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