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Sensors 2017, 17(1), 68; doi:10.3390/s17010068

SEALDH-II—An Autonomous, Holistically Controlled, First Principles TDLAS Hygrometer for Field and Airborne Applications: Design–Setup–Accuracy/Stability Stress Test

1
Physikalisch-Technische Bundesanstalt Braunschweig, Braunschweig 38114, Germany
2
Physikalisch Chemisches Institut, Universität Heidelberg, Heidelberg 69120, Germany
3
Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08540, USA
4
Center of Smart Interfaces, Technische Universität Darmstadt, Darmstadt 64287, Germany
*
Author to whom correspondence should be addressed.
Academic Editor: Vittorio M. N. Passaro
Received: 9 November 2016 / Revised: 11 December 2016 / Accepted: 20 December 2016 / Published: 30 December 2016
(This article belongs to the Section Physical Sensors)
View Full-Text   |   Download PDF [4007 KB, uploaded 30 December 2016]   |  

Abstract

Instrument operation in harsh environments often significantly impacts the trust level of measurement data. While commercial instrument manufacturers clearly define the deployment conditions to achieve trustworthy data in typical standard applications, it is frequently unavoidable in scientific field applications to operate instruments outside these commercial standard application specifications. Scientific instrumentation, however, is employing cutting-edge technology and often highly optimized but also lacks long-term field tests to assess the field vs. laboratory performance. Recently, we developed the Selective Extractive Laser Diode Hygrometer (SEALDH-II), which addresses field and especially airborne applications as well as metrological laboratory validations. SEALDH-II targets reducing deviations between airborne hygrometers (currently up to 20% between the most advanced hygrometers) with a new holistic, internal control and validation concept, which guarantees the transfer of the laboratory performance into a field scenario by capturing more than 80 instrument internal “housekeeping” data to nearly perfectly control SEALDH-II’s health status. SEALDH-II uses a calibration-free, first principles based, direct Tuneable Diode Laser Absorption Spectroscopy (dTDLAS) approach, to cover the entire atmospheric humidity measurement range from about 3 to 40,000 ppmv with a calculated maximum uncertainty of 4.3% ± 3 ppmv. This is achieved not only by innovations in internal instrument monitoring and design, but also by active control algorithms such as a high resolution spectral stabilization. This paper describes the setup, working principles, and instrument stabilization, as well as its precision validation and long-term stress tests in an environmental chamber over an environmental temperature and humidity range of ΔT = 50 K and ΔRH = 80% RH, respectively. View Full-Text
Keywords: trace gas measurement; absorption spectroscopy; TDLAS; hygrometer; calibration-free; airborne; field; SEALDH; metrology; traceable trace gas measurement; absorption spectroscopy; TDLAS; hygrometer; calibration-free; airborne; field; SEALDH; metrology; traceable
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Buchholz, B.; Kallweit, S.; Ebert, V. SEALDH-II—An Autonomous, Holistically Controlled, First Principles TDLAS Hygrometer for Field and Airborne Applications: Design–Setup–Accuracy/Stability Stress Test. Sensors 2017, 17, 68.

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