Principles of Electrostatic Protection and Safety Protection Principles
1. The principle of electrostatic protection
The general principles of anti-static hazards are different for different objects, and the effects of static electricity are also different, and the resulting hazards are also different, which can be expressed as:
1. In dangerous places where flammable and explosive gas mixtures exist and where there are electric explosive devices, static electricity hazards often lead to fires and explosions.
2. For electronic systems such as communication and data processing, the damage of static electricity is manifested as transient electromagnetic interference, which makes the system unable to work normally.
3. In the printing, textile, automated packaging and other industrial sectors, electrostatic hazards have become obstacles to production (or called obstacles). In addition, in different environments and different industrial sectors, the "dangerous static electricity sources" that produce electrostatic hazards are also different. For example, human body static electricity poses a hazard; machines are charged to cause harm; dust, explosives themselves are electrostatically charged, and they are also sensitive materials for electrostatic discharge.
Obviously, for different environments and different objects, there should be different technologies and measures for preventing electrostatic hazards. However, no matter what kind of environment and object, the law of electrostatic discharge is the same. Therefore, no matter how different the specific protection measures are, there must be a general principle of electrostatic protection, that is, the common principle of electrostatic safety protection.
2. Principles of Electrostatic Safety Protection
The most basic basis for establishing the principle of electrostatic safety protection is the three basic conditions for the formation of electrostatic hazards: 1. Generate and accumulate enough static electricity to form a "dangerous static power source", so that the local electric field strength reaches or exceeds the breakdown field strength of the surrounding medium. Electrostatic discharge has occurred. 2. There are flammable and explosive gas mixtures in the place where dangerous static electricity sources exist and reach the explosive concentration limit, or there are explosive dangerous goods such as electric explosives, gunpowder, or electrostatic sensitive devices and electronic devices, such as electrostatic explosive and easy Damage material. 3. Energy coupling can be formed between the dangerous static power source and electrostatic, explosive and vulnerable materials, and the electrostatic discharge energy is equal to or greater than the minimum ignition energy or electrostatic sensitivity of the former.
That is to say, as long as one of the three basic conditions is controlled according to the knowledge of static electricity, basic principles of discharge, and material electrostatic properties, so that it cannot meet the requirements of causing electrostatic hazards, electrostatic hazards can be prevented from occurring. In order to be safe and reliable, in actual electrostatic protection projects, it is generally necessary to control so that two of the conditions cannot be met. In addition, the mechanism and characteristics of electrostatic hazards, and the energy coupling path and mode between hazardous electrostatic power sources and electrostatic sensitive materials are also important basis for establishing electrostatic safety protection principles and electrostatic protection measures. According to the three basic conditions for the formation of electrostatic hazards, three electrostatic safety protection principles can be determined by reasoning: 1. Control the amount of static electricity and charge accumulation to prevent the formation of dangerous static electricity. 2. Use materials with low electrostatic sensitivity. 3. Adopt comprehensive protection and reinforcement technology to prevent ESD energy coupling.
According to the above three principles of electrostatic protection, in order to prevent electrostatic hazards, the following countermeasures can be taken:
1. Control the rate of static electricity to prevent the formation of dangerous static electricity. The formation of dangerous static electricity is due to the fact that the electrostatic electrification rate of the object (the increase in the amount of charge on the object per unit time) is greater than the charge dissipation rate on the object (the total charge leakage on the object per unit time and the total amount of charge neutralized by the air), so that the object The total amount of electric charge continues to accumulate to form an electrostatically charged body. The greater the electrostatic electrification rate compared to the charge dissipation rate, the more charge accumulated on the charged body, and the higher the ground potential, the more dangerous this electrostatic source is. Therefore, effective control of electrostatic charge rate is one of the basic countermeasures to prevent electrostatic damage. The main methods to reduce the electrostatic charge rate are as follows: ①Reduce the friction between objects. ②Control the speed and frequency of contact and separation between objects, and at the same time make the speed of objects change slowly. ③Reduce the contact area between the contacting and separated objects and reduce the contact pressure. ④Do not peel off substances that are in close contact abruptly. ⑤The surface of the object should be kept clean and smooth. ⑥ Use materials that are close to each other in the "frictional charging sequence". ⑦Pure gas should avoid mixing foreign particles such as impurities.
2. Increase the charge dissipation rate to prevent charge accumulation. Increasing the dissipation rate of charge can reduce the accumulation of electrostatic charge. When the dissipation rate is equal to or greater than the electrification rate, it will not form a source of electrostatic hazards. The main methods to increase the charge dissipation rate are as follows:
①Increase the relative humidity of the environment. When the relative humidity is moderately increased to 50%, the charge of general objects is significantly reduced; when the relative humidity is above 65%, the surface resistivity of almost all objects is reduced, which improves the charge leakage of the objects rate.
② Make a reasonable electrostatic grounding and overlap of the electrostatic conductor or electrostatic sub-conductor, so that the object maintains a channel for charge leakage.
③Use conductive materials or antistatic materials to replace static non-conductors, or use antistatic agents to reduce the surface resistivity of the object, and the charge can quickly leak through the grounding device.
④Use ionizing wind and other static eliminators to neutralize the charge on the charged body to increase the dissipation rate of the charge and prevent the formation of dangerous static electricity.
3. Use antistatic explosives and components to reduce the risk of the place. In some cases, the above two protective countermeasures cannot be fully realized. At this time, you should consider using antistatic electric explosives and antistatic components to prevent static electricity from causing harm.
4. Control the concentration of gas mixture to prevent explosion accidents. Use methods such as ventilation and reducing production rate to reduce flammable and explosive gases so that they are not within the explosive concentration limit.
5. Adopt anti-ESD design and protection and reinforcement technology to improve the circuit's anti-electromagnetic interference ability. In the circuit design, the anti-ESD technology is adopted, and the electrostatic protection and reinforcement technologies such as grounding, lap, shielding, and filtering are comprehensively used to make the circuit and the whole machine have the effect of anti-electromagnetic pulse generated by electrostatic discharge, and eliminate the harm of electrostatic discharge to electronic devices. .
6. Strengthen electrostatic safety management. Electrostatic safety management is the basic guarantee for the implementation of the above-mentioned "principles" and "countermeasures", and is also the most basic requirement in the work of preventing electrostatic hazards in various industries.
