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What are the steps of EMC rectification?

2025-01-18 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > Internet Technology >

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What are the steps of EMC rectification? in view of this problem, this article introduces the corresponding analysis and solutions in detail, hoping to help more partners who want to solve this problem to find a more simple and feasible way.

EMC rectification and reform

Electromagnetic compatibility EMC (Electro Magnetic Compatibility) refers to the ability that the equipment or system meets the requirements in its electromagnetic environment and does not cause unbearable electromagnetic interference to any equipment in its environment. Therefore, EMC includes two requirements: on the one hand, it means that the electromagnetic interference caused by the equipment to the environment can not exceed a certain limit; on the other hand, it means that the apparatus has a certain degree of immunity to the electromagnetic interference in the environment, that is, electromagnetic sensitivity.

The interference between all kinds of running electronic equipment is mainly related to each other and affects each other by electromagnetic conduction, electromagnetic induction and electromagnetic radiation, which will cause interference, influence and harm to the operating equipment and personnel under certain conditions. There are actually a lot of articles about rectification and reform in the specific field of EMC.

EMC rectification and reform

The specific ideas are shown in the following figure:

The first step: the methods to find and confirm the radiation source are exclusion method, frequency point search method of spectrum analyzer, and element natural frequency analysis method. The elimination method includes wire extraction method, partition work elimination method, human body touch method with low voltage and small current, and regional shielding exclusion method. Element natural frequency analysis method refers to the fixed frequency and frequency doubling frequency analysis and classification of some components, such as crystal oscillator and DDR and other components whose working frequencies are fixed.

Step 2: filtering is generally divided into capacitive filtering, RC filtering and LC filtering.

The third step: the methods of absorbing electromagnetic waves include circuit series magnetic beads method, magnetic ring piercing method and wave absorbing material method. When using the method of absorbing electromagnetic wave, we should pay special attention to: the frequency of radiation exceeding the standard electromagnetic wave must be within the frequency range of the electromagnetic wave absorbed by the absorbing material used, otherwise the absorbing method will fail.

Step 4: the grounding method is generally divided into single-point grounding method and multi-point grounding method.

Step 5: shielding methods generally include shielding method with shielding cover, shell shielding method and PCB layout shielding method.

The sixth step: the energy dispersion method means that the control software of some measured objects can use the technology of frequency spreading and frequency hopping to broaden the frequency band and jump the frequency to disperse the energy of the frequency band, so as to reduce the energy added to the single point frequency, that is, to reduce the intensity of the electromagnetic wave radiated by the single point frequency. Therefore, this method will have a significant effect on the over-standard frequency radiation of the spike-shaped waveform, but not on the envelope-shaped waveform.

This six-step method of EMC rectification is more suitable for the rectification of common electronic equipment. But the above six methods, in fact, Tianzongjun believes that although they help to improve the efficiency of EMC radiation rectification, save cycles, and quickly pass the EMC test, they are not a fundamental solution to the EMC problem. The EMC problem is best considered at the design side, rather than using some "encirclement, pursuit and interception" programs to meet emergencies afterwards.

EMC (Electromagnetic Compatibility) is what we often call electromagnetic compatibility technology. It contains the requirements of EMI and EMS, that is, under the common electromagnetic environment of the electrical device or system, it is neither affected by the electromagnetic environment nor interfered with the environment.

EMC rectification method

First of all, the products should be diagnosed according to the actual situation, and the sources of interference and the ways and ways of mutual interference should be analyzed. Then according to the results of the analysis, targeted rectification and reform.

Generally speaking, the main rectification methods are as follows

1. Weakening the interference source on the basis of finding the interference source, the interference source can be weakened within the allowable range. The methods of weakening the source are generally as follows:

A. Add a decoupling capacitor between the Vcc and GND of the IC. The capacity of the capacitor is between 0.01 μ F and 0.1 μ F. Pay attention to the lead wire of the capacitor during installation so that it is as short as possible.

B, add an attenuator while ensuring sensitivity and signal-to-noise ratio. For example, the crystal oscillator in VCD and DVD video players has a serious impact on electromagnetic compatibility, so reducing its amplitude is one of the feasible methods, but it is not the only solution.

C. another indirect way is to keep the signal line away from the source of interference.

2. Classification and arrangement of wires and cables in electronic equipment, wire-to-wire coupling is not only an important way, but also an important cause of interference, because the factor of frequency can be divided into high-frequency coupling and low-frequency coupling. Due to the different coupling methods, the rectification methods are also different, which are discussed below:

The main results are as follows: (1) low-frequency coupling refers to the case that the length of the wire is equal to or less than 16 wavelengths, and low-frequency coupling can be divided into electric field and magnetic field coupling.

The physical model of electric field coupling is capacitive coupling, so the main purpose of rectification is to reduce the distributed coupling capacitance or the amount of coupling.

