On-site calibration system for trace humidity sensors

• Published in: Measurement : journal of the International Measurement Confederation Vol. 91; pp. 251 - 257
• Main Authors: Hübert, Thomas, Tiebe, Carlo, Detjens, Marc, Majewski, Jacek
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2016
• Subjects: Measurement; Polymeric tubes; Sensor calibration; Trace humidity; Water vapour permeation; Measurement; Polymeric tubes; Sensor calibration; Water vapour permeation; Trace humidity
• ISSN: 0263-2241; 1873-412X
• DOI: 10.1016/j.measurement.2016.05.013

A portable device for calibration of trace humidity sensors and an adopted calibration procedure have been developed. The calibration device is based on humidity generation by permeating water through polymeric membrane tubes. Water vapour transmission rates for various polymers were experimentally determined in order to select the most suitable polymeric material. The developed trace humidity generator consists of a gas-flow polymeric hose immersed in a water reservoir thermostated by a sensor-controlled heater. Mole fractions of water vapour between 1μmolmol−1 and 350μmolmol−1 (equivalent to frost-point temperatures from −76°C to −31°C) were generated by varying either the operating temperature or gas flow. The operating temperature can be varied from 20°C to 60°C and kept stable within 0.1K. Uncertainty analysis indicated that the trace humidity generator produces gas flows of constant humidity amounts with a relative expanded uncertainty less than 3.4% (k=2) of the generated value.