PI Power Output

[Tinkerer]

How do you diffirentiate the different inductances that targets have,wont this alone give you different pivot points ?
As for the delay in signal growth this could be used to get an estimate of target size,larger targets would have slower growth rates and so more phase where as smaller targets with less inductance would have a quicker signal response and less phase.

Where is this pivot point measured,at the coil or at the output of an opamp,your pivot scenario has me confused,im a dodo with vlf.

Zed

The TC of the targets are determined by several factors. Putting some time and effort into it we will be able to define and quantify these factors.
Here is an example:
The US$ 5c coin is larger than the 1c coin, but, has a TC of about 20uS compared with a TC of about 70uS for the 1c coin.

The explanation can only lie in the conductivity of its alloy, that contains a lot of nickel.

Tinkerer

[Tinkerer]

Hi Tinkerer,
I don't know who suggested we can sample earlier with a balanced coil arrangement but it is clearly wrong. We have to obey certain rules and one important rule is that we must delay sampling until after the TX coil's back emf spike has decayed. There is no way around this.

Your waveforms in post #30 are clearly IB, not pulse induction. You have actually built a high powered IB detector and also given a good example of why we can't sample earlier than at the tx coil when using a balanced rx coil in a pi design.

Your figures in the other thread are L= 325 uH, total R = 2.8 ohm, U = 12v, T = 41usec, therefore the coil current at switch off should be 12(1-exp(-41*2.8/325))/2.8 = 1.27 amps so with this current I think it's safe to assume the tx coil's spike will still be settling at the far right of your screen (~7 usecs) but your sample begins 2.5 usec after switch off and ends 5.2 usecs after switch off so you are looking at a portion of the spike's waveform using a balanced receive coil.
In post #59 on this thread, your conclusions are based on the spike's properties which will be almost identical for the 43 and 100usec pulses so your results are similar because you are sampling the same spike in both cases. Pulse induction would give different results.

The problem with sampling during the pulse on time (or the spike's on time) is that we have to deal with the reactive soil component whereas we don't during a true PI off period.

With pi, we aren't looking at the spike or how the target affects the spike's amplitude, decay, width or settling time, we are looking at the signal the target induces in the rx coil. The two might appear to blend together at the tx coil but they are separate. Some articles, papers and patents may say otherwise but they have it wrong, such as in this paper written by someone who supposedly has a PhD....

http://engnet.anu.edu.au/DEpeople/Sa...aching/TA5.pdf

Dave Emery's patent is also IB, not PI. He makes the spike resonate with a cappy and he samples the oscillations similar to vlf although he makes no mention of cancelling the ground R component or that it even exists.

Allan Westersten's patent US20080224704 is a mix of pi and IB but he doesn't include a means to separate the off-period small target trigger signal from the huge ground signals we experience here in the Oz gold fields.

B^C,
Your pictures appear to be what we would see with a balanced RX coil, which is just IB? The time base appears to have been changed in each picture along with the pulse train so it's hard to say what we are supposed to be looking at?

Hi Robby_H,

I use a very standard TX pulse to induce eddy currents in the target. So is it a PI or not? I don't want to fight over the name.
OK, I will open a new thread asking for suggestions of names for the "New Tech" detector.

On post #59, I tried to detect if there is a carry over of eddy currents generated during the TX ON time. I conclude that if there are any, they are of such low amplitude that I can not detect them.
My sample point shows a signal of very high amplitude. Adding another sample point 10uS or whatever time later will only show a lower amplitude signal.

I would very much like to tap your vast knowledge of PI. Please post some suggestions.

All the best

Tinkerer

[B^C]

Gday Guys,

There's one thing i think we all agree on & that is there is a lot of differing opinions, idea's etc to as exactly what is what & how this works & how that doesn't. Or like mentioned by Simon before what means something to one person may have a different meaning to another so confusion rules.

On the other hand we would not have any idea who is posting some of the information in these threads & if it is just mileading or not?
As an example robby_h could be rob the project manager of minelab for all we know, he sure writes like he does. Or Zed could be the man himself--we just don't know & or about the information given, if it's correct or misleading?

