DEEPER PI DETECTION DEPTH

[Tinkerer]

It has been predicted, that the year 2012 will be a year of great advances in metal detector technology.
For some time now, it seemed that the PI as well as the VLF technology has reached a dead end. Everything has been tried and developed as far as it can go.
So what, we add a few bells and whistles and a new detector hit’s the market.
Is this the way it is?
Is there really nothing left to improve in detector technology?
As a tinkerer, I see it different. There are so many ways that detectors can be improved and I am sure that the common brain of the forum can come up with many excellent ideas.
Many of the ideas of course have been around for many years, but different priorities, or less perfect components made their use difficult.
I would like to start the new year exploring some ideas for real improvement of detector technology.
Starting with the Pulse Induction method:
Can we improve the detection depth?
More TX power gives more depth.
How can we improve TX power?
What are the pitfalls?
We have excellent light weight batteries available that make it possible to increase the power without increasing the weight beyond an acceptable limit.
We could also look at recycling some of the TX power.
Yes, it has been tried before. Can we really improve on that?
I say YES WE CAN.
I would like to see some new ideas presented here. OK, yes I have many ideas of my own, but I am sure that the common brain of the forum has many more ideas and probably even better ones than I have.
For the skeptics there is place too. I like to look at everything from every angle, therefore I appreciate if somebody comes up and shows me an angle that I have missed.
Tinkerer

[Carl-NC]

I am personally hopeful that 2012 will see some new technology. I wish I could offer more information on what that might be but, alas, I am constrained.

Obviously, PI applies more peak energy into the ground but does so in a narrow duty cycle so that the time-averaged power is still reasonable. So how can you improve on this? First, look at the limitation: coil tau. There are 2 ways I can think of offhand to deal with this. Radically lower L, or radically increase VCC. I'm personally partial to dangerous voltage levels. Partly because I like the idea of a "Danger: High Voltage" sticker on the detector.

Take it from there.

- Carl

[Tinkerer]

I am personally hopeful that 2012 will see some new technology. I wish I could offer more information on what that might be but, alas, I am constrained.

Obviously, PI applies more peak energy into the ground but does so in a narrow duty cycle so that the time-averaged power is still reasonable. So how can you improve on this? First, look at the limitation: coil tau. There are 2 ways I can think of offhand to deal with this. Radically lower L, or radically increase VCC. I'm personally partial to dangerous voltage levels. Partly because I like the idea of a "Danger: High Voltage" sticker on the detector.

Take it from there.

- Carl

Higher Flyback voltage = higher di/dt and faster decay.
There are excellent Mosfets available for voltages up to 1200V.
Is this safe?
I never tried. I went as far as 800V, several Amps. Does this make a big difference in safety from commonly used 500V?

Funny enough, my laptop computer gives me more electrical pricks than the TX connector with 800V Flyback, when I plug and unplug it under power.

Would wire insulation be a problem on the coil and cable?

How about charging a capacitor to 1000V and discharging it through a 100uH coil?
That gives a tremendous di/dt and a fast decay, good enough to make a quarter squeal loud enough to be heard by the RX coil through 3 feet of soil.

Tinkerer

[Aziz]

...
How about charging a capacitor to 1000V and discharging it through a 100uH coil?
...

Hi Tinkerer,

the PI TEM transmitter we have discussed earlier does it already.

Well, it's a so-called "synchronous step-up converter" and charges the capacitor with high voltage, which is rapidly discharged in the coil then.
Oh yes, it recycles the energy in the coil then. Why we should waste battery power?
Efficiency: Can be made up to 95% (or even higher).

Aziz

[Vortxrex]

Lock in Amplifier that can pull a signal out of the noise floor AND is small enough to incorporate into the detector.

Digital O Scope display that is part of the detector. Holds the signal & shows you the actual target trace.

[Tinkerer]

Hi Tinkerer,

the PI TEM transmitter we have discussed earlier does it already.

Well, it's a so-called "synchronous step-up converter" and charges the capacitor with high voltage, which is rapidly discharged in the coil then.
Oh yes, it recycles the energy in the coil then. Why we should waste battery power?
Efficiency: Can be made up to 95% (or even higher).

Aziz

Exactly, how long ago did you post a very detailed explanation on that? It seems nobody realized the potential.
I agree on the 95%, although I only achieved about 90% because I did not have the ideal components. The ideal components are available though.

Actually you jumped ahead to my next subject, the recycling of power.

If we want to zap the target with real power, say 10 or 20 amps, we definitely want to look at recycling some of the power. At 95% efficiency, we would only waste about 5%. compare this with 100% wasted TX power with damping resistor on a traditional PI.

Tinkerer

[Tinkerer]

Lock in Amplifier that can pull a signal out of the noise floor AND is small enough to incorporate into the detector.

Digital O Scope display that is part of the detector. Holds the signal & shows you the actual target trace.

This looks at the other avenue, better S/N. PI technology uses the Lock-In amplifier method.
We usually extract the target signal out of a background signal that has several magnitudes higher amplitude.
Cant the traditional signal processing be improved?

If we use an EMI cancelling coil, significant improvement can be expected.
If we generate a target signal that has one magnitude higher amplitude, many of the common noise problems are greatly reduced.

