What kinds of electromagnetic compatibility tests are there?
System function test, after meeting the needs of the field function, carry out electromagnetic compatibility test, electromagnetic compatibility test is easy to cause problems are static electricity, group pulse, surge, RF field conduction, etc.
1. Radiation emission detection, RF field radiation immunity detection
This test is mainly to test the system's anti-RF signal and overall shielding performance. As long as the system is well shielded, the system ground is well grounded and the system can pass the test.
Through the relevant electromagnetic compatibility test, the product can be put on the market, the test run is carried out, and the problems occurring in the trial run are summarized for the improvement of the product.
The electronic products meet the relevant electromagnetic compatibility test standards, and can be pushed to the market through testing, so that users can use them with confidence, greatly reducing accidents caused by electromagnetic interference, and playing a positive role in the efficiency of enterprises and the promotion of products.
2. Electrical fast transient pulse group immunity detection
An electrical fast transient burst is a series of high frequency, high voltage transient pulses applied to the device to see if the device is affected. The main method of protection group pulse is “sparing” and “blocking”. “Sparging” means providing bleed circuit. It is venting to the earth before entering the system. Good shielding layer is grounded, and it can vent a part of dynamic interference. "It is to filter the group pulse out of the device, increase the magnetic ring, the effect is obvious, the effect of closing the magnetic ring is better than that of the magnetic ring, or the magnetic ring can be added to the board level and fixed in the printed board. Make the device more reliable.
Adding a magnetic ring to both ends of the power line, signal line, and communication line can protect the group pulse interference.
3, lightning surge detection
Lightning surges mainly include two aspects, one is power supply lightning protection, and the other is signal lightning protection.
The lightning protection of the power supply is mainly for the system level. The system level design should be designed according to the three-level lightning protection design. The main power input terminal is set to the power supply lightning protection (such as OBO's V20-C/3-PH 385), which can be used for the system. The power supply performs the first-level protection. After the power supply is lightning-proof, it enters the isolation transformer. The isolation transformer can better protect the electromagnetic interference signal and suppress its influence on the system. After entering the UPS, the UPS can filter out some of the interference signals, so that the power supply enters the system equipment again. The power supply is a pure power source, which can make the system work better and more reliably.
An example of a system power supply design.
Signal lightning protection is to protect the signal path of the system. It mainly involves the board level design. In the board level design, lightning protection devices, such as gas discharge tubes, are added to increase the TVS bleeder circuit. When there is a large current, the matching resistor and TVS and gas discharge tubes are vented to protect the rear stage circuit. Then the signal is photoelectrically isolated and then enters the system. The system can collect a stable signal, so that the system can analyze and judge normally, and the command is issued normally and works normally. On the other hand, the signal range is designed to be wide, and the system works normally when the signal fluctuates normally.
4, static immunity test
Participated in the static immunity test of several projects, and had a certain understanding of static electricity. Static electricity is divided into contact discharge and air discharge. Static electricity is the accumulated high voltage. When it comes into contact with the metal casing of the equipment, it will discharge instantaneously, which will affect the normal operation of the electronic equipment, may cause equipment failure or restart, and have better safety requirements. This is not allowed on occasions.
Static electricity can affect the display, and flashing or black screens may appear, affecting normal display and operation. Static electricity can also cause the CPU to work abnormally, and the program may crash or restart.
If the electromagnetic compatibility related design is adopted in the detailed design stage of the product, it is not necessary to worry too much about the electrostatic test. By design, the charge accumulated by the static electricity is well discharged, and the normal operation of the system is not affected.
5. Immunity detection of RF field induced conduction
The sensation test may affect the display signal, acquisition drive, etc., which may cause the display to flicker or black screen, affecting the operation of the device, may cause the acquisition drive to work abnormally, and may not collect the required signal, and cannot drive the field device.
The RF test is to interfere with the signal line and power supply in the frequency range of 0.15k~80M, and the intensity of the third level is 10V/m.
The principle of radiation protection is to shield the power supply and signal lines, and the shielding layer is well grounded. Select the appropriate frequency for filtering and filter the interference.
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