The development of a virtual heat bath for calorimeters

All existing calorimeter systems for sensitive nuclear assay employ a heat bath surrounding the sample chamber. The purpose of the heat bath is to maintain a constant temperature so that a fixed temperature difference is maintained across the thermal resistance of the calorimeter. Present calorimeter systems all employ an active, feedback-controlled system to maintain a fixed temperature. An alternative would be to allow the heat-bath temperature to change, to measure it, and to compensate the assay for this change. Two significant observations make this approach possible: (1) the effect on the measurement of a temperature change in the heat bath is differential in form and (2) temperature measurement systems are very accurate when measuring differences in temperature (either in time or between two locations). From these observations, the authors have developed a virtual heat-bath compensation system. The control theory and results will be presented