Control system

Definitions: 1. Controlled Variable: It is the quantity or condition that is measured & controlled.
2. Controller: Controller means measuring the value of the controlled variable of the system & applying the manipulated variable to the system to correct or to limit the deviation of the measured value to the desired value.
3. Plant: A plant is a piece of equipment, which is a set of machine parts functioning together. The purpose of which is to perform a particular operation. 
6. Feedback Control:  Example:   Furnace, Space craft etc., 
4. System:  A system is a combination of components that works together & performs certain objective.
5. Disturbance:  A disturbance is a signal that tends to affect the value of the output of a system. If a disturbance is created inside the system, it is called internal. While an external disturbance is generated outside the system. It is an operation that, in the presence of disturbance tends to reduce the difference between the output of a system & some reference input.
7. Servo Mechanism: A servo mechanism is a feedback controlled system in which the output is some mechanical position, velocity or acceleration.
8. Open loop System: In an Open loop System, the control action is independent of the desired output. OR  When the output quantity of the control system is not fed back to the input quantity, the control system is called an Open loop System.
9. Closed loop System: In the Closed loop Control System the control action is dependent on the desired output, where the output quantity is considerably controlled by sending a command signal to input quantity.