System function test, after meeting the on-site function needs, conduct electromagnetic compatibility test. Electromagnetic compatibility test is prone to problems such as static electricity, group pulse, surge, radio frequency field conduction, etc.
01Static immunity test
Participated in the electrostatic immunity test of several projects, and have a certain understanding of static electricity. Static electricity is divided into contact discharge and air discharge. Static electricity is an accumulated high voltage. When it touches the metal shell of the device, it will be discharged instantly, which will affect the normal operation of electronic equipment, and may cause equipment failure or restart. This is not allowed on occasion.
Static electricity will affect the display effect, and the display may flicker or black screen, which will affect the normal display and operation. Static electricity may also cause the CPU to work abnormally, and program crashes or restarts.
If the relevant design of electromagnetic compatibility is adopted in the detailed design stage of the product, there is no need to worry too much about the static electricity test. Through the design, the accumulated charge of static electricity can be discharged well and the normal operation of the system will not be affected.
02Immunity detection of electrical fast transient pulse group
Electrical fast transient pulse group is a series of high-frequency and high-voltage transient pulses applied to the equipment, and observe whether the equipment is affected by it. The main method of protecting group pulses is to "drain" and "block". "Drain" is to provide a venting circuit. Before the interference enters the system, it is vented to the ground. "It is to filter the group pulses in the equipment and add a magnetic ring, the effect is obvious, the effect of the closed magnetic ring is better than the magnetic ring buckle, and the magnetic ring can also be added to the board level and fixed in the printed board. Make the equipment more reliable.
Adding magnetic rings to both ends of the power line, signal line, and communication line can protect against group pulse interference.
03Lightning surge detection
Lightning surge mainly includes two aspects, one is power supply lightning protection, and the other is signal lightning protection.
The power supply lightning protection is mainly aimed at the system level. The system level design should be designed in accordance with the three-level lightning protection design. The power supply lightning protection (such as OBO's V20-C/3-PH 385) is set at the main power input end, which can be used to protect the system. The power supply is protected at the first level. After the power supply is protected from lightning, the power supply enters the isolation transformer. The isolation transformer can better protect the electromagnetic interference signal and restrain its influence on the system. After entering the UPS, the UPS can filter out a part of the interference signal, so that the power supply enters the system equipment. The power supply is a pure power supply, which can make the system work better and more reliable.
Signal lightning protection is to protect the signal path of the system. It mainly involves board-level design. In the board-level design, lightning protection devices are added, such as gas discharge tubes, and TVS bleeder circuits are added. When there is a large current, it passes through the supporting resistor and TVS and gas discharge tubes are discharged to protect the subsequent 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, issue instructions normally, and work normally. The other is to design a wider signal range. When the signal fluctuates normally, the system works normally.
04Immunity detection of radio frequency field induction conduction
The radiation sensing test may affect the display signal, acquisition drive, etc., may cause the display to flicker or black screen, affect the operation of the device, may cause the acquisition and drive to work abnormally, collect the required signal, and cannot drive the field device.
The radio frequency test is to interfere with the signal line and power supply in the frequency range of 0.15k to 80M, and the level 3 intensity is 10V/m.
The principle of radiation protection is to do a good job of shielding the power supply and signal lines, the shielding layer is well grounded, and the appropriate frequency is selected for filtering to filter out interference.
05Radiation emission detection, radio frequency field radiation immunity detection
The test is mainly to test the anti-RF signal and overall shielding performance of the system. As long as the system is well shielded and the system ground is well grounded, the system can pass the test.
Through the relevant electromagnetic compatibility test, the product can be brought to the market for trial operation, and the problems arising during the trial operation will be summarized in preparation for product improvement.
Electronic products meet the relevant electromagnetic compatibility test standards. Only after passing the test can they be put on the market, and users can use it with confidence, greatly reducing accidents caused by electromagnetic interference, and playing a positive role in the benefit of enterprises and the promotion of products.