GPZ 7000 Pi Or………..???

[Gerry in Idaho]

As a dealer, I remember being told the GPZ-7000 is not a PI.  Now it was not Mr Candy who said it, but the way I was explained, it's different that a PI.

I agree with some of what you say Aureous but at the same time, I don't feel comfortable telling customers it is a PI.

Interesting read and I am all ears and willing to learn.

[Aureous]

Last comment:

Is ZVT a PI-evolved technology check-list.

ZVT: Time domain (PI)  CHECK

ZVT: Sub KHZ Frequency (PI) CHECK

ZVT: GP & GPX type audio with obvious MPS (PI) CHECK

ZVT: Explained by the designer as BiPolar PI in essence CHECK

Even Minelab's own published graph (as shown by Phrunt) shows it runs in time domain with BiPolar PI tech. CHECK

Has this tech been expanded, evolved and altered to make it the best gold prospecting detection technology EVER??? CHECK.

Hands down it will become the new benchmark in gold prospecting detection technology and one which will offer ML a heap of future expansion into the future. Geosense will surely be added to the new GPZ's at some point, Im certain.

[jasong]

I agree it's probably closer to PI than VLF. But I really think it's sort of a hybrid.

A PI basically works by doing a pulse, then being quiet (at 0 volts) and listening during a sample period. Then just repeats this pulse - sample period over and over. But really it's still a cyclic square wave maybe with variable duty cycle, it's just the lower cycle ends up at zero volts, but it's still basically a square wave with a 0v (aka ground) reference and no negative reference. Like this:

 

Whereas ZVT I believe is somewhat of a misnomer. I don't think there is any "zero volt transmission", in fact it's kind of a non-sensical term because transmission implies voltage - an electric field cannot exist without some voltage to begin with, that's literally the defintion of the electric field - volts/distance. Every changing magnetic field has an electric field associated with it, and vice versa.

I think what ZVT does is use a PI-like TX wave, but changes the voltage reference so that each part of the wave has both a positive and negative component. And then, the sample occurs when the magnetic field switches polarity due to the voltage switching polarity. So, in the white circled areas here:

That's the best I can make out of it from their weird patent language.

If this is somewhat along the lines of what ZVT is then it's basically a hybrid between PI and VLF. It samples somewhat like a PI (aka, decay time (time domain) not phase offset (frequency domain)) but uses a continuous wave. And it also means you can take the benefits from both (ground immunity and discrimination) selectively by sampling like a PI once cycle and like a VLF the next cycle.

Or actually, you could probably sample both ways simultaneously if this is really the way it works. 

I'm curious if Carl or Chet or someone can comment further, I'm sure they've looked at the TX waveform on an actual scope. I could be misunderstanding something, the language is so weird and hard to decipher. 

That's a simplification, an actual wave could have variable duty cycles or anything else and needn't be a perfect square wave either. For instance, something like this is still a continuous wave, but it'll sound like a "pulse" on a radio for instance. This duty cycle and pulse spacing likely what comprises the "timings" like Normal/Difficult, etc.

[Gold Catcher]

"A more complete definition actually would be Zero Reactive
Voltage Transmission. The transmit coil Reactive Voltage refers
to voltage associated with the transmit coil winding that is
proportional to changes in the transmitted magnetic field.
Signals detected directly from the transmit coil are given the
same name ‘reactive‘ because they are directly proportional to
the transmit coil reactive voltage.
The ZVT transmitted field is designed to be as constant
(unchanging) as possible during the receive periods; this means
that the transmit coil’s reactive voltage must be zero during
these constant field periods, and thus too is a receive signal
directly from the transmit coil’s field. Hence Zero Reactive
Voltage Transmission (ZVT) refers to this ultra‑stable transmitted
magnetic field period during which receiving occurs."

[jasong]

Not sure where that quoted paragraph came from - but that's pretty much the point I was making. "Zero voltage transmission" is sorta a non sensical term, scientifically speaking. The only time it makes sense is if the mag field is stable, which means there is no transmission occuring. EM waves by very defintion are changing, not stable, and stable EM fields don't transmit.

I might have my sampling on the diagram I drew 90 degrees off though. Dunno, and no desire to go read ML patents again to find out.  

[Gold Catcher]

1 minute ago, jasong said:

Not sure where that quoted paragraph came from

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.minelab.com/__files/f/254716/KBA%2024-1%20Basics%20of%20the%20GPZ%207000%20Technology%20Zero%20Voltage%20Transmission%20(ZVT).pdf

 

Sorry, long URL....

[jasong]

Another thought occurs to me too regarding hybrids - the fact that there are 2 RX loops could provide for some interesting sampling techniques vis a vis a little from column a, a little from column b, plus the ability to run in a mode similar to a gradiometer, not looking at RX strengths but instead analyzing the difference between two RX fields of any strength, or how a single field changes in time domain. A hugely important capability in experimental physics. Or maybe already does and that's why they use a DOD for the GPZ. Accurate depth discrim should technically be one possibility along that line.

Also, if running as PI, there is technically no reason why the GPZ couldn't just use the TX loop as an RX as well to give you effectively 2 different size coils in the same coil (a DOD and a smaller mono). Or for that matter, a true mono mode switch on the detector to run normal (aka lightweight) standalone mono coils, which would probably be better since the loop could be wound optimized for both TX and RX unlike a DOD TX loop.

Just some thoughts here pertaining to potential future developments. One thing I'm almost certain of though is discrimination is a possibility, somehow. Or maybe already is.

[PhaseTech]

To put it simply, a PI detector can use a Mono coil, because there is a pause between transmit and receive cycles. So the same winding can be used for both. ZVT cannot use a mono coil, so it isn't a Pulse Induction machine in the true sense. I have always explained the GPZ as taking the best characteristics from VLF and PI and meeting somewhere in the middle. 

I still love the GPZ, its performance, ground balance, audio, robustness etc etc. 

[Gold Catcher]

10 minutes ago, PhaseTech said:

I still love the GPZ, its performance, ground balance, audio, robustness etc etc. 

Could not agree more! Just the weight sucks. 

[flakmagnet]

On 6/20/2022 at 11:40 AM, jasong said:

I'd take a lightweight 7000 equivalent, sell my 6 and 7, and probably call it good there.

If ML did this, they would make a ton of money…and a bunch of us would jump off the incremental- train.

Come on MineLab, do it!