What is Electromagnetic Compatibility (EMC) Testing?

The concept of electromagnetic compatibility
IEC 60050 (161) is equivalent to GB/T4365-1995 “Electromagnetic Compatibility Terminology”, which defines EMC as “equipment or system can work normally in its electromagnetic environment and does not constitute unacceptable electromagnetic the ability to harass.” Electromagnetic compatibility is the research that under the conditions of limited space, limited time, and limited spectrum resources. A science in which various electrical equipment (subsystems, systems; in a broad sense, organisms) can coexist without causing degradation. Electromagnetic compatibility consists of the following two parts.

1. ElcetroMagnetic Interference
Electronic products interfere with the characteristics of other products in the electromagnetic environment.

(1) Conducted Emission
It refers to the process of propagating electromagnetic noise energy through one or more conductors (such as power lines, signal lines, control lines, or other metal objects). In a broad sense, conducted emissions also include common impedance coupling between different devices and circuits using a common ground or a common power line.

(2) Radiated Emission
It refers to the process of propagating electromagnetic noise energy through space in the form of electromagnetic waves. Radiated emissions sometimes also include inductive phenomena. Specifically, it includes electrostatic coupling, magnetic field coupling and electromagnetic coupling.

2. ElcetroMagnetic Susceptibility
The characteristic of electronic products are subject to interference from other products in the electromagnetic environment.
(1) Conducted Susceptibility
A measure of the level of conducted interference required to cause equipment, subsystems, system performance degradation, or undesired responses.

(2) Radiated Susceptibility
A measure of the level of radiated interference required to cause equipment, subsystems, system performance degradation, or undesired responses.

3. Three elements of electromagnetic compatibility
Electromagnetic disturbance source
Electromagnetic energy emitted by any form of natural or electrical device can cause harm to people or other creatures sharing the same environment, or cause electromagnetic hazards to other equipment, subsystems or systems, resulting in performance degradation or failure, which is called electromagnetic harassment source.

Characteristics of electromagnetic disturbance sources
1) The emission level under the condition of the specified bandwidth
2) Spectral width
According to the frequency distribution characteristics of electromagnetic disturbance energy, its spectral width can be determined. In the continuous wave disturbance, the frequency spectrum width of the hum disturbance is the narrowest, and in the impulse disturbance, the frequency spectrum width of the unit impulse function is the widest.

3) Waveform
Electromagnetic disturbances have various waveforms. Waveform is an important factor in determining the frequency width of electromagnetic disturbance.

4) Occurrence rate
The distribution of electromagnetic disturbance field strength or power over time is related to the occurrence rate of electromagnetic disturbance. According to the occurrence rate of electromagnetic disturbance, it can be divided into three types: periodic disturbance, non-periodic disturbance and random disturbance.

5) Polarization Characteristics of Radiated Disturbance
Polarization characteristics refer to the time-varying characteristics of the direction of the disturbance field strength vector at a given point in space, which depends on the polarization characteristics of the antenna. When the polarization characteristics of the disturbance source antenna and the antenna of the sensitive equipment are the same, the induced voltage generated by the radiated disturbance at the input end of the sensitive equipment is the strongest.

6) Directional characteristics of radiation disturbance
The disturbance source radiates electromagnetic disturbance in all directions of space, or the ability of sensitive equipment to receive electromagnetic disturbance from all directions is different. The parameters describing this radiation ability or receiving ability are called directional characteristics.

7) Antenna effective area
This is a parameter that characterizes the ability of sensitive equipment to receive disturbance field strength. Obviously, the larger the effective area of the antenna is, the stronger the ability of sensitive equipment to receive electromagnetic disturbance.

Classification of electromagnetic disturbance sources
1) According to the classification of electromagnetic disturbance sources: it can be divided into three categories: natural disturbance sources, man-made disturbance sources and transient disturbance sources.
a. Natural disturbance sources are characterized by their uncontrollability. According to their different causes and physical properties, natural disturbance sources can be divided into four categories: electronic noise, sky-electric noise, extraterrestrial noise, and sedimentary static electricity.
b. Man-made disturbance sources are characterized by being known and controllable. Man-made disturbances can be divided into two categories: radio disturbances and non-radio disturbances.
c. Industrial, scientific and medical equipment (ISM), vehicles, motor boats and spark ignition engine units, household appliances, portable power tools and similar appliances, fluorescent lamps and lighting fixtures, and information technology equipment are major sources of transient disturbances.

