complete project

[Tinkerer]

Hi Tinkerer,
The info on the small nuggets was just for reference, many of the small surface stuff like this has already gone, and what is left are targets just out of range, some the size of the coin are detectable up to about 40 cms with a 45cm mono coil, but I know there are many similar pieces much deeper.

I want to keep my cake and eat it also, like Elijah's bottomless oil and flour jars. Being able to detect the smaller stuff helps to locate patches and dabs of nuggets in the first instance. To then be able to clean up the small and deep larger bits is the ideal. Also in searching for float as Rob mentioned you need a pretty sensitive machine, sometimes a number of ounces can be found in one go, incognito, disseminated within large lumps of lode and reef material.

Perhaps for sensitivity when targeting smaller pieces the PRR could be increased above 5000, and pulse width reduced keeping the power output constant but concentrated within the surface zone.

Cheers
Kev.

Hi Kev,

with an integrator, like we use in the PI detectors, an increase in the pulse repetition rate also produces an increase in signal gain. Increasing the PPR to 10,000 or even 20,000 is no problem at all.

However, with the same coil size, reducing the TX pulse width by half, also reduces the magnetic field density by half. This is not good for small targets. The most important thing for generating a good response from very small targets, is high magnetic field density.

To maintain the same field density, we would need to increase the TX voltage. We could do this by adding a boost battery voltage regulator. This also has the advantage of making the TX power regulated and therefore equal from beginning to end of a battery charge.

There are many things that can be done to increase sensitivity and depth, but every added feature adds to the complexity and cost.

On a different subject: The audio. Could you describe the audio features that you would like?

Tinkerer

[Kev]

Hi Tinkerer,
The info on the small nuggets was just for reference, many of the small surface stuff like this has already gone, and what is left are targets just out of range, some the size of the coin are detectable up to about 40 cms with a 45cm mono coil, but I know there are many similar pieces much deeper.

I want to keep my cake and eat it also, like Elijah's bottomless oil and flour jars. Being able to detect the smaller stuff helps to locate patches and dabs of nuggets in the first instance. To then be able to clean up the small and deep larger bits is the ideal. Also in searching for float as Rob mentioned you need a pretty sensitive machine, sometimes a number of ounces can be found in one go, incognito, disseminated within large lumps of lode and reef material.

Perhaps for sensitivity when targeting smaller pieces the PRR could be increased above 5000, and pulse width reduced keeping the power output constant but concentrated within the surface zone.

Cheers
Kev.

[Tinkerer]

Hi Tinkerer,
This is all sounding very good, and being public, I'd be able to build units for other people such as Rob, whose been looking for such a device for years. I will dig up that thread of Aziz's and study it.

I didn't answer your question about rubbish yesterday. There is a strange situation where you can dig 9 bits of rubbish, mainly rusted iron, to 1 bit of gold, these are areas where the Old Boys have been working the gold, and then patches off to the side that the Old Boys have missed will be 9 pieces of gold to one piece of rubbish, usually more modern such as spent ammunition, i.e. non-ferrous. So the ability to notch out iron would be a boon especially when the target is in water, and so much harder to retrieve.

The iron rubbish can be very small so coil i measurements would be useless as a disc solution I believe, especially with ground variations having similar effects.
In fact much of the gold is small, I attach an image of such, the coin is about 23mm across. 2 of the pieces are 0.07 grams, or 1 grain (480 per ozt). All these were detected with the Minelab GPX-4500 between 2 and 12 inches with a 14 x 9 inch elliptical mono coil.

The ultimate would be a machine having software control of the pulse and sample timings so that either large or small gold could be targeted, in fact my dream has been for a machine that automatically cycles through a couple of sequences tailored for both large and small gold. I've tried this on a std PI before and it sadly generated a lot of noise, noise that I believe SETA was developed by Minelab to overcome. They now have the ability to have a full spectrum of timings cycling, but have perhaps held off releasing it.

How sensitive do you feel the TEM can be made, is it perhaps only effective with coin sized targets and above? Is an earlier sample required to detect small targets as in conventional designs?

I know you're using Paul's UniPI, and I've been playing with a PIC24H DSP which is similar, and he's provided some of the source, so I'm sure we can collaborate sufficiently to get some code working.

The fly in the ointment for me at present is the disorder of my house and equipment, and in a couple of months I'll need to move everything out of my house into a shipping container while some walls and ceilings are rebuild.

Kind regards
Kev.

