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process control[′prä‚səs kən‚trōl]
A field of engineering dealing with ways and means by which conditions of processes are brought to and maintained at desired values, and undesirable conditions are avoided as much as possible. In general, a process is understood to mean any system where material and energy streams are made to interact and to transform each other. Examples are the generation of steam in a boiler; the separation of crude oil by fractional distillation into gas, gasoline, kerosine, gas-oil and residue; the sintering of iron ore particles into pellets; and the polymerization of propylene molecules for the manufacture of polypropylene. In the wide sense, process control also encompasses determining the desired values.
Process control includes a number of functions, which can be arranged in a hierarchy, as follows:
Computerized instrumentation has revolutionized the interaction with plant personnel, in particular the process operators. Traditionally, the central control room was provided with long panels or consoles, on which alarm lights, indicators, and recorders were mounted. Costs were rather high, and surveyability was poor. In computerized instrumentation, visual display units can provide information in a concise and flexible way, adapted to human needs and capabilities. See Automation, Control systems
process controlThe automated control of a process. Process control is used extensively in oil refining, chemical processing, electrical generation and the food and beverage industries where the creation of a product is based on a continuous series of processes being applied to raw materials.
Such systems typically deal with analog signals from sensors and meters that are transmitted to specialized computers which cause the temperature, pressure and flow to be continually adjusted (see DCS and PAC). Process control makes extensive use of analog/digital and digital/analog conversion. See process controller, control loop and industrial automation.