2) According to the nature of electromagnetic disturbance source: divided into two types: pulse disturbance source and smooth disturbance source.

3) According to the action time of electromagnetic disturbance source, it can be divided into continuous disturbance source, intermittent disturbance source and transient disturbance source.
a. The continuous disturbance source is a long-term electromagnetic disturbance source;
b. The intermittent disturbance source is a short-term electromagnetic disturbance source;
c. The transient disturbance source is the electromagnetic disturbance source with short action time and non-periodic disturbance.

4) According to the function and non-functionality of electromagnetic disturbance source: it is divided into functional disturbance source and non-functional disturbance source.
a. The source of functional harassment refers to the harassment of other systems, such as the harassment caused by radio stations, industry, science, medical equipment, etc., while a system is working normally.
b. Non-functional harassment sources refer to the “by-products” of a system during normal operation, such as harassment caused by high-power switches and relays.

5) According to the way of electromagnetic disturbance source propagation: divided into radiation disturbance source and conduction disturbance source, or a combination of both.

Coupling pathway
The transmission path or medium of electromagnetic disturbance.
(1) Conductive coupling
The wire passes through the environment with interference, that is, it picks up the interference signal and conducts it to the circuit through the wire, causing interference to the circuit, which is called conduction coupling, or direct coupling.

In audio frequency and low frequency, because the shielding layer of power line, grounding conductor and cable presents low impedance, it is easy to spread when the current is injected into these conductors. When the noise is transmitted to other sensitive circuits, it can cause interference. At high frequency, the inductance and capacitance of the conductor will not be ignored, the inductive reactance increases with the increase of frequency, and the capacitive reactance decreases with the increase of frequency.

(2) Common impedance coupling
When the currents of two circuits pass through a common impedance, the voltage formed by the currents of one circuit across the common impedance will affect the other circuit.

(3) Inductive coupling
a. Inductive coupling
The port voltage of the interference circuit will lead to the distribution of charges in the interference circuit. The electric field generated by these charges can be partially picked up by the sensitive circuit. When the electric field changes with time, the time-varying induced charge in the sensitive circuit will form an induced current in the circuit. , this is called inductive capacitive coupling. The solution is to reduce the resistance value of the sensitive circuit and change the directional shielding or separation of the wire itself.

b. Magnetic induction coupling
A part of the magnetic flux density generated by the current in the interference loop will be picked up by other loops. When the magnetic flux density changes with time, an induced voltage will appear in the sensitive loop. The coupling between the loops is called magnetic induction coupling. The main forms are coil and transformer coupling, coupling between parallel double lines, etc. Core losses often make the transformer act like a low-pass filter that suppresses high-frequency interference. The coupling between parallel lines is the main form of magnetic induction coupling. To reduce interference, the mutual inductance between the two wires must be minimized.

c. Radiation coupling
The radiation source propagates electromagnetic waves to free space, and the two wires of the induction circuit are like antennas, accepting electromagnetic waves and forming interference coupling. When the interference source is relatively close to the sensitive circuit, if the radiation source has a low voltage and a large current, the magnetic field plays a major role; if the interference source has a high voltage and a small current, the electric field plays a major role. For the interference caused by radiation, shielding technology is mainly used to suppress the interference.

Sensitive equipment
It refers to people or other living beings that will be harmed by the electromagnetic energy emitted by electromagnetic disturbance sources, as well as devices, equipment, sub-systems or systems that will cause electromagnetic hazards and cause performance degradation or failure. Many devices, equipment, subsystems or systems can be both sources of electromagnetic disturbance and sensitive equipment.

In order to realize electromagnetic compatibility, we must proceed from the above three basic elements, and use technical and organizational measures. The so-called technical measures are to start from the analysis of electromagnetic disturbance sources, coupling paths and sensitive equipment, and adopt effective technical means to suppress disturbance sources, eliminate or weaken the coupling of disturbances, reduce the response of sensitive equipment to disturbances or increase the level of electromagnetic sensitivity. The so-called organizational measures are to formulate and follow a complete set of standards and specifications, to carry out reasonable spectrum allocation, to control and manage the use of the spectrum, to specify the working method according to frequency, working time, antenna directionality, etc., to analyze the electromagnetic environment and select the layout area for electromagnetic compatibility management, etc.

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