As one of the most widely used temperature measuring instruments in the world, thermocouples are widely applied in industrial production, scientific research, laboratory testing and other fields. Thermocouple types vary according to material and structure, each with unique performance characteristics, making them especially favored by foreign trade customers for their simple structure, stable performance and wide temperature measurement range. This article will elaborate on the origin, 10 types of index numbers and thermocouple working principle, helping global customers better understand this essential temperature measuring component.
Origin of Thermocouple | Thermocouple History
The invention and development of thermocouples are closely related to the discovery of the thermoelectric effect. As early as 1821, the German physicist T.J. Seebeck first discovered the thermoelectric effect, which laid the theoretical foundation for the birth of thermocouples. In 1826, the French physicist A.C. Becquerel applied this effect to temperature measurement and created the simplest thermocouple thermometer, marking the official entry of thermocouples into practical application.
Up to now, thermocouples have a history of more than 180 years. After continuous improvement and optimization, thermocouple performance has been continuously improved, and they have gradually become the core temperature measuring component in various industries, providing reliable temperature data support for global industrial production and scientific research.
10 Types of Thermocouple Index Numbers | Common Thermocouple Types
The index number of a thermocouple is the code representing its material composition and temperature measurement range, which is crucial for foreign trade procurement and application matching. According to international standards and industry norms, there are 10 common thermocouple index numbers, covering different thermocouple types to meet diverse application needs, which are divided into the following categories:
Standardized thermocouples (7 types): Since 1985, China has stipulated 7 standardized thermocouple index numbers (K, E, J, T, S, R, B) in accordance with the IPTS-68 International Practical Temperature Scale, which are widely used in general industrial and civil fields and are compatible with international mainstream equipment.
Added standardized thermocouple (1 type): Since 1997, in line with the ITS-90 International Practical Temperature Scale and IEC 584-95 International Standard, the N-type thermocouple has been added, which has better high-temperature stability and anti-oxidation performance, and is suitable for more complex industrial environments.
Tungsten-rhenium thermocouples (2 types): Tungsten-rhenium thermocouples entered practical application in the 1990s and currently implement industry standards, with two index numbers C and D. They have excellent high-temperature resistance and are mainly used in high-temperature measurement scenarios such as metallurgy, aerospace and high-temperature laboratories.
It should be noted that different index number thermocouples (different thermocouple types) have different temperature measurement ranges, material characteristics and application scenarios. When purchasing and using, customers need to select the appropriate index number according to their specific needs, ensuring the thermocouple works stably and efficiently.
Working Principle of Thermocouple | Thermocouple Working Principle
The temperature measurement of thermocouples is based on the Seebeck effect (thermoelectric effect) discovered in 1821. Its core thermocouple working principle is simple and easy to understand:
A thermocouple is composed of two different homogeneous conductors (also called thermoelectrodes or couple wires). One end of the two conductors is welded together to form a measuring end (also called a hot end), and the other end is connected to a galvanometer to form a closed loop. When the temperature of the measuring end is inconsistent with the temperature of the reference end (also called the cold end, i.e., the end connected to the galvanometer), an electric current will be generated in the loop. This phenomenon is the Seebeck effect.
The electromotive force (thermoelectromotive force) generated in the thermocouple loop is composed of two parts: temperature difference electromotive force and contact electromotive force. Among them, the contact electromotive force is relatively small and has little impact on the measurement result. The magnitude of the thermoelectromotive force is directly proportional to the temperature difference between the measuring end and the reference end. By measuring the thermoelectromotive force, the temperature of the measuring end can be accurately calculated.
With the continuous development of industrial technology, thermocouples are constantly innovating in material, structure and performance, and their application scope is also expanding. For foreign trade customers engaged in industrial equipment, instrumentation and other industries, understanding the relevant knowledge of thermocouples, including thermocouple types and thermocouple working principle, is of great significance for rational procurement and efficient use. We will continue to focus on the development of thermocouple technology and provide high-quality thermocouple products and professional technical support for global customers.