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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

Chapter 10S – Acceptance Sampling

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

SJSU Bus. 140 - David Bentley

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

SJSU Bus. 140 - David Bentley

single sampling plans
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
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
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

slide7

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
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 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