Principle and application of electrostatic tester
In some electrostatic sensitive areas, such as electronic component manufacturing, assembly areas, ultra-quiet rooms, computers, pharmaceuticals and RD testing, operating rooms, medical equipment manufacturers, printing plants, packaging manufacturers, etc., electrostatic testing instruments are needed, so The use of electrostatic testers is becoming more and more widespread.
The so-called static electricity, strictly speaking, refers to the fact that the charge does not move, but under normal circumstances, the application of static electricity also includes the application of electro-expulsion (such as corona discharge), which has been widely used in real life. The following briefly describes several Application and harm of static electricity.
1 Application of static electricity (1) Electrostatic dust collection. It refers to the use of electrical methods to remove small dust floating in the gas, the dust collecting electrode is grounded, and the DC voltage (-40 ~ -200kV) is applied to the discharge electrode to form a corona discharge. Dust-containing gas enters the discharge area from below the dust collecting electrode, and the dust will be charged with negative polarity. The negatively charged dust is adsorbed by the dust collecting electrode under the action of the electric field, which can remove the dust in the airflow. In addition, when the discharge electrode is negative, the discharge voltage between the electrodes is higher than when the discharge electrode is positive, so a higher electric field strength can be used. However, for small dust collectors for indoor air purification, in order not to generate harmful ozone, positive corona discharge is usually used. In recent years, high-performance and economical electric dust collectors have been developed and applied. For example, electric dust collectors are generally installed in thermal power plants, which have made outstanding contributions to preventing air pollution.
(2) Electrostatic spraying. Using the principle of electric dust collection, it can be sprayed efficiently. For example, if the paint is atomized and negatively charged, while the metal object being coated is grounded, the sprayed particles will move along the lines of electric force, making the paint firmly adhere to the surface of the object. Electrostatic paint has the following advantages: ① less paint waste; ② uniform and firm spraying; ③ streamlined operation, and large-scale production using conveyor belts. It is widely used in the spraying of automobiles, home appliances, and motors.
(3) Electrostatic photography. Electrostatic photography uses static electricity to record images. There are many methods. One of the methods is described below. First, the metal plate coated with selenium film is placed in a dark room, and corona discharge is used to make it positively charged. Then expose it to light. The part of the selenium film irradiated by the light will lose its positive charge. Sprinkle the negatively charged colorant (coloring ion) on the selenium film. The positively charged part of the selenium film will adhere to the colorant, which will The positively charged paper is attached to the surface, and after the pattern of the colorant is copied, the colorant can be fixed by heating. Electrostatic photography is also called electrophotography and is widely used in copiers.
(4) Electrostatic selection. Using electrostatic force to separate the components from the mixture of two types of particles with different conductivity is called electrostatic separation. For example, put the mixed particles on a metal plate and use corona discharge to charge the particles. Tilt the metal plate. At this time, since the particles with good conductivity lose more electric charge, the adhesion between the particles and the metal plate is reduced, and they quickly fall off the metal plate, so that particle selection can be carried out, such as electrostatic selection in agricultural production. Electrostatic sorting has been applied to ore sorting. Removal of foreign matter during food processing and selection of tea leaves.
(5) The generation of DC high voltage. The van der Graaff electrostatic generator uses corona discharge to charge the high-voltage ball to generate DC high voltage. It can be used for leakage current test and other inspection tests, and is widely used in the production of power equipment manufacturers and power systems.
(6) High pressure measurement. Electrostatic voltmeters and pulse voltage recorders are devices that use static electricity to measure high voltages, and are widely used in high-voltage tests of electric power.
(7) Ignition of fuel gas. The use of tiny electricity to release electricity can ignite gas water heaters, gas stoves, etc., and the peak discharge pulse voltage is tens of thousands of volts (discharge energy is about 1mJ). The ignition of automobiles also uses tiny electricity to release electricity to make the fuel gas in the engine cylinder. When the fuel gas is ignited, the peak value of the pulse voltage is 10-100kV.
2 Countermeasures against electrostatic hazards. Two objects will become charged after they come into contact with each other (such as separation after rubbing against each other). After a dead object or an ungrounded conductor is charged, there is little charge leakage, so it can remain charged for a long time. If the contact and separation are repeated, the charged amount will continue to increase, which will cause the following hazards.
(1) The harm caused by Coulomb force. Coulomb force can cause dust to adhere to the manufacturing process of precision instruments such as cameras and semiconductor devices, and it can also cause yarn entanglement in textile factories and entanglement of textiles.
(2) Hazards caused by discharge. Including the ignition and explosion of flammable gas, the breakdown of the transformer due to the electrification of the transformer oil, the communication failure of the aircraft, the electromagnetic noise during the discharge will cause the misoperation of the computer, and the exposure and damage of the photographic film and semiconductor devices during the manufacturing process. The human body was shocked and so on.