by: samah tout and bing liu team potassium sigma nov. 20,2007
TRANSCRIPT
By: Samah Tout and Bing LiuTeam Potassium Sigma
Nov. 20,2007
Statistical tool to improve and monitor quality
Detect the presence of variation A plot of some function of measurements of
process vs. time◦ Data points are compared
to UCL and LCL◦ All points should
fall within threestandard deviations of the mean
Mean is distributed according to a normal distribution
Measurements are independent of each other
Initial predictions taken when process is stable◦ Multiple subset of data must be collected◦ Grand Average(XGA), average range(RA), average
standard deviation(SA) are calculated
◦ n<15: use Table A to find the constants A2, A3, etc.
X-Bar chart◦ Grand average as the centerline
R-chart◦ Average range as the centerline
S-chart◦ Average standard deviation as the centerline
Given:
◦ Number of data points within each subset, n = 4 Need to Find
◦ Calculate XGA, RA, and SA
◦ Determine UCL and LCL
Subset # Value(Kg)
8(experimental) 1.02,0.99,1.01,0.99
9(experimental) 1.01,0.99,0.97,1.00
10(experimental) 1.02,0.98,0.99,1.00
11(experimental) 0.98,0.97,1.02,1.03
X-Bar limits◦ UCL= XGA + A2 RA= 1.04
◦ LCL= XGA - A2 RA= 0.96