Ultracortex electrodes contact for high quality EEG-signal [resolved]

mhadji05mhadji05 Cyprus
edited September 8 in Electrodes

How can I make sure that the contact of all the electrodes is high with the scalp and will give a high quality signal?
Can I check this out through the OpenBCI software?
Ιf yes then please give me the settings path to navigate.

Thanks in advance!

Comments

  • wjcroftwjcroft Mount Shasta, CA
    edited September 1

    Have you checked the impedance using the GUI? Generally the lower the impedance, the better quality the signal. It also depends on what electrodes you are using. Wet type (passive) will always perform better than dry passive.

    With the GUI, Cyton impedance is shown (one channel at a time) pressing the small 'ohm' symbol to the left side of each time series. Press the symbol to toggle on. Again to toggle off. Turn off after checking. With Ganglion, there is a special impedance widget.

  • mhadji05mhadji05 Cyprus
    edited September 1

    Dear @wjcroft,
    Thanks for your response.

    I don't understand how to check if the contact of the channels is ok.

    Can you please be more specific and give me instructions to navigate into the GUI and check the contact of every EEG.

    What means this message: "Railed 100.00% 3.28 uVrms" or Near Railed or Not Railed
    Please see the image of my GUI below! Thank you in advance.

  • wjcroftwjcroft Mount Shasta, CA

    The image shows your mains frequency is at 50 Hz. Whereas your notch filter is set at 60 Hz. WRONG notch. Press the button in the upper left.

    The 'ohm' symbol at the left of each time series graph, toggles the impedance mode on or off. 'Ohm' is an electrical unit of measurement for resistance / impedance.

    Ω

  • mhadji05mhadji05 Cyprus
    edited September 1

    Dear @wjcroft,
    So if i have small value "Ohm" that means I have very good contact and if "Ohm" is big value means the contact is poor?

  • wjcroftwjcroft Mount Shasta, CA

    Did you change your notch filter? That should improve the picture substantially. And return all channels to 'normal' operation.

    Pressing the ohm symbol to the left of each channel time series, will turn on the measurement of impedance for that channel ONLY. Pressing again turns it off. Impedance value is displayed on the time series while the measurement is active.

    Only measure ONE channel at a time. Turn off impedance of channels you are complete with.

  • Dear @wjcroft,
    Yes I changed it.
    I check the Impedance of channel 15 what means this "RAILED - 0.00 kOhm" ?

    Here is another example of channel 1 is it good 39.4 kOhm?

  • I checked the electrode cables and reference ear clips. Everything seems to be fine and the headset has not been used much it is very new .
    Unfortunately, now always electrodes 2(C4), 5(T3), 11(T5) are Railed.
    Please let me know how can I fix this issue.

  • wjcroftwjcroft Mount Shasta, CA

    If certain electrodes on the Ultracortex are 'always' railed, it usually means that those electrode holders need to be screwed in closer to the scalp. OR, possibly the connections to those channels are suspect. To check the latter, you can use a DVM multimeter / ohmmeter to measure from the Cyton pin to the electrode. Should be close to zero ohms.

    William

  • mhadji05mhadji05 Cyprus
    edited September 8

    Fortunately, I replaced heads of electrodes with the Dry EEG Comb Electrodes and the problem for the time seems to be solved.

  • wjcroftwjcroft Mount Shasta, CA

    Perfect, great. The tips on those are somewhat longer than the default 'spikey' combs, so that likely is bridging the gap that existed before.

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