Which of the following factors is considered when selecting PLCs?

• A. Number of I/O's
• B. Fieldbus system or standalone
• C. Modular or compact
• D. Operating voltage

Answer: (D)

Matching the PLC to the plant’s power needs is the key idea here. The operating voltage sets a hard constraint: it determines whether the PLC can be powered at all and whether its inputs and outputs can safely interface with the field devices. If the voltage isn’t compatible with the available power supply and the devices being controlled, the PLC won’t run or could be damaged, regardless of how many I/O points you need or how you want the system to be organized.

Once the voltage is compatible, other choices matter for meeting the application's requirements—how many I/O points you need, whether you want a fieldbus-enabled or standalone unit, and whether a modular rack or a compact form factor is right for the space and future expansion. But without the correct operating voltage, those other considerations can’t be implemented.