In a 2-out-of-3 voting scheme, when is the output considered valid?

• A. Any two of the three sensors agree.
• B. All three sensors must agree.
• C. Only one sensor is used.
• D. The output is taken from the sensor with the highest reading.

Answer: (A)

In a 2-out-of-3 voting setup, the output is trusted when at least two sensors report the same value. This majority consensus gives fault tolerance: if one sensor fails or drifts, the two agreeing sensors still determine the correct reading. If two sensors match, their value becomes the output (even if the third differs). If all three disagree, there’s no clear consensus, so the output isn’t considered valid. Using only one sensor or picking the highest reading ignores the redundancy and isn’t the intended functioning of this scheme.