Temperature Controller For Metrology Furnace Based On MCU DsPIC

Thermocouple is a very widely used temperature sensor in industryapplication. During the long term working period, the performance of thethermocouple will deteriorate so errors are brought into temperaturemeasurement. According to the metrology regulation in China,thermocouples should be certificated and calibrated at regular intervals inorder to guarantee the accuracy of temperature measurement. This requiresa metrology furnace used in thermocouple certification and calibrationwhich can provide an accurate and stable temperature. With theimprovement of the technique and standard in industry, the requirement ofthermocouple certification in Chinese regulation is higher than before. Thecurrent technique is hard to meet the requirement of specification intemperature range, accuracy and stability according to Chinese regulationfor thermocouple certification and calibration.According to the disadvantage of the control system for thermocouplemetrology furnace currently used in metrology field, a high accuracycontrol system solution based on DSC dsPIC is proposed, the controlmethod and hardware platform is also designed and realized. According tothe verification on the function and performance, as well as the EMC test,on the designed sample, the contrl system is proved to be able to stablywork on the specified wide temperature range for long term. The mainwork of this dissertation includes:1. In order to overcome the disadvantage in size and powerconsumption in traditional resistance heater, a new heater control structureis proposed. This system has a reconfigurable heater circuit, and each heater element of the heater can be connected and combined in differentyway in different time in each control cycle period. Rely on the calibrationand paremeter write-in during the manufacturing, and controlling the dutycycle of each triac in this control system, the temperature curve in thefurnace is guaranteed to be accurate, stable and symmetric.2. According to the requirements on this system such as reliability,real-time control, amount of calculation, and low power consumption, asinglechip structure design based on the platform DSC dsPIC is proposed.In this paper the peripheral circuit is appropriately designed and calculatedso as to meet the specifiacion for temperature control about accuracy andstability. And also a line power voltage measurement and thecorresponding compensation algorithm in software are used in order toprevent the temperature control from inaccurate and unstable when the linepower has an incident fluctuation.3. According to the EMC standard and electrical equipment safetyrequirement suitable for this product, the hardware platform for thistemperature control system is realized. The circuit board of this hardwareplatform has the characteristic of highly integration and small size.Through the varificaton executed by the professional certificationorganization TUV-Rheinland, this product meets the EMC requirementIEC61326-1:2006and safety requirement IEC61010-1. As a productapplicative in high temperature, this system is highly reliable and safe.