The DC control voltage used to control speed is measured in which units?

• A. Volts
• B. Amps
• C. Ohms
• D. Watts

Answer: (A)

The speed of a DC motor controlled by a DC control signal is set by the voltage level applied to the motor or its speed control input. The unit for this control signal is volts because voltage is the electrical potential difference that drives the current through the motor windings. Increasing the control voltage raises the motor speed (until back-EMF and losses balance the applied voltage). Amps would reflect current, which relates to torque but isn’t the primary control quantity for speed in this common arrangement. Ohms is resistance, a property of the circuit, and watts is power (voltage times current), not the signal used to set speed. Some systems may use current loops or PWM, but for a DC control voltage, the unit is volts, with typical ranges like 0–5 V or 0–10 V.