A tachometer/generator provides a feedback voltage that is directly proportional to which motor quantity?

• A. Speed
• B. Torque
• C. Acceleration
• D. Power

Answer: (A)

A tachometer/generator is used to provide feedback that directly tracks how fast the motor shaft is turning. The device converts rotational speed into an electrical signal, with the output voltage rising or falling in direct proportion to the shaft’s angular velocity. That linear relationship means doubling the speed doubles the tach output, which is exactly what a speed-control loop needs to regulate velocity.

This signal is not meant to reflect torque, which depends on current and load rather than rotation rate. It also isn’t a direct measure of acceleration—the tachometer gives the instantaneous speed, not how quickly that speed is changing. And since power combines both torque and speed, the tachometer’s speed-based voltage doesn’t represent power unless you also know the torque separately. In practice, the tachometer output serves as the speed feedback used to achieve stable, accurate speed control by comparing it to a reference and adjusting the drive accordingly.