Ideas to tinker

[Tinkerer]

Magnetic field simulation

I came across an old simulation I did years ago. It shows the magnetic field and how it interacts with a copper target andwith an iron target. Left side target is copper.
Right side target is iron in 2 different position.
Note how the iron target pulls the magnetic field lines into the target.

[waltr]

You keep mentioning GB. Don't you like the "Eric Foster Ground Balance Method". Why? Because of the target hole?
Yes, there are other methods to do GB, but like everything, nothing is perfect. It always ends up with a compromise between desired features and undesired features.

The concentric coil I have I don't how it's made its for the SD/GPX series which I just obtained but intend to put into some good work.
Never liked the GB method (target hole) of the TDI.
I think they tried to advertise it like a "discrimination" feature (*some dealers/or just users which aren't aware of how this turns out to work)
but anyway it's what it is - a drawback. I guess you're right it's hard to beat the game and come winning every-time.
Cheers!

I use a variation of the "Eric Foster Ground Balance Method" using three samples and it does work very well.
The 'hole' tends to be very narrow in mid-conductors so haven't consider it an issue.
On my HH2 the hole tends to fall on only a certain size rusty nail (one about 1-2cm long). Never found it good for disc'ing out iron but handy to determine a high verse a low conductor target.

[eclipse]

Well it has to be if you look at the price.

[Tinkerer]

The Minelab GPZ 7000 is definitely not a traditional PI.

[eclipse]

Well speaking of Whites I will slightly disagree.
PI wise what they did is obtain already working circuit (Eric's foster GS5) and put it for sale. After few models later they've slapped a MCU which basically is a timing generator and nothing more advanced (TDI SL). Un-released models in-lab beta circuits I'm not speaking.
Minelab is somewhat more advanced because I give them credit they've actually invented something and put it for sale 20+ years ago and probably still using it today for their latest models in some form.

[Orbit]

The concentric coil I have I don't how it's made its for the SD/GPX series which I just obtained but intend to put into some good work.
Never liked the GB method (target hole) of the TDI.
I think they tried to advertise it like a "discrimination" feature (*some dealers/or just users which aren't aware of how this turns out to work)
but anyway it's what it is - a drawback. I guess you're right it's hard to beat the game and come winning every-time.
Cheers!

Sometimes you should be satisfied what we have! Minelab and Whites have invested a lot and in the end it all comes down to something similar! Better a sparrow in the hand than a dove on a branch!

[eclipse]

The concentric coil I have I don't how it's made its for the SD/GPX series which I just obtained but intend to put into some good work.
Never liked the GB method (target hole) of the TDI.
I think they tried to advertise it like a "discrimination" feature (*some dealers/or just users which aren't aware of how this turns out to work)
but anyway it's what it is - a drawback. I guess you're right it's hard to beat the game and come winning every-time.
Cheers!

[Tinkerer]

I own a concentric commercial coil just wandered what you are using these days in your designs. I meant if you sample GB at the top of the half sine TEM pulse (voltage) but probably you cant talk about that in deeper details. Keep up the good work and keep us updated with some cool ideas we can play with. Cheers

Concentric coil:
This could be an induction balanced coil with outer TX coil and inner RX coil and a bucking coil near the RX coil or wound on top of the RX coil.
It could also be a (usually outer) TX coil, an RX coil and a passive compensation coil.
Or it could be an outer TX coil and an inner RX coil that is not induction balanced. This gives you the possibility to look at the RX response while the TX is ON.

Once you get involved in ON time and OFF time signal demodulation, You should also look at:
ZVS, zero voltage switching.
And ZCS, zero current switching.

You keep mentioning GB. Don't you like the "Eric Foster Ground Balance Method". Why? Because of the target hole?
Yes, there are other methods to do GB, but like everything, nothing is perfect. It always ends up with a compromise between desired features and undesired features.

