Capacitance between the two pole pieces of media, and then the shell will be the capacitor pole piece, the media package, in fact, the package shell is not 100% dense, gives the possibility of moisture infiltration. For example, the voltage in the 50V safety capacitor, moisture infiltration, plus 5V voltage across the capacitor when attached to the media on the moisture has become a leakage current channel, but because the voltage is low, the leakage current is not very Large, channel impedance generated heat is not large enough to evaporate the water vapor heating, but the destruction of the capacitor's energy storage characteristics is sufficient. As a result, the capacitor failed.
If the high voltage, the on-resistance still remains unchanged, with the voltage increases, the leakage current is bound to increase, the leakage current is not high, The increased leakage current in the on-resistance will have a greater heat I2R, this heat can also lead to moisture evaporation, the result is the capacitor leakage current gradually becomes smaller, until the restoration of energy storage function.
Therefore, the selection of the capacitor capacity of the pressure indicator is absolutely no margin to stay too much, which is prone to problems when selecting a key point.