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.

In this paper, a wireless mid-infrared spectroscopy sensor network was designed and implemented for carbon dioxide fertilization in a greenhouse environment. A mid-infrared carbon dioxide (CO2) sensor based on non-dispersive infrared (NDIR) with the functionalities of wireless communication and anti-condensation prevention was realized as the sensor node. Smart transmission power regulation was applied in the wireless sensor network, according to the Received Signal Strength Indication (RSSI), to realize high communication stability and low-power consumption deployment. Besides real-time monitoring, this system also provides a CO2 control facility for manual and automatic control through a LabVIEW platform. According to simulations and field tests, the implemented sensor node has a satisfying anti-condensation ability and reliable measurement performance on CO2 concentrations ranging from 30 ppm to 5000 ppm. As an application, based on the Fuzzy proportional, integral, and derivative (PID) algorithm realized on a LabVIEW platform, the CO2 concentration was regulated to some desired concentrations, such as 800 ppm and 1200 ppm, in 30 min with a controlled fluctuation of <±35 ppm in an acre of greenhouse.

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