ECN Forum Forums General Topics of the Trade General Discussion Area Cable Fault location

Using a tektronix we used the little jumper cable to a BNC "T" fitting. Go from the "B Gate" out on the side to the input. This gives you a pulse, then crank down the sweep until you are looking at nanoseconds and you will see the pulse go out and any reflections coming back. Generate a fault at a known location, usually the far end of the cable if it is working at all, to get your bearings. We mostly used it to find problems on 3270 coax or AS/400 Twinax.

Oh, I see, the garden variety Tektronix scope. If those are the scopes you keep in your garden, I can't wait to see the ones in your Florida room. I bought an old Dumont scope at a hamfest once and still have a 15MHz triggered Griefkit scope that I usually use in the garden.

I could use the Tek scopes in the lab at work in the clever way that you describe but they aren't as light and portable as the Tek TDR on the shelf. I can certainly see how you would have a good quality scope and not a TDR if you're fixing computers though. I wonder if I wasn't fixing minis back in the day when you were doing this?
Joe

Good to see the discussion re the options with a "garden variety" scope.
It is true that you see a deflection from the impulse at the end of the cable.

In case of utility mains, especially in 230/400 volts the cables there are a lot of joints and sometimes different sizes used mixed together.
These will all cause a deflection in the readings and the crew who digs up the fault will tell you quick enough if it's at the wrong location.
Hence the Pool of Potential is 99.9% accurate within ± 5 cm of the actual fault and my preferred method on non-screened cables.

With the HV cables as mentioned before, on long runs 2kms or more we use the dart to give us an approx. distance, then thump and listen for the noise generated at the fault.
quite often you can hear it above ground, and sometimes a Biddle listening set is used to pick up the magnetic flux and noise on your headphones and lcd display.
Cheers Ray

I have a 453 I will send you for the postage.