At 11:11 20/09/99 +1000, you wrote:
>Anyone got any bright ideas on a device which can be plugged into the end
of a single wire (say one core in a power cable) and the device will return
a length from the end of where the cable ends.
>
>the use would be for finding the break in a cable, so if you have a 20m
cable, and the device says the end of the active (hot) is 20m, and the
length of the neutral is 15m, and the length of the earth is 20m, then you
would know that the neutral has a break in it 5m from the other end of the
cable.
>
>You could also use it to measure (approximate) the length of a spooled
cable, or the kink in an underground cable.
>
>anyone know how to build such a beastie? Anyone ever built one?
>I envisage something along the lines of a pulse with a delay which is then
translated to length, but the detection of the echo, and processing speed
may make it harder. Would a PIC be able to keep up?
>
>Any ideas?
>
>Thanks ,
>Des Bromilow
>
>


Such devices do exist, the will see cable joints as an impedance change and
they work quite well. Try before you buy, have a look at the Tech Rentals
catledog, they have about three or four for the power industry, under cable
relfectometers (Measurement section)

Dennis