An Implementation of Regression Adjustment Control Chart into Production Water
Water is one of the most important element for human living things. The production water is water produced by water treatment plant owned by a water company in the city which currently has a production capacity of 1450 litres/sec. Water quality is controlled by several parameters i.e. the coagulant used (alum), turbidity, organic substances (KMnO4), and water pH and is used in a series of water treatment process which is univariately measured. Those measurement, in fact, is someway related among parameters. Those kind of relationship makes univariate measurement no longer suitable to be applied to. In a production process, if the critical of quality observed is devided into response and predictor, then the statistical quality control used to control the production process is regression adjustment control chart. The quality control chart is applied into regression residual, univariately and multivariately. This study is to propose the use of multivariate regression adjustment control charts to determine the mean and variability of the production process. The selected control chart is Generalized Variance (GV) and T2 Hotteling based on the presence of outlier in the multivariate regression residual. Phase I of the in-control GV chart yield the upper control limit (UCL) of 2,694 and the in-control T2 Hotteling chart yield an upper control limit of 20,99. Those two yielding UCL is then used to control Phase II production water to determine whether the production process is in-control or not.
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