An autonomous thermal control system has been developed for instruments with steady temperature requirements that are exposed to widely varying environmental conditions. The active thermal control system uses thermo-electric (Peltier) coolers with a programmable power supply, digital temperature sensors, and on-board proportional differential logic to track and predict temperature variations. This system is designed for instruments with large thermal mass and thermally sensitive electronic components that would be effected by variabilities in the local outdoor environment including weather, sunrise, and sunset. Presented are the test results of the design showing the temperature stayed within ±0.125°C during smooth ambient temperature changes (27°C ambient change over 80 min), remained within +0.375/−0.6875°C under a sharp ambient temperature drop (27°C sudden drop), and remained within +0.25/−0.875°C when random variabilities in the ambient were introduced (2–10°C degree variabilities over the time frame of minutes). For the thermal control system and test results presented, it is shown that several calibration and design points must be considered for a large thermal mass system in order to achieve steady thermal control. The system presented is capable of maintaining steady thermal control within the given constraints.
