What best describes a distributed direct digital control system?

• A. A control system designed with a single central processor.
• B. A control system that has multiple CPUs at the controller level.
• C. A system that uses only analog signals.
• D. A system that does not communicate between controllers.

Answer: (B)

Distributed direct digital control spreads the control tasks across several processors placed close to the processes they regulate. Each local controller runs its own microprocessor, handling sensor readings, performing the control calculations, and sharing information with other controllers to keep the overall system in sync. This setup lets the system scale, improve reliability, and respond quickly to local changes, while still coordinating with other controllers over a network.

The description matches having multiple CPUs at the controller level, rather than a single central processor. It’s not defined by using only analog signals—digital control can read analog sensors after conversion—and it’s defined by the presence of inter-controller communication, which distributed systems rely on to coordinate actions across the plant.