Control theory check: compared with an open-loop system, which attribute is generally improved when feedback is added to form a closed-loop control system?
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AAccuracy with respect to disturbances and parameter variations
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BComplexity (it becomes simpler than open-loop)
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CInherent stability under all conditions
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DAll of the above
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ENone of the above
Answer
Correct Answer: Accuracy with respect to disturbances and parameter variations
Explanation
Introduction / Context:Open-loop systems act without measuring the result; closed-loop systems measure output and compare it to a setpoint, adjusting inputs to reduce error. Adding feedback typically improves accuracy and disturbance rejection, but also introduces design trade-offs such as increased complexity and potential stability issues if the loop is not tuned correctly.
Given Data / Assumptions:
- We compare general attributes: accuracy, complexity, stability.
- Closed-loop implies sensor feedback and a controller adjusting actuation.
- “Generally improved” means the typical, intended benefit of closing the loop.
Concept / Approach:Feedback reduces sensitivity to disturbances and to changes in plant parameters. Classical results show that, within bandwidth limits, closed-loop control diminishes steady-state error (for appropriate controller design) and compensates for certain uncertainties. However, feedback adds components (sensors, controller, filters), increasing complexity. Stability is not automatically improved; poorly tuned loops can oscillate or become unstable.
Step-by-Step Solution:
1) Identify the primary benefit of feedback: error reduction and disturbance rejection. 2) Evaluate complexity: closed-loop adds parts, so it is not simpler. 3) Evaluate stability: depends on design; not guaranteed to “improve” universally. 4) Conclude that improved accuracy is the general, correct attribute.Verification / Alternative check:Bode sensitivity relations and standard control texts confirm that feedback reduces sensitivity and steady-state error but must be tuned to maintain stability margins.
Why Other Options Are Wrong:
Complexity: increases rather than decreases. Stability: can improve or worsen; not categorically “more stable.” All/None: Exactly one general attribute (accuracy) is appropriate here.Common Pitfalls:Assuming feedback always improves stability; ignoring bandwidth and phase margin considerations that can lead to oscillations.
Final Answer:Accuracy with respect to disturbances and parameter variations.