A control chart is a tool that monitors quality characteristics of a process to insure that process control is being maintained when monitoring multiple characteristics that are correlated, it is imperative to use multivariate control chart. Hotelling,s T2 quality control chart is used to determine whether or not the process mean vector for two or more variables is in-control. It is allow us to simultaneously monitor whether two or more related variables are in control, and it is shown that multivariate quality control chart do not indicate which variables cause the out-of-control signal so that the interpretation of the out-of-control signal. This paper effort explores designing the multivariate T2 quality control charts for process variability and methods that address which variable(s) caused the out-of-control signal. Industry fertilizers is important one of the chemical industries in Egypt, so that this work concerns the fertilizers industries quality control, especially urea fertilizer with application on Delta fertilizer and chemical industries which is considered on of the leading companies the field of fertilizer production in Middle east with application of multivariate quality control procedures to achieve best one procedure for multivariate quality control . This application shows that the company should use the multivariate quality control chart to determine whether or not the process is in – control because the production have several correlated variables, and the used of the separate control charts is misleading because the variables jointly affect the process. The used of separate univariate control charts in multivariate situation lead to a type I error and the probability of a point correctly plotting in-control are not equal to their expected values. |
