GPZ 7000 Pi Or………..???

[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!

[Chet]

GPZ 7000 ZVT

The GPZ 7000 Zero Voltage Transmission (ZVT) technology provides a stable processing period throughout the entire receive period. It also provides a stable magnetic field that reduces the amount of undesirable soil that is detected. This along with better signal processing provides improved detection of small nuggets and larger deeper nuggets. 

Bipolar (positive and negative) pulses can be generated in standard Pulse Induction detectors. But between pulses the transmit energy starts at zero voltage and builds until it peaks and discharges energy then it must start at zero again in the opposite polarity. This creates current and voltage variations on the power wiring that can adversely affect the receiver and processing circuits. Thus is not as stable as the GPZ 7000.

In the attached oscilloscope GPZ 7000 Transmit Waveform displays; the zero volt level is across the vertical center of the display.  Both the positive and negative excursions of the waveform pass up and down through the zero voltage level rapidly. 

In a standard Pulse Induction detector the waveform would stop at zero volts for a short period while the receiver timings and processing completed then start recharging the transmit coil for the next cycle.

In the GPZ 7000 the receiver coil timings and signal processing does not require the transmit function to return to zero volts to recharge for a new transmit cycle. 

In the time stretched displays; the squidgy somewhat sine shaped forms at the top and bottom is time periods where the receiver timings and signal processing can be applied to the receiver coil signals to determine if a target is present.

Note; only the Transmit waveform is shown in these displays. The receiver displays are a distorted mess of EMI and ground noise. That is where good engineers really excel in signal processing to extract target information that best fits the Time Constant curves that are displayed in a previous posting.

In my opinion reference to the Bipolar power and high voltage pulse with coinciding receive operation as being similar to a VLF detector is not false but somewhat of a stretch. But maybe a good sales pitch.

Have a good day,
Chet
 

[Gold Catcher]

35 minutes ago, Chet said:

GPZ 7000 ZVT

The GPZ 7000 Zero Voltage Transmission (ZVT) technology provides a stable processing period throughout the entire receive period. It also provides a stable magnetic field that reduces the amount of undesirable soil that is detected. This along with better signal processing provides improved detection of small nuggets and larger deeper nuggets. 

Bipolar (positive and negative) pulses can be generated in standard Pulse Induction detectors. But between pulses the transmit energy starts at zero voltage and builds until it peaks and discharges energy then it must start at zero again in the opposite polarity. This creates current and voltage variations on the power wiring that can adversely affect the receiver and processing circuits. Thus is not as stable as the GPZ 7000.

In the attached oscilloscope GPZ 7000 Transmit Waveform displays; the zero volt level is across the vertical center of the display.  Both the positive and negative excursions of the waveform pass up and down through the zero voltage level rapidly. 

In a standard Pulse Induction detector the waveform would stop at zero volts for a short period while the receiver timings and processing completed then start recharging the transmit coil for the next cycle.

In the GPZ 7000 the receiver coil timings and signal processing does not require the transmit function to return to zero volts to recharge for a new transmit cycle. 

In the time stretched displays; the squidgy somewhat sine shaped forms at the top and bottom is time periods where the receiver timings and signal processing can be applied to the receiver coil signals to determine if a target is present.

Note; only the Transmit waveform is shown in these displays. The receiver displays are a distorted mess of EMI and ground noise. That is where good engineers really excel in signal processing to extract target information that best fits the Time Constant curves that are displayed in a previous posting.

In my opinion reference to the Bipolar power and high voltage pulse with coinciding receive operation as being similar to a VLF detector is not false but somewhat of a stretch. But maybe a good sales pitch.

Have a good day,
Chet

Thanks, Chet. This is the most comprehensive and best description I have seen on ZVT. I will have a few dozen reads of it to try to fully understand it ??

GC

[jasong]

Thanks, I knew you'd have already looked at this on a scope. 

So unless I'm misunderstanding something, it's basically similar to what I diagrammed out on the previous page? Just with a real world square-like waveform that has ringing and finite sloped rise/fall edges due to real world impedence factors instead of the perfect ideal square wave I drew, right?

