1.Basic overview of EMC
Electromagnetic compatibility EMC (Electromagnetic Compatibility) refers to the ability of a device or system to operate in accordance with requirements in its electromagnetic environment without generating unbearable electromagnetic interference to any equipment in its environment.
Therefore, EMC includes two requirements: on the one hand, it is required that the electromagnetic interference of the sensor in the environment during normal operation cannot exceed a certain limit, that is, EMI; on the other hand, the sensor is required to have a certain degree of resistance to electromagnetic interference in the environment Disturbance, that is, EMS.
In simple terms: EMC = EMI + EMS. Electronic products have a certain anti-interference ability (EMS). When you work, you interfere with me, I interfere with you (EMI), but everyone can still live in peace (EMC).
It's as if you have twins, one naughty (EMI) and one quiet (EMS), but two children can still play happily together (EMC) every day.
So why do we do something that doesn't seem to have much value in EMC?
The official gave us this answer: It means that the signal and interference can coexist without damaging the information contained in the signal. The purpose of studying electromagnetic compatibility is to ensure that electrical components or devices can work normally in an electromagnetic environment, and to study the mechanism and preventive measures of electromagnetic waves that harm social production activities and human health.
In order to improve the reliability of the normal operation of electronic equipment before making the product into a commodity, and to keep it in line with international standards, and to ensure the safety of people and certain special materials, more and more electronics companies attach importance to EMC and carry out necessary Electromagnetic compatibility testing can greatly contribute to the stability of the product's own performance and quality improvement, and can save costs.
In short, follow the development of the times and make better products.
2. What is EMI?
Electromagnetic interference (Electromagnetic Interference for short) is an electromagnetic interference. In fact, all electrical equipment will have electromagnetic interference.
Electromagnetic interference is a compound word, we should consider "electromagnetic" and "interference" separately. It refers to the interference phenomenon caused by the interaction between electromagnetic waves and electronic components. There are two types of conducted interference and radiated interference. Conducted interference refers to the coupling (interference) of signals on one electrical network to another electrical network through a conductive medium. Radiated interference refers to the interference source coupling (interfering) its signal to another electrical network through space. In high-speed PCB and system design, high-frequency signal lines, integrated circuit pins, various connectors, etc. may become antennas. The characteristic radiation interference source can emit electromagnetic waves and affect the normal operation of other systems or other subsystems in this system.
For example, EMI is a naughty child. He likes playing with and surrounding children. Sometimes he gets too skinny and the surrounding children are bullied and crying. Then the harmonious environment (EMC) we want is destroyed.
3. What is EMS?
Electromagnetic waves interact with electronic components and cause interference, which is called EMS (Electromagnetic Susceptibility). For example, the "snowflake" common on TV screens indicates that the received signal is interfered by electromagnetic waves.
The electromagnetic compatibility requires the sensor to have a certain degree of immunity to electromagnetic interference in the environment, that is, the electromagnetic sensitivity is EMS.
EMS is like a quiet child. I was stunned by the small stones for a while, but nothing happened; I was stunned by the large stones, and started crying, no longer quiet.
Handling EMS can be grasped from three moves!
First, we need to understand the characteristics of interference sources and suppress them! To surge, the instantaneous voltage, climb time, fall time, internal resistance, that is, the characteristics of the interference source generator.
Second, we need to know the propagation path of the interference source and cut off the propagation interference path of the interference source! We know the characteristics and paths of interference sources, and we also adopt EMI rectification ideas to deal with them!
Third, we need to improve the anti-interference performance of sensitive devices. We all know the short board theory, and the same is true when dealing with EMS.
In summary, in the EMS rectification, we must first have a clear idea, combined with the circuit foundation, layout, and comprehensive treatment from the principle and the actual!
4.Three rules of EMC
Rule 1: The sooner EMC problems are considered and resolved sooner, the lower the cost and the better the effect (EMC cost-efficiency ratio relationship).
EMC design is carried out during the development of new products. Compared with when the product EMC test fails, improvements can be made. Costs can be greatly saved and efficiency can be greatly improved. Conversely, efficiency will be greatly reduced and costs will be greatly increased.
Experience tells us that it is the most time-saving and most economical to perform EMC design at the same time as functional design, and pass EMC testing to the prototype and prototype. On the contrary, EMC is not considered during the product development stage, and it is improved after it is found to be unqualified after being put into operation. Defects, unable to implement improvement measures, resulting in products not being marketed.
Rule 2: The larger the area S of the high-frequency current loop, the more severe the EMI radiation.
High-frequency signal current flows through the smallest path of the inductor. When the frequency is high, the reactance of the trace is generally greater than the resistance. The connection to the high-frequency signal is the inductance, and the series inductance causes radiation. Most of the electromagnetic radiation is generated by the high-frequency current loop on the EUT device under test. The worst case is an open-circuit antenna. The corresponding treatment method is to reduce and shorten the connection, reduce the high-frequency current loop area, and try to eliminate any antennas required for normal work, such as discontinuous wiring or excessively long pins of components with antenna effect.
One of the most important tasks to reduce radiated disturbance or improve the anti-interference ability of radio frequency radiation is to find ways to reduce the high-frequency current loop area S.
Rule three: The higher the loop current frequency f, the more severe the EMI radiation caused, and the electromagnetic radiation field strength increases in proportion to the square of the current frequency f.
The second most important way to reduce radiated disturbance or improve the anti-interference ability of radio frequency radiation is to find ways to reduce the high-frequency current frequency f of the disturbance source, that is, reduce the frequency f of the disturbance electromagnetic wave.
The above are some of my rough opinions on EMC. Welcome to review and correct the technical bulls. Thank you!
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