Phase 1 SPC
PHASE 1 SPC METHODS (Variables control chart)
Montgomery p.99
X-bar and R charts
Independence of measures of central tendency and of variance (for X-bar chart, but not for R chart)
Trial control limits
What if assignable causes cannot be found?
SPC as Hypothesis Testing
ARL1 and ARL2
ATS1 and ATS2
Choice of subgroup size and frequency based on ARL/ATS
Useful for the INITIAL QUALIFICATION of a process
If the SPC study includes multiple lots of product and raw materials (and it often should), then the process limits should be calculated for each lot.
We would prefer that each lot shows that the process is "in control" (stable) based on control limits calculated for each lot - AND ...
... we should also look for minimal (preferable none) shift if the process mean and process variance across lots.
See also: Phase 2 SPC