BioSemi.nl

Hi,

Problem:
After setting up the system (64 electrodes) on a subject, we inspected the online signals from the software panel. All signals belonging to the electrodes in the B-array seemed considerably more noisy than those in the A-array. The noise seemed as high frequency signal added to the EEG signal.

Things we tried to do:
Rechecking the electrode offsets, all seemed ok.
Changing batteries.
Inspecting the blue led on the box (was continuous blue).
Change the B-cable with an alternative B-Cable with have in the lab - problem persists.
All electrodes (A+B) reacted to the subjects facial expressions and thus reflected some real signal.

Does it necessarily imply on a problem in the box? Could it be related to the amount of gel?

We already used this system for several years with no such problem.

Thank you for your help.

Most probably pickup of alternating magnetic (50/60 Hz ?) field by a loop between A cable (with CMS/DRL) and B cable. Bundle the A and B cables as much as possible to minimize the area of the loop between A and B cables.

Best regards, Coen (BioSemi)

Coen wrote:
> Most probably pickup of alternating magnetic (50/60 Hz ?) field by a loop
> between A cable (with CMS/DRL) and B cable. Bundle the A and B cables as
> much as possible to minimize the area of the loop between A and B cables.
>
> Best regards, Coen (BioSemi)

Thank you, I will try that.
My intuition is to separate the cables as much as possible. You suggested to bundle the cables. Should I bundle the A and B cables together?

Yes, bundle all cables together.