Monroe Electronics Electrostatic Fieldmeter - Static Monitor - model 177A - Manual (Page 6)

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Section 3
ELECTRIC FIELDS AND FIELDMETERS
Electric Field
An electric field is a region in space characterized by the existence of an electric force (F) generated
by an electric charge (q). The electric force F acting on a charge q in an electric field is proportional
to the charge itself. The relationship of these quantities is expressed by the electrostatic force law
[1]:
F = qE
E is called the electric field strength and is determined by the magnitude and locations of the other
charges acting upon charge q
E = F/q
The electric field strength, E, is usually displayed in the unit of volt/meter (V/m), volt/centimeter
(V/cm) or volt/inch (V/in).
Electric Fieldmeters
Charge is often difficult or impossible to measure directly. We rely on detection and measurement of
the electric field from the charged object to determine the existence of the charged and to estimate
the relative magnitude of the charge. The electrostatic fieldmeter is the instrument that measures
electric field strength.
Electric field strength measurements can be difficult to measure and interpret correctly because of
several factors that can affect the electric field itself or affect the measurement of the electric field.
Guidance is given in this document to help understand or minimize the effects of these factors, and
to otherwise correctly interpret electric field measurements.
Fieldmeters measure the electrostatic field (voltage per unit distance) at the aperture of a grounded
probe. Ideally, a uniform electric field is established between a charged surface and a grounded
surface. The grounded surface may be the grounded surface of the fieldmeter probe, or the
fieldmeter probe may also be placed in the plane of a grounded surface (better). The electric field is
set up between the grounded surface and the charged surface some distance, D, away. Fieldmeters
are calibrated at a particular distance, such as V/inch or V/cm. Therefore, using the manufacturer’s
calibrated distance (one inch or one centimeter) makes the measurement easier to interpret. Probe-
to-surface separation should be carefully controlled for accurate measurement.
Figure 1: Probe-to-Charged-Surface Separation, D
Monroe Electronics electrostatic fieldmeters use a feedback-driven, null seeking design to assure
accurate, drift-free, non-contacting measurements. Accuracy is typically a moderate 3% in a carefully
controlled geometry.
Figure 2 illustrates a Monroe Model 1036 fieldmeter probe in simple graphical form. This particular
fieldmeter is a chopper-stabilized design that operates reliably in both ionized and non-ionized
environments (refer to Appendix II.)
D
Probe
Charged
Surface