Page 118 - Electromechanical Devices and Components Illustrated Sourcebook

80 Electromechanical Devices & Components Illustrated Sourcebook

Terminal
Rubber Stopper
Center Rod Schematic Symbol
Lip
Glass Jar
Plastic Case

Outer Foil
Covering Lead
Chain Plate Array

Inner Figure 4-136 Plate Capacitor
Foil Liner

Figure 4-134 Leyden Jar

Insulator
Conductor
plates and conductor sheets arranged in a stack. This design Coiled Sheets Insulator
has a profound effect on the size and capacity of these Conductor
devices. Figure 4-135 shows a bench built glass plate capaci-
tor. Notice that there are separate positive and negative stacks
of conducting sheets. These stacks form the storage elements
of the assembly. Figure 4-137 Coil-Wound Capacitor
Many commercial capacitors are miniaturized versions of
the glass plate design. Plate arrays are molded into a plastic
case, as shown in Figure 4-136. Other designs use coils of
conductive sheet sandwiched with insulating sheet, as shown
in Figure 4-137.
Commercial capacitors are available in nearly any size,
voltage, and capacity imaginable. Figure 4-138 shows just a
small sampling of commercial capacitors, that are designed
for a variety of applications.
Variable capacitors are not particularly effective because
Clamp Screws
the insulation between plates is generally air. Using air as the
insulator requires that the spacing between the plates must be
sufficient to prevent arcing and to provide required production
Clamp Plate tolerances for manufacturing. To improve the performance of
variable capacitors, some of these units are immersed into a
+ Plate
high dielectric oil bath.
Glass Plate Figure 4-139 shows a typical variable capacitor that may
− Plate be found in radio equipment to tune the resonant frequency of
the circuit. These assemblies are typically a set of fixed plates
and a set of moving plates that are set up to mesh together in
reference to the operator input.

Diodes
Terminal
Screw A diode, as shown in Figure 4-140 is essentially a one-way
valve for electricity. The device is commonly used for recti-
fying AC current into DC current. An example of this appli-
Figure 4-135 Bench Built Glass Plate Capacitor cation is shown in Chapter 3.