The percentage of Railed
Woody
Japan
in OpenBCI_GUI
Dear, all,
I use OpenBCI 8ch Cyton for EEG measurements. I received the "Railed error" in some measurement conditions. I understand this issue is caused by the electrode and connector. However, I have the following question. Please refer to the attached snapshot.
1) What is the meaning of the percentage of "Railed", "near Railed" and "not railed"?
2) How are these percentages calculated?
3) Which value (%) is recommended for high-quality measurement?
4）When I changed the Gain value of the hardware setting from x24 to x12, this percentage decreased.
Can we change the gain value freely?
Could anyone who has experience give me a comment and advice?
Thank you for your understanding!
Comments
Hi Woody,
Here is the section of GUI code that displays the Railed indications:
https://github.com/OpenBCI/OpenBCI_GUI/blob/master/OpenBCI_GUI/Extras.pde#L495
As you can see, the Railed percentage reflects how much the 'max' excursions of the time series values, get close to the maximum scale you have set for the Y axis graphs. As I see on your image, you have the scale max set at 50 uV, which is too low for EEG. Typical EEG ranges from a few uV to ~ around 80 or 100 uV. This explains why you are seeing 'warnings' of Railed condition.
What electrodes are you using? It is common with the dry electrodes and either Ultracortex or the velcro bands, to get occasional high EEG readings, if the impedance or contact of the individual electrodes is not optimal. There are multiple past threads giving hints on reducing Railed situations.
https://www.google.com/search?as_q=railed&as_sitesearch=openbci.com
https://openbci.com/forum/index.php?p=/discussion/1481/how-to-become-de-railed
https://openbci.com/forum/index.php?p=/discussion/comment/7687/#Comment_7687
Regards, William
Hello William,
Thank you for your comments!
Best Regards,
Woody