In a closed-loop control system, what is used to adjust the output?

• A. Random input signals
• B. Battery voltage only
• C. External weather data
• D. Sensor feedback is used to adjust the output

Answer: (D)

Feedback from sensors lets a closed-loop control system know how its output is actually behaving. The controller compares that measured output to the desired value and, when there’s a difference, adjusts the actuators to reduce that error. This automatic correction keeps the system on target even when disturbances occur. For example, a thermostat uses a temperature sensor to decide when to turn the heater on or off to maintain the set temperature. Without feedback, there’s nothing to compare against the target, so the system can’t self-correct. The other options don’t provide the mechanism for automatic adjustment: random inputs lead to unpredictable output, battery voltage alone doesn’t drive adjustment, and external weather data isn’t part of the internal feedback loop.