Improving the Usability of Calorimetric Measuring Chambers for Reliable Thermal Measurements

Abstract:
Calorimetric dissipation power measurement comes with a multitude of challenges, especially concerning robustness to environmental temperature fluctuation (even in double-jacketed architectures) and long settling time. This paper presents a control approach for the cooling liquid temperature (heat transportation) and the test chamber’s internal air temperature to improve the settling time and reduce the sensitivity to ambient temperature fluctuations making a measurement campaign much more robust. Utilizing a Smith predictor for the test chambers air temperature overcomes long dead-time effects and, in combination with an adaptive gain leads to aggressive control at high control errors and soft control closer to steady state. A water temperature controller for the cooling liquid reduces the influence of ambient temperature changes during the measurement significantly. The settling time to the final measurement result can thus be reduced from 8 hours to 2 hours in controlled operation.