With miniature high operating temperature cryocoolers becoming commonplace, there is an increasing importance of accurate determination of the thermal properties of infrared dewars such as heat load and thermal mass, as well as an increasing challenge to obtaining these properties. Especially in the case where operating temperature in the application is far from liquid nitrogen temperature, such as with HOT detectors, the use of the various known methods should be carefully evaluated. Inconsistencies in results between the various available methods, such as nitrogen boil-off, multi-slope warm-up calorimetry, and theoretical thermal modelling will be discussed, and the work being done at Thales Cryogenics to resolve these inconsistencies is presented.
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