Electromagnetic compatibility measurement refers to measuring equipment and systems through instruments and facilities

Electromagnetic compatibility refers to the ability of devices to coexist and function in a common electromagnetic environment, which means that devices will not be allowed to degrade due to electromagnetic emissions from other devices in the same electromagnetic environment; Other devices in the same electromagnetic environment will not be allowed to be degraded due to their electromagnetic emissions. The first half of this definition reflects the electromagnetic interference (EMI) characteristics of equipment, i.e., it does not cause electromagnetic interference to other equipment or electromagnetic pollution to the environment; The latter part reflects the electromagnetic sensitivity (EMS) characteristics of the equipment, i.e., it is not subject to electromagnetic interference from other equipment and has no sensitive response to the electromagnetic environment. Different electronic devices that comply with electromagnetic compatibility can work together normally. They are compatible with each other, otherwise they are incompatible.

Electromagnetic compatibility is sometimes called electromagnetic compatibility. In some cases, both are common, but it is clear that the meaning of electromagnetic compatibility is broader, and electromagnetic compatibility pays more attention to the description of performance.

Electromagnetic compatibility measurement:

Electromagnetic compatibility measurement refers to measuring the electromagnetic compatibility status of equipment and systems through instruments and facilities. Electromagnetic compatibility measurement is the most direct means to obtain electromagnetic compatibility performance data of equipment and systems, and is also the basis for mastering the electromagnetic compatibility performance and electromagnetic compatibility maintenance of equipment and systems. Electromagnetic compatibility measurement also refers to electromagnetic compatibility testing, electromagnetic compatibility testing, etc. Electromagnetic compatibility measurement mainly measures current or spatial electromagnetic waves in electronic equipment and internal circuits of the system, surrounding the three elements of electromagnetic interference, namely, electromagnetic interference sources, coupling channels, and sensitive equipment

       There are different ways and means of generating electromagnetic interference, among which electromagnetic radiation and conduction are the main electromagnetic activities or means of generating electromagnetic interference. Some electromagnetic interference propagates through radiation and conduction. In order to analyze and study the nature and impact of electromagnetic interference, it is necessary to determine the spatial, temporal, frequency, energy, signal form, and other characteristics of electromagnetic interference. Therefore, electromagnetic interference is usually described by the following parameters: frequency, level, waveform, occurrence rate, polarization, direction, etc. These characteristics are closely related to the three elements of electromagnetic interference. Electromagnetic interference can exist, and none of the three elements is indispensable. Therefore, the electromagnetic interference problem can be solved as long as any one of them is eliminated, as shown in Figure 1-2.

图1-2电磁干扰控制图

When dealing with electromagnetic interference, it is most important to start from the following five points:

Frequency: What is the frequency of interference;

Intensity: How strong the electromagnetic interference is, and how serious the consequences are;

Time: Is it continuous or only for a certain amount of time;

Size: What is the geometric size of the radiator and how long is the transmission line;

Impedance: What is the impedance of the interference source and sensitive equipment, and what is the impedance of the transmission circuit between them;

It should be noted that the higher the frequency, the greater the possibility of radiation coupling, and the greater the possibility of conduction coupling.

Interference source type

Generally speaking, electromagnetic interference can be divided into internal interference and external interference according to its sources, which are listed in Table 1-1 and Table 1-2, respectively. External interference sources include natural interference sources and artificial interference sources.

Natural interference sources mainly come from natural electrical noise in the atmosphere and cosmic noise in outer space of the Earth. Natural interference sources are not only fundamental elements of the Earth's electromagnetic environment, but also interference sources that interfere with radio communications and space technology. Natural noise can interfere with the operation of satellites and spacecraft, as well as the launch of ballistic missile carrier rockets.

Artificial interference sources are electromagnetic energy interference generated by electromechanical or other artificial devices, some of which are devices specifically used to transmit electromagnetic energy such as radio equipment such as broadcasting, television, communications, radar, navigation, etc., and are called intentional emission interference sources. The other part is to emit electromagnetic energy while completing its own functions, such as transportation vehicles, overhead transmission lines, lighting equipment, electric machinery, household appliances, industrial, medical radio frequency equipment, etc. Therefore, this part is also referred to as an unintentional emission interference source.

The nature of various interferences varies greatly. Table 1-3 lists the characteristics of several interferences.

Electromagnetic interference coupling path:

Any occurrence of electromagnetic interference inevitably involves the transmission and transmission of interference energy. It is generally believed that there are two modes of electromagnetic interference coupling: conduction and radiation. The specific classification is shown in Table 1-4. Therefore, from the perspective of interference sensors, interference coupling can be divided into two types: conductive coupling and radiation (spatial) coupling, as shown in Figure 1-3.

Conduction coupling must have a complete circuit connection between the interference source and the sensor, and interference energy is transferred to the sensor along the connection circuit, resulting in interference phenomena. The transmission circuit may include wires, conductive parts of equipment, power supplies, common impedance, floors, resistors, inductors, capacitors, and mutual inductance components. Radiation coupling is the propagation of electromagnetic waves through a medium, emitting interference energy into the surrounding space according to the laws of electromagnetic waves. There are three common types of radiation coupling: electromagnetic waves emitted by an antenna are accepted by a Class B antenna, known as antenna coupling; Space electromagnetic fields are inductively coupled through wires, known as coupling; Spatial electromagnetic fields are induced through a hole joint, known as hole joint coupling.

In practical electromagnetic compatibility engineering, interference between devices usually involves multiple modes of coupling. The existence of multiple coupling contracts, which repeatedly intersect, together generate interference, making electromagnetic interference difficult to control.