BioSemi.nl

Hi, what could be the source of this type of noise?

P4 does not make contact with the skin (not enough gel), or is defect (test in water).

Best regard. Coen (BioSemi)

Hi,

Thanks for this answer! I apologise for my totally beginner's questions, but with one of our subjects, the signal was terrible (see the picture) and we had to let the person go home. I checked the offset, the majority of electrodes was around -10 to -30 mV, but, they were all unstable (they were jittering). I of course tried adding more gel a couple of times and checking again. This would sometimes decrease the offset to -10 to -20 mV, but the electrode would still be unstable. By the way, the blue light was on and all the electrodes passed the bucket test.

Since we previously ran subjects in the same room, with the same setting, and didnt have these issues, it makes me think that there might be something specific to this subject (e.g. thick hair) - do you think this is the case? And can we do anything to improve the signal in those situations? Or does this look like something else, am I missing something?

Thanks,
Bojana

You probably added so much gel that there was a gel bridge between CMC and DRL (40 dB less CMRR). Apply just enough gel to fill the holder, but not more. Use the tip of the syringe to work the gel between the hair.

Offsets should be between approx. +100 mV and -100 mV and stable. If within this range, then closer to zero is not better.

Best regards, Coen (BioSemi)

Hi,

Thanks a lot for this answer. Yes, it was probably the gel.

Regarding the stability - is the way to improve it adding more gel (unless it is too much, of course)?


Bojana