So how about we do get on the same page as each other & then we can come to our own conclusions.

I have attached a very simple chart, if someone like the fence sitter Carl--nudge, or any of the other fence sitters would like to add to the chart & include all the relevant Ti's?, Td's?, Xy'?s & Zed'?s everybody then can relate to what were talking about & we have at least a basic layout to compare things.

If we test then we can add to the basic chart to show exact points at which we are testing & or trying to test etc.

See what you think but we have to have some sort of a basic standard to give relevant information to each other about what were trying to do & it is a visual example for everybody. There is a language barrier to consider as well so basic charts are the way to go to help people.
Don't know about you but i can do with all the help i can get, at the moment it seems we are just off on our own little trips each in different directions.

Of course if anybody wants to improve the chart then go for it, but lets achieve something hey?

[B^C]

Yes, i forgot the bloody attachment--DUH!!

[Unregistered]

[QUOTE=B^C;89577]Gday Guys,
As an example robby_h could be rob the project manager of minelab for all we know, he sure writes like he does.

Wondered the same thing myself. Wonder if he is consultant to ML or what if any direct or indirect involvement he has with ML?

[robby_h]

Simon,
The ground X signal is only present during transmission so it obviously can't be present during a period of non-transmission regardless of what unregistered Doug says in post #131.

We could though use an example from his forum where they claim to sample earlier than Minelab by using a balanced coil even though they don't do anything to make this possible.

They claim to be able to sample at 11usecs when using a mono and have all GB samples out of the way 15usecs after switch off when using a balanced coil.

At the time they made this claim their sampling routine occupied 12usecs (2usec on, 2 off, 2 on, ~4 off, 2 on), so it would appear their first sample commenced at around 3usecs.

This means they would be sampling the spike in their first and second samples and sampling the true off period in their last sample.

Zed,
There is huge potential for information during the on time as has been disclosed in some patents.
I was only pointing out that the reactive signal is a problem for the novice who is still trying to get up to speed. This doesn't mean that others haven't a solution though. Remember ML brought out the Sovereign well before the SD2000 and obviously know the on time advantages and problems intimately and if you know the problems then you can work out the best way to address them.
I think you will find they have most bases covered if you spend time ploughing thru their patents.

I don't get what you mean here "Now PI detectors have the natural ability to discriminate between ferrous and non ferrous targets but it all comes undone because of the second sample as in a conventional PI".
Any objects such as ground material or metal objects give a signal of one polarity after pulse switch off in conventional single sample pi so I'm not sure what you mean when you say PI is a natural discriminator?
Have you tested your idea and do you have any pictures of the waveforms?

Tinkerer,
Enough of the vast knowledge bit. I wish!
I'm only interested in clearing up the simple basics. If we don’t then it just ends up a confusing mess.

I mentioned Dave Emery's patent because he uses a pi type pulse to generate a large back emf at switch off then causes this to ring with a cappy, something we avoid in pi. He then samples the resulting oscillations similar to vlf (IB) so this is actually a high powered vlf and not pi.
You do much the same but sample the spike itself so it is high powered IB or TR.

B^C,
I for one agree that your chart accurately depicts pi when looking at an ideal target provided the tx coil's spike has settled for a suitable period before sampling begins when using a mono or balanced coil.
I don't work for ML!
Take no notice of the troll. He is only interested in destroying Minelab, me, JP and anyone who thinks ML makes good detectors, He gets everything wrong as he clearly demonstrates here...
http://www.geotech1.com/forums/showthread.php?t=15417

[ZED]

I don't get what you mean here "Now PI detectors have the natural ability to discriminate between ferrous and non ferrous targets but it all comes undone because of the second sample as in a conventional PI".
Any objects such as ground material or metal objects give a signal of one polarity after pulse switch off in conventional single sample pi so I'm not sure what you mean when you say PI is a natural discriminator?
Have you tested your idea and do you have any pictures of the waveforms?

