Sudden and intermittent electrode drift

[Kath]

Hi,

We are having trouble with a very strange electrode drift. All signal and offsets look good in ActiView, but every now and then, all 64 channels suddenly appear to go down in a sharp diagonal line and disappear off the screen, then reappear on the screen a few seconds later. This happens despite the participant sitting very still, and in a cool room where it is unlikely that they are too hot and sweaty. The blue CM in range light remains on the whole time.

Can you think of anything that might be causing this? Is there anything I can do to stop it happening?

Thank you,

Kath

[Coen]

When all electrodes show the same drift in the unreferenced display, then a contact or pollution problem of the CMS and/or DRL electrode is the most likely cause.

Best regards, Coen (BioSemi)

[Kath]

Hi Coen,

Thank you for your quick reply. When you say "contact problem", do you mean that the CMS/DRL electrodes have momentarily come away from the scalp? Perhaps we need more conductive gel?

And if it is a pollution problem, what should I do? Should I switch to using a different set of CMS/DRL electrodes?

Thanks again.

[Coen]

Yes, check that the gel holders are properly filled, and that the gel is contacting the skin properly. The gel has to be absorbed by the upper skin layers in order to do its work.

Test the electrodes in water. If you see the same behavior, then the CMS is probably polluted with traces of non-silver metal. Soaking in water for a few hours sometimes helps in mild cases, but replacement is best.

Best regards, Coen (BioSemi)