Control of a Two-State System
The smallest number of states that a controller or a system can assume is two, since by definition a single-state system cannot be controlled and similarly a single-state ‘controller’ can have no effect on the system. There are numerous examples of systems operating in a two-state mode: lighting circuits (the light is either ON or OFF), appointments by selection boards (a candidate is either accepted or rejected), and so on. The digital computer, which conforms to the rules of binary logic, is another such example. For the sake of convenience let us label the two states as 1 and 0, or ON and OFF respectively. There is no special merit in these names, except that 1 and 0 are used in binary arithmetic and ON and OFF describe the two states of a current flowing through electrical circuits. As the two-state operation is fundamental to the understanding of the control function, we shall now examine the two-state control process in some detail.
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