EMC Test Certification










Electromagnetic compatibility (EMC) is the branch of electrical engineering concerned with the unintentional generation, propagation and reception of electromagnetic energy which may cause unwanted effects such as electromagnetic interference (EMI) or even physical damage in operational equipment. The goal of EMC is the correct operation of different equipment in a common electromagnetic environment.

EMC pursues two main classes of issue. Emission is the generation of electromagnetic energy, whether deliberate or accidental, by some source and its release into the environment. EMC studies the unwanted emissions and the countermeasures which may be taken in order to reduce unwanted emissions. The second class, susceptibility is the tendency of electrical equipment, referred to as the victim, to malfunction or break down in the presence of unwanted emissions, which are known as Radio frequency interference (RFI). Immunity is the opposite of susceptibility, being the ability of equipment to function correctly in the presence of RFI, with the discipline of "hardening" equipment being known equally as susceptibility or immunity. A third class studied is coupling, which is the mechanism by which emitted interference reaches the victim.

Interference mitigation and hence electromagnetic compatibility may be achieved by addressing any or all of these issues, i.e., quieting the sources of interference, inhibiting coupling paths and/or hardening the potential victims. In practice, many of the engineering techniques used, such as grounding and shielding, apply to all three issues.


Types of interference

Main article: Electromagnetic interference

Electromagnetic interference divides into several categories according to the source and signal characteristics.

The origin of interference, often called "noise" in this context, can be man-made (artificial) or natural.


Continuous interference

Continuous, or Continuous Wave (CW), interference arises where the source continuously emits at a given range of frequencies. This type is naturally divided into sub-categories according to frequency range, and as a whole is sometimes referred to as "DC to daylight".

  • Audio Frequency, from very low frequencies up to around 20 kHz. Frequencies up to 100 kHz may sometimes be classified as Audio. Sources include:

    • Mains hum from: power supply units, nearby power supply wiring, transmission lines and substations.

    • Audio processing equipment, such as audio power amplifiers and loudspeakers.

    • Demodulation of a high-frequency carrier wave such as an FM radio transmission.

  • Radio Frequency Interference (RFI), from typically 20 kHz to an upper limit which constantly increases as technology pushes it higher. Sources include:

    • Wireless and Radio Frequency Transmissions

    • Television and Radio Receivers

    • Industrial, scientific and medical equipment (ISM)

    • Digital processing circuitry such as microcontrollers

  • Broadband noise may be spread across parts of either or both frequency ranges, with no particular frequency accentuated. Sources include:

    • Solar activity

    • Continuously operating spark gaps such as arc welders

    • CDMA (spread-spectrum) mobile telephony


Pulse or transient interference

An electromagnetic pulse (EMP), sometimes called a transient disturbance, arises where the source emits a short-duration pulse of energy. The energy is usually broadband by nature, although it often excites a relatively narrow-band damped sine wave response in the victim.

Sources divide broadly into isolated and repetitive events.

  • Sources of isolated EMP events include:

    • Switching action of electrical circuitry, including inductive loads such as relays, solenoids, or electric motors.

    • Electrostatic discharge (ESD), as a result of two charged objects coming into close proximity or contact.

    • Lightning electromagnetic pulse (LEMP), although typically a short series of pulses.

    • Nuclear electromagnetic pulse (NEMP), as a result of a nuclear explosion. A variant of this is the high altitude EMP (HEMP) nuclear device, designed to create the pulse as its primary destructive effect.

    • Non-nuclear electromagnetic pulse (NNEMP) weapons.

    • Power line surges/pulses

  • Sources of repetitive EMP events, sometimes as regular pulse trains, include:

    • Electric motors

    • Gasoline engine ignition systems

    • Continual switching actions of digital electronic circuitry.


Reference: http://www.emctest.it/

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