveguide. Basically like a radar, you send a fast electrical or optical pulse to the electrical cable or the optical fiber, the EM wave travels along the cable until it hits the break and reflects back. You record the time and listen for the echo. All discontinuities (such as damages) on the line will reflect and distort the original pulse. Use the speed of light to pinpoint the location of the fault.