A system for a blowout preventer (BOP) stack assembly includes one or more pairs of ultrasonic transducers coupled to a body that is configured to support a movable component of the BOP stack assembly, wherein each pair of ultrasonic transducers comprises a first ultrasonic transducer disposed on a first side of the body and a second ultrasonic transducer disposed on a second side of the body, opposite the first side. The system also includes a controller configured to receive a first signal indicative of a position of the movable component from the one or more pairs of ultrasonic transducers, to determine the position of the movable component based on the first signal, and to provide a first output indicative of the position of the movable component.