Calculating Dielectric Zero Shift in Capacitive Pressure Transmitters under Vacuum
Vacuum pull-down removes polarizable gas from capacitive pressure cells, causing a dielectric zero shift calculated via gas polarizability and gap geometry.
ASTM E595
Testing Standard
Standardized laboratory procedures for evaluating material outgassing in vacuum environments ensure the selection of stable compounds for aerospace applications. The procedure known as astm e595 defines the parameters for exposing specimens to high vacuum at elevated temperatures. This test prevents the use of materials that would release volatile condensable substances near sensitive optical surfaces.
Screening Methodology
Thermal vacuum exposure is conducted at a temperature of one hundred and twenty-five degrees Celsius for twenty-four hours. Specimens are placed in a vacuum chamber held at a pressure below seven millipascals, allowing volatile elements to escape. A cooled collector plate positioned above the specimen captures the released condensables for subsequent weight analysis.
Material Metric
Quantitative measurements of specimen weight before and after the test determine the percentage of mass lost. This measurement under astm e595 also determines the amount of collected volatile condensable material that deposits on the collector plate. These dual metrics provide a clear indication of how a polymer or adhesive will behave in the vacuum of space.
Acceptance Limit
Aerospace programs establish strict limits for material qualification based on the resulting mass ratios. Generally, a material must exhibit a total mass loss of less than one percent to be approved for flight hardware. Additionally, the collected volatile condensable material must not exceed one-tenth of a percent.
These limits ensure that optical sensors and solar panels remain free from performance-reducing films during the operational lifetime of the spacecraft. When a compound fails these thresholds, it must be replaced by a fully cured alternative or undergo an extended thermal bakeout process to pre-exhaust the volatile fractions.