Earth Current Pulsation Sensor

It is in the nature of electromagnetic (em) fields that for every changing magnetic field there is a corresponding changing electric field. Geomagnetic storms always include a great portion of rapid magnetic field variations that are seen at all latitude locations. The equivalent electric fields induced in the ground are called Earth Currents. For those readers who are adept at electronics, a simple detector of the storm-time Earth-current electric field pulsations can be constructed (Figure 5.5) for measurements in an area that is far from city electrical noises.

About 2 square feet (0.19 square meters) of thin lead sheeting (used in roofing) is sufficient for a ground probe. In typical soil, two probes, separated by about 200 feet (61 meters) or more, can sense the natural field pulsations as voltages of about 0.1 millivolt. That is about equivalent to a 30-second magnetic field pulsation reaching approximately 0.05 gamma (for most locations). Doubling the probe separation will double the sensitivity. Stout plastic-coated copper wire is soldered to the probes and connected to a recorder. The probes are buried approximately 1-foot (0.3 meters) deep into the ground and covered with mud (to insure full contact to the ground probe). A steady but adjustable

Ground Probe

Variable Resistor

Reversing

Variable Resistor

Near Ground Probe

Recording Meter

Variable Resistor

Reversing

Variable Resistor

__ Battery

Near Ground Probe

Recording Meter

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