What should be considered when choosing a thermocouple

Thermocouples are commonly used temperature measuring components in temperature measuring instruments. They directly measure temperature and convert the temperature signal into a thermoelectric potential signal, which is then converted into the temperature of the measured medium through electrical instruments (secondary instruments). The appearance of various thermocouples often varies greatly due to their needs, but their basic structures are roughly the same. They are usually composed of main parts such as hot electrodes, insulation sleeves, and junction boxes, and are usually used in conjunction with display instruments, recording instruments, and electronic regulators.

The selection of thermocouples should be based on a comprehensive consideration of the operating temperature range, required accuracy, operating atmosphere, performance of the measured object, response time, and economic benefits.

1. Selection of measurement accuracy and temperature measurement range

When the operating temperature is between 1300~1800 ℃ and high precision is required, B-type thermocouples are generally selected; The requirement for accuracy is not high, and the atmosphere allows for the use of tungsten rhenium thermocouples. Generally, tungsten rhenium thermocouples are selected for temperatures above 1800 ℃; S-type thermocouples and N-type thermocouples are available for use at temperatures ranging from 1000 to 1300 ℃, which require high accuracy; K-type and N-type thermocouples are generally used below 1000 ℃, while E-type thermocouples are generally used below 400 ℃; At 250 ℃ and negative temperature measurements, T-type thermocouples are generally used. At low temperatures, T-type thermocouples are stable and have high accuracy.

2. The choice of using atmosphere

S-type, B-type, and K-type thermocouples are suitable for use in strong oxidizing and weak reducing atmospheres, while J-type and T-type thermocouples are suitable for weak oxidizing and reducing atmospheres. If a protective tube with good airtightness is used, the requirements for the atmosphere are not very strict.

3. Selection of durability and thermal responsiveness

Thermocouples with larger wire diameters have better durability, but their response is slower. For thermocouples with larger heat capacities, their response is slower. When measuring temperatures with large gradients, temperature control is poor under temperature control. It is required to have a fast response time and a certain degree of durability, so choosing an armored puppet is more suitable.

4. The selection of thermocouples based on the properties and states of the measured object

The temperature measurement of moving objects, vibrating objects, and high-pressure vessels requires high mechanical strength, protective tubes are required for atmospheres with chemical pollution, and high insulation is required in the presence of electrical interference.