In a fixed and modular PLC, which interfaces provide the link between the PLC and external devices such as lamps, motor starters, and solenoids?

• A. Input interfaces
• B. Output interfaces
• C. Communication interfaces
• D. Power interfaces

Answer: (B)

The link between the PLC and external devices like lamps, motor starters, and solenoids is provided by the output interface. This interface is responsible for sending signals from the PLC to actuation devices, typically through output modules that switch current to energize relays, contactors, or solid-state switches. Input interfaces, by contrast, bring signals from sensors into the PLC; communication interfaces handle data networking; and power interfaces supply the necessary electrical power to the PLC system itself. So when the PLC needs to control actuators such as a lamp or a motor starter, it uses the output interface to drive those devices.