Inductor coils are devices that operate on the principle of electromagnetic induction. When a current flows through a wire, a certain electromagnetic field is generated around the wire, and the wire of the electromagnetic field itself induces a wire in the electromagnetic field. The effect on the wire itself that generates the electromagnetic field is called “self-inductance”, that is, the changing current generated by the wire itself produces a changing magnetic field, which further affects the current in the wire; the effect on other wires in the electromagnetic field range. It is called "mutual feeling."
The electrical characteristics of the inductor are opposite to those of the capacitor, "resisting high frequency, passing low frequency". When the high-frequency signal passes through the inductor, it encounters a large resistance and is difficult to pass. However, the resistance of the low-frequency signal when passing through it is relatively small, that is, the low-frequency signal can pass through it relatively easily. The resistance of the inductor to DC is almost zero.
Resistance, capacitance and inductance, they will have a certain resistance to the flow of electrical signals in the circuit. This resistance is called "impedance". The impedance of the inductor to the current signal is the self-inductance of the coil. Inductor coils Sometimes we refer to it as "inductance" or "coil", which is indicated by the letter "L". When winding an inductor, the number of turns of the coil is generally referred to as the "number of turns" of the coil.
Edit this paragraph main performance indicators
The performance index of the inductor is mainly the amount of inductance. In addition, the wire wound around the inductor coil generally has a certain resistance. Usually, this resistor is small and can be ignored. But when the current flowing in some circuits is very large, this small resistance of the coil can not be ignored, because a large current will consume power on this coil, causing the coil to heat up or even burn out, so sometimes it is necessary to consider The electrical power that the coil can withstand.
The inductance L represents the inherent characteristics of the coil itself, regardless of the current magnitude. Except for the special inductor (color code inductor), the inductance is generally not marked on the coil, but is marked with a specific name.
The size of the inductive coil that blocks the AC current is called XL, and the unit is ohm. Its relationship with inductance L and AC frequency f is XL=2πfL
The quality factor Q is a physical quantity indicating the quality of the coil, and Q is the ratio of the inductive reactance XL to its equivalent resistance, that is, Q = XL / R. The higher the Q value of the coil, the smaller the loss of the loop. The Q value of the coil is related to the DC resistance of the wire, the dielectric loss of the skeleton, the loss caused by the shield or the iron core, and the influence of the high frequency skin effect. The Q value of the coil is usually from several tens to several hundreds.
Any inductor coil, between the 匝 and 匝, between the layers, between the coil and the reference ground, between the coil and the magnetic shield, there is a certain capacitance, these capacitors are called the distributed capacitance of the inductor. If these distributed capacitances are combined, they become an equivalent capacitor C in parallel with the inductor. The presence of the distributed capacitance reduces the Q value of the coil and the stability is deteriorated, so that the distributed capacitance of the coil is as small as possible.
There are several types of inductive coils commonly used in circuits:
Classified by inductance: fixed inductance, variable inductance.
Classified according to the nature of the magnetizer: air core coil, ferrite coil, iron core coil, copper core coil.
Classified according to the nature of the work: antenna coil, oscillating coil, choke coil, trap coil, deflection yoke.
According to the winding structure classification: single-layer coil, multi-layer coil, honeycomb coil, tight-wound coil, inter-wind coil, tire-wound coil, honeycomb coil, chaotic coil.
1, single layer coil
The single-layer coil is wound around the paper tube or bakelite skeleton in a circle with insulated wires. Such as a transistor radio wave antenna coil.
2, honeycomb coil
If the coil is wound, its plane is not parallel to the plane of rotation, but intersects at a certain angle. This coil is called a honeycomb coil. And the number of times the wire is bent back and forth, often referred to as the number of vertices. The advantage of the honeycomb type winding method is that the volume is small, the distributed capacitance is small, and the inductance is large. The honeycomb coils are wound by the honeycomb winding machine. The more the folding points, the smaller the distributed capacitance.
3, ferrite core and iron powder core coil
The inductance of the coil is related to the presence or absence of a magnetic core. Inserting a ferrite core into the air core coil increases the inductance and improves the quality of the coil.
4, copper core coil
Copper core coils are used in the ultrashort wave range. The position of the copper core in the coil is used to change the inductance. This adjustment is convenient and durable.
5, color code inductor
A color code inductor is an inductor with a fixed inductance. The method of marking the inductance is marked with a color ring like a resistor.
6, choke (choke)
The coil that restricts the passage of alternating current is called a choke, and is divided into a high frequency choke coil and a low frequency choke coil.
7, deflection coil
The deflection yoke is the load of the output stage of the television scanning circuit. The deflection yoke requires: high deflection sensitivity, uniform magnetic field, high Q value, small size and low price.
The self-induced electromotive force in the coil of the inductor always competes with the change in current in the coil. The inductance coil has an obstructive effect on the alternating current, and the magnitude of the resistance is called xl, and the unit is ohm. The relationship between the inductance l and the alternating current frequency f is xl=2πfl, and the inductor can be mainly divided into a high frequency choke coil and a low frequency choke coil.
Tuning and frequency selection
The inductor coil and the capacitor are connected in parallel to form an lc tuned circuit. That is, the natural oscillation frequency f0 of the circuit is equal to the frequency f of the non-AC signal, and the inductive reactance and capacitive reactance of the loop are also equal, so that the electromagnetic energy oscillates back and forth between the inductor and the capacitor, and the resonance phenomenon of the lc loop. At the time of resonance, the inductive reactance and capacitive reactance of the circuit are reversed, the inductance of the total current of the loop is the smallest, and the current is the largest (refers to f=“f0” AC signal). The lc resonant circuit has the function of selecting a frequency and can An AC signal of a frequency f is selected.
