Net Faqs; General Issues - Geodesic Sensor Net Technical Manual

chapter 10
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ET
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CHAPTER
T
his chapter answers some of the most Frequently Asked Questions about the
Geodesic Sensor Net.

General Issues

What is the distinction between "reference" and
"common"?
Amplifier inputs are differential. The voltage measured at every channel is the
difference in voltage between the reference (vertex) sensor and that channel's sensor.
There is no "ground" sensor per se . The subject is never connected to earth ground.
This would make the subject vulnerable to electrical hazard, just as standing in water
makes one vulnerable to electric shock.
The "ground" sensor on the Net is actually an "isolated common," which means it is
tied to the zero level or common of the isolated amp circuit's power supply. This
supply is isolated, so it is not connected to earth, the computer, or anything else. Thus,
an electrical hazard would not make a dangerous circuit with the isolated common.
Why reference signals to vertex?
Choice of physical reference is somewhat arbitrary. EGI chose reference at the vertex
for reasons of symmetry. If you do not like the choice of reference, you can readily
reference signals in the software, on the fly, or after the fact to any particular Geodesic
Sensor Net sensor or group of sensors, including average reference.
Geodesic Sensor Net Technical Manual
FAQ
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S-MAN-200-GSNR-001 • January 31, 2007
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