DEEPER PI DETECTION DEPTH

[Midas]

You've got me confused now Tinkerer. How are you proposing to integrated the TEM method with Moodz's coil which obviously isn't IB ?

[Tinkerer]

Below is the Moodz variation.
The coil current is the yellow trace. Take note of the peak amperes.
Not much difference in the circuit, but different output. The pulses are positive only.
The power consumption is only very slightly more.
We get more PPS, that is good.
I added the target response of the 5 targets of different size. Take note of the signal amplitude.
The peak target amplitude is 472mA

Tinkerer

[Tinkerer]

Hi Tinkerer,

Sorry that was a little flippant. I am impressed that your able to do that. You must have achieved a wide dynamic range. Is the design very different to your published work? I assume its still IB and still uses differential amplifier.

Midas

Hi Midas,

the design is different in many aspects, but it could be called an evolution from my earlier published work.
I still use a differential approach and an IB coil.

I wish you luck with your work in progress.

Tinkerer

[Midas]

Hi Tinkerer,

Sorry that was a little flippant. I am impressed that your able to do that. You must have achieved a wide dynamic range. Is the design very different to your published work? I assume its still IB and still uses differential amplifier.

Midas

[Midas]

Simulate highly mineralized ground, hmm, I wish I knew how to do that.
We know that it needs high power pulses to penetrate deep into mineralized ground, but the whole Ground Balance thing is much more complex as just a TX pulse.

Much to do with the RX. But, let's make a little test.

Set your coil on the ground, mild or hot, it does not matter.

Then take a good size junk of iron, (I use a 6 pound cannon ball) and set it in the center of the coil. (static hot soil) Without ground balancing or re-tuning, sweep a one gram gold target over the coil, at a distance. Can you detect the gold?

My detector has no problem with that. It still detects the gold at the same distance.

Tinkerer

Yep I get the same detecting depth on a 1g nugget regardless of any ground effect. I can't detect a 1g nugget at all. My current detector is a poor specimen. A new one based on Moodz's and some of your own work is in progress... slow progress.

[Tinkerer]

No, no it was me that was arguing the semantics not you. But its OK I'm done now, there's no point in discussing "PI or not PI' any further unless someone else wants to offer their opinion.

I do appreciate you posting the Sim results, its interesting stuff. It does seem like a technique with a lot of merit. I'm also wondering how the much the effciency suffers when you've got the coil over some highly mineralization ground. I'm guessing that's hard to simulate though.

Simulate highly mineralized ground, hmm, I wish I knew how to do that.
We know that it needs high power pulses to penetrate deep into mineralized ground, but the whole Ground Balance thing is much more complex as just a TX pulse.

Much to do with the RX. But, let's make a little test.

Set your coil on the ground, mild or hot, it does not matter.

Then take a good size junk of iron, (I use a 6 pound cannon ball) and set it in the center of the coil. (static hot soil) Without ground balancing or re-tuning, sweep a one gram gold target over the coil, at a distance. Can you detect the gold?

My detector has no problem with that. It still detects the gold at the same distance.

Tinkerer

[Midas]

Hi Midas,

the simulations are not about semantics. I am trying to explain the different results by using one or the other method.
I posted the LTSpice file above, so that anyone can try all kinds of variations, but for the ones who do not have the time to face the learning curve, I show a few results.

I would also appreciate if some knowledgeable person would help improving the simulation.

You point out an important feature. If we adjust the traditional PI cycles to consume equal power as the TEM, what is the difference in the result?

I will show this with the simulations to come, but for now I can say that with the same power, the TEM generates a target response amplitude of about one magnitude higher.

Another very significant difference is the Signal to Noise ratio S/N. With the same power, we get also a ten times higher PPS, or Pulse Repetition Rate. This allows for integrating or averaging, 10 times more samples and that vastly improves the S/N.

Tinkerer

No, no it was me that was arguing the semantics not you. But its OK I'm done now, there's no point in discussing "PI or not PI' any further unless someone else wants to offer their opinion.

I do appreciate you posting the Sim results, its interesting stuff. It does seem like a technique with a lot of merit. I'm also wondering how the much the effciency suffers when you've got the coil over some highly mineralization ground. I'm guessing that's hard to simulate though.

[Tinkerer]

OK well I guess that's enough semantics. Allow me to point out a practical difference between the TEM and true PI. Its recycling a great deal of the power which is great and allows you to use a reasonably low duty cycle of input power just like PI and get superior current flows. But the one component that doesn't get a rest that normally would, is the coil. At some point the amount of heat generated in the coil by the constantly flowing current will exceed what the coil can dissipate. If the coil is potted then I think that limit may come up sooner than you think.

