Electric filter - a device for suppressing or conversely, separating a certain signal component. This, for example, on the frequency or phase. The amplitude of the electrical signals are usually not filtered.
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Filters communications equipment
Frequency filtering becomes the basis for creating a transmitting and receiving device for information dissemination over the air. Spectrum stronger signal is clipped on both sides of the channel to reduce the noise. As a result, the useful information is transmitted over long distances. Electric filters are considered a method of determining signal. Additionally used:
- Selection of wavelength. The best frequency is considered to be the frequency that satisfies the criteria. For example, long wave well encircle the Earth's surface, and the individual frequencies reflected from clouds and other celestial formations, allowing to transmit information anywhere in the world. Waves are good for communication at short distances. frequencies used for space communications, is not absorbed by water vapor. Detection of the frequency is carried out on the reception side of the input high-frequency filters.
- information encoding PN sequences. With the introduction of the practice of the binary signals of the signal transmission over long distances has become a real challenge. Using the PN code reduces power requirements, conceal the signal from the "enemy" against the background of the natural flow of air. Knowing the structure of the encoded signal may accept the information at a signal / noise ratio is less than unity. Actually detect such broadcast is impossible.
- Encoding information on the excessive length allows the receiving side to correct errors. This method combined with PN. The loss of information is excluded. Especially in the presence of double-sided (duplex) channel. PN sequence is composed of zeros and ones. From its length it is directly dependent on the sensitivity of the receiver - the more, the better. Each long sequence represents a single character, as a rule, the binary alphabet: toe or yedinichku.
In these cases, it allows to calculate signal electric filter. Different types of devices relating to the subject, crammed with communication equipment. On the reception side antenna catches wide range, being characterized by selective properties. Plate, wave channel, spike on the vehicle is allowed to call a specific range of electric filters. For this reason, in addition to the household receiver has built-in telescopic antenna ferromagnetic.
Wave detected by the input circuit, is The adjustable electric filters. Modern technology does not allow to create a device that will cover all the frequencies. Therefore, input filters for broadcast receivers several switch control knob. Each block comprises of adjustable capacitor, as the magnitude of change of inductance is difficult. Obtained bulky and inconvenient arrangement. Mobile Gadgets are miniature work at microwave frequencies, but also there are present the same kind of electric filters.
After the initial channel selection and cropping on the sides interference signal to the high frequency amplifier. Its selectivity greatly affects the receiver's sensitivity. In selected structures apply filters similar to the input for this stage. Then follows signal to a mixer, where it is converted to an intermediate frequency. Due to the fixed value, the subsequent stages of amplifiers manages finely tune receiving grand transmission coefficient. Filters are used especially with high selectivity. This is possible thanks to a fixed frequency.
Detector highlighted the useful signal in the form of human speech, is fed to the low-frequency amplifier. In the transmitting apparatus uses a technique of this kind for cleaning of the signal, but the requirements are much more loyal - ether zashumlyayuschego makes no impact.
Apart from the above in any apparatus installed power circuits filters. Their task is to pass into a voltage frequency of 50 Hz, the rest sift. Equipment manufactured in the Soviet Union was not able to boast of high-quality filtration, the requirements are different. Today sensitive electronics easily breaks down the static and the usual noise. Crosstalk easily burned graphics adapters of the first computers.
Gradually electronics become more secure, but the line filter is part of any equipment, which contains the chip. This is not quite right, running motors of any type make a lot of noise:
- Asynchronous create large voltage spikes at startup and commissioning. In the process, the impact on the supply chain is not so great.
- Collector permanently clog the power line interference due to arcing. Operating a vacuum cleaner greatly disturb the neighbors.
Filters regulatory and protective equipment
In addition to electrical filters household equipment supply circuits peculiar equipment with similar problems are encountered in the industry. Now it is a question of regulation. In the operation of engine causes interference, special filters are engaged in this situation, but there is a separate line efficiency. It means the power factor and reactive component.
