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Engineering grounding method described

2014/12/14 18:02:44 Viewers:

Proper grounding methods and technology would protect the monitoring system is good and reliable running, otherwise the security of the system and the video quality can not be guaranteed.

Ground from a literal point of view on a very simple thing, but for the people of electromagnetic interference experienced setbacks may be one of the hardest to master technology. Actually electromagnetic compatibility design, the ground is the most difficult technology. Faced with a system, no one person can propose an absolute right ground programs, how many are left with some questions. The reason for this situation is that there is no theory or model of a system grounded people considering grounding can only rely on past experience or see the experience from the book. But the ground is a very complex problem, in other occasions, a good solution here is not necessarily the best. About the grounding design relies heavily on the designer's intuition, is the concept of "grounding" the level of understanding and experience.

When the number of interconnected large volume of the apparatus (device physical dimensions and connection cable, compared with the wavelength of the interference signal of the existence of any large), there exists the possibility of interference by the role of the cabinet and cable. When this occurs, the interference current path is usually present in the system ground loops. When considering the problem of the ground, to consider two issues: one, the system self-compatibility issues, and the other is external interference coupled into the ground loop and cause the system to malfunction. Due to external noise is often random, thus solving often harder.

1, grounding requirements
There are many reasons grounding, Here are a few:
1) safety ground: using the AC equipment must pass the yellow-green safety ground ground, otherwise becomes smaller when the insulation resistance between the power supply and chassis equipment will lead to the risk of injury from electric shock.
2) lightning ground: facility lightning protection system is an independent system, under conductors and connected to the grounding system of the lightning rod, connector. The grounding system is usually used power reference ground and the ground of the yellow-green safety ground is shared. Lightning discharge in terms of the ground only to facilities, the device does not have this requirement.
3) EMC grounding: grounding requirements for electromagnetic compatibility design, including:
* Shield Ground: interfere with each other, in order to prevent the circuit due to the presence of parasitic capacitance between circuit radiated electric field or the necessary isolation shield must be sensitive to external electric field, these isolated and shielded metal must be grounded.
* Filter ground: filter generally contains the signal line or power line bypass capacitor to ground, when the filter is not grounded, these capacitors in a suspended state, would not achieve the role of bypass.
* Noise and interference suppression: the need to control the internal noise and external interference device or system on many points connected to the ground, so as to interfere with the signal to provide the lowest impedance channel.
* Circuit Reference: circuit between signal to be transmitted correctly, there must be a common potential reference point, the reference point of the common potential is ground. Therefore, all inter-connecting circuits must be grounded.

All of the above reasons grounded. Clear safety and lightning protection grounding requirements, but the general design requirements only, others are implicit in the electromagnetic compatibility requirements of the users of the system equipment. We want to build this concept: ground not every part of each system are needed, such as the single piece of circuit board does not have to ground in order to work properly. When you want to transfer data between devices, the ground will be very necessary.

The method of 2, ground

Grounding many ways, the use of that kind of method depends on the structure and function of the system. The concept of "grounding" for the first time used in the design and development of the telephone. The many grounding methods are derived from the successful experience of the past, these methods include:
1) single-point ground: This is the circuit together for many common potential reference point, so that the signal can be transmitted between different circuit. If there is no common reference point, there will be the transmission of the error signal. Single-point grounding requirements of each circuit ground once and then only at the same point. The point is often an earth reference. Since there is only one reference point, it can trust that no ground loop exists and therefore no interference problems.
2) multi-point grounding: circuit device to the cabinet as a reference point, the various equipment chassis to the ground as a reference point. This ground structure can provide a low impedance to ground, this is because of the multi-point ground, each of the ground can be very short; can reduce the total inductance of the grounding conductor and the plurality of conductors in parallel. The multi-point ground, and requires that the length of each grounding line is less than 1/20 of the wavelength of the signal must be used in high frequency circuit.
3) mixed ground: mixed ground contains both the characteristics of a single-point ground, but also contains a multi-point grounding characteristics. For example, the power system requires single-point ground RF signals require multi-point grounding, then you can mixed ground, ground through a single point ground, multi-point grounding line installation of capacitor. For the DC capacitor is open-circuited, the circuit is a single-point ground for RF, the capacitor is conductive, the circuit is a multi-point ground.