Which of the following is not a characteristic of open loop system?

Concept:

​Open-loop control system:

• ​The open-loop control system can be described by a block diagram as shown in the figure below.

• These are the systems in which the control action is independent of output.
• Examples: Traffic signals, bread toasters, sprinklers, ordinary washing machines, and systems having no sensor, etc.

Advantages:

• Simple construction and design Cost is less
• Maintenance is easy
• No problem of instability
• Convenient to measure when the output is difficult to measure

Disadvantages:

• These are less accurate, and their accuracy depends on the calibration.
• It does not contain feedback. Hence option 4 is correct
• Inaccurate results are obtained with parameter variations within the system.
• Re-calibration of the controller is required from time to time to maintain accuracy. 

Closed-loop control system:

• The closed-loop control system can be described by a block diagram as shown in the figure below. These are the systems in which the control action depends on the output. These systems have a tendency to oscillate

• Ex: Temperature controllers, speed control of the motor, systems having sensors, Human eye, household refrigerators, etc.

Advantages:

• More accurate
• Non-linear distortions are less
• The output is less sensitive to parameter changes within the system
• Bandwidth increases

Disadvantages:

• Design is complicated
• More expensive
• May become unstable,if there are malfunctions in the feedback.