INDUCTION BALANCED COILS FOR PI

[Tinkerer]

I have been doing a bit of experimenting with INDUCTION BALANCED COILS (IB COILS) for PI.
There seem to be lots of advantages in these coils, compared with MONO coils.

Why are the IB coils not used more often?

Below is a very good and detailed instruction by DAVID EMERY of how to construct a coplanar, concentric IB coil.

http://www.geotech1.com/pages/metdet...planar_300.pdf

Tinkerer

[Qiaozhi]

I have been doing a bit of experimenting with INDUCTION BALANCED COILS (IB COILS) for PI.
There seem to be lots of advantages in these coils, compared with MONO coils.

Why are the IB coils not used more often?

Below is a very good and detailed instruction by DAVID EMERY of how to construct a coplanar, concentric IB coil.

http://www.geotech1.com/pages/metdet...planar_300.pdf

Tinkerer

I think the answer is that mono coils are just easier to make. You only have look at the TGSL thread to see how difficult it can be to balance an IB coil correctly for a VLF-IB design, and no doubt the same will be true for a discriminating PI.

[Tinkerer]

I think the answer is that mono coils are just easier to make. You only have look at the TGSL thread to see how difficult it can be to balance an IB coil correctly for a VLF-IB design, and no doubt the same will be true for a discriminating PI.

The same will hold true for walking and flying. It is certainly easier to walk than to fly. Yet, at a certain time in evolution, some people decided that it would be cool to go flying and faced the challenge.

Tinkerer

[Qiaozhi]

Below is a very good and detailed instruction by DAVID EMERY of how to construct a coplanar, concentric IB coil.

http://www.geotech1.com/pages/metdet...planar_300.pdf

Tinkerer

This article makes it sounds easier than it is in practice. Correct phasing of the coils is not even considered, and for VLF detectors it is an important and poorly understand adjustment.

[Tinkerer]

This article makes it sounds easier than it is in practice. Correct phasing of the coils is not even considered, and for VLF detectors it is an important and poorly understand adjustment.

The method described, makes a very good IB coil for a PI. However, it does not make adjustments easy once the coil is cast.

By making the Bucking coil separate, with its own feed line, one can add circuits to compensate for heavy ground mineralization and slight shifting of the coils during casting, as well as shifts caused by aging, humidity and temperature.

Tinkerer

[Roughwater]

Advantages of Induction balanced coils

I have been doing a bit of experimenting with INDUCTION BALANCED COILS (IB COILS) for PI.
There seem to be lots of advantages in these coils, compared with MONO coils.

Why are the IB coils not used more often?

Below is a very good and detailed instruction by DAVID EMERY of how to construct a coplanar, concentric IB coil.

http://www.geotech1.com/pages/metdet...planar_300.pdf

Tinkerer

Tinkerer,

What are the advantages of a Induction Balanced coil for a PI compared to a Mono?

Thanks
Terry

[Tinkerer]

Tinkerer,

What are the advantages of a Induction Balanced coil for a PI compared to a Mono?

Thanks
Terry

Terry,

Induction Balanced coils for PI offer advantages like extreme sensitivity, and iron discrimination.
DD coils are the most common. Concentric coplanar IB coils are less common.

At the following link you can see some more information:
http://www.geotech1.com/forums/showthread.php?t=15441

Tinkerer

[simonbaker]

I have been doing a bit of experimenting with INDUCTION BALANCED COILS (IB COILS) for PI.
There seem to be lots of advantages in these coils, compared with MONO coils.

Why are the IB coils not used more often?

Below is a very good and detailed instruction by DAVID EMERY of how to construct a coplanar, concentric IB coil.

http://www.geotech1.com/pages/metdet...planar_300.pdf

Tinkerer

I am not expert in this, but my instincts say that the essence and elegance of the PI design is the mono coil. By using the time domain to isolate the TX and RX signals from each other (admittedly not perfectly!), the coil design is vastly simplified and the design stabilized.

This makes it ideal for commercial production.

If IB coils are used, I wonder if you might as well create an IB VLF detector with the same power as the PI detector and get better results.

I think in terms of phase stability, the broadband time domain is much less forgiving than when dealing with a single frequency, but Tinkerer probably knows much better from experiments. What I mean is that the shape of a pulse is very affected by specific phase shift of different frequencies. Since PI is dependent on exact pulse shape, anything that could destabilize the shape is a worry. So my question is: if the nulling shifts a tiny bit, what does it do to the received pulse?

I am not at all being negative about trying to do IB pulse. Every possible idea is worth investigating. It is just too bad it adds certain complications to an elegantly simple design. But improvements usually involve complications -- look at all the crazy stuff biology invented to give species an advantage.

It's all interesting!

