Chapter 10S

1
Chapter 10S Acceptance Sampling

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

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

3
Sampling Plans

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

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) gt specified limit, lot
  is rejected

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) gt specified value, lot
  is rejected

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

7
Operating characteristic curveStevenson, William
J., Operations Management, 8th Edition (mod.
09/15/04 DAB)

• Shows probabilities of accepting lots with
  various defect fractions

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

9
Type I and Type II Errors

• Type I (producers 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 (consumers risk)
• Conclusion randomness is present and the process
  is in control
• Action dont stop the process continue making
  defects
• Reality non-randomness is present and the
  process is out of control