Concentric coil for TGSL.

[satdaveuk]

Thanks Don
You done a nice tutorial with well laid out constructional details.
I for one have never got round to making a coil of this type but now feel the urge to do so.
Many thanks for sharing your well thought out idea.
Also like the sound of the 35k shielding should be ok for UK soils
Regards

[ApBerg]

Thanks for the great info...as always !

Ap

[Aziz]

Well here it is as promised. A complete guide to building your own Concentric Coplaner coil for the popular TGSL project.. It works!
Please let me know if anything is unclear or needs revised.
Happy building.
Don

Good job! Thank you for your very valuable contribution.

Aziz

[kt315]

nice work. thanks! I repeat again a data on all Tesoro coils. thinking it will useful.

====
Tesoro concentric
Tx 1,5 5.7mH 22 ohms
Rx 3,4 6.2mH 22 ohms
====
Tesoro early Lobo DD
Tx 2,4 10mH 55 ohms
Rx 1,3 1.35mH 12 ohms
====
Tesoro
Name TX-L TX-R (ohms) TX-fo TX wire RX-L RX-R (ohms) RX-fo RX wire
________________________________________
Brown 8" 5.59mH 21.2 --- --- 6.23mH 22.1 ---
---
Lobo 5x10 9.93mH 50.5 --- --- 1.33mH 10.97 --- ---
Lobo 8x15 10.52mH 62.8 --- --- 1.37mH 13.13 ---
========
Troy Shadow
Name TX-L TX-R (ohms) TX-fo TX wire RX-L RX-R (ohms) RX-fo RX wire
________________________________________
X2 S-9 9" 5.72mH 23.6 --- --- 6.25mH 25.2 --- ---
X5 7" 1.067mH 4.33 --- --- 6.53mH 32.2 --- ---
X5 9" 1.044mH 4.45 --- --- 6.50mH 32.7 ---
---
X5 1.1mH / selfrez = 255kHz 6.5mH / selfrez = 87kHz
====

[dfbowers]

Thanks guys! After looking through the simulatons that Aziz was coming up with, I thought the concentric coplaner would be a good one to experiment with, even though it's "old stuff"..
Now if I can only figure out how to box up a top hat coil and put it on the end of a pole.......

[dfbowers]

It's a well known fact that in general, low frequency detectors are best suited for deeper, higher conducting targets while high frequency detectors are better suited for shallower, low conductors.
Just how much of a difference is there REALLY???

Since I built 2 concentric coils with identical geometry (one for IDX and one for TGSL), I put them to the test! The question arose in my head as to why some of my air tests with my TGSL coil showed poor results as compared to the IDX while ground test seemed equal.. DOH!! I was using a quarter for air test and a lead ball for ground testing..

So.. Comparing oranges to oranges (or quarters to quarters) I was astounded by the results. No wonder manufacturers came up with multi frequency machines!!

I set my GB and DISC setting for my IDX and TGSL to approximately the same place.
As you can see from the tests, lead has an almost identical response to both detectors.. But look at the results for Aluminum foil and copper..Wow..

Again, the coils are both 7.5" hand wound concentric coils and.. these are AIR tests.
Don

[Gwil]

Hi Don

If you want to find out how the sensitivity to various targets varies with frequency, it might be better to adjust the discrimination in each test until you get the maximum range. Leaving the discrimination at the same setting all the time means that the “gain” of the synchronous detector is varying for each target in an unknown way. Just a thought…

[dfbowers]

Hi Don

If you want to find out how the sensitivity to various targets varies with frequency, it might be better to adjust the discrimination in each test until you get the maximum range. Leaving the discrimination at the same setting all the time means that the “gain” of the synchronous detector is varying for each target in an unknown way. Just a thought…

Yes.. I believe you are correct. The diagram probably has more to do with how the signals pass through the demodulators than anything. All metal tests produce more of a flat line across the conductivity range. And.. ground penetration was not taken into consideration. BUT at a given disc setting for both detectors this points out the strenghts of both.

[dfbowers]

For this evenings project. . how about a 10" concentric for the TGSL!!

Construction methods are identical to the 7.5" coil project posted previously. Building this way does not look impressive, but foam board with cardboard skins glued to the outside results in an extremely stiff and mechanically stable assembly. Also, light as can be!!

Tx coil - 127mm radius (5"). It's build on a 130mm radius foam board with a groove cut in the edge with a hot iron. , 11mm thick. 87 turns using .25mm wire - 6.0 mH.
Wire is wound counter clockwise.

Rx coil - 63mm radius (2.5"). It's built on a 63mm radius foam board, made into a spool . Foam board started at 11mm thickness but sanded a bit so all fits flush when finished. 157 turns using .25mm wire - 6.5mH. Wire is wound counter clockwise.

Bucking coil - 23.5 turns (about) on the outside of the Rx coil, again .25mm wire. Wire is wound clockwise.

You can refer to the previous post for the coil schematic.. just scale up a bit and substitute the above number of turns.

Initial testing shows that detection range is almost identical to a 10" DD coil - Coins can be detected up to 30cm or so. Not anything impressive but functions perfectly!!
Time to order more ABS plastic and break out the vacuum forming machine again..
Field test to come..

Don

[Thomas]

It's good that you're doing this, I just started a 10" using some foam cardboard composite stuff.
It is 5.25mm thick with 4.5mm foam using .25mm wire so this will hopefully be close to the same.

[dfbowers]

Here is a quick Video on what to expect. I'm using a gold ring for testing.

http://youtu.be/r-F5bu0m3N4
Don

[Thomas]

Don, any guess how deep a channel I should cut in the foam with a 4.5mm thickness?, I want to make sure I don't end up with spill over, or a deep recess. Or, what is the cross section diameter of your bundle of wire

[Thomas]

Also I found the graphite spray, It was in the spray lube section, the guy at the door and lock section had no idea what I was talking about. If I get results close to yours in the video I'll be happy.

[dfbowers]

Don, any guess how deep a channel I should cut in the foam with a 4.5mm thickness?, I want to make sure I don't end up with spill over, or a deep recess. Or, what is the cross section diameter of your bundle of wire

Thomas,
It really doesn't matter how your coil ends up. There are three important things though that you need to pay attention to:

1. The mechanical stability of the assembly when you are done - It must be stiff and your wires should be fused together - I use krazy glue, but be careful not melt your foam.
2. The final inductances of the Tx and Rx coils - otherwise your phasing will be off and GB and disc will not be within the adjustment range of your pots.
3. The final null - Get the deepest null possible. If the residual signal is too high, your first op amp may end up in saturation.

Your coil could end up looking really ugly and still work just fine.. If you get it to work, I will send you something in the mail to finish your coil as a reward


Don

[Thomas]

OK, got it, I think this is going to be a good one.