Dielectric mat - mat under the feet of material, non-conducting. Performs measure of protection against electricity.
Alternating current
electricians group equipped with special clothing. Most of the rubber products. Dielectric materials isolate the current acting basis of creating safeguards personnel from industrial frequency networks. Potential is not dangerous, because the touch of a charge will occur until allow the size of the human body capacitance. Then, since the radiation resistance is high, the victim will remove themselves from danger.
These measures do not always help working with high-voltage equipment. Rubber sole potential breaks, possibly fatal. To further reduce the danger to electrical boards and cabinets with high voltage insulating advisable to lay mats. Most are made from rubber, is added resistance between the ground-sole. A thicker coating can withstand higher potential. Additionally performed on the surface of the corrugated pattern depth of 3-5 mm, reduces the contact area increases the resistance of the current run-off surface of the article.
Withstand voltage, dielectric withstand mat, specified by the manufacturer. For rubber 6 mm thick is 20 kV power frequency current. Enough to work with the 10 kV substation.
A dielectric pad is made of special types of rubber, bravely withstand the aggressive media. Since the use of the product means the largest enterprise in the transformer box, the other unpleasant places. Resistance humidified (coated with acid, alkali) pad decreases sharply. There is a risk of death.
Use mats should be on any type of coating, excluding the dielectric. Trail on top of concrete, brick, cement screeds, ground. However, in the laboratory (also need protection against electric shock) is another danger. Avoid man pursues chips. Static electricity. It is shown below: in adverse conditions may harm the equipment, you (through reduction of the amount of wages of damage).
Static electricity
Needless to say, the static electricity appeared earlier than other species. Anticipating the era of Christ, the problem involved some pundits. The ups and downs of the epic read a thread DC. The history of the development of electricity are other references. Excess static electricity charge is called, the accumulated surface of the dielectric, the isolated conductor deprived grounding. Touching the subject will immediately cause a redistribution of electrons force natural equilibrium laws.
The charges can accumulate inside the dielectric, being distributed volumetrically. If the floor paved with rubber mat, a person touching the apparatus, hurt. Electricity will start to be redistributed, while hitting the chip. Applicable special shoes equipped with insulating soles. In addition, you can use in the laboratory, workshop, class anti-static mats. AC leakage path (to the earth) sharply increases, the resistance increases, the alternating current provided security. Static charge readily flows as product low surface resistance.
You should know, according to GOST concrete (5 - 8 ohm meters), brick floors equated earth. AC isolation does not provide. We have to use anti-static mats. In addition, charges can flow to the equipment man, on the contrary, drain. The body is endowed with greater surface conductive. In order to lock the wrist effect made to wear an antistatic wrist strap, allowing the charge to flow to the artificial, natural earthing. The bracelet is worn on both hands.
Many also have guessed, other clothing helps to accumulate charges. Affected wool, fur electrified by friction. Slowly accumulate charge during the day, people did not feel that was the chance of static generator. It should touch the sweater immediately hear a characteristic crack.
The potential of the atmosphere
It is known from a height above ground growth potential changes. Man adopts the potential of the surface on which you place. The house, being firmly grounded, usually located on the ground level. It becomes clear why the lightning likes to hit a tree, lightning rod on the roof: the current path is shorter! Man, trampling the roof, becomes ground potential.
Completely different matter with the antenna. As one part of the grounded presents some health hazard. Many surely beaten current conductor shielded cable common roof antenna. Electrified equipment while driving. aircraft discharge conducted special stekatelem equipped with a spark gap. The potential difference between the surrounding air stream and the wing becomes high overshoots miniature corona discharge partially quenching effect. With cars charge drain on the rubber band after dragging over the road surface.
Examples convince eloquently: Static electricity has been, is and will have trace components of electronic devices. If you do not learn how to defend themselves properly. For example, the tree is not a conductor, therefore, not always equal to the potential of the soil. During rain conductivity increases dramatically, the situation is changing. Lightning hit a tree. Knowledge of the laws is considered the basic condition for a successful defense.
