Development Of A Double-guarded Hot Plate Thermal Conduction Coefficient Measuring Instrument Based On ARM

The thermal conduction happens when there is a temperature difference between two neighboring objects or between two areas of one object. The coefficient of thermal conduction is an inherent physical parameter of the material giving its thermal conduction capability. There are many different ways and instruments to measure the coefficient of thermal conduction. The guarded hot plate method, based on the Fourier one-dimensional steady-state thermal conduction theory, is the most widely used one. According to the Fourier thermal conduction theory, the coefficient of thermal conduction can be obtained by measuring the thermal flow through the sample or the temperature gradient in the sample. The guarded hot plate method has a wide measuring range, and in principle, no calibration is required since it uses two same samples symmetrically placed on the two sides of the hot plates. The thermal conduction coefficient measuring instruments are widely used in heat preservation material manufacturing factories, colleges, universities and research institutes.In this paper, a new kind of thermal conduction coefficient measuring instrument is designed and tested. The mechanical part of the instrument is a double-guarded hot plate structure, while its electronic part, including its control module, data collection module, result display and print-out, is based on ARM(Advanced RISC Machines) microprocessor. The instrument has many advantages, such as high degree of automation, a user friendly interface, short measuring time, high precision and small volume.The main work of the thesis includes the following five aspects:1. Description and analysis of the Fourier one-dimensional steady-state thermal conduction theory;2. Improvement of analog circuits, including data collection analog circuit and temperature control analog circuit, which makes them suitable for the new instrument;3. ARM control circuit design based on the requisitions of the new instrument, including the device selection, circuit and PCB design. The automatization level is upgraded by the application of stepping motor, and the LCD and keyboard design makes the instrument smaller and reduces the cost compared with a PC-based instrument; 4. Hardware debugging, including instrument calibration and magnification adjustment, as well as eliminating the system error by software;5. Software debugging, tests of the standard sample and error analysis according to the test results.