05-04-2013, 04:55 PM
BASIC ELECTRONIC COMPONENTS
[attachment=52881]
RESISTORS
RESISTORS, What do they do?
The electronic component known as the resistor is
best described as electrical friction. Pretend, for a
moment, that electricity travels through hollow pipes
like water. Assume two pipes are filled with water
and one pipe has very rough walls. It would be easy
to say that it is more difficult to push the water
through the rough-walled pipe than through a pipe
with smooth walls. The pipe with rough walls could
be described as having more resistance to
movement than the smooth one.
Pioneers in the field of electronics thought electricity
was some type of invisible fluid that could flow
through certain materials easily, but had difficulty
flowing through other materials. In a way they were
correct since the movement of electrons through a
material cannot be seen by the human eye, even
with the best microscopes made. There is a
similarity between the movement of electrons in
wires and the movement of water in the pipes. For
example, if the pressure on one end of a water pipe
is increased, the amount of water that will pass
through the pipe will also increase. The pressure on
the other end of the pipe will be indirectly related to
the resistance the pipe has to the flow of water. In
other words, the pressure at the other end of the
pipe will decrease if the resistance of the pipe
increases. Figure 1 shows this relationship
graphically.
THE CARBON COMPOSITION RESISTOR
By grinding carbon into a fine powder and mixing it
with resin, a material can be made with different
resistive values. Conductive leads are placed on
each end of a cylinder of this material and the unit is
then heated or cured in an oven. The body of the
resistor is then painted with an insulating paint to
prevent it from shorting if touched by another
component. The finished resistors are then
measured and sorted by value (Figure 4). If these
resistors are overloaded by a circuit, their resistance
will permanently decrease. It is important that the
power rating of the carbon composition resistor is
not exceeded.
THE VARIABLE RESISTOR
When a resistor is constructed so its value can be
adjusted, it is called a variable resistor. Figure 6
shows the basic elements present in all variable
resistors. First a resistive material is deposited on a
non-conducting base. Next, stationary contacts are
connected to each end of the resistive material.
Finally, a moving contact or wiper is constructed to
move along the resistive material and tap off the
desired resistance. There are many methods for
constructing variable resistors, but they all contain
these three basic principles.
METAL FILM RESISTORS
Metal film resistors are also made by depositing a
film of metal (usually nickel alloy) onto a ceramic
rod. These resistors are very stable with
temperature and frequency, but cost more than the
carbon film or carbon composition types. In some
instances, these resistors are cased in a ceramic
tube instead of the usual plastic or epoxy coating.
[attachment=52881]
RESISTORS
RESISTORS, What do they do?
The electronic component known as the resistor is
best described as electrical friction. Pretend, for a
moment, that electricity travels through hollow pipes
like water. Assume two pipes are filled with water
and one pipe has very rough walls. It would be easy
to say that it is more difficult to push the water
through the rough-walled pipe than through a pipe
with smooth walls. The pipe with rough walls could
be described as having more resistance to
movement than the smooth one.
Pioneers in the field of electronics thought electricity
was some type of invisible fluid that could flow
through certain materials easily, but had difficulty
flowing through other materials. In a way they were
correct since the movement of electrons through a
material cannot be seen by the human eye, even
with the best microscopes made. There is a
similarity between the movement of electrons in
wires and the movement of water in the pipes. For
example, if the pressure on one end of a water pipe
is increased, the amount of water that will pass
through the pipe will also increase. The pressure on
the other end of the pipe will be indirectly related to
the resistance the pipe has to the flow of water. In
other words, the pressure at the other end of the
pipe will decrease if the resistance of the pipe
increases. Figure 1 shows this relationship
graphically.
THE CARBON COMPOSITION RESISTOR
By grinding carbon into a fine powder and mixing it
with resin, a material can be made with different
resistive values. Conductive leads are placed on
each end of a cylinder of this material and the unit is
then heated or cured in an oven. The body of the
resistor is then painted with an insulating paint to
prevent it from shorting if touched by another
component. The finished resistors are then
measured and sorted by value (Figure 4). If these
resistors are overloaded by a circuit, their resistance
will permanently decrease. It is important that the
power rating of the carbon composition resistor is
not exceeded.
THE VARIABLE RESISTOR
When a resistor is constructed so its value can be
adjusted, it is called a variable resistor. Figure 6
shows the basic elements present in all variable
resistors. First a resistive material is deposited on a
non-conducting base. Next, stationary contacts are
connected to each end of the resistive material.
Finally, a moving contact or wiper is constructed to
move along the resistive material and tap off the
desired resistance. There are many methods for
constructing variable resistors, but they all contain
these three basic principles.
METAL FILM RESISTORS
Metal film resistors are also made by depositing a
film of metal (usually nickel alloy) onto a ceramic
rod. These resistors are very stable with
temperature and frequency, but cost more than the
carbon film or carbon composition types. In some
instances, these resistors are cased in a ceramic
tube instead of the usual plastic or epoxy coating.