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Sensors 2012, 12(12), 17058-17073; doi:10.3390/s121217058
Article

Improved Membrane-Based Sensor Network for Reliable Gas Monitoring in the Subsurface

*  and
Helmholtz-Centre for Environmental Research, T.-Lieser-Strasse 4, 06120 Halle, Germany
* Author to whom correspondence should be addressed.
Received: 8 October 2012 / Revised: 21 November 2012 / Accepted: 5 December 2012 / Published: 12 December 2012
(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany 2012)
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Abstract

A conceptually improved sensor network to monitor the partial pressure of CO2 in different soil horizons was designed. Consisting of five membrane-based linear sensors (line-sensors) each with 10 m length, the set-up enables us to integrate over the locally fluctuating CO2 concentrations (typically lower 5%vol) up to the meter-scale gaining valuable concentration means with a repetition time of about 1 min. Preparatory tests in the laboratory resulted in a unexpected highly increased accuracy of better than 0.03%vol with respect to the previously published 0.08%vol. Thereby, the statistical uncertainties (standard deviations) of the line-sensors and the reference sensor (nondispersive infrared CO2-sensor) were close to each other. Whereas the uncertainty of the reference increases with the measurement value, the line-sensors show an inverse uncertainty trend resulting in a comparatively enhanced accuracy for concentrations >1%vol. Furthermore, a method for in situ maintenance was developed, enabling a proof of sensor quality and its effective calibration without demounting the line-sensors from the soil which would disturb the established structures and ongoing processes.
Keywords: gas; monitoring; soil; greenhouse gases; CO2; membrane; sensor gas; monitoring; soil; greenhouse gases; CO2; membrane; sensor
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).
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Lazik, D.; Ebert, S. Improved Membrane-Based Sensor Network for Reliable Gas Monitoring in the Subsurface. Sensors 2012, 12, 17058-17073.

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