Inductance is often represented by "L" plus a number in the circuit, such as: L6 represents the inductance numbered 6. The inductance coil is made by winding an insulated wire around an insulated skeleton for a certain number of turns. DC can pass through the coil, and the DC resistance is the resistance of the wire itself, and the voltage drop is very small; when the AC signal passes through the coil, a self-induced electromotive force will be generated at both ends of the coil, and the direction of the self-induced electromotive force is opposite to the direction of the applied voltage, hindering the AC voltage. Pass through, so the characteristic of the inductor is to pass DC and resist AC. The higher the frequency, the greater the coil impedance. The inductance can form an oscillation circuit with the capacitor in the circuit. Inductors generally have direct marking method and color marking method, and the color marking method is similar to resistance. Such as: brown, black, gold, gold means 1uH (error 5%) inductance. The basic unit of inductance is: Henry (H) conversion unit: 1H=10^3mH=10^6uH.