A motor control system that uses a tachometer to control the speed of the motor is called a(n) ? system.

• A. Open-loop
• B. Closed-loop
• C. Semi-closed
• D. Manual

Answer: (B)

Using a tachometer to control motor speed creates a feedback loop that continuously compares actual speed to the desired speed and automatically adjusts the drive to keep it there. This automatic correction, based on measured speed, characterizes a closed-loop control system. If there were no feedback, the system would drift with load and friction (open-loop). Manual control requires a person to adjust the output, not automatic regulation, and semi-closed isn’t a standard description for this setup.