Closed Loop Systems (Automatic Control)
Once the initial operating parameters have been set, an open loop system is not responsive to subsequent changes or disturbances in the system operating environment such as temperature and pressure, or to varying demands on the system such as power delivery or load conditions.
For continual monitoring and control over the operating state of a system without operator intervention, for more precision or faster response, automatic control systems are needed.
Negative Feedback
To meet these requirements "closed loop" systems are necessary. Also called feedback control systems, or negative feedback systems, they allow the user to set a desired operating state as a target or reference and the control system will automatically move the system to the desired operating point and maintain it at that point thereafter.