gold nugget simulation?

[dbanner]

Saw thisQUOTE)"How To Get Zinc from a Penny
Although pennies look like copper, they are really a thin copper shell that is filled with zinc. It's easy to separate the two metals because they have different melting points. Zinc melts at a lower temperature from copper, so when you heat a penny, the zinc runs out and can be collected, leaving you with a hollow penny.

To get zinc from a penny, you need:

United States pennies (minted in 1982 to get the right chemical composition)
pliers
a gas stove or torch
heat-proof container to collect the zinc
Get the Zinc
Turn on the stove or torch so it will be hot enough to melt the zinc.
Hold a penny with pliers and place it in the tip of the flame. This is the hottest part. If you have trouble melting the metal, make sure it's in the right part of the flame.
You'll feel the penny start to soften. Hold it over the container and gently squeeze the penny to release the zinc. Be careful, as the molten metal is very hot! You'll have zinc in your container and a hollow copper penny in your pliers.
Repeat with more pennies until you have as much zinc as you need. Allow the metal to cool before handling it."(END)
Sounds too easy

[green]

I agree completely with this. Maybe Im misunderstanding some of this thread.

I have a few nuggets I use for my testing. For example, using one of my detectors, 1 nugget will change its detection depending on how it is held. One side of it, the detector detects it at 4 inches but turn it over and its only detected at 2 inches, turn it on its edge and it detects less than 1 inch. Same goes with whatever detector used or nugget used.

Ferric toes, Do you or any of you other guys use any real nuggets at all for any of the tests you do?

Just curious to this subject as that is my primary source for detecting..

http://www.geotech1.com/forums/attac...9&d=1543333008 Don't know if you saw this graph. At 9usec the 18grain nugget flat has 100 times the signal as the 4grain nugget on edge. At 9usec the 18grain nugget flat has 10 times the signal as the 18grain nugget on edge.

[Skippy]

It would be interesting to know how much of that on-edge signal reduction is just due to the target presenting 'less area', and how much is due to the change in time-constant. Mr.Green - have you tried working out how your ( or any ) PI machine varies in sensitivity with target time-constant, with all other variables unchanged?
I'm thinking this is where a series of targets of different metals, but identical dimensions would be needed. Probably covering the whole range from cupronickel up to copper.
I don't really know how TC affects sensitivity of my VLF, I bet it's tricky to work out. The F75 has different characteristics to simpler analogue VLF's, and has two main operating modes that have markedly different characteristics, particularly to items low on the 'detector conductivity scale'. I've long been curious about this difference, I had in mind a modification that meddled with the ID circuitry ...

I'll try my dummy nuggets on edge, to see how much they lose in signal strength.

[geoscash1]

http://www.geotech1.com/forums/attac...9&d=1543333008 Don't know if you saw this graph. At 9usec the 18grain nugget flat has 100 times the signal as the 4grain nugget on edge. At 9usec the 18grain nugget flat has 10 times the signal as the 18grain nugget on edge.

Thanks green, I hadnt seen that. Nice work on charting all that..

[Ferric Toes]

You can get a lot of clamping force from a bench vice. I was doing some car repair a few years ago, inserting four wheel-fixing studs into a hub carrier. Not easy, I had an extension pipe on the vice tommy-bar. I later calculated 20 tons force (20000 kg-force, 200000 Newtons).

Should have said, I only used a small Record V75 vice with 3" jaws and done up hand tight with the 3.5" vice tommy bar.

Eric.

[green]

It would be interesting to know how much of that on-edge signal reduction is just due to the target presenting 'less area', and how much is due to the change in time-constant. Mr.Green - have you tried working out how your ( or any ) PI machine varies in sensitivity with target time-constant, with all other variables unchanged?
I'm thinking this is where a series of targets of different metals, but identical dimensions would be needed. Probably covering the whole range from cupronickel up to copper.
I don't really know how TC affects sensitivity of my VLF, I bet it's tricky to work out. The F75 has different characteristics to simpler analogue VLF's, and has two main operating modes that have markedly different characteristics, particularly to items low on the 'detector conductivity scale'. I've long been curious about this difference, I had in mind a modification that meddled with the ID circuitry ...

I'll try my dummy nuggets on edge, to see how much they lose in signal strength.

Chart I posted before, shows change in amplitude with constant area. TRT_28: left chart, total target area 4x4inches cut in pieces to change TC. Middle chart, each target 25x25mm layered to change TC. Right target: all targets 1x1inch(aluminum can side, lead sheet and copper clad board had similar TC and charted about the same decay curve). I have some charts with TC staying the same and target area changing, need to do a couple more to verify what happens. Could try something else?

[Ferric Toes]

This is the picture that should have accompanied my post 238. It appears not to have come out, according to one of my computers.



Eric.

