Design On Thermal Conductivity Measure Instrument With Double Guarded Hot Plate Apparatus

Thermal conductivity, as one of material's thermal parameters, indicates the material's capability of heat conduction. The measurement of thermal conductivity contributes much to new material development as well as proper use of materials, and therefore, has been a field of progressing. Double guarded hot plate apparatus has been widely used for its wide measurement range and non-demarcating, which is based on Fourier's law of heat conduction for one dimensional steady state temperature field. At present, however, the instruments have still much to be desired, such as higher measurement precision, better performance, more flexible functions, etc. A new kind of thermal conductivity measurement instrument is, therefore, developed, which can be used to measure the thermal conductivity and the thermal resistance of heat insulation material in steady conduction state.The whole instrument is made up of double guarded hot plate apparatus (stove) and the intelligent measuring-controlling system. The former provides the conditions for heat conduction in one dimensional steady state temperature field; the latter mainly realize the following functions: man-machine interaction, signal sampling and processing, procedure control and parameter calculation. The performance of the measuring-controlling system is the key point to the whole instrument's function realization, and its design & evaluation forms main parts of this thesis. The intelligent measuring-controlling system takes on the power-controls of the heaters and thermoelectric coolers, temperature-measurements, and calculations of the thermal conductivity and the thermal resistance.Introduced and discussed mainly in this thesis includes: the measurement principle, the whole instrument's design, the microcontroller design, the measurement and control module design and the system evaluating experiments, and the potential problems in field debugging. The apparatus structure, detailed circuits, programs, control arithmetic can also be found in this thesis.The outstanding point lies in following three aspects: the first, the highly intelligent design not only makes the man-machine-interaction friendly but also expands its functions. The second, use of highly integrate circuit chip makes the measuring circuits simpler and improves the measurement precision. Finally, as to the control arithmetic, PID and fuzzy control are colligated to improve the control precision and speed, which is helpful for solving the similar problems.