Mun-Wai Hon wrote:
>Electrical noise suddenly appeared in our Neuroscan EEG >collection
system. We can perform quick calibration tests that do >not show the
distortion. Yet, when we attempt to test a subject,
> we obtain electrical noise that distorts the EEG completely.
> Could this be an amplifier problem? The booths are only a year
> old and we have been able to collect good data a month ago.
Most common cause of electrical noise in an EEG system that was working
fine is a new ground loop. Make sure all of your equipment is being
drivin from the same circuit and make sure the equipment is properly
grounded (earth ground). Also, check the circuit for new devices that may
not be in your lab. I once lost a few weeks when the Coke company put a
coke machine near the enterance to our lab. It was driven from the same
circuit serving our lab. Every time the compressor on the machine cut in,
we had incredable noise! Please post what you found when you finally sort
the problem out.