complete project

[Tinkerer]

Hi Tinkerer,

What effect does putting the coil near, say a sheet of alu foil have on efficiency?

600mA is fine for power draw, thats about what the ML's use

Cheers Mick

One square foot of 1.6mm alu plate at the center of the coil, adds about 50mA.
2 square feet of thin steel plate, 15cm above the coil, add about 100mA power consumption.

The test coil is 1m x 0.5m.

Tinkerer

[Davor]

So you need only a multimeter as a receiver

[Tinkerer]

So you need only a multimeter as a receiver

I guess if the multimeter was capable of measuring femto amperes, it might even work for nuggets.

I must say that I am surprised at the relative large change in power consumption. My thanks to Midas and Mechanic for bringing up the subject.

Tinkerer

[Davor]

Whole point is that detection uses only a small portion of available energy, and it is not the femtoamperes that you detect, but the miliamperes that you don't. There just must be a better way of PI detection.

[Tinkerer]

Whole point is that detection uses only a small portion of available energy, and it is not the femtoamperes that you detect, but the miliamperes that you don't. There just must be a better way of PI detection.

The TINKERERS TEM method IS a better way.

You should take a closer look at it. Probably you could also bring many further improvements to it too. I would be happy to give you all information you need to be able to come up with new and better ideas.

Opes source depends on the contributions of the beneficiaries.

Tinkerer

[Davor]

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.

[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

[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

[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

[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

[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.

[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.

[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)

[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/showt...=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.

[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/showt...=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