l Classification of capacitors
1. According to function.
2. In accordance with the installation method. Can be divided into plug-in capacitors, SMD capacitors.
3. According to the role of capacitance in the circuit, it can be divided into coupling capacitor, filter capacitor, decoupling capacitor, high-frequency damping capacitor, resonant capacitor, load capacitance, etc.
l The main parameters of the capacitor
The capacity of a capacitor to store charge is called capacitance, or capacity.
The basic unit of capacity of capacitor is Farah, and F is used to indicate that other units are : mF, μF, NF, pF.
Among them : 1F = 1000mF, 1mF = 1000μF; 1μF = 1000 nF, 1nF = 1000pF.
2. Allowable deviation.
The maximum allowable deviation of the actual capacitance of the capacitor from the nominal capacitance is called the permissible deviation of the capacitor.
3. Rated voltage.
Rated voltage refers to the effective value of the maximum DC voltage or AC voltage that can be continuously added to the capacitor without damaging the capacitor within the specified temperature range. If the working voltage on the capacitor is greater than the rated voltage, the capacitor will be broken down.
4. Parameter reading.
The identification method of capacitance is basically the same as that of resistance, which is divided into four kinds : direct annotation method, literal symbol method, color standard method and digital standard method.
( 1 ) Direct Annotation. The direct labeling method is to directly mark the main parameters of the capacitor on the outer surface of the capacitor. Mainly used in high power, high voltage capacitor. Such as 10F / 16V, 4700 F / 50V.
( 2 ) Character Symbol Method. The literal notation method usually writes the integer part of the nominal capacity to the front of the capacity unit glyph, and writes the decimal part to the back of the volume unit glyph.
( 3 ) The color standard method is the same as that of the resistor color mark method, and the unit is pF.
( 4 ) the number standard method is to use three digits to represent the nominal value of a component. From left to right, the first two represent valid digits, and the third one is 10n ( n = 0 ~ 8 ). When n = 9 is a special case, it means 0.1. Their unit is pF.
For example : 102 indicates a nominal capacity of 1000 pF. 221 indicates a nominal capacity of 220 pF. 229 denotes a nominal capacity of 22X10-' pF = 2.2 pF.
l The detection of capacitors
1. Fixed capacitor detection.
When measuring, you should select the appropriate multimeter gear, and use two stylus to arbitrarily connect the two pins of the capacitor, and the resistance value should be infinite. If the resistance value is zero, the capacitor leakage damage or internal breakdown.
2. Detection of electrolytic capacitors.
The multimeter red pen is connected to the negative pole, and the black pen is connected with the positive electrode, and in the instant of contact, the pointer of the multimeter is deflected to the right with a larger angle ( for the same electric barrier, the bigger the capacity, the bigger the swing, and then gradually turn to the left until it stops at a certain position. The resistance at this time is the positive leakage resistance of the electrolytic capacitor, which is slightly larger than the reverse leakage resistance.
Practical experience shows that the leakage resistance of electrolytic capacitor should be more than a few hundred kilo-ohms, otherwise, it will not work properly.
In the test, if the positive and reverse no charge phenomenon, that is, the needle does not move, it shows that the capacity disappeared or internal circuit; if the measured resistance is very small or zero, it shows that the capacitance leakage is big or the breakdown is damaged, and can not be used again.
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