ohm meter to test for real from fake siler

There is an app for testing silver rounds that way...A ping tester.

 

Log in or Sign up to hide this ad.

Still thinking about this, the measurement of resistivity makes the comparison process simpler. That means all bars/coins of the same base metal should have the same reading, regardless of size/shape.

I looked up resistivity values at

https://www.thoughtco.com/table-of-electrical-resistivity-conductivity-608499

And it shows silver with a value of 1.59x10^(-8) Ω-m. My readings for bars and ASEs were 1.60 and 1.66. Good News: My readings are almost exactly the same as the resistivity value; and Bad News: the linked table resistivity value isn’t 1.59 micro Ω-m, it is 15.9 nano Ω-m.

So assuming the PMV’s “measurements” represent 10 nΩ-m, my readings are “1.60” = 16.0 nΩ-m and “1.66” = 16.6 nΩ-m, compared to the expected value of 1.59x10^(-8) = 15.9 nΩ-m.

Sounds good. Am I doing this right? I’m old and retired, and I had a big dinner tonight, I might be a little fuzzy.

Now looking at my gold measurements. Bars were “2.2” and AGEs were “8.0”. “2.2” = 22 nΩ-m compared to the expected value of 2.44x10^(-8) = 24.4 nΩ-m. That seems good, 22 compared to 24.4.

My AGEs are not so good: “8.0” = 80 nΩ-m. That’s way off from the expected value of 24.4 nΩ-m. According to the Table of Resistivity they’re more likely made of nickel. . Of course, the AGEs are only 22K, but the other 2K consists of silver and copper, both of which have lower resistivity than gold, which I would think would give me a resistivity even lower than gold.

More likely yet, the PMV isn’t measuring these small coins correctly in their air-times. I’ll go back and measure one out of its case and experiment between measuring with the PMV “main” sensor and the wands. The wands are intended, I believe, for small samples.

 

EXCELLENT work here, @Bacchus!

One note on the AGE measurements - I wouldn't be surprised if the AGE gold/copper alloy DOES have much higher resistivity than either pure gold or pure copper. Metallurgy is weird.

Of course, as you can probably guess, I also wouldn't be surprised if the PMV is having trouble with small coins. But overall, I'd say the results you're posting are somewhat improving my opinion of the machines...

 

More detailed testing of a 10 ozt silver bar and ASE.

Coin/Bar. PMV sensor case Meas. 1. Meas. 2. Meas. 3

ASE 2022. Main none 1.65 1.63 1.63
ASE 2022. Small Wand none 1.62 1.63 1.63
ASE 2022. Large Wand none 1.65 1.65 1.63

ASE 2022. Main Air-Tite 1.63 1.62 1.62
ASE 2022. Small Wand Air-Tite ——— no readings. ———
ASE 2022. Large Wand Air-Tite 1.62 1.61 1.64

10 ozt bar. Main none 1.59 1.59 1.59
10 ozt bar. Small Wand none 1.58 1.59 1.59
10 ozt bar. Large Wand none 1.59 1.60 1.59

10 ozt bar. Main zip bag 1.59 1.59 1.59
10 ozt bar. Small Wand zip bag 1.56 1.57 1.57
10 ozt bar. Large Wand zip bag 1.58 1.59 1.61

I was previously converting to 10 nΩ-m, but while measuring with the PMV using scientific notation based on metric prefixes (μ, n) is a needless extra step. I’ll guess that the PMV measurements are 10^(-8) Ω-m, but all I really need to do is compare the PMV measurement as displayed with the resistivity table material mantissa, which is the number before the exponent (I had to look that up.).

So, the table shows the resistivity for silver as 1.59x10^(-8), but the mantissa is 1.59. My PMV measurements above range from 1.57 to 1.65, and that’s all I really need. It’s good to know that the exponent and units are 10^(-8) Ω-m, if all of my conjecture here is correct, but not necessary to verify the readings indicate the expected metal.

And in the case of my silver bar and ASE I like the results. The resistivity table mantissa is 1.59, and that is what the PMV measurements show on the bar and pretty close on the coin.

