Is there any way to rectify EMC?
1. Improve the grounding system.
The ideal ground is a zero-impedance, zero-potential physical entity that is not only the reference point for the signal, but also does not generate a voltage drop when current flows. In a specific electrical and electronic device, such an ideal ground line does not exist, and a voltage drop is inevitably generated when a current flows through the ground. According to this, the mechanism of interference formation in the ground line can be summarized as the following two points. First, reduce the low impedance and power supply line impedance. Second, the grounding method and the ground loop are correctly selected. According to the grounding method, there are suspended ground, single-point grounding, multi-point grounding, and mixed grounding. If the interference of the sensitive line mainly comes from the external space or the system casing, it can be solved by means of floating ground. However, the suspended device is prone to static electricity accumulation. When the charge reaches a certain level, electrostatic discharge will occur, so the suspension should not be used. For general electronic equipment. Single-point grounding is suitable for low-frequency circuits. To prevent power frequency current and other stray currents from generating ground potential difference between the points on the signal ground, the signal ground is isolated from the power supply and the safety ground. Point connection. Single point grounding is mainly suitable for frequencies below 3MHz. Multi-point grounding is the only practical grounding method for high-frequency signals. In the case of radio frequency, the characteristics of the transmission line are presented. To make the multi-point grounding effective, when the length of the grounding conductor exceeds the maximum frequency of 1/8 wavelength, multi-point grounding requires an equipotential ground plane. Multi-point grounding is suitable for above 300KHz. Hybrid grounding is suitable for use in electronic circuits where there are high frequencies and low frequencies.
2, change the wiring structure of the circuit board
Some frequency points are determined by the distribution parameters of the traces on the circuit board. It is not very useful by the above methods. Such rectification changes the circuit parameter structure by adding small inductance, capacitance and magnetic beads to the traces, so that it moves to The limit requires a higher frequency point. For such interference, in order to fundamentally solve its impact, it is necessary to re-route.
Shielding is one of the important measures to improve the electromagnetic compatibility of electronic systems and electronic devices. It can effectively suppress various electromagnetic interferences transmitted through space. Shielding can be divided into magnetic field shielding and electric field shielding and electromagnetic shielding according to the mechanism. Electric field shielding should pay attention to the following points:
A. Choose materials with high conductivity and have good grounding.
B. Correctly select the grounding point and a reasonable shape. It is best to ground the shield directly. Magnetic field shielding usually refers only to shielding of DC or low frequency magnetic fields. Its shielding effectiveness is far less than electric field shielding and electromagnetic shielding. Magnetic shielding is often the focus of engineering. When magnetic shielding:
a, to choose ferromagnetic materials.
b. The magnetic shield should be away from the magnetic components to prevent magnetic short circuits.
c. Double-layer shielding or even three-layer shielding can be used.
d. The opening on the upper side of the shield should pay attention to the direction of the opening. As long as possible, the long side of the slit is parallel to the flow direction of the magnetic flux, so that the length of the magnetic circuit is minimized. Generally speaking, the magnetic shield does not need to be grounded, but it is better to prevent the electric field from being induced. When an electromagnetic field passes through a metal or a barrier that attenuates an electromagnetic field, it is subjected to a certain degree of attenuation, that is, a shielding effect on the electromagnetic field. In the actual rectification process, depending on the specific needs, which shield and shield shape, size, and grounding method are selected.
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