Which list accurately identifies the four parts of a closed-loop motor control system?

• A. Drive, comparator, sensor, and amplifier
• B. Controller, motor, actuator, power supply
• C. Sensor, encoder, switch, resistor
• D. Tachometer, encoder, drive, valve

Answer: (A)

In a closed-loop motor control system, the essential idea is feedback: the system continuously compares what you want the motor to do with what it is actually doing, then uses that information to correct the drive signal. The four parts that make this happen are a sensor to obtain the actual motor state, a comparator to form the difference between the commanded value and the feedback, an amplifier to boost that difference to a usable control signal, and a drive to power the motor based on that signal. This combination directly represents the feedback loop: sensor provides real data, comparator creates the error, amplifier scales it, and drive actuates the motor.

Why this set is the best fit: the drive powers the motor, the comparator generates the error signal by comparing command and feedback, the sensor provides the feedback, and the amplifier strengthens the control signal so the drive can respond effectively. Other options omit one or more of these essential elements or mix in components that aren’t part of the core closed-loop path, like passive components or devices not typically used to form the feedback loop for motor control.