New Concentric Co-planar Coil with Strong MF.

[Davor]

OK, so actual 1/2 flux is at 0.82 radius. It must look very much like a monocoil. I have a balance tuning idea: both coils are made slightly elliptical and balance is tuned by slightly turning one coil against the other.

[satdaveuk]

That is one BIG M.F. of a coil!!!
You must be very fit and strong, but I am not surprised that pinpointing is not it's strong point......its almost 10 meters (30Ft) across....
Can you show us pictures?
Regards
Andy

Lol Andy, just seen that , you know what i ment, would have been a real deep searcher

[Tinkerer]

OK, so actual 1/2 flux is at 0.82 radius. It must look very much like a monocoil. I have a balance tuning idea: both coils are made slightly elliptical and balance is tuned by slightly turning one coil against the other.

A simple way of looking at it, but it works perfectly, is to look at the coil area. r*r*pi, for each coil.

For example, TX=1, Bucking=0.5, RX=0.5 diameter. The area and turns ratio is 1:0.25. But we do not want to mess with incomplete turns, so we make the TX, say 12 turns and the Bucking and RX 3 turns.
This is fairly accurate, but, wire thickness and insulation as well as winding tightness play a role, so the balance is never perfect.

The simple way to correct the balance, is to increase or decrease the relative surface area. If it is a circular coil, pulling it a little oblong, reduces the surface area.

It is even easier with rectangular or square coils, where one can just pull out a side or push it in the increase or reduce the surface area.

Then the coils need to be "frozen" in their respective positions. We do this by casting the coils with resin.

What if the coils shift a little while casting? This is why we add a bucking control circuit. This little circuit makes it possible to shift the balance a little even if it is cast rock solid. It also solves some other problems.

Extremely simple really, as is the whole coil balancing matter, once one knows how, but it can also be made to look very complex covering a whole page with mathematical formulas.

Tinkerer

[ivconic]

ditto we made jigsaw puzzles with a fretsaw, and my dad made them for us when we were knee high to grass hoppers, I thought most people owned one.
Talking of comparing your DD coils with other types, I can only comment on personal experience of owing and using many different brand detectors over the years that to be honest with you even in are uk soils it largely depends on the detector design on whats good or better on which particular machine.
For instance the Whites DFX which is not so popular over here and never was for what reasons im not sure but at a guess I think your avarage detectorist just found them to complicated to use, but if they had grasped the way it operates and had done some good field tests by people like myself with my own custom settings which took a good 18months and hundreds of hours to master then the tables would have turned because even by todays standards of machines on the market there still way past half way to the top end machines.
Coil wise they work at there best with the circular coil they came out the factory which was a 950cm, I have done exstensive tests with the Whites 14x10 DD coil which Whites themselfs told me should give me that extra depth which never happened.
All it did was make pinpointing less accurate and ruin the balance of a perfectly made machine.
So tech boys work that one out because that coil been so much larger should in theory have at least produced more depth .
On the other hand I have a Minelab Quattro which is multifrequency with a 10DD coil factory fitted ,it gives a tad more depth with silver finds, most detectors are good with copper and lead so not worth the mention, but gold its crap, and that no disc and all metals, even my Whites 1v pics up better again with the circular coil.
So my point is between the two types of coils you have been chatting about its horses for courses, I really have come to the conclussion that some work better than others on different machines and yes even maybe the same makes and models because two machine will never be identical due to lots of factors, and thats why different people use different settings, its not just the types of soils etc there detecting on, its also the machines, What do you think?
Ive never made a circular coil for a induction balance machine because they seem so complicated, has anyone here got some uncomplicated instructions to build one say for the TGSL most of us built here because it will be interesting to see the results, Ive made loads of DD coils with very good results, or at least I think so.
May a add ive been reading this thread with great interest like so many others on here, your such a clever bunch I thought I was good but now I feel like a apprentice again
So a big thank you to all of you and as ive said previously if you was girls id give you all a big wet kiss.
On a serious note wish I had known about this forum years ago its been a education and such a learning curve.
Regards
Dave

I enjoyed reading this!
Very honest and very true!

[ApBerg]

Hello Dave & and other friends !

Dave writes : Ive never made a circular coil for a induction balance machine because they seem so complicated, has anyone here got some uncomplicated instructions to build one say for the TGSL most of us built here because it will be interesting to see the results, Ive made loads of DD coils with very good results, or at least I think so.




Look at http://www.geotech1.com/forums/showt...7250#post77250 there is a zip called "form.pdf" here you can see the coils I made and used for ' in water' searsing.
Have used the 22cm coil, with cable in tube, a lot with the Golden Sabre. Worked beter then a Fisher 1280, more depth and beter pinpointing by slow moving over targets.

On land the opencenter is better then DD for 'Hunts' ,better pinpointing and disc.
Have many time's told on Geotech how I made the opencentre coils ... I think they are easyer to make then DD coils.

Just my story.. ( coils&forms etc. from +/- 1989 )

Best regards to all.

