Thermistors are thermally sensitive resistors whose prime function is to exhibit a large, predictable and precise change in electrical resistance when subjected to a corresponding change in body temperature. Negative Temperature Coefficient (NTC) thermistors exhibit a decrease in electrical resistance when subjected to an increase in body temperature and Positive Temperature Coefficient (PTC) thermistors exhibit an increase in electrical resistance when subjected to an increase in body temperature. U.S. Sensor produces thermistors capable of operating over the temperature range of -100 ? to over +600 ? Fahrenheit. Because of their very predictable characteristics and their excellent long term stability, thermistors are generally accepted to be the most advantageous sensor for many applications including temperature measurement and control.
Since the negative temperature coefficient of silver
sulphide was first observed by Michael Faraday in 1833,
there has been a continual improvement in thermistor
technology. The most important characteristic of a
thermistor is, without question, its extremely high
temperature coefficient of resistance. Modern thermistor
technology results in the production of devices with
extremely precise resistance versus temperature
characteristics, making them the most advantageous sensor
for a wide variety of applications.
A thermistor's change in electrical resistance due to
a corresponding temperature change is evident whether the
thermistor's body temperature is changed as a result of
conduction or radiation from the surrounding environment or
due to "self heating" brought about by power dissipation
within the device.
When a thermistor is used in a circuit where the
power dissipated within the device is not sufficient to
cause "self heating", the thermistor's body temperature will
follow that of the environment. Thermistors are not "self
heated" for use in applications such as temperature
measurement, temperature control or temperature
compensation.
When a thermistor is used in a circuit where the
power dissipated within the device is sufficient to cause
"self heating", the thermistor's body temperature will be
dependent upon the thermal conductivity of its environment
as well as its temperature. Thermistors are "self heated"
for use in application such as liquid level detection, air
flow detection and thermal conductivity measurement.