GRAPHITE SHIELDING QUESTION

[daverave]

i have decided to try some graphite conductive paint in my latest coil...i have painted the inside of coil and now is completely dry but i have a resistance of about 1.1 k ohms...is this too high resistance for a shield ????

[rickb]

"resistance of about 1.1 k ohms"

Between what 2 points? Have you read about "ohms per square"? Are you referring to the coil or housing?
Having said all that, this is only for electrostatic shielding. Depending on how you measured it, it might even be to low. Using painted sheets of cardboard above and below the coil and connected to circuit ground would allow you to experiment with different resistances to be sure you don't loose sensitivity.

Rick

edit: see this post. http://www.geotech1.com/forums/showt...006#post208006

I do not know what the high and low limits are. You want it to be high enough to not support eddy current loops, and low enough to not detect your hand or wet grass.

[daverave]

thanks rickb for your reply...i painted the inside of a 10" coil housing with the guitar graphite paint and resistance about 1.1k ohms...but on the bottom of coil i used a cardboard sheet and painted with the graphite and this time i got a reading of around 600 ohms...the coil does not detect my hand so i guess its working ok.

[kt315]

Between what 2 points? Between what 2 points? Between what 2 points?

[daverave]

resistance measurement taken from one point of the coil housing to near enough the whole diameter of the !0" housing.

[rickb]

Do you know the distance to detect a known sample was before painting? And after?

[daverave]

i tested the depth this morning now the graphite is tried.....and i did a test on my 9ct gold wedding band and im getting a whisper signal at around 17" so im very happy with the depth...thats not bad for a 10" coil i guess...i would say the depth is better with the graphite shielding cause of less noise...this is the first time ive used graphite shielding and i think i will always use it now instead of scotch 24.

[6666]

wow 17" is excellent.

[BKY1337]

Which detector is it? And which brand is the conductive paint?

[daverave]

its for the surf pi and ive used a graphite paint used for guitars....ive also just made a big foot coil and used the same graphite shielding and im getting very good depth in air.

[ionut_mtb]

its for the surf pi and ive used a graphite paint used for guitars....ive also just made a big foot coil and used the same graphite shielding and im getting very good depth in air.

Hello Dave, how did you connect the ground wire to the graphite shield paint?

[daverave]

i just stripped some very thin wires from some cable and taped the wires into position and painted over them several times with the graphite paint...ive found the graphite gives less capacitance and you can slightly sample earlier...i always used scotch 24 mesh tape but i feel the graphite is better.