Standardized Tests for Metal Detectors

[baum7154]

[QUOTE=Davor;192175]
Can we agree on the standard coin features? Any idea on a standardized coin material that is easily obtained? Aluminium and copper are non-candidates for obvious reason - too pure and too conductive, but what else is there? Actual coins?

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I would like to understand why aluminum cannot be a standardized target simulant, especially for small gold. I use a 1/4" x 1/4 " piece of an ordinary soda can (0.004" thick)to simulate a 1.12 grain gold nugget, also a 1/2" X 1/2" .64 grain piece of can will approximate a 5 grain(1/3 gram) nugget but it is better to use a .64 grain piece of 1/8" TIG welding rod as it has less surface area. These targets test well with my PI detector against some actual gold samples I have.

Regards,

Dan

[WM6]

For example, heavily mineralized soil could be emulated using several toroidal ferrite cores glued to a board. We could devise many such "synthetic" tests, not just for comparing commercial detectors, but also for testing our own designs.
.

Good, but it is hard to get the same ferrite sample all over the world. It is significant value dissipation in permeability (mu) even in same series. Acceptable as individual test, but not comparable between testers.

Are you angry at me?

It is not about feelings, I simply haven't answers to your questions demand and didn't join debate. But I am planning to build much smaller coils for further test on those needles. We will see.

[Nupi]

It is not about feelings, I simply haven't answers to your questions demand and didn't join debate. But I am planning to build much smaller coils for further test on those needles. We will see.

If you have questions or would like to share experiences, you can always ask.

[Davor]

I would like to understand why aluminum cannot be a standardized target simulant, especially for small gold. I use a 1/4" x 1/4 " piece of an ordinary soda can (0.004" thick)to simulate a 1.12 grain gold nugget, also a 1/2" X 1/2" .64 grain piece of can will approximate a 5 grain(1/3 gram) nugget but it is better to use a .64 grain piece of 1/8" TIG welding rod as it has less surface area. These targets test well with my PI detector against some actual gold samples I have.

Thinned aluminium can be a very good simulant of small gold.
You need to understand the difference between bulk material and thin foils. Thinned aluminium is a good simulant of small gold because gold naturally appears pressed to chips and flakes that are also thin. When a sheet of metal has a thickness that approaches skin depth for a given frequency (span or bandwidth) and more so when it is even thinner, its effective conductivity becomes smaller.
Bulk aluminium is very conductive, copper even more so. Most of the targets are not nearly as conductive, so bulk aluminium (say, thicker than 1mm) or bulk copper can not represent real life bulk targets well enough.
For coin/artefact seekers bulk targets are mostly important. Big gold also responds as a good conductor, but gold seekers are mostly after small gold that is a poor conductor.

My suggestion for a bulk target is a 7g blob of 60/40 tin/lead solder that most of us have at home, and it may effectively simulate a coin made of some mid range conductivity non-ferrous alloy.

[baum7154]

I appreciate your response/info Davor. I understand now that you were referring to standardized targets for coins and artifacts. Should we also include some nugget target standards in the standardized tests for metal detectors?

Thanks,

Dan

[golfnut]

lead balls are fairly repeatable country to country - 1/2" ~ 12.5mm, good source is catapult ammo

[baum7154]

lead balls are fairly repeatable country to country - 1/2" ~ 12.5mm, good source is catapult ammo

A .490" lead round ball for a 50 cal muzzleloader weighs 182 grains in pure lead. I think that equates to about 11.9 grams.

Dan

[Davor]

In many countries weapons are heavily regulated, so perhaps using lead balls that are primarily used with weapons may not be the best choice. On the other hand, fishing sinkers might be a viable source... or not? Anyway, lead, or some alloy of it seem a perfect choice, only question is - what's the widest available option in 5-10g range.

Should we also include some nugget target standards in the standardized tests for metal detectors?

