Interesting Phenomenon with DD coil

[Riss]

Ha, ha, Bulgarian cooperation...

This about "Bulgarian cooperation..." is a rather difficult topic to understand, which would make an elite team of psychologists, clergymen (regardless of what religion they profess), philosophers and quantum physics specialists tear up their diplomas and cry in despair... here's a little help (the words of Obi-Wan Kenobi) - https://www.youtube.com/shorts/gawMzVSD1_0 . The ideas set out in the film "The Matrix" part one https://www.youtube.com/watch?v=vKQi3bBA1y8 would help to understand what is happening on this territory of the planet... but my post #11 could have ended with this laugh https://www.youtube.com/watch?v=X-Y6YfDBmh8 right? but I chose Woody . In various topics on the forum, what is happening in the coil - environment (soil) system is explained from an energy point of view. the coil and all the capacitances - its own, the cable's, the key transistors. What happens in this system of active and reactive (L, C) components? It's like an induction cooker - https://en.wikipedia.org/wiki/Induction_cooking. It's better to make someone think than to tell them. that way he will UNDERSTAND it . Maybe even better than yourself. Right? https://www.youtube.com/watch?v=exWQOAINF5k https://www.youtube.com/shorts/fXJkPqVV8jU

[nejdet]

Ha, ha, Bulgarian cooperation...

I didn't understand what provoked this attitude. The man was describing his observations and findings!

[Riss]

When you warn someone that there is a swamp in front of them – is it a good or bad (mockery) act? I was making an analogy between the cheerful woodpecker, filled with inspiration before flying with his newly built plane. Everyone has been through similar situations, so have I. Under my table there are several types of hot rocks and ceramics. Think of them as a long stick with which I feel the terrain in front of me – I am not Baron Munchausen - https://www.youtube.com/watch?v=8mht9JpeMjo ... the sense of humor is mysterious ... does anyone know if the latest generation of artificial intelligence ( AI ) has a "sense" of humor?

[Detectorist#1]

Hi boilcoil,
I think that another person should say "sorry" but that takes dignity.

[Detectorist#1]

As usually, the things are not so simple as seems at first time. When the RX signal is proceeded only at TX-OFF time is more difficult to catch the targets with low conductivity. When the RX signal is proceeded only at TX-ON time the sensitivity for gold (most important for us) is more low. No escape from more complex schematic with two channels - TX-OFF channel for max sensitivity and TX-ON channel for additional discrimination. No chance for sure discrimination Fe/non-Fe for very low signals. But this is logic - first you listen some signal and when the level of this signal increase - you are capable to understand the type of the massage. I continue to optimizing the more complex hybrid MD.

[Riss]

Hi boilcoil,
I think that another person should say "sorry" but that takes dignity.

1.listen without prejudice - https://www.youtube.com/watch?v=goro...o8dbLvSxqlH6zP
2.Twin Peaks ,,The Owls Are Not What They Seem‘‘ - https://www.youtube.com/watch?v=mbi7rq-TSk8
3. observer effect quantum physics - https://medium.com/@russfein/the-qua...t-959d6b68b644
4. observer effect - https://www.simplypsychology.org/obs...revention.html
5. The interesting thing is that the modern internet uses the observer effect more and more. In the so-called "social networks" this leads to a strong distortion of the facts and perceptions of people, which is the purpose of the networks. And what is caught with a net? - the meaning (in the figurative sense of this word) of the Turkish word for fish – ( balık ) .

,,O tempora, O mores‘‘-Cicero

[boilcoil]

In practice, when working only with signals from the IB coil, during the collapse time, the ferro/nonferro differentiation is made on the basis of the total magnetic resistance of the coil system, i.e. for ordinary high-conductivity targets, due to the target retransmission of energy , directed in the opposite way to the main flow, the common magnetic resistance of the system increases and the signal from the IB coil decreases (at the same level of TX ampereturns (H) ). For targets with high magnetic permeability (they seem to collect magnetic lines), the magnetic resistance is lower and the signal from the search coil is stronger.
For small targets, things are different. For example, small objects made of foil, thin gold, etc., due to the fact that they convert almost all the received energy into heat, there is no retransmission, there is no screen effect (not skin - screen effect), the total magnetic resistance slightly decreases and the result will be similar like ferro.
To solve this, you need to make at least two samples during the active period - one at the beginning, when the magnetic flux is small, but dB/dt is of high value (here the reaction is more pronounced for non-ferrous metals) and one in the exponential zone of the curve, where the flux is much larger, but dB/dt is much less (here the reaction to ferro targets is more pronounced).
Of course, you need a lot of experiments to find the optimal places for the samples.

To make it easier to do experiments, you have to make a not very complicated MD, but which one convenient for the purpose. Best with direct sampling and reading of live data directly from ADC.

Maybe something like this:
PI_TL072_082_MONO & IB COILS.rar


PS: BTW for the ordinary targets, active samples will repeat results of passive samples (off-time samples) at all.

