Application And Research Of PLC On The Temperature And Humidity Control For The Multi-span Glass Greenhouse In Kunming

Compared with development at home and abroad, some problems are discovered about the multi-span glass greenhouse in Kunming. The problems are mainly in three aspects:backward greenhouse control technologies and facilities, smaller scale of development and less study in control technology. This is obtained by fully considering greenhouse environment control technologies, greenhouse facilities and development of greenhouse agriculture in Kunming.Based on these features, control methods of two environment factors (multi-span glass greenhouse temperature and humidity) are discussed in the study. First, temperature and humidity data and environmental parameters of local greenhouse are collected. Environment features of inside and outside of greenhouse are analysed considering local geography. Second, air temperature and relative humidity coupling relation in both fully closed mode and natural ventilation mode is obtained by analyzing based on five kinds regression function. According to analysis, temperature and humidity control strategy suit to regional climate characteristics of Kunming is fixed, which is strategy combined separate of wet and dry season with the priority principle. Fuzzy control and variable-temperature management are also used for joint control of temperature and humidity considering multi-span glass greenhouse features, which can use correspondly accurate control and coarse control.According to control strategies and adjustment method, total design requirements of temperature and humidity joint control system based on PLC are proposed. Distributed on-site control network is used in the system. Rational system solutions and detailed design of the hardware and software systems are built on the basis of the requirements. In order to improve system reliability, feasibility analysis of the hardware configuration and design of the PLC fault handle program are completed. The upper machine temperature and humidity management software is designed for improve visual management of system using VB6.0.Finally, simulation and experiment about both PLC control programs and fuzzy rules are carried out. Rationality and reliability of temperature and humidity join control system which meets total design requirements are proved. Theoretical foundation is provided for farther study of multi-factor environment control in Kunming.