Boiler level control system based on ControlLogix5550 PLCAbstract-This paper is a research design based on EFPT process control device. In the design, actual industry field has been simulated and corresponding modeling has been carried on for the boiler level system. Then the appropriate PID parameter has been sorted out and ControlLogia5550PLC has been used to control the entire boiler level system.At last, a corresponding control interface has been established and the boiler level has been under a safe and accurate controlKeywords：EFPT，PID，Modeling，Boiler level;1 IntroductionThe task of the industrial boiler level control is to maintain a dynamic balance by controlling the water flow and evaporation, so that the drum level can be maintained in the technological level, which is a necessity for ensuring safe operation and also one of the main indicators of the boilers normal operation. Water level which is too high will affect the effect of the steam-water separation, but too low it is will break ring cycle or even cause boiler explosion. To ensure a safe and efficient production, the boiler level must be strictly controlled in maintaining constant or changing only according to a certain rule. Using Logix5550 PLC with analogy I/O modules, launched by Rockwell Automation Company as controllers, and EFPT process control experimental device as control object, this system have brought the boiler water level under an accurate control in a mini boiler system with sensors and actuators that used in industrial production.Fig. 1 Boiler level setting value adjustment system2 System Overview This system is composed of an EFPT process control device, an inverter, a Logix5550 PLC and a computer. EFPT process control device is a simulated heating and water supply and drainage system for a micro-small boiler. It realizes process control in a mini boiler system with sensors and actuators used in industrial production. The actuator includes not only measuring appliance, but also AC inverter, heating controller, heater and so on. The system simulates industry scene through a mini-boiler heating, water supply and drainage system, which is reliable and visual. In the design, boiler Level was selected as the controlled variable. The controlled object is composed of the water trough, the force pump, the boiler and the pipe-line valve. Micro Master 6SE9214-ODA40 inverter is taken as the actuator and the boiler level is controlled by Logix5550. Configuration software RSView32 and touch screen PanelView1000 are combined to realize the real-time monitoring. In the design, a simple design of single-loop boiler liquid level value adjustment is selected for the study. The composition of the system is shown in Fig. 1. In the design, the inverter as an actuator directly receives PLC analogy I/O port output, and converters into frequency of inverter so as to drive the 3-phase motor in the lift pump, change the inlet, and adjust the boiler level to the dynamic balance at last. And the configuration software is used to design monitoring picture to realize the computer and the touch screen to the boiler level long-distance and the scene monitoring. 3 Establishing Mathematics model for the charged object One of the main tasks of establishing control system mathematical model is to determine the mathematical model of the controlled object. Generally, there are two kinds of basic methods for establishing process control mathematical model: mechanism analysis and experimental method. However, for controlled object whose structure and internal process is very complex, it is very difficult to determine the object just by its own internal physical process and to solve out the differential equations systematically. Besides, considering the nonlinear factor, mechanism analysis used some approximation and hypothesis for mathematical deduction. Although these approximation and assumptions have practical basis, but not fully reflect actual situation, and even cause incalculable effects. Therefore, in this design, the experimental method is chosen to establish a mathematical model for controlled object. This kind of modeling is based on the input and output in the actual production process, that is to say, establishing mathematical model for the controlled object through process identification and parameter estimation. In this design, step response curve method is used to identify mathematical models of the process. A 20Hz step disturbance input signal is applied to the charged object, and the response curve of the output that changes with time can be mapped. After the analysis, the transfer function of the controlled object can be defined. In the process of experiment, the object was conducted several tests. Using RSLogix5000 trend monitoring function curve, more than 10 charged object step response curve have been recorded. To all the parameters for average,