GPZ 19 Accessory Coil - Coming Soon!

[Tortuga]

On April 26, 2016 at 3:50 PM, goldenoldie said:

Thanks RDD for your reply and the pic of your nugget.

Unfortunately Iron and Steel produce a better response than Gold.

I know you're right but isn't gold denser and more conductive?

Does it have something to do with iron and steel being refined metals or maybe just how they're found? Considering if a nugget is still "in situ" and not sitting in an old tailing pile or pothole, it can very be ancient and may have occupied a bedrock crack or clay bar for thousands of years. It should have a lot more clay and soil built up around it than a piece of iron or steel dropped or tossed 50-100 years ago. Maybe that's why manmade trash targets are typically louder and don't have that soft, quiet tone like some gold nuggets. 

[Norvic]

Yeah, solid gold is more dense and more conductive but ferrous objects because of time have corroded and leached into their surrounds unlike gold which is basically inert thus no "halo" whereas old ferrous objects have a halo. You`ll note this when you disturb that halo whilst digging ie the signal decreases.

[Steve Herschbach]

Metal detectors react to conductive targets or magnetic targets. Iron and steel having both conductive and magnetic properties present a metal detector with a double wallop.

[Randy Lunn]

With the new 19" coil it will be interesting to see the trade-off between small gold sensitivity and depth. The new ZVT (Zero Voltage Transmission) technology does not seem to as sensitive to the traditional trade-offs. Understanding the shape of the larger coil's "sweet spot" will be interesting too. Will power consumption be the same? Where will the trade-offs be?????

[robby_h]

Metal targets are represented as a coil with L (inductance) and R (resistance). The time constant is L/R (large bulky objects have a long time constant and small targets have a short TC).

The magnetic properties of iron enhances its inductance, which in turn increases its time constant making it appear to be much larger than it is.

For those interested in further reading download the following article by Bruce Candy, page 4.

http://www.minelab.com/__files/f/11043/KBA%2000-1%20Metal%20Detector%20Basics%20and%20Theory.pdf

[Norvic]

That`s a good read, perhaps that "halo" is the inductance Bruce Candy speaks of. Perhaps the ferrous oxide whilst not being magnetic,  creates the field, also explaining why the signal diminishes when we dig into it and break that field. Those eddies from nuggets shape, thus varying the inductance of the field may also help explain why we often get a reverse signal over some nuggets.

Dunno food for thought.

[Tortuga]

Thanks guys

[Gold Hound]

Cant wait for the new coil already got 2 years worth of area's to run it over!

I can see it being a near permanent fixture on my detector.

[Gold Hound]

On 4/28/2016 at 7:08 AM, Norvic said:

That`s a good read, perhaps that "halo" is the inductance Bruce Candy speaks of. Perhaps the ferrous oxide whilst not being magnetic,  creates the field, also explaining why the signal diminishes when we dig into it and break that field. Those eddies from nuggets shape, thus varying the inductance of the field may also help explain why we often get a reverse signal over some nuggets.

Dunno food for thought.

What hes talking about in the paper has got more to do with the conductive and ferro-magnetic properties of the different metals.

The rx size of the winding the time constants of the target the depth of the target and the inverse square law and mineralization all dictate the result you'll get on a particular target.