Which of the following correctly describes a disturbance in a process?

A disturbance in a process refers to an unexpected event that disrupts the normal operation or behavior of that process. In various engineering and industrial contexts, disturbances can arise from different sources, such as fluctuations in input materials, environmental conditions, or equipment malfunctions. When a disturbance is characterized as unexpected or unpredicted, it emphasizes that the changes occurring are outside of the anticipated or controlled range of conditions.

This definition is crucial for understanding how processes react to changes and how operators or engineers need to adjust settings or manage the system to return to stable operation. Disturbances may cause variations in outputs or performance, requiring interventions to restore equilibrium in the system. Identifying disturbances accurately allows for effective troubleshooting and enhances system resilience by preparing for unforeseen changes.

The other options do not align with the definition of a disturbance. An expected change would indicate a proactive or planned adjustment rather than an unpredicted event. A minor adjustment typically refers to a small, intentional change made to optimize the process, not something that interrupts normal functioning. A systematic error refers to a consistent, repeatable deviation that may not be due to unexpected events but rather flaws in the system or measurement process itself, which is different from the concept of a disturbance.