Introduction to Thermocouples

1. Working Principle

Two conductors of different components (called thermocouple wire or thermoelectrode) are connected at both ends to form a loop. When the temperatures of the two junctions are different, an electromotive force will be generated in the loop. This phenomenon is called the thermoelectric effect, and this electromotive force is called the thermoelectric potential. Thermocouples use this principle to measure temperature. Among them, the end directly used to measure the temperature of the medium is called the working end (also called the measuring end), and the other end is called the cold end (also called the compensation end); the cold end is connected to the display instrument or the matching instrument, and the display instrument will indicate the thermoelectric potential generated by the thermocouple.

2. Principle Structure

Thermocouples are commonly used temperature measuring elements in temperature measuring instruments. They directly measure temperature and convert temperature signals into thermoelectric potential signals, which are converted into the temperature of the measured medium through electrical instruments (secondary instruments). The appearance of various thermocouples is often very different due to needs, but their basic structure is roughly the same. They are usually composed of main parts such as thermoelectrodes, insulating sleeve protection tubes and junction boxes. They are usually used in conjunction with display instruments, recording instruments and electronic regulators.

3. Principle-related features and advantages

1. Simple assembly and easy replacement;

2. Compression spring type temperature sensing element with good shock resistance;

3. High measurement accuracy;

4. Large measurement range (-200℃～1300℃, -270℃～2800℃ under special circumstances);

5. Fast thermal response time;

6. High mechanical strength and good pressure resistance;

7. High temperature resistance up to 2800 degrees;

8. Long application life.

Advantages:

1 High measurement accuracy. Because it is in direct contact with the measured tool, it is not affected by the intermediate medium.

2. Wide measurement range. Commonly used thermocouples can be continuously measured from minus 50 degrees to 1600 degrees. Some special thermocouples can measure as low as -269 degrees (such as gold, iron, nickel, and chromium) and as high as 2800 degrees (such as tungsten and rhenium).

3. Simple structure and convenient application. Thermocouples are usually made of two different metal wires and are not limited by size or opening. They are covered with a protective sheath and are the most convenient to use.