Metropolitan Transportation Authority (MTA) Electrical Practice Test

The thing being tested is how a small input can be turned into a larger, controlled motion or force through an actuator with feedback. A servo is designed for exactly that: a compact control signal drives a motor, and through gearing and a feedback loop, the output shaft moves much more precisely and with greater torque than the input would suggest on its own. The small movement commanded by the control system is amplified by the motor and gears, while the feedback keeps the output in line with the desired position. A servomechanism describes the whole closed-loop system that uses feedback to achieve accurate control, but the device that actually provides the amplified motion is the servo motor (the actuator). A solenoid would give direct linear motion without the amplification and precise control, a transformer handles electrical energy conversion rather than motion, and while a servomechanism involves feedback, it isn’t the actuator itself.