Which control system does not compare output with input for control and often requires human intervention?

• A. Closed Loop System
• B. Single Circuit
• C. User Interface
• D. Open Loop System

Answer: (D)

Open-loop control is a setup where the system acts on input signals without checking the actual output. There’s no feedback path to compare what’s produced with what was requested, so there’s no automatic correction for disturbances or changes. Because of that, human intervention is often needed to adjust the input or operate the process again if results aren’t as desired. The other options don’t fit: a closed-loop system uses feedback to automatically adjust behavior based on the difference between output and input; a single circuit isn’t a defined control strategy; a user interface is just a way for a person to interact with the system, not the control method itself.