Shewhart Charts

Shewhart Charts

1. xbar-S Chart

2. xbar-R Chart

   • Advantages
     • Sensitive
       • Max use of info
   • Construction
     • 1. Find Xbar and R for each sample group
     • 2. Find centre line
       • Xbar
       • R bar
       • Conditions
         • During Initial commissioning
         • After major changes
     • 3. Set control limit
       • UCL (Upper Control Limit)
         • Shewart Chart
       • LCL (Lower Control Limit)
     • 4. Label and Date all Lines
     • 5. Revise + Improve system regularly

3. Interpretation

   • Most points in range
     • No problem!
   • Several points close to control limit
     • Not major. Should check for potential problems
   • Point(s) outside control limits
     • Unusual variation
     • Raises alarm Immediately

Images and files in the map