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General Metal Detector Type Question(s)


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Hi,

I work for a district water company and we frequently have to turn the water service on and off at a home or business. This is an area where it gets fairly cold in winter so the cut-off valve is buried in the ground and access to it is just down through a small tube with a cap about the size of a half dollar coin. We have a tool that we put down the tube to turn the valve. Often/Usually the caps that should be at ground level get buried under an inch or more of dirt or grass or snow or whatever is in the area and can cover them. We use a metal detector to help find them which sometimes works very well and other times not so well. I'm wondering if there is something we can put on the caps or bury beside the tube to make it a lot easier for the detector to pick it up and maybe distinguish between what we put there and other random junk that happens to be lying around in the area. Or is there a way to get more specific than that like some type of detector that will or can be set to only pick up a particular substance we could put in place that's not likely there is other similar material just lying around the area...something not expensive like gold. I may not have explained what we're trying to work out very well but hopefully you people get the idea and may have some suggestions on how to improve our situation.

Thank you for any help with this!!!

David

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Metal detectors like aluminum! the bane of all detectorists!  Cheap and very effective.  Epoxy it to the lid.  GaryC/Oregon Coast

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5 hours ago, GaryC/Oregon Coast said:

Metal detectors like aluminum!

Gary,

I was going to say the exact same thing, where I live our shutoff valves are as this person has described. The water plant person has placed 3 can bottoms surrounding the valve to make it more easy to locate. The cans were cut in half, then buried about 3 inches under the grass.

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I suppose the issue with cans is that cutting them is time consuming, different sizes will give different ID numbers, you have to drink a lot of cans of drink  😁


 Something like this (or a round version) should be cheap, easy and give a consistent ID figure on your detector.  As long as your detector has ID numbers?  

02835858-C985-4B70-A8DD-6E71B97D2C05.thumb.png.1f27bdc00394ad7d38c5e2bef3c5d7c0.png

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14 hours ago, nopeda said:

...a small tube with a cap about the size of a half dollar coin.

What are the compositions of the tube and cap?

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Ring-shaped objects give a stronger signal than solid discs, and read 'higher up' the discrimination scale that most detectors have. And aluminium is a good electrical conductor. So I think it's worth experimenting with large aluminium washers, example 1" / 26mm size.
A UK supplier for illustrative purposes:
https://www.gwr-fasteners.co.uk/aluminium-washers-244-c.asp

These should be quite distinctive and easily found with a detector, and they're reasonably cheap if you're going to be using lots of them.

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Absolutely need to know the composition of the cap and tube to answer the question. It also depends on the composition of the most likely junk in the area of search.

Precedent exists. I used to be a surveyor. Old monuments used to have a brass cap on a steel pipe and were located using a utility magnetometer like the popular Schonstedt locator. New monuments are constructed of aluminum which is much easier to store and transport. Magnets are added to make them easily located with a magnetometer. Magnetometers will only detect iron and steel. In areas where trash iron and steel abound this could be problematic.

If the access tube is copper or aluminum your best bet would probably be to simply make it larger and more easily located via a large aluminum washer or tag.

Work is being done to research the use of RFID tags for some buried applications, the main catch being the frequencies used in tags attenuate quickly in ground mediums.

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Good info Steve. I too was a surveyor for many years. The old dip needles - aqua boxes... ok..?

Then we got the Schonstedt. Great improvement. One of the best features was being able to null out metal fence lines. Good memories.

Mike

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  • 1 month later...
On 1/8/2020 at 5:03 AM, Northeast said:

I suppose the issue with cans is that cutting them is time consuming, different sizes will give different ID numbers, you have to drink a lot of cans of drink  😁


 Something like this (or a round version) should be cheap, easy and give a consistent ID figure on your detector.  As long as your detector has ID numbers?  

02835858-C985-4B70-A8DD-6E71B97D2C05.thumb.png.1f27bdc00394ad7d38c5e2bef3c5d7c0.png

I don't understand what you're showing us. I was really hoping there was/is something that could be a unique combination of material and detector. Like some unusual type of material that isn't common and likely to be lying around and a detector that would only detect that type of material. Really I was imagining there are such things made specifically for this type of situation, so you can turn the sensitivity way up and wave the detector around and it can tell you what part of the yard to move toward even if it's 50' way, then as you get closer turn the sensitivity down as you get nearer to the target. Maybe it's naive on my part to think there actually is such a system already available, but I don't think there's anything wrong with wishing that there was if there truly is not. Or is that what you have presented and I just don't understand what you're showing us yet?

Thanks to all of you for your suggestions!

David

Maine, USA

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