Closed loop systems are the most common form of control system.  In a closed loop system the output is measured and compared to the desired output, and the control action is determined by the results of that comparison.

• Why learn about closed loop systems?
• Closed loop systems are the most common kind of control system.  (Here is a short description of a typical closed loop system.) PID controllers, and many others are variations on the common theme of a closed loop system.  There are a lot of very basic facts about closed loop systems that you need to know to apply to the many different kinds of closed loop systems you will find.  (And, you don't need to look very far because your body has a large number of closed loop systems to control the amount of light that enters your eye, your body temperature, the CO₂ level in your blood, . . . )
• What should you know to learn about closed loop systems?
• The most important background item you need to know is how to manipulate block diagrams.
• What do you need to know about closed loop systems?
• The closed loop transfer function is not the same as the transfer function of any of the individual component parts.
• When you close the loop, if the system is stable, you can make the output approach the input.  That's dependent upon the gain of the system.
• When you close the loop, the poles move from the places where the poles were in the plant - the system being controlled.  The root locus details how that happens.
• How do you use closed loop system concepts?
• When you design a control system you are manipulating parts of the system in a closed loop in order to make the overall system - the closed loop system - behave in a way that you want - which may be a way specified by a purchaser, etc.
• Problems
• Additional Information