Electronic scale grounding type and function

What are the types and functions of the electronic scale grounding?

Electronic equipment "grounding" usually has two meanings: one is "earth" (safely); the other is "system reference ground" (signal ground); grounding is the establishment between the system and a potential reference plane Low resistance conductive path. "Connecting to the earth" is based on the earth's potential, and uses the earth as the zero potential to connect the metal casing and the circuit reference point of the electronic device to the earth. Since the capacitance of the earth is very large, it is generally considered that the earth's potential is zero. Grounding in weak current systems is generally not grounded in the true sense of the Earth. For power electronic equipment, the ground wire is directly connected to the ground or connected to a conductor as a reference potential. When a current passes through the reference potential, the grounding point is a common reference point in the circuit, and the voltage at this point is 0V, the circuit The voltage levels at other points in the middle are based on this point. There are many ways to ground, and we often use the following:

1. Safety grounding: The safety grounding is to connect the outer casing of the high-voltage equipment to the earth. One is to prevent the accumulation of electric charge on the casing, resulting in electrostatic discharge and endangering equipment and personal safety. Such as the grounding of the computer case. Second, when the insulation of the equipment is damaged and the casing is energized, the power supply is protected and the power is cut off to protect the safety of the workers. The third is to shield the huge electric field of the device and protect it.

2, lightning protection grounding: When the electronic weighing instrument is struck by lightning, whether it is direct lightning strike or induced lightning strike, if there is no corresponding protection, the equipment may be greatly damaged or even scrapped. In order to prevent lightning strikes, we generally set lightning rods at high places to connect with the earth to prevent the safety of equipment and personnel when lightning strikes.

3. Working ground: It is a reference potential provided for the normal operation of the circuit. This reference potential is typically set to zero. The reference potential can be set to a certain point, a certain section, or the like in the circuit system. When the reference potential is not connected to the ground, it is regarded as a relative zero potential. However, this relative zero potential is unstable, it will change with the change of the external electromagnetic field, and the parameters of the system will change, resulting in unstable operation of the circuit system. When the reference potential is connected to the ground, the reference potential is regarded as the zero potential of the earth, and does not change with the change of the external electromagnetic field.

4. Shield grounding: Shielding and grounding should be used together to achieve good shielding effect. When the charged conductor is surrounded by the complete metal shield, an electric charge of the same kind as the charged conductor is induced on the inner side of the shield, and the same kind of electric charge as the charged conductor is present on the outer side, so that there is still electric charge on the outer side. If the metal shield is grounded, the external charge will flow into the earth, and the metal casing will not have an electric field, which is equivalent to the electric field of the charged body in the casing being shielded.

First, the method of reducing interference between grounding devices

1. Increase the distance between the grounding devices. If the grounding body is not shared between the DC ground and the lightning protection ground, the distance between the two should not be less than 5 meters.

2. The greater the difference in buried depth between the grounding bodies, the less interference they have with each other. In practical applications, increasing the buried depth of the grounding body can reduce the grounding resistance, but it is not economical, and the length of the grounding body is appropriately increased. Can receive very good results.

3. The shielding effect of high conductivity objects can greatly reduce the interference from the other side. The thicker the object, the better the shielding effect. In practical applications, the naturally-conducting high-conductivity objects can be fully utilized according to the site conditions.

4. When the grounding wire is introduced, it should be kept away from other grounding systems to prevent interference, especially the lightning protection or power network neutral point grounding wire system. If the grounding wire is very long, in order to prevent large current induction, avoid parallel or tightly bonding with high-power power lines. If necessary, shield the grounding wire through the steel pipe.

Second, the grounding method

The grounding wire is ligated to the grounding pile of the foundation pit of the scale. This method is equivalent to the copper rod. When the pit is completed, the grounding conductor is connected to the grounding pile. In addition, when grounding pile is used, grounding wire is used to connect the grounding pile, because the grounding pile will be covered by concrete. When the pit is built, the grounding wire is connected with a grounding pile, and the surface is concrete. If the wire is inside the concrete, it will Corrosion, which leads to ineffective connections, is a very effective method of welding grounded piles from steel bars before concrete has yet to be formed.

When grounding is done, the distance between the grounding points of the weighing system is not less than 3 meters. When laying vertically, the depth of vertical driving into the ground should not be less than 2 meters, generally 3 meters. When laying horizontally, the buried depth should not be less than 0. ?7 meters. Moreover, the grounding body should be galvanized or copper plated, and painting is strictly prohibited. A copper wire having a cross section of not less than 25 mm 2 has a resistance of not less than 1 ohm. After the ground wire is completed, the grounding resistance is generally less than 4 ohms.