There are three ways of electromagnetic conduction, electromagnetic induction, and electromagnetic radiation between various operating power equipment that are related to each other and affect each other. Under certain conditions, it will cause interference, impact or even harm to the operating equipment and personnel. The electromagnetic compatibility EMC discipline that emerged in the 1980s aims at researching and solving this sentence, mainly researching and solving interference generation, propagation, reception, suppression mechanisms and corresponding measurement and measurement technologies, and based on this The most reasonable principle of technology and economy, to make clear provisions on the interference level, anti-interference level and suppression measures, so that the equipment in the same electromagnetic environment is compatible, and at the same time, it is not allowed to introduce any entity in the environment. The electromagnetic disturbance.
The main sources of man-made electromagnetic noise are as follows:
(1) Continuous interference generated by the equipment during operation, mainly radiated or conducted interference. Radio stations, high-power radars, motor noise, fixed and mobile communications, computers, display units, printers, high-repetition frequency ignition noise, AC/multiphase power rectifiers, and solar system and cosmic wireless noise are all sources of continuous electromagnetic interference. It is a noise source of a fixed frequency source. For some communication equipment, EMC testing is required to ensure the smoothness and quality of communication.
(2) The pulse interference generated by the electromagnetic transient process has a wide frequency spectrum and radiates interference to space. Lightning, nuclear electromagnetic pulses, power line sparks, switches and relays, electric welding equipment, low-repetition frequency ignition noise, electrical power ignition, human electrostatic discharge, etc. belong to pulsed electromagnetic interference sources, which are noise sources with a large frequency spectrum.
(3) Indirect interference sources related to mechanical movement, such as interference generated by frictional electrification between the shells of cars, ships, and airplanes and dust particles, smoke, snow, etc. in the air.
(4) The metal contact surface has complex impedance characteristics to generate induced current. Due to the effect of contact impedance, the contact impedance is variable during vibration, bumps, and impacts. The modulation of the change in contact impedance on the external strong radiation field will cause two Secondary radiation becomes a source of contact interference and generates additional frequency components. In addition to unintentional emission, the electromagnetic environment is also full of intentional radiation from radio, television and radar transmitters. These intentional radiators may interfere with devices that do not receive any form of reception and radios that can be tuned to different frequencies. One of them causes The most common cause of EMI is electromagnetic fields generated by radio transmitters.
EMC research dealing with electromagnetic noise. The beginning of the practical use of wireless communication has been seen in 1920. At that time, the sky was full of yellow sand in the northeastern region of China, and the wireless receiver was mixed with "chattering" sounds. This is one example of interference. At that time, electromagnetic noise was called "noise". It was because the initial interference caused by noise was perceived by people in the form of "sound". Many people now buy cars requiring low noise, so EMC testing of automotive electronics is now necessary.