-SB

[Tinkerer]

I am not expert in this, but my instincts say that the essence and elegance of the PI design is the mono coil. By using the time domain to isolate the TX and RX signals from each other (admittedly not perfectly!), the coil design is vastly simplified and the design stabilized.

This makes it ideal for commercial production.

If IB coils are used, I wonder if you might as well create an IB VLF detector with the same power as the PI detector and get better results.

I think in terms of phase stability, the broadband time domain is much less forgiving than when dealing with a single frequency, but Tinkerer probably knows much better from experiments. What I mean is that the shape of a pulse is very affected by specific phase shift of different frequencies. Since PI is dependent on exact pulse shape, anything that could destabilize the shape is a worry. So my question is: if the nulling shifts a tiny bit, what does it do to the received pulse?

I am not at all being negative about trying to do IB pulse. Every possible idea is worth investigating. It is just too bad it adds certain complications to an elegantly simple design. But improvements usually involve complications -- look at all the crazy stuff biology invented to give species an advantage.

It's all interesting!

-SB

Simonbaker,

The advantage of PI design is the power.
It is the di/dt that "kicks" the target with the PI as well as the VLF design.
The field strength of the time varying magnetic field is proportional to the Amps and the velocity it cuts through the target are the important factors.

A weak field does not penetrate as much into the ground as a strong field.

So when I zap the ground with 3A and 350uH there is a lot of energy discharged in a very short time.
I reckon that I zap that piece of ground with the target in it, with about 400Watts with each pulse. How does that compare with the VLF field strength?

Now comes the problem: With the traditional PI you have to wait until the Flyback has subsided and then capture the signal of the target. By the time you capture that signal, only a weak shadow of the original amplitude is left.

The VLF has the advantage there, because it captures the signal at the same time as the signal is generated.

With the IB-PI I can capture the signal at the same time it is generated, just like the VLF. This is why I can also discriminate with the IB-PI, just like the VLF does.

I don't know how to detail the mathematics of this, but I would welcome if you want to give it a try. I can supply the numbers, you do the number crunching.

It would be interesting to put the derivations of the IB-PI, the VLF and the traditional PI next to each other.

Tinkerer

[simonbaker]

Simonbaker,

The advantage of PI design is the power.
It is the di/dt that "kicks" the target with the PI as well as the VLF design.
The field strength of the time varying magnetic field is proportional to the Amps and the velocity it cuts through the target are the important factors.

A weak field does not penetrate as much into the ground as a strong field.

So when I zap the ground with 3A and 350uH there is a lot of energy discharged in a very short time.
I reckon that I zap that piece of ground with the target in it, with about 400Watts with each pulse. How does that compare with the VLF field strength?

Now comes the problem: With the traditional PI you have to wait until the Flyback has subsided and then capture the signal of the target. By the time you capture that signal, only a weak shadow of the original amplitude is left.

The VLF has the advantage there, because it captures the signal at the same time as the signal is generated.

With the IB-PI I can capture the signal at the same time it is generated, just like the VLF. This is why I can also discriminate with the IB-PI, just like the VLF does.

I don't know how to detail the mathematics of this, but I would welcome if you want to give it a try. I can supply the numbers, you do the number crunching.

It would be interesting to put the derivations of the IB-PI, the VLF and the traditional PI next to each other.

Tinkerer

Yes, it sounds right and I think you'll find a way to get it working - and you can let us know how easy to stabilize.

I think you have in mind some ways to perform discrimination if you can sample earlier than typical PI, so I understand your drive to get the IB version working. I'm wondering, though, if there may also be enough information with a mono coil to do reasonable discrimination, I'm sure everyone is working on that too.

Regarding VLF, I have not counted out higher "power" versions to compete with PI. I'm interested in toying with some high-Q (yes, bulky) TX coil designs to get the TX current way up there and with some higher voltage, see if it might dig deeper. Maybe it's being done; or maybe good reason not to!

We'll be interested in your progress.

Cheers,

-SB

[Tinkerer]

Yes, it sounds right and I think you'll find a way to get it working - and you can let us know how easy to stabilize.

I think you have in mind some ways to perform discrimination if you can sample earlier than typical PI, so I understand your drive to get the IB version working. I'm wondering, though, if there may also be enough information with a mono coil to do reasonable discrimination, I'm sure everyone is working on that too.

Regarding VLF, I have not counted out higher "power" versions to compete with PI. I'm interested in toying with some high-Q (yes, bulky) TX coil designs to get the TX current way up there and with some higher voltage, see if it might dig deeper. Maybe it's being done; or maybe good reason not to!

We'll be interested in your progress.

Cheers,

-SB

Yes, using a high current, low loss LC tank seems the logical answer for a VLF to go deeper. Dave Emery has patented something like that and Allan Westersten something different but along the same line of thinking.

