People who have exposed to EMC will often feel a mist: What is EMC? Can you eat? So, today I will introduce what is EMC.
1, EMC Basic Overview
Electromagnetic compatibility EMC (ElectromagNetic Compatibility), means that the device or system meets the ability to run in its electromagnetic environment and do not have an unbearable electromagnetic interference in any device in its environment.
Therefore, EMC includes two aspects: one aspect requires that the sensor generates electromagnetic interference to the environment during normal operation, ie, EMI; on the other hand, the sensor is required to have electromagnetic interference in the environment has a certain degree of resistance Distortion, ie EMS.
Popular lecture: EMC = EMI + EMS. The electronic product itself has a certain anti-interference ability (EMS), you interfere with me when you work, I interfere with you (EMI), but everyone can share peacefully (EMC).
It is like you have a pair of twins, a naughty (EMI), a quiet (EMS), but two children can play a happy play together (EMC).
So why we have to do EMC this seems to have anything to use?
The official gives us answered: refers to the signal and interference to coexist under conditions of information contained in the signal. The purpose of studying electromagnetic compatibility is to ensure that electrical components or devices can have normal operation in electromagnetic environments, as well as mechanism and preventive measures to study electromagnetic waves on social production activities and human health.
In order to make the product to improve the reliability of the normal operation of the electronic equipment before the product, make it in line with international, and to ensure the safety of the person and some special materials, more and more electronic companies pay attention to EMC, and carry out the necessary Electromagnetic compatibility detection can greatly contribute to the improvement of the stability and quality of product itself, and can save costs.
In short, it will be better than the era, do better products.
2, what is EMI?
Electromagnetic interference referred to as EMI, translation is electromagnetic interference. In fact, all electrical equipment will have electromagnetic interference.
Electromagnetic interference is synthetic words, we should consider "electromagnetic" and "interference" separately. It refers to the interference phenomenon generated after electromagnetic waves and electronic components, and there are two types of conductive interference and radiation interference. Conduct interference refers to a signal coupled (interference) to another by conductive medium to another electrical network. Radiation interference refers to the interference source to couple its signal to another (interfere) to another electrical network, in high-speed PCB and system design, high-frequency signal line, integrated circuit pins, various type connector, etc. may become antenna Features radiation interference sources that emit electromagnetic waves and affect other systems or other subsystems within the system.
For a better than the side, EMI is a naughty child, likes to play with the surrounding children, sometimes the skin, the child is bullied, then the harmonious environment (EMC) we want is destroyed.
3, what is EMS?
The electromagnetic wave will function with electronic components, generating interference, referred to as EMS (ElectromagNetic Susceptibility). For example, "snowflakes" on the TV fluorescent screen indicates that the received signal is electromagnetic interference.
Electromagnetic compatibility requires that the sensor has an electromagnetic interference in the environment to have a certain degree of immunity, i.e., electromagnetic sensitivity is EMS.
EMS is like a quiet child. It's just a little bit of small stones, and I didn't happen to do anything; I was more scratched by the big stone, but I have to cry, it is no longer quiet.
Processing EMS from three strokes can be taken!
First, we must understand the characteristics of the source of interference, and suppress the source of interference! In order to, instantaneous voltage, climbing the time, falling time, internal resistance, the characteristics of the source generator.
Second, we must know the propagation path of the interference source and cut off the dissembly of the source of the source! We know the characteristics and paths of the interference source, and also adopt the idea of EMI rectification!
Third, we must improve the anti-interference performance of sensitive devices. We all know that short board theory, the same, the sensitive components are the short board of EMS, first to get sensitive components
In summary, in EMS rectification, we must first have a clear idea, combined with circuit foundation, Layout, from the principle combination of actual comprehensive processing!
4, EMC three laws
Regularity 1: The earlring the EMC, the sooner, the smaller the cost, the better the effect (EMC cost ratio].
EMC design is performed in the new product development stage, and it is better to save the product EMC test. The cost can be greatly saved. The efficiency can be greatly improved; in turn, the efficiency will greatly reduce, the cost will greatly increase.
Experience tells us that EMC design is performed while functional design, to the model, the prototype is complete, and it is the most cost-effective and most economical. On the contrary, the product development phase does not consider EMC. After investment, it has been found to improve the EMC, but the technical brings are very difficult, and the rework must bring cost and time, even because of structural design, PCB design Defects, unable to implement improvement, resulting in products that the products cannot be listed.
Law 2: The larger the high frequency current loop area S, the more severe EMI radiation.
The high frequency signal current flows through the smallest path inductance. When the frequency is high, general trace electrical resistance is greater than the resistance, and the connection to the high frequency signal is inductive, and the series inductance causes radiation. Most electromagnetic radiation is generated by the high-frequency current loop on the EUT measurement device, the worst case is the antenna form of open circuit. The corresponding processing method is to reduce, decrease the connection, reduce the high-frequency current circuit area, and minimize an antenna for any abnormal operation, such as discontinuous wiring or an antenna effect is too long.
Reducing the most important task of radiation harassment or improving radio frequency radiation anti-interference ability is to try to reduce the high frequency current loop area S.
Regular three: The higher the loop current frequency f, the more severe the radiation of EMI, and the electromagnetic radiation field has an increase in the proportion of the current frequency f.
The two most important ways to reduce radiation harassment or improve RF radiation anti-interference ability is to find ways to reduce the high-frequency current frequency f, that is, reduce the frequency of harassment electromagnetic waves.
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