EMI EMC Tutorial: Definitions, Terminology

EMI EMC Tutorial:

What is EMI & EMC?
Electromagnetic Interference (EMI):
capacitorsDefinition: The process by which disruptive electromagnetic energy is transmitted from one electronic device to another via radiated or conducted paths (or both) is known as Electromagnetic Interference.
There are two main sources of EMI:
(1) Natural Events (lightning, Electrostatic Discharges(ESD) and cosmic discharges)
(2) Man-made interference ( Mainly generated by electrical equipment used for industrial and domestic power supply, communications and control applications)
Every electrical circuit should be considered to be a potential source of electrical interference, particularly circuits with switching of inductive or capacitive circuits.
Electromagnetic Compatibility:
Definition: The capability of electrical and electronic systems, equipment, and devices to operate in their intended electromagnetic environment within a defined margin of safety and at design levels or performance without suffering or causing unacceptable degradation as a result of electromagnetic interference(EMI).
EMC- Electromagnetic compatibility refers to the ability of equipment to function satisfactorily without producing emissions that degrade the performance of other equipment and also not affected by emissions from other equipment.

It is not possible to eliminate the EMI problem completely. The main objective is to minimize their effect on other electronic equipment.
The main sources of EMI in the industrial environment are
(1) Any circuit which produces arcs
(2) Circuits which generate non-sinusoidal voltages, produce electric fields
(3) Circuits which generate non-sinusoidal currents, produce magnetic fields

EMI & EMC Terminology:

Before going in-depth into the EMI & EMC measurement, testing and suppression techniques, it is good to know various terms related to EMI/EMC. The post is the part of series of EMI EMC tutorial. This post will serve as a reference guide for us during our complete understanding about EMI/EMC.

Radio Frequency:
A frequency range containing coherent EM radiation of energy useful for communication purposes - roughly the range from 9 kHz to 300GHz. This energy may be emitted as a by-product of an electronic device's operation.

Radio frequency is emitted through two basic mechanisms:

  • Radiated Emissions - The component of RF energy that is emitted  through a medium as an EM field. Although RF energy is usually emitted through free space, other modes of field transmission may be present.
  • Conducted Emissions - The component of RF energy that is emitted through a medium as a propagating wave generally through a wire or interconnect cables.  Line Conducted Interference (LCI) refers to RF energy in a power cord or AC mains input cable. Conducted signals propagate as conducted waves.

A relative measure of a device or system's ability to withstand EMI exposure while maintaining a predefined performance level.

Radiated Immunity
A product's relative ability to withstand EM energy that arrives via free space propagation.

Conducted Immunity
A product's relative ability to withstand Em energy that penetrates through external cables, power cords, and input-output(I/O) interconnects.

A relative measure of a device or a system's propensity to be disrupted or damaged by EMI exposure to an incident field. It is due to lack of immunity.

Electrostatic Discharge(ESD):
A transfer of electric charge between bodies of different electrostatic potential in proximity or through direct contact.

Line Impedance Stabilization Network(LISN):
A network inserted in the supply mains load of an apparatus to be tested that provides, in a given frequency range, a specified load impedance for the measurement of disturbance voltages and which may isolate the apparatus from the supply mains in that frequency range.

Read More EMI EMC Tutorials:
Transient Voltage Suppressor (TVS Diode): Selection Guide Tutorial

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