Digital control

Article By:

Mellichamp, Duncan A. Department of Chemical and Nuclear Engineering, University of California, Santa Barbara, California.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.195100

The use of digital or discrete technology to maintain conditions in operating systems as close as possible to desired values despite changes in the operating environment. Traditionally, control systems have utilized analog components, that is, controllers which generate time-continuous outputs (volts, pressure, and so forth) to manipulate process inputs and which operate on continuous signals from instrumentation measuring process variables (position, temperature, and so forth). In the 1970s, the use of discrete or logical control elements, such as fluidic components, and the use of programmable logic controllers to automate machining, manufacturing, and production facilities became widespread. In parallel with these developments was the accelerating use of digital computers in industrial and commercial applications areas, both for logic-level control and for replacing analog control systems. The development of inexpensive mini- and microcomputers with arithmetic and logical capability orders of magnitude beyond that obtainable with analog and discrete digital control elements resulted in the rapid substitution of conventional control systems by digital computer–based ones. With the introduction of microcomputer-based control systems into major consumer products areas (such as automobiles and video and audio electronics), it became clear that the digital computer would be widely used to control objects ranging from small, personal appliances and games up to large, commercial manufacturing and production facilities. Hence the focus of this discussion will be on computer-based control systems. See also: Microcomputer; Microprocessor; Programmable controllers

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