Jim Sulciner

Choosing RTDs and thermocouples

The two most common ways of measuring industrial temperatures are with resistance temperature detectors (RTDs) and thermocouples. But when should control engineers use a thermocouple and when should they use an RTD? The answer is usually determined by four factors: temperature, time, size, and overall accuracy requirements. What are the temperature requirements? If process temperatures fall from -328 to 932°F (-200 to 500°C), then an industrial RTD is an option. But for extremely high temperatures, a thermocouple may be the only choice. What are the time-response requirements? If the process requires a very fast response to temperature changes--fractions of a second as opposed to seconds (i.e.