The importance, content and method of implementing electromagnetic compatibility in household appliances
This paper discusses the influence of electromagnetic disturbance of household appliances on electromagnetic environment and the importance of implementing electromagnetic compatibility. Then it discusses the content and method of electromagnetic compatibility design of household appliances, and illustrates how to suppress electromagnetic disturbance generated by household appliances.
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The influence of electromagnetic disturbance of household appliances on electromagnetic environment
In recent years, with the development of science and technology, household appliances are rapidly developing towards the trend of energy saving, automation, intelligence, convenience and comfort. In this way, with the increasing variety of household appliances, the scale of production continues to expand; at the same time, imported products are also flooding the market. On the other hand, with the development of microelectronic control technology, a large number of electronic home appliances have emerged. The resulting electromagnetic disturbance has an impact on the normal use and reliability of other household appliances or electronic devices, and also has a direct impact on people's health. At present, protecting the electromagnetic environment and preventing electromagnetic pollution has caused widespread concern in countries around the world and relevant international organizations. In particular, the European Community Council Directed the "Consensus of Member States on the Law on Electromagnetic Compatibility" (89/336/EEC) after entering the substantive implementation phase on January 1, 1996, electromagnetic compatibility of electronic and electrical products. The passing of sex indicators has become a necessary condition for market access or market circulation of the European Community. With the establishment and improvement of China's electromagnetic compatibility certification system, the electromagnetic compatibility of China's electronic products, including household appliances, will continue to increase, and then gradually reduce the electromagnetic environment pollution and protect the vital interests of users.
According to the reasons that household electronics have an impact on the electromagnetic environment, household appliances can be classified into the following types:
(1) Household appliances such as vacuum cleaners, hair dryers, electric sewing machines, food blenders, electric shavers, which are generated by sparks and commutators in the operation of the motor with the commutator to form a spark. Etc.; electromagnetic disturbance refers to any electromagnetic phenomenon that may cause the performance of other household appliances or electronic equipment to be degraded or cause damage to human health;
(2) Household appliances that cause electromagnetic disturbance due to frequent switching actions, such as electric rice cookers, electric irons, electric ovens, refrigerators, washing machines, etc.;
(3) Household appliances that may cause the low-voltage distribution network to decline, causing other household appliances or electronic equipment to fail to operate normally, such as the large current required when the air conditioner is started, the grid voltage may temporarily drop, the motor or electricity Inductive load such as inductive ballast will cause the power factor of the power supply to decrease, and the power electronic components in the variable frequency speed control air conditioner will also generate power harmonics;
(4) Household appliances with thyristor devices, such as electronic dimming lamps, electric fan multi-function controllers, etc., will generate high-order harmonic disturbances;
(5) Various gas discharge lamps, such as plasmas formed by discharge of gas such as fluorescent lamps, may cause electromagnetic disturbance;
(6) Household appliances with microprocessors, such as fuzzy appliances, appliances with remote control, fully automatic washing machines, DVD players, stereos, home theaters, water heaters, microwave ovens, etc., the two-level digital signal they use Causing electromagnetic disturbances, and as the clock frequency continues to increase, its disturbance spectrum can be as high as hundreds of megahertz;
(7) Leakage of electromagnetic energy generated by microwave ovens, electromagnetic ovens, home theater power amplifiers, etc., not only causes electromagnetic disturbance, but also causes harm to human health.
If the electromagnetic disturbance generated by household appliances exceeds the limit specified by national standards, it will cause electromagnetic environment pollution. For example, harassing the radio, listening to and watching the TV; causing the computer and its controlled appliances to malfunction or lose data; making medical devices such as cardiac pacemakers work, etc.; affecting human health, including rapid blood flow, local Increased body temperature, decreased enzyme activity, protein degeneration, heart rate changes, local tissue damage, etc., in addition, adverse effects on the central nervous system, blood and immune system, cardiovascular system, reproductive system.
Electromagnetic compatibility of household appliances
Electromagnetic compatibility of household appliances means that household appliances can work normally in their electromagnetic environment without degrading performance, and will not constitute an unacceptable electromagnetic disturbance to anything in the electromagnetic environment. That is to say, in a complex electromagnetic environment, each household appliance must be able to withstand external electromagnetic disturbances and operate normally, and must not disturb the normal operation of other household appliances or electronic equipment, and may not cause harm to human health. This is the problem that the electromagnetic compatibility of household appliances needs to be solved. In short, household appliances should meet the immunity limit requirements stipulated by national standards on the one hand, and have the ability to avoid electromagnetic disturbances without degrading operational performance; on the other hand, they have the ability to not exceed the electromagnetic disturbance limits specified by national standards. . Electromagnetic compatibility is one of the important performance indicators of household appliances, and it is also an important means to ensure the quality of household appliances and to achieve the functions of household appliances.
Electromagnetic compatibility design of household appliances
The purpose of electromagnetic compatibility design of household appliances is to make electromagnetic compatibility of household appliances. This should start with the analysis of electromagnetic disturbance sources, disturbance coupling paths and sensitive circuits, design protection measures such as grounding, shielding and filtering, suppress electromagnetic disturbance at the source of disturbance, cut off the coupling of electromagnetic disturbance, and enhance the immunity of sensitive circuits. Experience has proved that in the initial stage of functional design of household appliances, electromagnetic compatibility design can be simultaneously solved, and electromagnetic compatibility problems such as electromagnetic disturbance and immunity can be solved before the product is finalized; if the product is finalized, even after the production stage or arrives After the user's hands, the problem will be solved, which will not only bring technical difficulties, but also cause great waste of manpower and financial resources. Therefore, it is very necessary to solve the electromagnetic compatibility problem as soon as possible. Regardless of electromagnetic compatibility, it is completely adventurous to perform product design only by routine, and then perform electromagnetic compatibility test on the sample. It is a very risky practice to remedy the problem. It is completely undesirable.
The key to electromagnetic compatibility design of household appliances is the choice of active devices and printed circuit board design. For example, digital circuits are one of the most common sources of broadband disturbances. The shorter the rise/fall time, the wider the disturbance spectrum and the higher frequency components can extend beyond megahertz. Therefore, while ensuring the function of the circuit, a lower pulse repetition frequency and a slower rise/fall time should be used. Another example is the power amplifier tube of the home theater is an important source of electromagnetic disturbance. In addition to selecting the appropriate power device, it should also be screened for technical indicators such as harmonic emission and spurious emission.
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