Ap

[ivconic]

In the past i made just a few cc coils with more or less success.
I had less knowledge than and lot of problems to make it right.
That's why i adopted kind a fear of those!
Than i gave up and switched mostly to dd coils.
But recently i had to service one original Tesoro coil.
Cable was extracted from coil by force, an accident.
Deep inside coil wires were broken.
I tried to remove epoxy filler somehow and that resulted with complete coil destruction!
So i was forced to make new one, using original enclosure, which i managed to save somehow!
So i made TX and RX windings easily.
Feedback was a bit of trial&error job. Not a big deal. After second attempt i got it!
But than i realised how easy making cc coil can be if things are done in right order!
CC coil is not deeper than DD but it is more "stabile" and kind a easier to null.
Once null is achieved by finding proper feedback specs - it stays perfectly nulled even if moved and knocked untill filler is applied and hardened.
Unlike DD coil.
At DD coil i have to pay attention on slightest move, knock, temperature change - before i apply filler and wait 10 and more hours to harden.
Great chances null to slip away and jitter a bit.
Not case with CC coil. Even without filler; it stays stabile nulled and immune to moves, knocks and sudden temperature changes.
CC coil is more precise at pinpointing, a bit more accurate at discrimination and making it is not that hard task as i had fears in the past.
I used Al foil and wrapped it around TX, also around RX. But not around feedback. No problem.
Later i tested serviced coil; seems is working only 5% worse than original.

[Aziz]

*LOL*
Reminds me to my horrible coil making experiences!!!


Fortunately, I can compensate the coil imperfections and (man-made) stress to the coil with the software now. So the coil can (almost) be loose assembled.


Cheers,
Aziz

[ivconic]

*LOL*
Reminds me to my horrible coil making experiences!!!


Fortunately, I can compensate the coil imperfections and (man-made) stress to the coil with the software now. So the coil can (almost) be loose assembled.


Cheers,
Aziz

You can't even imagine the "stress"!

If you can manage that - than you are on right track!
I always wandered how Minelab did it at their multifrequency machines (without involving in deep DSP analyze).
I guess there are lot of compromises to be accepted in such setups...

[ApBerg]

Hello Dave,

Made some photo’s from the coilwindig forms I used… they are from late 1980’s …so no computer software then, but the made coils worked fine.

To make a CC coil :

Start with the transmit coil, as seen on the large 22,5 cm form 97 turns give’s 14,5 KHz, (114 turns is 12.5 KHz.) Wire used is 0.25 mm and the coil is connected to the Tesoro transmitter so the cap from the oscillator has also influence at the transmit frequency !


The first receive coil, 18 turns, is added at the 22.5 cm coil, same wire and turn direction . Transmit coil and first receive coil both clockwise !

This 18 turns will , just like in a transformator, pick up a part from the transmit signal .
If the transmit signal is 15 volts then there is 15volt /97turns = ca. 0.15 volt per turn wire so the first receive coils 18 windings pick up 18x0.15 volt = 2,7 volt.

Now the trick is to null out this 2,7 volt … this must be done by the second small receive coil, As the distance to the transmit coil is greater the magnetic field is smaller, so less volts per winding.. so more turns are needed to get that 2,7 volt. AND that voltage needs to be in opposite faze , so the windings for the second receive coil have to be counter clockwise !
For a 10-12 cm coil form some 160-170 turns are needed, also 0.25 mm wire. The two receive coils are connected in series but picking up the volts in opposite faze's so the result is zero.

If you have to move the small receive coil towards the transmit coil (stronger magnetic field) then you have to add windings at the small coil….if you have to lift up the small receive coil (less magnetic field) than you have to reduce windings…

For the receive capacitor look at the first opamps output… select the cap for a nice sinus out.


Good luck !

Ap

And yes... some software to adjust the stuff....hmmm but we do not have that... so...here is the info I have... it works but it needs some experiments to get it right.. winding strength diameters from the coils.... all make’s differents... and I hope I have not made errors...

[Davor]

A simple way of looking at it, but it works perfectly, is to look at the coil area. r*r*pi, for each coil.

Yes, it is a simplified view of the matter. In reality the flux thing is a bit more complicated, especially near the outer loop wires. Calculations tend to be quite complicated.
Considering the mismatch due to the ground proximity you are much better off with inner coil being closer to the outer one. Aziz already confirmed such coils to be better for deeper scans.

[satdaveuk]

Thanks Apbergi
Ive saved the pdf file on your forms
Did you do a detailed construction pdf for making and setting up coplaner for the TGSL or any others would be helpful.

Many thanks

Regards

[ApBerg]

Thanks Apbergi
Ive saved the pdf file on your forms
Did you do a detailed construction pdf for making and setting up coplaner for the TGSL or any others would be helpful.

Many thanks

Regards

Hello Dave,

No.. I have not more detailed pdf's ... sorry...

Best regards.

Ap

[Tinkerer]

Yes, it is a simplified view of the matter. In reality the flux thing is a bit more complicated, especially near the outer loop wires. Calculations tend to be quite complicated.
Considering the mismatch due to the ground proximity you are much better off with inner coil being closer to the outer one. Aziz already confirmed such coils to be better for deeper scans.

Relative larger RX coils give more residual voltage. More residual means less head room for the pre-amp. Less headroom means less possible gain.

The best gain is at the pre-amp.

Tinkerer

[Davor]

There is no reason why it couldn't be well balanced as any other coil system. I dunno. I'll surely concentrate on possible causes of residual voltages. I have some ideas, but not too certain at the moment.

[simonbaker]

Relative larger RX coils give more residual voltage. More residual means less head room for the pre-amp. Less headroom means less possible gain.

The best gain is at the pre-amp.

Tinkerer

Hi Tinkerer:

My experiments (TGSL Experiments thread) seem to indicate that residual voltage is due to some non-magnetic coupling (capacitive?) in the wires of the coil and/or cable system. I got a much deeper null with a special Belden cable with shielded pairs than with a USB cable, for example. I do not know if that translated into detection superiority (couldn't test that). Also, both nulls happened to be well within the headroom of the pre-amp.

Magnetic coupling, in theory, should be able to be canceled quite well by shifting our coils I think. So maybe a little circuitry to cancel some of the "capacitive" coupling could be employed if needed to accomodate a coil whose residual null can't be knocked down enough by shifting the coils.

-SB