Control Hardware

Batch systems use a greater number of digital devices. Ranges of 65 to 85% digital and only 15 to 35% analog signals are typical. On-off valves and limit switches comprise the majority of digital devices although alarms, interlocks, and emergency shutdown equipment are also important (Procyk 1991).

In general, the analog PID controller is less prominent in batch operations because a batch process operates on a changing state instead of the steady-state environment maintained by the proportional integral and derivative (PID)-loop set point.

Batch processes are usually operated with more modularity and flexibility than are continuous processes. Thus, design engineers must anticipate and plan for what will be needed for future recipes and batches.

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