Front Panel Description - Extech Instruments EMF450 User Manual

Definitions
Electromagnetic Radiation

This meter is used to indicate radiated electromagnetic fields wherever there is a voltage,
current, electric (E) or magnetic (H) field. Examples include the electromagnetic fields from
radio broadcasting, TV transmitters and power lines.
Electric Field Strength

This is a field vector quantity that represents the force (F) on an infinitesimal unit positive
test charge (q) at a point divided by that charge. Electric field strength is expressed in units
of volts per meter (V/m). Use the units of electric field strength for measurements in near-
field power measurements.
Magnetic field strength (H)

This is a field vector that is equal to the magnetic flux density divided by the permeability of
the medium. Magnetic field strength is expressed in units of amperes per meter (A/m).
This measurement is for near-field power measurements.
Power density (S)

Power per unit area in the direction of propagation; usually expressed in units of watts per
square meter (W/m2) or, for convenience, milli-watts per square centimeter (mW/cm
The characteristic of electromagnetic fields

Electromagnetic fields propagate as waves and travel at the speed of light (c).
The wavelength is proportional to the frequency.
λ (wavelength) =
Near-field is assumed if the distance to the field source is less than three wavelengths. For
far-fields, the distance is more than three wavelengths. In the near-field, the ratio of
electric field strength (E) and magnetic field strength (H) is not constant, so measure each
separately. In the far-field, however, it is enough to measure one field quantity, and
compute the other accordingly.
Descriptions

Front Panel Description

1. 2.4" Color TFT display (240*320 resolution)
2. Select and Down button
3. Power and Menu button
4. Hold and Enter button
5. Battery compartment cover and
measurement chart on back of meter
c (speed of light)
f (frequency)
Figure 1 – Meter Description
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2 ).
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