A. Increasing the distance between circuits is the most effective way to reduce the distributed capacitance.

B, add a high conductivity shield, and make the shield single point grounding can effectively restrain the interference of low frequency electric field.

C. The additional filter can reduce the coupling between the two circuits.

D, reduce the input impedance, for example, the input impedance of the CMOS circuit is very high, and it is extremely sensitive to electric field interference, so it can connect a capacitor or a resistance with low resistance at the input within the allowable range.

The physical model of magnetic field coupling is inductive coupling, and its coupling is mainly through the distributed mutual inductance between lines, so the main method of rectification is to destroy or reduce the amount of coupling, generally speaking, the following methods can be adopted.

An append filter, pay attention to the input and output impedance and frequency response of the filter when appending the filter.

B reduce the loop area of the sensitive loop and the source loop, that is, make the signal line or current-carrying line close to or twist with its loop as far as possible.

C increase the distance between the two circuits in order to reduce the mutual inductance between lines to reduce the amount of coupling.

D if possible, make the sensitive circuit orthogonal or nearly orthogonal to the plane of the source loop to reduce the coupling between the two circuits.

E bandaging sensitive lines with high magnetic conductivity materials can effectively solve the problem of magnetic field interference, it is worth noting that to form a closed and magnetic circuit, efforts to reduce the magnetoresistance of the magnetic circuit will be more effective.

(2) High frequency coupling refers to the alignment longer than 1 to 4 wavelength, which will enhance the coupling due to the standing wave of voltage and current in the circuit, which can be solved by the following methods:

A, shorten the grounding wire as much as possible, and grounding with the shell adopts the way of surface contact as far as possible.

B, rearrange the input and output lines of the filter to prevent the coupling between the input and output lines and ensure that the filtering effect of the filter is not bad.

C. The shielding layer of shielded cable adopts multi-point grounding.

D. Connect the hanging pin of the connector to the ground potential to prevent its antenna effect.

3. Improve the ground wire system

The ideal ground wire is a physical entity with zero impedance and zero potential, which is not only the reference point of the signal, but also does not produce voltage drop when the current flows through it. In the specific electrical and electronic equipment, this ideal ground wire does not exist, when the current flows through the ground wire, it is bound to produce voltage drop. According to the interference formation mechanism in the ground wire, it can be summarized into the following two points: first, to reduce the low impedance and power feeder impedance. Second, the correct selection of grounding mode and barrier ground loop, according to the grounding mode can be divided into suspended ground, single-point grounding, multi-point grounding and hybrid grounding. If the interference of the sensitive line mainly comes from the external space or the shell of the system, it can be solved by suspended ground, but the suspended equipment is easy to produce electrostatic accumulation, and electrostatic discharge will occur when the charge reaches a certain level. therefore, the suspended ground is not suitable for general electronic equipment. Single-point grounding is suitable for low-frequency circuits. in order to prevent the ground potential difference between the points of power frequency current and other stray current on the signal ground wire, the signal ground wire is isolated from the power supply and safety ground wire. Single point grounding is mainly suitable for cases where the frequency is lower than 3MHz. Multi-point grounding is the only practical grounding method for high-frequency signals, which will show the characteristics of transmission lines at radio frequency. In order to make multi-point grounding effective, when the length of grounding conductor exceeds the maximum frequency of 1ppm 8 wavelength, multi-point grounding requires an equipotential grounding plane. Multi-point grounding is suitable for 300KHz or above. Hybrid grounding is suitable for electronic circuits with both high frequency and low frequency.

4. Shielding

Shielding is one of the important measures to improve the electromagnetic compatibility of electronic systems and electronic equipment. It can effectively restrain all kinds of electromagnetic interference transmitted through space. According to the mechanism, shielding can be divided into magnetic shielding, electric field shielding and electromagnetic shielding. The shielding of electric field should pay attention to the following points:

A. choose materials with high electrical conductivity and good grounding.

B, the correct choice of grounding location and reasonable shape, preferably the shield directly grounded. Magnetic shielding usually only refers to the shielding of DC or very low frequency magnetic field, its shielding effectiveness is far lower than electric field shielding and electromagnetic shielding, magnetic shielding is often the focus of engineering, magnetic shielding:

A. Ferromagnetic materials should be selected.

B, the magnetic shield should be far away from the magnetic components to prevent magnetic short circuit.

C. Double-layer shielding or even three-layer shielding can be used.

D. The opening on the upper side of the shield should pay attention to the direction of the opening, make the long side of the seam parallel to the magnetic flux flow direction as far as possible, and minimize the increase of the magnetic circuit length. Generally speaking, magnetic shielding does not need to be grounded, but it is better to ground in order to prevent electric field induction. When the electromagnetic field passes through the metal or the barrier which attenuates the electromagnetic field, it will be attenuated to a certain extent, that is, it will shield the electromagnetic field. In the actual rectification process, according to the specific needs, choose what kind of shield and shield shape, size, grounding mode and so on.

