Thermocouples: How do they work?

You may be wondering, exactly what is a thermocouple? In short, thermocouples are a type of thermometer that uses a chemical reaction to convert heat into an electrical signal. A thermocouple is a special type of chemical sensor that converts the temperature of an object into an electrical signal.

These sensors are typically used in industrial applications, as they allow for the measurement of temperature over a wide range. Because of the wide range of temperatures that thermocouples can measure, they are often used in industrial settings and for scientific applications.

Read on to understand the working principles of thermocouples and the different types of thermocouples available.

Working Principles of Thermocouples

There is a continuous current flowing in a thermoelectric circuit when at least two wires made of different metals are linked together at ends where one is heated. Subsequently, the current flow measures the temperature at the unknown end. If the circuit gets broken in the middle, the net open circuit voltage (also called the Seebeck voltage) is produced due to the composition of the two metals and the junction temperature.

Thus, when an intersection of two metals is cooled or heated, the voltage generation can be correlated back to the temperature. The variation in temperature between the two intersections produces voltage within the circuit at a particular time.

Types of Thermocouples

Several thermocouples present in the modern market are developed to deal with various environmental challenges or application scenarios. Also, each thermocouple grade has been developed to handle a particular temperature range. The thermocouples are usually set apart by letters, and the most common types are J, L, K, T and N.

Every letter represents a distinct metal combination utilised to make the thermocouple circuit junctions. The approach directly impacts the temperature sensitivity and secure range operation of the entire unit. Read on for diverse configurations and grades of thermocouples to understand the temperature ranges and environments where they should be deployed.

K-type Thermocouples

Type-K thermocouples feature massive scope of prospective applications because they are nickel-based. These units are developed from nickel-based wire combinations, and as a result, they are cost-friendly thermocouples that uphold accuracy and reliability across a vast range of operating temps. Its wires can operate at a specific massive series of temperatures and exhibit firm resistance to oxidation and corrosion. It is the most used variety in several sectors and industries.

J-type Thermocouples

Type-J unit’s positive leg is developed with iron wire, while the negative one is made of a copper-nickel alloy. This variety exhibits a generally shorter lifespan if frequently exposed to a lot of heat. It is the most used type and has a narrower temperature scope than K-types.

N-Type Thermocouples

It is composed of wires developed from nicrosil-nisil alloys and features multiple similar properties with K-type thermocouples. N-Type has operating temperatures ranging from -270 to +1300 Celsius. This variety is slightly more costly than K grade since it was developed to address some challenges faced by K variety in particular environments. The type-N provides whole stability in applications such as nuclear and has lower susceptibility to oxidation under extreme heat.

T-type Thermocouples

This type is made of copper-constantan alloy wires and has a temperature ranging from −200 to +350 Celsius. It has a stable thermocouple configuration and is suitable for extremely low-temperature applications and various cryogenic. It is ideal for deep freeze and laboratory conditions. T variety has a good functionality in oxidising atmospheres and is regularly utilised for differential measurement since only copper wires can directly contact the probes.

Uses of Thermocouples

Thermocouples are cost-effective and durable to survive in extremely harsh conditions, provided the metals used feature a higher melting point. They are extensively used in industry and science since they are accurate and can operate across a massive range of extremely cold and hot temperatures.

Considering that they produce electric current, thermocouples have proved their usefulness in making automated measurements. It is generally simpler to have a computer or an electronic circuit to determine a thermocouple’s temperature at particular intervals by performing it yourself by using a thermometer. Thus, the only difference is just a pair of metal strips.

Conclusion

The choice of thermocouple depends on the particular requirements of the task at hand. Thermocouples are used in household appliances, automotive mechanisms, laboratory settings and industrial machinery. For instance, they are used in medical thermometers, industrial sensors and probes, boilers and ovens, vehicle diagnostics and thermostats.