ABSTRACT
The word “automatic” indicates work done without the help of any human intervention, i.e., recording, understanding, taking necessary action, etc. As we know, a single person cannot watch recorders or machines continuously for 24 hours a day. He must be relieved by another person periodically, usually in eight-hour shifts. Besides these limitations, a human operator has dif›culty monitoring machines because of tiredness resulting from the drudgery and other natural human reactions. All these limitations lead to žuctuations and degradation in the quality and žow of products and may even lead to accidents. In addition to these problems, increasing demand for higher salaries and other expenses included in human operators’ cost of production also increase over time. In some plants, where explosive or radiation hazards are present, remote operations are possible only with automaticcontrol instruments. Hence, automatic process control should achieve the following bene›ts:
(i) Reduced human operations (ii) Closely monitored product quality (iii) Increased rate of production (iv) Reduced wastage of materials and energy consumption (v) Safe operations and reduced accidents (vi) Decreased operational costs (vii) Remote operation envisaged
There are ›ve basic elements of control hardware. These are the primary element or sensor, the secondary element or signal-generating element (transducer, transmitter, converter, etc.), the controlling element or controller, the transmission cable, and the ›nal control element.
