What happens when the control variable deviates from the set point?

When the control variable deviates from the set point, it indicates that the system is not operating within the desired range or parameters. The set point is the target value for the controlled variable, and when there is a deviation, it means that the system needs to take corrective action to return to the set point.

Adjustment is necessary to bring the control variable back to the desired level. This could involve modifying inputs, increasing or decreasing power, or implementing other control measures to ensure proper functionality and maintain system stability. It is essential for maintaining efficiency and safety within the system.

In this context, the other choices do not accurately represent the necessary response. Simply observing that no actions are required would not address the deviation, while shutting down the system or triggering signal isolation are typically extreme measures reserved for specific circumstances rather than the standard response to a minor deviation from a set point.