EMC theory basics - grounding design

Grounding is one of the important means to suppress electromagnetic interference and improve the electromagnetic compatibility of electronic equipment. Correct grounding can not only suppress the influence of interference, but also suppress the external radiation interference of the device; on the contrary, the wrong grounding will introduce serious interference, and even the electronic equipment can not work normally.

1, the concept of grounding

"Ground" in electronic devices usually has two meanings: one is "earth" and the other is "system baseline." Grounding is the establishment of a low-resistance conductive path between a selected point in the system and a potential reference. "Connecting to the earth" is based on the earth's potential as a reference, and the earth's metal casing, the selected point of the line, etc., connected to the earth through a grounding device composed of a grounding wire or a grounding pole. “System reference ground” refers to the reference conductor of the signal loop (electronic equipment usually uses metal base, casing, shield or thick copper wire, copper strip as the reference conductor), and the reference conductor potential is relatively zero potential, but not Earth zero potential, referred to as system ground. There are two purposes for grounding: one is for safety, called protective grounding. The metal casing of the electronic equipment must be grounded to avoid the danger of high voltages on the metal casing caused by accidents and endanger the safety of operators and equipment. The second is to provide a low impedance path for the current to return to its source.

2 Type of grounding

In fact, there are electrical or physical connections between various ground lines, and there is not necessarily a clear division. In the ground system, sometimes a place bears both the protection ground and the role of lightning protection; or it bears both the work place and the protection ground. The connection of different functions is different for the electrical objects, and the focus of the processing methods will be different.

a. Protective grounding

The protective grounding is to protect the safety of equipment, devices, circuits and people, to prevent lightning strikes, static electricity from damaging the equipment, or to protect personal safety in the event of equipment failure. Therefore, the grounding of the equipment, equipment, circuit chassis and metal casing must be taken.

The protection ground protection principle is: by short-circuiting the equipment casing with fault voltage to the earth or ground terminal, the short-circuit current generated during the protection process disconnects the fuse or the air switch, thereby achieving the protection of equipment and personnel safety.

b. Working ground

The working ground is the equipotential reference point or reference plane of the signal between the board, motherboard or system, which provides a low impedance path for signal reflow. Signal quality depends to a large extent on the quality of the working ground. Due to the characteristics of the grounded material and other technical factors, the connection or overlap of the grounding conductor is always good, and there is always a certain impedance. The return of the signal will cause a voltage drop on the working ground to form a ground ripple. Signal quality has an impact; the weaker the signal, the higher the signal frequency, the more severe this effect. Nevertheless, it is still important to minimize the impedance of the working ground conductor during design and construction.

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