Research On Protected Horticultural CO₂ Detection System Based On Infrared Absorption Spectroscopy

This paper comes from Chinese National Science and Technology Support Plan "modern energy efficient and efficient facilities gardening equipment development and industrialization demonstration",project number: 2014BAD08B00.Protected horticultural overcomes the shortcomings of traditional planting method and it is not easily affected by geographical and natural environment and climate and other factors,which makes greenhouse production achieve the purposes of high yield and high quality and has great significance to the development of agriculture.CO₂ as an important raw material for photosynthesis,the concentration of CO₂ has an important effect on the growth of crops in greenhouse,so it is necessary to detect the concentration of CO₂ in greenhouse.In the many methods of CO₂ concentration detection,infrared absorption spectroscopy method has been extensively concerned and widely used because of its unique advantages.In addition,the construction of wireless sensor network can be used to collect multipoint CO₂ concentration in the greenhouse,and overcome the disadvantages of wired transmission.Based on infrared absorption spectroscopy method,this paper studied the infrared CO₂ detection system of protected horticultural.Analyzed the infrared absorption spectrum of CO₂ molecules and chose the absorption wavelength of CO₂ molecules which is the strong absorption peak near 4.25 ?m.Then,selected the suitable infrared thermal light source and dual-channel pyroelectric detector.Used a spherical mirror to increase the optical path length and make the light converge to the detector,which optimized the optical path structure well.After that,designed and manufactured the constant current source drive circuit for light source,signal processing circuit and wireless communication circuit and other hardware circuits.In order to adapt to the high humidity environment in the greenhouse,the optical path and the circuit part were sealed,and the diffusion of the gas in the optical path was realized by the extruded polytetrafluoroethylene film.Then,programmed the system software,and the software included two parts: concentration acquisition and wireless sensor network.The CO₂ concentration detection nodes collected the data and joined the wireless sensor network,and sent the collected data through the network to the sink node.The sink node transmitted data to the computer through the serial port and the computer display and storage the received data.A gas experiment with different concentrations of CO₂ gas was carried out to perform the calibration of the sensor and the detection of the related properties.The detection range of the sensor was 0⁵000 ppm;the relative error of the measured value was between-6.0% and 9.9% in the range of 150⁵000 ppm;long time stability of the sensor at 0 ppm was measured,and the concentration fluctuation peak was 15 ppm and the standard deviation was 2.8 ppm;the Alan variance of the output at 0 ppm was calculated,and the 1? detection limit was 2.5 ppm.Used the detection system measure the CO₂ concentration in the greenhouse,and the result showed that the measured curve was consistent with the actual situation,which verified the detection system could be applied to the greenhouse well.The innovation of this paper contains two points.Firstly,the infrared CO₂ sensor was developed by using the self-made reflector chamber and differential mid-infrared absorption spectroscopy.And the sensor was moisture-treated to adapt to the high humidity environment in the greenhouse.Secondly,the wireless CO₂ sensor network was constructed by wireless radio frequency communication technology,and the multi-point detection of CO₂ concentration in greenhouse was carried out.In addition,the field experiment was carried out in solar greenhouse.