From: Stan Hilliard
Date: 3/7/2007
Time: 7:44:15 PM
Hi Sidney,
You said:
"I thought the Sample size is control by the Lot size, the arrow only indicate the Ac / Re for the AQL your chose."
I assume that ASQ/ANSI standard Z4 is used. If so, your thought is not correct. The arrow means that you use the ROW that the arrow points to -- including the sample size for that row.
The inspectors can stop inspecting for minor defects after n=13. However the fact that you say that they may see minor defects in the final 7 implies that they are inspecting for minors at n=20 also. If that is the situation, then the issue becomes what Ac to use for the minors for n=20. I do not think the Z4 standard addresses that situation.
I can imagine three strategies for determining a plan for minors in that situation:
(1) Use the Ac on the row with n=20. This will keep the producer's point nearly the same as for the n=13 plan while making the consumer's point more strict.
(2) Refer to the Z4 tables for LQ. Find the LQ for the minor plan on the row for n=13. Then find the LQ on the row for n=20 that is as close as possible to that original LQ. Use the Ac for that column -- regardless of that column's AQL heading. This will keep the consumer's point nearly the same as for the n=13 plan, while making the producer's point less strict.
(3) For n=20, use software program TP105 to evaluate the effects of various Ac's on the producer's point and the consumer's point.
samplingplans.com/software_oc.htm