automower cable fault detection

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

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

Leif

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https://www.paradiss.dk 

Eller begge.
Reply to
Leif Neland
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I've used a signal generator to send a 600KHz modulated signal onto the pow erline 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 d irectly 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 pas s the break. When you get past the break you will even be able to point th e radio antenna back at an angle to "see" where the break is. I am assumin g that you only energise the underground loop from one end and keep the oth er end as far as possible from the generator and the other line. I have al so 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 s ignal generator with a capacitor to protect the generator and yourself. So mething like a .01 uf should work. It might be best to just put the capaci tor in the circuit just in case there is a short that might put lethal volt ages on the line.

...Bob

Reply to
bobrweber

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 

Eller begge.
Reply to
Leif Neland

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.

Reply to
mike

r,

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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.

Reply to
ggherold

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.

Reply to
Tim R

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