What is the importance of electromagnetic compatibility testing?

The concept of electromagnetic compatibility

The so-called compatibility of electronic products actually refers to whether the electronic product itself can work normally in the working environment, and at the same time, it will not cause interference with other electronic products in the environment. During normal operation, the electromagnetic interference generated by it will not interfere with other electronic equipment in its working environment, affect their normal operation, cause damage and cause the impact to be maintained within a certain value range (that is, to other electronic devices). The limit of the influence caused by the equipment); on the other hand, the electronic product itself must have a certain degree of anti-interference ability to the working environment, and will not be affected by the electromagnetic interference generated by other electronic equipment in the working environment. Normal work or cause a certain degree of damage, which means that electronic products should have electromagnetic sensitivity capabilities.

The important role of electromagnetic compatibility

With the continuous recognition of electromagnetic compatibility, the importance of electromagnetic compatibility has gradually increased. The continuous development of science and technology has expanded the field of electromagnetic compatibility. Now the impact of electromagnetic compatibility is not only the electronic product equipment itself. As the internal structure of the electronic product itself has developed more and more compact and complex, the electromagnetic compatibility problem is also It is becoming more and more important. For example, due to electromagnetic interference, the radio cannot listen to the broadcast, the data of some electronic equipment is lost in the transmission process, some medical electronic equipment works abnormally, triggers the detonating device to explode, and a certain control function of the industrial process completely fails. Etc., electromagnetic interference or the radiation produced by it can also cause some subtle changes in the organism itself and produce certain effects. Because of these interference and interference electromagnetic problems, it is extremely important to study the electromagnetic compatibility of electronic products.

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The necessity of electromagnetic compatibility testing

1. For the reliability of electronic equipment

Electromagnetic compatibility refers to the ability of electronic equipment to work normally in an electromagnetic environment. Electromagnetic interference is an electromagnetic change phenomenon that is harmful to the working performance of electronic equipment. Electromagnetic interference not only affects the normal operation of electronic equipment, but even causes damage to certain components in electronic equipment. Therefore, the electromagnetic compatibility technology of electronic equipment should be given full attention. It is necessary to pay attention to the normal operation of electronic equipment without the surrounding electromagnetic interference, but also to note that the electronic equipment itself does not produce electromagnetic interference to other surrounding equipment and affect the normal operation of other equipment.

2, for the international connection of electronic equipment

Recently, electromagnetic compatibility has evolved from post-processing to pre-analysis, prediction and design. Electromagnetic compatibility has become an important part of modern engineering design. The electromagnetic compatibility standard has been developed from a country to a region, making electromagnetic compatibility and safety and environmental adaptability equally important.

For example, the European Community incorporates the electromagnetic compatibility requirements of products into technical regulations, enforces Directive 89/336/EEC, stipulates that electrical and electronic products must comply with electromagnetic compatibility requirements from January 1, 1996, and affix the CE mark Only then can it be sold in the market. Products without CE are not allowed to go on the market, and those that do not meet the requirements of the EMC directive will be ordered to withdraw from the market, and those who continue to violate them will be subject to heavy penalties. At present, the United States, Canada, Japan, Australia and other countries have issued corresponding regulations.

In order to be in line with international standards, the Ministry of Foreign Affairs of the People's Republic of my country and the State Entry-Exit Inspection Bureau have implemented mandatory electromagnetic compatibility tests on personal computers, monitors, printers, switching power supplies, televisions and audio equipment since January 1999. The State Bureau of Technical Supervision has stipulated that since October 2002, sound and television broadcasting equipment, information technology equipment, household appliances, power tools, power supplies, lighting appliances, electric ignition drives, financial settlement electronic equipment, security electronic products and low-voltage electrical appliances Implementation of mandatory electromagnetic compatibility.

3. For the safety of people and some special materials

The electromagnetic wave is inductively coupled with the control circuit of the electric explosive device, and the interference current formed may cause the explosion of the electric explosive device. Therefore, GJB786 stipulates that the electromagnetic interference induced current and voltage on the wire of the electric detonator must be less than 15% of the non-igniting current and voltage. In addition, various fuels may burn and explode under the action of strong electromagnetic fields (direct irradiation, electric sparks, electrostatic discharge); electromagnetic energy can produce harmful physiological effects through physical and chemical effects on human tissues. Therefore, for the safety of human body and some special materials, GJB786 also stipulates that the average power density of continuous wave of electromagnetic radiation of electronic equipment is not allowed to exceed 4mW/cm2, and the average power density of pulse wave is not allowed to exceed 2mW/cm2.

