metal dector for barbed wire fences

comp.arch.embedded,sci.electronics.components metal dector for barbed wire fences

Anybody here have any suggestions for possible ways to detect fence wire, mostly 1, 2 or 3 levels of barbed wire but also some 8 inch square matrix? Typical mounting would be on a tractor or trailer, so the detector would need a sense of direction, ie looking outward not inward. Minimum range would be around one foot with 4 feet probably optimum. Typical retail metal detectors have a short range and need a metal free environment, leaving the methods they use somewhat doubtful. Evidently, there are detectors with seperate heads/coils and 1-5 foot ranges but, once again, require a metal free environment. One possible area would utilize rf antenna's, one transmiting and the other recieving a reflection from the wire(s). A parabolic or corner reflector type antenna maybe if not for the high frequency - two 12 inch antenna's would be about max size and that's in the gigaherts range, which might be a problem. Any suggestions along this line will be appreciated.

Hul

Reply to
Hul Tytus
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What are you actually trying to do? Is this an operator aid, to keep from driving into the fence, or for a robotic tractor, or what?

You may be able to make a metal detector directional simply by backing up the detection coil with a metal plate, one or two feet back. Metal detectors work with near-field radiation of a low frequency signal (in the 100's of kHz, if I recall correctly), and look for changes in the coil inductance caused by nearby metal. Placing the coil a foot or two from the metal backing will leave the detector "detecting" the backing -- but it'll be constant; as long as there's enough change from the metal you want to detect, things should work.

Reply to
Tim Wescott

Alternatively use the barb wire fence as an antenna for LF low power signal and get the strength detection of carrier to denote when too close.

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Paul Carpenter          | paul@pcserviceselectronics.co.uk
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Reply to
Paul

Ultra sonic projected on the fence wire should make it vibrated. A ultrasonic mic just behind the transducer should detect this.

Fence wire is a hard surface and the only thing I can see that may hamper this is rust..

If you transmit a low frequency magnetic wave in the vicinity, surface rust on the metal may produce some nice G/T hz signals. Of course, you need a detector for that. Maybe IR . who knows.. ;)

Jamie

Reply to
Jamie

Paul - that's definite possibility but, as you say, an alternative if "plan a" doesn't prove feasible.

Hul

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Reply to
dbr

Driving the fence with VLF, if you can do it, is likely to be the most robust solution. I've done a similar thing for detecting underground wiring where only one end is accessible, a simple loop coil detector easily indicates proximities in the oo-1 metre range.

An unrelated thought, the barbed wire will make it easy to arrange a backup override, in case whatever it is gets too close to the fence. A vertical trip wire will catch on the barbs, and that can activate an energency stop.

Reply to
Bruce Varley

"Hul Tytus" skrev i nyhetsmeldingen: jri79h$opj$ snipped-for-privacy@reader1.panix.com ...

This application makes my head shouts "radar!".. not metal detector..

Reply to
Morten Leikvoll

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be

Hmmm, wondering if a vision system could be made to do this. maybe something with a very limited depth of field on 3 cameras such that, a correction signal is generated by the outlying cameras if the image from the central camera blurs.

Reply to
1 Lucky Texan

wire,

matrix?

need

be

free

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other

type

would be

problem.

something with a very limited depth of field on 3 cameras such that, a correction signal is generated by the outlying cameras if the image from the central camera blurs.

I was also thinking about a vision based system - of course if the tractor is going through fields with crops/grass/weeds blocking the camera's view of the fence, then it isn't going to be reliable in all situations.

A camera with focus set for near objects would have a sharp view of a wire fence. Edge detection techniques with some simple pattern matching would probably work quite well for picking the horizontal wires of the fence. It could be further developed to identify the actual 'barbed' pieces.

Maybe overkill for the intended application??

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Reply to
mikelake

All vision systems used outside suffer from problem below

tractor

Worst still heading towards the sun and see next to nothing.

Assumes all wire fences are nearly horizontal compared to camera perspective. No breaks or other things attached to barbed wire like signs syaing "keep out"..

Very possibly

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Paul Carpenter          | paul@pcserviceselectronics.co.uk
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Reply to
Paul

Search for "search coils pdf" will turn up a lot of documents on the topic. The one I keep around features many of the applicable patents.

Anyway, you do have some interesting contstraints. I'm thinking along the lines of how you could excite the wire strands (exciter coil at one end of the tractor) and a detector coil at the other.

It wasn't clear whether you are trying to prevent driving directly into a fence while crossing a planted field or if you are trying to monitor the fence location as in mowing close along the fence.

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Reply to
David K. Bryant

t.net ---

Yes, I think there have been farming vehicles for some time now that use GPS to mark the area in which they operate. I don't know how accurate they are or if they require a large 'buffer' zone for error. Perhaps switching from a GPS system to a more sensitive/accurate system is what the OP is attempting?

Reply to
1 Lucky Texan

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