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[Biomedical engineering] Question about ECG signal electrodes

  1. Apr 15, 2013 #1

    Could someone please explain to me how exactly, or why, does the ground electrode in ECG minimize the interference?

    And, also, why is it said that the patient could be at risk because of the ground electrode?

    I really don't get it, so if there's anyone here who could clarify this for me, that would be awesome!

    Much appreciated,
  2. jcsd
  3. Apr 16, 2013 #2
    Humans act as antennas, picking up interference from the mains at 50/60Hz depending on the country you're in. ECG signals are drowned out in the presence of this interference, so what's usually done is that the interference is measured by the circuit, flipped, and fed back in a small amount through the ground lead. Superposition of the two opposite signals means the net amount of interference is reduced.

    Simply connecting someone to ground is dangerous as it invites current to flow through the body along a relatively low resistance path.
  4. Apr 18, 2013 #3
    Hi, man, thank you for your answer!

    Would you happen to know some litterature/website where I could learn more about this? It sounds very interesting, and I am pretty new in all this.

  5. Apr 18, 2013 #4
  6. Apr 19, 2013 #5
    (this is my another account, can't remember the password at the moment :D)

    Whoa, that looks awesome! Thank you very much for that!

    I'll have a closer look when I come to the office. In the meantime, I tried to make a small drawing (before I saw this post) to see if I can graphically explain to myself what you have written in your first post.

    You can see it here:
    (sorry for the smallish text, but it should be readable if you zoom in a little)

    Maybe you can have a look and tell me if that is/isn't what you meant?

    Again, thank you very much for your help!

    P.S. Okay, just one question, I threw a glance at the paper before I get out. It says:
    Well, if we connect the right leg to the ground, shouldn't noise disappear because we short-circuited that capacitance between the human and the ground (SCENARIO 1 in my sketch above)?
    Last edited: Apr 19, 2013
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