1 Basic concept Electromagnetic Compatibility (Electromagnetic Compatibility) is an important quality indicator for electricians and electronic products. It can be considered that the product quality is mainly composed of two major contents: quality specifications and technical indicators. The former involves general norms, that is, the international IEC, the domestic basic standards set by the state; the latter is the product function regulations and technical requirements. Electromagnetic compatibility and safety requirements are fundamental standards. Now EMC has formed a complete system from basic standards, general standards, family standards, and product standards. In addition, there is special legislation in the international arena for this purpose. For example, the European Union has enacted regulations that, from January 1, 1996, electricians and electronic products must be qualified for LV Directive and EMC Directive before they can be sold in the market. Over the years, new EMC standards have been officially released in China. However, it should be pointed out that the IEC related EMC standards will continue to be upgraded from the draft or the old version to the official version. The relevant national EMC standards will also be continuously updated and released. The latest EMC version should be subject to the latest version. The so-called EMC, defined in GB/T4365-1996 "Electromagnetic Compatibility Terminology" is: the ability of a device or system to function properly in its electromagnetic environment without posing an unacceptable electromagnetic disturbance to anything in the environment. This definition summarizes the three aspects. First, electromagnetic disturbance can be restricted. Electromagnetic disturbance is ubiquitous, but it can be constrained by quality specifications and technically limited. This means that the product should be limited to the limit of the electromagnetic interference intensity sent out to ensure that the electromagnetic environment is qualified. Second, the immunity of electromagnetic harassment. This means that the product should work properly in an electromagnetic environment that specifies the intensity of electromagnetic disturbances and should not degrade its performance. Third, the normative and compatibility of the electromagnetic environment. That is, any measures taken against electromagnetic disturbances can not degrade themselves or other products or systems in the same electromagnetic environment, and can only coexist peacefully in a friendly manner. For example, in order to reduce conducted interference, a capacitor is connected between the phase line of the device power supply and the ground. For the equipment, the capacity of the capacitor must meet the limit value of the leakage current in the safety standard; for the system, to prevent it from becoming a system interference coupling source affects the system operation. Therefore, the EMC test of the product should include two aspects: (1) Test the electromagnetic disturbance intensity sent to the outside world to confirm whether it meets the limit value requirements of the relevant standards; (2) The electromagnetic disturbance intensity is specified in it. Sensitivity tests are performed under electromagnetic environment conditions to confirm compliance with the immunity requirements specified by the relevant standards. These two aspects in the EMC test project are Electromagnetic Interference or Electromagnetic Disturbance and Immunity to a Disturbance; the latter used to use the term Susceptibili-ty. The occurrence of electromagnetic interference depends on the strength of the interference source, the coupling mode of the interference, and the sensitivity of the instrument to the interference. Therefore, the performance requirements and test methods of the relevant standards for EMC are divided into different items according to different natures and different types. They are also divided into two categories according to different modes of electromagnetic disturbance propagation: conductive interference and radiation interference. The former mainly detects the intensity and frequency range of the harmonics and high-frequency noise of the power frequency power supply through the power line or signal line, which belongs to the near field and the induction field effect of electromagnetic disturbance. The latter detects the intensity and frequency range of the RF noise radiated directly from the device under test, which is mainly for the far-field effect of electromagnetic disturbance. It is worth noting that in recent years, the international attention has been paid to the harmonic interference of power supplies and the immunity requirements of equipment. The former involves the environmental requirements of the utility grid. The latter is to ensure the reliability of the equipment or system. To this end, many standards also specifically separate the power supply harmonic current content requirements and immunity as two technical requirements from the EMC project, a single independent item. It must be pointed out that for the information society, the losses caused by the malfunction of information technology equipment are often difficult to measure by currency. Under the realistic conditions that it is impossible to completely avoid electromagnetic disturbance, it is particularly important to improve the product immunity under the specified electromagnetic environment. Specifically, the manufacturer conducts routine tests on EMC specific products in addition to determining whether the EMC performance of the product meets the requirements of national and industry standards (according to domestic and foreign literature reports, serious EMC design and testing are not implemented and sufficient Technical measures, it is difficult to pass the EMC test), can also evaluate the degree of influence of external electromagnetic disturbance on the product and the effectiveness of the relevant suppression measures, and identify the specific reasons (source and action path) of the product being damaged by the EMC test in order to adopt corresponding Measures. Therefore, EMC testing at the beginning of product design is an indispensable part of the product's commercialization. On the other hand, understanding the EMC performance of a product is an important factor in commodity inspection and user-approved products. All of this requires knowledge of EMC's performance requirements and testing.


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