Modern electrovacuum devices owe their appearance to the American inventor Thomas Edison. It was he who developed the first successful way of lighting, using an electric light bulb.
The history of the lamp
Currently, it is hard to believe that electricity did not exist in all historical periods. The first incandescent light bulbs appeared only at the end of the nineteenth century. Edison managed to develop a model of a light bulb, in which carbon, platinum, and bamboo filaments were located. It is this scientist who is rightly called the "father" of the modern electric lamp. He simplified the light bulb circuit, significantly reduced the cost of production. As a result, not gas, but electric lighting appeared on the streets, and new lighting devices began to be called Edison lamps. Thomas worked on improving his invention for a long time, as a result, the use of candles became an unprofitable measure.
Working principle
What device do Edison incandescent bulbs have? Every device has a bodyfilament, glass bulb, main contact, electrodes, base. Each of them has its own functional purpose.
The essence of this device is as follows. When the heating body is strongly heated by a stream of charged particles, electrical energy is converted into a light form.
In order for the radiation to be perceived by the human eye, it is necessary to reach a temperature of at least 580 degrees.
Among metals, tungsten has the highest melting point, so it is from it that the heating body is made. To reduce the volume, the wire began to be placed in the form of a spiral.
Despite the high chemical resistance of tungsten, for its maximum protection against the corrosion process, the filament body is placed in a sealed glass vessel, from which air has been previously pumped out. Instead, an inert gas is pumped into the flask, which prevents the tungsten wire from entering into oxidation reactions. The most commonly used inert gas is argon, sometimes nitrogen or krypton is used.
The essence of Edison's invention is that the evaporation that occurs during prolonged heating of the metal is prevented by the pressure created by an inert gas.
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, differing in service life, size, power. Let's dwell on some types of these electrical appliances.
The most common vacuum tubes are LON. They are fully hygienic and have an average service life of 1000 hours.
Among the shortcomings of general purpose lamps, we highlight the low efficiency. Approximately 5 percent of electrical energy is converted into light, the rest is released as heat.
Spotlights
They have a fairly high power, designed to illuminate large areas. Electrovacuum devices are divided into three groups:
- film projection;
- lighthouses;
- general purpose.
The projector light source differs in the length of the filament body, it has a more compact size, which allows you to increase the overall brightness, improve the focus of the light stream.
Mirror electrovacuum devices have a reflective aluminum layer, a different bulb design.
That part of it, which is designed to conduct light, is made of frosted glass. This allows you to make the light soft, reduce contrasting shadows from various objects. Such electrovacuum devices are used for interior lighting.
Inside the halogen flask are compounds of bromine or iodine. Due to their ability to withstand temperatures up to 3000 K, the service life of the lamps is about 2000 hours. But this white light source also has its drawbacks, for example,halogen lamp, has a low electrical resistance when cooled.
Main parameters
In an Edison incandescent lamp, the tungsten filament is arranged in different shapes. For stable operation of such a device, a voltage of 220 V is required. On average, its service life is from 3000 to 3500 hours. Considering that the color temperature is 2700 K, the lamp provides a warm white or yellow spectrum. Currently, lamps are offered with different sizes of socles (E14, E27). If desired, you can pick up a lamp in the form of a hairpin, herringbone, spiral in a ceiling chandelier or wall lighting fixture.
Edison's invention is divided into separate classes according to the number of tungsten filaments. The cost of the lighting fixture, its power, and service life directly depend on this indicator.
EVL operation principle
Thermionic emission consists in the emission of electrons by a heated incandescent body into a vacuum or inert medium created inside the bulb. To control the flow of electrons, a magnetic or electric field is used.
Thermionic emission allows you to practically use the positive qualities of the electron flow - to generate, amplify electrical vibrations of various frequencies.
Features of radio tubes
Electrovacuum diode is the basis of radio engineering. The design of the lamp has two electrodes (cathode and anode), a grid. The cathode provides emission, for this the tungsten layer is covered with barium or thorium. The anode is made in the form of a nickel, molybdenum, graphite plate. Netis the separator between the electrodes. When the working fluid is heated, a powerful electric current is created from moving particles in a vacuum. Electrovacuum 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, radio-electronic industry.
Without them it was impossible to manufacture radios, televisions, special equipment, computers.
Application areas
With the development of precision instrumentation, radio electronics, these lamps have lost their relevance, ceased to be used on a large scale.
But even now there are such industrial areas that require EVL, because only a vacuum lamp is able to ensure the performance of devices according to the specified parameters, in a certain environment.
EVL are of particular interest for the military-industrial complex, since it is vacuum tubes that are distinguished by increased resistance to electromagnetic impulses.
One military apparatus can contain up to a hundred EVL. Most of the semiconductor materials, REC cannot function with increased radiation, as well as in natural vacuum conditions (in space).
EVL help improve the reliability and durability of satellites and space rockets.
Conclusion
In electrovacuum devices that allow generating, amplifying, converting electromagnetic energy, the working space is completely freed from air,shielded 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 connected to an electrical circuit, a current appears inside the device. When the polarity of the voltage changes, it disappears, and no matter how hot the cathode is. By maintaining a constant value of the temperature of the heated cathode, it was possible to establish a direct relationship between the anode voltage and the current strength. The results obtained were used in the development of electronic vacuum devices.
For example, a triode is a vacuum tube with three electrodes: an anode, a thermionic cathode, a control grid.
It was triodes that became the first devices used to amplify electrical signals at the beginning of the last century. At present, 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 weight and dimensions can be neglected.
Powerful radio tubes are comparable to transistors in terms of efficiency, reliability, but their service life is much shorter. For low-power triodes, most of the heat goes into 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 electricalsignals. These devices have a higher gain compared to the triode. Such design features make it possible to use tetrodes to amplify low frequencies in televisions, receivers, and other radio equipment.
Consumers actively use incandescent lamps, in which the filament body is a tungsten filament or wire. These devices have a power of 25 to 100 W, their service life is 2500-3000 hours. Manufacturers offer lamps with different bases, shapes, sizes, so you can choose the lamp option, taking into account the characteristics of the lighting device, the area of \u200b\u200bthe room.
