Gold Chains,

[JBM]

Some months ago we had a very educational thread about the problems and reason that most detectors will not pick up on gold chains.

At our dig today detectorists using all the usual detectors from a the main manufacturers gave 3 chains of different purity a checkout and we all failed.

Can the kind person who posted up the brilliant writeup on the reasons for this please post it again for me to help a few of our club members as I only remember the basics of the writeup.
Many Thanks,Jerry.

 

[Cody]

Actually we can cut through the tape by saying that some gold chains cannot be detected in all metal or discrimination because they look like soil minerals. A VLF detector detects or rejects based on a time constant associated with a targets. If the time constant indicates soil then it is rejected. If the time constant indicates anything other than soil then it depends on if we have selected that time constant to be accepted or rejected. While this is not 100% technically correct it is very close to the explanation in the patents and I guess close enough for government work. Ha

A time constant is generated by the flow of eddy currents on or near the surface of a conductive material. Iron has a very short TC due to the magnetic properties, precious metals have a long TC, soil mineral have similar but different attributes so can be rejected, and other metals have from medium to long TCs. Since the links in a chain are not connected and the flow of eddy current is disassociated like conductive soil minerals. In some ways this is also similar to the problem with nails in that the eddy currents flow around and down the length of the axis of the nail so adds up to a long TC which looks like silver. The complex eddy currents for a chain look like soil minerals although eddy current do not flow in soil minerals.

Some chains can and will be detected. I have a gold ring that is detected with my Explorer11 which is how I found the ring. I cut the band of the ring with dikes and the ring cannot be detected. If I solder the band together the ring can then be detected. This happens because the TC changes if the band is connected or broken. I mention this simply to show the relationship between a TC and if we do or do not detect a target.

The Explorer has a lookup table of TCs and compares a generated TC by a target to the lookup table. There is an established set of parameters for comparison or the detector would not know what to do with the raw data. The old TR detector simply reported all targets no matter so did not need this comparison.

What is virtually never understood is the Explorer Series, Quattro, and Sovereigns are PI detectors. Candy invented a sub-class of a PI detector that discriminates using time domain technology. My guess is most users of an Explorer do not realize they are using a PI detector. The new X-Terra in comparison is a single frequency VLF with the 50 able to change to a different frequency that is optimum for the coil size.

Hope this helps,

 

[JBM]

Thanks Cody,thats brilliant,Jerry.