THREE COINS IN THE P.I. FOUNTAIN

[Skippy]

I'm guessing that a lot of masking is taking place, and the second and third coins don't contribute much. But...I reckon there may be an effect where the first coin excites the second one, and subsequently the third one, giving a doubly and triply delayed response. The second and third responses will be weak, but visible?

[green]

What Carl said. I stacked nickels, 2,3,4,5 touching and insulated in a four inch coil. Five nickels more than doubled the TC with less than a 10% increase in amplitude

[Carl-NC]

I would expect the TC to increase somewhat for the 2nd coin, and a lesser amount for the 3rd.

[Ferric Toes]

Gues that traces are pretty the same in all cases.

But can you repeat this test with oxidated (instead of isulated) coins.

So called "oxidation" can be in some cases conductive enough to get "cache" response.

I also did the test without the insulation, so there was metal to metal contact and the results were exactly the same. The coins are two of 1965 and one 1977 and are in clean condition. Even holding them tightly together did not make a difference.

Eric.

[bernte_one]

i think there will be a raise in the line but all together smaller as you would multipli the raise from the first coin 3times

[WM6]

Gues that traces are pretty the same in all cases.

But can you repeat this test with oxidated (instead of isulated) coins.

So called "oxidation" can be in some cases conductive enough to get "cache" response.

[Ferric Toes]

What will the answer be…?

I have 3 identical coins which are British Crowns made of cupro-nickel alloy. Diameter 38.5mm. thickness 3mm, and weight 28gm. Electrical conductivity is 5.5 as measured on a Sigma 2000 conductivity meter. That is 5.5% of the conductivity of pure annealed copper (100%). True TC is 45uS.

Using a small solenoid coil (35mm D) I put one coin on axis, spaced such that no saturation is taking place in the RX circuit. On a scope I now see a clean decay curve which merges with the noise round about 100uS. Plotting the curve on log linear scales between 20 and 100uS, I get a nice straight line, so it is a classic exponential decay.

I now place a second identical coin on top of the first with a thin insulating layer between, and the results plotted.

The last part of the experiment is to place the third coin on top of the other two, again with the insulating layer and a plot completed.

Comparing the results and also the scope traces, it wasn’t quite what I expected. What do you think I saw? Good question for the theoreticians, and for those with practical gear to do a test.

What’s the relevance? Cache hunting where considerable numbers of coins are together, but not necessarily in electrical contact due to oxidation.

Eric.