Correct Answer - Option 2 : Has a feedback element
Open-loop system
-
A Control System which doesn’t have any feedback connected to it is called an Open Loop System.
- These types of systems don’t depend upon their output i.e., in open-loop systems, the output is not used as a control variable for the system and it has no effect on the input. Open-loop systems are one way signal flow systems.
- As these systems doesn’t contain any feedback i.e., the output is not fed back to the input, these are also known as Non-Feedback Systems.
- The control system which operates on a time basis is an open-loop system.
- For example, in automatic control of traffic, the time for each lamp (red, yellow, and green) is fixed.
-
The operation of each lamp does not depends upon the density of the traffic but depends upon the fixed time. Hence, the assertion is true. The reason is also true but, it is not the correct explanation of the assertion
Open-loop Motor Control
So for example, assume the DC motor controller as shown. The speed of rotation of the motor will depend upon the voltage supplied to the amplifier (the controller) by the potentiometer. The value of the input voltage could be proportional to the position of the potentiometer so there is no feedback so it is an open loop system.
Advantages of Open-Loop Control System
The main advantages of the open-loop control system are listed below:
- Open Loop Control Systems are very simple and easy to design.
- These are considerably cheaper than other types of control systems.
- The maintenance of an open-loop control system is very simple.
- Generally, open-loop systems are stable up to some extent.
- These types of systems are easy to construct and are convenient to use.
Disadvantages of Open-Loop Control System
The disadvantages of an open-loop system are:
- The bandwidth of the open-loop control system is less.
- The non-feedback system doesn’t facilitate the process of automation.
- Open-loop systems are inaccurate in nature and also unreliable.
- If their output is affected by some external disturbances, there is no way to correct them automatically as these are non-feedback systems.
Open Loop System Applications
We use open-loop control systems in many applications of our day-to-day lives. Some of the popular systems, which are designed based on the concept of open-loop control systems, are mentioned below:
- A field control d.c. motor
- Washing Machine
- Electric Bulb
- Electric Hand Drier
- Time-based Bread Toaster
- Automatic Water Faucet
- TV Remote Control
- Electric Clothes Drier
- Shades or Blinds on a window
- Stepper Motor or Servo Motor
- Inkjet Printers
- Door Lock System
- Traffic Control System
