Hi.
My MIL has just moved house and it has a number of outside lights. Some are 12v and some are 240v.
A couple of circuits aren't working and the cables are buried underground. Does anyone know of a way of finding the route and/or checking where a cable break might be, - without digging up the entire lawn! ??
TIA.
H.
Some people reckon that dowsing works and that most people can do it
- doesn't hurt to try (unless the neighbours start taking the piss too severely).
Owain
[1] Hire (7 day minimum)
Time domain reflectometer, I think. AIUI it has to be calibrated by cable type.
Even better, if you have the distances from two points, draw the arcs of the circles and where those arcs intersect is the point of break. Assuming the cable runs in reasonably straight lines of course.
Owain
Howie formulated on Sunday :
BT use an instrument which is basically an oscilloscope and a pulse generator. The pulse goes down the cable and bounces back from where the break is. The initial pulse followed by the 'echo' are displayed on the 'scope, from which can be determined the time between the two and thus the distance to the fault.
Probably does not help with where the cable is located - though you could do the same for both ends, add the two lengths together and it would give the limits of where it could be.
"Harry Bloomfield" wrote in news: snipped-for-privacy@tiscali.co.uk:
Suggest a metal detector would help you plot the cable route.
What Harry described is a Time-Domain Reflectometer (aka TDR). Not a lot of people know that.
It happens that Kinell formulated :
Only if the cable is no more than a few inchres deep in the ground.
I didn't ;-)
I remember when I did my HNC Electronics (30+ years ago now) we used an oscilloscope to measure signal reflections in a cable of different length.
Never used that technique since, but I know it does work.
Andrew
Not a lot know how expensive they are either. We use one for finding faults on co-ax cables up transmission towers.....
I used to run about 3km of thick and thin Ethernet in ceiling voids, and there was never a TDR on the market cheap enough for `them' to let me get one.
I wrote an ethernet driver for the first ethernet chipset, the AMD LANCE
7990. That has a built-in TDR, and when the cable broke, our systems (GEC 4000 minicomputers) output on the console the TDR values, which is the number of 10MHz clock cycles which pass between transmitting the preamble and seeing its reflection from a cable break. Customers found this incredibly useful, and many picked a quiet time and went round their networks breaking the ethernet every 10 metres or so to record the TDR values the GEC 4000's generated, so when it broke for real, they could instantly home in on the 10m region of suspect cable. To this day, I remain amazed that no one else ever seems to have put this feature into an ethernet driver (although with switched twisted pair networks, it's now become redundant). OK, it's not as fine grained as a separate TDR instrument, but it was damn useful on networks of 10base5 and 10base2 that were around for many years.
Wouldn't that depend on the quality of the metal detector and the size of the cable? Of course you wouldn't know whether your detector/cable combination was working if you didn't find the cable! You could experiment I suppose, if you knew what sort of cable you were looking for, but that would involve a bit of digging up the lawn too :-) I'm sure there would be someone knowledgeable on uk.rec.metal-detecting. Also a little Time Team style trench at a right angle to your suspected cable run might be helpful, you should find some marker mesh/tape above the cable. None of that would help you find the damaged area of the cable though, if that is what causing your problem.
I always thought that was the critical component of the TARDIS!
David
Sam Nelson formulated the question :
I often see the instrument on the surplus market at giveaway prices.
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