General Metal Detector Type Question(s)

[Chase Goldman]

1 hour ago, nopeda said:

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

What you are asking for (detection 50' away) does not exist, at least in a cost effective package in conventional induction loop metal detecting.  You are going to have to get the detector loop OVER/ABOVE the intended target and can detect down a few feet at best once you are over it.  If you can get a metallic ring, disc or tag that you can consistently manufacture that will give a single, stable ID number, for a specific detector, you can set the detector to ignore all other targets, but if you don't know the approximate area of the yard the access tube is located, you will still have to sweep the yard until the desired target passes under the edge if the loop.

"Two box" detectors effectively increase the detection loop diameter from a foot or so, to several feet, increasing your coverage area and depth, but still not 50' away.

There are other technologies out there such as Ground Penetrating Radar, but you still need to be within a few feet of abd basically above the target, and the cost is pretty high. 

A magnetometer can sense when a ferrous object is distorting the local magnetic field (called an anomaly) but it can't really be dialed in to ID a specific metal and works best with ferromagnetic metals which comprise a lot of the junk buried in yards.

I think your best bet is the setup described by Steve above or use of the Tag described in the post you quoted, none of which fully meet your requirements as stated.