Can Standard Alligator Clips Affect EMG Signal Quality?

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Discussion Overview

The discussion centers on the use of standard alligator clip cables for collecting EMG signals from AgCl stick-on ECG electrodes in the upper arm. Participants explore the potential effects of using these cables on signal strength and noise induction, particularly in the context of achieving a distinguishable signal for pattern recognition.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether alligator clip cables can be used with AgCl electrodes and expresses concern about potential effects on signal strength and noise.
  • Another participant suggests that alligator clips may introduce unwanted noise, particularly from power line sources, and emphasizes the need for a band-pass filter to isolate useful signal information.
  • A different viewpoint argues that alligator clips should work fine if contact resistance is managed, noting that strong clips can provide adequate connection as long as there is minimal motion.
  • Concerns are raised about the shielding of cables, with one participant highlighting that button cables have good shielding and that the length of the clip could also contribute to noise pickup.
  • A participant mentions the importance of grounding when using multiple electrode cables, asking if all shield leads should be connected to a common ground.
  • Another participant suggests twisting wires to improve common mode noise rejection, noting that most EMG lead sets are not shielded.
  • One participant acknowledges a misunderstanding regarding shielding in lead sets, indicating that some assemblies are indeed shielded.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of alligator clips for EMG signal collection, with some emphasizing potential noise issues while others argue for their adequacy under certain conditions. The discussion remains unresolved regarding the best practices for minimizing noise and ensuring signal quality.

Contextual Notes

Limitations include varying assumptions about the environment in which the electrodes will be used, the specific types of cables and connectors involved, and the potential impact of motion on signal quality.

abhiroop_k
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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.
 
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abhiroop_k said:
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.

Alligator clip cables as opposed to what? Snap-on cables?
 
Yes, I will be using button electrodes.
 
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.
 
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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.
 
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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.
 
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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?
 
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.
 
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.
 
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I stand corrected. I've seen shielded assemblies, so I assumed they were all shielded