In a temperature calibration laboratory, there are multiple calibration methods, each with its own advantages and disadvantages. Reasonable selection of calibration methods is crucial for ensuring calibration accuracy.
Common calibration methods include the fixed-point calibration method and the comparison method. The fixed-point calibration method uses the phase transition temperature of substances as fixed points, such as the triple point of pure water (0.01°C) and the melting point of gallium (29.7646°C). The advantage of this method lies in its extremely high accuracy and traceability, as these fixed points are defined based on the International System of Units (SI), and the calibration results can be directly traced back to international standards. However, its limitation is that the operation is relatively complex, requiring precise control of the state of substances and environmental conditions, and the calibration points are limited. It is usually suitable for the calibration of high-precision thermometers, such as platinum resistance thermometers used as national metrology standards.
The comparison method involves comparing the thermometer under calibration with a reference thermometer of known higher accuracy in the same temperature environment. Its operation is relatively simple, can be carried out in a wide temperature range, and can calibrate multiple thermometers simultaneously. However, the accuracy of this method depends on the precision of the reference thermometer. If the reference thermometer has a deviation, it may affect the calibration results. The comparison method is often used for the calibration of thermometers widely used in industrial production, such as in the food processing and chemical industries, where the accuracy requirements of thermometers are within a certain range and rapid, batch calibration is required.
In addition, there is a calibration method based on a mathematical model, such as the least squares calibration. This method corrects the error of the thermometer by fitting the measurement data of the thermometer at multiple temperature points and establishing a mathematical model. It is suitable for some thermometers with specific temperature response characteristics and can effectively improve the calibration efficiency and accuracy. However, it requires an in-depth understanding of the characteristics of the thermometer and a certain mathematical processing ability.
When selecting a calibration method, the laboratory needs to comprehensively consider factors such as the type of thermometer, accuracy requirements, operating environment, calibration cost, and traceability. For the high-precision and high-demand metrology field, the fixed-point calibration method is preferred; for the routine thermometer calibration in industrial production, the comparison method can often meet the requirements; and the calibration method based on a mathematical model can be used as a supplementary means to optimize the calibration effect of specific types of thermometers.