What are the causes of electromagnetic radiation disturbance?

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/ 2019-06-13 / News

radiative disturbance (RE) mainly refers to the phenomenon that energy is emitted from the source into space or energy in the form of electromagnetic waves in the form of electromagnetic waves. All electronic products have corresponding radiation harassment requirements.


The best way to suppress radiated harassment is to re-engineer the PCB design and re-design it, but we often find it in practice, such as the user at Moore Labs (MORLAB). When testing and finding that the radiation disturbance is unqualified, the products at this time are often designed and finalized in the final stage of waiting for the market. Re-modifying the PCB design work will not only increase the production cost, but also delay the product and miss the business opportunity. Therefore, it is of practical significance to study the suppression of radiation harassment in products. This article will take Moore's many years of EMC experience, using information technology products as an example to briefly introduce the test method of radiation disturbance and how to find the cause of failure and our common rectification countermeasures.


radiation disturbance test limit requirements


There may be differences depending on the specific requirements of the different products, but they can be summarized as follows:

频率

QP限值 (Class B)

参考标准

30MHz – 230MHz


230MHz – 1000MHz

40dBuV/m


47dBuV/m

EN 55022

频率

QP值 (Class B)

AV限值(Class B)

参考标准

1000MHz –3000M Hz


3000MHz –6000M Hz

70dBuV/m


74dBuV/m

50dBuV/m


54dBuV/m

EN 55022


General steps for radiation disturbance rectification


1. To understand the working characteristics of the product, try to know as much as possible about the current situation of excessive radiation harassment;

    

2 For the specific failure problem, understand the product circuit design principle, judge what type of over-standard according to the information provided by the customer, find out the source of the disturbance, and the oscillation signal required for the work;

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3.Analyze the circuit and use a near-field probe to probe to determine the source of the disturbance and its harassment path;

    

4. To ensure that the method is correct, take Necessary troubleshooting test and further confirmation of the problem;

    

5. Comprehensive analysis of the results to find the root cause of the harassment, then Measures can be taken to rectify. According to the severity of the excess, the source can be rectified or used to facilitate direct access from the harassment path (can be limited to 6dB);

    

6 Verification of the rectification effect, if the effect is not satisfactory, return to continue analysis to find the reason to change the rectification method, and the effect is better and more convenient and economical ideal method;

    

7. Summarize experience and record rectification methods;


How to find out the cause of radiation spurious harassment


In general, in most cases, you can use the exclusion method to find out the cause of radiation (especially if you don’t know much about the device). Happening). The specific analysis process is shown in the following table process:



Recommendations for cable and screening issues

1. Improvement of shielding performance of metal chassis

Improve the gap of the chassis, increase the number of the blocking parts on the joint surface and the flatness of the contact surface, adopt permanent seams, and use conductive pads to Improve contact performance in contact with the second; vents should use dust-proof panels, or use waveguide ventilators, keyboards should be used in compartments; printed boards and equipment internal wiring, etc., which may cause radiated disturbances, should be kept away from gaps or functions. The part of the hole,Or take a shielded remedy or re-layout.

2. Improvement of non-metallic chassis

Conductive spraying of the chassis, including the joint gap, and to ensure that the chassis has a conductive connection; for the part that produces or may generate radiation Take partial shielding and filter all the wires entering the shield or add an absorbing magnetic ring; rethink the layout of the board and minimize the loop of the signal and its return line.

3. Power cord problem

Install or replace the power line filter, pay attention to the installation position (can be installed in the inlet end of the power cord in the chassis) and the installation situation. Make sure that the filter housing and the chassis are well-connected and well grounded. For high-frequency filtering, consider setting the ferrite magnetic ring at the inlet of the power cable and replacing it with a shielded cable. For shielded cables, the shield is best with the chassis. Adopt 360 degree way.  

4. Signal line problem 

Set a ferrite ring on the signal line, or switch to a shielded cable and, if necessary, a ferrite ring ; filtering the signal line (common mode filtering),If necessary, change the connector to a filter array board or filter connector.

The above is based on the general information technology products (IT) to test the requirements of radiation disturbance, the source of the spurs and the corresponding method of finding. Shenzhen Moore Laboratory (MORLAB) has a wealth of practical testing experience in the field of EMC, and has a set of practical and effective analytical and problem-solving methods for the radiation harassment rectification strategy. We believe that our rectification experience will help our customers find the root cause of radiation harassment failure and help your product pass the radiation harassment test.


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