Which Siemens S7-3x series is known for modular CPUs and extensive I/O?

• A. S7-400
• B. S7-200
• C. S7-300
• D. S7-1200

Answer: (C)

Modular CPUs with room for extensive I/O describe the S7-300 family. It uses a central CPU module in a rack and lets you add expansion racks full of digital and analog I/O, timing, and communication modules as needed. This design lets you tailor the controller to the task size and scale by simply adding I/O without swapping the CPU. The other options don’t fit as closely: the S7-200 is a compact, single-chassis PLC with limited expansion; the S7-1200 is a newer compact line with built-in I/O and smaller expansion capability; the S7-400 is also modular and used for large-scale systems, but it targets much larger installations than the mid-range modular I/O approach described here.