First Assistant Engineer · 1AE01 · Engine · Automation and Control · CURRENT-Q511-Q0002
Control Systems: Recognizing Instability
Connect sustained or increasing oscillation to closed-loop control-system instability.
In a closed-loop process control system, what term is used to describe the undesirable characteristic in which the error of a control system oscillates with constant or increasing amplitude?
- A. Saturation
- B. Error
- C. Deadband
- D. Instability
Correct answer: D. Instability
Why this answer is correct
Constant or increasing error oscillations identify an unstable closed-loop control system.
Governing principle
A stable feedback system damps disturbances; an unstable system sustains or amplifies them.
Reasoning
- The question describes the error response after feedback is applied.
- Constant or growing amplitude means the response is not being damped.
- That behavior is instability.
Why the other choices do not fit
A. Saturation is an output or actuator reaching its limit, not the name for sustained oscillation.
B. Error is the difference between setpoint and measured value; it does not describe the system behavior.
C. Deadband is a range in which input changes produce no corrective output.
Related lesson
Control-Loop Dynamics — Damping, Offset, Floating Action and Automatic Reset
Flashcard preview
What is damping in a control loop?
The progressive reduction or suppression of oscillation so the response settles.
Sources
- NASA Technical Reports Server · Control-system stability discussion · Definition of an unstable control system and unbounded error propagation
- USCG National Maritime Center · Q511 General Subjects I · Question 2 and official answer key
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