Question 2 1AE01 - First Assistant Engineer

The Correct Answer is D **Explanation for Option D (Instensibility):** Instability, in the context of closed-loop process control systems, specifically refers to the condition where the system's output (or error) does not settle down to a steady state but instead grows continuously or oscillates with an amplitude that remains constant or, more dangerously, increases over time. This characteristic signifies a failure of the control loop to properly manage the process, leading to the system becoming uncontrollable. Therefore, it precisely describes the undesirable characteristic of an oscillating error with constant or increasing amplitude. **Why the other options are incorrect:** * **A) Saturation:** Saturation occurs when a control element (like a valve or actuator) reaches its physical or operational limit (e.g., fully open or fully closed) and can no longer respond to an increasing input signal. It limits the magnitude of the control action but is not the term used to describe uncontrolled, increasing oscillations. * **B) Error:** The error is simply the difference between the desired setpoint and the actual measured process variable. While instability is characterized by a problematic error signal, "error" itself is a fundamental measurement, not the term for the characteristic of uncontrolled oscillation. * **C) Deadband:** Deadband (or dead time) is a range of input values for which there is no resulting output change. It represents a region of insensitivity, often designed intentionally or caused by friction. It typically leads to sluggish or limit-cycle behavior, not the unbounded or constantly growing oscillation described by instability.