Hi Kev,

At present I have no solution for lead, brass or other non magnetic metals. They will show up the same like gold.
These nuggets in your picture are very small nuggets. I have not made any tests for such small targets yet. Rather, I have been working with large coils for deep RELATIVELY small targets. Like 1cm targets with a 1m coil. For this purpose I also use 24 to 30V TX to get sufficient magnetic field density.

I will build a smaller coil and make tests with very small targets, while keeping the TX voltage at 11 to 14V.

I would rather keep the PPS at 5000 to get good S/N. Therefore it is the TX voltage that is the limiting power factor, but we will still get 8 or 9A peak coil current.
Normally I take the first sample at 3 to 5us after switch OFF, when the target response peaks.
The timings for the first and second sample need to very precise for the Iron discrimination.
Software is the key.

Tinkerer

[Kev]

Hi Tinkerer,
This is all sounding very good, and being public, I'd be able to build units for other people such as Rob, whose been looking for such a device for years. I will dig up that thread of Aziz's and study it.

I didn't answer your question about rubbish yesterday. There is a strange situation where you can dig 9 bits of rubbish, mainly rusted iron, to 1 bit of gold, these are areas where the Old Boys have been working the gold, and then patches off to the side that the Old Boys have missed will be 9 pieces of gold to one piece of rubbish, usually more modern such as spent ammunition, i.e. non-ferrous. So the ability to notch out iron would be a boon especially when the target is in water, and so much harder to retrieve.

The iron rubbish can be very small so coil i measurements would be useless as a disc solution I believe, especially with ground variations having similar effects.
In fact much of the gold is small, I attach an image of such, the coin is about 23mm across. 2 of the pieces are 0.07 grams, or 1 grain (480 per ozt). All these were detected with the Minelab GPX-4500 between 2 and 12 inches with a 14 x 9 inch elliptical mono coil.

The ultimate would be a machine having software control of the pulse and sample timings so that either large or small gold could be targeted, in fact my dream has been for a machine that automatically cycles through a couple of sequences tailored for both large and small gold. I've tried this on a std PI before and it sadly generated a lot of noise, noise that I believe SETA was developed by Minelab to overcome. They now have the ability to have a full spectrum of timings cycling, but have perhaps held off releasing it.

How sensitive do you feel the TEM can be made, is it perhaps only effective with coin sized targets and above? Is an earlier sample required to detect small targets as in conventional designs?

I know you're using Paul's UniPI, and I've been playing with a PIC24H DSP which is similar, and he's provided some of the source, so I'm sure we can collaborate sufficiently to get some code working.

The fly in the ointment for me at present is the disorder of my house and equipment, and in a couple of months I'll need to move everything out of my house into a shipping container while some walls and ceilings are rebuild.

Kind regards
Kev.

[Tinkerer]

Hi Tinkerer,
Two of my batteries would give a 14Volt supply.
600mAh would make the batteries last almost as long as they do in a Minelab.
The peak switch on i would be much larger than this and I understand the TEM front-end to be only marginally damped and thus oscillatory, is this so? I can see that if it is then we get much more bang from our 8 watts than is first obvious.

I also think a non-motion detector would work extra well in these areas especially when one considers that the whole rim of a mono coil is "hot", not having to keep that in relative motion while poking into and between scrub, would no doubt illuminate targets way off to the side and under the tussocks themselves.

Perhaps, there is a way that both motion an non-motion can be realised in software, it may be as simple as time dependent clearing, or not clearing of some registers?

I need to spend some time searching here and reading up on the development of the TEM TX so that I can understand what is happening.

Regards
Kev.

Hi Kev,

OK for the 14V battery supply. We will work with that. (11 to 14V)

My underwater PI of 25 years ago was a non motion design. I can use that as a reference and improve it.

There is a lot that can be done with software. If somebody would like to contribute the that end, I would be glad to work together on it.

ML detectors use very high gain. This makes them sensitive, but also enhances EF and EMI problems.

The TEM TX method is about 10 times as efficient in power use. So you ask yourself, why does the TINKERERS TEM detector use just as much power?

I make good use of the power by making a very powerful TX pulse. This TX pulse is not damped at all. Rather, I use a capacitor instead of the damping resistor. This capacitor absorbs the Flyback and adds it to the coil pulse current. You could compare it to a voltage doubler, except that it doubles the current instead.

Not only is the current doubled, the current is also re conducted to the battery, or the TX capacitor bank, so the consumption is only the Ohmic loss of the Mosfet and coil.

This can be compared to a resonant circuit, although only the pulse is resonant.

So? How come it does not oscillate?

It is possible to avoid oscillations by bleeding the Flyback power in a damping resistor.

It is also possible to avoid the oscillations by adding more current to the current reversal, just the opposite of the bleeding.

