Humidity in Climatic and Test Chambers

Climatic and test chambers subject products and materials to controlled temperature and humidity cycles to validate their behavior. For the general context of this magnitude, see the humidity instrumentation landing.

Unlike a stable HVAC environment, a test chamber puts the sensor through extreme, changing conditions — and often shares the volume with the sealing materials and samples being evaluated themselves, which can interfere with the reading.

This note covers

• Why sealing materials and samples under test skew the humidity reading
• The condensation risk when there's a temperature drop of just 1°C
• How chemical purge and warmed probes solve both problems

Why Materials Inside the Chamber Skew the Measurement

Some sealing materials used for chamber walls or cable feed-throughs can release compounds like acetic acid during curing, causing humidity drift. The effect is usually reversible, but it can temporarily affect sensor accuracy while the material keeps releasing those compounds.

The same happens with materials under test: even a relatively small amount of released substances can delay chamber drying and contaminate the sensing surface, giving humidity readings higher than actual until the chamber stabilizes.

The Condensation Risk From a Minimal Temperature Drop

In high-humidity conditions, sensor installation matters as much as its rated accuracy: a drop of just 1°C on the probe surface at 40°C and 95% RH can reach the dew point and trigger condensation directly on the sensor, skewing the reading.

The limit also shows up at the hot end: in unpressurized systems, at 120°C the maximum achievable relative humidity is around 51%, limited by water's saturation pressure (roughly 1.987 bar) — a chamber reporting values above that limit under those conditions is signaling a measurement problem, not an actual condition.