GPZ 10" Xcoils In USA

[Norvic]

2 hours ago, madtuna said:

Yep...I don’t worry about all this alphabet stuff, I just get out there and do what works for me. But then I might be one of these crap detector operators I’ve been reading about lately.

while it’s great having all this knowledge about how the detector works, I’d prefer to master how to work it and I’m getting there by experimenting, testing, swinging the damn thing and experience.

Often the more you read about X, G, Y etc..the more confuddled you get, the more self doubt you create and therefore the less success and enjoyment you have.

Well I`m the same if it works gets gold, then that`s all I ask. Fortunately the country I detect in the Z runs with a more stable steady threshold then any detector before it without dumbing it down, with all 3 X coils I have. I also had no trouble before with the ML coils either thus from Andyys experience, I can only assume I have been very fortunate with the ground I work.

[Andyy]

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2 hours ago, jasong said:

Further, saturation point implies very little mag field change in the ferrite/ferrous material with increased TX strength, which should be a good thing. Less ground noise. So why do we want to avoid it? Would it be best to just saturate the crap out of the ground since everything past that point generates very little noise? Like the B curve for magnetite is almost flat after saturation even if you quadruple the external mag field, whereas up to that point the saturation effects B exponentially...

But something JP said was interesting.  Saturation will be amplified by the ferrite.  My guess is that the Rx can only translate a set range of magnetic field.  Maybe saturated ground with the Tx overloads the electronics that the Rx coil can handle. 

in JP's personal method of ferrite balancing, it was said: 

  "If the Ferrite balance is out the resultant X signal will blend with or elevate ground signals potentially causing spurious indefinable signals and generally make the detector noisier to listen to, all of this will affect depth. "

This is what happens with the Xcoil that cannot handle the return signals in "saturated" ground...

I think it is simple to JP because he has been so enveloped by all of the parameters and definitions for so long.  That makes it difficult and maybe frustrating to explain it to us.  I hope for his further input. 

[Chet]

My understanding of the how Ground and Ferrite balancing may work???

Soil contains minerals such as iron and other particles that create a somewhat constant Ground signal that can be averaged and fed into the GPZ 7000 mathematical equations as a Ground tracking value.  

Ground tracking across different up/down distances of unleveled ground is possible as long as the magnetic ground response is linear. Linear meaning that as the coil goes close to the ground and then away from the ground a uniform Ground signal strength change is expected.

The GPZ equations know from constant Ground tracking and/or you pumping the coil up and down periodically what kind of linear/uniform Ground signal response it should receive from the ground at different heights.    

Superparamagnetic particles normally do not have magnetic hysteresis or B curve like a small particle of iron. 

They do not retain a magnetic charge or north/south alignment like a small iron particle will. They change characteristics as the soil changes temperature. 

They are easily magnetically saturated.
 
When the soil contains great numbers of these Superparamagnetic particles and they become saturated they generate a non-linear/non-uniform Ground signal that disrupts the GPZ ground tracking and target processing equations.

To mitigate this X Signal problem the Ferrite balancing routine is providing a value into the GPZ mathematic equations to handle normal soil X Signal levels. The Ferrite value may be weighted in the different ground modes Normal, Difficult and Severe.

The Superparamagnetic particles nearest the overlap of the Transmit and Receiver windings near the center of the coil are the most susceptible to becoming saturated. 

The Transmit winding is 2 cm above the Receiver windings to increase the distance to the soil and reduce the stronger magnetic lines of force that are close to the transmit coil from saturating these particles.

Why is Proper Ferrite and Ground balancing important?

The transmit pulse energizes the metal target that causes magnetic currents to generate a short duration magnetic field that is sensed by the receiver coils.

The detectable duration of the target return is called the Time Constant of the target.

Small gold nuggets have a very short Time Constant as well a weak signal return. Larger nuggets, bullets, nails, and junk have long Time Constants.

Soil has a Time Constant that is similar to small nuggets. 

Small nuggets that have Time Constants that are shorter or longer than soil can be detected.

Small nuggets that have the same time constant as soil may not be detected.

For small nugget detection it is important that accurate, narrow Ground and X Signal values be maintained. 
  
Have a good day,
Chet
 

[flakmagnet]

Chet you have blown my mind. AND I think I can intuit (rather than understand), what you are saying. You, Jason,  and Andyy are in a realm of your own but it's intriguing to try to decipher. JP probably knows what you are talking about and some other's, but it's rarified air you guys are breathing.

[jasong]

Thanks for explanation Chet, you are speaking my language... 

