Industrial Process Control Systems

Process control is the statistics and engineering discipline that deals with architectures, mechanisms and algorithms for maintaining the output of a specific process within a desired range.

In some of the common use control device called a programmable logic controller, or a PLC, is used to read a set of digital and analog inputs, apply a set of logic statements, and generate a set of analog and digital outputs. A PLC program would then either open or close the hot water valve, an incremental amount, depending on whether more or less hot water was needed. Larger more complex systems can be controlled by a Distributed Control System (DCS) or SCADA system.

The process control systems can be characterized as one or more of the following forms:

• Discrete – It is 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 – Most of the applications require that specific quantities of raw materials be combined in specific ways for particular durations to produce an intermediate or end result. Let us consider the example of 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. It also includes in the production of food, beverages and medicine. Batch processes that are generally used to produce a relatively low to intermediate quantity of product per year (a few pounds to millions of pounds).

• Continuous – Often in a physical system it is represented through variables that are smooth and uninterrupted in time. The control system of the water temperature in a heating jacket, for example, is an example of continuous process control. Some important types of continuous processes are the production of fuels, chemicals and plastics. Continuous processes in manufacturing are used to produce very large quantities of product per year (millions to billions of pounds).