Sorry Robby i cocked up,i was thinking of the signal waveforms during the transmit period and how ferrous and non ferrous signals are generally opposite to each other,i was thinking it would continue to be the case after the flyback but on reflection it doesn`t.

Zed

[ZED]

Zed,

I understand this differently.
A the end of the TX pulse, lets call it TX Omega, when it is "flat top" or more than 5 coil TC long, the coil current is at steady state.
No eddy currents are generated. Not in the ground and not in the target. (Unless, in a target with very long TC where the eddy current generation might continue a little due to the charge lag.)
With no eddy currents generated in the ground at TX Omega, it is not a good spot to measure the ground signal.
However, it is a good spot to receive the common mode noise, to subtract it then in the difference amplifier.

Tinkerer

Tinkerer your right about there being no eddy currents near the end of the transmit when the coil field is static just before switch off.
The ground signal i am referring to is the magnetic one,its when the magnetic domains begin to align themselves with the coil field during the transmit cycle and after switch off the magnetic domains slowly return to there relaxed state,this is the ground signal we hear when we sample after switch off,its also referred to as the resistive ground signal or R signal,why i dont now i haven`t figured it out yet.

Zed

[ZED]

Robby -Quote "You obviously aren't aware of this but if we transmit two wildly different pulse lengths and the tx waveform flat tops before the end of each pulse then the ground signal after each pulse will be identical!!!!!!!!"


Robby if i have a 150 u/sec wide transmit pulse and then a little latter a 350 u/sec wide transmit pulse and both transmits have the coil field at a static state before switch off are you saying the ground signal will be of the same amplitude at the end of both transmits ?
I would of thought the amplitude of the ground signal would of been the greatest after the 350 u/sec transmit.

Zed

[Altra]

Hello,

Is anybody doing low side current sensing on the TX? For ground tracking or other information?

Thanks Mark

[simonbaker]

Simon,
The ground X signal is only present during transmission so it obviously can't be present during a period of non-transmission regardless of what unregistered Doug says in post #131.

We could though use an example from his forum where they claim to sample earlier than Minelab by using a balanced coil even though they don't do anything to make this possible.

They claim to be able to sample at 11usecs when using a mono and have all GB samples out of the way 15usecs after switch off when using a balanced coil.

At the time they made this claim their sampling routine occupied 12usecs (2usec on, 2 off, 2 on, ~4 off, 2 on), so it would appear their first sample commenced at around 3usecs.

This means they would be sampling the spike in their first and second samples and sampling the true off period in their last sample.

Zed,
There is huge potential for information during the on time as has been disclosed in some patents.
I was only pointing out that the reactive signal is a problem for the novice who is still trying to get up to speed. This doesn't mean that others haven't a solution though. Remember ML brought out the Sovereign well before the SD2000 and obviously know the on time advantages and problems intimately and if you know the problems then you can work out the best way to address them.
I think you will find they have most bases covered if you spend time ploughing thru their patents.

I don't get what you mean here "Now PI detectors have the natural ability to discriminate between ferrous and non ferrous targets but it all comes undone because of the second sample as in a conventional PI".
Any objects such as ground material or metal objects give a signal of one polarity after pulse switch off in conventional single sample pi so I'm not sure what you mean when you say PI is a natural discriminator?
Have you tested your idea and do you have any pictures of the waveforms?

Tinkerer,
Enough of the vast knowledge bit. I wish!
I'm only interested in clearing up the simple basics. If we don’t then it just ends up a confusing mess.

I mentioned Dave Emery's patent because he uses a pi type pulse to generate a large back emf at switch off then causes this to ring with a cappy, something we avoid in pi. He then samples the resulting oscillations similar to vlf (IB) so this is actually a high powered vlf and not pi.
You do much the same but sample the spike itself so it is high powered IB or TR.

