Process Temperature Measurement Practice -- Thermocouples And RTDs

Temperature is one of seven basic values in the current SI-System of units and is probably the most important parameter in measurement technology. Temperature measurements roughly divide into three application categories:

• Precision temperature measurements for scientific and basic research
• Technical temperature measurements for measurement and control technology
• Temperature monitoring using temperature indicators.

This article will cover typical contacting methods for industrial processing and control. A second article to appear subsequently will cover non-contacting methods such as radiation thermometers.

In the mid-18th century Scottish physicist James Clerk Maxwell defined temperature as a property that makes possible the transfer of heat energy to or from one body to another. For Maxwell, temperature was the measure of the average kinetic energy of the molecules within a system. Measurement of temperature provided a way to determine the heat energy content of that system.