The Development Of Measurement And Control System Of A High Accuracy Differential Scanning Calorimeter

Calorimetry is the foundation of all the material properties researchand the heat-related experiments. Thermal analysis technology associate thethermodynamics and kinetics of all subjects by research the physical andchemical changes in the process of material heating. As the most widely usedthermal analysis instrument, differential scanning calorimeter measure the heatflux difference between the material and the reference when under thetemperature program and the atmosphere. Differential scanning calorimeter isused in petroleum, chemical, materials research. In recent years, with thevigorous development in the field of new material, new energy, biology ofChina, differential scanning calorimeter is increasingly demanded. While thedomestic differential scanning calorimeter can’t meet the demand of materialtesting and chemical research in China, especially in the baseline straightstability, accuracy of temperature control and heat-flux measurement.For the disadvantages of domestic differential scanning calorimeter, thispaper put forward a kind of measurement and control system, which takerapid-response and high-resolution heat flux measurement as core. The mainresearch include:Firstly, inorder to research the influence of the spacing between the sampleand the reference of the heat-flux sensor on the furnace temperature uniformity,this paper established furnance models of different spacing and simulated thetemperature field by ANSYS, certained the optimal spacing by comparing thetemperature gradientant and the temperature distribution. At last, verify thesimulation results by the uniformity experiment.Secondly, this paper take ATMEGA128as the core, designed the24-bit highaccuracy temperature and heat-flux signal acquisition module, heating controlmodule, atmosphere control module, human-computer interaction module. Realized constant temperature and uniform velocity temperature control withwide range, certained the relationship between thermoelectromotive force andthe heat-flux by several experiments based on the high accuracy heat-flux sensor,and put forward an algorithm which deducted the impact of the unbalancedresistances and capacities between the sample and reference endpoints afteranalyzing the influence factors of baseline drift, etc.Lastly, test the differential scanning calorimeter system with serials of tests ofbaseline and temperature program. Results reveal good repeatability and accuracy.The baseline noise is within0.1mJ/s, repeatability deviation of temperaturecontrol is within0.22%, deviation of linear heating by2,5,10,20℃/min iswithin10%. The measuring and control system of differential scanningcalorimeter can meet the requirements of rules in A grade.