Quantifying Water Vapor Diffusion across Elastomer Pressure Sensor Seals
Water vapor diffusion across elastomer seals causes reference cavity pressurization and dielectric drift, requiring coulometric ISO 15105-2 verification.
ASTM E96
Gravimetric Standard
Standard gravimetric test methods define the rate of water vapor transmission through semi-permeable sheet materials under controlled temperature and humidity conditions. Testing laboratories execute astm e96 using either the desiccant cup method or the water cup method to establish mass change over time. The measured weight gain or loss indicates the vapor permeance of building materials, barrier films and packaging structures.
Boundaries of this testing scope apply strictly to flat flexible or rigid sheet samples and exclude porous woven assemblies.
Test Procedure
Environmental chambers maintain specific relative humidity differentials across the test specimen to induce moisture transport. In astm e96 testing, small changes in ambient temperature alter the saturated vapor pressure, which distorts mass loss calculations. Specimen preparation requires sealed perimeter mounting using microcrystalline wax or custom mechanical clamps to prevent edge leakage.
Technicians weigh test assemblies at scheduled intervals until the mass change rate becomes linear over three consecutive measurements. Water vapor transmission rate calculations incorporate total exposure area, time interval and net mass differential. Gravimetric resolution depends directly on environmental chamber air velocity, which must remain constant to stabilize boundary layer resistance.
Calibration Boundary
Analytical balances require calibration against traceable mass standards before gravimetric measurements begin. Compliance with astm e96 demands a balance sensitivity of zero point one milligram for low-permeance barriers. Environmental sensors monitoring test chamber temperature and relative humidity must undergo periodic calibration to maintain strict measurement accuracy.
Vapor Drift
Air velocity across the open surface creates edge effects that alter boundary layer resistance. Operational measurements under astm e96 remain valid only when sealing wax maintains an airtight perimeter without leaking into the active exposure area.