Sure, but many detectors such as low frequency VLF-s won't be able to excel with such targets, and using small gold simulants may provide insight how good a detector is for such conditions. Such simulants are easily obtained - just grab a tin of coke and scissors, and make a 5mm x 5mm chip.

Thrash simulants may be a little bit more difficult than it seem, as most of the new iron/steel is galvanised, and thus provide mixed reaction depending on orientation. The only way of knowing a nail is a good simulant is if it is covered in rust.

Kitchen aluminium foil is easy, just grab any and squash it into a ball of certain size, say 5cm diameter.

Ferrite toroids as suggested by WM6 seem a perfect choice for hot rocks simulants, as they are both highly permeable, and also conductive due to their ring geometry. Some materials also show some viscosity, and Eric Foster may give some insight on which core material would be the best.

[WM6]

If you have questions or would like to share experiences, you can always ask.

Asked for real test and not only presumption, couple of times, in another thread (see here example for GB small coil), but got no answer:

http://www.geotech1.com/forums/showt...750#post153750

[Nupi]

Asked for real test and not only presumption, couple of times, in another thread (see here example for GB small coil), but got no answer:

http://www.geotech1.com/forums/showt...750#post153750

Yes I read it. Some people have a big mouth and would seem important to others. Unfortunately, we all sometimes suffer from. In theory,
you can say anything but only have value if it corresponds in practice.

I have not tried itself with a small coil. But what do you call a small coil? I think 10 to 15 cm.
The results I posted are made with a modified DeepTech Smart. The coil is elliptical 11" frequency is 15-Khz I thought.
But probably it would work better with a small coil.But I have my doubts about high frequencies,
as others claim. But everything has to be tested in practice. Not only blablablaaaaa ....

In the thread: Can pinpointer detecting thin chain? have had something about, You were then skeptical, and rightly,
I am, too. But here is a PP good example.It has a relatively large coil for a PP and no high operating frequency (16 Khz)
and yet he detects tiny gold links, BUT he can not detect any hypodermic needles, while the Smart it detects.A miracle? No.

http://www.geotech1.com/forums/showt...old-with-an-MD

[WM6]

But what do you call a small coil? I think 10 to 15 cm.

The results I posted are made with a modified DeepTech Smart. The coil is elliptical 11" frequency is 15-Khz I thought.

Yes, 4" to 6" I would call small coil. Deeptech Vista can be delivered with such small coil too.

Detecting small hypodermic needle using 11" coil with IB VLF detector (no matter of brand), we could really call a miracle.
Sorry, but I don't believe in such "miracle".
Most probably you detected your own hand and not needle in it, as happen to me too.
Stick hypodermic needle on some sort of plastic ruler (hold your hand away from coil) and check it again.

[Nupi]

Yes, 4" to 6" I would call small coil. Deeptech Vista can be delivered with such small coil too.

Detecting small hypodermic needle using 11" coil with IB VLF detector (no matter of brand), we could really call a miracle.
Sorry, but I don't believe in such "miracle".
Most probably you detected your own hand and not needle in it, as happen to me too.
Stick hypodermic needle on some sort of plastic ruler (hold your hand away from coil) and check it again.

I do not have to try. I never ever do it by hand, but with a plastic ruler. Disc on en reject rusty nail.
So I'm afraid it's time that you start to believe in miracles.
I've already done some experiment on the ground with the result: a miracle.

[WM6]

OK, show us video of those miracle.

[Nupi]

OK, show us video of those miracle.

If I show it, then what ?
Just as some that criticism had on my pinpointer ideas, and when I proved it with the video,
I heard nothing more from them.
Is that the purpose of the video. It takes a lot of effort to make a video for me, because I want not my son burden and have to do it myself.

So come up with something better than: "OK, show us video of those miracle".

[WM6]

If you are not ready to prove your exaggerated claims, then don't make it.

Are you ready to send me sample of hypodermic needle you use in test?