Minelab GPZ 7000

[Monolith]

Some people still believe it is a PI

Is it a PI or not?

The simulation shows Flyback at about 270V

Target response:
1=Tau 500us
2= Tau 100us
3= Tau 10us
4=Tau 5us
5=Tau 1us

[Davor]

Simulations also show global warming, yet there is no such thing going on for 18 years or so.

It is all in a patent. No need to dig any deeper.

[deemon]

However, it simply is not a PI device. It is a step voltage IB, a VLF if you like, and a proof that there is a lot for VLF to catch up.

But don't forget , Davor , that every device of this kind ( square current wave ) does produce a target response that has an exponential decaying shape , like PI does . So we can say that it has properties of PI and VLF devices at the same time This is why I called my topic "Square wave Pulse Induction" ...

[deemon]

Is it a PI or not?

The simulation shows Flyback at about 270V

Target response:
1=Tau 500us
2= Tau 100us
3= Tau 10us
4=Tau 5us
5=Tau 1us

Yes , the simulation looks real-like .... by the way , I already had watched such a pictures on my scope 2 years before this GPZ-7000 appeared

http://www.geotech1.com/forums/showt...nduction/page3 ( post 51 )

[Monolith]

Yes , the simulation looks real-like .... by the way , I already had watched such a pictures on my scope 2 years before this GPZ-7000 appeared

http://www.geotech1.com/forums/showt...nduction/page3 ( post 51 )

Deemon, you also gave a very good description and explanation of how it works, just a few days ago.http://www.geotech1.com/forums/showt...472#post208472

Somebody else mentioned that the method is in the public domain since many years.
ZONGE published several documents describing the method. Does anybody know of any older publication?

[Davor]

This one is only a incy wincy bit different than your classical TEM in a sense that the high voltage is achieved using ... high voltage. Directly, and with no coil flyback.
Look at what I made in ~3 minutes. The current in between the spikes is forcibly constant by means of + and - 1.69V supplies. Either 1.69V or 200V sources must be regulated to maintain that current constant.

[moodz]

Deemon, you also gave a very good description and explanation of how it works, just a few days ago.http://www.geotech1.com/forums/showt...472#post208472

Somebody else mentioned that the method is in the public domain since many years.
ZONGE published several documents describing the method. Does anybody know of any older publication?

Hi mono ... the older prior art is US 3317744 A and US 4157579 ... I dont think that "those skilled in the art" could not see the obvious application of these two patents to metal detecting. It is really interesting why these two patents are not cited in some later patents that seem to be claiming the same invention ????

[moodz]

This one is only a incy wincy bit different than your classical TEM in a sense that the high voltage is achieved using ... high voltage. Directly, and with no coil flyback.
Look at what I made in ~3 minutes. The current in between the spikes is forcibly constant by means of + and - 1.69V supplies. Either 1.69V or 200V sources must be regulated to maintain that current constant.

Here is an actual tx circuit ( built some months ago as a demo ) with auto "tilt" compensation based on US 4157579 ..

The green trace shows the effect of the tilt control on coil current too low , too high and just right. :-) .. there is no ringing and the current swings in the coil are 4.8 amps.

[deemon]

Hi mono ... the older prior art is US 3317744 A and US 4157579 ... I dont think that "those skilled in the art" could not see the obvious application of these two patents to metal detecting. It is really interesting why these two patents are not cited in some later patents that seem to be claiming the same invention ????

Of course , they are directly speaking about "geophysical prospecting" purpose of these applications . Anyhow , my circuits are different from both patents ...

[Davor]

.. there is no ringing and the current swings in the coil are 4.8 amps.

I'd be very surprised to see any ringing there. By PI criteria, the coil is terribly overdamped.

[Monolith]

Hi mono ... the older prior art is US 3317744 A and US 4157579 ... I dont think that "those skilled in the art" could not see the obvious application of these two patents to metal detecting. It is really interesting why these two patents are not cited in some later patents that seem to be claiming the same invention ????

Thanks for the links to the patents. This really goes way back and so much to the point.

[crane]

By stumbling upon a conversation on another forum I realised many people do believe GPZ is a PI, and seeing you froth about it I just had to throw a bone. No malice intended.

As you (almost) pointed before, GPZ is a step voltage device, not a PI. The obvious advantage of every step voltage IB device is that you may sample right away, and hence it is much better approach for detecting small targets, since PI is inherently deaf to those. There is also a disadvantage in sense that the X and R components bleed to each other due to the finite coil resistance, and the fact that there is a voltage change across a Tx coil during R sampling period. A certain manufacturer whose-name-must-not-be-said tried to fix this before using a negative resistance approach, and arrived - nowhere. Negative resistance is achieved by a device that utilises a noisy positive feedback loop, and instead of X bleeding in, they got noise instead.
GPZ fixes that by using a fixed low voltage source to compensate for resistive loss during R sampling period. To achieve momentary transition to steady current flow through a Tx coil during R sampling period, there must be a regulation loop that sets the high voltage properly. I have no idea if that's working any good in GPZ, but it is a clever way to go about it.
However, it simply is not a PI device. It is a step voltage IB, a VLF if you like, and a proof that there is a lot for VLF to catch up.

