# capacitance

A capacitor is an energy storage element used in circuits for tuning, filtering, coupling, bypassing, energy conversion and delay. Capacitor is usually called capacitor, according to its structure can be divided into fixed capacitor, semi-variable capacitor, variable capacitor three, in the circuit commonly used letter "C", according to its dielectric material can be divided into electrolytic capacitor, mica capacitor, ceramic dielectric capacity, glass glaze capacitor.

2.1.4 Identification of capacitance labels

1. Main parameters of capacitance

The main parameters of capacitance are nominal capacity, allowable error and rated DC operating voltage, etc.

(1) capacitance is the capacity of the capacitor to store charge, its unit is Farad, referred to as "law", with the letter "F", commonly used units and micro method (㎌), skin method (㎊), capacitor calibration capacitance is the nominal capacity of the capacitor.

(2) There will be a deviation between the nominal capacity of the capacitor and its actual capacity, and the deviation falls within the allowable range is the allowable error.

(3) Within the specified operating temperature range, the capacitor can work reliably for a long time, and the dc voltage it can withstand is the voltage resistance of the capacitor, also known as the rated DC operating voltage of the capacitor. 2. Label method of capacitor

Capacitors are marked by direct label method, text symbol method, number label method and color ring method.

Direct mark method: capacitor direct mark method and resistance direct mark method is similar, directly indicate capacitor capacity, deviation and voltage resistance, more intuitive. Generally, the capacitance of the current size is directly marked, such as 2700㎊±5%.

Literal notation: A method by which units of literal symbols and numbers are arranged in a regular order to indicate nominal capacity. The number before the unit character symbol is the integer part, and the number after the unit character symbol is the decimal part. For example, p10 indicates 0.1㎊, and 6p8 indicates 6.8㎊.

Numerical notation: the first two digits represent the capacitance value significant number, and the third digit indicates how many power times 10. The unit is ㎊. This method is generally used for capacitor with small volume, for example, the dielectric capacity of porcelain is marked with "103". Table method 10 x 103=10000㎊=0.01㎌.

Color ring method: Color ring method is the same as resistance color ring method, so pay attention to distinguish components during maintenance. The basic unit of color ring capacitance is "skin method".

For capacitor voltage, if it is in the AC circuit, but also pay attention to the MAXIMUM AC voltage can not exceed the dc operating voltage value of the capacitor. Common capacitor operating voltage is 6.3V, 10V, 16V, 25V, 50V, 63V, 100V, 250V, 400V, 500 V, 630V, 1000V.

3. Label the chip capacitance

With the increasing integration of the circuit, many circuit motherboards now use SMT capacitance for welding, this capacitance is generally relatively small. Their capacity is usually marked directly on the package, not on the surface of the capacitor. For the larger size of the chip electrolytic capacitor will be marked on the surface, the unit is generally μF.

3. Capacitance detection

Ω insert red pens and "V" jack, black pens and inserted into the "mA" insert, the multimeter place Settings in capacitance measuring block, and select the appropriate range, red, black pens and respectively set on the two pins of the capacitor under test, observe the multimeter displays the measured values are read and, under normal circumstances, should have a fixed electric capacity, and close to the nominal capacitance. If the measured capacitance differs greatly from the nominal capacitance, it indicates that the capacitor is damaged.

When the capacitance is less than 10pF, the capacitance of such capacitors is too small, and the detection with a pointer multimeter can only roughly determine whether there is leakage, internal short circuit or breakdown. In this case, the R ×10k ω range of the pointer multimeter can be used to detect the resistance value, which should be infinite under normal circumstances. A zero resistance indicates a leakage or internal breakdown of the measured capacitor.

When the capacitance is 10pF ~ 0.01μF, the charging and discharging process of the capacitor can be amplified on the basis of connecting the triode amplifier components. Under normal circumstances, if the pointer of the multimeter has obvious swing, it indicates that the performance is normal.

Note: it takes a certain time to return to zero each time the range is switched. After the return to zero, insert the measured capacitor. When the capacitor is tested, discharge the capacitor first, and do not touch the two pins of the measured capacitor at the same time. When measuring large capacitors, it takes some time for the display to display stable values. For a digital multimeter without a capacitor, you can measure the capacitance in analog charging mode by referring to the measurement method of a pointer multimeter.