Distributed computer control, hierarchical systems

Distributed control refers to a number of control computers which are linked to each other and to peripherals such as operators consoles by high speed data channels. A hierarchical structure may be imposed by having certain processors operating in a supervisory mode. Figure 7.48 shows a distributed control system. Such a system is less liable to failure than the central computer based DDC system in Figure 7.47 because each component can operate independently of the others. 

The trade-offs among process design, optimization and control must be considered. The hierarchical or distributed nature of the plant or process may need to be exploited in an advanced control scheme. The operation of energy-integrated plants requires design of control systems which are decentralized (such as with microprocessors) but which respond to overall plant objectives via a communication link to a larger computer. 

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