[Detectorist#1]

Hi boilcoil,
Thank you for this explanations. Now I use 3 different connections:
1. Only TX-ON processing
2. Only TX-OFF processing
3. Two channels processing -TX-ON and TX-OFF
Yes, my observations points the same - in only TX-ON processing the sensitivity for thin gold is reduced in comparison with only TX-OFF processing. I will test your suggestion for two samples in this case. Yes, your schematic with MCU and many switches is universal for all these tests.
Also, some day I will test the possibility of VOODOO project - IB connection with different analysis of the RX signal on TX-OFF time.

[Riss]

As usually, the things are not so simple as seems at first time. When the RX signal is proceeded only at TX-OFF time is more difficult to catch the targets with low conductivity. When the RX signal is proceeded only at TX-ON time the sensitivity for gold (most important for us) is more low. No escape from more complex schematic with two channels - TX-OFF channel for max sensitivity and TX-ON channel for additional discrimination. No chance for sure discrimination Fe/non-Fe for very low signals. But this is logic - first you listen some signal and when the level of this signal increase - you are capable to understand the type of the massage. I continue to optimizing the more complex hybrid MD.

,,economy is the mother of misery‘‘ – Todor
Kolev - https://www.tiktok.com/@bnt.bg/video...93214715645210 ; https://en.wikipedia.org/wiki/Todor_Kolev_(actor) & https://www.youtube.com/watch?v=LMFeeNH7624

[Riss]

In practice, when working only with signals from the IB coil, during the collapse time, the ferro/nonferro differentiation is made on the basis of the total magnetic resistance of the coil system, i.e. for ordinary high-conductivity targets, due to the target retransmission of energy , directed in the opposite way to the main flow, the common magnetic resistance of the system increases and the signal from the IB coil decreases (at the same level of TX ampereturns (H) ). For targets with high magnetic permeability (they seem to collect magnetic lines), the magnetic resistance is lower and the signal from the search coil is stronger.
For small targets, things are different. For example, small objects made of foil, thin gold, etc., due to the fact that they convert almost all the received energy into heat, there is no retransmission, there is no screen effect (not skin - screen effect), the total magnetic resistance slightly decreases and the result will be similar like ferro.
To solve this, you need to make at least two samples during the active period - one at the beginning, when the magnetic flux is small, but dB/dt is of high value (here the reaction is more pronounced for non-ferrous metals) and one in the exponential zone of the curve, where the flux is much larger, but dB/dt is much less (here the reaction to ferro targets is more pronounced).
Of course, you need a lot of experiments to find the optimal places for the samples.

To make it easier to do experiments, you have to make a not very complicated MD, but which one convenient for the purpose. Best with direct sampling and reading of live data directly from ADC.

Maybe something like this:
PI_TL072_082_MONO & IB COILS.rar


PS: BTW for the ordinary targets, active samples will repeat results of passive samples (off-time samples) at all.

Unfortunately, I did not have a 4-channel oscilloscope (I worked with a two-channel one) when I was making intensive measurements of the processes explained in your post #22 - that was 11 years ago. Now I don't need it - I need 3 pairs of hands to speed up the assembly work.

[Detectorist#1]

Hi boilcoil,
For small targets, for TX-ON time (active period), you mention that I need to make two samples - one at the beginning and second at the exponential zone (maybe you mean using of additional resistor in series of TX coil or use of TX coil with high resistance of the wire to have good exponential process of TX current with saturation zone). In current case (low resistance of the TX coil), I see linear voltage ramp answer during all TX time and for me it is not clear where I need to put the second sample. What is your comment?

[boilcoil]

For small targets, I experimented with short time constant coils (60-70 us) and a pulse of about 2 tau (100-150 us). The settings and adjusting of the discriminating algorithm I made on base of the real data from the ADC, not from the oscillograms.
The optimal times for me were about 7-15 us for the first sample and later then 70 us for the second one, (for ex. 75-83 us), with a sample width of 8us.
I suppose that, maybe, there will be some variations in the timing optimization, depending on the hardware, but the rules I have already written to you.
The differences are both in the trends of change in these two samples and in the values that are read from the ADC.
The experiments were done with MD, the scheme of which I uploaded, and the data are the values from the ADC in real time.

PS: I forgot to mention that the specified coil tau is also formed with additional resistors (0.8 ohm of MOSFET and 1 ohm serial for measuring the coil current).

[Detectorist#1]

Is additional resistor (1 ohm) is AC blocked with capacitor to ground or have active influence on the shape of the TX current?

[boilcoil]

There are not any capacitors. I measure the instantaneous current through the coil.
See the diagram.

[Detectorist#1]

OK. Sorry for the question. This resistor is involved in the shape of the current on TX-ON time. As for joke - this scheme have to be read very carefully - many connections go to left or right direction.