Temperature measurement of low pressure condensable vapors

Attention is given to a dynamic isotope power system, in particular, a temperature error analysis at selected locations, sensor selection, and special probe sensor design analysis. Special thermocouple probes designed, fabricated, and installed at selected critical locations within the vapor portion of the system operating cycle are described. To meet the requested probe design error band of + or - 0.28 K, each location is analyzed for conduction, velocity, and radiation errors. The analysis leads to two basic probe designs, circular shield and fin styles, both reducing the possible radiation effects to the required error level. It is stressed that probe design selection must be employed to reduce the sensor error to the design goal and that thermocouple wire must be carefully inspected, processed, and calibrated to establish a documented base measurement. It is also emphasized that probe installation design must be such as to facilitate positioning while minimizing the damage and leakage points.