Open loop systems
In control systems , systems are classified into two groups:
- Open loop systems,
- Closed loop systems.
Open loop systems are systems in which the output of a system is not used as a variable to control the system.
Open loop control systems use the input variables to calculate the output based on the "open loop transfer function" of the system. The output is not fedback to modify the controlled output. There are many reasons to use open loop control such as simplifying the control system, quicker response of the system, to reduce the possiblility of oscillation and sometimes to lower cost.
An example of the use of open loop transfer function in control system is in the control of the wing surfaces on a modern figther plane. The closed loop implenmentaion would make the control much slower (cost is clearly not an issue in this example).
There are very good references for the fundamentals on the main wikipedia.org site such as http://en.wikipedia.org/wiki/Transfer_function
Note for moderators, the statements below are incorrect. Open loop systems are systems in which input to the system is not controlled by the present output.
In open loop systems, problems are solved by trying to avoid them in the first place, ie., by good design.