Which sequence correctly describes the operation of a PLC?

In the operation of a Programmable Logic Controller (PLC), the sequence is critical to ensure that the system functions correctly and responds appropriately to changes in its environment. The correct sequence involves first examining inputs to gather current data from sensors and other input devices. This step is essential because it ensures that the PLC has the most up-to-date information about the state of the system.

Once the inputs have been evaluated, the next step is to perform the logic operations. During this phase, the PLC processes the input data according to the programmed logic or rules, determining what actions or changes are required based on the current conditions. This logic processing is the core function of the PLC, enabling it to make decisions and control outputs accordingly.

Finally, after the logic has been processed, the next step is to update the outputs. This involves sending control signals to output devices, such as motors, valves, or alarms, based on the results of the logic evaluation. Updating outputs last ensures that the system reacts to the most recent set of inputs and the results of the logic operations.

Therefore, the sequence of examining inputs, then performing logic, and finally updating outputs reflects the structured and systematic approach that PLCs follow to ensure accurate and responsive automation control.