Different Metals

[nugget hunter]

can anyone  give me a idea on what ratio or scale  there is between different metals and depth with the same detector ....say  made out of  6 different metals ...  US nickel  size coins    .... silver , gold , alum , nickel , platinum ,steel and stainless steel ......

[Steve Herschbach]

There is no such thing that I have ever heard of. Depth is determined more by target size than the metal involved. However, if you had test coins all exactly the same size made of different metals you would see depth differences. The difference will depend mostly on the frequency the detector operates at if we are talking single frequency detectors. Lower frequencies tend to favor high conductors and high frequencies favor low conductors. However, there is more to it than just frequency, such as ground balance efficiency at different frequencies for example. Long story short the differences would be relatively small except when comparing the highest conductors to the lowest conductors, and the difference will vary model to model depending on the frequency and other factors.

Some info here on the subject.....

https://www.detectorprospector.com/forums/topic/3778-vlf-punching-deeper/?do=findComment&comment=41284

Once you get into multifrequency operation even the information regarding relative frequencies gets tossed out the door.

Here is a post about the White's V3i and several coins compared at different frequencies. Notice how the difference between coins changes with the frequency change...

Link deleted since Findmall Forum update broke all old links

[Alluminati]

Typical VLF induction balance detectors discriminate on a conductivity scale.  You can google various "resistivity chart" to see the metals displayed in order and to get an idea of how similar they are, conductivity wise. This assumes all samples are the same size, typically coin sized.

Regardless if the detector has a scale of 50 or 100 for conductivity it will always be silver at the highest and small foil right above iron.

Certain detectors like the CTX-3030 and the ETrac also display a "Fe" number. Basically this number tells you how inductive a target is, (How magnetic it is, or it's inductive it is for a non-ferrous metal) This gives you an extra indication if its a deep piece of iron or not, an iron false will usually have a high Fe number.  (Dropped cursor on the quick-mask screen)

As far as the actual depths a certain machine will detect a certain target, will depend on what the target is and the operating frequency, assuming everything else is equal.

Low frequencies excite high conductors, high frequencies excite low conductors however beware target plots on a bell curve. While a low frequency is good for a silver coin, a high frequency may be better due to increased sensitivity to small objects. That is why I say it assumes all targets are the same size comparatively speaking.

Another factor is rings. You can take a ring that reads a 75 out of 100, cut it and the number will drop to 30. This is due to the Foucault currents induced by moving the coil over the ring. Here again, the conductivity scale is relative, assuming all rings are the same size.

 

 

[Alluminati]

For a pulse machine short delay, small coil and a fast decaying coil will get you the smallest nuggets deepest. (Low conductors) Adjust these three parameters as a compromise.

Other metals can be detected easier with a longer delay, coil decay can be relaxed somewhat and target size is still more or less tied to coil size. (Though a shorter delay will increase sensitivity to the smaller low conductors for a given coil size.)