waecE-LEARNING
Electronics Paper 2, Nov/Dec. 2011  
Questions: 1 2 3 4 5 6 7 8 9 10 Main
General Comments
Weakness/Remedies
Strength















Question 10

(a)      Distinguish between open loop and closed loop control systems.
(b)     Classify the following into open loop and closed loop control systems:

  1. operating a toggle switch;
  2. traffic light controller;
  3. bread toaster;
  4. bicycle-riding process.

(c)      State the three conditions under which closed loop systems can become unstable.

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OBSERVATION

The expected answers were:

(a)      An open loop control system is one in which the control actions is independent of the output while a closed loop control system is one in which the control action is somehow dependent on the output.

Classification:

Open loop

Closed loop

Operating a toggle switch

Traffic light controller

Traffic light controller

Bread toaster

 

Bicycle-riding process

(i) Positive feedback

(ii) Feedback factor with magnitude of unity (1)
(iii) Feedback factor with a phase of 1800

The question was on Control Circuits. The question was unpopular. The performance of the very few candidates that attempted it was reportedly poor.
                                 
                       

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