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ECG/EMG Electrode Measurement

  1. Feb 11, 2014 #1
    I need to collect data via measuring EMG signals in the upper arm. I have standard AgCl stick-on ECG electrodes. My question is, if I can use normal alligator clip cables for collecting this signal from the electrode and feed it into an instru-amp?
    Will this affect the signal strength and/or induce noise and if yes, to what extent?

    P.S. I need a decently distinguishable signal, to be used later for pattern recognition.
     
  2. jcsd
  3. Feb 11, 2014 #2

    berkeman

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    Staff: Mentor

    Alligator clip cables as opposed to what? Snap-on cables?
     
  4. Feb 11, 2014 #3
    Yes, I will be using button electrodes.
     
  5. Feb 15, 2014 #4
    Abhiroop,

    Such a signal with this small amplitude is very sensitive to noise, so ofcourse aligator clips will introduce sufficient amount of unwanted signal especially from power line source.

    In all cases you will need for band pass filter to filter out the noise & get the usefull info from the signal, however the hardest noise to eleminate is the power line noise.

    So give it a try & make sure to use a short wire as much as you can in order to reduce the noise.
     
  6. Feb 15, 2014 #5
    Contact Resistance

    Alligator clips should work just fine. The only issue is contact resistance. With any connector, the spring constant of the contact mechanism, the surface resistance of the mating metals, and the contact area are what determine contact resistance. If you use strong alligator clips, it should be just as good as any other style connector as long as it is sitting still. If you have a dynamic environment (like a stress test on a treadmill) then you hay have some other issues as the contacts move around.
     
  7. Feb 15, 2014 #6

    meBigGuy

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    Gold Member

    ScienceGeyser isn't considering that button cables have very very good shields.

    Obviously there is no issue with ohmic contact unless there is a lot of motion.

    I think you need very good shielding up to and even around the clip. Even the length of the clip itself will pick up noise.
     
  8. Feb 15, 2014 #7
    Okay, a basic doubt but, I have individual button cables that have a main and a shield lead. I need to use 3 of these electrode cables together, so do I connect all their shield leads' to a common ground?
     
  9. Feb 15, 2014 #8

    meBigGuy

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    Gold Member

    Depends on your receiver. Do a google search on "ECG amplifier circuit" and look over the images. You will see different methodoligies. Study those and decide what you want/need.
     
  10. Feb 15, 2014 #9
    Most EMG lead sets are not shielded. If you have problems with ambient noise, the most common solution is to twist the wires for as far as possible. Twisting improves the common mode noise rejection that is inherent in the analog front end of most biosignal instruments.
     
  11. Feb 16, 2014 #10

    meBigGuy

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    Gold Member

    I stand corrected. I've seen shielded assemblies, so I assumed they were all shielded
     
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