TY - JOUR A1 - Detjens, Marc A1 - Hübert, Thomas A1 - Tiebe, Carlo A1 - Banach, Ulrich T1 - Coulometric trace humidity measurement in technical gases N2 - Trace humidity was measured by using miniaturized planar coulometric sensors in technical gases such as hydrogen, nitrogen, helium, nitrous oxide, and synthetic air. Frost point temperatures tf in the gases ranged from −60 °C to −30 °C, which is equivalent to a vapour mole fraction xv from 10 μmol mol−1 to 376 μmol mol−1. In addition, the generated humidity was determined by using a precision dew point hygrometer as reference. Nonlinear calibration functions were calculated that correlated electric current (sensor signal) and reference humidity. Parameters of functions were tested with one-way analysis of variances (ANOVA) to prove if all used sensors had a similar behavior in the same gas during experiments. Results of ANOVA confirmed that averaged functions can be applied for trace humidity measurement in nitrogen, helium, nitrous oxide, and synthetic air. The calculated functions were negligibly different for nitrogen, helium, and synthetic air. In humidified nitrous oxide, a minor change of parameters was observed due to lower electrical currents. In total contrast to that, the measured sensor signals were significantly higher in humidified hydrogen and each sensor required its own calibration function. The reason was a recombination effect that favoured multiple measurements of water molecules. Nevertheless, it was possible to measure continuously trace humidity in all tested gases by using coulometric sensors with an expanded uncertainty below 2 K (k = 2). KW - ANOVA KW - Trace humdity measurement KW - Coulometric sensors KW - Chemical sensors KW - Measurement uncertainty PY - 2018 U6 - https://doi.org/10.1063/1.5008463 SN - 0034-6748 SN - 1089-7623 VL - 89 IS - 8 SP - 085004, 1 EP - 8 PB - American Institute of Physics (AIP) CY - Maryland (USA) AN - OPUS4-45956 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Tiebe, Carlo A1 - Detjens, Marc A1 - Banach, Ulrich A1 - Hübert, Thomas T1 - Measurement uncertainty of coulometric trace humidity sensors N2 - Especially trace amounts of water vapour in gases can be reliably determined by coulometric trace humidity sensors. The principle of these sensors is based on water vapour absorption in a hygroscopic layer and its subsequent electrolytic decomposition. The calibration of sensors was performed in the humidity range, expressed as frost point temperature, from −30°C to −80°C . This range is equivalent to volume fractions smaller than 376 µL·L−1. Generated humidity was measured with coulometric sensors and a chilled dew point hygrometer that was used as reference. An empirical non-linear function was found between sensor signal and measured reference humidity. This function consists of two parameters with a measurement uncertainty. Both calibration parameters were checked by means of one-way analysis of variance. It showed that gas specific function can be used for humidity measurement in nitrogen, hydrogen, dinitrogen monoxide, compressed and synthetic air. It is possible to determine trace humidity in all tested gases with an expanded uncertainty less than 2.1 K (coverage factor k=2 ) regarding frost point temperature. KW - Trace humidity KW - Coulometric sensor KW - Measurement uncertainty KW - ANOVA PY - 2018 U6 - https://doi.org/10.1515/teme-2018-0031 SN - 0171-8096 VL - 85 IS - 12 SP - 746 EP - 753 PB - De Gruyter CY - Oldenbourg AN - OPUS4-45959 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -