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