A control system in which the control action is totally independent of output of the system then it is called open loop control system. A manual control system is also an open loop control system. The figure below shows a control system block diagram of an open loop control system in which process output is totally independent of the controller action.
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Practical Examples of Open Loop Control System
- Electric Hand Drier – Hot air (output) comes out as long as you keep your hand under the machine, irrespective of how much your hand is dried.
- Automatic Washing Machine – This machine runs according to the pre-set time irrespective of washing is completed or not.
- Bread Toaster – This machine runs as per adjusted time irrespective of toasting is completed or not.
- Automatic Tea/Coffee Maker – These machines also function for pre adjusted time only.
- Timer Based Clothes Drier – This machine dries wet clothes for pre-adjusted time, it does not matter how much the clothes are dried.
- Light Switch – Lamps glow whenever light switch is on irrespective of light is required or not.
- Volume on Stereo System – Volume is adjusted manually irrespective of output volume level.
Advantages of Open Loop Control System
- Simple in construction and design.
- Economical.
- Easy to maintain.
- Generally stable.
- Convenient to use as output is difficult to measure.
Disadvantages of Open Loop Control System
- They are inaccurate.
- They are unreliable.
- Any change in output cannot be corrected automatically.
