W. H. Cooke & Co., Inc.

Manufacturer of thermocouples and RTD's. Supplier of industrial controls, heaters, and sensors since 1963.


Email: sales@whcooke.com

RTD Reference Guide & FAQ

A guide for non-engineers.

What is an RTD?

An RTD (Resistance Temperature Detector) is a temperature sensor that measures temperature based on electrical resistance.

How does it work?

An RTD works on the principle of electrical resistance. All known materials are either conductors or insulators. Conductors allow electrical current to flow freely and insulators inhibit or resist electrical current. When a conductor is heated it decreases conductivity and when an insulator is heated is decreases resistance. Based on these principles a change in resistance can be used to calculate a change in temperature.

What materials are used in building RTDs?

Although a variety of materials could potentially be used to make an RTD, the most popular is platinum. Platinum is used because of its linear resistance-temperature relationship and its chemical inertness. Linear is a mathematical term meaning a straight line. In practical terms it means that only simple multiplication is needed to calculate a change in temperature. Inertness is a chemical term meaning that the molecules are very resistant to chemical reactions. In other words, it takes a lot more energy to change the chemical composition of a material that is inert then a material that is not inert.