Statistical Quality Control Using Control Charts

Control charts are used to monitor a process for some quality characteristic such as e.g., thickness, weight, defective fractions, etc. The common elements of quality control charts are outlined below:

• The Y-axis (vertical axis)) is a value axis that is scaled according to the unit of the corresponding summary statistic (e.g., standard deviation, mean, etc.)
• The X-axis (horizontal axis) is categorical and represents sample ID, order, sequence, run time, site, etc.
• Each point represents a summary statistic based on computation results from subgroup measurements of a continuously varying quality characteristic.
• The center line displays the average of the summary statistic.
• The upper and lower control limit lines (UCL and LCL) display the range of expected variations in the summary statistic.
• Points above the UCL or below the LCL lines are out-of-control points, while points inside the UCL and LCL are in-control-points.

  
  
  
  

  Shewhart Control Charts for Variables Xbar (R) chart Xbar (S) chart R chart S chart

  Shewhart Control Charts for Attributes p chart np chart c chart u chart