"Thermistor" is the generic name given to
thermally sensitive resistors.
Negative temperature coefficient thermistor
is generally called as thermistor. Thermistor
is a semiconducting ceramic resistor
produced by sintering the materials at high
temperature and made mainly from metal
Depending on the manufacturing method
and the structure, there are many shapes
and characteristics for various purposes
such as temperature measurement,
temperature compensation and etc.
The thermistor resistance values, unless
otherwise specified, are classified at a
standard temperature of 25ЊC.
B constant is calculated from the resistance
values at 25ЊC and 85ЊC.
Resistance -Temperature Characteristics
The resistance of a temperature is solely a function
of its absolute temperature. Since electrical power
being dissipated within a temperature might heat
above its ambient temperature and thereby reduce
its resistance, it is necessary to test for resistance
with temperature. The resistance so measured is
called RT, which means the resistance at essentially
The mathematical expression which relates the
resistance and the absolute temperature of
a thermistor is as follows:
RaϭRb exp B
Where: Ra is the resistance at absolute temperature T1
Rb is the resistance at absolute temperature T2
B is a constant which depends on the
material of the thermistor
Unless otherwise specified,all values of B are
determined from measurements made at 25ЊC and
The temperature coefficient of resistance
␣ is expressed in the following equation:
2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9
Dissipation factor (␦) is power in milliwatts
required to raise thermistor temperature 1ЊC.
Measured with thermistor suspended by its leads in
a specified environment.
␦ ϭ⌬Pt (mW/ ЊC)
⌬ t:Raise temperature(ЊC)
Thermal time constant
Thermal time constant (a) is the time required by a
thermistor to change 63% of the difference between
its initial and final temperature. Measured with
thermistor suspended by its leads in specified