What is a typical limitation of a programming device in runtime operation?

• A. It does not control the machine during normal operation; the PLC does
• B. It can continuously control the machine in real time
• C. It powers the entire plant
• D. It handles all I/O switching

Answer: (A)

During runtime, the machine is controlled by the PLC’s CPU running the programmed logic and driving the outputs through I/O modules. A programming device’s job is to create, download, modify, and monitor that logic, not to operate the machine on a real-time basis. So the typical limitation is that it does not control the machine during normal operation—the PLC handles the control, while the programming device serves as a tool for developing and diagnosing the program. It may be used online for diagnostics or edits, but the actual control remains with the PLC and its I/O hardware. It doesn’t power the plant and it doesn’t perform all I/O switching on its own; those duties belong to the PLC and its I/O modules.