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Humidity Measurement in Carbon Dioxide with Capacitive Humidity Sensors at Low Temperature and Pressure

Lorek, Andreas and Majewski, Jacek (2018) Humidity Measurement in Carbon Dioxide with Capacitive Humidity Sensors at Low Temperature and Pressure. Sensors, 18 (8), p. 2615. Multidisciplinary Digital Publishing Institute (MDPI). DOI: 10.3390/s18082615 ISSN 1424-8220

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Official URL: http://dx.doi.org/10.3390/s18082615

Abstract

Abstract: In experimental chambers for simulating the atmospheric near-surface conditions of Mars, or in situ measurements on Mars, the measurement of the humidity in carbon dioxide gas at low temperature and under low pressure is needed. For this purpose, polymer-based capacitive humidity sensors are used; however, these sensors are designed for measuring the humidity in the air on the Earth. The manufacturers provide only the generic calibration equation for standard environmental conditions in air, and temperature corrections of humidity signal. Because of the lack of freely available information regarding the behavior of the sensors in CO2, the range of reliable results is limited. For these reasons, capacitive humidity sensors (Sensirion SHT75) were tested at the German Aerospace Center (DLR) in its Martian Simulation Facility (MSF). The sensors were investigated in cells with a continuously humidified carbon dioxide flow, for temperatures between −70 ◦C and 10 ◦C, and pressures between 10 hPa and 1000 hPa. For 28 temperature–pressure combinations, the sensor calibration equations were calculated together with temperature–dependent formulas for the coefficients of the equations. The characteristic curves obtained from the tests in CO2 and in air were compared for selected temperature–pressure combinations. The results document a strong cross-sensitivity of the sensors to CO2 and, compared with air, a strong pressure sensitivity as well. The reason could be an interaction of the molecules of CO2 with the adsorption sites on the thin polymeric sensing layer. In these circumstances, an individual calibration for each pressure with respect to temperature is required. The performed experiments have shown that this kind of sensor can be a suitable, lightweight, and relatively inexpensive choice for applications in harsh environments such as on Mars.

Item URL in elib:https://elib.dlr.de/121369/
Document Type:Article
Title:Humidity Measurement in Carbon Dioxide with Capacitive Humidity Sensors at Low Temperature and Pressure
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Lorek, AndreasAndreas.Lorek (at) dlr.dehttps://orcid.org/0000-0002-8960-6214
Majewski, JacekDepartment of Automation and Metrology, Faculty of Electrical Engineering and Computer Science, Lublin University of TechnologyUNSPECIFIED
Date:9 August 2018
Journal or Publication Title:Sensors
Refereed publication:Yes
Open Access:Yes
Gold Open Access:Yes
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:18
DOI :10.3390/s18082615
Page Range:p. 2615
Editors:
EditorsEmail
UNSPECIFIEDMDPI
Publisher:Multidisciplinary Digital Publishing Institute (MDPI)
ISSN:1424-8220
Status:Published
Keywords:capacitive humidity sensors; SHT75; carbon dioxide; humidity; Mars in-situ measurements; experimental simulation chambers; Martian atmosphere; low temperature; low pressure; CO2
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Science and Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Erforschung des Weltraums
DLR - Research theme (Project):R - Vorhaben Planetary Evolution and Life
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research
Deposited By: Lorek, Dr.rer.nat. Andreas
Deposited On:10 Sep 2018 16:14
Last Modified:14 Dec 2019 04:27

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