[eclipse]

I own a concentric commercial coil just wandered what you are using these days in your designs. I meant if you sample GB at the top of the half sine TEM pulse (voltage) but probably you cant talk about that in deeper details. Keep up the good work and keep us updated with some cool ideas we can play with. Cheers

[Tinkerer]

So the curious (at least to me) questions next are: how do you do the GB sampling?
Do you take GB sample on the top of the half sine pulse (described in US9285496) or you do something else for doing GB?
How do you do the RX to null and sample during TX ON? Do you apply the method you described here(link) or you rely on your method with the P mosfet and the small nulling coil in reverse or no special care to null the coils (essentially usage of any commercial coil would be possible in this case)?

Thanks!

I can not remember to ever have used a half sine current pulse.

Looking at the link you gave described here(link), I don't remember what it was about, just vaguely remember having given simulation a first try. I would have to go back and read the whole thread, for which I do not have the time right now.
What I can say, in the 10 years since then I have continued to work on the original ideas and these ideas have evolved a long way. I just kept trying and trying and over the years got to understand better and better of how these things work. Even today, it happens that I make a break through and then realize that I had been there many years ago, but at the time did not understand what happened.

What exactly the status is now, I can not say, because I sold my soul to the "The commercial".

Ah, the "nulling coil" If I remember right, Dave Emery posted an article giving all the details on IB coil construction. Generally we call it a bucking coil. The resistor in parallel with the bucking coil, serves as damping resistor, but also allows to bypass some of the coil current, which gives some degree of compensation for aggressive ground that would saturate the preamp. Ha, see, if prodded, sometimes I manage to remember something.

[eclipse]

So the curious (at least to me) questions next are: how do you do the GB sampling?
Do you take GB sample on the top of the half sine pulse (described in US9285496) or you do something else for doing GB?
How do you do the RX to null and sample during TX ON? Do you apply the method you described here(link) or you rely on your method with the P mosfet and the small nulling coil in reverse or no special care to null the coils (essentially usage of any commercial coil would be possible in this case)?

Thanks!

[Tinkerer]

Symmetrical TEM

Here is the current waveform tweaked a little bit to make it more symmetrical.

I separated the cycle with a long "dead period" to make the view easier to understand.

[Tinkerer]

I'm thinking if it's possible to construct a FPGA software that does the signal sampling and complex math, and a Windows based graphical app where you
can add sampling windows at specific times; adjust sampling gain; do calculations like add/substract S1+S2 - S3 etc. (multiple of these) then set weight of each calculation
0 - 100 so if formula overlaps with another (and another) the FPGA can decide which one is highest priority. When done with the formulas just click on generate and load in the FPGA.

At the end output:
- Do GB subtraction
- Do we have a signal, how strong is it
- Is it gold; Is it iron; Is it both

This is a very good idea.
I strongly believe the TEM TX method makes a lot of target information available. However the complexity of the 4 different exponentials demands also a demodulation capable to unravel this complexity.
To do this in analog, was beyond my capabilities.

I did observe good target separation by TC of the targets and good magnetic/non magnetic separation at times. But changing something means changing a lot of other things too. A digital system can do that.

[waltr]

Yes, this could be done with an FPGA. Could even be done with a PIC32MZ EF or even an STM32.

[eclipse]

.

Trying to layout 10 sample window signal paths in analog finally got so complicated that I searched for a digital solution.
Could not find any help for DSP. DSP needed real programming skill, whereas I just barely managed to setup a sequential timing schedule for an 8bit PIC.

I'm thinking if it's possible to construct a FPGA software that does the signal sampling and complex math, and a Windows based graphical app where you
can add sampling windows at specific times; adjust sampling gain; do calculations like add/substract S1+S2 - S3 etc. (multiple of these) then set weight of each calculation
0 - 100 so if formula overlaps with another (and another) the FPGA can decide which one is highest priority. When done with the formulas just click on generate and load in the FPGA.

At the end output:
- Do GB subtraction
- Do we have a signal, how strong is it
- Is it gold; Is it iron; Is it both