Wire tracer, how

I need to trace a cut cable for a robotic lawn mower

This one seems to work:

formatting link

But how does it work?

1kHz ac signal and pickup coil?

Cheers

Klaus

Reply to
Klaus Kragelund
Loading thread data ...

not even a pickup coil, Just a high gain amp, and the source is usually a square wave. I have a DIY one that works that way, and no problem finding the signal in a bundle after traveling 100ft.

Cheers

Reply to
Martin Riddle

Ok. So even if the wire is burried lets say 20cm below ground surface?

Cheers

Klaus

Reply to
klaus.kragelund

The devil is in the details and we have none. Assuming this is a buried cable... Assume you can't just let the mower trace the cable until it stops? You sure the transmitter is working? You sure the receiver is working?

The buried pipe locators used long ago by utilities companies use about 8Khz and magnetic pickup coil. Actually it's a LOT more complicated than that, but it's all you need to know here.

Here's what I did...

I started with a function generator because it was easy. Any generator that can put out about 8Khz. works.

I used a 12V AC Wall wart wired backwards to boost the voltage. DC wall wart won't do. Any high ratio transformer works.

Hook the AC input connections to the wall wart to the cable. One wire goes to the cable. Drive a ground rod into the earth and connect the other wire to that.

You need an AC pickup coil. I found a big coil of wire wound around an open core in the junk box and used that. It's not critical except that you can't use an enclosed coil, like toroid or E-core. has to have open ends to the core/rod

Plug the coil into the microphone input of an android smart phone. I put two diodes across it so I wouldn't destroy the phone if I encountered a big electric field.

Download a spectrum analyzer program from the playstore. That works better than an oscilloscope program because it allows log scale and it's easier to see your signal among the noise.

Waive the coil around the wire connected to the buried wire to see which orientation gives the best signal. YMMV.

Problem with the HF solution is that it may not work well on a buried cable. It might not be sensitive enough.

Reply to
mike

For my own circuits (where I have the layout) I power it with a current limited supply and chase down the short with a DMM. (DC)

George H.

Reply to
George Herold

Oh Buried. A pickup coil may help. Is the cable a perimiter cable? You might be better off running the mower thru the perimiter until it actually goes thru. Then you found the area by the break.

Cheers

Reply to
Martin Riddle

Den onsdag den 27. september 2017 kl. 22.21.49 UTC+2 skrev Klaus Kragelund:

formatting link
?

Reply to
Lasse Langwadt Christensen

I had good results using an AM BC pocket radio as tracer and cable driven with a sharp edged rectangular wave. I used a vintage pen style "signal injector" a 1.5V cell powered 1.5kHz multivibrator as source but any pulse or function generator should do. Using the volume knob and ferrite loopstick directionality helps pick out the driven cable.

However don't know how well that setup would work on 20cm buried cable.

piglet

Reply to
piglet

...but only if one can get the pickup CLOSE to the wire.

Reply to
Robert Baer

Yes. Close. Very close. Useless if the wire is buried.

Why not try a simple TDR based on a 74AC14. Original was described in EDN, October 1, 1998, later modified by Tomi Engdahl. Detects opens and shorts:

formatting link

The only problem I have is if the wire is buried, how does it get damaged?

Reply to
Steve Wilson

On a sunny day (Fri, 29 Sep 2017 10:29:37 GMT) it happened Steve Wilson wrote in :

That article already mentions: 'water ingress'. Where I grew up we had moles, those would ruin the nice green grass field with many mud heaps where they would come the surface. My father put mole traps, sort of small bear traps, near or in the holes to catch those. Would not surprise me a bit if moles chewed on cables too.

Nice artilce BTW.

Reply to
Jan Panteltje

Yeah, now bookmarked! (thanks Steve)

George h.

Reply to
George Herold

On a sunny day (Fri, 29 Sep 2017 06:30:54 -0700 (PDT)) it happened George Herold wrote in :

Apart from bookmarking, I now often just select 'print to file as pdf'

18 pages for tdr.pdf You never know, storms, censors, links sometimes die lead nowhere.

With TB storage at hand no problem, 'locate' will find anything if you gave it a logical name. Magnetic storage that is :-)

Reply to
Jan Panteltje

interesting.... I think I'd have an additional problem that TDR wouldn't be very effective on a single wire in a very lossy medium with an undefined impedance and return path.

Reply to
mike

You have a loop with a break in it and you want to locate the break?

e-field (capacitive pickup) and amplifier probably not directly useful to you.

--
This email has not been checked by half-arsed antivirus software
Reply to
Jasen Betts

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.