Types of Temperature Sensors

Temperature sensors can be grouped by the physical principle they use to convert heat into a measurable change. Each principle leads to a family of devices with characteristic ranges, accuracies and costs. Understanding the differences helps in choosing the right sensor for a given range, environment and required precision.

The bimetallic strip is one of the oldest principles: two bonded metals with different thermal expansion coefficients cause the strip to bend as temperature changes, an effect long used in mechanical thermostats and dial thermometers. Thermistors use a semiconductor whose resistance varies strongly with temperature, offering high sensitivity over a limited range. Resistance temperature detectors such as the Pt100 use the gentler, very stable resistance change of a metal like platinum for accurate measurement.

Semiconductor temperature sensors often rely on the bandgap principle, in which the temperature dependence of the voltage across a forward-biased semiconductor junction is used to produce a signal proportional to absolute temperature. These integrated devices give a calibrated, easily interfaced output and are common in electronic equipment. Thermocouples, generating a voltage from a junction of dissimilar metals, cover very wide ranges and harsh conditions, while infrared pyrometers measure temperature without contact by sensing emitted thermal radiation. The right choice depends on the temperature range, accuracy, response time and the kind of output the system needs.

Frequently asked questions

How does a bimetallic strip sense temperature?

Two bonded metals expand at different rates, so the strip bends as the temperature changes, a movement used to operate thermostats and dial thermometers.

What is a bandgap temperature sensor?

A semiconductor sensor that uses the temperature dependence of a junction voltage to produce an output proportional to absolute temperature.

Which sensor type covers the widest temperature range?

Thermocouples generally span the widest ranges and tolerate harsh conditions, though they are less accurate than RTDs at moderate temperatures.