Inductor is usually called the feeling, the self inductance coil is called inductance, mutual inductance coil is called transformer, they are all with enameled wire, cotton covered wire or plastic skin line in insulation skeleton or core (typically high-frequency transformer), iron core made of round a set series of electromagnetic induction of coaxial circle element, Inductor is also one of the common components in electronic circuit, used in the circuit for tuning, filtering, coupling, energy conversion, isolation of variable current signal, etc. Inductance is denoted by the letter "L" in a circuit. According to its structure, it can be divided into fixed inductor and adjustable inductor.

Transformer uses a primary (primary), secondary (secondary) winding between the number of turns (turns) ratio difference to change the voltage ratio or current ratio, to achieve electric energy or signal transmission and distribution. Its main role is to reduce or enhance the AC voltage, signal coupling, conversion impedance, isolation, etc., transformer in the circuit with the word line "T".

When an electric current passes through the coil, a magnetic field is created around the coil. When the current in the coil changes, its turnover magnetic field also has a corresponding change, this change of magnetic field can make the coil itself induced electromotive force, which is self-induction. When two inductance coils are close to each other, the magnetic field change of one inductance coil will affect the other inductance coil, and this effect is mutual inductance. The mutual inductance depends on the degree of coupling between the inductance coil and the inductance coil.

2.1.5 Inductor and transformer reading

1. Main parameters of inductor

The main parameters of inductor include inductance, allowable deviation, quality factor, distributed capacitance and rated current, etc. Inductance, also known as self-inductance coefficient, is a physical quantity that indicates the ability of inductor to generate self-inductance.

(1) The basic unit of inductance is Henry, denoted by the letter "H". The common units are milliheng (mH) and microheng (μH). The inductance of the inductor mainly depends on the number of turns of the coil, the winding method, whether there is a magnetic core and the material of the magnetic core. In general, the more turns of the coil, the more dense the winding, the greater the inductance. Usually the coil with a magnetic core has a higher inductance than the coil without a magnetic core. The greater the core permeability of the coil, the greater the inductance.

(2) The allowable deviation refers to the allowable error value between the nominal inductance and the actual inductance of the inductor. Generally, the inductor in the oscillation or filtering circuit requires high precision, and the allowable deviation is ±0.2%~±0.5%; For coupling, high-frequency choke coil precision requirements are not high, the allowable deviation is ±10%~±15%.

(3) Rated current refers to the maximum allowable current value of the inductor during normal operation. If the working current exceeds the rated current, the inductor will change its performance parameters because of heating, and even burn out because of overcurrent.

(4) Quality factor is also your Q value or optimal value, is the main parameter to measure the quality of inductance. It refers to the ratio of the inductive reactance of an inductor to its equivalent loss resistance when operating at a certain frequency of AC voltage. The higher the Q value of inductor is, the lower the loss is and the higher the efficiency is. The inductor quality factor is related to the dc resistance of the coil wire, the dielectric loss of the coil frame, the loss caused by the iron core and the shielding cover.

2. Marking inductance

Inductance labeling methods mainly include direct label method (e.g. 100μH±10%), numerical label method (e.g. 471K, 47×101μH±10%), color ring method (the same as resistance color ring method, mainly used for small fixed inductors shaped like fixed resistors). The basic unit of color ring method inductance is "micro hm".