GATE 2020 PI – Question 32

Quality and Reliability · Quality Management · 1 mark · Multiple choice

Which formula defines process capability ratio Cp? USL/LSL are specification limits, UCL/LCL control limits and σ process standard deviation.

$(USL-LSL)/(6\sigma)$
$(UCL-LCL)/(6\sigma)$
$6\sigma/(USL-LSL)$
$6\sigma/(UCL-LCL)$

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Correct answer: (A) $(USL-LSL)/(6\sigma)$

Explanation

Cp compares allowed specification width with natural process spread, conventionally6σ. Thus Cp=(USL−LSL)/(6σ), A. Control limits estimate statistical process behaviour and cannot replace engineering specification limits in this definition.

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