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In computer process control, a digital computer  is used to direct the operations of a manufacturing

process. Although other automated systems are typically controlled by computer, the term computer

process control is generally associated with continuous or semi-continuous production operations

involving materials such as chemicals, petroleum, foods, and certain basic metals. In these operations the

products are typically processed in gas, liquid, or powder form to facilitate flow of the material through

the various steps of the production cycle. In addition, these products are usually mass-produced. Becauseof the ease of handling the product and the large volumes involved, a high level of automation has been

accomplished in these industries.

The modern computer process control system generally includes the following: (1) measurement of

important process variables such as temperature, flow rate, and pressure, (2) execution of

some optimizing strategy, (3) actuation of such devices as valves, switches, and furnaces that enable the

process to implement the optimal strategy, and (4) generation of reports to management indicating

equipment status, production performance, and product quality.

An example of computer process control in the metals industry is the rolling of hot metal ingots into final

shapes such as coils and strips. This was first done in the steel industry, but similar processing is also

accomplished with aluminum and other metals. In a modern steel plant, hot-rolling is performed under

computer control. The rolling process involves the forming of a large, hot metal billet by passing it through

a rolling mill consisting of one or more sets of large cylindrical rolls that squeeze the metal and reduce its

cross section. Several passes are required to reduce the ingot gradually to the desired thickness. Sensors

and automatic instruments measure the dimensions and temperature of the ingot after each pass through

the rolls, and the control computer calculates and regulates the roll settings for the next pass.

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