possible defective electrode

[juank]

Hi,

we observed that 2 electrodes (pin-type, active two) starts to present a lot 50Hz noise if we close a normal lamp, the other 126 electrodes seems normal (without noise). If move the lamp outside the electrically shielded room, all electrodes presents normal activity (without noise).

Our hypothesis is that there is some problems with the connections. What do you think?

It is possible to replace only two electrodes?

Thanks in advance,

juan

[Coen]

Are the two problematic electrodes located close to the DRL electrode ? If yes, the cause for interference is almost certainly a gel bridge between the DRL and the problematic electrodes.

Try to use just enough gel to fill the electrode holder, but not more. Try to prevent that the cap shifts on the subject's head after the gel is applied.

It is possible to replace individual eletcrodes. However, in your case I am quite sure that it is not a contact or electronic problem (blue light would blink, no signal on any electrode)

Best regards, Coen (BioSemi)

[juank]

Hi,

yes, most of the time are the A31 and A32 electrodes... but sometimes there are more no neccesarily located near DRL. I think we didn't use too much gel, in fact I'm sure that we use less gel than when we start with biosemi... and the data had very good quality a month ago. It is possible that the problem is that the cap stretched?

thanks,

best,

juan

[Coen]

A stretched cap is unlikely to caused interference problems.

In case of a larger number of electrodes showing 50 Hz, try to bundle the cables as much as possible (to reduce the included area of the loops formed by the electrode cables, cable loops may generate interference voltages by alternating magnetic fields)

Best regards, Coen (BioSemi)