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Six steps to EMC EMC rectification

Electromagnetic Compatibility (EMC) refers to the ability of a device or system to operate satisfactorily in its electromagnetic environment without causing unbearable electromagnetic interference to any device in its environment. Therefore, EMC includes two requirements: on the one hand, it refers to that the electromagnetic interference generated by the equipment to the environment during normal operation cannot exceed a certain limit value; On the other hand, it refers to that the appliance has a certain degree of immunity to electromagnetic interference existing in the environment, namely, electromagnetic sensitivity.

The interference between various operating electronic devices is mainly related and affects each other in three ways: electromagnetic conduction, electromagnetic induction, and electromagnetic radiation. Under certain conditions, it can cause interference, impact, and harm to operating equipment and personnel. There are actually quite a few articles on rectification in specific EMC areas. This article summarizes the six step approach to EMC rectification done by predecessors for reference and learning by colleagues.

The six step method for EMC rectification is as follows: Step 1: find and confirm the radiation source, Step 2: filter, Step 3: absorb waves, Step 4: ground, Step 5: shield, and Step 6: energy dispersion method. The specific idea is shown in the following figure:



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Step 1: The methods for finding and confirming radiation sources include elimination method, frequency point search method of spectrum analyzer, and element natural frequency analysis method. Exclusion methods include wire pulling method, zoning work exclusion method, low voltage and low current human touch method, and area shielding exclusion method. The natural frequency analysis method of components refers to the analysis and classification method for the fixed frequency and frequency doubling frequency of some components, such as crystal oscillator and DDR, where the operating frequencies of components are fixed.

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

Step 3: The methods for absorbing electromagnetic waves include circuit series magnetic beads method, winding through magnetic rings method, and attaching absorbing materials method. When using the method of absorbing electromagnetic waves, special attention should be paid: the frequency of electromagnetic waves with excessive radiation must be within the frequency range of electromagnetic waves absorbed by the wave absorbing material used, otherwise the method of absorbing electromagnetic waves will fail.

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

Step 5: Generally speaking, shielding methods include shielding with a shield, shielding with a housing, and shielding with a PCB wiring layout.

Step 6: The energy dispersion method refers to the control software of some measured objects that can use techniques such as frequency spreading and frequency hopping to broaden the frequency bandwidth and frequency hopping rate of the frequency band where energy is concentrated, thereby reducing the energy attached to a single point frequency, which is to reduce the intensity of electromagnetic waves radiated by a single point frequency. Therefore, this method will have a significant effect on the excessive frequency radiation of spike and burr shaped waveforms, but not on the excessive frequency radiation of envelope shaped waveforms.

This six-step EMC rectification method is relatively suitable for the rectification of common electronic equipment. However, the above six methods actually believe that although they can help improve the efficiency of EMC radiation rectification, save cycles, and quickly pass EMC testing, they are not a fundamental solution to EMC problems. EMC's problems are ideally considered at the design side, rather than using some "catch up" solutions to deal with them afterwards.


keywords: EMC
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