5. Change the wiring structure of the circuit board

Some frequency points are determined by the wiring distribution parameters on the circuit board, but the aforementioned method is not useful. This kind of rectification changes the circuit parameter structure by adding small inductance, capacitance and magnetic beads in the wiring. Move it to the frequency point with higher limit requirements. For this kind of interference, if you want to fundamentally solve its impact, it is necessary to rewire.

Summary: in short, the above methods are good for improving electromagnetic compatibility, but the most widely used methods are to change the ground wire structure and the classification and arrangement of wires and cables. these methods not only save costs, but also are the most effective rectification methods. Although shielding will increase the cost, its shielding effectiveness is sometimes unmatched by other methods. Therefore, in the actual rectification and reform, the main methods should be to change the structure of ground wire, the classification and arrangement of wires and cables and shielding, supplemented by other methods.

Three important laws in EMC Field and three elements of EMC problem

First, the three important laws of EMC

Rule 1. The law of EMC cost-effectiveness ratio: the earlier the EMC problem is considered and solved, the smaller the cost and the better the effect.

In the new product research and development stage to carry out EMC design, than wait until the product EMC test is unqualified to improve, the cost can be greatly saved, the efficiency can be greatly improved; otherwise, the efficiency will be greatly reduced and the cost will be greatly increased. Experience tells us that it is the most time-saving and most cost-effective to carry out EMC design at the same time of functional design and pass the EMC test when the template and prototype are completed. On the contrary, the product research and development stage does not consider EMC, after putting into production, it is found that EMC is unqualified before improvement, which not only brings great technical difficulty, but also rework will inevitably lead to a great waste of cost and time, and even due to structural design, PCB design defects, can not implement improvement measures, resulting in products can not be on the market.

II. Three elements of EMC problem

Switching power supply and digital equipment will produce strong radiation because of the rich high-frequency harmonics of pulse current and voltage. Electromagnetic interference includes radiant (high frequency) EMI and conductive (low frequency) EMI, that is, the problem of EMC is mainly caused by two ways: one is in the form of space electromagnetic wave interference, the other is in the form of conduction, in other words, the three elements of EMC problem are: electromagnetic interference source, coupling path, sensitive equipment. Radiation interference mainly interferes with the space electromagnetic environment in the form of electromagnetic waves through the shell and connection lines; conducted interference is to disturb the public power grid through the power line or affect the connected equipment through other terminals (such as radio frequency terminals, input terminals).

大佬总结的电磁兼容知识,EMC整改六步走,看完感觉太简单了点

Possible sources of disturbance for T and AV devices:

A) the FM receiver and TV receiver oscillate locally, and the fundamental and harmonics are generated by the high frequency head and the local oscillation circuit

B) switching pulse and high-order harmonics of switching power supply, square wave and high-frequency harmonics of synchronous signal, line and field signals and high-frequency harmonics generated by line-scanning imaging circuit.

C) all kinds of clock signals and high frequency harmonics needed for digital circuit operation, and their combinations, all kinds of clocks such as CPU chip working clock, decoder working clock, video synchronous clock, etc.

D) Square wave and high frequency harmonics of digital signal, high order harmonics produced by crystal oscillator, useless signals and stray signals caused by nonlinear circuit phenomena (nonlinear distortion, Intermodulation, saturation distortion, cut-off distortion), etc.

E) non-sinusoidal waveform, waveform burr, overshoot, ringing, parasitic frequency point in circuit design.

F) external disturbances to sensitive receptors through the coupling pathway include surges, fast pulse groups, static electricity, voltage sags, voltage changes and various electromagnetic fields.

Characteristics of electromagnetic disturbance:

The spectrum of ① unit pulse is the widest.

The low frequency content in the ② spectrum depends on the area of the pulse, and the high frequency component depends on the steepness of the front and rear edge of the pulse.

The oscillation level of ③ crystal must meet a certain amplitude before the digital circuit can work in a certain time sequence, so that the disturbance caused by crystal oscillator has the characteristics of covering bandwidth and high disturbance level.

When the polarization and directional characteristics of ④ transceiver antennas are the same, the radiation and reception of EMI are the most serious, and the larger the area of EMI transceiver antenna is, the greater the harm of EMI is.

⑤ harassment pathway: the combination of radiation, conduction, coupling and radiation, conduction and coupling.

The conducted disturbance of ⑥ power cord is mainly caused by common mode current.

The radiation disturbance of ⑦ is mainly caused by the loop formed by differential mode current.

True biography of a word, false biography of ten thousand books. We have a clear understanding of the three laws and three elements in EMC, which will make the EMC problem simple and regular. Understand the laws and communication elements of EMC, in fact, the methods and ideas to solve the EMC problem will be clear, as long as we interrupt one of the factors, the EMC problem will certainly be greatly improved.

The answer to the question about the steps of EMC rectification and reform is shared here. I hope the above content can be of some help to you. If you still have a lot of doubts to be solved, you can follow the industry information channel to learn more about it.

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