(1) When selecting and using an inductive coil, first consider the inspection and measurement of the coil, and then judge the quality of the coil and its advantages and disadvantages. In order to accurately detect the inductance of the inductor and the quality factor Q, special instruments are generally required, and the test method is complicated. In actual work, such detection is generally not performed, and only the on-off check of the coil and the judgment of the magnitude of the Q value are performed. The multi-meter resistance can be used to measure the DC resistance of the coil, and then compared with the original resistance or nominal resistance. If the measured resistance is much larger than the original resistance or nominal resistance, even the pointer does not move. (The resistance value tends to infinity X) It can be judged that the coil is broken; if the measured resistance value is extremely small, it is judged that it is a severe short circuit. The local short circuit is difficult to compare with two people. It can be judged that the coil is bad. can not be used. If the sense resistor is not much different from the originally determined or nominal resistance, it can be determined that the coil is good. In this case, we can judge the quality of the coil, that is, the Q value, according to the following conditions. When the inductance of the coil is the same, the smaller the DC resistance, the higher the Q value; the larger the diameter of the wire used, the larger the Q value; if the multi-strand wire is used, the number of strands of the wire is increased, and the Q value is higher. High; the smaller the loss of the material used for the coil bobbin (or core), the higher the Q value. For example, when a high silicon silicon steel sheet is used as an iron core, its Q value is higher than that of an ordinary silicon steel sheet as a core; the smaller the coil distributed capacitance and the leakage magnetic flux, the higher the Q value. For example, the coil of the honeycomb type winding method has a higher Q value than that of the flat winding, and is higher than that of the tangled winding; the coil has no shielding cover, and when there is no metal member around the mounting position, the Q value is high, and on the contrary, the Q value Lower. The closer the shield or metal member is to the coil, the more serious the Q value is reduced; the position of the magnetic core should be properly arranged; the antenna coil and the oscillating coil should be perpendicular to each other, which avoids the influence of mutual coupling.
(2) Before the coil is installed, visual inspection is required.
Before use, check whether the structure of the coil is firm, whether the wire is loose or loose, whether the wire contacts are loose, whether the core rotation is flexible, and whether there is a slide buckle or the like. These aspects are checked and then installed.
(3) When the coil needs to be fine-tuned during use, the fine-tuning method should be considered.
Some coils need to be fine-tuned during use, and it is inconvenient to change the number of coil turns. Therefore, the method of fine-tuning should be considered when selecting. For example, a single-layer coil can adopt a method of removing the number of trapped coils at the end point, that is, winding 3 to 4 turns at one end of the coil in advance, and when the fine adjustment is performed, the position can be changed to change the inductance. Practice has proved that this adjustment method can achieve a fine adjustment of ± 2% - ± 3% of the inductance. For coils used in short-wave and ultra-short-wave circuits, a half turn is often left as a fine adjustment, and the half-turn is removed or folded to change the inductance and achieve fine adjustment. The fine adjustment of the multi-layer segment coil can be realized by moving the relative distance of one segment, and the number of turns of the movable segment should be 20%-30% of the total number of turns. Practice has proved that this fine-tuning range can reach 10%-15%. The coil with the magnetic core can achieve fine adjustment of the inductance of the coil by adjusting the position of the magnetic core in the coil tube.
(4) Use coils to keep the inductance of the original coil
When the coil is in use, do not change the shape of the coil at will. The size and distance between the coils, otherwise it will affect the original inductance of the coil. In particular, the higher the frequency, that is, the smaller the number of turns. Therefore, the high frequency coil currently used in television sets is generally sealed and fixed with high frequency wax or other dielectric materials. In addition, it should be noted that during maintenance, do not arbitrarily change or adjust the position of the original coil to avoid detuning.
(5) The installation of the adjustable coil should be easy to adjust
The adjustable coil should be mounted in an easily adjustable position of the machine to adjust the inductance of the coil for optimum operation. 
The inductance is the ratio of the magnetic flux of the wire to the current in which the flux is generated when an alternating current is passed through the wire to produce alternating magnetic flux in and around the wire.
When a direct current is passed through the inductor, only a fixed magnetic line of force is present around it, which does not change with time; however, when an alternating current is passed through the coil, magnetic lines of force appearing around it will appear around the time. According to Faraday's law of electromagnetic induction, magnetoelectricity, the varying magnetic lines of force produce an induced potential across the coil, which is equivalent to a "new power supply." When a closed loop is formed, this induced potential generates an induced current. It is known by Lenz's law that the total amount of magnetic lines generated by the induced current is intended to prevent the change of the original magnetic lines. Since the original magnetic field line changes from the change of the external alternating current power supply, the objective coil has the characteristic of preventing the current change in the alternating current circuit from the objective effect. Inductor coils have similar characteristics to the inertia in mechanics. They are electrically named "self-sensing". Usually, when the knife switch is turned on or the knife switch is turned on, sparks will occur. This is the phenomenon of self-inductance. Highly induced by the induced potential.
In short, when the inductor coil is connected to the AC power source, the magnetic lines of force inside the coil will change with the alternating current, causing the coil to continuously generate electromagnetic induction. This electromotive force generated by the change of the current of the coil itself is called "self-induced electromotive force".
It can be seen that the inductance is only a parameter related to the number of turns of the coil, the size and shape, and the medium. It is a measure of the inertia of the inductor and is independent of the applied current.