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160 Part III: Inspection and Test
Number of nonconforming units
Reject zone
sn + h 2
Continue testing
Accept zone
sn – h 1
Number of units inspected
Figure 15.5 Decision areas for a sequential sampling plan.
Part III.B
MIL-STD-1235B
This standard uses the same parameters, i and f, as previously defined. The standard
includes CSP-1, CSP-2, CSP-F, CSP-T, and CSP-V plans.
CSP-1 and CSP-2 plans operate in the same way as Dodge’s CSP-1 and CSP-2
plans, but they are selected based on a sample size code letter and an AQL value
used as a quality index. The sample size code letter is selected based on the number
of units in the production interval.
CSP-F plans work the same way as CSP-1 plans, providing alternating
sequences of 100 percent and sampling inspection procedures, but the difference
in this case is that the AOQL and the number of units in the production interval
are used to characterize the plans. Once AOQL and f values are selected, go to the
corresponding table to read i, the clearance number. CSP-F is a single-level continuous
sampling scheme.
CSP-T plans add the provision of reduced sampling frequency once the product
shows superior quality.
The CSP-T plan works as follows:
1. Start with 100 percent inspection
2. When i (clearance number) consecutive number of units are found
free of nonconformities, 100 percent inspection is then substituted with
sampling inspection
3. A fraction of f units is randomly selected and then inspected
3.1 If one nonconformity is found, the inspector reinstates 100 percent
inspection