The ability of the IB-PI to discriminate iron and to indicate the TC of targets is not because of the early sampling, but because of the different response of reactive and resistive targets and the different TC of different conductivity targets.
There is also information obtainable about the shape of the target by sampling early response and late response.
The fact that there is so much information obtainable is very exciting, but it is also a challenge to convert this information into something that the operator can grasp.
I do multiple sampling to obtain multiple information but have only scratched the surface of all the possibilities.

Tinkerer

[B^C]

Gday everybody,

In the field there is a big difference between Mono coils & say the Double D design & both have very different characteristics & depth capabillities.

The Mono coil will find targets a lot deeper but also has a lot of associated noise in bad ground which can be a big problem.
Ground balancing for these coils in bad ground certainly cancels out targets which is also an issue.

The Double D design will not find targets as deep as the mono but it has a substantial decrease in noise in bad ground which allows for detecting in these conditions but at less depth than the mono coils.

If it was possible to get a Double D coil to detect at the same depth as a Mono coil it would be fantastic.

I prospect on some very highly mineralised ground & i can't use a mono coil at all on the GPX4500, it's impossible, but i can run the Double D coil with no issues at all.

Both coil types have distinct advantages & disadvantages in differing soil conditions, we need an in between coil that doesn't require to much of a ground balance to cancel out smaller targets or larger ones at depth in bad ground.

On a PI machine discrimination doesn't seem possible with a Mono coil, the discrimination on the GPX4500 only seems to work with Double D coils.
In saying that, the discrimination is not that good for obvious reasons & it is best to dig ALL targets or otherwise you will be missing things.

There are to many variables & ground conditions, depth etc to discriminate each & every target.

I take no notice of the discrimination as i have seen all to often that large nuggets for instance have been left behind & not dug believing they were ferrous metals.
There's nothing worse than trying to sleep at night thinking if you should have just dug that target you didn't dig. It just maybe the one you've spent a lifetime looking for.

Just the other day i had a bit of a look not far from home & detected what certainly appeared to be a ferrous object & the 4500 certainly recognised this as ferrous material. When i dug it i found a fairly large piece of copper which surprised me & strengthened my belief that you have to dig all target discrimination or not with a PI machine.

Increased depth is far more important than discrimination, targets at good depth are very often valuable where trash & ferrous objects are nearer the surface being left behind by other people not so long ago.

[simonbaker]

Yes, using a high current, low loss LC tank seems the logical answer for a VLF to go deeper. Dave Emery has patented something like that and Allan Westersten something different but along the same line of thinking.

The ability of the IB-PI to discriminate iron and to indicate the TC of targets is not because of the early sampling, but because of the different response of reactive and resistive targets and the different TC of different conductivity targets.
There is also information obtainable about the shape of the target by sampling early response and late response.
The fact that there is so much information obtainable is very exciting, but it is also a challenge to convert this information into something that the operator can grasp.
I do multiple sampling to obtain multiple information but have only scratched the surface of all the possibilities.

Tinkerer

Yes, I meant with IB you can now sample parts of RX pulse that were previously obscured by TX... earlier parts... and see differences better.

I think it will be very valuble when you can show pictures of actual targets response for different targets and depths.

I agree with others that discrimination very tricky -- I was just testing phase of a steel washer. When placed flat on ground, it was like silver coin. When turned on edge, closer to ferrite, way below nickel. Very tricky.

-SB

[Tinkerer]

Yes, I meant with IB you can now sample parts of RX pulse that were previously obscured by TX... earlier parts... and see differences better.

I think it will be very valuble when you can show pictures of actual targets response for different targets and depths.

I agree with others that discrimination very tricky -- I was just testing phase of a steel washer. When placed flat on ground, it was like silver coin. When turned on edge, closer to ferrite, way below nickel. Very tricky.

-SB

SB,

I have posted a lot of pictures. Carl was kind enough to move many of them to a new forum at:
http://www.geotech1.com/forums/forumdisplay.php?f=53

I look at the target response at the same time it is generated, during TX time.
I get the same response with the steel washer that you get.
Move the coil at a different angle, so that the coil's field hits the washer at a different angle, you should see a difference.
I see the resistive response of a target as a positive going amplitude and the reactive response as a negative going amplitude.
Only magnetic targets give a reactive response.

Tinkerer

[grungymike]

Minelab SD series detectors are sold with an 11" DD coil for standard equipment. I'm not sure but I think White's TDI is a concentric.

Concetrics are better in mineralized soil than mono's (I think), DD's are better than either...

I'm here now trying to sniff out concentric and DD coil design data for the Hammerhead II design, especially a pending article by bbsailor...

Seen any good info?

grungymike