E-Field Mill

27-08-10

A new project is ready !! The construction of a Field Mill. This instrument measures the static electric field generated by thunderclouds and can detect the atmospheric conditions which precede lightning.

A field-mill is used to measure an electrical earth field (V/m). A field-mill is based on static electric influence on a conductive plate. If an electrode in an E-field is covered by a rotating wing then the charge is flowing from the electrode to ground. If the electrode is not covered influence charges are flowing back to the electrode.
The current is proportional to E-field.
At stable weather E-field is about 100–150 V/m (direction is from atmosphere to earth). Earth is negative and atmosphere is positive. During a lightning there are a lot of charge separations in the cloud. This charging is very strong and under the lightning cloud the E-field can be up to 30000 V/m. Also without lightning strokes the E-field can be very high. This could be used as lightning warning. Depending on cloud type (negative or positive cloud base) E-field is positive or negative. Please visit also the official web site: www.e-field.org

I've developed the software for the E-Filed Mill in LabView.
With this one I have the possibilities to send data in graphic images to a specified ftp site, or via socket. It's possible to filter the data received from the field utilizing mediated values, inverting the sign and deciding an Offset.
It's also possible to set two type of alarms, only visible at the moment, for high alarms and very high alarms.
I opened a SourceForge project dedicated to the FEM Software: https://sourceforge.net/projects/femsoftware/

Electromagnetic field graphs of the field mill in Scandriglia (updated every 5 minutes)

5 minutes graph	1 hour graph
4 hours graph	24 hours graph

Electric fields develop wherever there is a difference in electric potential. If the

electric field gets high eno

ugh you can feel your hair stand on end (if this happens outdoors during a thunderstorm crouch down with your feet together as you are about to be struck by lightning.) An electric field is what attracts your hair to a charged comb or a charged balloon.

The electric charge contained in a thundercloud also generates an electric field. This field can be measured on the ground.

Electric field is measured in Volts per meter (3.3 feet) The electric fields which accompany thunderstorms normally measure in the thousands of Volts per meter, usually abbreviated to kV/m.

Lightning is detected as a sudden change in the static electric field.

From the EFM-100 Boltek:

Often the first indication of an approaching thundercloud is a positive field reading followed by a
field reversal to a negative field as the cloud moves overhead.

With the thundercloud directly overhead the polarity of the field has reversed to a negative electric field.

Once the cloud has passed over the field will often reverse back to positive before decaying to a
normal fair-weather electric field reading of about 0.1 kV/m. This field reversal at the end of the
storm has been referred to as the “End of Storm Oscillation” (ESO).

Step changes in the magnitude of the electric field indicate lightning. Closer lightning produces larger
field changes than distant lightning. The EFM-100 can detect lightning out to about 30 miles.

Rain, snow, and dust can carry an electric charge. If charged particles contact the field mill sense
plates the electric charge will transfer from the particle to the sense plate and will be detected as noise
on the field mill reading. During periods of heavy rain the precipitation noise can get quite severe.
Once the storm passes the noise will disappear. Precipitation noise can reduce the ability of the
software to detect distant lightning but nearby lightning can still be detected.

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Ultimo aggiornamento: 25-01-10