Study On The Measurement And Control System Of Continuous Maize Dryers

China has a huge population base and grain production,which is steadily increasing every year.According to the incomplete statistical data analysis,however,the harvested grain in transportation,storage,processing and production has not been properly dried,resulting in mold and decay up to 70 billion kilograms,which account for almost 5% of China's total grain output.The direct economic losses caused should not be neglected.As an important part of former grain storage management,grain drying is directly related to grain security and has an important strategic significance.It's important to use grain dryers to mechanize the post-harvest treatment of grain,which can effectively reduce the drying time,greatly improve work efficiency,besides,reduce manpower input,increasing economic income.In the entire mechanized production process,it's the core technology that measurement and control system of dryers,also which is the premise to ensure the grain completely dry.This paper puts forward the concept of Accumulated Temperature(AT)based on fully considering the characteristics of drying process of maize,and combines process control technology,virtual instrument technology and fuzzy PID control technology to design an intelligent measurement and control system.Meanwhile,the results have been verified by experiments on continuous maize dryer.The main content of this paper is as follows:(1)It's introduced that the development process and status quo of domestic and foreign grain dryers,and the current measurement and control system of the mainstream dryers,also described application of fuzzy control and fuzzy PID control in grain dryers,and proposed solutions which are based on the existing problems.This paper expounds the basic idea of AT control,uses the AT theory as the core idea of control to establish the relationship between the AT and the outlet moisture and mainly introduces the AT prediction model in the process of deep-bed drying of maize under the analysis of the differences between deep-bed drying and thin-layer drying of maize.Meanwhile,the measurement and control system has establish the moisture prediction model,which was built by a thin layer drying mathematical model that can predicted moisture of each section of the dryer in real-time.(2)In the entire measurement and control system,the AT value is used as a long-term control variable,the predict value of outlet moisture as a short-term control variable.By judging the difference between the current AT value and the target AT value,it's can automatically switch the long-term adjustments and short-term adjustments.If the difference between the current AT value and the target value is out of the standard range,the fuzzy control is used to adjust until the AT value meets the requirements,then enters the short-term adjustment phase;In the short-term adjustment,the fuzzy PID control is used to adjust until the predicted moisture is meet the standards.Then calculate the idle time output to the inverter control motor work.Besides,introduced the concept of weighted temperature used to determine whether the drying process into a steady state in the control system.The adjustment which is judging the outlet moisture and changing the theoretical AT value can make measurement and control system to achieve new steady state when the external environment has suddenly changes in the drying process.(3)According to the theoretical calculations and artificial experience to analyze the measurement and control system,it is concluded that the moisture can be divided into different types of variation.To establish each control rule of fuzzy controller and fuzzy PID controller by means of the different working conditions.Combined the LabVIEW software to write the control program of the measurement and control system,and performed the corn drying test on the small maize dryer.Using the computer to communicate with the PLC,temperature control instrument,temperature and humidity sensors,and inverters to collect data and control them in real time.The test results showed that the stability and reliability of the system can meet the control requirements of maize drying based on tracked and measured moisture of the maize.