Field mill

An electric field meter, and electric field meters, rotary voltmeter or field mill (English " field mill" ) called, is a device used to measure the electric field strength. At a defined measuring distance to an object, it can be used as relatively insensitive voltage meter.

As the electroscope deprives the electric field meter the object to be measured, no energy and thus falsify the measurement result is not, but is much more sensitive. Depending on the design of a resolution to be achieved may reduce to 10 V / m (for the rotary voltmeter in handier electric field meters only to about 1 kV / m).

Operation

Is located at the front of the device a gilt electrostatic chopper ( impeller, so stirred the term " field mill "). Gold reduced according to some producers the measurement error, as it has a similar position to oxygen in the electrochemical voltage series. The impeller is periodically free window openings and closes it again. Therefore, the sensor electrode behind the chopper alternately charged and discharged by influence of the external electric field. This change in charge can be measured in different ways:

• In the simplest case, the sensor electrode is connected to ground over a very high resistance in order to obtain a sufficiently large time constant. Thereto, the charge-reversal current generates an alternating voltage, which is made low by a voltage follower ( electrometer amplifier).
• Greater demand a charge amplifier generates the measuring voltage. This ensures through its virtual zero point that the sensor plate always remains at zero potential, which reduces the insulation problems drastically.

After sufficient amplification, the AC voltage is in a synchronous rectifier, the switching frequency matches the frequency of rotation of the impeller, in the same direction and displayed. In this way, the polarity of the voltage or the direction of the electric field can be determined.

This principle allows to determine static electrical charges and fields to remove them without energy - to measure, no current flows.

Applications

From the measured field strengths can be deduced to adjacent surface charges, among other things, in an electrostatically protected areas ( ESD workstations ) and must be avoided in the manufacture and packaging of electronic parts and components. You could give rise to electrostatic discharges.

In meteorology and climate research changes in the electric field are measured in the atmosphere, which are generated by weather phenomena such as thunderstorms, cold or warm front passes, rain clouds and other electrostatic phenomena in the atmosphere. Emergency rocket launch to be postponed.