Given the superparamagnetism stuff, is there a possibility here that "X" from Minelab actually represents susceptibility and not saturation? Magnetic susceptibility is represented in physics by the Greek letter Chi. Which looks a lot like "X". And it's used in reference to paramagnetic materials far more often than is saturation.

That would also (potentially) explain how some salts can throw the X balance off (A question I keep asking over and over), some salts exhibit paramagnetism. So while not saturable in a ferromagnetic sense, I believe some salts can exhibit postive magnetic susceptibility values. Aka "X". Though I have no idea if they exhibit superparamagnetism or not. I hadn't considered paramagnetic effects with salt, only conductive/inductive, I guess it can affect both though in theory.

I still have a ton of questions, but it's late. 

[Chet]

The X Signal term has been used in metal detector technology for many years. The X Signal is the magnetic effects generated by the transmitter and detected by the receiver. 

Another received signal used in VLF detectors is a resistive R Signal.

This website will automatically download a .pdf file that may help some on this subject.

https://www.iaom.info/wp-content/uploads/06mdpkgwc17.pdf

The original GPZ equations may have had problems with auto ground balancing tracking because of the non-linear effects that the nanoparticles created in the magnetic X Signal returned from highly mineralized soil. 

Thus the Ferrite balancing routine was incorporated to provide a workaround for the problem.

When detecting in Nevada after a rainstorm the GPZ gets a lot of ground noise and on buried test targets it loses depth. 

A combination of effects caused by the wet desert soil should be considered; soil temperature is affecting the nanoparticles; wet salt may be causing some kind of magnetic change in the soil; wet salt may be causing more conductivity loss through the soil.

Have a good day,
Chet
 

[flakmagnet]

?

[jasong]

The question I can't seem to get straight in my head is this: Why track X at all in the GPZ if we aren't tracking it in our local grounds and using the ferrite value instead?

Semi-auto locks X to the ferrite, which doesn't change with location as we move around (unless we QT, which we are told should never be done without the ferrite). In another post I saw JP and someone else talk about balancing to the ferrite in the air to eliminate the effects of the local ground too. If that's the case, then why even track X in the ground at all, why not remove it from the tracking program altogether and just have the ferrite saved in the firmware, or embedded in the coil? 

Is it only to update the program with temperature changes on the ferrite through the day?

Also having trouble understanding why a constant ferrite value in the yellow ring will work anywhere - Australia, NV, the moon... Why have a tracker at all for that component if it's held constant to a ferrite that doesn't change in those places? I thought it had something to do with how the ferrite affects the ground underneath it, but if you can do the balancing with the ferrite in the air, that throws that idea off.

So, in places with very little temperature variation and very little ferrite component in the soil, is there still a need for the ferrite? Conversely, is the need for the ferrite much greater in places with high temperature variation and high mineral content? Just taking a wild guess here at why I'm not seeing much effect from the ferrite in AZ where I detect in mild ground and places where it's around 50 degrees and cloudy all day.

And a different note, does the ferrite in the Z14 coil over the wire solder points affect the GPZ's X balance? 

[jasong]

This kinda leads back to Andy and X Coils because I'm wondering now if there is a work around to having to switch back to the Z14, balance to the ferrite, then switch back to the X Coil where ground is particularly gnarly such as where Andy is at.

Chet's idea of just raising the coil up another 2+cm over the ferrite is definitely the first thing to try and the easiest.

But if that doesn't work, I wonder if a ferrite taped to a stick and waved 5+cm in front of the coil while it's in the air might also be worth trying too since it removes the local ground ferrite component (salt will still get picked up a bit at hip level though). Based on a thread I saw discussing doing ferrite balance in the air with the Z14. If all the detector needs is a balance to the ferrite, and not the ground itself, for X anyways, then this may work in particularly bad ground with the X10. And the let Semi Auto track the G in your local ground as normal. Just never run in Auto if that works.

Not a great solution I know, but potentially worth trying just to see if it works or not and then go from there. The problem being needing to carry the contraption around if the temperature change thing requires rebalance.

[Nevada Brian]

The yellow ferrite ring is fixed, the ferrite value never changes within that ring, so why not incorporate that value into the equation through firmware everytime the QT button is depressed, as suggested by Jasong.  

Last summer, I spoke with a GPZ user from Australia, his recommendation was to balance the yellow ferrite ring in the air.  I have yet to try this technique as carrying around a stick is the last thing I need and finding sticks in the desert is no easy task.

Brian.