When the engine is running, it happens sometimes that the energy is given back to the network. For example, during dynamic braking the shaft briefly enters into the generation zone, the power supply circuit receives the voltage jump. But the power of the return process develops in the nominal mode.
Substation transformers forming voltage to return. The presence of reactive resistances in the circuit leads to such. Formed a kind of oscillation circuit, in which the energy around snuot to and fro. Heats the wires, not performing useful work. It has long been noted, sometimes the company is fined. Energy meters require the installation of reactive (returned) power.
For the analysis of the industrial chain in 1918 developed the method of symmetrical components. It was found that current consumption is represented in the form of three components:
- Direct sequence.
- The reverse sequence.
- Zero sequence.
In the literature, especially modern, there is no clear description of the meaning of expressions. Intentional introduction confusion only dulls readers. In fact, the name clearly define the subject of the conversation, as if reflecting the essence. Direct sequence is present in a purely active power when the energy is not reflected back, and zero indicates whether the currents flowing in the neutral circuit. The latter happens when accidents asymmetrical load. Contact within the meaning of the reactive power characteristic and occurs under identical conditions.
Due to the presence reactances of lines of three-phase AC voltage unbalanced. It deviates from the nominal value by a certain angle in the vector diagram. As a result, it becomes difficult to analyze. Current flows simultaneously to power the equipment and back - reflected the reactive part of the resistance.
Coined analysis by symmetrical components. Wherein each signal is decomposed into a sequence, as indicated above. Any asymmetric voltage or current is a sum of three symmetrical components. Each characterized by a specific process. For example, direct sequence characterizes the power consumption. The vector addition of all three provides the voltage or current in the phase in which they flow through the circuit.
The positive sequence vectors in adjacent lines are shifted by 120 degrees to form a supply transformer. In the back - the same, but the order is reversed phases. If we take the direct procedure, the phase shift is 240 degrees. This is the reason the reverse order in name. Third row vectors is fundamentally different from the two others. It the phase difference between the voltages or currents is zero. They rotate synchronously.
To carry out these mathematical operations created a special formula. Result decomposition asymmetric sequences - in Fig. Since the method is artificial, can not see the components using conventional ammeter and voltmeter. The exceptions are the ideal case:
- The perfectly symmetrical consumption modes for all phases or the same kind of short-circuit seen on the oscilloscope direct sequence.
- The reverse sequence is marked in the case of a short circuit on one or two phases. Or in the case of a pronounced asymmetry of consumption.
- A similar spoken about zero sequence. When short circuits between phases such component is absent. And clearly manifested exclusively by leaks to the ground.
Thus, any three-phase network is represented by three fictional where the flow sequence listed separately. And the values of currents and voltages then acceptable to use regulation and protection. To implement it in practice, apply filters, relays symmetric sequences.
Filters symmetrical components
Symmetrical components filters operate with a voltage or a current and are connected via respective transformers. The input to said input device receives the recorded values, a control signal is produced at the output. The voltage is usually selected in a star, you want to get information on each line separately.
Filters sequences are considered specific equipment and are so called because in the absence of the target signal not issue control actions. Even if the parameters are present in the input. It turns out, acts as a filter. Hence the requirement for three types. For example, filters are used for direct sequence Registry active energy. But in most cases, the equipment becomes part of the equipment of large enterprises.
There are combined filters. All kinds of short circuits are not tracked on the same sequence type. Filters symmetric sequences include part of the relay are not able to work with conventional, commercially-produced. When you try to adjust their load characteristic is greatly increased volume, increased weight. This is the secret of strange names - Filter relay.
An additional feature becomes absence of a single body. Constituent filter disposed separately because of the presence of heterogeneous devices consisting of: transformers, inductors, capacitances, resistors, and so forth. In addition to current and voltage, these devices are able to monitor and power. In the latter case, it becomes possible to implement on the basis of their counters. But, as mentioned above, electric filters, relays much more frequently used in protection circuits.