Measurement uncertainty of coulometric trace humidity sensors

Carlo Tiebe; Marc Detjens; Ulrich Banach; Thomas Hübert

doi:10.1515/teme-2018-0031

Article

Measurement uncertainty of coulometric trace humidity sensors

Carlo Tiebe
Carlo Tiebe is working in the division 8.1 Sensors, Measurement and Testing Methods of BAM. He studied analytical and environmental chemistry at the University of applied sciences Magdeburg-Stendal and Martin-Luther-University Halle-Wittenberg and received his doctoral degree (PhD) at the Technical University Ilmenau on the topic “Detection of microbial volatile organic compounds by ion mobility spectrometry”. His current research focuses are trace humidity determination by coulometric humidity sensors, sensor based quality control for spices and spice mixtures, air mail and cargo screening methods as well as metrology of ammonia in ambient air. In 2016 he passed the examination of a further education on quality management and quality auditor.
, Marc Detjens
Marc Detjens works in the division 8.1 Sensors, Measurement and Testing Methods at BAM. He studied Biotechnology and Process Engineering at Flensburg University of Applied Sciences. His current research, which is part of his PhD thesis, focus on trace humidity determination and moisture measurements by coulometric sensors.
, Ulrich Banach
Dr. Ulrich Banach worked at BAM from 1992 until 2018. He had expertise in the preparation of test gases for the calibration, certification of gas and humidity sensors and standardisation. Now he is a retiree.
and Thomas Hübert
On 15 November 2017, our co-author, colleague and employee Dr. rer. nat. habil. Thomas Hübert died after a short illness at the age of 65. He joined BAM in 1992 and worked last in the division 8.1 Sensor Technology, Measurement and Testing Methods. His scientific career began 17 years ago at the Institute of Inorganic Chemistry at the Academy of Sciences of the GDR, where he established himself early in the field of glass and ceramic development and sensor technology. In the recent past, his work focused on gas and humidity sensors as well as sol-gel processes. His developments in the field of nanotechnologies and trace humidity measurement technology gained international attention and industrial significance, and he played a decisive role in the development of international standards and regulations in these areas. https://trauer.moz.de/traueranzeige/thomas-huebert.

Published/Copyright: August 28, 2018

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From the journal tm - Technisches Messen Volume 85 Issue 12

Abstract

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.

Zusammenfassung

Die Spurenfeuchte in technischen Gasen kann zuverlässig mit coulometrischen Feuchtesensoren bestimmt werden. Das Prinzip dieser Sensoren basiert auf der Absorption von Wasser in einer hygroskopischen Schicht und anschließender elektrolytischer Zersetzung. Die Kalibrierung der Sensoren erfolgte mit einem Spurenfeuchtegenerator bei Frostpunkttemperaturen kleiner als −30°C bzw. einem Volumenanteil kleiner als 376 µL·L⁻¹. Die generierte Feuchte wurde zusätzlich zu den coulometrischen Sensoren mit einem Taupunktspiegelhygrometer, welches als Referenz diente, gemessen. Zwischen dem coulometrischen Sensorsignal und der gemessenen Referenzfeuchte wurde eine empirische nichtlineare Funktion gefunden. Die resultierende Kalibrierfunktion, die aus zwei Parametern besteht, wurde hinsichtlich ihrer Messunsicherheit bewertet. Zusätzlich erfolgt die Überprüfung der Kalibrierparameter mittels einfaktorieller Varianzanalyse (ANOVA). Die ANOVA zeigte, dass eine gemittelte Funktion für die Feuchtigkeitsbestimmung in Stickstoff, Wasserstoff, Distickstoffmonoxid, Druckluft und synthetischer Luft für mehrere Sensoren angewendet werden kann. Mit coulometrischen Sensoren ist es möglich, die Spurenfeuchte in technischen Gasen mit einer erweiterten Unsicherheit bezogen auf die Frostpunkttemperatur kleiner als 2,1 K (Erweiterungsfaktor k=2) zu messen.

Keywords: Trace humidity; coulometric sensors; measurement uncertainty; ANOVA

Schlagwörter: Spurenfeuchte; coulometrische Sensoren; Messunsicherheit; ANOVA

Funding source: Bundesministerium für Wirtschaft und Energie

Award Identifier / Grant number: MNPQ 20/09

Funding statement: This work was funded by Federal Ministry for Economic Affairs and Energy (Germany) MNPQ 20/09 and the Central Innovation Programme of Germany funding ID KF2201085KM4.

About the authors

Carlo Tiebe

Carlo Tiebe is working in the division 8.1 Sensors, Measurement and Testing Methods of BAM. He studied analytical and environmental chemistry at the University of applied sciences Magdeburg-Stendal and Martin-Luther-University Halle-Wittenberg and received his doctoral degree (PhD) at the Technical University Ilmenau on the topic “Detection of microbial volatile organic compounds by ion mobility spectrometry”. His current research focuses are trace humidity determination by coulometric humidity sensors, sensor based quality control for spices and spice mixtures, air mail and cargo screening methods as well as metrology of ammonia in ambient air. In 2016 he passed the examination of a further education on quality management and quality auditor.

Marc Detjens

Marc Detjens works in the division 8.1 Sensors, Measurement and Testing Methods at BAM. He studied Biotechnology and Process Engineering at Flensburg University of Applied Sciences. His current research, which is part of his PhD thesis, focus on trace humidity determination and moisture measurements by coulometric sensors.

Ulrich Banach

Dr. Ulrich Banach worked at BAM from 1992 until 2018. He had expertise in the preparation of test gases for the calibration, certification of gas and humidity sensors and standardisation. Now he is a retiree.

Thomas Hübert

On 15 November 2017, our co-author, colleague and employee Dr. rer. nat. habil. Thomas Hübert died after a short illness at the age of 65. He joined BAM in 1992 and worked last in the division 8.1 Sensor Technology, Measurement and Testing Methods. His scientific career began 17 years ago at the Institute of Inorganic Chemistry at the Academy of Sciences of the GDR, where he established himself early in the field of glass and ceramic development and sensor technology. In the recent past, his work focused on gas and humidity sensors as well as sol-gel processes. His developments in the field of nanotechnologies and trace humidity measurement technology gained international attention and industrial significance, and he played a decisive role in the development of international standards and regulations in these areas. https://trauer.moz.de/traueranzeige/thomas-huebert.

Acknowledgment

This manuscript is written in memoriam to Dr. Thomas Hübert. He was substantially involved in the research on coulometric humidity sensors and established the humidity sensors testing lab. He will be sadly missed. With deep respect to you Mr. Hübert!

The authors thank Roland Wernecke and Andreas Lorek for related experience exchange as well as Andreas Subaric-Leitis, Jörg Schlischka and Marcus Thomas for technical support.

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Received: 2018-03-29

Accepted: 2018-07-16

Published Online: 2018-08-28

Published in Print: 2018-12-19

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Articles in the same Issue

https://doi.org/10.1515/teme-2018-0031

Keywords for this article

Trace humidity; coulometric sensors; measurement uncertainty; ANOVA