Process control is a general term applied to describe the many methods of regulating the values of variables involved in industrial operations, temperature, and flow rate of raw materials. In fact any quantity that requires regulation in an industrial process can be treated as a variable for process control.
An integral part of the industrial resolution and the ensuing manufacturing innovations was the necessity to many different production parameters. For example, to manufacture plastic it may be necessary to maintain the temperature of a reason vessel at a constant value. If the process were not controlled, the temperature of the vessel might vary radically and create a poor-quality product or even a dangerous situation. Procedures have been developed to provide such regulation. Regulation was accomplished manually at first, through measurement, evaluation, and adjustment of the variable. Later, automatic systems were developed that could measure, evaluate, and adjust without direct human interaction. Automatic regulation of this type makes use of the feedback of the value of a variable in order to effect necessary adjustments of the process involving that variable.
The complete assembly of the three elements, measurement, evaluation, and adjustment, constitutes what is called a process control loop, where the word loop convey the idea of feedback of adjustments to the process following measurements in the process. Most industrial operations involve many variables to be regulated and thus many such process control loops. Sometimes the loop variables interact with each other so that adjustments for one variable affect a second variable, and so on. The overall process-control system is the assemblage of all these loops.
Since the late 1970s, microprocessor-based process control systems have come into wide use. Depending on the user’s need, such systems use an array of microprocessors to control from one to hundreds of variables. Further, these microprocessors are “cross-coupled,” or connected, with each other in such a way that complex adjustments can be made across a series of variables based on information traded between microprocessors.