The selection of thermocouple should be based on comprehensive considerations such as the use temperature range, the required accuracy, the use atmosphere, the performance of the measurement object, the response time and the economic benefits.
1. Selection of measurement accuracy and temperature measurement range
When the operating temperature is 1300~1800℃ and the accuracy is relatively high, the B-type thermocouple is generally used; the accuracy is not high, and the atmosphere allows the use of tungsten rhenium thermocouples. Generally, tungsten rhenium thermocouples are used when the temperature is higher than 1800℃; 1000~1300℃ requires high accuracy and high accuracy. Available S-type thermocouple and N-type thermocouple; below 1000℃ generally use K-type thermocouple and N-type thermocouple, below 400℃ generally use E-type thermocouple; below 250℃ And the negative temperature measurement generally uses T-type thermocouple, which is stable and high precision at low temperature.
2. The choice of atmosphere
S-type, B-type, and K-type thermocouples are suitable for use in strong oxidizing and weak reducing atmospheres, J-type and T-type thermocouples are suitable for weak oxidizing and reducing atmospheres. If a protective tube with better airtightness is used, The atmosphere requirements are not too strict.
3. Choice of durability and thermal response
Thermocouples with large wire diameters have better durability, but have a slower response. For thermocouples with large heat capacity, the response is slow. When measuring temperatures with large gradients, the temperature control is poor in the case of temperature control. It requires a fast response time and a certain degree of durability, so it is more appropriate to choose an armored couple.
4. The nature and state of the measuring object to choose the thermocouple
The temperature measurement of moving objects, vibrating objects, and high-pressure vessels requires high mechanical strength. Chemically polluted atmospheres require protective tubes. In the case of electrical interference, higher insulation is required.
Selection process: model-index number-explosion-proof grade-precision grade-installation and fixed form-protective tube material-length or insertion depth
