Unexpected tone on the Goldscan 5

[bakergeol]

Unfortunately because of job commitments I have only gotten out with the GS5 a couple of times since receiving my GS5 from Mr. Bill. While testing the GS5 at a local freshwater beach on my first day I dug a sweet little high tone and was surprised to snag a thin gold band. The GS5 really is hot on small gold. Although mainly a gold nugget/specimen hunter I can see how beach hunting can be addictive.
There is one tone that surprised me. Silver coins being high conductors will of course produce a low tone in GB mode. However, place a silver coin on edge(dimes and quarters) and it will produce a high tone. As copper coins don't do this I was curious as to why small silver coins do this on all coil sizes.

George

 

[Eric Foster]

Hi George,

I have noticed this in testing and it appears to be due to eddy currents generated in the vertical cross section. i.e the coil field is then parallel to the plane of the coin, rather than perpendicular to it. Looking at the eddy current decay on a scope, it is considerably faster when a coin is vertical, than when it is horizontal. If you pass a vertical silver coin from one edge of the coil to the other, it should go Low tone initially, as the coil flux has a high horizontal component, then a short High tone as it crosses the coil axis, followed by a Low again as it moves toward the other edge. I'll set up a Goldscan to check this, in the next couple of days.

I suspect a copper coin does not exhibit this, because the conductivity of the copper coin is less than that of the silver, and the resulting eddy current decay is too fast. A silver 25c coin I have has a conductivity of 90, compared to pure copper which is 100 (measured with an Autosigma 2000 conductivity meter). However, a copper coin only reads about 50. Both coins have other metals alloyed with the base metal to improve hardness and wear resistance, resulting in the silver's drop from 108 to 90, and the coppers drop from 100 to 50.

Fortunately coins and rings are generally lying horizonally in the ground, so the detector just responds to the major eddy current path.

Eric.