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