automower cable fault detection

[Leif Neland]

The perimeter loop cable around my lawn for my automower is broken.

I have a cable fault detector with a tone generator and a "pen"
receiver, which can trace along the cable, but it doesn't work when the
single wire goes under ground or concrete.

I wonder if a network/telephone cable tester can work on a single wire
underground.

I'm looking at

http://www.ebay.co.uk/itm/Portable-Network-LAN-Cable-Tester-Phone-Wire-Tracker-LCD-RJ45-BNC-Scanner/181692076054

After all, a single wire in the ground should look a little like a
coaxial cable?

Leif

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Ting til konen eller kĂŚresten.
Eller begge.

 

On Monday, April 13, 2015 at 2:36:24 PM UTC-4, Leif Neland wrote:

The perimeter loop cable around my lawn for my automower is broken.

I have a cable fault detector with a tone generator and a "pen"
receiver, which can trace along the cable, but it doesn't work when the
single wire goes under ground or concrete.

I wonder if a network/telephone cable tester can work on a single wire
underground.

I'm looking at

http://www.ebay.co.uk/itm/Portable-Network-LAN-Cable-Tester-Phone-Wire-Tracker-LCD-RJ45-BNC-Scanner/181692076054

After all, a single wire in the ground should look a little like a
coaxial cable?

Leif

--
https://www.paradiss.dk
Ting til konen eller kćresten.
Eller begge.

I've used a signal generator to send a 600KHz modulated signal onto the powerline in my house to trace outside power lines 2 ft in the ground. I use a portable AM radio that I can point the iron core loop antenna vertically at the ground over the wire to null the signal so that the antenna points directly at the line. Just follow the line around until you lose the signal by swinging the radio back and forth listening for the null and the signal level. (If you can't get a good null reduce the signal generator level. The lower the better.) The signal should get weaker really fast as you pass the break. When you get past the break you will even be able to point the radio antenna back at an angle to "see" where the break is. I am assuming that you only energise the underground loop from one end and keep the other end as far as possible from the generator and the other line. I have also found a break in a power line for a barn this way so it should work for your purpose. Warning.... If the line has any voltage on it isolate the signal generator with a capacitor to protect the generator and yourself. Something like a .01 uf should work. It might be best to just put the capacitor in the circuit just in case there is a short that might put lethal voltages on the line.

....Bob

 

[Leif Neland]

Leif Neland formulerede spørgsmület:

The perimeter loop cable around my lawn for my automower is broken.

I have a cable fault detector with a tone generator and a "pen" receiver,
which can trace along the cable, but it doesn't work when the single wire
goes under ground or concrete.

I wonder if a network/telephone cable tester can work on a single wire
underground.

I'm looking at

http://www.ebay.co.uk/itm/Portable-Network-LAN-Cable-Tester-Phone-Wire-Tracker-LCD-RJ45-BNC-Scanner/181692076054

After all, a single wire in the ground should look a little like a coaxial
cable?

Just for the record: It does not work.

But apperently, the manual says it only shows if a coax or phone cable
is open or shorted, not the length, so it couldn't find the length of
bu broken underground wire.

On the other hand, it does work as specified: It has shown a fault in a
ethernet cable.

Leif

--
https://www.paradiss.dk
Ting til konen eller kĂŚresten.
Eller begge.

 

[mike]

On 4/26/2015 9:08 AM, Leif Neland wrote:

Leif Neland formulerede spørgsmület:
The perimeter loop cable around my lawn for my automower is broken.

I have a cable fault detector with a tone generator and a "pen"
receiver, which can trace along the cable, but it doesn't work when
the single wire goes under ground or concrete.

I wonder if a network/telephone cable tester can work on a single wire
underground.

I'm looking at

http://www.ebay.co.uk/itm/Portable-Network-LAN-Cable-Tester-Phone-Wire-Tracker-LCD-RJ45-BNC-Scanner/181692076054


After all, a single wire in the ground should look a little like a
coaxial cable?

Just for the record: It does not work.

But apperently, the manual says it only shows if a coax or phone cable
is open or shorted, not the length, so it couldn't find the length of bu
broken underground wire.

On the other hand, it does work as specified: It has shown a fault in a
ethernet cable.

Leif

What you need is an underground pipe locator.

Don't know how technically inclined you are or how much effort
you want to put into this.

I did a bunch of experiments of this nature.
I used a function generator into the secondary of a 12VAC wall wart
and took the 150ish volts off the primary. Also built an oscillator
with a 555.
Hook one end to the wire and the other into a ground rod.
Don't forget to disconnect whatever electronics you have hooked
to the wire so you don't bust it.

To sense the field, I used a big coil of wire wound on a chunk
of iron.
Plugged that into the microphone input of a Dell Axim X51 PDA.
Use a spectrum analyzer program to distinguish the signal from
the noise. I like Pocket Instrument best.
5.5KHz. worked best for this setup.
Works better than I expected on shallow wires.

The concept should work with any device with a microphone
input and a spectrum analyzer program. There are dozens of
them for android. Suggest you put a pair of diodes across
the coil so you don't bust your phone from a transient.

If the wire is not insulated, you can sometimes stuff currrent
into it and probe the ground along the wire path to find
out where it stops.

 

On Sunday, April 26, 2015 at 12:08:17 PM UTC-4, Leif Neland wrote:

Leif Neland formulerede spřrgsmĺlet:
The perimeter loop cable around my lawn for my automower is broken.

I have a cable fault detector with a tone generator and a "pen" receiver,
which can trace along the cable, but it doesn't work when the single wire
goes under ground or concrete.

I wonder if a network/telephone cable tester can work on a single wire
underground.

I'm looking at

http://www.ebay.co.uk/itm/Portable-Network-LAN-Cable-Tester-Phone-Wire-Tracker-LCD-RJ45-BNC-Scanner/181692076054

After all, a single wire in the ground should look a little like a coaxial
cable?

Just for the record: It does not work.

But apperently, the manual says it only shows if a coax or phone cable
is open or shorted, not the length, so it couldn't find the length of
bu broken underground wire.

On the other hand, it does work as specified: It has shown a fault in a
ethernet cable.

Leif

--
https://www.paradiss.dk
Ting til konen eller kćresten.
Eller begge.

This is probably a silly idea, but you could try measuring capacitance (to ground)
of both halves. That might give you some idea of where it is...

George H.

 

[Tim R]

We had a broken power line at work that ran underground from a housing area out into some forested area. It was one of those old coaxial lines.

We couldn't find the break so we hired this expert.

He had something called a thumper. I was told it was a high voltage DC pulse.

It made a noise like a gunshot when it arced across the break. We started walking the line to find where the noise was loudest when it stopped.

The arc had welded the break together and the line held power again, though I never really trusted it.