Development Of Carbon Dioxide Monitoring And Controlling System Applied In Protected Horticulture Based On Mid-infrared Absorption Spectroscopy

In recent years,with the rapid development of communication,automation and sensing technologies,greenhouse engineering technologies which owns characteristics including refinement,intellectualization and networking has gradually become the main development direction in protected horticulture.In order to achieve the target of increasing production and improving quality of crops,greenhouse technology commits itself to regulate the environmental factors effectively to optimize the growth conditions for plants.The effective monitoring and controlling of environmental factors including temperature,humidity and luminance has been achieved in developed countries.However,as one of the main components of plant photosynthesis,CO₂ is still difficult to be controlled for numerous reasons such as the technical difficulty of real-time accurate measurement,late development and lack of technical maturity.Therefore,in order to solve the above problems,a high performance real-time CO₂ detection system applied in greenhouse is developed in this paper.The performance of CO₂ detector determines the accuracy,stability and response time of in-situ CO₂ concentration regulation in greenhouse.Compared with traditional electrochemical and semiconductor sensors,the sensors based on infrared absorption spectroscopy have several advantages including high precision,quick response,desired selectivity and high stability.Besides the high precision,the direct absorption spectroscopy as one of the infrared absorption spectrum technologies also has the advantages of high cost-performance ratio and less constraint conditions which implying a suitable application for CO₂ concentration monitoring in greenhouse.The environment of greenhouse is usually complex and inconvenient to layout cables.This constrains the traditional methods of wired communication.Meanwhile,greenhouse has characteristics including non-linearity,time varies and large lag which mean regular methods can not satisfy the rapid and effective control requirements.In consideration of the above issues,wireless sensors are developed and implemented to constitute the communication network for the detection purposes.A control platform with a function of fuzzy PID controlling is designed to satisfy the regulation requirement in greenhouse.In this paper,the main research content is divided into three parts and in-situ experiments are carried out to verify the reliability of the research results.Firstly,in this paper,based on the direct absorption spectroscopy,an infrared CO₂ detector is designed and fabricated.In the optical part,a spherical reflective concentrating chamber is fabricated to increase the optical path.The moisture-proof function is realized by a breathable waterproof made of expanded polytetrafluoroethylene?e PTFE?for the application targeting the high humidity conditions in greenhouse.A dual-channel detection method with single light source is adopted to effectively suppress influence from the light source and optical path.In the electrical part,the received signals from two channels are processed by a digital quadrature phase locked amplifier,which can improve the detection accuracy and stability.The dynamic gas distribution method is used to test the indicators including detection limit,repeatability and stability etc.The experimental results show that the available detection range of the detector is from 20 ppm to 4000 ppm.The fluctuations for the long-term stability measurements on a 500 ppm CO₂ sample and a 2000 ppm CO₂ sample are 3.6 % and 1.05 % respectively.Through the Allen variance analysis,the theoretical detection limit of the detector is lower than 1 ppm which could satisfy the application requirements in the greenhouse environment.Secondly,under the circumstance of ensuring the real-time accurate detection of CO₂ concentration by the self-developed infrared CO₂ detector,the detector was optimized as a sensor node for the application in wireless sensor network.In this way,every sensor node is available for multiple functions including wireless communication,temperature & humidity detection,luminance detection and portable charging etc.The relationship between transmission distance and Received Signal Strength Indication?RSSI?was analyzed.In order to ensure the reliability of the wireless communication and adjust the transmission power,the RSSI value was used to evaluate the signal quality.The communication experiments show when the transmission distance is shorter than 35 meters;the wireless communication in the 2.4 GHz frequency band has a desired performance than that in the 433 MHz frequency band.In the 433 MHz frequency band,the reliable communication distance is up to 100 meters with a loss rate less than 2 %.According to the actual requirements in greenhouse,the more suitable communication mode could be selected to ensure the universal applicability of the wireless sensor network.Finally,a set of intelligent CO₂ concentration control platform based on Lab VIEW software platform was designed to realize the real-time display,storage,remote sharing and intelligent control of CO₂ concentration in greenhouse.A fuzzy Proportion Integration Differentiation?PID?controller was designed for CO₂ regulation.The related CO₂ concentration model was set and used as the controlled object to optimized the fuzzy rules and verify the performance of the designed controller.The control platform was transplanted in embedded platform,which effectively improves the applicability to different greenhouse environment.In order to validate the performance of the monitoring and controlling system,the in-situ experiment was carried out in the actual solar greenhouse in a north city in China.In the long-term monitoring test,the developed infrared CO₂ detector has a stable performance.According to the environmental factors measurements and related calculation,there is a risk of condensation on the surface of leaves which implying a reasonable dehumidification treatment is essential.The designed fuzzy PID controller was used to regulate the CO₂ concentration in the greenhouse,the under controlled CO₂ concentration was able to arrive stable region in 36 minutes with the fluctuation less than 4.9%.The designed and implemented monitoring and control system has a desired applicability and potential economic benefits for the greenhouse environment.According to the actual requirement in greenhouse,a CO₂ monitoring and controlling system based on mid-infrared absorption spectroscopy is developed.The functions including environmental factors measurements and smart regulation of CO₂ concentration are realized.The highlight of innovation in this paper mainly includes the following aspects:?1?A CO₂ detector based on infrared absorption spectroscopy applied in greenhouse is designed and fabricated.A dual-channel detection method with single light source was adopted.A spherical reflective concentrating chamber is designed and fabricated to match the optical structure.In order to improve the signal and noise ratio,a digital orthogonal locked-in amplifier is used to extract the required signal.Besides the desired detection performance,the detector with the anti-condensation function which effectively guarantee the reliability of the detector's application in greenhouse environment.?2?A control platform for smart regulation of CO₂ concentration in greenhouse is established.The platform realizes the storage and remote data sharing of environmental factors.A fuzzy self-tuning PID controller is designed to regulate the CO₂ concentration in greenhouse.Based on the embedded transplantation,the miniaturization of the control platform is realized.?3?The developed detector is optimized as a sensor node and deployed in the WSN used in the greenhouse.?4?The developed infrared CO₂ detector and control platform were evaluated by a serious of long-term in-situ experiments in greenhouse.The experiments' results verify the reliability and application value of the monitoring and controlling system.