Microcontroller-based multi-sensor apparatus for temperature control and thermalconductivity measurement

Abstract

A microcontroller-based multi-sensor temperature measurement and controlsystem that uses a steady-state one-dimensional heat-flow technique forabsolute determination of thermal conductivity of a rigid poor conductorusing the guarded hot-plate method is described. The objective of thisproject was to utilize the latest powerful, yet inexpensive, technologicaldevelopments, sensors, data acquisition and control system, computer andapplication software, for research and teaching by example. The system uses anST6220 microcontroller and LM335 temperature sensors for temperaturemeasurement and control. The instrument interfaces to a computer via the serialport using a Turbo C++ programme. LM335Z silicon semiconductortemperature sensors located at different axial locations in the heat sourcewere calibrated and used to measure temperature in the range from roomtemperature (about 293 K) to 373 K. A zero and span circuit was used inconjunction with an eight-to-one-line data multiplexer to scale the LM335output signals to fit the 0–5.0 V full-scale input of the microcontroller’son-chip ADC and to sequentially measure temperature at the differentlocations. Temperature control is achieved by using software-generatedpulse-width-modulated signals that control power to the heater. Thisarticle emphasizes the apparatus’s instrumentation, the computerizeddata acquisition design, operation and demonstration of the system as apurposeful measurement system that could be easily adopted for use in theundergraduate laboratory. Measurements on a 10 mm thick sample ofpolyurethane foam at different temperature gradients gave a thermalconductivity of 0.026 ± 0.004 W m−1 K−1.