Guide To Cabling - Geodesic Sensor Net Technical Manual

8: Connectivities
Shared Reference
Because a Geodesic Sensor Net has only a single reference electrode, and because
amplifiers measure potentials between an electrode and reference, amplifier arrays
must share the reference level. For example, in the GES 250, the reference electrode
lead of the GSN is connected to the input side of the reference channel inside the
Net Amps 200.
Shared Common
For the isolated portion of each amplifier's electronics to be at the same potential as
the Geodesic Sensor Net common, amplifier arrays must share the common. Hence,
the common lead on the GSN is terminated inside the amplifier at the amplifier
common.
WARNING!: Do not confuse the zero potential point of common with that of earth
ground. With EGI's Geodesic Sensor Net, common is isolated from earth ground.
For further details, read "What is the distinction between "reference" and
"common"?" on page 101.

Guide to Cabling

In the GES 120 and 140, the GSN connects directly to the Hypertronics connector on
the front of the Neurotravel amplifier. This connectivity scheme is shown
diagrammatically in Figure 1-5 on page 26.
In the GES 200, 250, and 300, the Geodesic Sensor Net interface cable connects the
GSN to the Hypertronics connector on the front of the Net Amps 200 or 300 amplifier.
EEG signals travel from the Net to the Net Amps 200 or 300 through this intervening
GSNIC. This connectivity scheme is shown diagrammatically in Figure 1-6 on
page 26.
For information about the connector, see "Hypertronics Connector" on page 83. For
information about the GSNIC, see the GES Hardware Technical Manual .
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Geodesic Sensor Net Technical Manual
S-MAN-200-GSNR-001 • January 31, 2007