A cruise control system maintains a car's speed by comparing the actual speed to the desired speed and adjusting the throttle. This is an example of which type of control?
AOpen-loop control
BFeedforward control
CClosed-loop (feedback) control
DBang-bang control
The system continuously measures the actual output (speed), computes the error relative to the setpoint, and uses that error to drive the actuator — the defining structure of closed-loop feedback control. Open-loop control would apply a fixed throttle without measuring actual speed.
Question 2 True / False
Increasing the feedback gain in a closed-loop control system usually improves performance by reducing error faster.
TTrue
FFalse
Answer: False
High gain amplifies the error correction signal, which can cause the system to overcorrect repeatedly, leading to oscillation or outright instability. There is a fundamental tradeoff between speed of response and stability: gain must be tuned to balance these competing demands.
Question 3 Short Answer
What is the role of the error signal in a closed-loop control system, and how is it computed?
Think about your answer, then reveal below.
Model answer: The error signal is the difference between the desired output (setpoint) and the actual measured output. It is computed at the summing junction by subtracting the feedback signal from the reference input. The controller acts on this error to drive the plant toward the setpoint.
The error signal is the core mechanism of feedback: if error is zero, the system has reached its goal and no correction is needed. If error is nonzero, the controller uses its magnitude and sign to decide how much corrective action to apply. Without measuring error, there is no feedback.