Problems with 'CM in range'

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Joined: Thu Dec 01, 2016 6:28 pm

Problems with 'CM in range'

Post by cpanitz » Thu Dec 01, 2016 7:04 pm

Dear everyone,
we are currently experiencing some problems with the CMS/DRL electrodes (ActiveTwo system): We repeatedly have the ‘CM in range’ light flashing even though the electrodes are properly attached as it seems to us. To be more specific: we recently tested a series of participants with GSR (left palm), monopolar EX electrodes (right forearm, left leg, two below left eye), no EEG electrodes connected. The plan was to attach both CMS & DRL from the amplifier's front to the inner left forearm. However, in the very most cases, the blue light just blinks. If we attach CMS & DRL to the fingertips (left index & middle finger) it works fine in most cases (although we would like to avoid that for practical reasons). It also seemed to work when we attached the CMS & DRL electrodes to the right leg, although we recently had two participants where this also failed initially. In some cases, the blue light became steady when we removed the GSR electrodes from the left palm. At first, it seemed to help to first attach CMS & DRL and then the GSR electrodes when preparing a participant. However, this turned out to not work in all participants either. Other things that we tried out:
- We conducted salt water tests which do not indicate broken wires (i.e., steady blue light).
- We attached the CMS & DRL pin electrodes to the forearm but did not get different results. So, it most likely is not a problem of the electrodes.
- We massaged some electrolyte (Parker Signagel) into the skin before reattaching CMS & DRL. Sometimes it worked afterward, sometimes not (might rather be the effect of reattaching the electrodes).
- We tried out different distances between CMS & DRL with no effects.
- We tried it outside of the participant’s chair to rule out any grounding/conduction effects of it. No effects here either.

We are using new electrodes and had the amplifier upgraded this year (32 to 64 EEG channels). Therefore we don't think that it has anything to do with worn out material or whatsoever. To this point, we have always been able to make it work after some trying around and reattaching. However, if we are not mistaken, the position of CMS & DRL should not play a role in terms of getting the CM in range? Therefore, we would appreciate any ideas and advice about what could be causing these inconsistencies and how to resolve the issue. We are happy to provide further information if needed.

Best regards,

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Joined: Tue Dec 20, 2016 2:48 pm

Re: Problems with 'CM in range'

Post by Felix » Tue Dec 20, 2016 4:15 pm

Thanks for filing this request, Chris.
We experience a very similar problem at the moment when trying to record (pure) ECG. In our setting we just use three external electrodes (2 wrists, 1 leg) as well as the external CMS/DRL-combo (no EEG-sets). Even if just CMS and DRL are attached to the subject (we originally planned to put CMS on the subject's sternum and DRL on the shoulder) the 'CM in range' LED is blinking. I strongly doubt that this is due to a broken cable/electrode.
(a) we use a brand new electrode set
(b) we did the salt bucket test, and everything was fine (continuous blue light). Moving the cable or electrode head could not make it blink.
(c) we replicate exactly the same pattern with an older CMS/DRL-set.

I made observations similar to the ones that Chris described: Putting CMS and DRL on the fingertips usually leads to a stable 'CM in range'. On nearly all other body parts this was not possible. We also tried multiple distances, more or less gel, ...
If anybody has an idea how we could get rid of this problem, we would be incredibly thankful!
Best regards -

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