Process control languages

The most successful and user-friendly approach, which is now adopted by virtually all commercial systems, is the fill-in-the-forms or table-driven process control languages (PCLs). The core of these languages is a number of basic functional blocks or software modules. AU modules are defined as database points. Using a module is analogous to calhng a subroutine in conventional programs. 

Process control documents (PCDs), 26 745 Process control languages (PCL), 20 672 Process control system, 20 730-731 Process cut-offs, in life cycle assessment, 24 813... 

We will use English to solve some simple problems. But we will find that more complex problems are easier to understand and solve using Russian. As problems get even more eomplex and realistie, the use of Chinese is required. So we study in this book a number of very usefiil and practical process control languages. 

All process control languages contain PID control blocks of different forms. Other categories of function blocks include... 

In the process control language the object upon a control system is applied is called often a plant . This can be a single unit, or an assembly of several units, as two heat-integrated distillation units. However, when the control system design embodies the whole process and regards the Interrelation between different units, we speak about plantwide control. 

Figure A.8a shows the process diagram of a mixing process under analog ratio control. A flow controller (FC) is used to maintain ingredient A at the desired amount. An analog calculator (FY) computes the amount of ingredient B to be maintained (by a second FC), based on the desired amount of A and the ratio between the two ingredients. All hardware components beyond the process equipment can be replaced by PCL modules, as illustrated in Fig. A.86. The fill-in-the-forms process control languages owe their success, at least partly, to their resemblance to process schematics and control strategy diagrams.

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