Field or real-world devices refer to

• A. All devices physically wired to the PLC
• B. Software modules inside the PLC
• C. External networks only
• D. Internal timers

Answer: (A)

Field devices are the sensors and actuators located in the real-world process that connect to the PLC through its input/output hardware. They are the hardware in the field that either provide data to the PLC or execute commands from it, and they are typically physically wired to the PLC or to remote I/O modules attached to it. Examples include pushbuttons, limit switches, temperature or pressure sensors, flow meters, valves, and motor starters. This is why describing field devices as all devices physically wired to the PLC matches what the term means: it focuses on the actual hardware that interfaces with the control system. Software modules inside the PLC handle the logic, internal timers are PLC resources, and external networks may carry data from field devices but are not by themselves the field devices.