Automatic Calibration System For Industrial Thermocouple

Thermocouples are commonly-used temperature sensors in many manufacturing processes, and have found a wide range of applications. After a long-term run, the performance of a thermocouple may change, resulting in temperature measurement error. Therefore, the Metrology Law in China stipulates that thermocouples have to be calibrated periodically in the course of its usage to ensure the accuracy of the temperature measurement.In this thesis, a novel automatic industrial thermocouple calibration system is designed by taking full advantages of computer control and data acquisition technologies, as well as a wealth of current software and hardware resources. The system can calibrate thermocouples automatically, intelligently and in a standardization fashion, and can replace the traditional calibration method which is fully manual, inefficient and labor-intensive.Based on the analysis of the Specification of Thermocouple Calibration, this thesis discusses in detail the overall design ideas of the automatic thermocouple verification system, hardware configuration, software design and solutions to some technical problems. The calibration system first uses a low thermoelectric potential relay set and a switching value control interface card (PC-6408) to form a multichannel scanning device, and then uses a high precision programmable multifunctional instrument (HP34401A Multimeter) to acquire the calibration data automatically. To control the calibration furnace temperature, an optimized algorithm is designed by combining the PID control and fuzzy control. The optimized algorithm can tune the PID parameters automatically and in an on-line fashion. As a result, the furnace temperature can be heated up fast in a short control time, and achieves a satisfactory effect for constant temperature control. Written using a building block design fashion, the system monitoring software has a friendly graphical user interface, and is powerful, flexible and easy to operate.The automatic thermocouple verification system meets all the requirements of the Specification of Thermocouple Calibration, and has been able to work steadily since it was put into use. The system has good scalability. New types of thermocouples can be simply and easily added into the system. Compared with the traditional manual calibration method, the automatic thermocouple calibration system can significantly shorten the calibration time, increases calibration efficiency, reduces the labor strength and improve the level of automation.