Advances in temperature derivative control and calorimetry

Temperature stabilization by inertial feedback control has proven a powerful tool to create the ultrastable environment essential for high resolution calorimetry. A thermally insulated mass, connected to a base through Seebeck effect sensors (thermopiles) is used as a reference to control the base temperature. The thermopile signal is proportional to both the heat capacity of the reference mass and the derivative Θ of the base temperature Θ. Using vacuum insulation and bismuth telluride thermopiles, we designed and tested temperature derivative sensors (TDSs) with sensitivities up to 3300 V s K−1. Standard industrial controllers with approximately ±1 μV input noise and stability, permit control of temperature derivatives to ±3×10−10 K s−1. Single‐cup thermoelectric calorimeters coupled to the TDS‐controlled base permitted measurement of heat flow from samples in a power range from 3 μW to 10 W with high accuracy (±100 ppm), resolution (±0.2 μW), and reproducibility (±1 μW). The design of two instruments ...