Types
Protective grounding
Safety grounding is the system is usually not charged metal parts (cabinet shell, operating console shell, etc.) and the ground to form a good conductive connection between the protection of equipment and personal safety. The reason is that the power supply system is a strong power supply (380, 220 or 110V), usually the enclosure and so on is not electrically charged, when a fault occurs (such as a host power failure or other faults) caused by the power supply of the power supply line of fire with the enclosure and other conductive metal parts of the short-circuit, these metal parts or the enclosure is formed a charged body, if there is no good grounding, then the charged body and ground between the high potential difference, if a person accidentally touches these charged body and the ground, the potential difference between the two is high. If a person accidentally touches these charged bodies, it will form a pathway through the person, creating a hazard. Therefore, it is necessary to make a good connection between the metal enclosure and the ground so that the enclosure and the ground are equipotential. In addition, protective grounding prevents the buildup of static electricity.
Working ground
Ground is in order to make the system as well as the instrumentation connected to it can operate reliably and ensure the accuracy of measurement and control and set the ground. It is divided into machine logic ground, signal circuit ground, shielding ground, in the petrochemical and other explosion-proof systems and intrinsically safe ground.
Machine logic ground, also known as the host power supply ground, is the logic level of the computer inside the negative end of the public **** ground, but also +5V and other power supply output ground.
Signal circuit ground, such as the negative end of each transmitter ground, the negative end of the switching signal ground.
Shield grounding (grounding of the analog signal shield).
Intrinsically safe grounding, is the grounding of intrinsically safe instruments or safety barriers. This grounding in addition to suppressing interference, there is one of the measures to make the instrument and the system has the nature of intrinsic safety. Intrinsically safe grounding will be different because of the use of intrinsic safety measures for different equipment, the following Zener type safety grids as an example, to illustrate the content of its grounding.
The function of the grid is to protect the hazardous field terminal is always within the safe power supply and safe voltage range. If the field end is short-circuited, the current on the wire will be limited to a safe range due to the current limiting effect of the load resistor and the safety grid resistor R, so that the field end does not generate a very high temperature and cause combustion. In the second case, if a fault is generated at one end of the computer, the high voltage electrical signal is added to the signal loop, then the voltage is also kept in the safe range due to the embedding effect of the Zener secondary.
It is worth reminding that, due to the introduction of the Zener safety grid, so that the signal loop resistance increases a lot, therefore, in the design of the load capacity of the output circuit, in addition to consider the real load requirements, but also to fully consider the resistance of the safety grid, to leave room for manoeuvre.
In addition to the above grounding, in many cases easy to cause confusion, there is a power supply system ground, also known as the AC power supply ground, it is the power system for the operation of the grounding needs to be set up (such as neutral grounding).
Lightning protection ground
Lightning protection ground is subject to lightning strikes (direct, induction or line introduction), in order to prevent damage to the grounding system. Often signal (weak) lightning ground and power (strong) lightning ground points, the reason for the distinction is not only because of the requirements of the grounding resistance is different, and in engineering practice, signal lightning ground often attached to the signal on an independent ground, and the power supply lightning ground separate construction.
Lightning protection ground as part of lightning protection measures, its role is to introduce the lightning current into the earth. Lightning protection of buildings and electrical equipment is mainly with lightning arrester (including lightning rods, lightning straps, lightning nets and lightning devices, etc.) one end of the connection with the protected equipment, the other end of the grounding device, when a direct lightning strike occurs, the lightning arrester will be led to itself, the lightning current into the earth through the lead wire and grounding device. In addition, due to lightning caused by electrostatic induction side effects, in order to prevent indirect damage, such as house fires or electrocution, etc., usually also need to be grounded in the building of metal equipment, metal piping and reinforced structures; lightning waves will be invaded along the low-voltage overhead line, TV antennae into the house, caused by insulation breakdown of electrical equipment inside the house, resulting in fires or personal injury or death from electrocution, so it is also necessary to be on the line and into the house before the Insulated porcelain vase iron foot grounding.
Shield grounding
It is an effective measure to eliminate the hazards of electromagnetic fields on the human body, but also to prevent electromagnetic interference. High-frequency technology in electric heating, medical, radio broadcasting, communications, television and navigation, radar and other aspects have been widely used, the human body in the role of electromagnetic fields, absorbed radiant energy will occur in the biological role of the human body causing harm, such as slight trembling of the fingers, skin scratches, vision loss. Generate magnetic field equipment shell shielding device, and shielding body grounding, not only can reduce the shielding body outside the electromagnetic field strength, to reduce or eliminate the electromagnetic field on the human body harm, but also to protect the shielding grounding equipment from the outside world from the impact of electromagnetic field interference.
Anti-static grounding
To prevent the effects of electrostatic hazards and discharge, is the most important part of electrostatic protection.