PI Power Output

[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

[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

[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.

[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]

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,

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

[Mechanic]

Hi B^C,
What is the sweep speed of the bottom 2 pics? And could you also please put up some pics which show the tx pulse with the flyback voltage on ch1, and the target test results on ch2 for a comparison between them? And how did you set up the rig to measure the response in the target?
Nice work!
Cheers

[Zed,]

You cant saturate targets ol`boy

[Woody.au]

The whole gang is here...lol

Best performance out of a Minelab? Recode the Eprom, or should I say reburn another Eprom or 5 volt flash EEprom with some modified data.

[Tinkerer]

PI DISCRIMINATION

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

- Carl

Thanks Carl,

so I am not crazy after all. What I have observed hundreds of times, is real.

Now, let's tackle the other persistent myth. Hey, I like the "Myth busters"

The myth says that the ON transient can not generate as much Eddy Currents as the OFF transient. Laws of physics are blamed for that. After all somebody or something has to be blamed for our mistakes no?

I keep insisting that this is a fallacy but my whining falls on deaf ears. (Didn't use the right language, dahh..)

So lets look at this explanation, does this make sense?

Hmm maybe I should make a sketch, they say a picture is worth a thousand words...

Looking at the sketch,

a) represents the TX coil current with about 1.5 TC, at switch ON.
b) and c), from post #43, the fast and slow Flyback.

Now, look at the "area under the curve" which one is the largest? Ooops, small mistake here, will have to come back on that later.

d) is the TC current in black and the target response in red. There is a lag between the target response and the stimulation. As the di/dt diminishes, the stimulation of the target and its response diminish. This slowdown is a bit exaggerated on the sketch.

e) is the TX charge curve with a "flat top", like a about 6 TC. The response of the 2 different TC targets (red and green) raises with a time lag, relative to their TC. The lower TC target (red) has reached its peak earlier and as the di/dt diminishes, the eddy currents start decaying.
The longer TC target (green) lags more, the time is too short for it to reach its maximum eddy currents.

OK, this is the first try at drawing the picture. It is not all that good, but maybe it gets the idea across and somebody with better skill and knowledge could improve on it.

Tinkerer

[B^C]

Gday Zed,

All targets are saturated with a magnetic field this is what creates the eddy currents, the extent of the saturation, well that's another story,
Old Boy!
These targets are being belted with a very strong magnetic pulse & they
only seem to produce so much even with a time variant so one would assume they can't be saturated any more?
I'm open to , advice, critisism, or whatever as long as it sparks healthy debate we might get somewhere, the one liners are packed full of info.

Mechanic, yes i will set things up correctly now & supply some pics etc when done, i am currently working on a new device to get better readings which should give even better results. Let me get on with a few things & i'll post some info on the device i made up, seems to be working pretty good at this stage. It's virgin ground i'm treading on, for me anyway, so understanding what's going on takes time & tests.

How ya goin Woody, yeah everybody has there own way to go about things.
As soon as i can understand what the hell is goin on with this mod i have i'll come down & give it a run against what you have if you like.
It will be interesting, i think you'll be more than impressed with the performance.
I have tested it against everything so far with more than excellent results.
It's a powerful mod & runs deep & sweet in real bad ground, my son the other day asked how it works & i said, technically speaking, F*** Knows?
I need to find out why it works & go from there.

[Woody.au]

Fingers crossed B^C that you are onto something. Now do not go and tell the World what is is, go and get a Patent put on it. If you cannot afford it talk to me.

[nick_f]

Thanks Carl,

e) is the TX charge curve with a "flat top", like a about 6 TC. The response of the 2 different TC targets (red and green) raises with a time lag, relative to their TC. The lower TC target (red) has reached its peak earlier and as the di/dt diminishes, the eddy currents start decaying.
Tinkerer

Hi Tinkerer,
I don't understand why is the difference between targets with different TC important to you. Is it useful for discrimination?
Correct me if I'm wrong, but can't I have a gold target with the same TC as an aluminium target (or any other metal).

From what people say, an aluminium foil can be cut to a specific size, that corresponds to a desired TC, which means size of the target changes the TC.

Regards,
Nicolae

[B^C]

Gday Tinkerer, i was just reading your last post where you say about the Myth as you put it:

Why not just test this & see, it should be a pretty easy test, all the physics in the world can't explain a lot of things.
In a perfect mathematical enviroment where most of this stuff comes from is a far cry from real world testing.
I was having a look at a similar thing while playing around with things.

[nick_f]

Thanks Carl,

Now, look at the "area under the curve" which one is the largest?
Tinkerer

Hi Tinkerer,
At this stage, I have a model in my mind related to targets.

I imagine a target like a church bell. If you want to "hear" the target, you want to hit it with a heavy object at a high speed and to remove that object after hitting the bell as soon as possible. To me, heavy object = high energy pulse. Remove the object after hit = fast turnoff.

On the other side, I can think about a target the same I think of a coil.
If I want to get a high energy flyback pulse out of a coil, I have to energise the coil as much as possible, then stop the current through the coil as fast as possible.

I am not sure which of these two models fit to a target. I need to read more about eddy currents here: http://en.wikipedia.org/wiki/Eddy_current
And if I remember correctly, there are two physical effects that disclose a target, eddy currents and something else. Can't remember what the something else is...

Regards,
Nicolae