Questions on the Ultracortex Electrode

abhijithabhijith
edited December 2018 in Electrodes
Hi all,

I like to know the sensitivity of the electrode we are using in OpenBCI Ultracortex mark IV. I searched in many websites and but I didn't get a satisfying answer. Also, I like to know what is the range of the signal that we can measure ?. Kindly help me in this queries

Thank you

Comments

  • wjcroftwjcroft Mount Shasta, CA
    Abji, hi.

    Silver Chloride electrodes (as used in the headset), are an industry standard. Used for decades in all sorts of applications, EEG, ECG, EMG, etc. Range is determined by the biosignal: EEG is in microvolts, ECG and EMG in millivolts. The amplifiers used in Cyton and Ganglion can handle all signal ranges.


    Regards,

    William

  • abhijithabhijith
    @wjcroft
    Thank you for the response


    Is there any specific range for the cyton board? 


  • wjcroftwjcroft Mount Shasta, CA
    Cyton measures microvolts and millivolts just fine. I would not go higher than 1 volt, the actual specification is in the data sheet.


    In terms of microvolts, the ADC resolution at max gain is actually much less than a microvolt. The low order bit of the 24 bit ADC value represents .02 microvolts. Of course this is not usable as a signal value, because of inherent noise issues.

  • abhijithabhijith
    Ok sir, I will check. Thank you @wjcroft
  • abhijithabhijith
    edited December 2018
    Hi all,
    Since we are using the active dry electrode in Ultracortex Mark IV, I like to know what is the power range that we are giving to the electrode. Also, like to know what is the maximum frequency signal that the cyton board can detect?

    Kindly help
    Thank you
  • wjcroftwjcroft Mount Shasta, CA
    @abhijith, hi.

    The Cyton amplifier has a very high input impedance, 1 gigaohm. Because of this, there is no 'power' transferred. We previously mentioned the amplitude range, microvolts to millivolts, to approximately 1 volt.

    Frequency is determined by the sample rate, according to the Nyquist limit. Typically you want about 4 or 5 samples per waveform. So 250 / 5 = ~ about 50 Hz max. Nyquist would say divide by two, 250 / 2 = 125 Hz max, but that can give very inaccurate 'aliasing' effects. Imagine what happens if the samples are at the peaks or zero crossings etc.

    Regards,

    William

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