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Progress in the Svet-3 space greenhouse project: Temperature measurements; thermoelectric sensor calibration apparatus

The presented work is a part of the Bulgarian “Svet-3 Space Greenhouse” project for development of a plant growth facility with adaptive environmental control and automatic optimization of plant growth conditions during the experiment. The paper discusses the performance analysis, development and testing of a laboratory calibration and check calibration thermoelectric apparatus for preparing sensors for precise temperature measurements of plant environment. The apparatus uses an insulated chamber that accommodates a temperature-stabilized aluminum plate holding both the sensors to be calibrated and the feedback one. A thermoelectric module with heatsink-fan assembly is mounted outside the chamber and in thermal contact with the plate. The apparatus uses a standard Peltier module of TEC1-12703 type, an analogue PID control system and miniature stable thermistors of 10 kΩ at 20°C for feedback temperature control. The insulated chamber provides access for an external high-precision thermometer to monitor permanently the plate temperature. The operational characteristic of the apparatus is measured and the standard deviations of the steady state temperature for each set point are calculated. The results are depicted graphically and discussed.