A thermocouple is a temperature sensor made by joining two dissimilar metals. A small voltage is produced as the junction is heated or cooled due to the Seebeck effect. They are widely used due to their wide operating temperature ranges, ruggedness, and relative low cost.

Thermocouple junctions may also be grounded and brought into direct contact with the material being measured. This can also improve the response time of the thermocouple, but an isolated signal conditioner should be used.

The voltage vs temperature relationships of thermocouples is not as linear as with platinum RTDs, and thermocouples used in challenging conditions may drift over time.

The alloy combinations that form industry standard thermocouples are organized by “types,” where each is identified by specific color-coding, operating temperature range, and more.

The standards IEC 60584-1 and ASTM E230 / ANSI MC96.1 specify the EMF vs temperature characteristics. All RdF thermocouples are built using to the ASTM E230 Special tolerance grade, which represents higher accuracy compared to standard.

For thermocouples to be used successfully, there must be a temperature gradient between the work end where the measurement is being made (hot junction) and where the leads meet the instrumentation (cold junction) such as a transmitter or controller.

Once users have determined they would like to use a thermocouple, we recommend defining whether the measurement is of a surface, or is needed.

From there, the operating temperature range, geometry of the install locations, response time needs and environmental conditions are used to identify appropriate options.

Application specific details, such as the fluid or gas to be measured, expected pressures and flow rates, can help our team make better suggestions.