An O Scope readout on the detector would be a great tool for testing and fine tuning, but most detectorists would find it of little use in the field.

But if we can see the target on the O Scope, we should be able to convert what we see into a sound that the operator can interpret.

The human ear is capable of discerning very complex sounds. This could be further developed.

Tinkerer

[Aziz]

Exactly, how long ago did you post a very detailed explanation on that? It seems nobody realized the potential.
I agree on the 95%, although I only achieved about 90% because I did not have the ideal components. The ideal components are available though.

Actually you jumped ahead to my next subject, the recycling of power.

If we want to zap the target with real power, say 10 or 20 amps, we definitely want to look at recycling some of the power. At 95% efficiency, we would only waste about 5%. compare this with 100% wasted power with a traditional PI.

Tinkerer

I think it was one and a half year or so. Found the different phases of the transmitter now:
http://www.geotech1.com/forums/showp...&postcount=819

Aziz

[Tinkerer]

I think it was one and a half year or so. Found the different phases of the transmitter now:
http://www.geotech1.com/forums/showp...&postcount=819

Aziz

Thanks for the link. This is an excellent explanation.

While we are at it, this bi-polar saw-tooth TX wave form, has a strange effect that I do not totally understand.
Due to it's bi-polarity, the target excitation is nearly twice as much as a single polarity pulse of the same amps and di/dt.

There is an article (ZONGE), unfortunately I don't find it anymore, that explains this, but I did not believe it was true until I thoroughly tested the effect with real coils and real TX pulses and real RX response analysis.

Now, usually we talk about the TX pulse during TX, generating eddy currents in the target and eddy currents of opposite polarity during the Flyback and the later eddy currents have to kill the earlier eddy currents.

But with the bi-polar saw-tooth TX wave, the resulting eddy currents are nearly twice as much amplitude.

Tinkerer

[Alexismex]

Starting with the Pulse Induction method:
Can we improve the detection depth?
More TX power gives more depth.
How can we improve TX power?
What are the pitfalls?
We have excellent light weight batteries available that make it possible to increase the power without increasing the weight beyond an acceptable limit.
We could also look at recycling some of the TX power.
Yes, it has been tried before. Can we really improve on that?
I say YES WE CAN.
I would like to see some new ideas presented here. OK, yes I have many ideas of my own, but I am sure that the common brain of the forum has many more ideas and probably even better ones than I have.
For the skeptics there is place too. I like to look at everything from every angle, therefore I appreciate if somebody comes up and shows me an angle that I have missed.
Tinkerer

Yes we can improve the PI design a lot for more deph with a easy method:
- switch between 12V to 24 V TX voltage....
- give more stability to the signal reception to "mix" 3 closed Frecuency (eJ: 515, 540, 593 PPS ) to cancel each other interferences and to forget the infamous potentiometer FCY adjusts of the majority of Classic PI
- for the battery ....still use the heavy but proved Gelcel battery7 amps 12V like the Lorenz...and PulstarII PI

[Carl-NC]

How about charging a capacitor to 1000V and discharging it through a 100uH coil?

Now you're talking!

[moodz]

I think it was one and a half year or so. Found the different phases of the transmitter now:
http://www.geotech1.com/forums/showp...&postcount=819

Aziz

This is not the most efficient realisation of a target stimulation or power saving ... it is missing one component ( maybe deliberately ??? )

The circuit with the diode provides double the magnetic power and double the efficiency .. do the sims yourself or build real circuit. ( watch out ... circulating currents are so high in the coil that the capacitor gets hot )

The pulse repetition should be at the resonant frequency of the LC tank.

The duty cycle of the pulse will control peak current.

moodz

[Aziz]

This is not the most efficient realisation of a target stimulation or power saving ... it is missing one component ( maybe deliberately ??? )

The circuit with the diode provides double the magnetic power and double the efficiency .. do the sims yourself or build real circuit. ( watch out ... circulating currents are so high in the coil that the capacitor gets hot )

The pulse repetition should be at the resonant frequency of the LC tank.

The duty cycle of the pulse will control peak current.

moodz

[ATTACH]17773[/ATTACH]

Oh yes, this one should even be better.
Good one! I'll run the sims..

Aziz

[Aziz]

No! It's not better. A simple push-pull configuration on a LC tank achieves better results.

And I'm missing one important feature:
wide bandwidth response

Aziz

[Tinkerer]

This is not the most efficient realisation of a target stimulation or power saving ... it is missing one component ( maybe deliberately ??? )

The circuit with the diode provides double the magnetic power and double the efficiency .. do the sims yourself or build real circuit. ( watch out ... circulating currents are so high in the coil that the capacitor gets hot )

The pulse repetition should be at the resonant frequency of the LC tank.

The duty cycle of the pulse will control peak current.

moodz

[ATTACH]17773[/ATTACH]

Many variables to the basic circuit are possible.

For example, try an IGBT instead of the Mosfet and see how different the wave form turns out. (Caution)

As for the diode. It increases the resistance and therefore reduces the efficiency.

The diode also isolates the drain capacitance of the Mosfet. What is the influence of the drain capacitance? Is this capacitance in series? and therefore reduces the tank capacitance?

What is the capacitance of the diode itself? The resistance? the voltage drop? the speed?

A lot of things to check.

Tinkerer