4. For the needs of present and future wars

The electromagnetic pulse generated during a nuclear explosion radiates outward at the speed of light. The electric field strength can reach 105V/m, the magnetic field strength can reach 260A/m, the pulse width is on the order of 20ns, and the frequency at the peak of the electromagnetic pulse is 105Hz. When this kind of electromagnetic pulse acts on electronic equipment, the lighter ones will cause the performance of the electronic equipment to deteriorate, and the heavy ones will cause damage to the circuit components.

Especially in today's and future wars, both the electromagnetic pulse bombs that have been used and the high-power microwave weapons being developed have similar electromagnetic pulse radiation generated during nuclear explosions, which will pose a fatal threat to electronic equipment. The electromagnetic compatibility can provide basic technical guidance for countering this threat.

In daily life, some possible harms caused by electromagnetic interference:

① Interfere with TV watching and radio listening.

②Data loss in the process of digital system and data transmission.

③ Destruction of normal operation at the equipment, sub-system or system level.

④Medical electronic equipment (such as medical monitors, cardiac pacemakers, etc.) malfunctions.

⑤ The operation of the automated microprocessor control system (for example, the brake system of the car, the anti-collision airbag protection system) is out of control.

⑥ The navigation system is malfunctioning.

⑦ Unintentional explosion of the initiating device.

⑧Invalidation of industrial process control functions (for example: petroleum or chemical industry).

In addition, strong electric fields can also affect living organisms, and so on. It can be seen that the deterioration of the electromagnetic environment will lead to many consequences. Carrying out electromagnetic compatibility research, strengthening electromagnetic compatibility management, reducing electromagnetic interference, and avoiding electromagnetic interference are the top priorities.

In order to make the product meet the corresponding electromagnetic compatibility standards before it becomes a commodity, the necessary electromagnetic compatibility testing during the development process will greatly benefit the stability of the product's own performance and the improvement of quality, and it can save costs. Therefore, high-performance shielded computer rooms, EMC anechoic chambers and related electromagnetic compatibility test instruments have become essential equipment for electronic product development companies and manufacturers, and are also important signs of the company's R&D strength and testing level.

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Electromagnetic compatibility detection technology analysis

1, power supply electromagnetic compatibility detection

Analysis of electromagnetic compatibility detection technology on the power supply can make its control ability get better performance detection. When the power supply is interfered by electromagnetic or other electronic equipment in its working environment, see whether it will be damaged or performance degradation. The test item is the surge voltage immunity. This test method is mainly for the power cord. Apply the voltage of the surge waveform, and apply the same waveform voltage to the shell of the power cord, so that it can be seen whether the power cord will be destroyed when it is interfered, and whether it will also be damaged under normal working conditions with a shell. The working condition is bad or destroyed due to interference. Once the power cord is instantly broken down, it indicates that the filter model in the circuit device does not match or the input filter withstand capability is insufficient, or it may be that the filter has not been added to the electronic product.

2, radiation detection

This kind of test needs to know whether electronic products produce electromagnetic radiation during normal operation, or whether the electromagnetic radiation produced will affect or harm humans or other electronic equipment in the working environment. The equipment used for detection is relatively simple and a safer way. Use the radio on the AM channel to distinguish the noise emitted by the electromagnetic interference radio. This method can perform related testing on mobile phones and computers. When testing the display of the computer, the limit of 12V/m stipulated by the state must not be exceeded.

3, external magnetic interference detection

This test is mainly to understand whether the produced electronic products have a certain degree of anti-electromagnetic interference ability and whether they will be affected or even damaged under a certain degree of electromagnetic interference. It is tested and analyzed through the radiation generated by radio frequency electromagnetic field interference. The general method of testing is to place electronic products in a dark space and keep them in normal working conditions, and then interfere with them to a certain degree. This interference requires Within the range that the electronic product can withstand, and ensure that the interference can continue for a period of time, observe whether the electronic product has changed during the period of the interference and whether it is within the range of normal working conditions. If there is a problem during the period, the product design should be appropriately modified, and the important components or more sensitive components in the electronic product should be effectively isolated and effective anti-interference measures should be taken.