Some comments, though, about these measurements with the PMV. I made these measurements using the following finesses:

1. On the ASE, the wand measurements are smaller if taken from the flat part of the fields. Readings from some of the “busier” parts of the design could range up to 1.73. I moved the wand around the coin face to find the lowest value. It is also important to make sure all of the wand disc sensor is over the coin. If some of the wand is just off the edge of the coin, the readings go way up.
2. On the bar, the readings were lower on the flat reverse. The obverse had lettering and also rounded edges at the sides. The obverse readings could easily be as high as 1.65 or more, depending on where you placed the wand. There are probably lots of bars with lettering on both sides, I was lucky to have a flat side with no lettering. I think it is what is called a cast bar.

I’ll redo my gold tests later. A complication will be that I won’t be willing to remove my gold bars from their assay sleeves, but I can certainly take an AGE out of its air-tite. The AGE is what I’m most curious about given its poor measurements with the PMV.

And I don’t think there is anything wrong with the PMV or its design, it is probably my technique: maybe the 1/4 ozt AGEs shouldn’t be tested in the air-tites.

By the way, the PMV has more than one sensor, based on the form of the item being tested. There is a “main” sensor, a small wand, a large wand, and a bullion wand (which I don’t have). In my two items above, there didn’t seem to be a results difference between the main sensor and the wands, except the small wand wouldn’t give me a reading for the ASE in air-tite.

 

More detailed testing of a 1 ozt gold bar and 1/4 ozt AGE.

Coin/Bar, PMV sensor, case, Meas. 1, Meas. 2, Meas. 3

AGE, Main, none, 7.47, 7.49, 7.43.
AGE, Small Wand, none, 7.88, 7.82, 7.79.
AGE, Large Wand, none, 7.70, 7.73, 7.73.

AGE, Main, Air-Tite, 7.76, 7.79, 7.76.
AGE. Small Wand, Air-Tite, ——— no readings. ———
AGE. Large Wand, Air-Tite, 7.73, 7.75, 7.72.

1 ozt gold bar, Main, bar holder, 2.18, 2.18, 2.17.
1 ozt gold bar, Small Wand, bar holder, 2.16, 2.16, 2.20.
1 ozt gold bar, Large Wand, bar holder, 2.17, 2.19, 2.21.

The resistivity table shows the resistivity for gold (mantissa)is 2.44 My PMV measurements for the 1 ozt gold bar range from 2.16 to 2.21, so my PMV measurements are close but a little low. I don’t know if that has anything to do with the bar being in an assay case. If anything I might have thought that would cause a slightly higher reading. Too bad I’m unwilling to remove the bar from its case and then measure it. That would be the no-holds-barred, no excuses test.

The AGE coin consistently measured about 7.47 out of the air-tite using the PMV main sensor, about 7.7 to 7.8 using the two wands. In the Air-tite it measured about 7.76 except it wouldn’t measure with the small wand at all. The ~7.50 measurements are the most confounding result, unless it has something to do with it only being 22K gold. But still!

Too bad I don’t have a 24K gold coin to test. Anybody have a gold Maple Leaf they want to send me? In the interest of science, of course!

I’d feel a lot better about it if the AGE results were close to 2.44, but I’ll be satisfied with the consistency of the measurement I got for the AGE. Testing every coin I get will give me more confidence that 7.76 is what I should get for any 1/4 ozt AGE.

 

The AGEs test just fine (i.e., they pass) with the PMV in its pass/fail mode. That tells me that when selecting a PMV p/f mode to test a coin, the difference in resistivity is factored in to the p/f test result (of course), and the differences are big enough to require different metal selections. The PMV has gold and silver metal selection options as follows.

For gold:

99.9%
91.7%. (22K AGEs, for example)
90%
American Eagle (22K again)
Krugerrand
98.6%
Britannia 1990-2012

For silver:

99.99%
99.9%
92.5%
90% US pre 1900
90% US pre 1945
90% Coin 1960
96% Britannia
80% Canadian

Interesting about the pre 1900 and pre 1945 90% silver coins. Maybe the pre 1900 coins had a different 10% makeup than the pre 1945?

But I can see the need for the different metal selections if 24K gold has a resistivity mantissa of 2.44 and 22K AGEs are about 7.70. There is no way that each would sneak in under the limits and pass a test designed for the other.

I think I’m done. I returned all borrowed gold and silver used for these tests. Thank you jeffB for nudging me in the right direction with your pointers on resistivity.