Its a 32 channel EEG cap and I am wondering if a single broken electrode could cause all the other channels to say they have an impedance of zero with the ground electrode...
Perhaps if the electrode was to short to the shield?
Dear Mr Winter, do you have other reference switch with your system? If yes, did you try if the output would the same with external reference for ground?
Not a reference external to the cap but we did try using one of the other electrodes on the cap as the reference with the same result. I am unsure if we have something that can plug into the ANT without going via the pinout to the cap but will investigate ASAP.
Thank you for the response.
The ANT waveguard caps usually come with a test electrode that snaps into an electrode position (in case it is broken). Can you try connecting that electrode to the amplifier at the reference position but not snap the electrode tip to the cap? Do you get the same result? Another way to check shorting would be to use a multimeter on two separate electrodes and between an electrode and the reference (all on the cap side). If they are showing connected then something is shorted somewhere. Switching among different electrodes might help you figure out which one is to blame.
Cheers guys, it turned out that leakage to the shield pins at the plug caused the problem in multiple caps simultaneously....
Thanks again for the input Arnaud and Paolo.
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