Australian Dirt

[brucester]

Hello,

Just trying to better understand the situation with PI's in highly mineralized soils.

What exactly is the problem? I mean, dont PIs just ignore the ground?

I still havent been metal detecting and rarely get out into the goldfields so not sure what the challenge is when it comes to designing a detector that performs well in the australian outback.

I have been fooling around with my surf pi and it works well on the lawn and on the beach. But when i used it over clay tiles inside the house for example, it completely stops working.

Is it a penetration issue? Or a false signal issue due to all the iron in the soil? Or what?

What does a minlelab PI do in the outback that the surf pi isnt doing?

No specifics, just after a general explanation of the problem and rough solution :P

Oh, and why do hard tiles generate a false signnal then max out the detector so it no longer detects anything when it is close to tiles. For example, if i put a coil on the lawn, the detector beeps when skimmed over it. Put the coin on the tiles, and nada.

Thanks

[mikebg]

Bruchester, see the block diagram that explains how it is formed TGT signal.

http://www.geotech1.com/forums/showt...793#post163793

This block diagram is valid for all types of metal detectors. Think what mathematical operations should be performed in a metal detector to compute H (s) - transfer function of the target. So it is no wonder the opinion of Dave J. - a world-class designer of metal detectors:

http://www.geotech1.com/forums/showt...831#post163831

[Dave J.]

Hello,

Just trying to better understand the situation with PI's in highly mineralized soils.

What exactly is the problem? I mean, dont PIs just ignore the ground?

I still havent been metal detecting and rarely get out into the goldfields so not sure what the challenge is when it comes to designing a detector that performs well in the australian outback.

I have been fooling around with my surf pi and it works well on the lawn and on the beach. But when i used it over clay tiles inside the house for example, it completely stops working.

Is it a penetration issue? Or a false signal issue due to all the iron in the soil? Or what?

What does a minlelab PI do in the outback that the surf pi isnt doing?

No specifics, just after a general explanation of the problem and rough solution :P

Oh, and why do hard tiles generate a false signnal then max out the detector so it no longer detects anything when it is close to tiles. For example, if i put a coil on the lawn, the detector beeps when skimmed over it. Put the coin on the tiles, and nada.

Thanks

Deja vu!

Back in the early to mid 1980's I was doing PI R&D and seemed to be making a lot of progress. Until I made the mistake of swinging a prototype over the red brick walkway to my front door. I put those bricks there myself and knew the walkway wasn't underlain by metal. I pulled a brick out and busted it up with a hammer-- all the pieces did the same thing that the walkway did. There was no metal, but there was ferric oxide. Gamma ferric oxide specifically, although I didn't know that at the time.

Aussie laterite is just about the same thing as your clay tiles and my fired bricks.

Not long after that I built a PI that cancelled out the ferric oxide. It discriminated out iron metal too, you could search in any kind of mineralization and not get ground pickup, and not dig trash either, just high-conductivity US coins. A real sweetheart of a machine, about 2 pounds (less than a kilogram), ran off a single zinc-carbon 9 volt battery. But not sensitive enough to be a marketable product in places without high mineralization. Had I been living in Australia, I might have grasped the importance of what I had and developed it further. As it was, all we ever got out of it was the Fisher Impulse, a competent but boring underwater machine.

--Dave J.

[mikebg]

GENIAL IDEA

I have an idea how to use a lightweight PI machine in places without high mineralization. Simple make search head weighty and mineralized.

[Ferric Toes]

I have an idea how to use a lightweight PI machine in places without high mineralization. Simple make search head weighty and mineralized.

Too late! You can't patent it now it's in the public domain. Could have called it a BB (Brick Balanced) coil. Why would you want to use it over non-magnetic ground? Suppose the susceptibility would concentrate the field slightly. Better to use a slab of ferrite.

Ferric Feet.

[mikebg]

Too late! You can't patent it now it's in the public domain. Could have called it a BB (Brick Balanced) coil. Why would you want to use it over non-magnetic ground? Suppose the susceptibility would concentrate the field slightly. Better to use a slab of ferrite.

Ferric Feet.

Eric, You started to become more and more made of Fe (iron).
Since you already was Ferric Toes, now you became Ferric Feet.

Do you know what is Johnson noise, who and how generate it?

http://www.geotech1.com/forums/showt...758#post134758

[Ferric Toes]

Eric, You started to become more and more made of Fe (iron).
Since you already was Ferric Toes, now you became Ferric Feet.

Do you know what is Johnson noise, who and how generate it?

You don't have to generate it - it just happens. It is thermal agitation of electrons in a conductor. No applied voltage needed. That is why resistors are noise generators. Discovered by John Johnson, not Dave Johnson.

My feet are firmly planted on the ground, just like your BB coil. I sometimes go up on my toes to see what is outside the box.

Ferric #

[Ferric Toes]

Hello,

Just trying to better understand the situation with PI's in highly mineralized soils.

What exactly is the problem? I mean, dont PIs just ignore the ground?

I still havent been metal detecting and rarely get out into the goldfields so not sure what the challenge is when it comes to designing a detector that performs well in the australian outback.

I have been fooling around with my surf pi and it works well on the lawn and on the beach. But when i used it over clay tiles inside the house for example, it completely stops working.

Is it a penetration issue? Or a false signal issue due to all the iron in the soil? Or what?

What does a minlelab PI do in the outback that the surf pi isnt doing?

No specifics, just after a general explanation of the problem and rough solution :P

Oh, and why do hard tiles generate a false signnal then max out the detector so it no longer detects anything when it is close to tiles. For example, if i put a coil on the lawn, the detector beeps when skimmed over it. Put the coin on the tiles, and nada.

Thanks

Hi Brucester,

This report might help.

Eric.

Soil Tests 2001.pdf

[Prospector_Al]

Hello,

Just trying to better understand the situation with PI's in highly mineralized soils.

What exactly is the problem? I mean, dont PIs just ignore the ground?

I still havent been metal detecting and rarely get out into the goldfields so not sure what the challenge is when it comes to designing a detector that performs well in the australian outback.

I have been fooling around with my surf pi and it works well on the lawn and on the beach. But when i used it over clay tiles inside the house for example, it completely stops working.

Is it a penetration issue? Or a false signal issue due to all the iron in the soil? Or what?

What does a minlelab PI do in the outback that the surf pi isnt doing?

No specifics, just after a general explanation of the problem and rough solution :P

Oh, and why do hard tiles generate a false signnal then max out the detector so it no longer detects anything when it is close to tiles. For example, if i put a coil on the lawn, the detector beeps when skimmed over it. Put the coin on the tiles, and nada.

Thanks

Hi brucester,
Here's an answer to your question without any fancy theory:

That PI detectors ignore the ground is wishful thinking. Certain ground minerals mimic metallic targets. Tile and bricks often contain high levels of these offensive minerals, to a degree that will overload the metal detector and put it out of business.

Most metal detectors have a "ground balancing" system whose object it is to minimise the effect of the offensive minerals. However, the ground balancing systems have a limited dynamic range, and when the magnitude of the ground signal exceeds that range, the detector stops working.

The most unfortunate part of this story is that even when the ground balancing system works as advertised, it decreases the sensitivity to desirable targets. When the ground signal matches the signal form a target, the target response may disappear altogether.

The degree of signal loss depends of the setting required to balance out the ground.

Beach sand is largely devoid of offensive minerals, that's why less complicated (and less expensive) detectors work well there.

The metal detector technolgy is still evolving and what I said above will become incorrect within a year...

In the mean time, have fun,

Prospector_Al