From Measurement and Control Basics Fourth Edition
Like the RTD, the thermistor is also a temperature-sensitive resistor. The
name thermistors is derived from the term “thermally sensitive resistors,”
since the resistance of the thermistor varies as a function of temperature.
While the thermocouple is the most versatile temperature transducer and
the RTD is the most linear, “most sensitive” are the words that best
describe thermistors. The thermistor exhibits by far the largest value
change with temperature of the three major categories of sensors.
A thermistor’s high resistance change per degree change in temperature
provides excellent accuracy and resolution. A standard 2,000-ohm thermistor
with a temperature coefficient of 3.9%/°C at 25°C will have a resistance
change of 78 ohms per °C change in temperature. A 2000 Ω platinum
RTD would have a change of only 7.2 ohms under the same conditions. So,
a standard thermistor is over ten times more sensitive than a RTD. This
allows the thermistor circuit to detect minute changes in temperature that
could not be observed with an RTD or thermocouple circuit. A thermistor
connected to a bridge circuit can readily indicate a temperature change of
as little as 0.0005°C.
The cost of this increased sensitivity is loss of linearity, as the...
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