Which acronym describes a control approach using digital signals to manage building systems?

• A. ATC
• B. BAS
• C. CxA
• D. DDC

Answer: (D)

Direct Digital Control describes a control approach that uses digital signals from sensors, a microprocessor-based controller performing discrete-time computations, and digital outputs to actuators. This is the foundation of modern building automation, enabling precise sequencing, scheduling, fault detection, and networked interaction across HVAC, lighting, and other systems. It’s the method that directly uses digital information to manage equipment, unlike broader system concepts or roles. Building Automation System is the overarching framework that hosts these digital controllers, while CxA is the commissioning role, and ATC isn’t the standard term for this control approach.