For this purpose I use the current that I send back to the battery.

There is much more to it, I really need to make a full explanation of the TINKERERS TEM DETECTOR METHOD, but I will do that once we have the FULL OPEN SOURCE DESIGN ready to be released.

In the meantime, you might look at Aziz's full TEM TX analysis and explanation, given in scientific engineering terms, some 2 years or so ago.

With this very strong pulse I get a stronger signal response, that needs less amplifying. With less signal amplification, the EF and EMI noise is also less amplified.

Tinkerer

[Tinkerer]

Yeah, I know, and I might have something up my sleeve, but it is not nearly ripe yet, and it may end up as complete waste of time.
There is so much energy in there that goes wasted. Actually, prior to your posts I was wandering how come that no one did not notice rising current consumption and concluded that I must be reasoning wrong. Now I know better. Thanks.

We need to give Aziz some credit here. He spent a considerable amount of time trying to get somebody to come up with some numbers on the difference in current consumption caused by aggressive ground.
The problem is, that this information takes some work to get. I just happened to have the circuit hooked up the right way to take the approximate measurement.

Tinkerer

[Tinkerer]

A non-ferrous target such as a coin presented to the coil will decrease the inductance resulting in higher coil current.

A ferrous target such as a nail will increase the inductance resulting in lower coil current.

You can see this during the pulse on-period and during the flyback. If we could somehow subtract the signal due to eddy currents, the flyback would take longer to settle for ferrous objects and would actually take less time to settle for non-ferrous objects. Square the spike to a diode drop above ground with a fast opamp to ignore the eddy currents and the change in width is easy to see. The coil current and flyback amplitude also varies when the ground alters the coil's inductance.

This is a bit easier to see in a diagram at the following link, post #278.

http://www.geotech1.com/forums/showthread.php?t=12523&page=12

Note that this information isn't available where sampling takes place in a conventional PI. The same information though is available during the pulse so it makes no sense to sample the flyback.

The diagram of post #278 is very good. It shows how the signal response of ferrous and non ferrous target is in relation to the no target signal.

This does not show the current consumption.

The difference in current consumption is very small for a gold nugget. Taking the measurements above, the difference in current consumption for a gold nugget would be about 9e-7A.
Compared to the difference in current consumption of an aggressive ground that is about 100mA.

Tinkerer

[crane]

A non-ferrous target such as a coin presented to the coil will decrease the inductance resulting in higher coil current.

A ferrous target such as a nail will increase the inductance resulting in lower coil current.

You can see this during the pulse on-period and during the flyback. If we could somehow subtract the signal due to eddy currents, the flyback would take longer to settle for ferrous objects and would actually take less time to settle for non-ferrous objects. Square the spike to a diode drop above ground with a fast opamp to ignore the eddy currents and the change in width is easy to see. The coil current and flyback amplitude also varies when the ground alters the coil's inductance.

This is a bit easier to see in a diagram at the following link, post #278.

http://www.geotech1.com/forums/showthread.php?t=12523&page=12

Note that this information isn't available where sampling takes place in a conventional PI. The same information though is available during the pulse so it makes no sense to sample the flyback.

[RKC]

Gid'day Rob,
We've slowed down for winter, don't fancy detecting in the snow, a good time to work on the house. I wish they'd stop though, we've just started to do some painting, and that 5.2 we had last Friday has put cracks in the the bog and paint all over again.

Are you in New Guinea for the Winter?
I'm itching for spring so we can get back into it.

Better get back on topic here, I think Tinkerer has some ideas that could help us get some of those deeper bits we've been missing.

All the very best.
Kev.

G'day Kev,

Here on the West Coast we have been getting more and more Christchurch residents moving here to get away from the bureaucratic incompetence that has sprung up since the earthquake. I haven't been anywhere near Christchurch since the first earthquake and it takes a lot to get me away from The Coast these days. I won't be going to PNG any time soon. I'll probably spend all of this winter on The Coast ... actually winter can be the best time of the year here (for a number of reasons). Its crazy here during summer with all the hordes of amateur fossickers invading The Coast and waving their Goldbugs about ... everywhere, except where the gold is most likely to be.

If there is one thing we need in NZ more than any other MD technical development is more depth. Anything anyone can do to achieve this will get a lot more gold from the ground.

All the MD kits that are becoming available these days are an interesting development. I will soon need to replace my Goldquest SS (for going after float) and I can't decide on a worthy replacement detector that is a PI MD (for depth), yet will still get specimens.