I also think most people throwing away their GPZ-s are simply those that are used to PI simplicity, cradled into the minds of OZ prospectors by the same manufacturer whose-name-must-not-be-said. It resembles a bit a lad that learns storks are not delivering babies - on his bachelors party.

I think knowing more is a good thing. Knowing X gives you discrimination, yet another thing OZ prospectors have no clue about. But moodz does. Guess giving the OZ prospectors a VDI would grant a manufacturer whose-name-must-not-be-said a permanent ban from Australia, so there you haven't got it.

I'm not sharing my method of killing X during R, not yet.

The "other forum" you refer to is the misinformation forum. He actually says the GPZ is just an expensive VLF.

It seems you didn't object to Q calling the GPZ a PI here?
http://www.geotech1.com/forums/showt...474#post208474

You can call the GPZ a step voltage device if you wish but if so then a PI is also a stepped voltage device.
You also compare it with VLF but it has nothing in common with detectors that TX single or multiple frequency sine waves.
Fisher has made detectors that TX rectangular wave forms for about two decades now but these process information in the frequency domain at basically two frequencies whereas BBS/FBS and the GPZ process information in the time domain, same as PI.
BBS and FBS extracts X and three different bands of time constants, this is obviously different to VLF which processes info in the frequency domain.
So I suppose you could say a stepped voltage device that processes information in the TD is PI and this includes the GPZ and FBS etc.

BTW, constant current TX doesn't automatically solve the X problem so perhaps you might wish to give it some more thought.

And the manufacturer you are too scared to name has never used a negative resistance approach and failed. Where do you get this stuff??

You make a big thing about X, but we all know it is essential for accurate discrimination, this isn't new!!! but it does an even better job when combined with time constant discrimination.

Every novice at some time or another discovers how the spike behaves when fe and non-fe metal is presented to the coil. The sensible ones assume this must be well known, but a few rather naive people actually believe they have discovered something new.
Surely it must be incredibly obvious by now that the same information, plus a lot more, is available during the low voltage TX on-period where X and TC disc can be combined??

[Davor]

You don't read much. How about patents AU2004290091, US7652477?

And you don't seem to keep a story straight. The CZ in your explanation is a VLF just because of processing information in frequency domain, whereas everything that processes information in time domain is a PI. And GPZ doing precisely the same only with a twist in Tx is a PI. I could live with that, but... no. The whole difference is in analogue vs. digital signal processing. ZVT does separate X from R by means of Tx running constant voltage during R sample, while CZ separates it by means of addition/subtraction. We may argue which approach is better, but otherwise it is a same thing. Only 20 years later and several k$ more.

Guess what, even CZ obtains Rx signal components by time domain method. Feel free to be amazed that every VLF has a switching demodulator akin to a PI. So by your reasoning every VLF is a PI, at least those with step voltage Tx.

The main difference between a PI and everything else is in (Tx) coil being terminated with high impedance during Rx. So far it was advertised as the dominant feature and the biggest advantage of PI, but it also makes it deaf to small targets. Unlike PI, GPZ' Tx is effectively a short circuit during Rx. Now, how is it a PI?

I said it is a step voltage IB because it steps alternatively between 4 carefully regulated voltages, keeping the impedance as low as possible. If you prefer you may call it a VLF, a CW, or any other name from a vast supply of meaningless babble of a certain manufacturer whose-name-must-not-be-said. But it is not a PI. A VLF by any other name is still a VLF.

I mention you froth about your overpriced VLF. You provide. I happy. Mission accomplished

[crane]

"Guess what, even CZ obtains Rx signal components by time domain method. Feel free to be amazed that every VLF has a switching demodulator akin to a PI. So by your reasoning every VLF is a PI, at least those with step voltage Tx".

Why should I be amazed? A VLF demodulates in the frequency domain and PI demodulates in the time domain?

"The main difference between a PI and everything else is in (Tx) coil being terminated with high impedance during Rx. So far it was advertised as the dominant feature and the biggest advantage of PI, but it also makes it deaf to small targets. Unlike PI, GPZ' Tx is effectively a short circuit during Rx. Now, how is it a PI?"

The biggest advantage of conventional PI is that it doesn't have to deal with the large X component that plagues all CW detectors (except the GPZ), which brings me back to the fact that Moodz's demo in the following link is heavily contaminated with the X component, care to comment on this or will you ignore it again??

A GPX5000 can detect gold smaller than one grain and an SDC can detect smaller bits and yet you say a PI is deaf to small targets, when in fact the GPZ does better than conventional PI on long TC targets.

[Davor]

That's because GPZ is a nice VLF. You have precisely 0 understanding of moodz approach, or in fact even basic signal processing. Asking you to elaborate your views would be a torture. I have no urge to answer any loaded questions coming from profound ignorance of the subject, and yes, I'll continue ignoring those. If you had capacity to read, you'd find your answers in a previous post.

Keep dreaming though