Posted: Mon Sep 15, 2008 7:22 pm Post subject: Metal classification?
Not all metal is equal....
Just on a whim I went to the yard of our apartment to scan before the mosquitoes went to bed. I found a pull tab and a similar tab within feet from my back door. No suprise there. Then I got some silver hits and ...... Just alum. flashing.
Does aluminum read back as silver? Is there a chart somewhere that "ranges" the metals you might find?
In the meanwhile I will feed the mosquitoes and clean up the back yard..
can slaw and scraps from siding suck, plain and simple. I can pretty much figure out a deep whole aluminum can on my DFX but once you get into the chopped up stuff, all bets are off. Just do your part in helping clean mother earth.
Hey Guy: If you're look for a list of metals and how they fall in the numeric value. A great place to find info of that type is at; Treasure net.com. It's is almost as good as our web page. Just kidding, this site is not a club web site. Email me and I'll send you a copy of my list. Good Hunting
Henry _________________ Metal detecting/Treasure Hunting
A Hobby for those with an Adventurous Heart and a Inquisitive Mind[/i]
A metal detector can not positively identify every type of metal under all types of conditions. Sometimes silver will look like iron to a metal detector. Like when it's on edge and down real deep. Sometimes tin or aluminum will sound like silver. Like when it's coin sized and close to the surface. The problem is, that a metal detector emits a type of radio wave into the ground. The only properties those radio waves can measure is the conductance and inductance of a metal target. By using some rather complex algorythms in the software, a target is "hopefully" identified from the models that the engineers have constructed. However depending on ground moisture, depth, surface area, shape, oxidation, mineralization, EMI, and other variables, many metals can "look" the same to a metal detector under certain conditions. How many of us has had a SOLID quarter signal, only to dig up a hot wheels car 4 inches deep? This is why, on an older site, the experienced coinshooters will often hunt in all metal, and dig EVERY target that will repeat and pinpoint. Yeah, they dig a lot of junk.....but that is the price you must pay, to get the deep good stuff that others have passed over as too "iffy". Sometimes digging up a piece of junk, will reveal a coin very close to it...
I think I get the concept of how this all works and the differences as metal ages and degrades.
I found this chart along with others that give a visual reference.
I will just have to dig it all until I get a feel for it.
Thanks
That chart is based on White's metal detectors which use a scale of -95 to +95 with Ferrous metals (iron) in the negative range and non ferrous metal in the positive range of the VDI numbers associated with machines that use the VDI scale. However, other manufactures have differnt scales in which their systems are based. Also, many machines do not have VDI numbers at all, the the conductivity and amount of time the "sent frequency" takes to reach the "received frequency" determines how the machine identifies if the metal is ferrous/non ferrous and determine if the target identified is in the accepted discrimation level the user has set.
The bottom line is, there is no sure fire way to determine the exact metal type, size or depth, since most machines are calibrated on coin size targets. Therefore, as noted above, an aluminum can at 6 inches may ring in as a dime or quarter at 2 inches since the machine "sees" the target as being in the calibrated range of one of those coins and at 6 inches "looks" the size of a coin that would be 2 inches deep. But as you learn the sounds and behaviors of your machine, you will be able to mentally discriminate out trash targets from good targets.
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