Pulse width modulation is a control technique in which a sequence of short pulses is used to position an actuator.

• A. Building automation system output
• B. Current sensing relay
• C. Latching relay
• D. Pulse width modulation

Answer: (D)

Pulse width modulation controls an actuator by turning the drive on and off rapidly and adjusting the on-time (the duty cycle) to set the average power delivered. By changing how long the signal stays high within a fixed switching period, you change the average voltage or current seen by the actuator, which moves it toward the desired position. The idea of using a sequence of short pulses to position an actuator matches PWM precisely: the pulses provide fine-grained control over how much energy reaches the actuator, enabling smooth and accurate positioning.

The other options describe different things that aren’t the modulation method itself—one is a general output concept from building automation, another is a device that detects current, and another is a type of relay. None of those explain controlling an actuator by varying pulse width in a timed on/off pattern the way PWM does.