Open Loop control system

Open loop control system is a control system in which the control action is independent of the output. (on effect on the control action)

An open loop control system utilizes an actuating (controlling) device to control the process directly without using feedback.










Features of an open loop control systems

• Accurate performance is determined by their calibration.
  (Calibrate means to establish or reestablish the input - output relation to obtain a desired system accuracy.
• They are not usually trouble with the problems of instability.
• The main problem encountered in open loop control system is that the variation in the external condition or internal parameters of the system (disturbences) may cause the system to behave in an uncontrolled manner.

Example of a open loop system.
Automatic toaster controlled by a timer.
Input - setting time
Controller (Acturator) - Timer
Output - Toasted bread

The time required to make a "good toast" must be estimated by the user who is not a part of the system. Control over the quality of the toast (the output) is removed once the time, which is both the input and the control action has been set.

Washing machines (Soaking, Washing and rinsing operate on a time basis.)
Input - Setting Time
Controller (Actuator) - Timer
Output - Washed clothes

The machine does not measure the output response, the cleanliness of the clothes.