Cable fault locator for underground PSTN cables

Thread Starter

efarook

Joined Aug 5, 2009
4
Hello everybody,

I want to build a cable fault locator for my own use. I know there are some ready made stuffs out there in the market, but I want to build my own version.

This fault locator will be able to monitor and detect open and short cable faults. This is simple, I will be able to design a circuit for this.

But what I could not get after a long search on the net is that how to locate the fault. I read about TDR (Time Domain Reflectometry) but this is not so handy for my field use.

Are there any other simpler techniques to find the location of the fault?

Thanks in advance.
 

Bernard

Joined Aug 7, 2008
5,783
It would be helpfull to know more about the cables. Is access available to ends of the cables? How long are the cables. My experiance with cable fault detection was with 13 pair, 1320 ft, on surface cables that had plugs on each end. One step used a capacitance bridge for opens, good for about +- 10 ft. Resistance measurements worked fairly well for shorts. Tone tracing located fault to +- 1 inch.
 

studiot

Joined Nov 9, 2007
4,998
It would be helpfull to know more about the cables.
+1

What are they under? "underground " is too vague.

Since they are underground do they have an earthed armoured sheath?
In which case TDR may be your only option for an intenal break, although you can send a signal down the sheath.
 

JoeJester

Joined Apr 26, 2005
4,390
You can make a TDR with an oscilloscope and a pulse generator.

The rest is knowing the velocity factor of the cable and the time difference between the main pulse and the return pulse. It's based on the same philosphy as radar.

It will not get you down to an inch ... you could get close if you know how and your oscilloscope is equiped with the venier dial and a delayed function.

on edit

http://www.epanorama.net/circuits/tdr.html
 
Last edited:

davebee

Joined Oct 22, 2008
540
Where I live, the underground residential power cables regularly corrode and fail.

What the repairmen do to find the location is isolate the failed cable section, send a high voltage down the isolated cable section, then walk along the ground above the cable path and listen for the sound of sparking!
 

retched

Joined Dec 5, 2009
5,208
Where I live, the underground residential power cables regularly corrode and fail.

What the repairmen do to find the location is isolate the failed cable section, send a high voltage down the isolated cable section, then walk along the ground above the cable path and listen for the sound of sparking!
Thats true. We have had a tech use audio to find power and water supply line faults.

You can also use FLIR, depending on how BAD the fault is.
 
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