Forum General General questions and discussions Getting all green sensors while not being on the head

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  • #867
    van Kaathoven Max
    Participant
    @braingineersint-62a843f23e3af

    Hi,

    I’m having an issues where the EEG sensors show all green when the felts are wet, but the EEG is just sitting on the table instead of being on someones head. How can this happen? Is this electro magnetic fields in the surrounding?

    Thanks,

    Max

    #869
    luckham jerill
    Participant
    @starex12-6058fa0f16135

    Hello Max. Thank you for your post.  For the headset to work, it requires the two reference sensors to be connected to a human. When the headset is turned on but not on a wearer’s head, clearly this condition is not met and the electronics float on the room noise, which can be huge! EEG signals are measured in microvolts – that is, one-millionth of a volt. Any object in a normal 21st Century room oscillates in synch with the electrical power circuits, transformers, motors, power supplies, phones, wireless transmitters of all kinds and also massive electrostatic signals. The scale of these variations is huge – electrostatic signals can be 20,000 volts without any problem, room pickup can be several volts. All of these signals mashup in the electronics and generate random noise in the circuits which can’t be canceled unless our noise circuits are properly connected. Unfortunately, the thing about random noise is that it tends to look a lot like just about anything else at some time or other, so the contact quality detectors will sometimes fire up randomly as well and the application will show activity. The headset will work perfectly when fitted, but randomly when the noise cancellation circuit is disconnected. It is not a sign of a faulty headset. Every known EEG system including $60,000 medical units will behave the same way.

    If you have other questions, please let us know.

    #1322
    Australia Seepar seeperaus
    Participant
    @seeparaus-63a595a8b8d92

    Thanks for sharing this article.

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