Capacitance units are: F, uf, pf. Generally, we don't take the method as a unit because it is too big. The conversion relationship between each unit is:

1F = 1000000 uf 1uf = 100000 pf

In use, we often see the unit: nf. 1uf = 1000 nf 1nf = 1000 pf

Several methods of capacitor capacity appraisal;

First, direct identification: The electrolytic capacitor capacity in the above figure is 47uf, and the capacitor withstand voltage is 25v.

2. Use unit nf: The polyester capacitor in the above figure is nominally 4n7, that is, 4.7nf, which is 4,700 pf when converted into PF. Other examples: 10n, that is, 0.01uf; ; 33n, that is, 0.033uf.

The latter 63 refers to the capacitor withstand voltage of 63v.

3. Mathematical counting method: As shown in the above figure, the nominal value of ceramic capacitor is 104, and the capacity is10x10000pf = 0.1uf. If the nominal value is 473, it is 47X 1000pf=0.047uf (the following 4 and 3 both represent the power of 10). Another example is: 332=33X 100pf=3300pf.

The use of capacitors should work under the specified withstand voltage. At present, many products with low quality are faulty due to the use of capacitors with insufficient withstand voltage (common capacitor bursting). Second, capacitance identification

1. Capacitance is generally represented by "c" plus a number in the circuit (for example, C 13 is represented by the number 13). Capacitor is an element with two metal films attached to each other and separated by insulating material. The characteristics of capacitors are mainly blocking DC and circulating AC.

The size of the capacitor means the amount of electric energy that can be stored. The blocking effect of capacitance on AC signal is called capacitive reactance, which is related to the frequency and capacitance of AC signal.

Capacitance XC= 1/2πf c (f stands for the frequency of AC signal, and c stands for capacitance) The commonly used capacitor types in telephones are electrolytic capacitor, ceramic capacitor, patch capacitor, monolithic capacitor, tantalum capacitor and polyester capacitor.

2. Identification method of capacitance: The identification method of capacitance is basically the same as that of resistance, which is divided into three methods: direct standard method, color standard method and number standard method. The basic unit of capacitance is farad (F), and other units are millifarad (mF), microfarad (uF), nanofarad (nF) and picofarad (pF).

Where: 1 method = 10 3 millifarad = 10 6 microfarad = 10 9 nanofarad =10/2 picofarad.

The capacitance value of a large capacitor is directly indicated on the capacitor, such as10uf/16 v.

The capacitance value of a capacitor with a small capacity is represented by letters or numbers on the capacitor.

Letter symbol:1m =1000uf1p 2 =1.2pf1n =1000pf.

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