Introduction to "Double sampling plan"

source:KF Quality    author:KFQ    2021-02-18 17:20:35

Besides Single sampling plan which is widely used in the inspection industry, there is another "Double sampling plan".

The advantages of Double sampling plan is that the sample size for the first sampling is less, and does not need to do the second sampling if
- both Major and Minor defects are within the AQL (Acceptable Quality Limits). Workmanship result is Passed. or
- either Major or Minor defects are beyond the AQL. Workmanship result is Failed.

Then, how does the double sampling plan work?

1) Find relevant code letter from the "Code Letter Table" based on the lot size and inspection levels. (Same as Single sampling plan)

2) Determine the sample size for the first sampling and Ac (accepted) & Re (rejected) number as per attached table.

3) Do the second sampling only when the result of 1st sampling is either:
- Major is within AQL, Minor is between Ac and Re
- Major is between Ac and Re, Minor is within AQL
- Major and Minor both is between Ac and Re

4) Add the defects found together in the first & second sampling, then determine the workmanship result.


From kfquality.com