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Disturbed equipment

Electrical devices, equipment and/or systems subject to interference and which can be adversely

affected by it are termed disturbed equipment.

In the same way as interference sources, disturbed equipment can also be categorized correspond-

ing to frequency characteristics. A distinction can be made between narrowband and broadband

susceptibility (fig. 6).

Narrowband systems include radio and TV sets, for example, whereas data processing systems are

generally specified as broadband systems.

Fig. 6

Disturbed equipment

2.3

Propagation of electromagnetic interference and EMC measurement techniques

As previously mentioned, an interference source causes both conducted and radiated electro-

magnetic interference.

Propagation along lines can be detected by measuring the interference current and the interference

voltage (fig. 7).

The effect of magnetic and electric interference fields on their immediate vicinity is assessed by

measuring the radiated magnetic and electric field components. This method of propagation is also

frequently termed electric or magnetic coupling (near field).

In higher frequency ranges, characterized by the fact that device dimensions are in the order of

magnitude of the wavelength under consideration, the interference energy is mainly radiated direct-

ly (far field).

Conducted and radiated propagation must also be taken into consideration when measuring the

susceptibility of disturbed equipment.

Interference sources e.g. sine-wave generators as well as pulse generators with a wide variety of

pulse shapes are used for such tests.

Radio and TV receivers

Digital and analog systems

Radio reception equipment

Data processing systems

Modems

Process control computers

Data transmission systems

Control systems

Telemetric radio transmission devices

Video transmission systems

Frequency-coded signalling equipment

Interface lines

Disturbed equipment (affected by EMI)

Narrowband susceptibility

Broadband susceptibility

General Technical Information