Each of us saw on power cords or cables harmonizing electronic devices small cylinders.They can be found on most conventional computer systems, both in the office and at home, at the ends of the wires that connect the system unit to the keyboard, mouse, monitor, printer, scanner, and so on. D. This element is called "ferrite" (orferrite filter).In this article, we will deal with what purpose computer manufacturers and high technology equipped with its cable products mentioned elements.
main purpose
ferrite ring is capable of reducing the impact of radio frequency and electromagnetic interference on the signal that is transmitted over the wire.Length of signal and power cables as the computer, and other power equipment have the parasitic properties, that is, act as an antenna.They are very effective radiated into the environment various noises that are generated within the device, thereby creating interference on radio stations in the radio and other electronic equipment.Conversely, by taking the interference from ether from transmitting devices, computer or other electronic device can not operate correctly.This is to eliminate this phenomenon and use the ferrite ring, put on a feed, or adapter cable.
physical properties
ferrite is ferromagnetic, non-conducting, that is, in fact this is a magnetic insulator.This material does not create eddy currents and therefore it is very fast remagnetized - the beat frequency of the external electromagnetic fields.This material property is the basis for the effective protection of electronic devices.Ferrite core, put on the cable, can create a large common-mode currents active impedance.
This material is formed from a chemical compound of iron oxides with other metal oxides.It has unique magnetic characteristics and low conductivity.With this ferrites have little or no competition among the other high-frequency magnetic materials in the art.Ferrite ring 2000nm significantly increase the inductance of the cable (a few hundred or a thousand times), which provides high-frequency noise suppression.It is installed on the cord during its manufacture or cut into two semicircles, it is put on the wire immediately after its manufacture.Ferrite filter is packed in a plastic case.If you cut it, you can see the inside of a piece of metal.
And you need a ferrite?Or is it another hoax?
Computers are very "noisy" (in terms of electromagnetic) devices.So, the motherboard inside the system unit is able to oscillate at a frequency of one kilohertz.The keyboard has a microchip, which also operates at a high frequency.All this leads to the so-called radio noise generation near the system.In most cases, they are eliminated by shielding the board from electromagnetic fields metal casing.However, another source of noise - it's copper wires that connect a variety of devices.In fact, they act as a long antennas that capture signals from other cable radio and television equipment, and affect the operation of "his" instrument.Ferrite filter eliminates noise and electromagnetic signals broadcasting.These cells convert electromagnetic high-frequency vibrations into heat energy.That is why they are set at the ends of most cables.
How to choose a ferrite
To install the ferrite ring on the cable with his hands, it is necessary to understand the types of products.After all, on the type of wire and its thickness depends on what kind of a filter (of any material) will need to use.For example, a ring mounted on the multi-core cable (power cord, data, video, or USB-interface), it generates on this site so-called phase transformer overlooking antiphase signals that carry useful information, and also reflects the common mode noise.In this case, it should not be used to prevent ferrite absorbing violations transmit information, and more high-ferromaterial.But the ferrite rings to the antenna cable is preferably selected from a material that will dissipate high-frequency noise, rather than reflect them back in the wire.As you can see, the product is capable of properly chosen degrade the performance of your device.
ferrite cylinder
most effectively cope with interference thick ferrite cylinder.Note, however, that too bulky filters are very inconvenient to use, and the results of their work hardly in practice will be very different from the slightly smaller in size.Always use filters optimum dimensions: internal diameter should ideally coincide with the wire, and its width should match the width of the cable connector.
Do not forget that with the noise not only help fight ferrites.For example, for better conductivity is recommended to use a cable with a large cross section.When choosing the length of the cord, do not make a large supply lengths between the connected devices.In addition, the source of interference and can serve the poor quality of the connection wires and connectors.
Marking ferrite rings
The most common type of record marking ferrite rings is as follows: K d × D × H, where:
- K - an abbreviation of the word "ring";
- D - outer diameter of the product;
- d - inner diameter of the ferrite ring;
- H - the height of the filter.
Besides the dimensions product labeling encrypted type of ferromagnetic material.Example entries may be as follows: 1 K-M20VN 4h2,5h1,6.The other half corresponds to the overall dimensions of the ring, and in the first encrypted initial permeability (20 μi).In addition to these parameters, the background description, each manufacturer indicates the critical frequency, the parameters of the hysteresis loop, resistivity and Curie temperature for the particular product.
How else to use ferrite rings
Besides the well-known use as a high frequency protection, ferromagnetic materials are used for the manufacture of transformers.They can often be seen in the power supplies of computer equipment.It is generally known that the transformer is a ferrite ring is highly effective in balanced mixers.However, not everyone knows that there is an opportunity to "stretch" balancing.This modification of the transformer is capable of performing the balancing operation more accurately.In addition, widely used transformers on ferrite rings for matching input and output impedances of stages of transistor devices.This transformed resistance and reactance.Thanks to the latter device can be used for modifying the capacitance tuning range."Stretching" transformers work well at frequencies below 10 MHz.
Conclusion
Those interested in how self wound ferrite core, it should be noted that the series impedance, which introduced a high-frequency ferrite core, you can easily zoom in on it if you make a few turns of the conductor.As suggested by the theory of electrical impedance of such a system will increase in proportion to the square of the number of turns.But it is in theory but in practice, the picture is somewhat different due to the nonlinearity of ferromagnetic materials and waste in them.
A couple of turns on the core increases the impedance of four times, as it should be, but a little smaller.As a result, in order to able to accommodate a few turns in the cable filter, you should choose a ring obviously larger size.If this is unacceptable, and the wire must be of the same length, it is better to use multiple filters.
