Armored thermocouple and assembled thermocouple

1.Regarding 400 ℃:

Temperature sensors used to detect temperature in industrial processes mostly use thermocouples and thermistors. When the temperature is usually below 400 ℃, a thermistor is selected; When the temperature is high at 400 ℃, use a thermocouple. What is the reason for this? Platinum resistors have much higher temperature measurement accuracy than thermocouples, and are the preferred choice for temperature measurement in low-temperature areas. In the production process of platinum resistors, the maximum operating temperature of the product is determined by the performance of Pt100 components. 400 ℃ is the critical point for selecting platinum resistors and thermocouples, considering both temperature and long-term service life.

2. Principle of thermocouple:

Thermocouples use two conductors with different compositions connected together. Due to the temperature difference between the hot and cold ends, a thermoelectric potential is generated in the circuit, which is called the thermoelectric effect. Thermocouples use this principle to measure temperature.

3. Structure of Armored Thermocouples

The structural types of thermocouples are divided into ordinary assembly type and armored type, with armored thermocouples being widely used currently. Armored thermocouple is a compression structure formed by combining and stretching thermocouple wire, insulation material (usually high-purity magnesium oxide powder), and metal tube; Prefabricated thermocouples are thermocouples with thermocouple wires threaded in ceramic beads and installed in hollow metal tubes.

4. Comparison between Armored Thermocouples and Prefabricated Thermocouples

Compared with prefabricated thermocouples, armored thermocouples have the following characteristics and are therefore widely used. Nowadays, they have replaced prefabricated thermocouples in many occasions.

The main characteristics of armored thermocouples are:

① The outer diameter can be made very small (minimum of 0.25mm), so the thermal response time is small and the reaction speed is fast.

② Has good mechanical properties and can withstand strong vibrations and impacts.

③ Has significant flexural performance, with a bending radius of 2-5 times the diameter, suitable for devices and situations with complex structures.

④ The thermocouple wire is covered with insulating material and metal armor, which makes it less susceptible to erosion by the medium and thus has a longer service life.

⑤ It can be used as a temperature sensing element in ordinary thermocouple protection tubes or thermometer sleeves.

Similarly, armored thermistors also have the above characteristics, replacing ordinary assembled thermistors in many places.