Fuzzy Logic Control Of Electric Heater And Its Application In PLC

Temperature is a very popular parameter of pyrology in flow industry, so temperature control is an emphases of process control. Considering some special condition such as heating mechanism and the special structure of heater, there are often some features such as long time lag, nonlinearity and difficulties of modeling of targets of process. It's difficult to control very well by traditional PID algorithm.Fuzzy control is an important application filiation of fuzzy mathematics based on the theory fuzzy sets. It's a kind of new control algorithm formed by the combination between fuzzy mathematic and automation. When the target or process which is controlled have some features such as long time lag, nonlinearity, intensive multi-parameters coupling, stochastic noises, the complicated mechanism of process and uncertain measurement condition in the working field, the precise mathematic model of target or process can't be built. Then fuzzy control, a kind of algorithm similar to expert rules, offered a kind of ideal algorithm for these target and process.Programmable logic controller (PLC) is a kind of electronic device for digital operation which is designed for industrial application specially. It have programmable memorizer in which some operation instructions such as logic operation, sequence operation, timing, counting is saved and runs, and then it can control kinds of mechanism and process through input and output of digital or analog signal.In this thesis, a set of two dimension fuzzy controller by which the temperature control of water in the heater is achieved is researched and designed. And the engineering application and actualization of fuzzy control is researched, based on SIEMENS S7-300 PLC. It use STEP 7, the software for S7-300 PLC, to realize fuzzy control for electric heater, and shows the LAD program of pivotal parts. At the same time, it shows the whole monitoring interface of operation based on WinCC that SIEMENS configuration software.According to the experiments, the control effects of fuzzy control and traditional control have been analyzed and contrasted to each other. The result shows that fuzzycontrol resolved the long time lag and nonlinearity of electric heater control well without depending on the precise mathematic model. When there is not much the content in fuzzy querying table, this method for programming is more compact and the response is faster. The control effect is better. So it can be used in similar field of industrial control and is a kind of better strategy for temperature control.