[waltr]

Saw thisQUOTE)

To get zinc from a penny, you need:

United States pennies (minted in 1982 to get the right chemical composition)

Only US 0ne cent minted AFTER 1982 are copper clad zinc, 2.5% Cu, 97.5% Zn.
Any minted 1982 and earlier are 95% copper, 5% Sn/Zn.

[green]

Only US 0ne cent minted AFTER 1982 are copper clad zinc, 2.5% Cu, 97.5% Zn.
Any minted 1982 and earlier are 95% copper, 5% Sn/Zn.

Both were minted in 1982. I have at least one of each.

[dbanner]

Only US 0ne cent minted AFTER 1982 are copper clad zinc, 2.5% Cu, 97.5% Zn.
Any minted 1982 and earlier are 95% copper, 5% Sn/Zn.

Clearly AFTER 1982. Yeh.

[Ferric Toes]

Only US 0ne cent minted AFTER 1982 are copper clad zinc, 2.5% Cu, 97.5% Zn.
Any minted 1982 and earlier are 95% copper, 5% Sn/Zn.

I tested a 1978 US one cent on the Hocking conductivity meter and it read 54.8% IACS. Next was a 1998 US one cent which measured 28.3%. Zinc is listed as 28 - 29% so the reading is spot on and not affected by the thin copper plating.

http://eddy-current.com/conductivity...y-resistivity/

Instead of melting out the zinc you simply just chop up the coin into smaller pieces.

Eric.

[Skippy]

I had a quick go at sanding a 'zinc' cent, the copper disappears in seconds, it's very thin. But it will only be good for targets 1.1mm thick or less, I think. Hence my interest in the old WW2 coins, which were more substantial, close to 2mm thick.

Trying to revive my test detector is proving troublesome. The stock coil is not working, looks like the TX is dead, so I've got to dismantle the cable plug. I tried with the small 5" coil, but it's not giving the same readings as the large one, it's more picky about target sweep speed.
I did do some provisional tests, which showed the difference in time-constant between square and circular targets was much less than the rough estimates I made earlier in this thread. It looks like the difference is 95%, that is to say a circular target has 95% of the TC of a square one ( same diameter / edge length). It seems the current doesn't flow into the corners much. This is for thin targets - in this case 0.102mm aluminium foil.
It's looking like the multiplier was a bit high in our T-C formula, perhaps more like 0.065 for square, 0.061 for circular.
I'll have to dig out the original targets ( alu drinks can sheet ) that I used when devising the '0.072' figure ... I think one potential error may have been the use of a different can for the IACS measurement. I have some newer cans 'in stock' that are from the same batch, so I can get matching IACS samples and targets.

[Carl-NC]

I found my Hocking AutoSigma, it's a 3000 handheld model. It is dual frequency, 60kHz & 200kHz, but the 200kHz doesn't seem to work. I get an overload error even when trying to calibrate.

Tried a whole bunch of metals:

.999 10-oz copper bar = 76.4
.999 20-oz silver bar = 106.2
.999 10-oz gold bar = 75.1
.999 1-oz aluminum bar = 60.1
.999 1-oz titanium bar = 3.74
.999 1-oz nickel bar = error
.999 1-oz tin bar = 15.2
.999 1-oz lead bar = 8.30
.999 1-oz brass bar = 24.6
$20 gold piece = 15.8
1922 Peace dollar = 77.1
1928 Peace dollar = 81.8
Fake Trade dollar = 25.1
Fake Bust dollar = 26.8

Tried several silver dollars, the 2 examples above were indicative of the skews I was seeing. The fake dollars are easy to distinguish. The copper bar was curious, I expected higher. The nickel bar, I dunno what was going on there. But I have doubts about these "0.999-fine" bars anyway... after all, what is a 0.999-fine brass bar?

[TH'r]

Only US 0ne cent minted AFTER 1982 are copper clad zinc, 2.5% Cu, 97.5% Zn.
Any minted 1982 and earlier are 95% copper, 5% Sn/Zn.

1982 was a year of transition between the two, and I have not been able to find any info on what percentages of each was minted. I have here about 14 pounds of unsorted and ungraded 1982 pennies from change. They can readily be sorted by alloy with a good VLF detector. Out of a random hand full (was 95 pennies) my F75 LTD identified 16 as plated and 79 as solid.

[Skippy]

"The nickel bar, I dunno what was going on there."
As nickel is ferromagnetic, I guess it's something to do with skin depth, the metals permeability having a dominant effect.
From wikipedia 'Skin effect' page:

Skin depth also varies as the inverse square root of the permeability of the conductor.
In the case of iron, its conductivity is about 1/7 that of copper. However being ferromagnetic its permeability is about 10,000 times greater. This reduces the skin depth for iron to about 1/38 that of copper, about 220 micrometres at 60 Hz.
Iron wire is thus useless for AC power lines (except to add mechanical strength by serving as a core to a non ferromagnetic conductor like aluminum). The skin effect also reduces the effective thickness of laminations in power transformers, increasing their losses.

So at 60kHz, your nickel sample is appearing too thin to register.