In practice, process control systems can be characterised as one or more of the following:
Discrete – Found in many manufacturing, motion and packaging applications. Robotic assembly, such as that found in automotive production, can be characterized as discrete process control. Most discrete manufacturing involves the production of discrete pieces of product, such as metal stamping.
Batch – Some applications require specific quantities of raw materials to be combined in specific ways for particular durations to produce an intermediate or end result. One example is the production of adhesives and glues, which normally require the mixing of raw materials in a heated vessel for a period of time to form a quantity of end product. Other examples include the production of food, beverages and medicine. Batch processes are generally used to produce a relatively low to intermediate quantity of product per year (a few pounds to millions of pounds).
Continuous – Often, a physical system is represented through variables that are smooth and uninterrupted in time, for example the control of the water temperature in a heating jacket. Other examples include the production of fuels, chemicals and plastics. Continuous processes in manufacturing are used to produce very large quantities of product per year.
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