What constitutes an element, as a capacitor? It is a small radioelement with createchannel electrical capacitance formed by two or greater number of electrodes. In some cases this element is also called the lining. These little details are separated such a thing as a dielectric (special paper, a thin layer of mica, ceramics, etc.). The capacity of this details will depend on such factors as the size (area) of the plates, the distance between these elements, and the properties of the dielectric.
A Very important fact. The capacitor has one property, which manifests itself in an AC circuit. For this circuit this part will be the resistance, the magnitude of which will depend on the frequency. If the frequency increases, the resistance will decrease, and Vice versa.
There are basic units with which it is possible to determine the identity of a capacitor. These include Farad, microfarad, etc. Designation on the elements of these units, respectively, is: f, UF.
The variable Capacitor is composed of such parts, like sections of plates of metallic material. One of these sections can implement a smooth movement relative to the second. During this movement occurs so that the plates of the movable part, i.e. the rotor, most often introduced into the gaps existing between the plates of the stationary part - the stator. Due to this motion is the following. The area of overlap of the plates of some other changes, resulting in change and the capacity of the variable capacitor.
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Dielectric in such elements is often air. Although it is worth noting that, if we talk about equipment with small dimensions, for example, a transistor pocket receivers, they often used a variable capacitor with a solid dielectric. As this item there is wear-resistant and high-frequency raw materials. Most often it is Teflon or polyethylene.
The Main parameter for such items, which will help to determine the possibility of operation of the device in the resonant circuit, the minimum and maximum capacity. This figure often appears next to the variable capacitor on the circuit device.
It Should be noted that in such devices as radio receivers and radio transmitters that uses multiple resonant circuits. In order to configure the operation of several parts, use blocks of capacitors. One block usually consists of two, three or more sections of the variable capacitor.
The Rotary part for these units is usually mounted on a common shaft for all of the variable capacitor. This is done for convenience, since the rotation of only one rotor there is a possibility of changes in the capacitance of all devices located in this section.
It is Important to note that in the diagram, each capacitor is included in the unit is displayed separately. In order to indicate that the capacity of the variable condenser of this unit and other elements can be changed with just one knob that controls all block those arrows, which denote the regulation, must be connected to one dashed line mechanical connection.
It is Worth noting that there are some varieties such KPE. One of the types is a differential capacitor, which has found its application, for example, in the shoulders of the capacitive bridges. A feature of this view is that it has two sets of stator plates and one row of rotary. The arrangement of groups of plates is as follows: when one group goes out of the gap, the second immediately takes their place. At this point, the capacitance of the capacitor AC differential type will decrease between the plates of the first group of the stator and the rotor. But between the second group of plates of the stator and the rotor group, this figure will grow. Thus, the total value will remain unchanged.
Another type of variable capacitor is the trimmer capacitor. They are used in order to specify the initial capacity of the oscillating circuit, which will determine the maximum frequency settings. The capacitance of the capacitor in the AC circuit of this type can be changed from several units picofarads to several tens of picofarads. In some cases, can be achieved and high capacity.
These types of KPE is presented the main requirement is the ability to smoothly change the capacity values. Also, this capacitor must provide reliable fixing of the rotor in a predetermined position.
The Most common type of trimmer capacitor is ceramic. The design of this device is as follows. Base details - ceramic stator and the movable base mounted thereon in the form of a disc - rotor. Plates in this element serve as thin layers of silver.They are applied using vigania. Viganj is on the stator and on the outer wall of the rotor.
In order to change or determine the capacity of the variable condenser of this type, it is necessary to rotate the rotor. If we talk about the most simple equipment, it is most commonly used wire trimmer capacitor. This is the detail of cut copper wire with a diameter of 1-2 mm. the Length of this element is about 15-20 mm. the wire very tightly, turn to turn, is wound insulated wire with a diameter of 0.2-0.3 mm. in order to change the capacitance in this device, it is necessary to rewind the wire. So at this time did not slip off the coil with it, it is necessary to impregnate it with any insulation composition.
It is important to note that the current in the circuit in which a capacitor can flow only in the condition that will change the applied voltage. You also need to understand that the strength of current which will circulate in the circuit during discharge and charge of this element will be greater, the greater the capacity of the condenser, and will depend on the speed with which the changes of the electromotive force (EMF).
Another property. A capacitor with a variable capacitance, which is included in circuit with an alternating current, will be for this circuit resistance. In other words, the value that is capacitance and resistance will be the smaller, the greater the value of the vessel itself and the higher frequency the effective current. However, this statement is true only for the circuit in which the current variable. The capacitance of the capacitor is infinite, that is, its resistance would be infinite, if you place an element in a circuit with a constant current.
There are several basic parameters for such capacitors.
One of the main reasons is the law of change of capacitance. This law defines the nature of the changes in the capacitance. Changing this setting will occur depending on the angle of rotation or linear movement of the moving part of the capacitor plates relative to their fixed parts.
One of the properties is temperature stability. This indicator directly depends on the design of the condenser. Most often, this indicator is positive, and for capacitors with air as the dielectric does not exceed (200:300) 10-61/deg. If we talk about the capacitors with a solid dielectric, they have this value higher.
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