Graphite coil shielding for TGSL problems

[rickb]

2k ohms is to low! The detector is detecting the eddy current in the shield. I have never heard of anyone panting the tx coil in an I/Bdetector. With resistance that low, the depth is reduced. Read the link I posted about ohms per square. I see no alternative but to strip off the paint and try again.

Commercial detector mfg. paint the inside of the housing.No need to paint the coil, and much easier to fix a mistake. Painting 2 sheets of cardboard or thin plastic has been done. Read the link I posted about ohms per square (sheet resistance).

Thin the paint and apply thin coats, and test for acceptable shielding between coats. Each coat will lower the resistance. Don't go any lower than necessary to achieve static elimination.

Has the detector and coil been tested for proper operation and detection distance before shielding?

Use the forum search for shield, shields, shielding, static.

[billr]

Thanks Rick.
I'm getting nearly 2k ohms on the shielding of each coil when checked from start to finish points of the paint. The coil housing was only in the low hundreds so I added another coat to that to see what changed.

The range is the same as before but I noticed after making the best nulling a slight audio signal is given off and no adjustment can cancel it out. However. When I touch the coil housing the noise goes away and the range stays the same.

Is this telling me the coil or the housing needs more paint?

When the coils are removed from the housing and placed on a board. Nulling can be achieved to silence. But there is some noise given off when my finger touches either coil.

Both coils are isolated from making contact with each other using pvc tape.

[rickb]

First, the coil must be grounded. Second, the resistance of the shield must be low enough to eliminate electrostatic interference, but high enough to not reduce electromagnetic pickup. The resistance should be high enough to not need the gap.

Read this and the link.

https://www.geotech1.com/forums/show...187#post241187

[billr]

I made a new coil coated with graphite paint being sure to leave a 1/2 space between start and finish. The graphite of each coil was grounded by wire to the circuit. The coil itself works well for range but it is very sensitive to any contact with my hand when placed close or on the coils. Don't want to pot it up until it has been given the best chance of interference suppression.

Managed to reduce the interference by hand when a thin uncoated wire was wrapped around each coil and grounded but this also reduced the range. So not ideal.

Can someone walk me through or link the procedure of shielding the coils and shell for best performance using graphite?

Thanks.