For the determination of the Coefficient of Moisture Expansion (CME) the mass loss and the change of length has to be measured with high accuracy. The ratio of length to mass variation by moisture absorption or evaporation is the CME in m/m/wt% H2O.
The main advantage of AAC CME test method is a highly accurate measurement within some days of a process, which takes typically weeks or months. AAC measures the mass loss in vacuum with an accuracy of 1 µg (Advanced Outgassing Test Rig) and the length change with an accuracy of 10nm. Both measurements are done in vacuum and are therefore close to real space conditions.
Optionally, the samples can be conditioned from fully dry to different saturated states (standard: 22°C/55%rHd) or vice versa to have their mass loss over lifetime and calculate the length change of the flight hardware.
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