Q. Open-loop control system?

An open-loop system is one in which the control action is independent of the output or desired result, whereas a closed-loop (feedback) system is one in which the control action is dependent upon the output. In the case of the open-loop system, the input command (actuating signal) is the sole factor responsible for providing the control action, whereas for a closed-loop system the control action is provided by the difference between the input command and the corresponding output.

The elements of an open-loop control system may be divided into two parts: the controller and the controlled process, as shown by the block diagram of Figure. An input signal or command r is applied to the controller, whose output acts as the actuating signal u. The actuating signal then controls the controlled process such that the controlled variable c will perform according to some prescribed standards. The controller may be an amplifier, mechanical linkage, or other basic control means in simple cases, whereas in more sophisticated electronics control, it can be an electronic computer such as a microprocessor.