A Novel PLC Based Automatic Control Cleam In The Place System

In order to ensure the quality and safety of food,the goverment has issued a series of mandatory policies on dairy products factories,one of which is that those factories must be equipped with automatic CIP(Clean in Place)system to solve the problem of excessive level of bacteria in domestic dairy products caused by poor cleaning process and cleaning equipment.In China,most of factories have not been equipped with automatic CIP systems duo to the lag in technology of domestic CIP systems and expensiveness of foreign CIP systems.In order to design a system which is cheaper,more functional,more suitable for domestic dairy products enterprises,the following study has been carried out to improve the performance of automatic CIP control systems and to reduce their cost.First,the principles,composition and processes of foreign CIP systems are analyzed,and the functions of each components of those systems are studied.Combined with the characteristics of domestic and foreign CIP systems,a simplified system is designed to realize the functions of CIP system while to reduce the cost of the system,for the purpose to achieve higher cost performance.Second,to improve its reliability further,the design and lectotype are optimized.By comparing the cost and performance of some key components,such as controllers,actuators and sensors.the touch screen is selected to replace the PC as human-computer interface and S7-200 PLC(Programmable Logic Controller)is applied to replace S7-300 PLC as the core part of the whole system.Furthermore,the conductivity meters is employed to measure acid-base concentration.Third,the electrical control loop and instrument acquisition loop is built.In those loops,PLC gets the data from the sanitary PT100 temperature sensor,liquid level sensor,concentration sensor,flow sensor.According to these collected production process data,PLC controls actuators such as pneumatic regulating valve,cleaning process pump,pneumatic diaphragm pump and so on,which realize an effective automatic CIP system.At last,by consulting operators of some major domestic diary product enterprise and referring to the function and man-machine interface of foreign advanced CIP systems,the ladder diagram-based PLC programs and touch screen-based interface are developed to satisfy the requirements of domestic dairy product factories.To summarize,a new automatic CIP system is developed through optimal lectotype of key components and elaborate design of PLC programs,which is with high cost performance and suitable for domestic dairy product factories.