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Title: Principles And Application Of Automatic Control
Author: L. K. Jones
Source: 1966 Southwestern Gas Measurement Short Course (Now called ISHM)
Year Published: 1966
Abstract: To some people the term automatic control suggests computer automation. To others, automatic control is as simple as the thermostat on babys bottle warmer or the timer on an oven. Modern toasters, washing machines, dishwashers and clothes dryers all use some form of automatic control. Many of these everyday examples of automatic control are classified as open loop devices that is, there is no feedback of information from the process to modify the control cycle. If the clothes in the automatic dryer are not dry, the dryer has not necessarily malfunctioned. What is required is feedback from the housewife in the form of an adjustment of the timing cycle. This closes the control loop and makes what is known as closed loop control. This same control could be accomplished if a device were available to sense the dryness of the clothes and adjust the timing cycle accordingly. Closed loop control is encountered more frequently in industrial process work than it is in the home. Automatic control may be defined as a technique for balancing the supply against the demand, over a period of time, in order to maintain the process at some predetermined level of operation. To maintain this balance, it is necessary to measure system outflow and use this information as feedback to regulate system input. This feedback may be external as in the case of the everyday open loop control or internal to the control loop as in many industrial applications.

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