PGA gain and Vrms [resolved]
giuseppetx1
Italy
Dears, referring to the values expressed in Vrms in the GUI channels during acquisitions, I would like and need to understand deeply how the value reported (Vrms) is calculated, and how it is referred to the value of the PGA Gain.
Can someone explain this to me? or send me any references I can study ?
Thank you for your support. G.
Comments
uVrms == MicroVolts Root-mean-square
https://en.wikipedia.org/wiki/Root_mean_square
http://mathworld.wolfram.com/Root-Mean-Square.html
PGA Gain allows you to adjust the gain on any given channel. This works similar to how gain is used for Audio processing on a mixing board.
https://www.musicianonamission.com/gain-vs-volume/
Giuseppe, hi.
The default value of the PGA (programmable gain amplifier) on each channel is 24; which is appropriate for EEG. This can be changed (lowered) for example with EMG or ECG electrodes, where the voltage tends to be in the millivolts vs microvolts range. The actual formula that converts channel binary sample values into voltage is here:
https://docs.openbci.com/docs/02Cyton/CytonDataFormat#interpreting-the-eeg-data
This is done automatically by the GUI and other programs reading the data stream.
The RMS values shown on the time series just give an indication of the average amplitude of the channel signals. RMS is not otherwise used. For example the channel sample values, converted to voltage, are the components of the data stream or recorded data.
Regards, William