1. Capacitance in the circuit is generally represented by "C" plus a number (for example, C25 represents the capacitance numbered 25).

A capacitor is a component composed of two metal films close to each other and separated by insulating materials. The main characteristic of capacitor is that it flows through AC directly. The size of capacitance is the size of the stored electric energy. The blocking effect of capacitance on AC signal is called capacitive reactance, which is related to the frequency and capacitance of AC signal.

Capacitance reactance XC = 1 / 2 π F C (F is the frequency of AC signal, C is the capacitance capacity)

2. Capacitance identification method

The identification method of capacitance is basically the same as that of resistance, which can be divided into three kinds: direct marking method, color coding method and number standard method. The basic unit of capacitance is expressed in farad (f), and other units are: millimetre (MF), micromethod (UF), nanomethod (NF) and skin method (PF).

Among them: 1 farad = 103 nm = 106 MF = 109 nm = 1012 PF

The capacitance value of large capacitance is directly indicated on the capacitance, such as 10 UF / 16 v

The capacitance value of small capacitance is represented by letters or numbers on the capacitance

Alphabetic representation: 1m = 1000 UF 1P2 = 1.2pF 1n = 1000pf

Digital representation: generally, three digits are used to represent the capacity, the first two digits represent the effective number, and the third digit is the multiplier.

For example: 102 means 10 × 102pf = 1000pf, 224 means 22 × 104pf = 0.22uf

3. Capacitance error table

Symbol F G J K L M

The allowable error is ± 1% ± 2% ± 5% ± 10% ± 15% ± 20%

For example, if the capacitance of a ceramic chip is 104j, the capacity is 0.1 UF, and the error is ± 5%.

4. Fault characteristics

In practical maintenance, the main faults of capacitor are: (1) open circuit fault caused by pin corrosion.

(2) Open circuit fault of desoldering and false soldering. (3) Leakage causes small capacity or open circuit fault.

(4) Leakage, serious leakage and breakdown fault.