Iron Gold Silver VDI

[greydigger]

Having trouble understanding VDI numbers.

Iron does not conduct electricity very well. OK
Silver and copper do the best. Huh?
Gold is in between. ?
Why then are gold contacts in electronics the best?

Resistance does not seem to apply.
Tell me how I am wrong please.

 

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[cosmic]

gold doesn't oxidize...

 

[Digger]

cosmic is right. Gold is virtually indestructible, although very mailable, and lasts for ever as well.

 

[Ant]

Gold is comparatively lower on a conductivity graph or scale when place up against high conductors like as silver and copper, silver being the highest. If you looked at gold on a graph or scale, gold depending on its purity would fall below zinc pennies. And range anywhere below that with lead and foil and many other metals. I would say that gold is a medium/high conductor. I agree with the other guys as well.

HH

 

[dahut]

Having trouble understanding VDI numbers.

1. Its okay, it can be a little confusing at first. Imagine a scale starting at zero, on the left and going to 99 at far right. That is the accepted VDI scale.

Iron is at 0-10 and below - yes, iron can be said to go into the negative realm. For us, we don't really care about that for most uses and so start at zero.

Silver is at the high end from about 80 - 94

Copper/bronze comes in around 65-80

Gold is between 15-65, depending on it's alloy and configuration, and can rightly be said to "be anywhere"... at least figuratively.
- Pure gold (24K), is very close to lead, so get some small lead fishing sinkers to test how your detector responds to it. You'll find it is around nickle-pulltab, 18-30
- Fine work and filigree gold comes in even lower, around 13-18, down into the foil range.
Alloy gold, with varying amounts of copper to temper it, comes in higher than other golds. My 14K wedding band hits dead on 33-35.**
I've found other alloy gold pieces that are closer to screwcap, somewhere around 55-60. Class rings (10K) tend to come in at this range.
** RINGS are dead easy, as they can be considered single loop inductors (SEE below, item 3.)

2. Like the others have said, gold is used in hi-quality connectors because it doesn't corrode.

3. Resistance does apply, but it is secondary to inductance. Our VLF detectors can more rightly be called "inductance coupled, phase response detectors."

Our instruments utilize an oscillating sine wave to couple (induce) an electrical signal into a target. This induced signal shifts phase slightly from the original frequency, due partly to the resistance - actually, impedance - of the target. This phase shift is both measurable and constant for various metals and is the basis of discrimination.

In fact, I prefer to think of discrimination as annunciation, not elimination.

 

[greydigger]

OK so the only reason for using gold in high=end electronics is that it doesn't corrode.
I had thought it had the least resistance and more conductivity.

Thanks for the replies folks.

 

[dahut]

You got it. Comparatively speaking, Gold is a poor conductor of electricity. Copper and Silver are better.

In practical terms, however, makes little difference. If you are familiar with digital electronics, you'll note components, circuit boards, sockets, etc. are not assembled with gold. They use solder and plated copper almost exclusively.

Where exposure to harsh external environmetns may be an issue, thats where you'll most often see gold plated connectors. An everyday example of this is the terminal connectors on most cell phones. A jeans pocket, or waistband, can be a pretty funky place! So they use gold plated connectors there.

You can also charge more for gold plated connectors, because it impresses people to have them. Aside from a few examples, there is little genuine need for them in everyday living.

 

[XL-PRO PRO]

I worked an inland beach sunday that was mostly mud.My vdi's were all over the scale,a nickle on edge gave no vdi but a good tone;a deep pulltab vdi'd in the quarter range while other coins checked dead on.Soil conditions,moisture and depth greatly affect the return signal on most detectors.Most conductivity tests are air tests which have no bearing on "real world conditions".(I did find a 18k-hge ring on this hunt!)Thanks DBULL

 

[dahut]

Well, that pretty much shoots this discussion of VDI numbering down in flames, eh?

And there you have it, both extremes. VDI numbering and other forms of TID (Target IDentification) are not perfect - that is a fact. I beg to differ a bit, however, with the impression that they are of little use.

Air tests ARE of limited value in that they are contrived practice. The real world is indeed a different place than a laboratory. Lab practice is not utterly useless, though, as the pundits would have you believe. It helps one to establish some sort of a baseline, a practical neccesity when attempting to assign repeatability to real world occurence.
In other words, it IS a place from which to start.

Much of the time, under much of our detecting circumstances, the TID features of modern, up to date detectors are pretty darn good - down to about 6". There can be circumstances where this is compromised, sometimes even severely, depending on local condition. So it is the wise man who knows both his location and his equipments limits.

Yet, when used within their limits, modern TID circuits are more accurate than you may be led to believe by their outspoken opponents. I recall when TID features first hit the scene. By those standards, today's equipment is light years ahead and is the fulfillment of a dream for most of us long-time detectorists.

So, don't be misled into believing that VDI and TID features are useless. Just know their limits and don't bet on them to be faultless.

PS - Here's a Detecting Rule Of Thumb for you:

When searching for gold, learn to love the midrange: nickle coins and all the useless trash we denounce.

Pulltabs, foil, canslaw, screwcaps, eraser ends, bottle seals... these are all the low-brow kin of gold and gold jewelry. It behooves you to go where gold jewelry is most commonly found, and then plan to dig everything at foil and above.

 

[XL-PRO PRO]

Dahut; you are correct in that vdi readings are very useful.I hit a ballfield for a couple of hours this afternoon and dug a nice 14k earring that vdi'd dead on poptop & a small silver cross that rang in as a solid dime.Most coins other than zinc pennies(which show readings from tab-penney depending on how corroded)lock right on target.However,when I beach hunt my disc is usually just above salt & my signal is set at 3 o'clock which greatly alters vdi readings.When hunting jewelry I usually dig everything but can signals.Thanks DBULL

 

[cosmic]

Pure metals conductivity.. highest to lowest... silver, copper, gold, aluminum, iron, steel, lead...

 

[greydigger]

Thank you cosmic.