The principle of electrostatic tester and the scope of simple use
In some static sensitive areas, such as electronic component manufacturing, assembly areas, ultra-quiet rooms, computers, pharmaceuticals and RD tests, operating rooms, medical equipment manufacturing plants, printing plants, packaging production plants, etc., electrostatic test equipment is required, so The use of electrostatic testers is also becoming more widespread.
The so-called static electricity, strictly speaking, refers to the fact that the charge does not move, but in general, the application of static electricity also includes the application of electric discharge (such as corona discharge), which has been widely used in practical life. The application and harm of static electricity.
1 static application
(1) Electrostatic dust collection. It refers to the electrical method of removing tiny dust floating in the gas, the dust collecting electrode is grounded, and a DC voltage (-40 ~ -200kV) is applied to the discharge electrode to form a corona discharge. The dust-containing gas enters the discharge zone from below the dust collecting electrode, and the dust carries a negative polarity charge. The negatively charged dust is adsorbed by the dust collecting electrode under the action of the electric field, thereby removing the dust in the airflow. Further, when the discharge electrode is a negative electrode, the discharge voltage between the electrodes is higher than when the discharge electrode is positive, so that a high electric field strength can be employed. However, for a small dust collector for indoor air purification, a positive corona discharge is usually used in order not to generate harmful ozone. In recent years, high-performance, economical electric dust collectors have been developed and applied. For example, electric dust removal devices are commonly installed in thermal power plants, and outstanding contributions have been made to prevent air pollution.
(2) Electrostatic spraying. Using the principle of electrical dust collection, it can be sprayed efficiently. For example, the coating is micronized and negatively charged, and the coated metal object is grounded, and the ejected particles move along the power line, allowing the coating to adhere firmly to the surface of the object. Electrostatic coatings have: 1 less waste of paint; 2 can be evenly and firmly sprayed; 3 can be used for running water, and can be used for large-scale production by conveyor belts, and is widely used in the spraying of automobiles, home appliances and electric motors.
(3) Electrostatic photography. Electrostatic photography is an image recorded by static electricity. There are various methods. One of the methods is described below. First, a metal plate plated with a selenium film is placed in a dark room, and a positive charge is applied by corona discharge. Then, it is exposed, and a part of the selenium film will lose a positive charge. A negatively charged coloring agent (colored ion) is sprinkled on the selenium film, and a positively charged portion on the selenium film will adhere to the coloring agent. A positively charged paper is attached to the surface, and after being copied to the pattern of the coloring agent, the coloring agent is fixed by heating, and electrostatic photography is also called electrophotography, and is widely used in a copying machine.
(4) Electrostatic sorting. The separation of each component from a mixture of two types of particles having different electrical conductivity by electrostatic force is called electrostatic separation. For example, the mixed particles are placed on a metal plate and the particles are charged by corona discharge. Tilt the metal plate. At this time, since the particles having good conductivity lose a large amount of electric charge, the adhesion to the metal plate is lowered, so that the particles are quickly slid off from the metal plate, whereby particle sorting, such as electrostatic seed selection applied in agricultural production, can be performed. Electrostatic sorting has been applied to ore sorting. The removal of foreign materials during food processing and the selection of tea.
(5) Generation of DC high voltage. Van der Graff's electrostatic generator is a high-voltage ball that is charged by corona discharge to generate DC high voltage. It can be used for leaking current test and other exhaustive inspection tests. It 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 measure the high voltage by using electrostatic phenomena, and are widely used in the field of high voltage testing of electric power.
(7) Ignition of fuel gas. Gas heaters, gas stoves, etc. can be ignited by using a small electric discharge device. The peak value of the discharge pulse voltage is tens of thousands of volts (discharge energy is about 1 mJ), and the ignition of the automobile is also using a small electric discharge to make the fuel gas in the engine cylinder. The power is obtained by the explosion, and the peak value of the pulse voltage when the fuel gas is ignited is 10 to 100 kV.
2 countermeasures against electrostatic hazards
After the two objects are in contact, the separation will be charged (such as separating from each other after rubbing). When the object or the ungrounded conductor is charged, there is little charge leakage, so it can be charged for a long time. If the contact is repeated and separated, the charge is continuously increased, which may cause the following hazards.
(1) Hazards caused by Coulomb force. Coulomb force can cause dust to adhere to precision instruments such as cameras and semiconductor devices, and it can also cause entanglement of yarns in textile mills and entanglement of textiles.
(2) Hazards caused by discharge. Including the igniting and igniting of flammable gases, the transformer oil is charged, causing the transformer to break through, the communication failure of the aircraft, the electromagnetic noise during discharge may cause computer mishandling, photographic film, semiconductor devices, etc. in the manufacturing process, exposure and damage, The human body is shocked, etc.