Ganglion Channel Railed or near railed

alirazaaliraza Islamabad
edited March 2019 in Ganglion
I am connecting three leads, one to channel (Upper) , one to D-G (Upper) and another to Ref (upper) and then taking brain data from user but i am getting railed at openbci GUI.
Please note this device used to work well and would gave me data in range of 15-25uV, when i connected one channel to forehead and ref and D-G to separate ear lobes, but now after a month of storage it started giving railed or near railed data at output.
I checked the lead with all four channel still no avail and swapped the ref and D-G pins as well. Proper gel amount is used (Neuro pep and ten20).
When i donot connect any of electrode i get between 3-6uV output , which seems reasonable with amount of noise present but connecting electrodes to a person or device gives me railed data.

What could be wrong?
Is device hardware malfunctioned.
Something wrong with electrodes gold cups ( i.e Expired ,rusted (though can't see rust any on them).
Or someother issue.

Please help we are at end of our project and we have to submit the project but if device didn't work we can fail the semester and have very bad impact on our degree.

Comments

  • wjcroftwjcroft Mount Shasta, CA
    edited March 2019
    Ali, hi.

    If you are seeing low microvolts with nothing connected, that is a sign that the Ganglion board is likely ok. Another test you can do is use an alligator clip to connect one or more channels directly to reference. That should produce close to ZERO microvolts.

    It sounds like you may have a problem with your electrode leads or cups going bad. Do you have a multimeter / ohmmeter there, to check the resistance value in ohms of all your leads? Each lead, connector to cup should be close to zero ohms.

    One thing that can happen with gold cup electrodes, is that the gold plate becomes chipped or cracked with use. This can be very tiny imperfections that are hard to see. Once there is a break in the plating, a "galvanic circuit" (battery) is then formed between layers of the base metal (brass or tin) and the gold plate. This battery effect generates a millivolts level DC signal, which swamps out the microvolts you are trying to see.

    Solid metal electrodes do not have this battery effect possible. So instead of gold you could try silver cups or tin cups.

    When cleaning gold cup electrodes, it's best not to use any rubbing or scraping.


    Regards,

    William

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