Ground Balanced On The GPZ

[russ]

I have noticed the GPZ is for less susceptible to false ground noise and mineralization than my previous Minelab's, just go easy the sensitivity.  But I have more trouble with tree roots and burned tree roots or charcoal. I've had several targets that turned out to be 2 inch Saguaro roots as far away as 10 feet from the cactus. I've also had trouble with Palo Verde roots several feet away from the tree. I've found nuggets caught in tree roots and Saguaro roots before and now this new detector causes a bigger challenge to make sure it's not a nugget.

[hawkeye]

Russ,

Signaling on tree roots? Some months ago a forum member had an issue with his 2300 falsing when touching Palo Verde branches. Not sure if this is even related, but when he checked with Minelab they asked him to return it and they sent him a new one. Is anyone else having this issue?

[G.B.]

Appreciate the input GB Thanks.  Yeah the white paper would have put a halt a lot of things, but there's still plenty to chew on.

May I ask why you were stunned?

 

The response initially got loader as you would expect from a true target and l belived from the response of the detector that there was a definate taget in the hole only to have the detector do its thing and balance it out which left me shaking my head in amazement as I truely believed and would have bet money on it being a nugget

[russ]

Russ,

Signaling on tree roots? Some months ago a forum member had an issue with his 2300 falsing when touching Palo Verde branches. Not sure if this is even related, but when he checked with Minelab they asked him to return it and they sent him a new one. Is anyone else having this issue?

 

The base of saguaro cactus has almost always given a signal on Minelab Pi's, but now I get them on 2 inch diameter roots several feet from the saguaro at 8 inches deep. I have chopped the roots out of the hole looking for the target and the signal disappears. The roots are full of moisture, so not sure why but they will give off a signal.

[Gold Hound]

Detection patterns are far more complex than the blade and cone mythology sold by the marketers. One only need observe reality in the field to see that patterns for large targets and small targets are entirely different, even on the same coil. How many people know that the detection pattern for a small nugget on a large PI mono coil is a hula hoop, not a cone?

Same with GPZ. With large targets it acts like a mono coil but smaller targets react more to proximity to the coils winding overlap. The small targets also reverse tones in relation to where they are relative to said windings, producing some complex signals.

From the GPZ owners manual:

More information on the GPZ 14 coil http://www.detectorprospector.com/forum/topic/670-gpz-14-coil-for-minelab-gpz-7000/

That explanation is still simplified and dose not explain what is hapening correctly.

Both the transmit and recive are governed buy the 'inverse square law'.

The transmit field is emitted by the detector's coil this disipates at the square to the distance from the source, the coil winding.

Detector technician's know this, that is why all coils are a closed loop and the most efficent shape is a circle.

As the shape of the coil concentrates the signal under the middle of the coil.

To plot the field all you have to do is ise the 'inverse square law' and draw circles radiating from the coil winding where these overlap under the coil is where the field is strongest.

This concentrated field energizes the target, the target now produces its own signal, many times weaker than the original signal.

And this signal now dissipates acording to the inverse square law in more or less a spherical pattern depending on the target shape.

And the detector now has to try and recive this much weaker signal.

Now think about how the different types of coil's recive this signal that is dissipating according to the inverse square law.

Once you get an undersanding of this simple law of physics and think about what is happening under the coil you will get a real understanding of what is happening under the coil what ever type it is.

If I had any computer skills I would make an animation or a diagram of what is happening but I don't.

Simple physics really!

I blame all of the detector manufacturers for spreading over simplifed information on this subject when it is not that complcated.

[Reno Chris]

Radiant energy disperses into all three dimensions and so decreases in the cube of the distance. So it's the inverse distance cubed.

since the.energy goes out both from the coil and then from the target back to the receive coil, the total energy loss in both directions is the distance times 10 to the 6th power, or a million times.

[Ken Walls]

Radiant energy disperses into all three dimensions and so decreases in the cube of the distance. So it's the inverse distance cubed.

since the.energy goes out both from the coil and then from the target back to the receive coil, the total energy loss in both directions is the distance times 10 to the 6th power, or a million times.

 

 Yep, what he said. I guess I should have stayed at a Holiday Inn.

[jasong]

It's kinda tangential to the original subject, but... Radiated EM waves decrease as 1/r, any changing magnetic field produces radiation which has both an electric and magnetic component perpindicular to each other. Static electric fields decrease as 1/r^2. Static magnetic fields decrease as 1/r^2 near the dipole/coil and then crossover to 1/r^3 in the far field which is defined relatively speaking.

 

The GPZ appears to have both static and dynamic components though I still don't understand exactly what it's doing enough to assume anything about how it really works.

 

As to the subject of field geometry, a mono coil is simply just a flat solenoid so googling solenoid field diagram will give a person a good idea of what the field under a mono coil looks like - it's not a cone. On my old computer I have models I created in an FEA program when I got curious myself. 

 

I couldn't model DD's in that program since they aren't radially symmetric. But I can guarantee they aren't blades since there is no coil geometry that creates a blade or wedge shape. In fact I believe it's a physical impossibility, if one knows vector calculus they could probably prove this since it would imply the curl of the magnetic field is zero if I'm remembering my electrodynamics courses correctly, only possible when i or B = 0, magnetic monopoles, etc in other words cases that aren't metal detectors.

 

The DOD coil has a weird semi circular or rectangular TX coil so it isn't going to look like a DD or mono, but probably closer to a mono.

 

Once upon a time I got a degree in physics and did research in pulsed EM. Those days and memory have faded though.

 

As to the subject of the original post, I had that happen to me today too coincidentally, screaming target about 6 inches deep, dig more, go to pinpoint still screaming and then bam, gone. I think it was just a really nasty hotrock but I'm going to hike back again with my 4500 to double check sometime.

[Gold Hound]

Radiant energy disperses into all three dimensions and so decreases in the cube of the distance. So it's the inverse distance cubed.

since the.energy goes out both from the coil and then from the target back to the receive coil, the total energy loss in both directions is the distance times 10 to the 6th power, or a million times.

Look up 'inverse square law' on Wikipedia and you will se what I am talking about.

You're right about energy traveling out from the source in 3 dimensions, it travels out in an ever expanding sphere.

My explanation and mathematics are correct the inverse square law takes into consideration all 3 dimensions.

[DDancer]

Whether its addressed to me or not these are my thoughts :

 

I'm pretty sure I said its a useful myth.  It has some practical application in that those who follow it find it easier to visualize their activity with some result.  Simple is better for some.  Perspective not conversion is why I felt the view was worth the airing.  Observed results that conform to mythical patterns seem to work for some reason.

I also understand the need to state the facts.  Facts and faith both are powerful drivers.

 

I feel little need to break out a slide rule or explain the differences of various wave forms, their propagation or explain the mathematics of such. *shurgs*  In this thread anyrate.

 

Now I'm going to sound defeatist in this but this is way further off topic than I anticipated.  I almost regret having said anything at all.

Holiday Inn indeed

 

I'm hoping to see the result of GB's second check on the video in question.

I feel reasonably certain it was hot ground and a few other factors that stunned him and his mate.  The GPZ is not immune to hot ground from what I've been observing but its a heck of a lot better at tackling it.

 

My thoughts, and No I'm not really put out by the discussion. Hehh   The GPZ's ground balancing capabilities tied to other posts and advice are probably one of the least understood facets of the machine.  Signals and settings follow right along.

Thanks,

DD