Design of R control Chart Assuming a Gamma Distribution

This article presents the method how to design a R control chart by variables, assuming that the quality characteristic that is being controlled follows a Γ-distribution. The use of an R-control chart shall be complementary to the application of a control chart for the process average. The problem is to find a coefficient that allows the estimation of the process standard deviation by means of the sample range and determines the values of the control chart limits. The sample size and the sampling interval, on the other hand, may be taken from the design of the complementary chart. (Gonzalez, Viles, Economic Quality Control 15: 109-118, 2000)