Large 50Hz noises when recording ECG

chensxchensx
in Hardware
I used channel IN1P, IN1N, and BIAS to measure ECG using V3 hardware. I had set SRB1 and SRB2 to OFF, and included only channel 1 for bias generation. But there were large amplitude of 50Hz noises and its harmonics (like 150Hz, 250Hz, etc), which was so large that it was impossible to observe the ECG signal. I did use the RLD to reject the common mode using the bias pin, but it seemed not working. Any suggestions? Thanks in advance.

Comments

  • wjcroftwjcroft Mount Shasta, CA
    Can you confirm you have the OpenBCI_GUI notch filter set at 50 hz? It might be set at the 60 hz position.

    Is the noise also present with EEG tests? I assume you've followed all the steps in the doc,

    http://docs.openbci.com

    William

  • qwer1304qwer1304
    edited February 2016
    Notice that the spectrum panel shows the spectrum BEFORE filtering (notch included).
    You need to look at the spectrum AFTER filtering is applied.
    The time domain panel shows the signal AFTER filtering (but it's in the time-domain).
    Also, the saved file is the RAW signal (before any filtering).
    You'd need to filter it yourself.

  • chensxchensx
    Since the power line frequency is 50Hz, why there were 150Hz, 250Hz (and etc.) harmonics? I am stuck here.
  • wjcroftwjcroft Mount Shasta, CA
    What happens when you do the EEG and ECG tests mentioned in the tutorial? In other words, something you are doing with the Chan Set tab in the GUI, might be responsible for this. Were you able to get the tutorial steps working correctly? If not, where did that process go wrong?

    What electrodes are you using, paste, gel, etc.? The RLD / Bias cannot completely eliminate common mode noise, though it does decrease it substantially. If you are getting harmonics that sounds suspicious. A 50 hz sine wave distorted (chopped / limited) could generate harmonics.

    Have you tried testing in other areas with perhaps less EMF fields? You definitely do not want to be sitting right next to a wall wart / power brick or over a power extension cord.

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