1. Twenty random samples, each containing 6 items, were taken in a control chart application and it was found that the grand average is = 5.240 cm and = 0.25.
a. What would be the upper and lower control limits for the X and R charts. Please draw both X and R chart.
Given: overall average= Xbarbar= 5.24, Rbar= 0.250, sample size= n= 6
Answer: D4, D3 and A2 are taken from table of factors computing 3 sigma control limits, sample size= 6
| D4 (n=6)= | 2.004 |
| D3 (n=6) | 0 |
| control limits for Range, | |
| CL or R-bar= | 0.250 |
| UCL= R-bar*D4 | 0.501 |
| LCL= R-bar*D3 | 0.000 |
| A2 (n=6) | 0.483 |
| control limits for X bar, | |
| CL or Xbarbar | 5.240 |
| UCL= Xbarbar+ (A2)*Rbar | 5.361 |
| LCL= Xbarbar- (A2)*Rbar | 5.119 |
1. Twenty random samples, each containing 6 items, were taken in a control chart application and...