Power supply electromagnetic compatibility technical term
Electromagnetic compatibility is an emerging interdisciplinary comprehensive applied discipline. As an edge technology, it is based on the basic theory of electrical and radio technology, and involves many new technical fields, such as microwave technology, microelectronics technology, computer technology, communication and network technology, and new materials. Electromagnetic compatibility technology has a wide range of applications, and almost all modern industrial fields, such as electric power, communication, transportation, aerospace, military industry, computer and medical care, must solve electromagnetic compatibility problems. The hot topics of its research mainly include: characteristics of electromagnetic interference sources and their transmission characteristics, harmful effects of electromagnetic interference, suppression technology of electromagnetic interference, utilization and management of electromagnetic spectrum, standards and specifications of electromagnetic compatibility, measurement and Test technology, electromagnetic leakage and electrostatic discharge, etc.
The English name of electromagnetic compatibility is Electromagnetic Compatibility, or EMC for short. The so-called electromagnetic compatibility refers to the coexistence state in which equipment (subsystems, systems) can perform their respective functions together in a common electromagnetic environment. There are two meanings here, that is, the electromagnetic radiation generated during its work must be limited to a certain level, and it must have a certain anti-interference ability. This is the compatibility problem that must be solved in the development of equipment. The frequency range involved in electromagnetic compatibility technology is as wide as 0 GHz to 400 GHz. In addition to traditional equipment, the research objects also involve the chip level, down to the electromagnetic environment of various ships, space shuttles, intercontinental missiles and even the entire earth.
The three elements of electromagnetic compatibility are interference source (disturbance source), coupling path and sensitive body. Cutting off any of the above items can solve the electromagnetic compatibility problem. Commonly used methods to solve electromagnetic compatibility mainly include shielding, grounding and filtering.
2 Electromagnetic Compatibility Technical Terms
(1) Electromagnetic Compatibility
Electromagnetic compatibility refers to the ability of a device or system to work normally in its electromagnetic environment without causing unacceptable electromagnetic disturbance to anything in the environment.
(2) Electromagnetic disturbance
Electromagnetic disturbance refers to any electromagnetic phenomenon that may degrade the performance of equipment, equipment or systems or cause damage to living or non-living substances. Electromagnetic disturbance can cause degradation of equipment, transmission channel or system performance. Its main elements include natural and man-made disturbance sources, coupling through public ground impedance/internal resistance, electromagnetic disturbance and radiation interference conducted along the power line, etc. The path of interference to the electronic system is: through the power supply, through the signal line or control cable, field penetration, and directly through the antenna; through cable coupling, conduction interference from other equipment; internal field coupling of the electronic system; radiation interference from other equipment; External coupling of electronic equipment to internal fields; broadband transmitter antenna systems; external environmental fields, etc.
(3) Electromagnetic environment
The electromagnetic environment is a time-varying electromagnetic phenomenon that apparently does not convey information, and which may superimpose or combine with useful signals.
(4) Electromagnetic radiation
Electromagnetic radiation is the phenomenon in which electromagnetic waves are emitted from a source into space. The meaning of the word "electromagnetic radiation" can sometimes be extended to include the phenomenon of electromagnetic induction. RFI/EMI can radiate through openings, ventilation holes, entrances and exits, cables, measurement holes, door frames, hatch covers, drawers and panels of any kind of equipment casing, as well as non-ideal connection surfaces of the casing. RFI/EMI can also be radiated by wires and cables entering sensitive equipment, and any good radiator of electromagnetic energy can also act as a good receiver.
(5) Pulse
An impulse is a physical quantity that undergoes a sudden change in a short period of time and then rapidly returns to its initial value.
(6) Common mode interference and differential mode interference
There are two types of interference on the power line: common mode interference and differential mode interference. Common mode interference exists between any relative ground of the power supply or between wires and ground. Common mode interference is also sometimes called longitudinal mode interference, asymmetrical interference or ground interference. This is the interference between the current carrying conductor and the earth. Differential mode interference exists between the phase line and the neutral line of the power supply and between the phase line and the phase line. Differential mode interference is also called normal mode interference, transverse mode interference or symmetrical interference. This is interference between current carrying conductors. Common mode interference indicates that the interference is coupled into the circuit by radiation or crosstalk, while differential mode interference indicates that the interference originates from the same power circuit. Usually these two kinds of interference exist at the same time. Due to the imbalance of line impedance, the two kinds of interference will be transformed into each other during transmission, so the situation is very complicated. After the interference is transmitted over a long distance, the attenuation of the differential mode component is greater than that of the common mode, because the line-to-line impedance is different from the line-to-ground impedance. For the same reason, common mode interference will also radiate to adjacent spaces during line transmission, but differential mode will not, so common mode interference is more likely to cause electromagnetic interference than differential mode. Different interference methods require different interference suppression methods to be effective. An easy way to determine the method of interference is to use a current probe. The current probe loops around each wire individually to get the inductance of a single wire, and then loops around two wires (one of which is ground) to detect the inductance. If the induction value increases, the interference current in the line is common mode; otherwise, it is differential mode.
(7) Immunity level and sensitivity level
Immunity level refers to the maximum disturbance level when a given electromagnetic disturbance is applied to a certain device, equipment or system and it can still work normally and maintain the required performance level. That is, the device, equipment, or system will exhibit reduced performance when this level is exceeded. The sensitivity level, on the other hand, is the level at which performance degradation is just beginning to occur. Therefore, for a certain device, equipment or system, the immunity level and the susceptibility level are the same value.
(8) Immunity margin
Immunity margin refers to the interpolation between the limit value of the immunity level of equipment, equipment or system and the electromagnetic compatibility level.
