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Chapter 15: B. Sampling 159
Section A
AQL conversion
and inspection
levels
Variability known
Variability unknown
Standard deviation
method
Variability unknown
Range method
Single specification
limits
Double
specification limits
Process average
estimation and criteria
for reduced and
tightened inspection
k-method
Procedure 1
M-method
Procedure 2
M-method
Procedure 2
Figure 15.4 Structure and organization of ANSI/ASQ Z1.9-2003.
Part III.B
To develop a sequential sampling plan, the following parameters must be
defined:
a = producer’s risk
AQL = acceptable quality level = p 1
b = consumer’s risk
RQL = rejectable (or unacceptable) quality level = p 2
Figure 15.5 shows the accept, reject, and continue testing areas for a sequential
sampling plan. The y-axis represents the number of nonconforming items in
the sample and the x-axis shows the number of units inspected.
CONTINUOUS SAMPLING PLANS
Many production processes do not produce lots, and thus lot-by-lot acceptance
sampling plans discussed earlier cannot be applied. In cases such as these, continuous
sampling plans are developed. In continuous sampling plans, 100 percent
inspection and sampling inspection are alternately applied. The most recent standard
for developing continuous sampling plans is MIL-STD-1235B.