Switch from ANSI/ASQ Z1.9 to ANSI/ASQ Z1.4?

PLCs, programmable logic controllers



We are using ANSI Z1.9 for a dimension test of packaging components. As dimension is under variable, can we switch to ANSI Z1.4? The reason for this is to align with our supplier who is using ANSI Z1.4.

Can you please advise if this switching is acceptable. If yes, what should be taken into consideration like AQL, etc.?


The ANSI/ASQ Z1.4 standard is for incoming inspection of attribute characteristics.  As your measurement is a variable measurement, it is appropriate to use ANSI/ASQ Z1.9.  Both plans are indexed by AQL, but have different sample size requirements based on the level of protection you are looking to maintain.  I assume your real question is can you switch from a variable plan (Z1.9) to an attribute plan (Z1.4) for your inspection to align with your supplier’s use of Z1.4.   Though I do not believe harmonizing with the supplier’s use of Z1.4 for your acceptance testing is necessary, it is possible to use Z1.4 by redefining the variable measurements as either good or no-good.  Choosing to move to Z1.4 from Z1.9 will increase your sample size for the same level of protection and same lot size.  For example, a lot size of 5000 would have a sample size of 75 in Z1.4 and 200 for Z1.4 for a General Inspection Level II plan.  Both plans give approximately the same AQL and LTPD, though the Z1.4 will require 2.67x more samples.

Steven Walfish
Chair Z1, U.S. TAG to ISO/TC 69
Staff Statistician, BD

For more about this topic, please visit ASQ’s website.

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