Thermal-electrical modeling of absolute cryogenic radiometers

Abstract

This study employs finite-element (FE) software to model the nonlinear thermal-electrical dynamic response of absolute cryogenic radiometers (ACRs). The high-accuracy cryogenic radiometer (HACR) and laser-optimized cryogenic radiometer (LOCR) have been analyzed to determine the input geometric and thermal parameters. Comparisons between the FE model and experimental results for the HACR and LOCR show an agreement in temperature within 2%. A proportional-integral-derivative (PID) temperature-control algorithm has been developed for both the receiver and the heat sink. The optimized control parameters are related to the thermal conductances and time constants of the radiometers. The LOCR receiver has the advantage of a reduction in measurement time over the HACR receiver; whereas the HACR heat sink offers the advantage of better temperature stability over the LOCR heat sink. The time constant of the HACR receiver can be significantly reduced without degrading the performance. The temperature stability of the LOCR heat sink can be improved by a factor of two by using a larger heat-sink heat capacity, C HS≥80 mJ/K. This research will help improve future design of ACRs.