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Refer to figure.
Smoke detection in the aircraft cargo compartments is performed by four sensors: C1, C2, C3 and C4. Which of following will activate the alert?
  • A
    When only the C1 and C3 sensors detect smoke.
  • B
    Only when all sensors detect smoke.
  • C
    When the C1 and C2 sensors detect smoke.
  • D
    When only one sensor detects smoke.

Refer to figure.
Here you see that the two left gates are OR Gates and the one on the right is an AND Gate.

The OR Gate will pass the signal trough when; either one or both sensors detect smoke.
The AND Gate will only give an alert when both input give a positive signal.

Concluding, the AND Gate will need both OR Gates to give a positive signal.
Therefore:
“When only the C1 and C3 sensors detect smoke” is incorrect because When only C1 and C3 detect smoke the bottom OR Gate will not give a positive signal.

“Only when all sensor detect smoke” is incorrect because of the word: “Only”

“When the C1 and C2 sensors detect smoke” is correct because when C1 and C2 detect smoke, both OR Gates will give a positive signal resulting in the AND Gate to give an alert

“When only one sensor detects smoke” is incorrect because with only one smoke detector detecting smoke there will be only 1 OR Gate with a positive signal and this will not make the AND Gate give an alert.

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