On 2018-08-08 14:48:54
How to choose different types of thermocouples
Different types of thermocouples are used in different occasions, and the application environment is different. So is the selection of thermal resistance. It is necessary to consider the temperature used, what kind of medium to be measured, the accuracy of the medium to be measured, the response time, and the object to be measured. So the general situation will be from the following aspects. The specific reference standards for thermocouple selection are:
One: select the measurement accuracy and temperature measurement range. When the operating temperature is 1300-1800 ℃, and the required accuracy is relatively high, type B thermocouples are generally used; when the required accuracy is not high, tungsten rhenium thermocouples are allowed to be used in the atmosphere, and when the temperature is higher than 1800 ℃, tungsten rhenium thermocouples are generally used; when the operating temperature is 1000-1300 ℃, type s thermocouples and type N thermocouples are generally used, and when the temperature is lower than 1000 ℃, type K thermocouples and type N thermocouples are generally used, and the temperature is lower than 400 ℃ E-type thermocouple is generally used; T-type thermocouple is generally used for measurement at 250 ℃ and negative temperature. T-type thermocouple is stable and has high accuracy at low temperature.
Second, the choice of using environment atmosphere. S-type, B-type and K-type thermocouples are suitable for use in strong oxidation and weak reduction atmosphere. J-type and T-type thermocouples are suitable for use in weak oxidation and reduction atmosphere. If a protective tube with good air tightness is used, the requirements for atmosphere are not strict.
Third, choose durability and thermal response. The thermocouple with large wire diameter has good durability, but its response is slower. For the thermocouple with large heat capacity, the response is slower. When measuring the temperature with large gradient, the temperature control is poor under the condition of temperature control. It is required that the response time is fast and the durability is certain. It is more suitable to choose armour couple. The thermal correspondence is also an important reference standard for the selection of bimetal thermometer.
Four: the choice of thermocouple by the nature and state of the measurement object. The temperature measurement of moving objects, vibrating objects and high-pressure vessels requires high mechanical strength, protective pipes are required for the atmosphere with chemical pollution, and high insulation is required in the case of electrical interference.
Model selection process: Model -- graduation number -- explosion-proof grade -- precision grade -- fixed installation form -- material of protective tube -- length or insertion depth.
After all these factors have been considered, it is relatively simple to select manufacturers and prices. For the selection of specific models and the application of specific environment, let's analyze the specific situation. The most important thing is to analyze the specific situation. One key can only open one lock, one type of thermocouple, and the thermal resistance can only be used in the specific working environment and the specific measured liquid. It is not allowed to use other temperature measuring tools at will.