PRocess control Chapter flow diagrams

This chapter presented a flow diagram of a PID feedback control loop with the process streams and instrument lines labeled. The proportional, integral, and derivative actions of the controller were defined mathematically and described for the example in the diagram. 

During the framework design phase (Fig. 30.4), first principles, process type conceptions and process expertise are combined to form a physical framework. In addition, the parameters that will be modeled by sub-models have to be identified. The output of each sub-model is the parameter concerned. However, independent variables are not always clear. It may be necessary that those input variables are determined by means of a sensitivity analysis. The conceivable candidates for these independent variables are all state and control variables used in the framework. In this example fuzzy logic will be used to build these sub-models, but other black-box modehng techniques, which are discussed in the previous chapters, such as, for example neural networks, may also be appropriate. The result of the framework design phase is the framework, which can be represented by a behavioral model. This is a data flow diagram of the model stmcture. 

In Chapters 1 and 8 we have shown that a block diagram provides a convenient representation of the flow of information around a feedback control loop. The previous discussion of block diagrams was qualitative rather than quantitative, because the blocks were labeled but did not indicate the relationships between process variables. However, quantitative information can also be included by showing the transfer function for each block. 

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