Influence of Environmental Factors on Thermocouple Calibration and Countermeasures
The environmental factors of thermocouple calibration have a non-negligible impact on the calibration results. Among them, ambient temperature and humidity are two main influencing factors.
The change of ambient temperature will interfere with the calibration process. If the ambient temperature is unstable, it will lead to uncertainty in heat transfer, thus affecting the thermal equilibrium between the thermocouple and the calibration equipment. For example, in a high-temperature environment in summer, if the calibration laboratory does not have a good air-conditioning system, the heat emitted by the calibration furnace or the constant temperature bath may be difficult to effectively dissipate, causing the ambient temperature to rise and further affecting the accuracy of calibration. To reduce the influence of ambient temperature, the calibration laboratory should be equipped with a stable temperature control device to control the ambient temperature within a relatively stable range. Ideally, the ambient temperature fluctuation should be less than ±1℃.
Humidity also has an effect on thermocouple calibration. A high-humidity environment may lead to a decrease in the insulation performance of the thermocouple, causing leakage phenomenon and affecting the accuracy of measurement. Moreover, humidity may also have a corrosive effect on the metal parts of the calibration equipment, reducing the service life and accuracy of the equipment. Therefore, the calibration laboratory should maintain an appropriate humidity level. Generally, it is recommended to control the humidity between 40% - 60%. A dehumidifier or a humidifier can be installed to adjust the ambient humidity and ensure that it is within a suitable range.
In addition to temperature and humidity, electromagnetic interference is also an environmental factor that needs attention. In some industrial environments or laboratories close to large electrical equipment, electromagnetic interference may affect the normal operation of the electronic components of the thermocouple and the calibration equipment. To avoid electromagnetic interference, shielding measures can be adopted, such as placing the calibration equipment in a shielding room or using a shielded cable to connect the thermocouple and the measuring instrument to ensure that the calibration work is not affected by electromagnetic interference.
