Capacitors parameters
1, nominal electric capacity and allow the deviation
Nominal electric capacity is marked on the capacitance in the capacitor.
The basic unit is the farad capacitor (F), but this unit too seldom used in the field tagging.
The relationship between other units are as follows:
1F = 1000mF
1mF = 1000μF
1μF = 1000nF
1nF = 1000pF
The actual capacitor capacitance and the nominal electric capacity, said deviation error said the allowed deviation range accuracy.
Accuracy grade correlation with the permissible error: 00 (01) - ± 1%, 0 (02) - ± 2%, Ⅰ - ± 5%, Ⅱ - ± 10%, Ⅲ - ± 20%, Ⅳ - (+20% -10%), Ⅴ - (+50% -20%), Ⅵ - (+50% -30%)
General capacitor used Ⅰ, Ⅱ, Ⅲ grade, electrolytic capacitors Ⅳ, Ⅴ, Ⅵ level, selected based on usage.
2, rated voltage
Rated at the lowest ambient temperature and ambient temperature can be continuously added to the maximum DC voltage capacitor rms, generally directly labeled in the capacitor case, if the voltage exceeds the capacitor voltage, capacitor breakdown, resulting in permanent damage can not be repaired.
3, insulation resistance
DC voltage added capacitors and generate leakage current, insulation resistance as the ratio between the two.
When the capacitor is small, depending on the surface state capacitance, capacity> 0.1uf hours, depending on the performance of media, the smaller the better insulation resistance.
Capacitance time constant: In order to properly evaluate the insulation of large-capacity capacitors, instead of the time constant, he is equal to the capacitance product of insulation resistance and capacity.
4, loss
Capacitor in the electric field, in unit time, the energy consumed by internal heat loss is called. Various types of capacitors are provided in a frequency range of its loss within the permissible value capacitor depletion mainly by dielectric loss, conductivity and capacitive loss for all metal parts caused by the resistance.
In the DC electric field under the effect of capacitor leakage losses in order to guide the form of loss is generally small, in the alternating electric field under the influence of the depletion capacitance and the leakage is not only derivative, but also to the polarization of the establishment of periodic processes.
5, the frequency characteristics of
As the frequency increases, the general capacitance capacitors have shown a downward pattern.
6, commonly used formulas
Parallel-plate capacitor formula C = εS/4πkd |