4. Current status of electromagnetic compatibility technology development

Since the 1960s, modern electronic science and technology has developed in terms of high frequency, high speed, high sensitivity, high installation density, high integration, and high reliability. Its application range has become wider and wider, and it has penetrated into every corner of society. Therefore, developed countries A lot of manpower and material resources have been invested in EMC research. The study of electromagnetic compatibility started relatively late in our country. As early as the 1980s, developed Western countries had issued mandatory laws and regulations on the electromagnetic compatibility of electrical equipment. Any electrical equipment must meet the requirements of relevant laws and regulations. To be put on the market, it is only allowed to sell on the market after obtaining a certificate.

A few years ago, my country’s electrical products did not make specific requirements for electromagnetic compatibility indicators, and relevant laws and regulations are still being formulated. Domestic product developers have not yet understood the concept of electromagnetic compatibility. Many products are being designed and developed. At this stage, the issue of electromagnetic compatibility was not considered at all, and coupled with the lack of understanding of foreign electromagnetic compatibility standards, the products developed could not pass the compulsory electromagnetic compatibility test abroad, and the products could not be put on foreign markets. The products designed and developed need to be sent overseas for electromagnetic compatibility testing, constantly modified and tested continuously. Many detours were taken, a lot of manpower and material resources were wasted, precious time was wasted, and many business opportunities were even missed.

With my country’s entry into the WTO, electromagnetic compatibility has received more and more attention in my country. The Chinese government has formulated relatively complete standards and corresponding implementation rules, promoted domestic electromagnetic compatibility testing and research from multiple channels, and carried out various Various training activities centered on electromagnetic compatibility design, development, testing, etc., enable product developers to understand and understand the theory of electromagnetic compatibility, and to a certain extent promote the implementation of this technology.

Application of electromagnetic compatibility technology

1. Electromagnetic compatibility control technology

Electromagnetic compatibility control is a system engineering, which should be fully considered and implemented at all stages of equipment and system design, development, production, use and maintenance. Scientific and advanced electromagnetic compatibility engineering management is an important part of effective control technology. Measures to suppress interference such as shielding, filtering, reasonable grounding, and reasonable layout are all very effective and are widely used in engineering practice. However, with the integration and synthesis of electronic systems, the application of the above measures will often conflict with cost, quality, and functional requirements. We must weigh the pros and cons to develop reasonable measures to meet the electromagnetic compatibility requirements. Another example is the emergence of new conductive and shielding materials and process methods, which have brought new measures to electromagnetic compatibility control technology. It can be seen that electromagnetic compatibility control technology has always been an active research topic in electromagnetic compatibility science.

Electromagnetic compatibility control strategies and control technology solutions can be divided into the following categories:

(1) Transmission channel suppression: specific methods include filtering, shielding, overlapping, grounding, and wiring.

(2) Spatial separation: location control, natural terrain isolation, azimuth control, electric field vector direction control. (3) Time separation: time sharing criteria, radar pulse synchronization, active time separation, passive time separation. (4) Frequency management: frequency control, filtering, frequency modulation, digital transmission, photoelectric conversion. (5) Electrical isolation: transformer isolation, photoelectric isolation, relay isolation, DC/DC conversion.

2, electromagnetic compatibility test technology

The use of electromagnetic compatibility testing technology in my country mostly started around the 1960s. At that time, the laboratory conditions were poor and the measurement equipment was mostly self-developed simple measurement equipment, and the measurement methods were relatively backward. In 1966, the shipbuilding industry took the lead and formulated its own industry measurement standard JB-854-66 "Measurement Methods and Allowable Values of Industrial Radio Interference Terminal Voltage of Marine Electrical Equipment." Compared with other fields, the electromagnetic compatibility field relies more on measurement, and electromagnetic compatibility measurement has strict requirements on test conditions. Therefore, with the application and transformation of international electromagnetic compatibility standards, my country's high-standard laboratories have been built one after another, and the technical team has continued to expand, bringing opportunities and conditions for the development of electromagnetic compatibility test technology.