Regards,
Rob (RKC)

[Kev]

G'day Kev,

Good to see you have been doing well down in Otago ... and managing to get away from the city! Enjoyed seeing the pictures of the tussock country (I think I recognise that part of the country). I can't seem to manage to get down that way these days but might make a trip next summer.

Hope your house repairs are going ahead without too many problems. With Christchurch still getting shakes it must be a nightmare trying to repair a house.

Regards,
Rob (RKC)

Gid'day Rob,
We've slowed down for winter, don't fancy detecting in the snow, a good time to work on the house. I wish they'd stop though, we've just started to do some painting, and that 5.2 we had last Friday has put cracks in the the bog and paint all over again.

Are you in New Guinea for the Winter?
I'm itching for spring so we can get back into it.

Better get back on topic here, I think Tinkerer has some ideas that could help us get some of those deeper bits we've been missing.

All the very best.
Kev.

[Kev]

About the battery:

The TEM TX method makes very good use of the power. Therefore I like to use a high power TX at a high pulse repetition rate, like 10A peak coil current at 5000 PPS.

This consumes about 600mA out of a 12V battery.

It has the advantage of a powerful TX pulse that generates strong eddy currents in deep targets. The high repetition rate allows for integrating or stacking many samples, thus giving a good S/N.

For this, it is good to have a relatively high TX voltage, 12V is OK, more is even better. You mentioned 12V earlier, so I have started designing around this voltage, but it seems that the battery pack you mention above, is only 7.3V.

Comments?

Tinkerer

Hi Tinkerer,
Two of my batteries would give a 14Volt supply.
600mAh would make the batteries last almost as long as they do in a Minelab.
The peak switch on i would be much larger than this and I understand the TEM front-end to be only marginally damped and thus oscillatory, is this so? I can see that if it is then we get much more bang from our 8 watts than is first obvious.

I also think a non-motion detector would work extra well in these areas especially when one considers that the whole rim of a mono coil is "hot", not having to keep that in relative motion while poking into and between scrub, would no doubt illuminate targets way off to the side and under the tussocks themselves.

Perhaps, there is a way that both motion an non-motion can be realised in software, it may be as simple as time dependent clearing, or not clearing of some registers?

I need to spend some time searching here and reading up on the development of the TEM TX so that I can understand what is happening.

Regards
Kev.

[Davor]

I think this is one of the reasons that ML use low resistance coils, to prevent/reduce tx voltage/current modulation effects from "hot" ironstone ground etc.

By virtue of transforming action the coil resistance is added to target resistance and it modifies tau

[Tinkerer]

Hi Guys,

Of course when you bring a metal target near the coil it will consume more power. Same with ground too. There is definitely good information to be gleaned measuring the current consumed by the coil. I would not rely on this information alone, but it is one piece of the puzzle. You could even sample along the coil current curve and perhaps pick up more info again on target tc by taking an early sample a middle sample and a late sample or have separate dedicated channels for each +sample, with a -EF sample taken at the end of tx or at another point during tx period. Or use an adc and direct sample and do dsp on them. You will probably need amplification before the adc.

I think this is one of the reasons that ML use low resistance coils, to prevent/reduce tx voltage/current modulation effects from "hot" ironstone ground etc.

Cheers Mick

The TEM coils are low resistance, this does not prevent or reduce the modulation, rather it makes it more notable. A way to counteract, would be to make a constant current control.
I believe some detectors do that.

Tinkerer

[Tinkerer]

Yeah, I know, and I might have something up my sleeve, but it is not nearly ripe yet, and it may end up as complete waste of time.
There is so much energy in there that goes wasted. Actually, prior to your posts I was wandering how come that no one did not notice rising current consumption and concluded that I must be reasoning wrong. Now I know better. Thanks.

Traditional PI consumes about 10 times more power, because it burns it all off in the damping resistor. With all that power wasted, that little difference was not important.

With the TEM method it shows up because of the greatly improved power efficiency.

Tinkerer

[Mechanic]

Hi Guys,

Of course when you bring a metal target near the coil it will consume more power. Same with ground too. There is definitely good information to be gleaned measuring the current consumed by the coil. I would not rely on this information alone, but it is one piece of the puzzle. You could even sample along the coil current curve and perhaps pick up more info again on target tc by taking an early sample a middle sample and a late sample or have separate dedicated channels for each +sample, with a -EF sample taken at the end of tx or at another point during tx period. Or use an adc and direct sample and do dsp on them. You will probably need amplification before the adc.

I think this is one of the reasons that ML use low resistance coils, to prevent/reduce tx voltage/current modulation effects from "hot" ironstone ground etc.

Cheers Mick