PI Power Output

[nick_f]

Hi B^C,

Nice to hear you found some mod that improves specs of ML.
Is is just one modification that increases Tx power and Rx sensitivity, or at least two separate mods. Because we are talking about independent circuits and improving one of them doesn't quite improve the other one. As far as I know, ML push up quite hard the Tx transistors to their limits, I am not sure how you can get more juice from them

Regards,
Nicolae

[B^C]

Gday Nick,

I'm working on the same Questions & have been for some years, i have a modification to suit ML detectors that blows everything out of the water in TX power & also recieve signal capabilities in very BAD ground.
The big question is why does this work so good, i have no answer to this?
There's no doubt it works great but why, this is what i am trying to find out.

The problem with some forums is that not many who know some of the answers are eager to share the results, one can only guess for pieces of paper reasons--money?.
There's an old saying that two heads are better than one & many heads rule.
It would be good if people would actually reply be it with, the good, the bad or the ugly comments & from these we can all learn something.

One thinks sometimes that some of these forums are only setup to gather other peoples thought's because they have none of there own, i would hope that this is not that type of forum!

Believe me, there's no so called secrets that can't be shared when the rest of the world is about 20yrs behind ML & ML are 10yrs in front of where they are now already!


Hey Aziz, get away from that new O-scope you got & post some more info!

[nick_f]

Hi B^C,
You say the copper target gives a much higher pulse than the gold. Isn't possible to use a smaller copper target (cut a piece of yours), as to get very similar pulses compared to the gold nugget? If you have a gold ring to test, apart for the gold nugget, do you still get the spikes? If you have more gold nuggets, with different sizes, I would like to find if that spike appears for any gold targets, or only for the specific one you tested.

Regards,
Nicolae

[B^C]

Hi Guys,

I setup a quick experiment that turned into some long interesting hours testing the Transient spike effect on targets & the induction time.
I think i have had some success trying to read these targets better & the effects on them by being induced, indeed it seems the Transient spike is worth it's weight in GOLD!

I have built a device for testing that does seem to work ok & is for the first time repeatable without any filtering for noise at all, see what you think & please, advise, curse or whatever.
It is the purest signal i can get at this stage from the targets & it gives an indication on the effects of the induction pulse on a particular Target.
You can see from the pictures that they clearly show the Copper being induced vs a Gold nugget.
The Copper gets induced readily & the amplitude is greater due to it's properties, interesting to note how quickly the induction time is & that these small targets saturate very quickly.
Obviously from the initial testing just with an O-scope i need to hook up some better equipment to have a closer look at the signals with the same Volt/Div & Time & then introduce some delay, noise etc from the data i have collected & then get a better picture on what is happening in terms of lag etc in real world ground conditions.

Any help & advice would surely be appreciated, i'm not in this to make money from detectors, all i want is the shiny Gold Nuggets.

The first picture is with no target & the test device is being pulsed with the same magnetic wave as the rest of the tests. You will see a very small indication of the pulses, test done at 5mV /.1uS

The Second picture is a Copper target that has been placed in the test device & being induced vs the Test pulse time.
It seems the speed & intensity of the magnetic wave is quick to induce these targets with little or no lag.

The Third picture is the Gold Nugget being induced vs the test pulse time.

The Gold nugget was tested at 10mV Div, the "Copper Target" at 10mV was way of the screen & at 20mV so was tested at 50mV.

I will add two more pictures & they give a closer look at both signals.

[Carl-NC]

On the graphs, we can see that there is a time lag between the stimulation of the target and when the target response reaches it's peak.
This is what has been called the "Charge Time"

Yes! And this lag time in the impulse response corresponds to a phase shift in a sinusoidal response.

- Carl

[Tinkerer]

THE ENIGMA OF THE PIVOT

Tinkerer,

Your findings in post #59 above are quite interesting. When I get back to it, I will find some of the simulations that I ran and perform some similar tests. I recall some differences in target response by varying the pulse width, but I'll have to dig through my notes, or recreate the tests, to figure out the details.

hobbes,

it will be very interesting to compare results. I am looking forward to it.

Thanks to Aziz's simulations in post #43 and #45, I finally got to understand what is happening with the stimulation time of the target. (Took me only a few years to catch on)
On the graphs, we can see that there is a time lag between the stimulation of the target and when the target response reaches it's peak.
This is what has been called the "Charge Time"
This time is different for different target TC's as well as it is different for FE targets.
The location of the peak in time is what makes discrimination with a PI possible.

I am going to set up an experiment to demonstrate my theory above.

I will use sampling during TX for this, as the peak response is much more visible at that time. It is the cause of "THE PIVOT" that I have been observing. The kind of invisible sine wave I am talking about on my post earlier.

Tinkerer

[hobbes_lives]

Tinkerer,

Your findings in post #59 above are quite interesting. When I get back to it, I will find some of the simulations that I ran and perform some similar tests. I recall some differences in target response by varying the pulse width, but I'll have to dig through my notes, or recreate the tests, to figure out the details.

[Tinkerer]

HIGH POWER AND LOW GAIN

Changed C10 to 1500u, C6 to 6800u, C7 to 3300u.
Changed PPS to 900
Changed TX pulse to 72uS at 12V, that comes to 2A coil current at switch OFF.
Sample taken at 2.5uS after Switch OFF

Gain of preamp 69

S&H

Low pass R/C filter (R4k7/C940n) at output of S&H

Dynamic testing, swinging the target suspended from a string, across the coil.
Results:
1" square alu foil detected at 25 cm
0.55 gram silver ring at 30 cm
0.5 gram gold ring at 25 cm

I feel the results are good.
Does anybody have some numbers to compare with?

Tinkerer

[Tinkerer]

Tinkerer's schematic with more resolution

Thanks for all the help.

I have traced the problem.
Q1 and Q2 do not provide enough current.
The switching frequency is limited to 10k because of the ICL7662 (not ICL7660)

I am changing the capacitor C6 for 6800uF. (Amazing all the old stuff forgotten in the parts box)

Tinkerer

[Mustafa]

Tinkerer's schematic with more resolution

[nick_f]

Hi B^C,
The pdf works, I opened it. Maybe you need a newer version of acrobat reader?
How can you read the eddy currents directly from the target? Unless your target is a very tiny coil, followed by a preamplifier?

Regards,
Nicolae

[B^C]

Sorry forgot to log in, my message above---unregistered about the target signal.

Tinkerer, i tried the pdf but all i get is a message saying insuffient data for image, not sure?

I should have explained more about the target response signal, i need to read this direct from the target itself, read the eddy current strength directly from the target.
I want to eliminate everything & then once i get a signal from that i can then see how everything else affects this pure signal if you get what i mean.

I have a lot of data that is from very bad ground conditions, if i can get a pure signal from a target then i can compare these signals & put numbers to the ground noise interference etc.
I have no issue sharing the info but i have to get the pure target comparitive figure as a constant before i can proceed with anything.

I have tried many methods but still there are questions regarding the tests so obviously i am not getting it correct.

[nick_f]

Hi Tinkerer,
I suspect you refer to the +12V output of the LM317. When the output is noisy, can you check the signal at its input, if it also gets noisier?
I don't know if it helps, but can you try a large capacitor between V+ and AGND? (2200uF maybe).
What's the voltage at the input of LM317? Do you have at least 3V more?
I also think you can put a small cap in parallel with R4 (isn't one in the recommended circuit?).

Regards,
Nicolae

[Tinkerer]

Once more

Tinkerer