Effect of Temperature on
Resistance
A component whose function in a circuit is to
provide a specified value of resistance is called a
resistor
The principal application of resistors are to limit
current, divide voltage and in certain cases, generate
heat.
The following are the commonly used
resistors in electrical and electronic circuits:
• Carbon composition types
• Film resistors
• Wire-wound resistors
• Cermet resistors
Carbon composition type
This type of resistors is made with a mixture
of finely ground carbon, insulating filler and a
resin binder. The ratio of carbon and insulating
filler decides the resistive value.
mixture is formed into a rod and lead
connections are made. The entire resistor is
then enclosed in a plastic case to prevent the
entry of moisture and other harmful elements
from outside.
Carbon resistors are relatively in expensive to
build. However they are highly sensitive to
temperature. The car resistors are available in
power ratings ranging 1/8 to 2W
Film resistors
In a film resistors, a resistive
material is deposited uniformly onto a
high grade ceramic rod. The resistive film
may be carbon (carbon film resistor) or
nickel chromium (metal film resistor). In
these types of resistors, the desired
resistance value is obtained by removing
a part of the resistive material in a helical
pattern along the rod. Metal film resistors
have better characteristics as compared
to carbon film resistors.
Wire-wound resistors
A wire wound resistor is constructed by
winding a resistive wire of some alloy
around an insulating rod. It is then
enclosed in an insulating cover. Generally,
nickel chromium alloy is used because of
its very small temperatures coefficient of
resistance
Wire-wound resistors can safely
operate at higher temperatures than
carbon types. These resistors have high
power ratings from 12 to 225W
Cermet resistors
A cermet resistor is made by
depositing a thin film of metal such as
nichrome or chromium cobalt or
ceramic substrate. They are cermet
which is a contraction for ceramic and
metal . These resistors have very
accurate values
Effect of temperature on resistance
Effect of temperature on resistance
In temperature. Hence these materials have
negative temperature co-efficient of resistance.
Effect of temperature on resistance
Temperature Co-efficient of resistance
at a temperature of 100OC, it will have a life expectancy of only four years at a temperature of 110oC, of two years
at a temperature of 120 oC and of only one year at 130oC