Distilled water machine's work process is very complicated. The main steam pressure, temperature of its hot exchange loop and the pressure, temperature, liquid quantity of raw material water connect closely and present nonlinear relation. In terms of traditional methods, it's very hard to establish a precise mathematics model. regarding hot exchange principle of chemical engineering as the foundation, we start from double-function evaporation equipment in this paper, then process it.
During the process, we need to control two important parameters:one is the electric conductivity rate of distilled water at exit; another is the temperature of distilled water at exit. Electric conductivity rate generally is controlled by regulating the raw material water's valve door, while export temperature generally is controlled by regulating steam quantity passed into the heat exchanger. This is a typical control system with double inputs and double outputs. Because the distilled water machine has the characteristics of serious delay, nonlinear, strong interference etc., this system is a closely coupling system. In this design, we adopt simplified method to remove the coupling of this system with double inputs and double outputs. Because the pure vapor output loop and cool water loop are all hot exchange loop's strong interference resource, common PID can't achieve satisfactory effect. For this reason, this paper adopt PID controller composed of PID controller and expert system to control the system.
Combined the actual evaporating process, on the basis of expert system, this paper establish the perfect knowledge warehouse and adopt forward-reasoning mechanism, inspiring research method, exchange person-machine junction to design an expert system applicable to the distilled water production.
