| A frugal PLC automatic control system design ed for the small falling film evaporator is introduced in this thesis, which can be applied into medicine, food and many other industries. This system is designed for the small evaporator that its evaporation is under500kg per hour and we pay special attention to the design cost reduction of PLC control system to improve the application value of our system on the small evaporator. Besides, the falling film evaporator designed by us becomes more convenient,effective, safe and stable due to our research on the energy saving, the HMI (HumanMachine Interaction) design, the co-working system of PLC and touch screen and PIDcontrol module.To resolve problem that the cost of PLC automatic system grabs too large a slice of the total cost, we reduce the design cost through changing the read method of analog value, adjusting the sensors and simplifying the working mode to semi-automation. We improve the energy reuse structure of cooling steam and condensate to increases the heat usage efficiency of falling film evaporator. The HMI of our system holds the characteristics of easy to learn, easy to operate and etc.The HMI have many different modules, such as monitor, settings, trends, manual/automatic switch, historical data, flow monitor and alarm. Our PLC control system can set the blind zone of the PID, PID control parameters and alarm trigger conditions via touch screen without modifying the program. The setup of blind zone has greatly increased service life of the sensors. Moreover, we can test and verify the reliability of our system through on-site experiment. The improved falling film evaporator can be widely used in medicine, food, chemical industry, light industry, food, pharmaceutical, metallurgy and desalination industry for evaporation and concentration of water or organic as an efficient evaporationequipment. |
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