Graphite coil shielding for TGSL problems

[Goaty]

I hope this is not too far off topic but I recently found this video on making a quite professional conductive paint and also shows how to measure square conductivity.

https://www.youtube.com/watch?v=zyGX-VyXXTQ

Lots of other info on graphene as well which may prove interesting for experimenting with shielding materials.

[Qiaozhi]

I've just taken a resistance reading on the graphite coating in a White's Eclipse coil shell, and it measures around 60 ohms with the probes 1 inch apart.

[surfdetector]

To get higher resistance value in the coating up to 10K the only way I know how to do that is by ADDING more paint making it thicker.
Thinner paint would be less over all and equal less resistance. Would it not?
Unless I am missing something. You cant have it both ways.

As graphite is a conductive material, the more graphite that is added = the more conductive material that is present and hence the lower the resistivity on the region of the coating.

[billr]

Thanks for that Goaty.
Will look at it as soon as I post this.

Hi George.
Do you think this would be a good baseline to start with for the TGSL?
60 Ohms would be a really thin coat but I think its possible with a cotton swab to get a more even coverage at such a low value.
Alternatively I could try this spray for a more controllable outcome.

https://uk.farnell.com/kontakt-chemi...00ml/dp/832959

[Qiaozhi]

Hi George.
Do you think this would be a good baseline to start with for the TGSL?
60 Ohms would be a really thin coat but I think its possible with a cotton swab to get a more even coverage at such a low value.
Alternatively I could try this spray for a more controllable outcome.

https://uk.farnell.com/kontakt-chemi...00ml/dp/832959

If it's good enough for White's then it will be good enough for TGSL.

Eric has said previously that wrapping the coil with copper fabric tape over a spacer is better for PI detectors.
However, graphite coating seems be suitable for VLF detectors, but I suspect it has more to do with making it easier to manufacture and less costly.

[billr]

As graphite is a conductive material, the more graphite that is added = the more conductive material that is present and hence the lower the resistivity on the region of the coating.

Ok that's it I quit.
It's official....I'm a dork.
Just tried the probes on 2 papers painted with the stuff and the thinnest coat achieved the highest value.
Throughout this project of mine I convinced myself that thicker meant greater. More paint more better. Had no idea how graphite behaved.
Now I see why Rick kept saying thin fella .......make it THIN.

Well. Wont be the first or last time I messed up but I'm learning.
Thanks again Surf.

Come back Rick.
Everyone has to start from somewhere.
I'll let ya call me more names if you do. I can take it.

[Koala]

If it's good enough for White's then it will be good enough for TGSL.

Eric has said previously that wrapping the coil with copper fabric tape over a spacer is better for PI detectors.
However, graphite coating seems be suitable for VLF detectors, but I suspect it has more to do with making it easier to manufacture and less costly.

is that one of Whites old white concentric


They were really stable in use


if i remember correctly some of Tesoro plastic housing was also conductice

[Qiaozhi]

is that one of Whites old white concentric

Yes.

[billr]

So I made two paper discs today each coated with paint. One at 5 - 8K resistance . The other 60 ohms pretty much across the board.
The 8K performed badly in range only allowing 8" max before breakup. The 60 produced about the same as my aluminum coil 12.5" but both exhibited breakup of audio in the 75% range making it hard to tell if it was a true signal or background interference.

Removal of the center sections of the paper in the form of a double D to match the outline of the coil showed no improvement.

Back to plan A and re-coat the coils instead of the shell with some other ideas to implement.

Failing that........there is always the trash can.

[IBGold]

Billr,

The resistance of the shielding is measured as others have said PER INCH so probes should be 1 inch apart not measured across the diameter of the coil for PI coils I was told by a manufacturer 20 years ago that the measurement to go for is 60 to 80 ohms per inch but over the last 15 years have found up to 100 ohms per inch will be OK I think your understanding of resistance is upside down (less resistance means it is more resistive) as I only build PI coils I cannot help with VLF coils as I have not built one since the mid 1970's.

Regards, Ian.

[rickb]

IBGold

You are incorrect. "Ohms per square" has no units. It can be a 1 or 10 in square, but still has the same resistance. Read the article if you don't believe me.

https://www.edn.com/ohms-per-square/

There are a lot of articles about the subject on the web.


"(less resistance means it is more resistive)" In what universe is this statement true?

[billr]

Enough. !!
Don't want my thread turning into a p&^% match. Take it someplace else.
It's bad enough I have very limited understanding in the world of electronics. I enjoy it for what it is, a pass time and don't mind doing it the hard way to overcome obstacles if that's what it takes.
Everyday I learn so much from many on here. Including myself when I get it all wrong.
Inaccurate info makes no difference to me as I see it as a way to better understand the fundamentals from a different angle.
Ultimately if I cant figure out how to make a coil better than the one I have,then I'll find something else to challenge my interests.

A absolutely appreciate EVERYONES input right or wrong.
That is why I am here.

[kt315]

at first you have to learn basic knowledge what is Electrostatic Field and what is Electrostatic Field Influence - EFI.
without this you can not step no one. you do not understand why you do EFI protection and for what.
noone are able to give you right direction because you are like the blind squirell.

[billr]

Patience Kt. Patience
Agree with everything you say. However.
1 yr ago I was making LED circuits on a breadboard now I'm assembling detectors and learning why things are what they are.
I'm moving at a pace I can keep up with regardless of my unorthodox approach.
With a little curiosity thrown in.

Regards
Blind Squirell

[kt315]

Bill look at this. repeat this with your cat right now -! https://www.youtube.com/watch?v=-PCS9A_WjsM
you have TO SEE THE FIELD -!