Modern electrovacuum devices owe their appearance to the American inventor Thomas Edison. It was he who developed the first successful way of lighting, using a light bulb for this.
History of the lamp
At present, it is difficult to believe that electricity did not exist in all historical periods. The first incandescent bulbs appeared only at the end of the nineteenth century. Edison managed to develop a model of a light bulb in which charcoal, platinum, bamboo threads were located. It is this scientist who is rightly called the "father" of a modern electric lamp. He simplified the circuit of the light bulb, significantly reduced the cost of production. As a result, it was not gas, but electric lighting that appeared on the streets, and new lighting devices were called Edison lamps. Thomas for a long time worked on improving his invention, as a result, the use of candles became an unprofitable event.
Principle of operation
What device do Edison incandescent bulbs have? Each device has a glow body, a glass flask, a main contact, electrodes, a base. Each of them has its own functional purpose.
The essence of this device is as follows. With strong heating of the glowing body by a stream of charged particles, the conversion of electrical energy into a light form occurs.
In order for the radiation to perceive the human eye, it is necessary to reach a temperature of at least 580 degrees.
Among metals, tungsten has a maximum melting point; therefore, it is from it that the glow body is made. To reduce the volume, the wire began to be arranged in the form of a spiral.
Despite the high chemical resistance of tungsten, for its maximum protection against the corrosion process, the glow body is placed in an airtight glass vessel from which air has been previously pumped. Instead, an inert gas is pumped into the flask, which prevents the tungsten wire from entering the oxidation reaction. Most often, argon is used as an inert gas, sometimes nitrogen or krypton is used.
The essence of Edison’s invention is that the pressure created by an inert gas prevents the evaporation that occurs during prolonged heating of the metal.
Lamp features
There are quite a few different lamps designed to illuminate a large area. A feature of Edison's invention is the ability to adjust the power of this device taking into account the illuminated area.
Manufacturers offer different types of lamps that differ in service life, size, power. Let us dwell on some types of these electrical appliances.
The most common vacuum tubes are LON. They fully comply with hygiene requirements, and their average service life is 1000 hours.
Among the disadvantages of general-purpose lamps, a low efficiency is highlighted . About 5 percent of the electrical energy goes into light, the rest is released as heat.
Flood lights
They have a sufficiently high power, designed to illuminate large areas. Vacuum devices are divided into three groups:
- film projection;
- lighthouse;
- general purpose.
The searchlight light source is distinguished by the length of the glowing body, it has more compact dimensions, which makes it possible to enhance the overall brightness and improve focusing of the light flux.
Mirror electrovacuum devices have a reflective aluminum layer, a different bulb design.
The part that is intended for conducting light is made of frosted glass. This allows you to make the light soft, reduce contrasting shadows from various objects. Such electric vacuum devices are used for interior lighting.
Inside the halogen flask are bromine or iodine compounds. Due to their ability to withstand temperatures up to 3000 K, the operational life of the lamps is about 2000 hours. But this white light source also has its drawbacks, for example, a halogen lamp, has a low electrical resistance when cooling.
main parameters
In Edison's incandescent lamp, a tungsten filament is located in a different shape. For the stable operation of such a device, a voltage of 220 V is necessary. On average, its life is from 3000 to 3500 hours. Given that the color temperature is 2700 K, the lamp provides a warm white or yellow spectrum. At present, lamps with different sizes of socles (E14, E27) are offered. If desired, you can pick up a lamp in the form of a hairpin, Christmas tree, spiral into the ceiling chandelier or wall-mounted lighting device.
Edison's invention is divided by the number of tungsten filaments into separate classes. The cost of the lighting device, its power, and operational life directly depend on this indicator.
The principle of the EVL
Thermoelectronic emission consists in the emission of a heated filament of electrons into a vacuum or inert medium created inside the bulb. To control the flow of electrons, a magnetic or electric field is used.
Thermoelectronic emission makes it possible to practically use the positive qualities of the electron flow - to generate, amplify electrical vibrations of various frequencies.
Features of the radio tubes
Electrovacuum diode is the basis of radio engineering. In the design of the lamp there are two electrodes (cathode and anode), a grid. The cathode provides emission, for this a layer of tungsten is coated with barium or thorium. The anode is made in the form of a plate of nickel, molybdenum, graphite. The grid is a separator between the electrodes. When the working fluid is heated, a powerful electric current is created in a vacuum from moving particles. Vacuum devices of this type form the basis of radio engineering. In the second half of the last century, vacuum tubes were used in various fields of technical, electronic industry.
Without them, it was impossible to manufacture radios, televisions, special equipment, computers.
Fields of application
With the development of precision instrumentation, electronics, these lamps have lost their relevance, are no longer used on a large scale.
But even now there are such industrial areas in which EVL is required, because only a vacuum lamp is able to ensure the operability of devices according to given parameters, in a certain environment.
EVLs are of particular interest for the military-industrial complex, since it is vacuum tubes that are characterized by increased resistance to electromagnetic pulses.
In one military device can contain up to hundreds of EVL. Most semiconductor materials, REC cannot function with increased radiation, as well as in natural vacuum (in space).
EVL contribute to increasing the reliability and durability of satellites and space rockets.
Conclusion
In electrovacuum devices that allow you to generate, amplify, and convert electromagnetic energy, the working space is completely freed from air, enclosed from the atmosphere by an impenetrable shell.
The discovery of thermionic emission contributed to the creation of a simple two-electrode lamp, called a vacuum diode.
When it is included in the electrical circuit, a current appears inside the device. When the polarity of the voltage changes, it disappears, regardless of how much the cathode heats up. By maintaining a constant temperature value of the heated cathode, it was possible to establish a direct relationship between the anode voltage and the current strength. The results obtained were applied in the development of electronic vacuum devices.
For example, a triode is an electronic lamp having three electrodes: an anode, a thermionic cathode, a control grid.
It was the triodes that became the first devices used to amplify electrical signals at the beginning of the last century. Currently, triodes have been replaced by semiconductor transistors. Vacuum triodes are used only in those areas where it is necessary to convert powerful signals with a small number of active components, and the mass and dimensions can be neglected.
Powerful radio tubes are comparable to transistors in terms of efficiency, reliability, but their service life is much shorter. In low-power triodes, most of the heat goes to the consumed cascade power, sometimes its value reaches 50%.
Tetrodes are an electronic two-grid lamp, which is designed to increase the power and voltage of electrical signals. These devices have a higher gain compared to the triode. Such structural features allow the use of tetrodes to amplify low frequencies in televisions, receivers, and other radio equipment.
Consumers are actively using incandescent lamps in which the tungsten spiral or wire is the filament body. These devices have a power of 25 to 100 watts, their operational life is 2500-3000 hours. Manufacturers offer lamps with different cap, shape, size, so you can choose the lamp option taking into account the characteristics of the lighting device, room area.