Coins as Test Objects

[Anonymous]

For some years now, I have used readily available coins as a means of comparing detection ranges both for air and in ground tests. Depending on the application, different coins can simulate different types of non-ferrous target. For example a US 5c coin has similar electrical characteristics to a medium 14k gold ring. Hence a detector that gives a good range on a US 5c will be efficient at finding a wide range of rings. In the UK a similar coin in size and electrical conductivity would be a 20p piece. We also have a smaller 5p coin which is useful for testing the ability to find lower conductivity items. Recently, there was suggestion from an Australian detectorist about using their 5c coin as a standard test object for gold nugget detectors. I had an initial look at the coins to see how they compared in size, thickness and weight. Here are the results.
US 5c, 21.13mm diameter, 1.9mm thickness, 5.00gm weight
UK 5p, 18.01mm diameter, 1.72mm thickness, 3.2gm weight
Aus 5c, 19.41mm diameter, 1.38mm thickness, 2.8gm weight
I have not yet had a look at comparative detection ranges but the Australian 5c looks the most difficult target as it is the thinnest. I don

 

[Anonymous]

Eric, the US nickel is also 75% copper and 25% nickel.
Terry in Hawaii

 

[Anonymous]

Eric I had one of your mini pulses some years ago it had a problem seeing the aussie.5 cents.
so your right it is a difficult target
regards
kris
PS a friend of mine still uses the mini-pulse up in Queensland

 

[Anonymous]

Hi Kris,
Yes, the Minipulse would have had difficulty with the Aussie 5c. It had a longer pulse delay than later machines; 30uS if I recall correctly. Most of the signal would be gone by then. Tried an air test with the 5c on an Aquastar with 10in coil. Got 13in in the workshop where the electrical noise level is quite high. Also got he same range for an English 5p, which is slightly smaller diameter, but thicker.
Eric.