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A mid-infrared carbon dioxide (CO2) sensor was experimentally demonstrated for application in a greenhouse farm environment. An optical module was developed using a lamp source, a dual-channel pyre-electrical detector, and a spherical mirror. A multi-pass gas chamber and a dual-channel detection method were adopted to effectively enhance light collection efficiency and suppress environmental influences. The moisture-proof function realized by a breathable waterproof chamber was specially designed for the application of such a sensor in a greenhouse with high humidity. Sensor structure of the optical part and electrical part were described, respectively, and related experiments were carried out to evaluate the sensor performance on CO2 concentration. The limit of detection of the sensor is 30 ppm with an absorption length of 30 cm. The relative detection error is less than 5% within the measurement range of 30-5000 ppm. The fluctuations for the long-term (10 h) stability measurements on a 500 ppm CO2 sample and a 2000 ppm CO2 sample are 1.08% and 3.6%, respectively, indicating a good stability of the sensor. A wireless sensor network-based automatic monitoring system was implemented for greenhouse application using multiple mid-infrared CO2 sensor nodes. A monitor software based on LabVIEW was realized via a laptop for real-time environmental data display, storage, and website sharing capabilities. A field experiment of the sensor network was carried out in the town of Shelin in Jilin Province, China, which proved that the whole monitoring system possesses stable sensing performance for practical application under the circumstances of a greenhouse.
Wang et al. (Fri,) studied this question.