Gmobilab+: a question about Sourcechgain

[biocc]

Hi,

I'm using gMobilab+ and I have a doubt about the configuration of the parameter SourceChgain in the source module. I've load the gMobilab.prm and the value of this parameter is 0.019. Does it have any relationship with the sensibility of the amplifier?in that case it is reported to be 0.0153 microvolts and calculated as 1miliVolt/2^16, and it does not match with 0.019.

Thanks in advance for your answer.

Best regards,

Carol

[pbrunner]

Carol,

you find information on the translation from A/D units into microvolts, i.e., the SourceChGain, on the BCI2000 wiki [1].

Regarding the g.MOBIlab [2] there are two versions, both with 16-bit A/D converters. On paper these have the following sensitivity:

Multi-Purpose version:
EEG channels 1 and 2: Sensitivity: +-500 µV
EEG channels 3 and 4: Sensitivity: +-2 mV
ECG channels 5 and 6: Sensitivity: +-5 mV

8 channel monopolar EEG version:
EEG channels 1 to 8 Sensitivity: +-500 µV

However, as in reality the analog gain in these amplifiers varies over time, you need calibrate them every now and then.

To calibrate the amplifiers, please connect a signal generator with a precise output amplitude (e.g., a sinus with 100 µV peak amplitude) to all channels. Record the signals with BCI2000 and load the data file into MATLAB using the load_bcidat mex interface [3]. For each channel, determine the translation from the peak-to-peak digital values to the peak-to-peak amplitude of the signal generator's sinusoid. For each channel, use this translation as the SourceChGain. Next, repeat the experiment with these SourceChGain values and load the data into MATLAB using the '-calibrated' parameter in the load_bcidat function. Now you should see the calibrated signal, with precisely the peak-to-peak amplitude that you originally fed into the amplifiers.

Regards, Peter

[1] http://www.bci2000.org/wiki/index.php/U ... b_Hardware
[2] http://www.bci2000.org/wiki/index.php/U ... urceChGain
[3] http://www.bci2000.org/wiki/index.php/U ... oad_bcidat

[biocc]

Thank you very much for your answer, I'll try what you propose.

Regards,

Carol