Practical Thermocouples

Thermocouples are widely used thanks to their broad temperature range, robustness, flexibility in size, and the extensive variety of housings and packages available for different applications. They're also relatively easy to make.

For basic setups, thermocouples can be made using lengths of bare or insulated wire. The insulation and wire diameter (typically from 0.1mm to over 3mm) should be chosen based on the application. The measuring junction is ideally formed by welding the wires together. While soldering or twisting is possible, these methods are less reliable unless supported by clamping mechanisms to ensure a solid electrical connection.

When welding, the method depends on the materials. Base metal thermocouples are often welded in an argon atmosphere, while platinum types use an oxy-hydrogen flame. Base metal wires are usually pre-annealed, whereas platinum wires require annealing after construction.

At the other end, wires are joined to copper to form the reference junction. Welding is again preferred, but careful silver soldering is acceptable if all flux is fully removed. The junctions are then secured in closed-end tubes or immersed in an ice bath for reference.

This DIY method is simple and well-suited for labs and experimentation. It delivers accurate results since the thermocouple elements can be positioned close to the measurement point, allowing the sensor to approximate the theoretical ideal described earlier in this guide.

Further Reading

What are the various thermocouple types?
Explore the features and characteristics of the various thermocouple types

Thermocouple Output Tables
View EMF versus Temperature tables for all thermocouple types.

What are the thermocouple colour codes?
Explore thermocouple colour codes for cable and connectors.