Elma Instruments Elma 92, Руководство пользователя

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Elma 92 side 38
Electric field strength (E) :
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 the following situations:
•
In the near-field area of the source.
•
Where the nature of the electromagnetic field is unknown.
Magnetic field strength (H) :
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).
The meter uses of magnetic field strength for measurements only in the far-field area of
the source.
Power density (S) :
Power per unit area normal to the direction of propagation, usually expressed in units of
watts per square meter (W/m
2
) or, for convenience, units such as milliwatts per square
centimeter (mW/cm
2
).
•
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) =
c (speed of light)
f (frequency)
If the distance to the field source is less than three wavelength, then we are usually in the
near-field. If the distance is more than three wave length, the far-field conditions usually
hold.
In the near-field, the ratio of electric field strength (E) and magnetic field strength (H) is not
constant, so we have to measure each separately.
In the far-field, however, it is enough to just measure one field quantity, then the other
could be computed accordingly.
Application
Quite often routine operation, maintenance and service work has to be done in areas
where active electromagnetic fields are present, e.g. in broadcasting stations, etc.
Additionally, other employees may be exposed to electromagnetic radiation. In such
cases, it is essential that personnel are not exposed to dangerous levels of
electromagnetic radiation, such as:
•
High frequency (RF) electromagnetic wave field strength measurement.
•
Mobil phone base station antenna radiation power density measurement.
•
Wireless communication applications (CW, TDMA, GSM, DECT).
•
RF power measurement for transmitters.
•
Wireless LAN (Wi-Fi) detection, installation.