The importance of electronic products passing the ELECTROMAGNETIC compatibility test

EMC test

After the system test reaches the site function, the electromagnetic compatibility test shall be conducted. The key of EMC test is electrostatic discharge, electric fast transient pulse group, lightning surge, RF field transmission, etc

1. Electrostatic discharge immunity EMC test

Participated in the static electricity anti-interference test of several projects, and had a certain understanding of static electricity. Static electricity is divided into touch discharge and air discharge. Static electricity is a kind of accumulated high voltage. When it comes into contact with the plastic shell of the machine, it will discharge immediately, which will lead to the normal operation of electronic products, and may cause mechanical failure or restart. It is not allowed in places with better safety regulations.

Static electricity will affect the display effect, and may cause the meter to power on or crash, endangering the normal display and operation. Static electricity may also cause the CPU to work abnormally, the program to get stuck or restart.

If the design related to electromagnetic compatibility is selected in the detailed design of the product, there is no need to worry too much about the electrostatic experiment. According to the design, the charge accumulated by static electricity will be better discharged and will not affect the normal operation of the system.

2. EMC test of electrical fast transient pulse group immunity

Electrical fast transient pulse group is to add a series of high-frequency and high-voltage transient pulses to the equipment to observe whether the equipment is damaged. The key method to protect the group pulse is "unblock" and "block". "unblock" is to supply the discharge circuit, which is to affect the discharge to the ground before entering the system. The better shielding layer is grounded, which can discharge most of the dynamic effects. "block" is to filter the group pulse outside the equipment, improve the magnetic ring, which has a significant effect. The effect of closing the magnetic ring is better than that of the magnetic ring. It can also add the magnetic ring to the board level and fix it in the printed board to make the equipment more reliable.

The magnetic rings on both sides of the power line, power line and communication line can protect the group pulse interference.

3. Lightning surge EMC test

Lightning surge mainly includes power lightning protection and signal lightning protection.

The power supply lightning protection is mainly used at the system level. The system level design is set according to the three-level lightning protection device. The power supply lightning protection (such as V20-C/3-PH385 of OBO company) is set at the main power supply inlet to provide the first-level protection for the system power supply. After lightning protection of the power supply, enter the isolation transformer. The isolation transformer can better protect the interference signal and suppress its impact on the system. Then enter UPS, which can filter some electromagnetic interference, and then enter the system equipment. Power supply is a pure power supply, which can make the system stronger and more reliable.

Design example of system power supply

Signal lightning protection is the protection of system signal channel, which mainly involves the lightning protection device TVS in board-level design, gas discharge tube and other board-level design. When there is a large current, the subsequent circuit can be protected according to the matching resistance and the discharge of TVS gas discharge tube. Then the signal is photoelectrically isolated, and then enters the system. The system can collect stable signals to make the system analyze normally, send commands normally and operate normally. On the other hand, when the signal fluctuates normally, the system operates normally, and a wide signal category is designed.

4. Immunity EMC test of frequency field induction transmission

Radioactive test may indicate signal. The influence of collection and promotion may indicate flicker or death, endanger the operation of equipment, make the collection and promotion work abnormal, unable to collect necessary signals, and unable to promote field equipment.

The frequency emission test is that 0.15k~80M power line is in the frequency range. The power intensity is 10V/m

The principle of radiation protection is power supply. The power line is well shielded, and the shielding layer is well grounded. Selecting the appropriate frequency for filtering will affect the filtering.

5. Radiated emission and field radiation EMC test

Detection is usually to detect the anti-RF signal and overall shielding characteristics of the system. As long as the system is well shielded and grounded, the system can pass the detection.

According to the relevant electromagnetic compatibility test, the product can enter the market for trial operation, summarize the problems in trial operation, and improve the product.

Electronic equipment shall comply with relevant EMC test specifications. Only through testing can we enter the market, and customers can use it easily, reduce accidents caused by interference signals, and benefit enterprises. Product promotion plays a positive role.