According to statistics, every third chip loses its efficiency because of the buyer. The loss of production caused by the same reason, is 8 - 24%. Static electricity causes annual losses of the globe economy, estimated at billions of dollars. Subtracting the cost of eliminating the consequences.
The mechanism of formation of static electricity on a dielectric mat
Allocated a lot of charge transfer mechanisms. Interesting question is said to be the gradual accumulation. When it comes to touch, play an important part of the surface conductivity. In order smaller volume dielectric. What explains the advantage over the non-metallic conductors to accumulate charge. Iron is part of the electronic wire inside, chaotic currents of small magnitude quickly extinguished, the suppression of the interaction with the crystal lattice, is getting warmer. Conductor harder to inform the charge.
Excess electrons can accumulate dielectrics arbitrary aggregate state, including liquids. Clouds wind friction easily emit lightning, though rashly assumed conductor pairs. Similarly, there is electrifying man walking! The mechanism is explained by two reasons:
- Friction sole surface plus the instantaneous rupture of two dissimilar materials.
- Gradual charge distribution body.
Accompanied by the opposite process - discharge. With each step the person stores a certain amount of electricity, a part of trying to drain. The context makes it clear why people who walk feel enthusiasm, gradually taking away the rest. The effect is enhanced running. Of course, in wet weather electrification nearly completely blocked.
Over time, the static growth with each step becomes equal to the descending of the time that the foot tramples on the ground. There comes a dynamic balance of the speed. The resulting curve, which describes the charge increase, reminiscent of the output current-voltage characteristic transistor: first parameter demonstrated fast growth, then the system tends to a fixed value.
When walking on insulated cover, which includes a dielectric pad, man accumulates the charge level is gradually increasing. The calculated data show that in the "ideal" conditions of 21 seconds potential difference reaches enormous quantities of 3.5 kV. Upon termination walk there was a decline to almost zero literally 5 seconds. That is why the floor of the laboratory is made of special material, safety shoes equipped with anti-static sole. This class of remedies refer dielectric mat. charge loss does not occur instantaneously, manufacturers data show that half a second is enough to no longer pose a danger chips.
antistatic mat
Thus, the dielectric pad will not always be the best one for the laboratory, although a number of uzhivutsya group of electricians. Laboratories need special insulating mats that have a special design, specific characteristics. The composition may be as follows:
- A thin layer of PVC that provides the outer cover of sufficient strength to the top you can walk quietly.
- Conductive while reinforcing mesh required to shaky structure is not broken up.
- The lower layer of polymeric foam (PVC). It reduces noise in the movement of people on the mat, promoting run-off charge.
The resistance of the product AC, DC reaches 200-300 MW, in line with the requirements of modern insulation. It is necessary that the worker is simply not killed, when suddenly a part of the body touches the antistatic mat, the other - to the conductor, which is under capacity.
Dielectric materials do not prevent draining of the statistical charge. To receive quicker, mat to earth for a special hole. Otherwise, the design provides for installation on metal fasteners, the underlying surface conductive, vanishes, is grounded as required.
A suitable pad is off, is not afraid of aggressive media, absorbs noise, demonstrates a decent view, has many other features. The insulation resistance is not less than 20 megohms, such are the demands of modern Russian standards. Foreign mats comply with generally accepted standards:
- ANSI / ESD (Electrostatic Discharge Association) S20 «On measures for the protection of electronic circuits, assemblies of equipment." The text in English is available for free download.
- ANSI / ESD S1. Sold at the price of the interrogation, a complimentary domestic version (GOST R 53734.4.1).
Mat, devoid of connectors connecting the zero conductors are pressed earthed metal constructions, assembled with punched through conductive fasteners current. Otherwise, the run-off the charging process can not be guaranteed one hundred percent. The shops have enough options rugs execution, little explanatory descriptions.
