Ganglion Impedance vs. Electrode Response

Hello forum,
I've been conducting EEG tests with the Ganglion using two different types of electrodes.
1) OpenBCI's Goldcup Electrodes with Ten20 Conductvie Paste
2) Sintered Silver-Silver Chloride Electrodes from Biomed (no paste)

The Goldcups have lower impedance(3~20kOhm), but the Sintered silver electrodes seem to be giving me a better response with higher impedance(anywhere between 50~200kOhm).

As such, I'm considering to go with the sintered electrodes, but the high impedance certainly is bothering me.

Does a high impedance value make EEG measurements untrustworthy? What are impedance measurements returning?

I understand that the Ganglion sends a current through the connected electrode to make the impedance measurement. If V=IR and the current(I) is constant, I'm thinking that high impedance(R) means that the voltage(V) is high, so the EEG voltage values should be stronger. I seem to be missing something.


  • wjcroftwjcroft Mount Shasta, CA

    Hi BWB,

    Sintered silver chloride electrodes are almost always used with paste or gel. With EEG electrodes, higher impedance means that those channels are more subject to external noise conditions, such as EMF electromagnetic fields.

    The impedance measurements from Ganglion and Cyton are returning the channel's skin-electrode electrical resistance at a given AC frequency (simulating EEG at that frequency).

    EEG amps that measure impedance do inject a very small current, like in the micro or nano amps region. Then the voltage drop is measured, giving resistance as R = V / I. The injection is a special "constant current" source.


  • wjcroftwjcroft Mount Shasta, CA

    A more common setup with dry electrodes is using a headband and both flat and comb style electrodes. The latter do better in areas with hair.

    The velcro tension is adjusted to ensure even and constant pressure. Velcro used on above pages is this simple material with holes punched.

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