Thermocouples: Thermocouple Types, How Humidity and Temperature sensors work

Thermocouples are widely used temperature sensors that work on the principle of the Seebeck effect. They consist of two dissimilar metals or alloys that are connected at two points, forming a junction. When the junction is exposed to a temperature gradient, a voltage is generated, which is proportional to the temperature difference between the two points. This voltage is measured and used to calculate the temperature of the object being measured. In this post, we will explore what thermocouples do, how they work, the different types of thermocouples available, how uncertainties are determined, and the common types used in climatic test chambers.

Thermocouples: What is a thermocouple?

Thermocouples are used to measure temperature in a wide range of applications. They are commonly used in industrial processes to monitor and control the temperature in various equipment, such as furnaces, ovens, and boilers. Thermocouples are widely used for temperature measurement in a variety of applications, including industrial processes, laboratory experiments, and climatic test chambers. They are preferred over other temperature measurement devices, such as resistance temperature detectors (RTDs) and thermistors, because of their wide temperature range, fast response time, and ruggedness.

How Do Thermocouples Work?

Thermocouples work based on the principle of the Seebeck effect, which is the phenomenon of generating an electromotive force (EMF) at the junction of two different metals or alloys that are exposed to a temperature gradient. In a thermocouple, two different metals or alloys are connected at two points to form a junction, which is the point where temperature is measured. When this junction is exposed to different temperatures, a voltage is generated that is proportional to the temperature difference between the two points.

The voltage generated by the thermocouple is measured using a voltmeter or a temperature measurement device, and then converted into temperature using a calibration table or equation that relates voltage to temperature. The voltage generated by the thermocouple depends on the type of metal or alloy used, as well as the temperature difference between the two points.

Different types of thermocouples are made by using different combinations of metals or alloys. The most commonly used thermocouples are Type K, Type J, Type T, and Type E. Each type of thermocouple has different properties that make them suitable for different temperature ranges and environments.

Thermocouple Types:

Thermocouples are identified based on the two types of metals or alloys used in their construction. The first letter of the thermocouple type indicates one of the two metals or alloys used in the thermocouple, while the second letter indicates the other metal or alloy used.

For example:

Thermocouple type k

Type K thermocouples are one of the most commonly used thermocouples. They are made of Chromel (90% nickel and 10% chromium) and Alumel (95% nickel, 2% aluminum, 2% manganese, and 1% silicon) and are suitable for use in a wide temperature range from -200°C to 1350°C.

J type thermocouple

Type J thermocouples are made of Iron and Constantan and are suitable for use in a temperature range from -210°C to 1200°C. They have a lower temperature range than Type K thermocouples.

T type thermocouple

Type T thermocouples are made of Copper and Constantan and are suitable for use in a temperature range from -200°C to 350°C. They have a lower temperature range than Type J thermocouples.

E type thermocouple

Type E thermocouples are made of Chromel and Constantan and are suitable for use in a temperature range from -270°C to 1000°C.

The letter codes for the different thermocouple types are standardized and recognized by national and international organizations such as ANSI, IEC, and NIST.

Thermocouple Uncertainties: How are they determined

The accuracy of a thermocouple is determined by its uncertainty, which is the degree of confidence that can be placed in the measurement result. The uncertainty is influenced by a number of factors, including the type of thermocouple, the temperature range, the accuracy of the reference measurement device, and the calibration method used.

Common Types Used in Climatic Test Chambers

In climatic test chambers, the temperature needs to be precisely controlled and measured. Thermocouples are commonly used to monitor and control the temperature in these chambers. Type K thermocouples are often used in climatic test chambers because they can operate in a wide temperature range and are highly accurate. Other types of thermocouples, such as Type J and Type T, can also be used depending on the specific requirements of the test.

Conclusion

Thermocouples are versatile and widely used temperature sensors that play a vital role in many industries, including climatic test chambers. Understanding how thermocouples work, the different types available, and how uncertainties are determined can help ensure accurate temperature measurement and control. By selecting the appropriate thermocouple for the specific application and following proper calibration procedures, users can achieve reliable and accurate temperature measurement results.