MULTIPOINT FIBEROPTIC HUMIDITY MONITOR
作者:
N Goldatein,
F Bien,
M.E Garah,
J Lee,
M.R Zakin,
期刊:
Drying Technology
(Taylor Available online 1991)
卷期:
Volume 9,
issue 4
页码: 833-847
ISSN:0737-3937
年代: 1991
DOI:10.1080/07373939108916723
出版商: Taylor & Francis Group
关键词: absorption;near infrared;diode laser;remote detection;sensor;process control;drying;Yankee dryer;modular
数据来源: Taylor
摘要:
Spectral Sciences, Inc. is developing a multipoint humidity monitor for drying application in the pulp and paper industry. The humidity is measured by monitoring near-infrared optical absorption in the process stream atmosphere. An array of sensor heads distributed throughout the plant is linked by fiber optic cables to a single source/readout device which can be located in a control room hundreds of meters away. The sensor heads and cables are modular. allowing for raid installation and reconfiguration of a distributed sensor system in process control applications. The method used for quantifying the optical absorption provides substantial stability, accuracy, and signal processing advantages over standard wavelength scanning or band pass techniques. The laser diode's output wavelength is actively locked to the center of a water absorption line, thereby providing a constant monitor of water vapor concentration which is insensitive to all other species in the process stream. Wavelength modulation and second harmonic detection techniques are used to quantify the water vapor concentration. A simultaneous temperature measurement then permits an output of the absolute humidity or humidity ratio for process monitoring or control
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