Introduction to Control Systems - 1 - GATE EE Free MCQ Test with solutions

A closed loop system is:

• More accurate: It uses feedback to correct errors, improving the precision of the system's output.
• More stable: Feedback helps maintain desired performance despite disturbances or changes in system parameters.
• Comparison to open loop: Open loop systems lack feedback, making them less capable of correcting deviations and maintaining stability

Thus, option A is correct: A closed loop system is more accurate and more stable than an open loop system.

Linear system obeys both reciprocity theorem and principle of maximum power transfer.

A step function is commonly used as a input signal in a control system because:

• If we go through first order system, here we calculate steady-state error by providing input function then we got zero steady-state error.
• Actually in step function, output follows input always that means steady error is minimum.

Step Function:

Correct answer is D. e^−4s

• In closed loop system there is the presence of a feedback path and this feedback path has connected from output of the system to the input of the system.
• The whole operation is controlled by the output of the system.

• The main difference between an open-loop system and a closed-loop system is that the closed-loop system has the ability to self-correct while the open-loop system doesn't.
• Consequently, closed-loop systems are often called feedback control systems while open-loop systems are also known as non-feedback controls.

Option D is correct.

A is false. Operating on a time basis (having actions scheduled with respect to time) does not by itself determine whether a system uses feedback; time-driven behaviour can occur in both open-loop and closed-loop systems.

Closed-loop systems may perform actions at specified time intervals while still using feedback to adjust those actions based on output measurements; the presence of time-based scheduling does not imply absence of feedback.

R is true when interpreted as referring to a field-control implementation without speed feedback. Changing the field current of a d.c. motor to control speed, without measuring the motor speed or using that measurement to correct the control action, is an open-loop arrangement.

If the field is adjusted using a measured speed signal and a controller that corrects deviations, the arrangement becomes closed-loop.

Therefore, A is false but R is true, so the correct choice is Option D.

• A closed-loop system automatically corrects errors and disturbances by using feedback. so C is correct 
• It continuously compares the output with the desired value and adjusts accordingly.
• Open-loop systems do not correct errors since they lack feedback.
• While closed-loop systems reduce steady-state error, they may not always eliminate it completely (hence D is incorrect).
• They are more complex and costly than open-loop systems, making A incorrect.
• Closed-loop systems require feedback, so B is incorrect.

Ramp function occurring at t = 0 is denoted by r(t) = tu(t).
Ramp function occurring at t - a will be denoted: 

- In open loop control systems, the control action is independent of the desired output signal.
- The system operates without feedback, meaning it doesn't compare the output with the desired value.
- Control actions are predefined and do not adjust based on output changes.
- This can lead to inaccuracies if the system or external conditions change.
- Open loop systems are typically simpler but less accurate compared to closed loop systems, where feedback adjusts the control action.