Definitions for "Earth ground"
1) Using a grounding rod or another suitable device to tie a system or device to the earth at the datalogger site. Such a connection is used as a sink for electrical transients and possibly damaging potentials, such as those produced by a nearby lightning strike. 2) A reference potential for analog voltage measurements. Note that most objects have a "an electrical potential" and the potential at different places on the earth ? even a few meters away ? may be different. See ground loop.
A ground circuit that has contact with the earth.
A conductor that will dissipate large electrical currents into the Earth.