Devices such as switches and sensors, motor starters, pilot lights, and solenoid valves connected to a PLC are identified as which type of devices?

• A. Field devices
• B. External devices
• C. Internal devices
• D. Peripheral devices

Answer: (A)

Field devices are those components that interact directly with the actual process and are located where the equipment or process operates, not inside the control cabinet. The switches and sensors provide input signals to the PLC, allowing the system to monitor conditions and respond. The motor starters, pilot lights, and solenoid valves are actuators that the PLC drives to control machinery or process actions. Because these devices live out in the field and connect to the PLC via field wiring to input/output modules, they are categorized as field devices. They aren’t internal components housed inside the PLC cabinet, nor are they simply peripheral items like printers or keyboards; external devices is a broader term that doesn’t capture the essential field-location relationship as clearly as field devices does.