From: Stan Hilliard
Date: 22 Jan 2001
Time: 15:35:17
Hi Dave,
There is good methodology available for lot-by-lot variables sampling for chemical analyses. The materials can be in any form -- liquids, powders, pellets, etc. They can be packaged in bags, drums, bottles, etc.
The natural approach for homogeneous materials is to based the sampling plan on an oc curve for the mean. Typical examples would be sampling pure solutions or small containers that were filled from well-mixed larger containers.
Here are some sources of more information. You can print your own copies:
Sampling of Bulk Liquids, Powders, Pellets: www.samplingplans.com/outputvariablesmean.htm
Tutorial on applications (20 pages): www.samplingplans.com/modern3.htm
Using OC Curves to develop sampling plans: www.samplingplans.com/usingoccurves.htm
Software program TP414 ($245) supports both kinds of plan: 1) bulk materials based on OC Curves for the mean of the variable, and 2) individual items based on oc curves for the fraction of items not conforming to a specification limit(s). www.samplingplans.com/software.htm
TP414 also supports sequential sampling for variables. You use sequential sampling plans when it is important to use the smallest sample size possible.
Sincerely, Stan Hilliard