Study On Temperature Control System Of Rapid Freezing And Thawing Testing Machine For Concrete

Agricultural engineering construction is an important content of the modern agriculture construction. Concrete is the important materials of agricultural engineering construction. Its durability is directly related to the building structure safety of agricultural engineering structure, and to the use life of roads, pool, wet compost pool and the other fundamental instrument. To ensure safety and reliability in the process of the agriculture construction, concrete durability research has been paid more and more attention. Concrete rapid freezing and thawing test machine is the experiment apparatus that tests concrete durability under the corporate action of water and the negative temperature. The stand or fall of its performance is directly related to results of the concrete quality inspection.In this paper, through analysis of the method of national standard on the fast freeze-thaw test concrete requirements, the freeze-thaw cycle test target temperature curve and the temperature control requirements is given. This paper introduces the working principle of freezing and thawing test machine and the freeze-thaw cycle control process.According to the control requirements, the work in the selection of main hardware system has been done. The electrical principle of control system is introduced. And the PLC and the main electrical wiring diagram of the hardware are presented.During freezing and thawing test, specimen is putted in the antifreeze which is in the freezing and thawing box. Through heat transfer with antifreeze the temperature is changed.Through the compressor refrigeration or heating tube heating, temperature of the test case implementation does the freeze-thaw cycle. The temperature system is big inertia system with pure lag. The existing control methods are based on the experimental data and experience to adjust the control parameters and to set control parameters change rule. In order to realize high precision control of specimen core temperature changes, this paper adopted fuzzy control method. In order to verify the validity of the control law and realize the precise control system, this paper use MATLAB to do the system simulation. The temperature system mathematical model of the testing machine need to be established. Due to the control mechanism difference of refrigeration and heating stage, the experimental modeling method is adopted. The mathematical model of refrigeration and heating system are established respectively. By using the experimental data, the validation of the model is completed. In the cooling stage, by establishing the transfer function that descript therelationship between the frequency conversion compressor and refrigeration power,cooling power frequency and test case, box temperature and specimen core temperature,mathematical model of transitive relation of a specimen core temperature and frequency of compressor is established. By adjusting the frequency of the compressor, the specimen core temperature is controlled. In the heating stage,, by establishing the transfer function that descript the relationship between the heating tube of the heat duty ratio and heating power, The heating power and the test case, box temperature and specimen core temperature,mathematical model of transitive relation of a specimen core temperature and heating pipe heating duty ratio is established. By adjusting the duty ratio, Specimen core temperature is controlled.Based on the mathematical model of the machine, in order to make the system less sensitive to the mode, this article uses the fuzzy control scheme on the system control strategy. According to the principle of the design of fuzzy controller, the fuzzy control rules of fast freezing and thawing of concrete testing machine has been designed. By using the MATLAB software, simulation research was conducted on the fuzzy control system. And this paper adjust the fuzzy control rules according to the simulation results.At last, the PLC control program and touch screen control of the system interface has been designed and written. And this design content is summarized and prospected.