Fuzzy Control Based On Virtual Instrument Thermocouple Test Furnace

In the industrial production process, thermocouple is the temperature sensor with a wide range of applications and characterized by its simple structure,stable performance,small thermal inertia,high measurement accuracy,wide temperature measurement range, long-distance transmission ability ang so on. However, in the process of using, Thermocouple pyroelectricity will change as a result of hight temperature, oxidation, recrystallization, environmental corrosion and pollution, etc.When the change exceeds the range, the thermocouple temperature measurements will be distorted and the error will become lager and larger.But the accuracy of the measurements is an important factor for improving the quality and stability of industrial product. Therefore, thermocouple as a temperature measuring duvice must be calibrated regularly in accordance with national standard procedures to determine whether it may continue to use according to the size of the error.The traditional thermocouple calibration is operated by man.In this way, the engineer tieds the themocouples and a standard thermocouple into a bunch and insers them into the furnace, making the measurement points in the center of the furnane and putting the reference points into a freezing container.Operating the DC potentiometer and switches near the calibration temperature point and recording the thermocouples voltage value at this time.The finally getting the test result via data processing and computing. Because this method is entirely manual, there is a large man-made error and delay error, and the work efficiency is low.It can not meet the technical requirements for thermocouple calibration.This topic is based on the background that The Thermocouple Calibration Device of laboratory of Kunming University of Science and Technology, is out-date and manually operated.The purpose of this topic is improving the original thermocouple calibration of laboratory, upgrading the equipments,and developing a Thermocouple Auto-calibration System with a friendly,efficient and convenient man-machine interface.The design of the system Combine with the lab hardware and use the current most widely used virtual instrument graphical programming software LabVIEW. Firstly studying the fuzzy control algorithm and designing the fuzzy controller for the furnace temperature system with the fuzzy control toolkit in LabVIEW. Based on the realization of continuous automatic control of furnace temperature, developping a Thermocouple Auto-calibration System which own a friendly man-machine interface and realize automation of temperature controlling, data processing, and printing the results.At the end of paper, the error of the system is analysised.The system results are compared with the manual results to prove the data handing of this software.After several runs, the system is stable with correct results, improving the efficiency and accuracy of the thermocouple calibration in laboratory.