If we instead truly pulse the coil at a low duty cycle then we should be able to generate far higher instantaneous current flows, and greater depths for the same average coil current.

I think what we want for the ultimate deep seeking metal detector is the recycling power of the TEM combined with the advantages of intermittent current flow that comes with PI.

Hi Midas,

the simulations are not about semantics. I am trying to explain the different results by using one or the other method.
I posted the LTSpice file above, so that anyone can try all kinds of variations, but for the ones who do not have the time to face the learning curve, I show a few results.

I would also appreciate if some knowledgeable person would help improving the simulation.

You point out an important feature. If we adjust the traditional PI cycles to consume equal power as the TEM, what is the difference in the result?

I will show this with the simulations to come, but for now I can say that with the same power, the TEM generates a target response amplitude of about one magnitude higher.

Another very significant difference is the Signal to Noise ratio S/N. With the same power, we get also a ten times higher PPS, or Pulse Repetition Rate. This allows for integrating or averaging, 10 times more samples and that vastly improves the S/N.

Tinkerer

[Midas]

OK well I guess that's enough semantics. Allow me to point out a practical difference between the TEM and true PI. Its recycling a great deal of the power which is great and allows you to use a reasonably low duty cycle of input power just like PI and get superior current flows. But the one component that doesn't get a rest that normally would, is the coil. At some point the amount of heat generated in the coil by the constantly flowing current will exceed what the coil can dissipate. If the coil is potted then I think that limit may come up sooner than you think.

If we instead truly pulse the coil at a low duty cycle then we should be able to generate far higher instantaneous current flows, and greater depths for the same average coil current.

I think what we want for the ultimate deep seeking metal detector is the recycling power of the TEM combined with the advantages of intermittent current flow that comes with PI.

[Tinkerer]

Below is the TEM current wave form.

What is different?

About the same coil current and Flyback voltage.

A higher TX voltage and a much higher pulse repetition rate.

How does the target response compare? We will see the pictures later.

How does the power consumption compare? Big surprise, The TEM method uses a fraction of the power, because it recycles the power instead of burning it off in the damping resistor.

Tinkerer

[Tinkerer]

Midas,

you are splitting hairs again.

The only difference is, that the damping resistor is absent and you have an increased "coil capacitance" (the parasitic capacitance exist further). All the coils energy isn't burnt into heat and therefore, you have to recycle it after the "pulse" before transmitting another pulse.

This TEM (tuned electro-magnetic ) transmitter is somehow genius. It's prior art and it's free. And it can handle huge coil pulse energy (well, it's a little induction heater ).

Cheers,

Aziz

When we look at the schematics, they look deceptively similar. However, the resulting TX pulses are radically different.

I will add some current wave form pictures of 4 different methods. The TEM method is by far the most efficient. Note: I show the current wave form, not the voltage wave form, because it is the current that generates the magnetic field.

The first picture attached is the traditional PI current wave form.

later we can look at the target response that this current pulse achieves.

[golfnut]

With Pi's we turn the juice off and allow the flux around the coil to decay and this is the enengy used for the target search.


If we could encourage the flux decay - by applying a large potential to the coil at the instant of shut off - current would be ripped out of the coil at higher rate in the same time frame - giving more energy emitted for target illumination.

Steve

[Aziz]

Midas,

you are splitting hairs again.

The only difference is, that the damping resistor is absent and you have an increased "coil capacitance" (the parasitic capacitance exist further). All the coils energy isn't burnt into heat and therefore, you have to recycle it after the "pulse" before transmitting another pulse.

This TEM (tuned electro-magnetic ) transmitter is somehow genius. It's prior art and it's free. And it can handle huge coil pulse energy (well, it's a little induction heater ).

Cheers,

Aziz

[Midas]

Hi Midas,

you don't see the real point!
You are splitting hairs.

There is a sudden change in a quantity:
The quantity is the coil current and is changing during the pulse-off time. If you look at the coil voltage, you can see the half-sine voltage pulse too.

Aziz

Hi Aziz,

I'm really not trying to split hairs, in my opinion there's a clear line to be drawn. Let me ask you this, if you take a VLF sine wave output signal and distort it just a little bit so it rises a little bit more slowly than it falls. Does it then instantly become a PI? If not distort it a little more. At some point on the way towards the saw tooth your circuit produces does it suddenly become a PI? Where exactly are you going to draw the line?

PS Please don't take this any of this as criticism of the circuit, I do see its considerable advantages. Its only about what it should be called.

Midas

[Aziz]

Hi Midas,

you don't see the real point!
You are splitting hairs.

There is a sudden change in a quantity:
The quantity is the coil current and is changing during the pulse-off time. If you look at the coil voltage, you can see the half-sine voltage pulse too.

Aziz