ELECTRONIC PRINCIPLES - OD1647 - LESSON 1/TASK 1
The type of dielectric used and its thickness govern the amount
of voltage that can safely be applied to the electrolytic
capacitor. If the voltage applied to the capacitor is high
enough to cause the atoms of the dielectric material to become
ionized, arcing between the plates will occur. In most other
types of capacitors,. arcing will destroy the capacitor.
However, an electrolytic capacitor has the ability to be self
healing. If the arcing is small, the electrolytic will
regenerate itself. If the arcing is too large, the capacitor
will not selfheal and will become defective.
(5) Oil Capacitors. OIL CAPACITORS are often used in high
power electronic equipment. An oilfilled capacitor is nothing
more than a paper capacitor that is immersed in oil. Since oil
impregnated paper has a high dielectric constant, it can be used
in the production of capacitors having a high capacitance value.
Many capacitors will use oil with another dielectric material to
prevent arcing between the plates of an oilfilled capacitor,
because the oil will tend to reseal the hole caused by the
arcing. Such a capacitor is referred to as a SELFHEALING
capacitor.
m. Variable Capacitors. A variable capacitor is constructed in
such a manner that its value of capacitance can be varied. A
typical variable capacitor (adjustable capacitor) is the rotor
stator type. It consists of two sets of metal plates arranged
so that the rotor plates move between the stator plates. Air is
the dielectric. As the position of the rotor is changed, the
capacitance value is changed. This type of capacitor is used
for tuning most radio receivers. Its physical appearance and
its symbol are shown in figure 45 on the following page.
Another type of variable capacitor (trimmer capacitor) and its
symbol is shown in figure 46, on the following page. This
capacitor consists of two plates separated by a sheet of mica.
A screw adjustment is used to vary the distance between the
plates, thereby changing the capacitance.
n. Color Codes For Capacitors. Although the capacitance value
may be printed on the body of a capacitor, it may also be
indicated by a color code. The color code used to represent
capacitance values is similar to that used to represent
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