PI Power Output

[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

[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?

[B^C]

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

[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?

[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/Salman.Durrani/_teaching/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

[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]

"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."

He is correct about X during Tx on but WRONG about its effects during the Pi off period.High X particularly with frequency dependent susceptibility(and domains with very long relaxation times) increase the total R signal component during Tx off.
.

Unregistered, hmm which one is it? Why don't you just add a handle so we know you are not that troll that we put on the ignore list?

Here is a simple experiment to demonstrate what you are saying.
Take a copper or brass washer and set it on a plastic spacer box on the coil of a PI in the flat position.
Note the amplitude of its response.

Now repeat with the washer in the vertical position. You will note immediately that the vertical position gives a very much fainter response.

Now repeat both tests with a steel washer of the same dimensions.

You will note that the steel washer on edge produces nearly the same response as when it is in the flat position.

This is because you are now seeing the X response of the steel.

Tinkerer

[Tinkerer]

Robby the idea of the static coil field was to get a ground sample just before switch off,the reason being is as you mentioned,"very poor target response"so the intent is to get a ground sample with little or no target signal left in it,the purpose of this is so it can be summed up against the first sample taken after the transmit,effectively removing the ground signal from the sample taken after the transmit and at the same time preserving the integrity of the target signal meaning no target signal is subtracted out of the ground balancing cct......earth field cancling will require seperate samples.
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,the above ground cancling cct described preserves this because only one sample is required after the transmit,[earth field samples aside] so this sample will more accurately reflect wether a target is ferrous or non ferrous to full depth.
Personally i think there is a huge potential for information during the ontime,we just need to go in and have a look and try to understand what we see and give up on this nonsense about its all a waste of time because the reactive signal plays such a large roll and its nigh impossible[PI WISE].

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

[ZED]

B^C it helps if you can tell us what your doing,i know your sampling during the flyback because the target signal peaks with a flat top,this flat top also suggests that the flyback voltage is being regulated and not allowed to reach its peak plus you said so,also there is no flyback signal this would suggest an IB coil yet you say this is not the case,i see a number of indications that your using a standard tank cct with an IB coil of sorts but you say non of it is so.
So dude whats the story ?

Zed

[ZED]

Zed,

Now sampling during the ontime while the coil field is static.....thats an interesting place to go".

But this then dictates when you can sample and you will miss a lot of targets. There are other ways around the problem if you have been reading the relevant patents.

Robby the idea of the static coil field was to get a ground sample just before switch off,the reason being is as you mentioned,"very poor target response"so the intent is to get a ground sample with little or no target signal left in it,the purpose of this is so it can be summed up against the first sample taken after the transmit,effectively removing the ground signal from the sample taken after the transmit and at the same time preserving the integrity of the target signal meaning no target signal is subtracted out of the ground balancing cct......earth field cancling will require seperate samples.
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,the above ground cancling cct described preserves this because only one sample is required after the transmit,[earth field samples aside] so this sample will more accurately reflect wether a target is ferrous or non ferrous to full depth.
Personally i think there is a huge potential for information during the ontime,we just need to go in and have a look and try to understand what we see and give up on this nonsense about its all a waste of time because the reactive signal plays such a large roll and its nigh impossible[PI WISE].

Zed

Would you explain that some more, I don't understand the idea.

Regards,

-SB

"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."

He is correct about X during Tx on but WRONG about its effects during the Pi off period.High X particularly with frequency dependent susceptibility(and domains with very long relaxation times) increase the total R signal component during Tx off.
.

[simonbaker]

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/Salman.Durrani/_teaching/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?

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.

Would you explain that some more, I don't understand the idea.

Regards,

-SB

[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/Salman.Durrani/_teaching/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?

Robby_H,
It shows that your knowledge of PI is vast. I am honored by your participation in our conversation. Tomorrow I will answer on your post.

All the best

Tinkerer

[Tinkerer]

Gday Zed,

Thanks for the replies, things will be more understood if there is more conversation.
The problem i have is that there are NO Fets, no MD circuit at all, all this was avoided for the reasons you mentioned.
The Target reading device is 1mtr away from the inductor.

A bigger Target has no flat top as you put it on the signal but more peaks to a point & then decays but small targets do indeed have a flat top signal as mentioned, it does appear that they have reached there maximum.

Increases in voltage on the same smaller targets deliver the same signal results, but on larger targets there is a marked difference in the signal readings.

I get what your saying about saturation being the end etc, but this depends on how one looks at things i guess. Remember only yesterday when we all thought the world was flat?

I would explain more but i need a friendly response hahaha!

Any thought's would be appreciated.

B^C,
I find your experiments very interesting. Did I understand right in that the responses you show have been generated by pulses at high voltage?

At what point in time were the responses sampled?

All the best

Tinkerer

[Tinkerer]

Right, I think we're talking about the same thing, it's in the equations but not everyone is familiar with the equations. Graphs work well. Seems like Aziz was making some headway with his graphs. I think if we keep making those graphs we'll at least get the answers for idealized targets on many of the questions.

Cheers,

-SB

I think Aziz is doing a fantastic job with the graphs. What we need to do is to compare the results with real targets and real TX pulses, to look for discrepancies that could give information for possible improvements.
There are a great many factors involved with target response.
Maybe the most evident at the beginning of the response is the surface area that the target presents to the B field.
Take a coin for example, on edge the surface it presents is very different from the surface it presents when lying flat.
The surface eddy currents or skin effect are the first. They influence mostly the shape of the response curve at the leading edge.
The core eddy currents from a minimal surface target, a sphere, will appear after the skin effect eddy currents have already mostly decayed.

We probably can divide all targets into a few broad categories with common characteristics.
Then try to simulate each category.
Then verify with real component tests if the responses correspond.

Tinkerer