If so, then I have 2 more questions. But I want to make sure I have this part clear in my head first.

 

 

[Chet]

"a real world square-like waveform that has ringing and finite sloped rise/fall edges due to real world impedance factors"

Yes, the amount of ringing and slope of the ringing waveform is shaped by damping resisters (impedance loading).

The slope and length of the sloped wave will be altered/strecthed by Eddy Curents emitted from metal targets that were energized by the transmit pulse.

Target detection is determined by sampling for changes in the sloped wave with high speed gating/timing circuits of different timings/mode selections. Examples; High Yield timing  favoring short Time Constant targets (small nuggets); General timing favoring Long Time Constant targets (large deeper nuggets).
 

 

[jasong]

Ok cool, think I have the basics straight in my head.

The main question I have is since the TX wave is continuous, why can't they also sample and measure the phase offset of the RX wave relative to the TX, similar to a VLF? And if that's technically possible, then isn't discrimination possible with ZVT too? 

In my head it seems just a matter of having enough CPU power to multitask and look at things both in time and frequency domains. 

Edit: or maybe it's the phase offset of the same TX when it passes over a target? I can't remember now how it all works. But just in general, possible with ZVT too?

[Chet]

First some background on discrimination;

VLF discrimination is normally dealing with measuring phase shift referenced between a transmitted sine wave and a relatively strong sine wave caused by a target that unbalances a null between the transmitter and receiver coils. 

This works quite well for small shallow targets that are expected to cause phase shifts within reasonable design limits. The design limits might range from iron nails to large rings or large coins with aluminum, lead and gold in the middle of the range within 12 inches of depth. Also the targets are expected to be within a size range that allows the phase shift to be within limits of the expected possible targets.

They do not work well for shallow large targets that exceed the capability of the phase shift measuring circuitry. Nor do they work well for weak deep targets.

There are a lot of unknown variables encountered with a Pulse Induction detector to incorporate into the design of discrimination processing. There are so many false variables to deal with unknown target sizes, shapes, wires, rusted metal shapes, and mineralized soil from oxidized metals.  

Some pulse induction detectors have been built that have some discrimination capabilities. My GPX 5000 with a Double D coil has that capability. It worked on some targets such as nails but overall I found that running the more sensitive Mono coil and digging all targets was faster and produced more gold. 

I have built a couple of prototype pulse induction discrimination circuits (based on target time constant) which worked on the bench with good solid targets. But failed when junk targets out the ground were tried they failed miserably.  Measuring phase shift of the transmitter power waveform similar to what you suggest works well with good targets but falls apart when various questionable or weak targets are tested. 

A GPZ 7000 or GPX 6000 like detector could be designed from the ground up with a lot of software processing to make some reasonable target evaluations of phase shift and/or target time constant and display a result along with a percentage of probability number. It will take a lot of work and testing with an engineering expenditure to match the task.

Hopefully Minelab will find a way to do it. But they may not appreciate the complaints from us users when we are unhappy with some of the limitations. 
 

[jasong]

Is there anything to be gained with regards to accuracy via a hybrid discrimination - ie looking at how a target affects both the time constant and the phase shift combined? Does one potentially give useful info the other doesn't give in some cases? 

Reason I ask is because as detectors get more sensitive, those little bits of tin cans and wire that are like 0-4 inches deep become a higher and higher percentage of dug targets.

Being able to discrim just those shallow targets out would save a lot of time, even if accepting a certain amount of gold loss for 1st/2nd passes during the general prospecting phase. In some places it'd allow me to literally 2x the amount of ground I could cover. Anything deeper than 6-8 inches probably all needs dug anyways even when just prospecting. So just having some fairly decent shallow discrimination on a prospecting machine would be pretty useful in many cases and save a lot of time just being able to concentrate on digging the targets that are higher probability of being gold, especially in cases where the gold is usually always deeper than 6" or so and the trash is usually always shallower. 

In that sense - accurate depth discrimination would be an extremely useful tool in the prospecting realm.