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Precision Flow Measurement Under Humid Conditions: Alicat’s RH Sensing Approach
Technical insight courtesy of Alicat Scientific
Accurate gas flow measurement is fundamental to maintaining control in chemical and process engineering—but water vapor in the gas stream can introduce significant error if not properly accounted for. To address this, Alicat Scientific offers mass flow meters and controllers equipped with integrated relative humidity (RH) sensors, enabling real-time correction for humidity effects on gas density, viscosity, and compressibility.
Alicat’s RH sensing technology uses capacitive polymer-based sensors to detect changes in dielectric constant as moisture levels fluctuate. This allows for sub-second updates on RH, dew point, and water vapor percentage—parameters critical for ensuring consistent performance in environments where humidity can shift quickly, such as during gas-phase reactions, fuel cell testing, or downstream gas drying.
With its COMPOSER™ gas selection and normalization feature, Alicat devices adjust flow readings to represent the dry gas equivalent—removing the need for manual compensation and preserving accuracy even as humidity rises. This is particularly valuable for stoichiometric control in reactive gas mixing, where excess moisture could skew reaction ratios or contribute to unwanted byproducts.
Compared to thermal mass flow technologies, Alicat’s differential pressure–based approach offers improved measurement fidelity under humid conditions. For example, at 25 °C and 1 atm with a 20 °C dew point, Alicat reports flow uncertainties as low as ±0.032% for O₂ and ±0.077% for H₂—well below what typical thermal sensors achieve in similar conditions.
It’s worth noting that RH sensor accuracy can decline at high temperature and humidity extremes (e.g., ±5% above 50 °C and 90% RH). However, pre-heating or post-cooling measurement strategies can mitigate these limitations, providing valuable insight upstream or downstream of thermally active zones.
We at Finn and Conway value our ongoing collaboration with Alicat Scientific, whose engineering-forward approach continues to advance real-time gas analysis in demanding industrial settings. For further technical details—including sensor compatibility and environmental limitations—please refer to the original article here:
Relative Humidity Sensing with Alicat Devices
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