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Chapter 10S – Acceptance Sampling

Chapter 10S – Acceptance Sampling. Definition, purpose, sampling plans, operating characteristic curve, AQL, LTPD, risks. Acceptance Sampling. Form of inspection applied to lots or batches Before or after a process, not during the process

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Chapter 10S – Acceptance Sampling

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  1. Chapter 10S – Acceptance Sampling Definition, purpose, sampling plans, operating characteristic curve, AQL, LTPD, risks SJSU Bus. 140 - David Bentley

  2. Acceptance Sampling • Form of inspection applied to lots or batches • Before or after a process, not during the process • Purpose: determine whether lot satisfies predetermined standards SJSU Bus. 140 - David Bentley

  3. Sampling Plans • Plan defines: • Lot size • Sample size • Number of samples • Acceptance/rejection criteria SJSU Bus. 140 - David Bentley

  4. Single-sampling Plans • One random sample from each lot • Every item in sample inspected and classified: good or bad • If number of defects (bad) > specified limit, lot is rejected SJSU Bus. 140 - David Bentley

  5. Double-sampling Plans • Upper and lower defect limits set for each lot • Results of initial sample • Defects ≤ lower limit: lot accepted • Defects ≥ higher limit: lot rejected • Defects between two limits: take 2nd sample • If 2nd sample needed, compare number of defects from both samples to third value • If number of defects (bad) > specified value, lot is rejected SJSU Bus. 140 - David Bentley

  6. Multiple-sampling Plans • More than 2 samples • 2 limits specified for each sample • Cumulative number of defects compared to limits for each successive sample • Defects ≤ lower limit: lot accepted • Defects ≥ higher limit: lot rejected • Defects between two limits: continue sampling SJSU Bus. 140 - David Bentley

  7. 1 0.9 0.8 0.7 0.6 Probability of accepting lot 0.5 0.4 0.3 0.2 3% 0.1 0 0 .05 .10 .15 .20 .25 Lot quality (fraction defective) Operating characteristic curveStevenson, William J., Operations Management, 8th Edition (mod. 09/15/04 DAB) • Shows probabilities of accepting lots with various defect fractions SJSU Bus. 140 - David Bentley

  8. Acceptance Levels • Acceptable Quality Level (AQL) • Customers may be willing to accept lots containing less than a specified % defects • Lot Tolerance Percent Defective (LTPD) • Upper limit of defects tolerated in accepted lots SJSU Bus. 140 - David Bentley

  9. Type I and Type II Errors • Type I (producer’s risk) • Conclusion: non-randomness is present and the process is out of control • Action: stop the process which was OK • Reality: randomness is present and the process is in control • Type II (consumer’s risk) • Conclusion: randomness is present and the process is in control • Action: don’t stop the process; continue making defects • Reality: non-randomness is present and the process is out of control SJSU Bus. 140 - David Bentley

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