Geodesic Sensor Net - Improper Net Preparation and;or Application

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11: Troubleshooting

110

Geodesic Sensor Net Technical Manual

S-MAN-200-GSNR-001 • January 31, 2007

• certain channels exhibiting wide, high-amplitude oscillations that greatly

exceed the levels of neighboring channels (

ﬂailing

)

• waveform drift

Such phenomena can be due to user inexperience in the area of Net application, a

plug-type electrical connector being incompletely inserted in its matching receptacle,

or a hardware problem involving the GSN or the ampliﬁer. When troubleshooting

poor EEG, you should study the following remedies offered and implement the ones

that seem most likely to correct the problematic EEG.

If Net application remedies do not solve the problem, and loose Hypertronics

connectors are not to blame, you should suspect a hardware problem involving the

GSN or the ampliﬁer. Where such hardware problems have user-implementable

remedies (the replacement of faulty sensors in a GSN 200 or the replacement of

sponges in an HCGSN), a description of the remedy or where to ﬁnd it in the manual

will be given (see the

GES Hardware Technical Manual

for ampliﬁer remedies).

Otherwise, you should contact EGI Technical Support (Appendix A).

Improper Net Preparation and/or Application

The following guidelines will help to diagnose Net application issues. See Chapter 6,

"Applying the GSN,” for expanded coverage of this topic.

• Check that the sensor sponges of the GSN 200 or HCGSN are properly wetted

with electrolyte. Start with dry sensor sponges for best absorption, or

alternately squeeze and release the sponges to improve the uptake of

electrolyte by the sponges.

• When preparing for application of the GSN 200, do not pat the sensors too

vigorously in an attempt to prevent dripping. It is possible to cause the sponges

to lose too much electrolyte this way. (For the HCGSN, do not pat the sensors at

all because the sponges are smaller and absorb less electrolyte.)

• Check for cold electrolyte. Sensors are thermally sensitive, and movement from

cold electrolyte to a warm head will induce sensor drift. As the temperature

stabilizes, so does temperature-induced drift.

• Check that the electrolyte was properly prepared. Weak electrolyte degrades

data quality. If uncertain, use fresh electrolyte.