BOOK_CONTENT
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 O 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...


More >>
© 2007 ISA

Products & Services
Pressure Sensors
Pressure sensors include all sensors, transducers and elements that produce an electrical signal proportional to pressure or changes in pressure.
Resistive Temperature Devices (RTD) Elements
Resistive temperature device (RTD) elements are wire windings or other thin-film serpentines that exhibit changes in resistance with changes in temperature. They are usually made of metallic elements or alloys such as copper, nickel, or nickel-iron.
Level Sensors
Level sensors are used to detect liquid or powder levels, or interfaces between liquids. There are two basic level-measurement types: continuous and point or multi-point.
Noncontact Infrared Temperature Sensors
Noncontact infrared temperature sensors absorb ambient infrared (IR) radiation given off by a heated surface. They are used in applications where direct temperature measurement is not possible.
Dial Thermometers
Dial thermometers are bimetal or bi-metallic, liquid or gas-filled, and vapor-tension-based. These devices display temperatures in Fahrenheit, Celsius, or both.

Topics of Interest

Integrated-circuit temperature transducers are available in both voltage and current-output configurations (Figure 7-20). Both supply an output EXAMPLE 7-8 Problem: A typical thermistor has the...

Extended range and higher accuracy aren't the only good points about solid-state temperature sensors. Designers face many chal lenges when placing thermal-sensing components in embedded systems. The...

There is a variety of temperature sensors on the market all of which meet specific application needs. The most common sensors that are used to solve these application problems include the...

Thermistors What is a thermistor? A thermistor is a temperature-sensing element composed of sintered semiconductor material which exhibits a large change in resistance proportional to a small change...

This application note shows how to select a temperature sensor and conditioning circuit to maximize the measurement accuracy and simplify the interface to the microcontroller. Practical circuits and...