Chapter 10S – Acceptance Sampling

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# Chapter 10S – Acceptance Sampling - PowerPoint PPT Presentation

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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### Chapter 10S – Acceptance Sampling

Definition, purpose, sampling plans, operating characteristic curve, AQL, LTPD, risks

SJSU Bus. 140 - David Bentley

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

Sampling Plans
• Plan defines:
• Lot size
• Sample size
• Number of samples
• Acceptance/rejection criteria

SJSU Bus. 140 - David Bentley

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

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

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

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

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

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