What Inspection Level for Small Lot Size and Special Levels (S1-S4)?

Mike S.

Happy to be Alive
Trusted Information Resource
#11
I don't know your product or process, and you aren;t providing much detail, so I can't give much guidance. But if you are using SPC to monitor your process and can create rational subgroups maybe a subgroup sample size appropriate for a X-bar and R chart like 5-10 is reasonable.

There are a lotta books and articles out there on sampling, read-up and find a plan that works for you based on costs and risks.
 
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Wolf.K

Quite Involved in Discussions
#12
I don't know your product or process, and you aren;t providing much detail.
My boss does not like it if I provide too much information about or products or processes, sorry...

And I did not find any source explaining the AQL S-1 to S-4 levels, therefore I posted my questions here.
 

Mike S.

Happy to be Alive
Trusted Information Resource
#13
My boss does not like it if I provide too much information about or products or processes, sorry...

And I did not find any source explaining the AQL S-1 to S-4 levels, therefore I posted my questions here.
The info on Z1.4 on S-1 to S-4 that you posted is about all the explanation that is out there, except you can use the tables and OC curves in the standard to calculate quality parameters for the S sampling plans.

I understand wanting to keep info private, but you can't expect much help when you ask, essentially, "how do I get from this place to that place" when you want to keep the address a secret. We can tell you about maps and GPS, but you have to find out on your own.
 

Jim Wynne

Staff member
Admin
#14
So, I have two questions: 1. How to apply S-1 to S-4 for finished batches, and 2. how to calculate in-process sample number.
I can't help with the derivation question, although I seem to remember searching for this information myself a long time ago and coming up empty. Two observations, though: The sampling tables are lot inspection requirements and should not be applied to moving processes. Also, unless you're sampling is random--each member of the population has an equal chance of being chosen--all bets are off anyway. The sampling plans are based on the assumption that sampling is random.
 

Wolf.K

Quite Involved in Discussions
#15
The info on Z1.4 on S-1 to S-4 that you posted is about all the explanation that is out there, except you can use the tables and OC curves in the standard to calculate quality parameters for the S sampling plans.
I think, the issue is that I miss either intuitive examples or straight numbers in the standards.
 

Wolf.K

Quite Involved in Discussions
#16
I can't help with the derivation question, although I seem to remember searching for this information myself a long time ago and coming up empty. Two observations, though: The sampling tables are lot inspection requirements and should not be applied to moving processes. Also, unless you're sampling is random--each member of the population has an equal chance of being chosen--all bets are off anyway. The sampling plans are based on the assumption that sampling is random.
Yes, we do not manufacture, we have contract manufacturers. And they ship the products to our warehouse, and we do incoming inspections according to AQL. And they manufacture according to our product specifications, and do the in-process samplings also according to our specifications. I just try to find out, how these numbers were calculated years ago, but nobody involved at that time is working either here nor at the CM...

Most examples I have found so far are for APIs in pharmaceutical industries, but they are not very transferable to my processes, I think.
 
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