bucket testing new electrode sets

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sassecon
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Joined: Fri Jun 17, 2016 3:35 pm

bucket testing new electrode sets

Post by sassecon »

Hello,
we have just bucket tested our 2 full sets of electrodes for a 64 system.
I am not sure what to expect therefore I calculated few quantities from 5 min of data:
- single-channel histogram: should I expect a Gaussian histogram (white noise?) or something more uniform?
- single-channel PDS: i see very low power with some power line contamination, is this what I should expect in healthy electrodes?
- single-channel mean over time: I would expect a stable mean or slowly changing (in case of drift)?
- single-channel standard deviation over time: I would expect a stable value over time and no sudden changes

Is there any other sensible measure I should include (we would like to define a set of measures to run periodically on the system for maintenance)?

If everything I said above makes sense I have few problems with my electrodes.

FIRST 64 set: the PSD of electrodes bundle 1 doesn't show any power line contamination, while bundle 2 is clearly contaminated. Why differetn bundles in the same conditions show different PSD content? How would this affect my data when half of the electrodes are collected with one bundle and the other half with another bundle? Also some spikes in the standard deviation over time in both bundles. Is this something to expect? Quite strange histogram distributions for both bundles.

SECOND 64 SET: a strangely oscillating PSD in TP8, a noisy electrode and a huge artefact on another one.
Any thoughts?
I have figures and screenshot but I would appreciate some feedback first, so that I could be more specific.

Thank you in advance
Best regards
Sara

Coen
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Location: Amsterdam, Netherlands
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Re: bucket testing new electrode sets

Post by Coen »

Electrode noise is generally pink noise (Gaussian noise with an 1/f spectrum).

A loop formed by the CMS wire and the electrode wire picks up 50/60 Hz magnetic fields. The A set with integrated CMS/DRL has minimal area of the loop. Reduce the area of loop formed by the B set with the CMS wire by bundling and twining the wires.

Spikes and sudden changes on particular electrodes indicate pollution of the tips with non-silver traces of metal. Clean the tips with sand paper and soak in salt water for a few hours. Be careful to prevent the tips from touching metal objects.

Best regards, Coen (BioSemi)

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