The application of sensor design and modelling techniques from earlier work in differential heat conduction calorimeters to DSC (Differential Scanning Calorimetry) has produced a prototype DSC with a 10-fold increase in effective sensitivity. The effective increase in sensitivity was due to two factors: 1) new thermopile design with increased thermal sensitivity, and 2) an improved cell mounting design that increased the common-mode rejection of the system. The prototype was placed in service and evaluated in late 1985. After several months, noise problems developed that were traced to the sensors. Since these sensors are designed and manufactured for use as heat pumps (peltier mode of operation) and non sensors (Seebeck mode of operation), the manufacturers could not supply information on noise performance. We then initiated a program to evaluate the noise and failure modes of sensors from several different manufacturers. The noise was traced to mechanical failures in the thermocouple elements caused by large stresses developed across the thermopile when the calorimeter temperature was ramped from 30 deg. C to 80 deg. C. The sensor assembly consisted of four different materials held in place with stainless steel screws. The difference between the coefficients.