B^C,
I for one agree that your chart accurately depicts pi when looking at an ideal target provided the tx coil's spike has settled for a suitable period before sampling begins when using a mono or balanced coil.
I don't work for ML!
Take no notice of the troll. He is only interested in destroying Minelab, me, JP and anyone who thinks ML makes good detectors, He gets everything wrong as he clearly demonstrates here...
http://www.geotech1.com/forums/showthread.php?t=15417

The ground X signal is only present during transmission so it obviously can't be present during a period of non-transmission regardless of what unregistered Doug says in post #131.

I guess I need clarification on the term "ground X signal". Is that the coupling of the TX and RX coils through a ferrite-like magnetic medium in the ground? If so, is the assumption that such ferrite-like medium does not have a current and therefore no time-lag, but rather has an instantaneous effect on the magnetic field and has no effect once the mag field is gone? Is that what is meant by PI has a natural ability to discriminate out ferrite like objects (if you sample after TX field -- and ferrite effect -- gone)?

Regards,

-SB

[simonbaker]

Tinkerer your right about there being no eddy currents near the end of the transmit when the coil field is static just before switch off.
The ground signal i am referring to is the magnetic one,its when the magnetic domains begin to align themselves with the coil field during the transmit cycle and after switch off the magnetic domains slowly return to there relaxed state,this is the ground signal we hear when we sample after switch off,its also referred to as the resistive ground signal or R signal,why i dont now i haven`t figured it out yet.

Zed

I think this touches on my question about "ground x signal" and ferrite. How fast do we assume the magnetic domains return to relaxed state. Or do they? Could they stay permanently magnetized by the pulse, therefore no affect after?

Three cases:
1. Return instantaneously -- we don't see them during sampling after TX.
2. Return with small delay -- they become part of post-TX sample.
3. Return very very slowly -- we don't see them during post-TX sample.

Which is most accurate?

Regards,

-SB

[simonbaker]

Robby -Quote "You obviously aren't aware of this but if we transmit two wildly different pulse lengths and the tx waveform flat tops before the end of each pulse then the ground signal after each pulse will be identical!!!!!!!!"


Robby if i have a 150 u/sec wide transmit pulse and then a little latter a 350 u/sec wide transmit pulse and both transmits have the coil field at a static state before switch off are you saying the ground signal will be of the same amplitude at the end of both transmits ?
I would of thought the amplitude of the ground signal would of been the greatest after the 350 u/sec transmit.

Zed

Hi Zed:

Would you clarify your meaning of "ground signal" and how you measure it?

Regards,

-SB

[Altra]

Hi Sb,

Read the "Background " section of this patent. It explains reactive X, resistive R, and instantanious/historical ground matrix. When he says salt is a 1mhz target invert it to time 1uS. R/L is used = frequency just convert to T= 1/(R/L). I am sure someone will explain in plain english.

Mark

[simonbaker]

Hi Sb,

Read the "Background " section of this patent. It explains reactive X, resistive R, and instantanious/historical ground matrix. When he says salt is a 1mhz target invert it to time 1uS. R/L is used = frequency just convert to T= 1/(R/L). I am sure someone will explain in plain english.

Mark

Thanks, that is a good reference.

I read along a bit lazily so I could use some help understanding his idea.

I noted that most of his equations assumed the TX field was linearly growing to the point of turn-off, which seems quite different from our discussions where we routinely assume the TX pulse current stabilizes to a near constant before turn-off.

It seems he wants to estimate the portion of the RX signal due to "FRD" (ferrite relaxation decay) using a formula and a couple of signal samples. He distinguishes FRD effects from "ground eddy current" effects. He assumes that ground eddy current effects decay very fast and all sampling is done afterwards, but FRD effects do overlap the target signal.

The patent, as usual, is hard to read because of alternative designs interwoven. For example, he speaks of an alternate design with differing pulse intervals, not sure if that implies different TX pulse durations also. Other variations too.

It would be a lot clearer if somewhere he showed the total received signal (FRD + target) and how the math extracts the target from the combination.

Any help clarifying it would be appreciated.

The PDF file is a bit frustrating because it is an image and prevents text search or cut-and-paste.

Regards,

-SB