Electric Field Mill Fabrication


Posted on Feb 5, 2014

This page describes the construction of an electric field mill. This is a device to measure the electric field strength on earth due to the static electric field and the charge of clouds passing overhead. It can also be used to investigate static electricity effects. The body and chopper of the field mill are fabricated from a 4 inch diameter duct


Electric Field Mill Fabrication
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fan. The signal conditioning electronics uses a chopper blade position detector and a synchronous detector to reduce noise and recover the field sign (positive or negative) as well as magnitude (strength in V/m). 1. Martin A. Uman - Lightning, McGraw-Hill Book Company, New York (1969), 264 pages. Russian translation (1972), revised edition, Dover, New York (1984). (Available at Borders) The strength of the electric field could be measured, in principle, by placing a volt meter across plates placed some distance apart. However, because the meter will have some input impedance (10 Meg typically), any voltage induced on the plates will quickly drain away, and would not be useful for measuring the static field. To make measurements of the static field, the chopper technique is used. The chopper blade is arranged over the Sense Plate and rotated so that it periodically shields, and exposes the Sense Plate to the electric field. To properly do this, the Rotor must be grounded. The Sense Plate is grounded through a transconductance amplifier, which converts the Sense Plate`s ground current to a voltage. As the Sense Plate is exposed to the Field, the field induces ground currents as it attracts or repels charge from the Sense Plate. As the plate is shielded from the field, the induced charge drains away. So the chopper induces an AC ground current which is proportional to electric field strength. This AC signal could then be...




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