The output from the detector, or scanning system, constitutes the input to the comparator, whose function is to compare the state of the control object against the predetermined standard, or norm. The results of this comparison are then tabulated, and this record of deviations becomes the input to the activating system.
The control object's behavior can be either stable or unstable. Both of these states are necessary for system survival. Although stability is the ultimate long run goal, short-term and periodic instability is necessary for system adaptation and learning. The system, in other words, pursues long-run stability via short run changes in its behavior manifested in its output's deviations from a standard.
In general terms, stability is defined as the tendency for a system to return to its original position after a disturbance is removed. In systems nomenclature, a control object is stable if, once an input disturbance has been removed, it exhibits a return to the initial state exhibited at time to. Were the control object not able to return to or recover the initial state, the system would be said to exhibit instability. The input disturbance may be initiated by the feedback loop, or it may be a direct input from the system's environment.
When there are significant differences between the output and the goal, the system is said to be out of control. A lack of control generally implies that the goal formulated is unrealistic and/or unsuitable for the system being monitored, in which case either the goal or the system must be altered. For example, if a production goal cannot be met, either the goal must be altered, more people must be put on the production line, or more equipment must be employed.
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