TABLE OF CONTENTS The essential idea in this chapter is the principle of correct sampling:
Every part of the lot has an equal chance of being in the sample and
the integrity of the sample is preserved during and after sampling.
Always examine tools and their use in light of this principle. Know whether it is violated, how it is violated, and to what extent it is violated. There are several things we can do to improve our chances of following this principle in practice.
Reduce the sampling dimension if possible. In practice, correct sampling of three-dimensional lots is not possible, so we must try to sample across one or two of the dimensions. Sampling the lot during transfer, before it becomes three-dimensional, is generally preferable.
Define a correct sample. Every part of the lot must have the same chance of being in the sample. We must use the correct geometry for the sampling dimension: a cylinder for two-dimensional sampling and a slice for one-dimensional sampling.
Condition (mix) a one-dimensional enclosed liquid or gas stream. Since a cross-stream sample is impossible to obtain, giving the stream a more homogeneous cross section reduces the grouping and segregation error (GSE) and the impact of incorrect delimitation. It also reduces the impact of taking an incorrect sample.
Choose the right sampling tool. Examine the tool and look for violations of the principle of correct sampling. The tool must be capable of taking the sample that is defined and taking...
