Model designation of capacitance:

1) The names of capacitors in different countries are very different. The names of domestic capacitors are composed of four parts

Part I: the name is indicated by letter, and the capacitor is C

The second part: the letter is used to represent the material.

The third part: use numbers to represent classification.

The fourth part: the number is used to represent the serial number.

2) Marking method of capacitance:

(1) Direct marking: mark the model and specification directly on the shell with letters and numbers.

(2) Text symbol method: the capacity is represented by the regular combination of numbers and text symbols. The unit of the capacity expressed by the text symbol: P, N, u, m, F, etc. The same as the resistance. The nominal allowable deviation is also the same as the method of resistance expression. Capacitance less than 10PF, its allowable deviation shall be replaced by letter: B-- ± 0.1pF,C-- ± 0.2pF,D-- ± 0.5pF,F-- ± 1pF.

(3) Color coding method: the same as the resistance expression method, the unit is pf. the voltage withstand voltage of small electrolytic capacitor is also used by color coding method, and the position is near the root of positive lead line. The meaning of the expression is as follows:

Color black, brown, orange, yellow, green, blue, purple grey

Withstand voltage 4V 6.3V 10V 16V 25V 32V 40V 50V 63v

(4) The mark method of imported capacitor: the imported capacitor generally consists of 6 items.

Item 1: letter for category:

The second item: the shape, structure, packaging mode, lead line start and the relationship with the axis are represented by two digit numbers.

The third item: temperature characteristics of temperature compensation capacitor, which are of letters and colors, have the following meanings:

Serial number letter color temperature coefficient allowable deviation letter color temperature coefficient allowable deviation

1 a gold +100 R yellow-220

2 B gray + 30 s green-330

3 C black 0 t blue-470

4 G ± 30 u purple-750

5 h brown-30 ± 60 V -1000

6 J ± 120 W -1500

7 K ± 250 X -2200

8 L Red-80 ± 500 Y -3300

9 M ± 1000 Z -4700

10 N ± 2500 SL +350~-1000

11 P orange-150 yn-800~-5800

Note: the unit of temperature coefficient is 10e-6/ ℃; The allowable deviation is%

The fourth item: the voltage is expressed by numbers and letters, letters are valid values, and numbers represent the power of 10 of the multiplier.

Item 5: nominal capacity, expressed by three digits, the first two digits are valid values, and the third is the power of 10. When there is a decimal, it is expressed by R or P. The unit of ordinary capacitor is PF, and the unit of electrolytic capacitor is uf

Item 6: allowable deviation. It is expressed in one letter, and the meaning is the same as that of domestic capacitor.

It is also useful to use color labeling method, which has the same meaning as the mark method of domestic capacitor.

3. main characteristic parameters of capacitance:

(1) Capacity and error: the maximum allowable deviation range of actual and nominal capacitance. Generally divided into three levels: I level ± 5%, class II ± 10%, class III ± 20% in some cases, there is a 0 level, and the error is ± 20%.

The allowable error of precision capacitors is small, while the error of electrolytic capacitors is large, and they adopt different error levels.

The accuracy level of the commonly used capacitor is the same as that of the resistor. In letters: d-005-- ± 0.5%; F-01 level-- ± 1%; Grade g-02-- ± 2%; J-I level-- ± 5%; K-ii-- ± 10%; M-iii-- ± 20%.

(2) Rated working voltage: the maximum DC voltage that the capacitor can work stably and reliably for a long time in the circuit, also known as voltage withstand. For devices with the same structure, medium and capacity, the higher the voltage withstand, the larger the volume.

(3) Temperature coefficient: the relative change value of capacitance for each change of temperature 1 ℃ in a certain temperature range. The smaller the temperature coefficient, the better.

(4) Insulation resistance: used to indicate the leakage size. Generally, small capacity capacitance, insulation resistance is very large, in hundreds of megaohms or thousands of megaohms. The insulation resistance of electrolytic capacitor is generally small. In contrast, the larger the insulation resistance, the better, the less leakage.

(5) Loss: the energy consumed by the capacitor heating in unit time under the action of electric field. These losses are mainly due to the dielectric loss and metal loss. It is usually expressed by tangent value of loss angle.

(6) Frequency characteristics: the property of the electric parameters of the capacitor changing with the frequency of the electric field. The capacitance of capacitor working at high frequency is reduced because the dielectric constant is smaller at high frequency than that at low frequency. The loss also increases with the increase of frequency. In addition, the distribution parameters of capacitors, such as the resistance between the lead and the electrode, the inductance of the electrode, the inductance of the lead, etc., will affect the performance of the capacitor. All of these make the frequency of capacitor limited.

The highest frequency of capacitor is different. The small mica capacitor is within 250MHz; The wafer type porcelain dielectric capacitor is 300MHz; The circular tube type porcelain dielectric capacitor is 200MHz; The disc type porcelain medium can reach 3000MHz; The small paper dielectric capacitor is 80MHz; Medium sized paper dielectric capacitors are only 8mhz