A
Anonymous
Guest
I did some quick tests today, using the conductivity meter I bought on Ebay. Having tried a range of US and UK coins, it appears to give consistent results. I
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A
Anonymous
Guest
Hi Eric
What's the name of the conductivity meter you have bought?
Regards
Mark
What's the name of the conductivity meter you have bought?
Regards
Mark
A
Anonymous
Guest
[No message]
A
Anonymous
Guest
Hi Eric
Thanks
Mark
Thanks
Mark
A
Anonymous
Guest
US 5c 75%Cu 25%Ni
US $1 90%Ag 10%Cu
US clad outside 75%Cu 25%Ni inside 100%Cu
I am surprised to see such a low value for clad 25c. Is the frequency of the meter high enough to see skin effect?
Robert
US $1 90%Ag 10%Cu
US clad outside 75%Cu 25%Ni inside 100%Cu
I am surprised to see such a low value for clad 25c. Is the frequency of the meter high enough to see skin effect?
Robert
A
Anonymous
Guest
Hi Robert,
The frequency of the meter is 250kHz. Perhaps it is only seeing the outer coating and not the copper core?
Eric.
The frequency of the meter is 250kHz. Perhaps it is only seeing the outer coating and not the copper core?
Eric.
A
Anonymous
Guest
HI Eric and all
Interesting result regarding the gold.
Perhaps we should send over some samples for testing. The results would certainly be of interest to those developing new gold detectors. What size nuggets are required for the meter to work???
Have you access to any gold coins for that would be suitable for tests? Perhaps even gold jewelery test results would be of interest to treasure hunters.
Most interesting
Thanks Eric
Cheers
Steve D
Interesting result regarding the gold.
Perhaps we should send over some samples for testing. The results would certainly be of interest to those developing new gold detectors. What size nuggets are required for the meter to work???
Have you access to any gold coins for that would be suitable for tests? Perhaps even gold jewelery test results would be of interest to treasure hunters.
Most interesting
Thanks Eric
Cheers
Steve D
A
Anonymous
Guest
Yes, 250 kHz explains the clad reading. Too much of the current is flowing in the outer layer. It also explains why the 10c reads higher than 25c because the outer layer of the dime is thinner.
But I still do not see why the $1 reads so low.
Robert
But I still do not see why the $1 reads so low.
Robert
A
Anonymous
Guest
The silver dollar is dated 1889, so maybe the alloy was different (less pure) than for a modern one. I don't have a later one to compare with. Regarding copper coins, I measured our 1p and 2p coins and got readings of 50 and 53 respectively. I guess there must be another metal alloyed with the copper to give it greater hardness, maybe tin or zinc. The Hocking meter has a calibration piece of annealed copper on the front panel. This gives the correct reading of 101.2.
Eric.
Eric.
A
Anonymous
Guest
Remove the cladding and the reading goes up to 90.0.
I also wondered what effect the surface irregularity due to the design on a coin was having. Took a 1965 large English penny and took a reading on both faces at 51.00. Filed one face down to a flat surface and the reading was still 51.00.
Some 13th century silver hammered coins give readings between 20 and 40, but then they are only 0.6mm(0.025in) thick.
So it looks as though the conductivity meter provides useful information on coins, provided they are not clad or plated, not too thin, and greater than 10mm diameter, which is the size of the active part of the probe.
I've only got it to read on one gold ring which has a band 0.5in wide. The reading was 13.6 and I believe it is 9 carat from the rather indistinct hallmark.
Eric.
I also wondered what effect the surface irregularity due to the design on a coin was having. Took a 1965 large English penny and took a reading on both faces at 51.00. Filed one face down to a flat surface and the reading was still 51.00.
Some 13th century silver hammered coins give readings between 20 and 40, but then they are only 0.6mm(0.025in) thick.
So it looks as though the conductivity meter provides useful information on coins, provided they are not clad or plated, not too thin, and greater than 10mm diameter, which is the size of the active part of the probe.
I've only got it to read on one gold ring which has a band 0.5in wide. The reading was 13.6 and I believe it is 9 carat from the rather indistinct hallmark.
Eric.
A
Anonymous
Guest
Good idea Steve; just send me over a big bag of large nuggets <IMG SRC="/forums/images/smile.gif" BORDER=0 ALT="
"> <IMG SRC="/forums/images/smile.gif" BORDER=0 ALT="">. Seriously though, testing coins and other flat metal samples is easy, testing gold nuggets, rings and jewelry is rather more difficult and in some cases impossible. Ideally the sample needs to be flat and a minimum of 10mm diameter. Minimum thickness, similar to a standard coin. As I said in the previous post, I can only get it to work on one ring that has a band 0.5in wide. There is curvature in both directions with this ring and with the ring touching the middle of the sensor, it is about 1mm off at the edges of the measurement area. If there is insufficient signal an L appears on the display, so I assume that the reading is correct. The gold nugget, which is from Oz (maybe you sent it as it was attached to a card signed Steve) weighs 1.9gm. It is 19mm long x 6.75 max width and 2.15mm maximum thickness. Ideally, I would think that a disc or oval shaped nugget, flat on one side, with a 2mm minimum thickness and minimum diameter of 10mm would give a reliable reading. Guess that would be about 5gm weight.
Testing of gold coins would also be interesting as they would be of a known purity. I have some detectorist friends who have found gold sovereigns so I could probably get one for a test OK.
Eric.
"> <IMG SRC="/forums/images/smile.gif" BORDER=0 ALT="">. Seriously though, testing coins and other flat metal samples is easy, testing gold nuggets, rings and jewelry is rather more difficult and in some cases impossible. Ideally the sample needs to be flat and a minimum of 10mm diameter. Minimum thickness, similar to a standard coin. As I said in the previous post, I can only get it to work on one ring that has a band 0.5in wide. There is curvature in both directions with this ring and with the ring touching the middle of the sensor, it is about 1mm off at the edges of the measurement area. If there is insufficient signal an L appears on the display, so I assume that the reading is correct. The gold nugget, which is from Oz (maybe you sent it as it was attached to a card signed Steve) weighs 1.9gm. It is 19mm long x 6.75 max width and 2.15mm maximum thickness. Ideally, I would think that a disc or oval shaped nugget, flat on one side, with a 2mm minimum thickness and minimum diameter of 10mm would give a reliable reading. Guess that would be about 5gm weight.Testing of gold coins would also be interesting as they would be of a known purity. I have some detectorist friends who have found gold sovereigns so I could probably get one for a test OK.
Eric.