In a modular PLC, which modules provide the link between the PLC and external devices that measure process conditions?

• A. I/O modules
• B. CPU modules
• C. Power supply modules
• D. Communication modules

Answer: (A)

The interface between the PLC and field sensors that monitor the process is provided by I/O modules. These modules connect external devices to the PLC, turning real-world signals from sensors (like temperature, pressure, or flow) into digital or analog signals the PLC can process. They also convert the PLC’s control signals into appropriate outputs for actuators. This role makes I/O modules the bridge for measuring and controlling the process. The CPU handles the logic, power supply provides power, and communication modules link the PLC to other systems, but the actual link to external measurement devices lives in the I/O modules.